PUBLICATION

Division of Water

~s c

An OwnersGuidance ManualFor the Inspectionand Maintenance

of Dams in New York State

June 1987

New York State/Department of Environmental Conservation

:E

FOREWORD

As a safety guide for dam owners,this manual includes important stepsthat dam owners can lake on a directand indirect basis to reduce the con­sequences of dam failure. The bene­ficiaries of such programs includeboth the general public and the damowners themselves.Although dams and reservoirs areimportant components of the nationalinfraslnIcture, existing dams are get­ting older and new dams are beingbuilt in hazardous areas. At the sametime, - development continues inpotential inundation zones down­stream from dams. More people areat rist from dam failure than everbefore despite better engineering andconstruction methods, and continuedloss of lives and property from damfailures must be expecteil.Many different people and organiz:o­tions now contribute to dam safety,and many are striving to improve thenational record. In addition, signift­cant contributions to dam safety canbe made by the owners themselves.Therefore, the authors strongly urgecontinued reference to and use of this

manual. If but one life is savedthrough the application of the guide­lines discussed in this manual, theeffort involved in its developmentwill be fully justified.This manual stresses the importance

. to the dam owner of the developmentand active pursuit of a dam safetyprogram oriented to the specific damslnIcture and site. Also emphasizedare those public policy measureswhich the dam owner may be able toinIluence indirectly. These includeland use decisions, public dam safetyawareness and conununity warningand evacuation planning. All aresteps that can mitigate life and prop­erty loss.

Appendix E, an integral part of themanual, provides space for each stateto incorporate references to or dis­cussions of individual state laws andpolicies relating to dam safety. Ofcourse, if any portion of this manualis in conflict with individual statepolicies or statutes, the latter apply.Each slale is encouraged to includethis information prior to dissemin:o­tion of the manual.

ACKNOWLEDGEMENTS

This dam owner's guidance manua)·isthe result ofthe work ofmany peopleand organizations. The Federal Emer­gency Management Agency suppliedthe impetus and fuuding fur the pro}ecL The Colorado Division of Disas­ter Emergency Services (DODES)(John P. Byrne, Director) undertookthe actual development of the manualand contributed several of the chap­ters. Jeris A. Danielson, ColoradoState Engineer ,and John P. Byrneserved as Co-chairmen of the techni­cal advisory commillee. PatriciaHagan, DODES Project Officer, ledthe development and writing learn ofJack Truby, DODES and ProfessorsLynn Johnson P.E. and Charles Bar­tholomew P.E. (University of Colo­rado at Denver, Department of CivilEngineering). Hal Simpson, Colo­rado Deputy State Engineer, also pro­vided direction and assislance.Development ofthis national manualwould not have been possible withouldrawing from the excellent damsafety manuals now in use by manystates. In particular, the followingstates provided considerable assis­tance: Arkansas, Colorado, Ken­tucky, North Carotina, North Dakota,Ohio, Pennsylvania, Virginia andWyoming; also, STS Consultanls.The Colorado, Ohio, and Pennsyl­vania manuals were particularlyhelpful and supplied many ofthe engineering fundementals andgraphics.

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The authors are indebted 10 the co­chairmen and the members of thetechnical advisory commillee ofdamsafety officials - group representing awide range of expertise and localinsighls - who helped define dam·owners' needs and thus, the scope ofthis book.

John Molt - ColoradoJohn Diebel - ColoradoJ arneS Doody - CatiforniaJoseph Ellam - PennsylvaniaCharles Gardner - North CarotinaDan Robert Lawrence - ArizonaWilliam Riebsame - ColoradoSpecial thanks are extended to BillRiebsarne, University of Colorado, .Johan Stolpe and David Butler, aswell as Steve Slane and DeborahHanderhan, from the Colorado StateDesigo Center,- who contribuied si~

nilicantly to the graphic production.The production tearn could not haveaccomplished such a large lask with­out the support of Irwin Glassman,DODES Planning Chief, and theentire DODES staff. Special recogni­tion goes to Nora Rimando for herdedication, creativity and insight intyping the manual.

DAM SAFElY:AN OWNER'SGUIDANCE MANUALEXECUTIVE SUMMARY12/86

AN APPROACH TODAM SAFETYThere is an urgent and continuingneed for dam safety in the UnitedStates because of thousands of damsare now in place across the U.S. andmany more are being built each year.These dams are essential elements ofthe national infrastructure, but thepublic risk in case offailure is great;large and growing numbers of livesand valuable properties are at stake.Although there are many who areconcerned about dam safety, legaland moral responsibility essentiallyrests with the dam owner.

Dam owners serve society by meet­ing important national needs and ofcourse,. may also profit from damoperations. However? these reasonsdo not justify the utility and effective­ness ofownership ifthe owner cannotprovide safety for people and pro!>­erty. The costs of dam safety aresmall in comparison 10 those whichfollow dam failure, particularly in ourmodem "litigious" society. Liabilitydue to failure could easily offsetyears of profitabilily.The dam owner can directly inJJuencethe safety of a dam. Owners can andshould develop Iheir own safety prlrgram which includes such importanIelements as inspectin~ monitoring.through instrumentation, maintainingthe structure, emergency action plan­ning and operating. Such a programis directly related to the dam struc­ture and its immediate environmentand depends on the owner's knowl­edge of the dam and how it works.

INTRODUCTION TO DAMSDams may be either man-made orexist because of natural phenomena,such as !andslides or glacial deposi­tion. The majority of dams are man­made structures nonnaJly constructedof earthfill or concrete. It is impor­tant that a dam owner be aware of thedifferent types of dams, essentialcomponent parts of a dam, important

physical conditions likely to inJJuencethe dam, and how the key com­ponents function.

HAZARDS, RISK, FAILURESPresent national loss statistics fromdam failure fully justifY the need fordam owners to better understand thepublic risks involved with damownership, the kinds of hazards thatpromote these risks and the reasonswhy dams fail. Public risk is highbecause people have been allowed tosettle below dams in potential inun­dation zones and because new damsare being built in less than idealsites~

Other elements of risk include naturalphenomena such as l100ds, earth­quakes and landstides. These hazardsthreaten dam structures and their sur­roundings. Floods that exceed thecapacily ofa dam's spillway and thenerode the dam or abutments are par­ticularly hazardous, as. is seismicactivity that may cause cracking orseepage. Similarly, debris from land­slides may block a. dam's spillwayand cause an overflow wave thaterodes the abutments and ultimatelyweaken the structure~

The International Commission ofLarge Darns (ICOLD) has deler­mined that the three major categoriesor dam failure are overtopping by1100d, foundation defects and piping.For earthen dams, the major reasonfor failure was piping or seepage. Forconcrete dams, the major reasons forfailure were associated with foun­dations. Overtopping was a signifi­cant cause ofdam failure primarily incases where there was an inadequatespillway.

DEVELOPING A DAM SAFETYPROGRAMRecognition of ihe causes and possi­ble impacts of dam failure points oulthe need for a program to enhancedam safety. Such a program must bebased on a safely evaluation to deter-

mine a dam?s structural and opera­tional safety. The evaluation shouldidentify problems and recommendeither remedial repairs? operationalrestrictions and modifications? or fur­ther analyses and studies to determinesolutions.A safety program comprises severalcomponents that address the spec­trum of possible actions to be takenover the short and long term. Devel­opment of a safety program involvesa phased process beginning withcollection and review of existinginformation, proceeding to detailedinspections and analyses, and cuI­min ating with formal documentation.Much of the preliminary work can beaccomplished by the dam owner withthe assistance of state and localpublic agencies. However, dependingupon the number and seriousness ofproblems identified by the initialassessmen~ professional assistanceby qualified engineers and contrac­tors may be required

Information presented in this manualprovides direction on how to proceedwith establishing an action to increasethe safety of a dam. The discussiondetails technical and proceduralcomponents of the safety program,and necessary forms are provided

The program of inspection for boththe initial and continuing safetyevaluations establishes the conditionof the dam and provides the informa­tion necessary for determining specificactions to be taken regarding repairs,operations, and monitoring. The pro­gram is cyclical recognizing the needfor continued vigilance. Emergencyaction can hopefully be avoided, buta well thought out plan of action incase of imminent or actual failure cangreaUy reduce damage and possibleloss of life.

INSPECTION GUIDELINESAn effective inspection program isessential to identify problems and toprovide for safe maintenance of adam. The inspection program shouldinvolve three types of inspections:(I) periodic technical inspections,(2) periodic maintenance inspec­tions, and (3) informal observationsby project personnel as they operatethe dam. Technical inspections in­volve specialists familiar with thedesign and construction of dams andinclude assessments of structuresafety. Maintenance inspections areperformed more frequently than

technical inspections in order todetect, at an early stage, any det­rimental developments in the dam;they involve assessment of opera­tional capability as well as structuralstability. The third type ofinspectionis actually a continuing eITort by on­site project personnel (dam tenders,powerhouse operators? maintenancepersonnel) performed in the course oftheir normal duties.

INSTRUMENTATIONAND MONITORINGGUIDELINESInstrumeritation of a dam furnishesdata to determine if the ·completedstructure is functioning as intended 'and provides a continuing sur-'veillance of the structure to warn ofany unsafe developments.

Means and methods available tomonitor physical phenomena thatcan lead to a dam failure include awide spectrum of instruments andprocedores ranging from very si",pleio very complex. Any program ofdam safety instrumentation mustinvolve proper design consistent withother project components, must bebased on prevailing geotechnicalconditions at the dam, and mustinclude consideration of the hydre>­logic and hydraulic factors presentboth before and aIIer the project is inoperation. Instrumentation designedfor monitoring potential deficienciesat existing dams must take intoaccount the threat to life and prop­erty that the dam presents. Thus, theextent and nature ofthe instrumenta­tion depends not only on the com­plexity of the dam and the size of thereservoir, but also on the potential forloss of life and property downstream.

An instrumentation program shouldinvolve instruments and evaluationmethods that are as simple andstraightforward as ~e project willallow. Moreover, the dam ownershould make a defmite commitment toa continuing monitoring program; ifthe program is not continuing, theinstallation of instruments and proce­dures will be wasted. Obviously, theinvolvement of qualified personnel inthe design? installation, monitoring,and evaluation of an instrumentationsystem is of prime importance to thesuccess of the programInstrumentation and proper monitor­ing and evaluation are extremelyvaluable in determining the perform­ance of a dam. Specific information

that instrumentation can provideincludes:

• Warning of a problem.• Definition of and analyzing a

problem• Proof that behavior is as expected• Remedial action perfonnance

evaluation

MAINtENANCE GUIDELINESA good maintenance program willprotect a dam against deteriorationand prolong its life. A poorly main­tained dam will deteriorate and canfail. Nearly all the components of adam and the materials used for damconstruction are susceptible to dam­aging deterioration if not properlymaintained. A good maintenanceprogram provides not only protectionfor the owner, but for the generalpublic as well. Furthermore, the costof a proper maintenance program issmall compared to the cost of majorrepairs or the loss of life and propertyand resultant litigation against thedam owner. A dam owner shoulddevelop a basic maintenance pro­gram based primarily on systematicand frequent inspections. Inspec­tions, as noted in Chapter 5, sho~ldbe done monthly and after majornood or earthquake events. Duringeach inspection, a checklist of itemscalling for maintenance should beused.

EMERGENCY ACTION PLANGUIDELINESAlthough most dam owners have ahigh level of confidence in the struc­tures they own and are certain theirdams will not f.il. history has shownIhat on occasion dams do faii and thatonen these failures cause loss of lire~

injuries and extensive property dam­age. A dam owner should prepare for.this possibility by developing anemergency action plan which pre>­vides a systematic means to:

• Identify emergency conditionsthreatening a dam

• Expedite effective response actionsto prevent failure

• Reduce loss of life and propertydamage should failure occur

A dam owner is responsible for pre­paring a plan covering these measuresand listings actions that the ownerand operating personnel should take.He should be familar with the localgovernment officials and agenciesresponsible for warning and evacuat­ing the public.

Itis important that dam owners makefull use of others who are concernedwith dam safety; emergency plans,will be more effective if they integratethe actions ofothers who can expediteresponse. People and organizationswith whom the dam owner shouldconsuh in preparing an emergencyaction plan include nwnerous localparticipants, state and federalagencies.

An essential part of the emergencyaction plan is a list of agencieslpersons to be notified in the event ofapotential failure. Possible inclusionsfor this list should be obtained·fromand coordinated with local lawen­forcement agencies and local disasteremergency services. These are keypeople or agencies who can activatepublic warning and evacuation pro­cedures or who might be able to assistthe dam owner in delaying or prevent­ing failure.

Certain key elements must be includedin every notification plan. Informa­tion about potential inundation (Drod­ing) areas and travel times for thebreach (0000) wave is essential.Inundation maps are especially use­ful in local warning and evacuationplanning. Detailed information aboutidentification of inundation areas orthe development of maps can befound by contacting the StateEngineer's Office or local planningoffices.

OPERATIONS PLANGUIDELINES

Establishing an operations procedureor plan calls for detailed:

• Dam and reservoir physical char­acteristiCs data

• Descriptions of dam components• Operations instructions for oper­

able mechanisms• Inspection instructions• Instrumentation and monitoring

guidelines• Maintenance operations guidelines• Emergency operations guidelines• Bibliographical informationA schedule should be established toinclude both day-to-day tasks andtasks performed less frequentlythroughout the year. The schedulefonnalizes inspection and main­tenance procedures so that even aninexperienced person can detenninewhen a task is to be done.

MEASURES TO REDUCE THECONSEQUENCES OF DAMFAILUREliabilities which are determined fol­lowing a dam failure strongly affectboth organizations and individuals t

governments and dam owners. Esta~lishing liability is the legal meansdeveloped by society to recoverdamages due to a "wrong>? (in thiscase, lack of dam safety) and reJ>­resents another perspective on thedam safety problem. A thoroughunderstanding of this legal processcan help the dam owner decide thesteps to be taken to reduce liability.

The darn owner can directly andindirectly influence the introductionand use ofa variety ofother measuresthat will serve to reduce the conse­quences ofdam failure. For example,insurance against the costs which willaccrue after a failure will save thedam owner money by spreading costsfrom a single dam_ owner to others.Some land use measures instituted bygovenunents represent better meansof mitigating future disasters. If peo­ple are restricted from living in inun­dation zones, then safely is radicallyimproved Instituting land use mea­sures represents one of the mosteffective ways to save lives and prop­erty over the long term, but such stepsare not always acceptable to govern­ments. Thus, given that lives andproperty are at stake, increasingputJIjc awareness an~ gove"rnmentalplanning are vital measures that alsomust be considered as ways to reducethe consequences of darn failure.Dam owners can obtain insurancedirectly 3J!d should do so. The othermeasures discussed here -- land use,.public awareness and preparednessplanning - are essentially controlledby local governments. Therefore,darn owners would be wise to encour­age as strongly as possi!>le awarenessand action in the public sector.Finally, they may also wish to hireconsultants from the private sectorwhen the informalion needed for pru­dent decisions exceeds their ownexpertise.

TABLE OF CONTENTS

CHAPTER 1AN APPROACH TO DAM SAFETY

1.0 General ...........................................• I1.1 Urgency for Dam Safety I1.2 Dam Ownership and Safety I1.3 The Increasing Complexity of the Dam Safety Problem '" I1.4 An Approach to Dam Safety.... . . . . . . . . . . . . . . . . . . . . . . . 2

CHAPTER 2INTRODUCTION TO DAMS

2.0 General .....• . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1 The Walershed System 32.2 Types of Dams 32.3 Water Retention Ability ........•....................• 62.4 Release of Water .........•.......................... 6

CHAPTER 3HAZARDS, RISKS, FAILURES

3.0 General 93.1 Hazards As Sources of Risk 9

3.1.1 Natural Hazards That Threaten Dams 93.1.2 Hazards From Human Activity II

3.2 Site-Specific SlnJctural Risk 123.3 Sources of Dam Failure 12

3.3.1 Three Categories of SlnJctural Failure................ .. 123.3.2 Failures By Dam Type 133.3.3 Age And Its Relation To l'ailure 15

CHAPTER 4DEVELOPING A SAFETY PROGRAM

4.0 Objectives of a Safety Program 174.1 Guidelines for Assessing Existing Conditions 174.2 Procedural Guidelines - A Source Book 184.3 Documenting the Safety Program 18

. CHAPTER 5 .INSPECTION GUIDEUNES

5.0 'Introduction 215.1 Inspection Guidelines 215.2 Organizing for Inspection 225.3 Embankment Dams and Structures 23

5.3.1 Upstream Slope 235.3.2 Downstream Slope 235.3.3 Crest 245.3.4 'Seepage Areas 24

5.4 Concrele Dams and SlnJctiJres 245.5 Spillways... . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . .. 265.6 Inlets, OuUets, and Drains.. . . . . . . . . . . . . . . . . .. .. . . . . . .. 275.7 Other Areas '" . . . . .. .. .. . .. 29

CHAPTER 6INSTRUMENTATION AND MONITORING

GUIDELINES

6.0 General 516.1 Reasons for Instrumentation 516.2 Instrument Types and Usage 52

6.2.1 Visual Observations .................................• 526.2.2 Movement ...................................•...•.. 526.2.3 Pore Pressure and Uplift Pressure 546.2.4 Water Level and Flow 556.2.5 Seepage Flow 556.2.6 Water Quality 556.2.7 Temperature .....................................•.. 566.2.8 Crack and Joint Size 566.2.9 Seismic Activity 57

6.2.10 Weather and Precipitation 576.2.11 Stress and Strain 57

6.3 Frequency of Monitoring 57

CtiAPTER 7MAINTENANCE GUIDEUNES

7.0 General 617.1 Maintenance Priorities. 61

7.1.1 Immediate Maintenance 617.1.2 Required Maintenance at Earliest Possible Date 617.].3 Continuing Maintenance 61

7.2 Specific Maintenance Items 62·7.2.1 Earthwork Mainlenance and Repair 627.2.2 Riprap Maintenance and Repair 637.2.3 Vegetation Maintenance :... 647.2.4 Livestock Control 647.2.5 Rodent Damage Control 647.2.6 Traffic Damage Control 657.2.7 Mechanical Maintenance........ .. .. 657.2.8 Electrical Maintenance 667.2.9 Cleaning :.. . . . . . . . . . . . . . . .. . . . . . . .. 66

7.2.10 Concrete Maintenance 667.2.11 Metal Component Maintenance 66

•CHAPTER 8

EMERGENCY ACTION PLAN GUIDEUNES

8.0 The Emergency Aclion Plan : 698.1 Identification of Emergency Conditions and Initiation of

Emergency Response Actions 708.2 Guidelines for Emergency Notification 71

CHAPTER 9OPERATIONS GUIDEUNES

9.0 General .......................•.................... 759.1 Operations Plan Guidelines ...•.••..••.••...........•. 75

9.1.1 Background Data ...•...•..•.........•..•.......•.... 759.1.2 Operations Instructions and Records ...•.........•..... 76

9.2 Schedule of Routine Tasks .•..••••••.••.•.....••...... 769.3 Record Keeping .......••...••.••••.•........... '" . .. 76

CHAPTER 10REDUCING THE CONSEQUENCES OF DAM FAILURE

10.0 Supplements to a Dam Safety Program ,................ 7910.1 Liability. . . . . . . . . . . . . • • . • . • . . . . . . • . . • . . . . . . . . . . • . . •. 7910.2 Measures to Reduce the Consequences of Dam Failure... 80

10.2.1 Insurance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8010.2.2 Governmental Assistance '.' . . . . . . . . . . . . . . . . . . . .. 8110.2.3 Consultants Role in Dam Safely 82

APPENDIXES

A Inspection Forms ..............•...........•......... 83B Report Form ..........•.......••.•..••.•••••.•...••. 95C Glossary. . . . . . . . . . . . . . . . • . . . • . • . . . . . . . . . . . . . . . . . . . .. 99D Selected Bibliography .......••..••••.•..•..•..•...... 113E State Background and Perspective .......•.............. 117

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UST OF TABLES

Table 1.1 Loss of Life and Property from Notable U.S. DamFailures .................................• . . . . . . . . . . 2

3.1 Hazard Potential Classification for Dams 113.2 Examples of Earthen Dam Failures 153.3 Examples of Concrete Dam Failures 155.1 Inspection Guidelines Directory ...............•. :..... 195.2 Inspection Equipment and lis Use 226.1 . Instrumentation and Monitoring Guidelines Directory. . . .. 497.1 Maintenance Guidelines Directory 598.1 Emergency Action Guidelines Directory ....•........•.. 678.2 Potential Problems and Immediate Response Actions ... 70-718.3 Checklist for Dam Emergency Plans :..... 729.1 Operation Plan - Schedule of Routine Tasks 77

10.1 Comparison of Warning Success for Selected Dam Failuresand Flash Floods ..........................•...•..... 81

UST OF FIGURES

Figure 2.1 Typical Dam Site. . . .. . . . . .. . .. .. .. . .. .. . . . .. . . .. . .. . 42.2 Embankment Dams ..............................•... 42.3 Concrete Gravity Dam ...........................•... 52.4 Concrete Arch Dam 52.5 Cutoff Trench and Upstream Blanket 73.1 Estimated Proportion of Land in Floodplain 103.2 Seismic Risk Map of the United States ........•..•..... I 13.3 Dam Failures 1900-1975 133.4 Failed Dams. in Percent of Dams Built. .. . . . . .. . . . .. 133.5 Dam Failures, Age in Years 144.1 Procedural Guidelines for a Dam Safety Program........ 18

5.3.1 Inspection Guidelines - Embankment UpsITeam Slope 315.3.2 DownsITeam Slope 325.3.3 Embankment Crest . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 355.3.4 Embankment Seepage Areas 39

5.4 Concrete UpsITeam Slope 425.5 Spillways .. .- , 425.6 lnJets, Outlets and Drains : ' 46

6. Ia Installation of Permanent Points 526.1b Plan of Alignment System : 52

6.2 Monitoring Cracks on Embankment 536.3a Inclinomett:r......................................... 536.3b Plot of Inclinometer Readings 53

6.4 Measuring Displacements 546.5 Porous Stone Piezometer . . . . . . . . . . . . . . . . . . .. 556.6 Typical Observation WeU Installation 556.7 Standard Weirs 566.8 ParshaU Flume 566.9 Bucket and Stopwatch Method 57

CHAPTER 1AN APPROACH TO DAM SAFETY

1.0 GENERALThis manual is a safety guide for damowners. There is a critical and con­tinuing need for dam safely becauseof the thousands of dams now inplace and tbe many new dams builteacb year. Altbough these dams areessential elements of the nationalinfra·structure, tbe risks to tbe publicposed by tbeir possible failure aregreat; large and growing number oflives and valuable property are atstake. Although lbere are many wboare concerned about dam safely,legal and moral responsibility essen­tiaIly resls witb the dam owner.

1.1 URGENCY FOR SAFETYThe critical need ror dam safety isclear. World and national statisticson dam failures show an unaccept­able record or Josses in bolh lives andproperty. Tbe International Commis­sion on Large Dams (ICOLD)reports tbat more than 8000 peoplebave died so rar this century becauseof the failure of major dams. Therecord ror U.S. losses from majordam failures in recent years, sbownin Table 1.1 is also not encouraging.Actual national losses are mucbhigher than indicated because tbestatistics sbown cover neither smalldam railures nor many combinalionsor dam failure and natural flooding

.events. A more specific examinationortbe national experience sbows thatover an 18·year period (1965-1983)thirty lesser failures, or seriousincidents that almost led to railure,occurred in Coloradb. The Johns­town, Pennsylvania disasler or 1889is regarded as one of the nation~s

great catastrophes, and the potentialfor future similar catastrophes due 10dam railure remains strong. Only acooperative effort in dam safetyinvolving owners and communitiescan lessen this potenlia!.

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1.2 DAM OWNERSHIP ANDSAFETYThis manual can be applied to damsowned and operated by a wide rangeor organizations and people, includ­ing state and local governments,public and private agencies, andprivate citizens. Typical reasons rorbuilding dams include water storagefor buman consumption, agriculturalproduction, power generation, 1l00dcontrol, reduction of soil erosion andrecreation. Thus, dam owners servesociety by meeting important nationalneeds and may also personally profitfrom dam operations. However,these are not sufficient reasons forbuilding or owning a dam ir the ownercannot provide safety ror people andproperty in potential inWldationzones.In botb financial and moral terms,successrul dam ownersbip and themainlenance of safety standards gohand in hand. Investment in damsafety should be accepted as anintegral part or project costs and notviewed as an expendable item thatcan be eliminated if a budget becomestight (Jansen, 1980). Tbe costs ofdam safely are small in comparisonto Ibose wbicb rollow dam failure,particuiarly in our mooern "litigious"society_Liability due 10 a failurewould probably negale years orpolential profits. Many difTerent con­cerns and possible rewards resultfrom dam ownersbip, but in the end,success will be in large part measuredby a conlinuing record or damsafety.

1,3 THE INCREASINGCOMPLEXITY OF THE DAMSAFETY PROBLEMAs nalional needs for water intensiryand the value of water increases,more dams are being built. At tbesame time, many existing darns arereaching or passing their design lifespans and, for various reasons, peo­ple continue to settle near dams. ~Further, as builders are forced to usepoorer sites for dams, the job or pr~tecling lire and property becomesmore dillicult. Therefore, as dam

TABLE 1.1Loss of Life and Properly Damage from Notable U.S. Dam Failures,

1963·1983 .

Name & Location Date or Number or Damagesor dam failure lives lost

Moht«Bn Park., Conn Mar 1963 6 53 millionuttle Deer Creek. Utah June 1963 1 Summer cabins damaged.BaJdw;" H;Us. Calif. Dee 1963 5 41 houses destroyed, 986 houSes

damaged. J00 apartment buiJd..ings damaged.

Swift. Mont. June 1964 19 Unknownlower Two Medicine, Monl June 1968 9 Unknownl..ce La.te. Mass. Mar 1968 2 6 houses destroyed. 20 houses

damaEed. J manufacturinl plantdamaged or destroyed.

Buffalo Creek, West Va. Feb 1972 125 546 houses deslroyed, 538.houses damaged.

Lak. "0·' Hills, Art. Ap< 1972 1 Unknown.Canyon Lake. S. Dak. June 1972 3J Unable to assess damage

benuse dam failure accom-panied damage caused by naturalfJoodins.

Bear WaUow. N.C. Feb 1976 4 1 house destroyedTeton. Idaho June 1976 II 771 houses deslrol.ed. 3,002

houses damased. 46 businessdam.zed or destroyed

Laurel Run. Pa. July 1977 39 6 houses destroyed. 19 howesdamazed.

Sandy Run and 5 others. Pa. July 1977 5 Unknown.Kelly Bames. Ga. Nov 1979 39 9 houses. 18 house uaiJen and 2

coUege buildinp destroyed; 6houses, S collee. buiJd;"CS

North Creek. N.Y. -darnazed.

Nov. 1979 0 UnbowaAboul 20 dams in Conn. June 1982 0 Unknown.Lawn Lake. Colo. July 1982 3 18 bridles destroyed,. 111

businesses and 108 housesdam.zed Campgrounds. fish-eries. power plant damazed

DMAD, VI"" June 1983 Unknown.

Source: Graham. 1983.

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construction continues and the pop­ulation grows. exposure of the publicto dam failure hazards increases andthe overall safety problem becomesmore difficulL

Governments across the nation haveshown increasing Concern for thisproblem and have enacled laws,statutes and regulations that place anincreased burden of responsibility onthe dam owner. In most states, damowners are held s!ricUy liable forlosses or damages resuhingfrom damfailure. ConcurrenUy, liability insur­ancecosts have risen rapidly.

1.4 AN APPROACH TODAM SAFETYAn owner should be aware of and useboth direct and indirect means ofachieving dam safely. He can, ofcourse, monitor and work on factorsdirecUy in his conlrol (example,structural inlegrily), and these directefforts are detailed below. However,the owner may also innuence govern­mental policy and work for positivechange in slatules and laws thataffect dam safety (example, zoninglaws). Such indirect innuedce by anowner could result in a significant

contribulion to the reduction or the 'likelihood and consequences of damfailure and thus.. to overall 'com­munity safety.liability, insurance coverage, andthe roles or the Federal and stalegovernments should aU be wellunderstood by an owner. Addition­ally, an owner should have a thoroughknowledge of a dam's physical andsocial environment, including knowl­edge of natural and technologicalhazards that threalen the dam,understanding of the developinghuman setllement patterns aroundthe dam, and understanding of otherevents that can lead to structuralfailure. These indirect means ofachieving dam safety are covered inmore detail in Chapters 2, 3 and10.Dam owners, can also funuence thesafety of dams in more direct ways.Owners can and should develop theirown safety programs. These pro­grams should include such importantelements as inspection, monitoringthrough instrumentation, main­tenance, emergency action planning.­and proper operati';>n. Such a pro­gram is directly related to a specificdam's structure and its immedialeenvironment and depends on Iheowner's knowledge of the dam andhow it works. Chapter 2 stresses theneed for owner's knowledge aboutthe d31D, while Chapters 4 Ihrough 9cover the development of a damowner's safely program.

CHAPTER 2INTRODUCTION TO DAMS

2.0 GENERALThe purpose of a dam is to impound(store) water for any of severalreasons., e.g., flood control, humanwater supply. irrigation. livestockwater supply. energy generation. rec­reation. or pollution control. Thismanual primarily concentrates onearthen dams which constitute themajority of structures in place andunder development.

2.1 THE WATERSHED SYSTEMWater from rainfall or snowmeltnaturally runs down hill into a streamvalley and then int~ larger streams orolber bodies of water. The "watershedsystem" refers to the drainage pro­cess through which rainfall or snow­melt is collected into a particularstream valley during natural runoff(directed by gravity). Dams con­structed across such a valley thenimpound lbe runoff water and releaseit at a controlled rate. During periodsof high runoff, water stored in thereservoir typically increases andoverflow through a spillway mayoccur. During periods of low runoff,reservoir levels usually decrease.The dam owner can nonnally controllbe reservoir level to some degree byadjusting the quantity of waterreleased by the dam. Downstreamfrom the dam. lbe stream continuesto exist, but because the quantity ofwaler flowing is normally controlled.very high runoffs (noods) and verylow runoffs (drought periods) areavoided

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3

2.2 TYPES OF DAMSDams may be eilber man-made orexist because of natural phenomena,such as landslides or glacial deposi­tion. The majority of dams are man­made structures normally constructedof earthfill or concrete. Naturallyoccurring lakes may also be modifiedby adding a spillway to provide safe.efficient release of excess water fromthe resulting reservoir.Dam owners should be aware of thedifferent types of dams, essentialcomponents of a dam. how the com­ponents function, and importantphysical conditions likely to alTect adam. This chapter discusses severalof lbese factors.Man-made dams may be classifiedaccording to the type of constructionmaterials used. the melbods used inconstruction, the slope or cross­section of the dam, the way lbe damresists the forces of the water pres­sure behind it. the means used forcontrolling seepage, and occasionally.according lbe purpose of lbe dam.

A. Component Parts - The compo­nent parts of a typical dam areillustrated in Figure 2.1. Nearlyall dams possess the featuresshown or variations of thesefeatures. Definitions of lbe termsare given in lbe glossary of thismanual, Appendix C. The vari­ous dam components are dis­cussed in greater detail later inlbis manual.

B. Construction Materials - Thematerials used for constructionof dams include earlb, rOCK•tailings from mining or milling,concrete, masonry, steel, timber,miscellaneous materials (such asplastic or rubber). and any com­bination of these materials.

I. Embankment Dams - Em­bankment dams are lbe mostcommon type of dam in usetoday. They have lbe general

4

FIgure 2.1 Typical Dam sne

shape shown in Figure 2.2.Their side slopes typicallyhave a grade of two to one(horizontal to vertical) or lIat­ter. Their water retentioncapability is due to the lowpermeability of the entiremass (in the case of ahomogeneous embankment)orofa zoneoflow-permeabilitymaterial (in the case of azoned embankment dam).Materials used for embank­ment dams include naturalsoil or rock obtained fromborrow areas or nearby quar­ries~ or waste materialsobtained from mining or mill­ing operations. H the naturalmaterial has a, high per­meability. then a zone of verylow permeability materialmust he included in the damto retain water.An embankment dam is termedan "earthfiliH or "rocklill"dam depending on whether itis comprised mostly ofcompacted earth or mostlycompacted or dumped per­vious JOck.

··: .·6

CUTOFF

Figure 2.2 Embankment Dam

The ability of an embank­ment darn to resist the hyUrD­static pressure caused byreservoir water is priiitarilythe result of the mass weightand strength of the materialsfrom which the darn is made.

2. Concrete Dams ~ Concretedarns may be categorized intogravity and arch dams ac­cording to the designs used toresist the stress due to reser­voir water pressure. A con­crete gravity dam (shown inFignre 2.3) is the most com­mon form ofconcrete dam. Init. the mass weight of the con­crete and friction resist thereservoir water pressure. Abuttress dam is a specific typeof gravity darn in which thelarge mass of concrete isreduced. and the forces arediverted to the darn founda­tion through vertical orsloping buttresses. Gravitydarns are constructed of non­reinforced vertical blocks ofconcrete with lIexible seals inthe joints between the blocks.

UPSTREAMBARRIER

5

Concrete arch dams are typ­ically rather thin in cr.oss­section (Figure 2.4). Thereservoir water forces actingon an arch dam are carriedlaterally into the abutments.The shape of the arch mayresemble a segment of a cirdeor an ellipse, and the archmay be curved in the verticalplane as well. Such dams areusually constructed of a seriesof thin vertical blocks that arekeyed together; waterstopsare provided between theblocks. Variations of archdams include multi-arch damsin which more than one cur­ved section is used and arch­gravity dams which combinesome features of the twotypes of dams.

A recently developed methodfor constructing concrete grav­ity darns involves the use of arelatively weak concrete mixwhich is placed and compact­ed in a manner similar to thatused for earthfill dams. This"roller compaction" con­struction technique has theadvantage of both decreasedcost and time. In addition,there are no joints whereseepage could occur.

3. Other Types - Various con­struction techniques could beused in a single dam· Forexample, a dam could includean earth or rocklill embank­ment as well as a portionmade of concrete. In such acase~ the concrete sectionwould normally contain thespillway or other outletworks.

Other construction materialssuch as timber or timberfaced with steel sheeting havebeen used for dam construc­tion in the past. In othercases, crib walls conslructe~

of timber, steel, or steel meshfilled with soil or rock wereused. In addition, many typesof embankment and cril>-waJldams employed a concrete orother impermeable facing toaid in water retention. Masonrydams (usually designed asgravity dams) were also POJ>­ular about I DO years ago.

: -~-~

•..

I

...

----.::: : =--=-=--=/ RESISTANCE TO MOVEMENTOFFERED BY KEY IN FOUNDATION

.:.....:......:......:....+j ...~.:: ...... ~ .•. ' .. ~-:~~:::~~.~::::~~--:"---=

SUr~RTOFFERED·'· • .. . ..•. RESISTANCE TO MOVEMENT BYaYFOUNDATlON - - -t\ KEYIN FOUNDATION

RESISTANCE TO MOVEMENT(FRICTION BETWEEN DAM & FOUNDATION)

SUPPORT OFFEREDBY FOUNDATION

PRESSURE OF·RESERVOIR·

..,__,",a·

e.

PRESSUREFROMiitESEli.Vt>Ilt ':

Figure 2.4 Concrete Arch Dam

Figure 2.3 Concrete Gravity Dam

6

A recent and increasinglypopular design for low-headdams (minimum height ofwater behind dam) involvesthe use of inflatahle rubber orplastic materials anchored atthe bottom by a concreteslab.

Some dams are constructedfor special purposes such todivert water or permit con­struction of other facilities inriver valleys. These dams aretermed diversion dams andcofferdams, respectively.

2.3 WATER RETENTIONABIUTYBecause the purpose of a dam is toretain water effectively and safely,the water retention ability of a dam isof prime importance. Water maypass from the reservoir to thedownstream side of a dam by:

• Seeping through the dam• Seeping through the abutments• Seeping under the dam• Overtopping the dam• Passing through the outlet

works• Passing over an emergency

spillway

The fITst three modes are consideredundesirable, particularly if the seeJ>­age is not limited in areal extent orvolume. Overtopping of an embank­ment dam is also very undesirablebecause the embankment materialmay be eroded away. Additionally,only a small number of concretedams have been designed to be over­topped. Water normally leaves adam by passing through an outletworks; it should pass over anemergency spillway only duringperiods of very high reservoir levelsand high water inflow.

A. Seepage Through a Dam - Allembankment dams and mostconcrete dams have some seepagethrough the dam. The earth orother material used to constructembankment dams has somepermeability, and water underpressure from the reservoir willeventually seep through. How­ever, it is important to controlthe quantity of seepage by usinglow permeability materials in theconstruction of the dam and bychannelling and restricting thenow so that erosion of embank­ment materials does not occur.

Seepage through a concrete damis usually minimal and is almostalways through joints betweenblocks or through cracks ordeteriorated concrete which mayhave developed. Maintenance ofthese joints and cracks is thereforeessential. The seepage watershould be collected and chan­nelized, so that the quantity ofwater can be measured and ero­sion Can be minimized.

B. Seepage Around a Dam ­Seepage under a dam, throughthe dam foundation material, oraround the ends of a damthrough the abutment materialsmay become a serious problem ifthe flow is large or if it has suffi­cient velocity to cause erosion.Seepage under a dam alsocreates high hydrostatic uplift(pore water) pressures whichhave the effect of an upwardpressure diminishing the massweight of the dam, making theweight of a gravity dam lesseffective and therefore, the damless stable.Seepage through abutments orfoundations can dissolve theconstituents of certain rockssuch as limestone, dolomite. orgypsum so that any cracks orjoints in the rock become pro­gressively larger aod in tumallow more seepage. Abutmentor foundation seepage may alsoresult -in upipingH internal ero­sion in which the flow of water isfast enough to erode away smallparticles of soil. This erosionprogresses from the water exitpoint backward to the waterentrance point. When that pointis reached, water may then flowunrestricted resulting in evengreater erosion and probabledam failure.Obviously, it is nol desirable toallow large UTlTestricted seepageto occur. To minimize thispossibility, dams are construcledwith internal impermeable bar­riers and internal drainage facili­ties such as drain pipes, filtersystems, or other drainage sys­tems such as toe drains, blanketdrains, or chimney drains.Flow through a dam foundationmay be diminished by groutingknown or suspected highly per­meable material, constructing a

culoff wall or trench below adam, or constructing an upstreamimpermeable blanket. Figure 2.5i1hrstrates a cutoff trench and anupstream blanket.In summary, the overall waterreteotion ability of a dam de-­pends, on the permeability oflhedam, the abutments, the founda­tioli, aod the efforts made toreduce that permeability or re­strict the flow of water throughthose components.

2.4 RELEASE OF WATERIntentional release ofwater, as statedearlier, is confmed to water releasesthrough outlet works or over emer­gency spillways. An outlet workscommonly has a principal or mech­anical spillway and a drawdownfacility. Additionally, dams shouldbe equipped with emergency spillwaysto manage extreme floods.

A. Principal or Mechanical Spill'way - The principal or mechani­cal spillway maintains the normalwater level in the reservoir. Itsfunction is 10 pass expected floodflows past the dam in a safe andnonerosive manner. It may con­sist of a simple metal or concrete·pipe through the dam or a systemof gates that discharge waterover the top into a concretespillway. Either method uses theoverflow principle. When thero:servoir reaches a certain level,water flows into a stand pipe orriser pipe or over a gate. Intakestructures for spillways musthave systems that prevent clog­ging due to accumulations oftrash or debris.

B. Drawdown Facility - All damsshould have some type of draw­down facility which can:'

• Quickly lower the water levelif failure of the dam isimminenl

• Serve the operational pur­poses of the reservoir

• Lower the waterlevel for damrepairs

• Purposely fluctuate the poollevel to Jr.ill weeds andmosquitoes

SANDA: GRAVEL

Figure 2.5 Culoll Trench andUpstream Blanket

The valve regulating the draw­down facility should be on theupstream end of the conduit tominimize the risk to the damposed by a possible internal rup­ture of the pipe.

C. Emergency Spillway - As thename implies, an emergencyspillway functions during emer­gency conditions to preventovertopping of a dam. A typicalemergency spiJIway is an exca­vated channel in earth or rocknear one abutment of a dam. Anemergency spillway should al­ways discharge away from thetoe of a dam. so that erosion ofthe toe will noi occur. Further­more, the spillway should be

..;.'

constructed in such a mannerthat the spillway itself will notseriously erode when it is in use.Obviously, erosional failure ofthe spillway could be as cata­strophic as failure of the damitself. An emergency spillwayshould be sized to convey the so­called "design nood" the rare,large magnitude nood used toestablish design criteria. Thespillways of many existing damsare now considered undersizedbecause standards for the designnood have increased over theyears.

•

7

CHAPTER 3HAZARDS, RISKS, FAILURES

3.0 GENERALDam failures are severe threats to lifeand property and are now beingrecorded and documented muchmore thoroughly than in the pasLRecorded losses have been high. Ufeand property Joss statistics fully jus­tify the need for dam owners to betterunderstand the risks to the publicposed by dams, the kinds of hazardsthat promote these risks, and, gener­ally, the reasons why dams fail.Improving a dam owner's under­standing of realistic risks and possi­ble reasons for failure is an essentialfirst step in any overall effort toimprove dam safety and preserve thebenefits of dam ownership.

3.1 HAZARDS AS SOURCESOF RISKDam structure itself can be a sourceof risk due to possible constructionflaws and weaknesses which developbecause of aging. The site immedi­ately surrounding the structure mayalso increase structural risk if thedam is not positioned or anchoredproperly or if excessive reservoirseepage erodes the foundation orabutments.The physical hazards which· cancause dam failure are translated intohigh risks when people or propertyare threatened, and where the highrisks to which Americans are exposedare exacerbated by a number ofimportant factors. For instance, inmost states, people are allowed tosettle below dams in-potential inun­dation zones, thereby compoundingrisk.Natural hazards such as floods,earthquakes and landslides are alsoimportant contributors to risk. Thesenatural phenomena are considered"hazards" because development hasplaced people and property in theirway. since most natural phenomenaexisted long before mankind esta~

lished patterns of settlement. Failureto adjust to these events has been

9

costly both to dam owners and thepublic in general.Human behavior is another elementof dam failure risk; simple mistakes,operational mismanagemen~ unnec­essary oversights or destructiveintent can interact with other hazardsto compound the possibility offailure. Thus, a broad range ofnatural and human hazards existthat, taken separately or in combina­tion, increase the probability of damfailure and injury to people andproperty.The following discussion of some ofthe most significant hazards that leadto public risk illustrates the interrela­tionship of events that can lead todam failure.

3.1.1 Natural hazards that threat­en dams - The most importantnatural hazards threatening damsinclude:• Flooding from high precipitation• Flooding from dam failure• Earthquakes• LandslidesFlooding from high precipilQ!ion ­Ofthe natural events that can impactdams, floods are the most significanLA noodplain map of the U.S. (Figure3. I) gives some idea of the m'\iorflood-prone areas. Flash noods canhappen anywhere - even on smalldrainages - ·but especially in thewesl Floods are the most frequentand costly natural events that lead todisaster in the U.S. Therefore, floodpotentials must be ·included in riskanalyses for dam failure. Dams aresometimes constructed 10 withstanda probable maximum flood (PMF)assumed to occur on .the upstreamwatershed; this assumed event be­comes the basis for the design ofsafety factors built into the dam (e.g.,enhanced structural elements orspillway capacity). However, damsare ollen built in areas whereestimates of the PMF are based onrather short precipitation and runoff·records. As a result, spiUway capacitymay be underestimated.

to

Figure 3.1 Estimated Proportion 01 Land In FloodplaIn

Reprinted from the Journal of Soil.nd W.ttrConservation. September-October 1985.­Volume 40. Number S.

Copyright 1985 Soil Conservation Socitty of America 1_' ..I ,~••; """ "O~"'"

l'.;I .1 .... ;.. ' r , ....;~. 1••_ 1~.oIl;l••• )

" ,,-,,\ f

.'

c=J o· , ..,~) .',c=J., ·'.-9mm"-_ ........ v.." ....

Floodingfrom damfailure- When adam fails as a result of a flood, morepeople and property are generallyplaced in jeopardy than duringnatural floods. The Rapid City.South Dakota flood of 1970. which'killed 242 people, caused a damfailure which added significantly tothe loss of life. When a natural floodoccurs near a dam. the probability offailure and loss of life almostalways increases.

l1le sudden surge of water generatedby a dam failure usually exceeds the .maximum flood expected naturally;dam failure inundation zones and100-year floodplains are seldom con­gruent. The upper portion of an inun­dation zone abnost. always exceedsthe lOO-year floodplain con­siderably; therefore. residences andbusinesses that would escape naturalflooding can be at extreme risk fromdam failure flooding. Hence. it isimportant to make residents of thosestructures cognizant of the full risk towhich they are exposed so that theycan respond accordingly.

When one dam fails. the suddensurge of water may well be powerfulenough to destroy another down-

stream dam. compounding the disas­ter. The potential for such a snowballeffect is great. but the problem mayseem remote to a dam owner who hasnot studied the potential impacts ofupstream dams on his own structure.Upstream dams may seem ·too faraway to be a real threat, but inunda­tion zones and surge crests canextend many miles downstream ­especially if the reservoir behind thecollapsed dam held a large quantityof water.Earthquakes - Earthquakes are alsosignificant threats to dam safety.Both earthen and concrete dams canbe damaged by grouad motionscaused by seismic activity. Cracks orseepage can develop. leading toimmediate or delayed failure. Damssuch as those in California, locatednear relatively young, active faultsare of particular concern; but dams(especially older concrete and earthenstructures) located where relativelylow-scale seismic events may occurare also at risk. Areas 'of the U.S.where significant seismic risks existare indicated in Figure 3.2. However.recenl detailed seismic analyses haveindicated a much broader area of

seismicity sufficient to dam age darns;the seismic risk is essenthlUy nation­wide. Dam owners should be awareof the history of seismic activity intheir' locality and should develop'their dam safely emergency pr~

cedures accordingly.Landslides - Rock slides and land­slides may impact dams directly byblocking a spillway or by eroding andweakening abutments. Indirectly. alarge laridslide into a reservoirbehind a dam can cause an overllowwave which will exceed the capacityof the spillway and lead.to failure. Aland (or mud) slide can form anatural dam across a stream whichcan then be overtopped and fail. Intum. failure of such a natural damcould then cause the overtopping of adownstream dam or by itself causedamage equivalent to the failure of ahuman-made dam. In addition. largeincreases in sediment caused by suchevenlS can materially reduce storagecapacity in reservoirs and thusincrease 8 downstream dam~s vulner­ability to flooding. Sedimentationcan also damage low-level gates andwater outlels; damaged gates andoutlelS can lead to failure.

Figure 3.2 SeIsmic Map 0' the Unlled states: Reproduced from the Uniform BuildIngCode, 1979 (1982)(1985) edlllorL

tt

SEISMIC RISK MAP OFTHE UNITED STATESZONE 0 No damage.ZONE I Minor damage, dislanl earthquakes

may cause damage to slrUctureswith fundamental periods greaterthan 10 seconds, conesponds tointensities V and VI or the M.M..Scale.

ZONE 2 Moderate damage: corTt:sponds toint.cnsity V)) or the M.M..· Scale.

ZONE 3 MlUor damage. ronespoods tointensity vln and roper of theM..M.- Scale.

ZONE 4 Those BR:1lS wilhin Zone 3 deter­mined by the proximity to certainmajor r.uh systems.

-Modified Mercalallntensity Scale or 1931

TABLE 3.1

HAZARD POTENTIAL CLASSIFICATION FOR DAMSEconomic Loss

Minimal (Undeveloped 10occasional structures oragriculture).Appreciable (Notableagriculture, industry).

E:l.Ccssive (Extensive com­munity, industry ()£ agriculture).

often permit development in haZard­ous areas despite Jong-term dangerand the risk or high future disastercosts. Diversion or settlement awayfrom potential inundation zones is asure means orreducing risk, but is notalways a policy suitable to theintmediale needs or local govern-·ment Perhaps the ullimate irony rora dam owner is In have developed

Urban Development

No permanent structures forhuman habitation.

Significant

High

Category

Low

Urban development with morethan a small number of habit­able structures.

No urban development andmore than a small numberhabilable structures.

(Sou",,, U.S. Army corps ojEnginu,., 1981b)

•

ment below dams. More high andsignificant hazard dams are con­tinually being "created" as develop­ment occurs in potential inundationzones.Many other complell aspects or set­tlement and development must beconsidered in assessing dam risks.Because ohbart-term revenue needsor other pressures~ governments

3.1.2 Hazards rrom human acliv­ity - Human activity must also beconsidered when analyzing the risksposed by dams. By convention,classification or potential dam railurerisk is based on the severity orpolen­tial impact, not on the structuralsarety or the dam. Thus, dams thatmay be or very sound constructionare labeled "high hazard" if railurecould resull in catastrophic loss orlire.- in other words, ir people havesettled in the potential inundationrone. The "high hazard" designationdoes not necessarily imply structuralweakness or an unsare dam. Lowerclassifications include "significanlhazard" dams ror which railure isestimated In result in large propertyloss, and "low hazard" dams rorwhich railure is estimated to result inminimal property loss. The rollowingis a recommended guide ror classify­ing dam hazards (Table 3.1).

Risk may weD increase through timebecause few governmental entitieshave round the means In limit settle-

12 . \

ami implemented a safety programand then to have setUement permit­ted in the potentia] inundation zoneso that the owner's liability increases.Two extremes of human purpose ­the wiD to destroy through war orterrorism and the urge 10 develop andto construct - can both result inpublic risks. Dams have proven to beartractive wartime targets, and theymay be tempting to terrorists. On theother hand, a terrorist's advantagefrom holding the public at risk maywell be illusory; the deliberate des­truction of a dam is not at all easy tobring about Yet the possibility existsthat such an act could take place, andit should not be discounted by thedam owner.All sorts of other human behaviorshould be included in risk analyses;vandalism for example cannot beexcluded and is in fact. a problemfaced by many dam owners. Vegetatedsurfaces of a dam embankment,mechanical equipment, manholecovers and rock riprap are par­ticularly susceptible to damage bypeople. Every precaution should betaken to limit access to a dam byunauthorized persons and vehicles.Dirt bikes (motorcycles) and four­wheel drive vehicles, in particular,can severely degrade the vegetationon embankments. Worn areas lead toerosion and more serious problems.

Mechanical equipment and associatedcontrol mechanisms should be pr<>.tected from purposeful or inadvertenttampering. Buildings housing mech- .anical equipment should be sturdy.have protected windows, heavy dutydoors, and should be secured withdeadbolt locks or padlocks. Detach­able controls. such as handles andwheels, should be removed when notin use and slored inside the pad­locked building. Other controls shouldbe secured with locks and heavychains where possible. Manholecovers are often removed and some­times thrown into reservoirs orspillways by vandals.

Rock used as riprap around dams issometimes thrown into the reser­voirs, spillways, stilling basins, pipespillway risers. and elsewhere. Rip­rap is often displaced by fishermen toform benches. The best way to pre­vent lhis abuse is to use rock too largeand heavy to move easily or to slushgrout the riprap. Otherwise, the rockmust be regularly replenished and

other damages repaired Regularvisual inspection can easily detectsuch human impacts.Owners should be aware of their re-

- sponsibility for the safety of peopleusing their facility even though theirentry may not be -authorized "NoTrespassing" signs should be posted,and fences and warning signs shouldbe erected around dangerous areas.As discussed in Chapter 10. liabilityinsurance can be purchased to pro­tect the owner in _the event ofaccidents.

3.2 SITE-SPECIFICSTRUCTURAL RISKDeveloping site-specific risk analysesinvolves consideration ofa number ofhazards. Such analyses are helpful instimulating better awareness. plan­ning and design. In some caseS darnstructure analyses are quantitativelybased. and precise conclusions aboutengineering and design can be made.Probabilistic analyses can also beimportant and useful. Still, exactquantitative and probabilistic toolsare not yet applicable in manysituations and do not fully supple­ment or replace qualitative analyses- informed perception and judgmentof the risks. Judgment and engineer­ing experience should play an impor­tant role in reaching useful conclusionsin any site-specific analysis of strue:rurm risk. .

As mentioned in Chapter 2. struc­rural risb tend to result from desigoand construction problems related tothe dam materims, construction prac­tice and hydrology. The complexityof the hazard is such that structuraldesign and causes of dam failure aresignificant areas of research inengineering. Indeed belter designcriteria have been developed andsafer dams are being built, but thereis no basis for complacency. Damscontinue to age. people continue tomove into inundation zones andenough hazards exist that the net riskto the public will remain high formany years.

3.3 SOURCES OF DAMFAILUREThere are many complex reasons ­both structural and nOl}-strucrural ­for dam failure. Many sources offailure can be traced to decisionsmade during the design and construc­tion process and to inadequate mainten­ance Of. operational mismanagement.Failures have also resulted from thenarurm hazards already mentioned ­large scale flooding and earthquakemovement However, from the per­spective ofthe owner, the strucrure ofa dam is the starting point for thoroughunderstanding of the potentials forfailure.The International Commission ofLarge Dams (ICOW) conducted asrudy of dam failures and accidents.Figures 3.3 through 3.5 summarizethe data (which pertain only to damsmore than 15 feet high and includeonly failures resulting in waterreleases downstream).

3.3.1 Three categories of struc·rural failure - Three categories ofstructural failure alluded to in Chap-­ter 2 are:

• Overtopping by nood• Foundation defects• PipingOvertowing may develop from manysources, but often evolves frominadequate' spillway design. Alter­natively even an adequate spillwaymay become clogged with debris. Ineither situation, water pours overother parts of the dam. such as abut­ments or the dam toe and erosion andfailure follow.Concrete dams are more susceptibleto roundation failure than overtop-­ping whereas earthlill darns suffer

. from seepage and piping. However.when overtopping and foundationfailures are lumped together, theyrepresent 82 percent of the failuressrudied by the ICOLD.Figure 3.3 shows the relative impor­tance of these three main categoriesoffailure. Overml, these three eventshave about the same rate of incidence.A more specific analysis of thepotential sources of failure has totake into account types of darns.Similarly. the characteristics of thetype of dam being monitored willpoint to problems requiring morecareful attention by the owner whendeveloping a safety program.

Dam failures 1900-1915 (over 15 m heighl)

Dam failures 1900-1915 (over 15 m heighl)

13

3.3.2 Failures by dam type - Figure3.4 shows the relation between damsbuill and those thaI failed for vanousdam types from 1900 10 1969.Gravity darns appear the safest,followed by arch and nn dams. BUI­tress darns have Ihe pooresl recordbul are also the ones used least.

Embankment or Ear/1r/i1l Dams ­The major reason for failure of nu orembankmenl dams was piping orseepage (38 percenl; Figure 3.3).Other hydrologic failures were sig­nmcant, including overtopping anderosion from waler nows. All earthendarns exhibil some seepage; however,as discussed earlier, this seepage canand musl be controlled in velocityand amount. Seepage occurs Ihroughthe structure and, ifuncontrolled, canerode malerial from Ihe downstreamslope or foundation backward lowardthe upstream slope. This "piping"phenomenon can lead 10 a complelefailure of the structure. Piping actioncan be recognized by an increasedseepage now rale, the discharge ofmuddy or discolored waler below Ihedam, sinkholes on or near theembankmenl, and a whirlpool inthe reservoir.Earth dams are particularly suscepl­ible 10 hydrologic failure since moslsediments erode al relatively lowwalerIJow velocilies. Hydrologicfailures result from the uncontrollednow of waler over the dam, aroundthe dam, adjacenllo the dam, and theerosive action of water on the dam'sfoundation. Once erosion has begunduring overtopping, il is almoslimpossible 10 slop. In a very specialcase, a well-vegelaled earth embank­ment may wilhsland limiled overtop­ping if waler nows over the lop anddown Ihe face .as an evenly dis­tribuled sheel and does nol becomeconcentrated in a single channel.Table 3.2 lists examples of earthendam f.ilures caused by some ofthese conditions.

•

Overtopping

FILL

Piping~e-

r-­Foundation

o

. 138

I 53I-'-----'----------~_ ___J

Overtopping

CONCRETE

Foundation

CONCRmOVERTOPPING

FOUNDATION

PIPING ANDSEEPAGE

OTHERS

100

AU lYPES

OVERl:OPPING 134

FOUNDATION .... 130PIPING AND 1----'------,1r-'28SEEPAGE

OTHERS ~8

o 20 40

PERCENT OF F AlLURES

(excl failures during construction and acts of war)

Figure 3.3 Cause 0' 'allure.Source: ICOLD (1973).

OJ

~

~c;!;,.50gOJ

'"..zOJ

~OJ..

o'--__....L__----'-__--.J

o 10 20 30 0 10 20 30

AGE IN YEARS AGE IN YEARS

(excl. failures during coDStruction and acts of war)

Figure 3.4 Age at 'allure.Source: ICOLD (1973).

,..TABLE 3.2

EXAMPLE OF EARTHEN DAM FAILURES

SOUTHF0RK. PENNSYLVANIAThe famoua Johnatovm diluier, caused by the failure afthe South Fort Dam in 1889 inwhich 2,209 people were tilled, is on eIample of the overtopping of on earthen dam.Heavy rainfall in the upper drainage basin of the dam filled the reservoir and caused over­topping. It was later calculated thaI ifaspillway had betin huih according to specification.and if the original ondel pipes had been available for CuD capacity discharge, there wouldhave heen no overtopping.

TETON DAM, IDAHOThe Teton Dam failure in 1976 was attrihuted to(I) internaleTOsion (piping) of the coreof the dam deep in the righl foundation key trench, with the eroded .oil particles fmWngeIits through channel. in and along the interface ofthe dam with the highly pervious ahut­ment rock and talus 10 points at the right groin of the dam; (2) destruction of the eIitavenues and their removal by the outrusb ofreservoir waler, (3) the existence ofopeningsthrough inadequately sealed rock joints which may have developed through cracks in thecore zone in the key trench; (4) the development of piping through the main body of thedam that quickly led to complele failure; and (5) the design ofthe dam did _adequatelYtale into account the foundation conditions and the characteristics of the soil used for fill­ing the key treoch.

BALDWIN HILLS AND ST FRANCES DAMS, CAUFORNIATheBaJdwin Hills Dam failed in ]963 following displacement of its foundation. Founda­lion problems were ultimately traced to seismic activity along nearby rBults~ The failure ofthe large Sl Francis Dam (part oflbe water supply system for Los Angeles) in 1928 wasalso attributed to a variety of problems reJated to foundation pressures. seepage aroundthe foundation and operation.

(Jansen. 1980).

TABLE 3.3EXAMPLES OF CONCRETE DAM FAILURES

AUSTIN, PENNSYLVANIAAn example of a foundation problem can be found in tbe failure of·the Austin.Pennsylvania Dam in September, 1911. Evidently, the reservoir was f1IJed before theconcrete had set sufficiently. Eventual failure near the base occurred because ofweaknessin the foundation or in the bond 1?etween the foundation and the concrete.

WALNUT GROVE, ARIZONA .In 1890. the Walnut Grove dam on the Hassayompa River failed due to overtopping, till­ing ahuut 1SO people. The failure was blamed on inadequate capacity oflbe spillway andpoor construction and workmanship. A spillway 6 X 26 feet had been blasted oul ofrockon onc abutment. but with a drainage area above the dam site of about 500 square miles.the spillway could not provide nearly enough discharge capacity.

(Jansen. 1980)

•

Concrete Dams - Failure ofconcreledams is primarily associaled withfoundation problems. OvertoPPing·i.also a significant cause again primar­ilywhen spiUways are buill· withinadequate capacity. Other causesinclude failure to leI concrete setproperly, and earthquakes. Theexamples summarized in Table 3.3iIluslrate typical foundation pr0b­lems leading 10 dam failure.

3.3.3 Age and ils relalion 10failure- Figure 3.5 iUuslrates canseof failure as a function ofa dam's ageat the time of failure. Fotmdationfailures occurred relatively early,while other· causes generaDy tookmucb longer 10 malerialize. Thus, itis not surprising thaI a very large per­centage of all dam failures occur dur­ing initial fiUing, since this is whendesign or coDStruction naws, or lalentsite defects, appear.

In summary, this outline of thebazards, risks, and failures associ­ated with dams is provided so thaIowners will bave an overview of tbeproblem with which they must deal.Each aspect of a safety programshould be visualized by the damowner in lenns relaled to the mostprobable sources of failure for a par­ticular dam.

FILL

IArch

Buttress

Gravity

FILL

IArch

Buttress

Gravity

Dams Buill

~~UZoU

Failed Dams

~UZou

o 20

58

I I

40 60PERCENT

74

80

15

~ Arch

~ ButtressZ G.o ravltyU TOTAL

CONCRETEFILL

2.6

o I 234FAILED DAMS IN PERCENT OF DAMS IiUILT

(Excl. Failures During Construction and Acts of War)

Figure 3.5 Dam .types (WeslernEurope and USA, 1900·1969).Source: ICOLD (1979).

•

CHAPTER 4DEVELOPING A SAFETY PROGRAM

4.0 OBJECTIVES OF ASAFETY PROGRAMThe significance of the dam failureproblem points out the need for adam safety program Such a programshould be based on an evaluationto determine a dam's structural andoperational safety. The evaluationshould identify problems and recom­mend either remedial repairs, opera­tional restrictions and modifications",or further analyses and studies todetermine solutions to the problems.A safety program comprises severalcomponents addressing the spectrumof possible actions to be taken overthe short and long term. Theseactions include:

• Assessing the condition of thedam and its components

• Conducting preliminary anddetailed inspections

• Identifying repairs and continu­ing maintenance needs

• Establishing periodic and con­tinuous monitoring capabilitiesover the long' term

• Establishing an emergencyaction plan to help minimizeadverse impacts should the damfail

• ESlablishing operations pr<>'cedures which recognize damfailure hazards and risks

• - Documenting the' safety pro­gram so that Ihe informationestablished is available al timesof need and can be readilyupdaled

Development of a safety programinvolves a phased process beginningwith collection. and review of existinginformation, proceeding to detailedinspections and analyses, and cuI·minaling with formal documentation.Much of the preliminary work can beaccomplished by the dam owner withthe assislance of state and localpublic agencies. However, dependingupon the number and seriousness ofproblems identified by the initialassessmen~ professional assistanceby qualified engineers and conlJac·Iors may be required.

17

4.1 GUIDELINES FORASSESSING EXISTINGCONDITIONSThe guidelines for assessing existingconditions are a sequence of stepsthat will enable a dam owner tosecure the information needed todetermine the need for subsequentdetailed investigations, repairs andmaintenance. The sleps include:

• Reviewing existing data• Visiting the site• Inspecting the dam• Assessing significance of ob-

served conditions• Deciding what to do nextReviewing Existing Data - Theimportant first step is to collect andreview available information on thedam - its design, construction, andoperation. A first requirement is agood map of the site. Maps of thewatershed and the downstream chan­nel reaches are also valuable. Thedesign ofthe dam and its appurtenantstructures should be reviewed toassess its actual performance com­pared 10 that intended. Engineeringrecords originating during construc­tion should be reviewed to determineif structures were constructed asdesigned. Records of subsequentconstruction modifications should becollected, as well as operation recordswhich document the performance ofthe dam and reservoir. Any pre­viously prepared emergency actionplan should be reviewed to determineif it is up to date and workable. All

- these records should be incorporatedinto a notebook or file; they are mostimportant in establishing a safetyprogram and its supporting documen­tation. Chapters 5 through Chapter10 provide information to aid thedevelopment ofsuch documentation.It may be, however, that no recordsexist In this instance, a detailedexamination of the structure isappropriate.Visiting Ihe Dam Site - The nextstep is to visit the site. Undoubtedly,the dam site is well known and hasbeen visited numerous times. but inthis visit, there are some particularthings to look for. A fresh look at the

Figure 4.1 Procedural Guidelines lor A Dam Safety Program

and monitoring. The now chart illus­trates the cyclical nature of the pro­gram and the need for ~ntinuing

vigilance. Emergency actIOn ~an

hopefully be avoided, but a wellthought out plan of action (Chapter8) in case of imminent or actualfailure can greatly reduce damageand loss of life.

4.3 DOCUMENTING THESAFro PROGRAMIt is important to document a safetyprogram in order to make maximum,reliable use of information aboutlhedam. The procedural guidelines thatfollow can serve as an ouUine or tableof contents for a safety programreport. The operations plan (Chapter9) presents a detailed outli,!e of theinformation that should be mcludedin the documentation. The chapterswhich follow suggest forms for

_ inspections, moniioring~ etc. whichcan be used to record information. Itis helpful to maintain all the materi~1in a single notebook or file so that Itcan be updated and available whenneeded. Duplicate copies of much ofthe liIe should be stored at a differentlocation from the original.

v~g...5l;.c:'i!

~

INSPECTION

I ....

~

REPAIRS &.MAINTENANCE

l/,.- ..

•OPERATIONS MONITORING

v

~ ~

EMERGENCYACTION v

4.2 PROCEDURALGUIDEUNES·A SOURCEBOOKThis chapter provides an overview ofbow to establish a safety program.Subsequent chapters detail technicaland procedural steps of the varioussafety program components. Theyinclude:• Detailed Inspection Guidelines

(Chapter 5)• Monitoring and I nstrumenta­

tion Guidelines (Chapter 6)• Maintenance Guidelines (Chap­

ter 7)• Emergency Action Guidelines

(Chapter 8)• Operations Guidelines (Chap-

ter 9)These program components can bevisualized as a sequence ofinitial andcontinuing 8ctiv~ties to insure damsafety. They are illustrated inFigure 4.1.Again, the program of ~s~ction forboth the initial and conbnumg safety­evaluations establishes the conditionof the dam and provides the base ofinformation necessary for specificactions involving repair, operation,

dam structure and its surroundingsfrom the point of view of its potentialhazard is required

Inspecling the Dam - It will benecessary to take a detailed and sys~

tematic look at all components of thedam and reservoir system. The des­cription of the site's components(Chapter 2) should aid this inspec­tion. The descriptions are generalized,and it must be recogniz.ed that dams.and their components come in variousshapes and sizes and differ greatly indetail. Features to inspect include:

• Access roads and ways• Upstream slope• Crest• Downstream slope• Left and right abutments• Spillways• Outlets and drains• Reservoir area (exposed and

submerged)Conditions to look for range fromobvious deterioration, cracks andslumps, and boiling seepage to not­so-obvious internal corrosion andweathering, settlement, and founda­tion rock deterioration and/or dis­solution. A dam may look stable butbe susceptible to failure resultingfrom gradual deterioration of itsinternal structure. Regular and verydetailed inspections (Chapter 5) andfollow-up monitoring (Chapter 6)and maintenance (Chapter 7) areneeded to assure the l)Iaximum levelof safety.Assessing Significance of Observed

. Condilions - Chapter 5 presentsdetailed information on conductinginspections and assessing the signifI­cance of observed conditjons. Typ­icaUy, eroded areas, seepage,. slides.and outflow draw the most attention.Deciding What To Do Next- Theseinitial activities will have provided agood start to establishing a damsafety program. Available informa­tion on design and construction of thedam and later structural mod­ifications provides perspective on itsexisting condition relative to thatinlended. Ifno documentation exists,then development of equivalent detailshould be a first priority.Inspection and documentation assis­tance is available from several sour­ces including state and local agenciesresponsible for dam safety. Pr<>­fessional engineering consultants canalso provide detailed inspections,lesting, analyses. and documentation(Chapter 10).

z ~ <.:-0 ;> \11 0

~ 6 ~.... ZZ 0 ~< \11 ~ \11 ~'" ~0 Z 0 \11

'" D! 0

~ ~>- 0 ~'" ti ::c

D! - Cl < ~@....'" '"

~ '" 0 <'" .... 0 < \11

~'" \11 <.: ~~ '" ~"" ~Cl Cl '" ::c '"

TABLE 5.1INSPECTION GUIDEUNES DIRECTORY

CONCRETE DAM (5.4)Upstream FaceDownstream FaceAbutmentsCrests

19

---- JI:---x-- -~--- -----j----t----I-- ---x-- ---}

I r._-'-, ] -,--_- t -t-==1="---- ~ - ,~....:.::t~-=i -:-- ----x -I----t-~ ----i----1- 1------- -;t----- -Jl:------ ---f-----*--l-j--- ---- --

-r--- -I1I--x---*----

'"~o.... g!Z ~

~ ~Z ~

- _. g ~INSPECT FOR -- -< :<

I-I JX x*t--~ t:-~*I~-~­t-..: -- --I I}--r-

FEATURE

EMBANKMENT DAM (5.3)Upstream SlopeDownstream SlopeAbutmentsCrestSeepage AreasInternal DrainageRelief Drains

Tabl~ 5.1 lists featurrs '0 b~ inspec'ed 0' adam and 'hI! problems or d(/iciencin to b~

looktd fOT. 11l~ specific sections of thismanual j" which rhl! ",ariousfearurn art dis­cussed art also I-ndica'ed.

SPillWAYS (5.5)Approach ChannelStilling BasinDischarge ChannelControl FeaturesErosion ProtectionSide Slopes

---J f--- ...--- ----

------1;

---oJ ­t----col-----, ---

INUTS, OUTUTSAND DRAINS (5.6)Inlet & OutletsStilling BasinDischarge ChannelTrashracksEmergency Systems

---- ---- - -t--t--t--- 1-------

GENERAL AREAS (5.7)Reservoir SurfaceShorelineMechanical SystemsElectrical SystemsUpstream WatershedDownstream FIO<Xl-

Plains

--•--- -t----

CHAPTER 5INSPECTION GUIDELINES

5.0 INTRODUCTIONAn effective inspection program isessential for identifying problemsanti providing safe maintenance of adam. An inspection program shouldinvolve three types of inspections:(I) periodic technical inspections;(2) periodic maintenance inspec­tions, and (3) informal observationsby project personnel as they operatethe dam. Technical inspections mustbe performed by specialists familiarwith the design and construction ofdams and should include assessmentsof structure safety. _Maintenanceinspections are perfonned more fre­quently than technical inspections inorder to detect at an early stage anydevelopments which may be det­rimental to the dam. They involveassessing operational capability aswell as structural stability. The thirdtype of inspection is actually a con­tinuing effort by on-site project per­sonnel (dam tenders, powerhouseoperators, maintenance personnel)perfonned in the course of their nOf­

mal duties. Education of new person­nel is required to assure the continuedeffectiveness of these inspections.

Visual. inspection performed on aregular basis is one of the mosteconomical means a dam owner canuse to assure the safety and long lifeof a dam and its immediate environ­ment. Visual inspection is a straight­forward procedure that can be usedby any properly trained person tomake a reaSonably accurate assess­ment of a dam's condition. Theinspection involves careful examina­tion or the surface and .11 parts of thestructure, including its adjacentenvironment The equipment requiredis not expensiv-e9 and the inspectionusually can be completed in less thanone day.

21

5.1 INSPECTION GUIDELINESTable 5.1 lists dam components andconditions which may be observedduring an inspection. The table sum­marizes the detailed guidelines pre­sented in subsequent sections ofthis chapter.

Section 5.3 Embankment damsSection 5.4 Concrete damsSection 5.5 SpillwaysSection 5.6 Inlets, outlets and drainsSection 5.1 Other areas

At the end of the chapter, diagramsand tabular listings of the guidelines(Figures 5.3 through 5.6) are pre­sented for the various dam corn­ponents. The guideline tables providea quick reference to be used inassessing observed conditions9 theirprobable cause and possible conse­quences9 and remedial actions. Theguidelines also point out theHAZARDOUS problems whereevaluation by an ENGINEER isrequired.The dam owner, by applying themaximum prudent effort, can identifyany changes in previously noted con­ditions that may indicate a safetyproblem. Quick corrective action toconditions requiring attention willpromote the safety and extend theuseful life of the dam while possiblypreventing costly future repairs.

TABLE 5.2Inspection Equipmenl and Its Use

Inspeclion Checklisl - Serves as a reminder of all importanl conditions 10be examined.NOlebook and Pencil- Should be on hand so that observations can be wrillendown at the time they are made, thus reducing mistakes and avoiding the need toreturn to the site to refresh the inspector's memory.Tape Recorder - Can be effective in making a record of field observations.Camera - Can be used to provide photographs of observed field conditions.Photographs taken from the same vantage points can also be valuable in compar­ing past and present conditions.Hand Level- May be needed to accurately locate areas ofinterest and 10 deter-'mine embankment heights and slope.Probe - Provides information on conditions below the surface, such as the depthand sollness of a saturated area.Hard Hat- Should be used when inspecting large outlets or working in construc­tion aress.

Pocket Tape - Provides accurate dimensional measurements so that meaningfulcomparisons can be made of movements.

Flashlight - May be needed to inspect the interior of an outlet in a smalldam.

Shovel - Useful in clearing drain outfalls, removing debris, and locating monitor-ing points. . .

Rock Hammer - Can be used to check questionable-looking riprap or concretefor soundness. Care must be taken not to break through thin spots or causeunnecessary damage.

Bonker - Is used to determine the condition of support material behind concreteor asphalt faced dams by flIlDly tapping the surface of the facing material. Con­crete fully supported by /ill material produces a "click" or "bink" sound, whilefacing material over a void or hole produces a "clonk" or "bonk" sound A bonk­ercan be made of I I/~inch hard wood dowel with a metal tipfmnly fIXed to thetapping end.

Binoculars - Are useful for inspeeling limited access areas, especially on con­crele dams.

Volume Container and Timer- Are used to make accurate measurements oflherate of leakage. Various container sizes may be required, depending on thenow rales.

Stakes and Flagging Tape - Are used to mark areas requiring future attentionand to stake the limits of existing conditions, such as cracks and wet areas, forfuture comparison.

Watertight Boots - Are recommended for inspecting areas of the site wherestanding water is present

Bug Repellent - Is recommended during warm weather. Biting bugs can reducethe efficiency and effectiveness of the inspector.

First Aid Kit- Is particularly recommended for inspections in areas where rat­tlesnakes or other poisonous snakes might be present

22

5.2 ORGANIZING FOR. INSPECTIONAll inspections should be organizedand systematic, and inspectors shoulduse equipment appropriate for thetask, record observations accurately,and survey the structure and sitecomprehensively.Equipment - Equipment useful forinspections is listed in Table 5.2.

Recording Inspection Obser­vations - An accurate and detaileddescription of conditions observedduring each inspection will enablemeaningful comparison of conditionsobserved at different times. Allmeasurements and observed detailsrequired to get an accurate picture ofa dam's cunent condition and possi­ble problems should be recordedThis information has three elements:

I) Location - The location of anyquestionable area or conditionmust be accurately desenDed'sothat the area or condition can beevaluated for changes over funeor reexamined by experts. Photo­graphs can be helpful in thisregard. The location along thedam, as well as above the toe orbelow the crest, should be estal>­lished and recorded Problems inthe outlet or spillway should besimilarly located.

2) Extent or Area - The length,width, and depth or height of anysuspected problem area should bedetermined

3) Descriptive Detail - A brief yetdetailed description of an anom­alous condition should be given.Some items to include are:• Quantity of drain outflows• Quantity of seepage from

point arid area sources• Color or quantity of sedi-

ment in water ..• Depth of deterioration in

concrete• Length, displacement, and

depth of cracks• Extenl of moist, wet, or.

saturated areas .• Adequacy of prolective

cover• Adequacy of surface drain­

age• Sleepness or configuration

of slopes• Apparent deterioration rate• Changes in conditions

Coverage - An inspection is conduct­ed by walking along and over a damas many times as is required toobserve the entire structure. Fromany given location, a person canusulilly gain a detailed view for 10 to30 reel in each direction, dependingupon the smoothness of the surfaceor the Iype of material on the surface,(i.e., grass, concrete, riprap, brush).On \be downstream slope a zigzaginspection path should be used toassure that any cracking is detected.Sequence - A sequence of inspectioninsuring systematic coverage of anentire site is:

• Upstream slope• Crest• Downstream slope• Seepage areas• Outlet• Spillway

Following a consistent sequencelessens the cbance of an importantcondition being overlooked. Re­porting inspection results in the samesequence is recommended to ensureconsistent records. Inspection fonnsare included in Appendix A. Theforms sbould be supplemented withadditional details specifIC 10 a givendam.

Record Keeping - A dated reportshould be filled out for each inspec­tion, and sbould be flied along withany photographs taken (wbich shouldalso be dated). In addition 10 inspec­tion observations, monitoring mea­surements and weather conditions(especially recent rains, extended dryspells and snow cover) sbould also besystematically recorded and includedin the inspection recordImmediately following an inspection,observations sbould be comparedwith previous records to see if thereare any trends that may indicatedeveloping problems. If a question­able cbange or trend is noted, andfailure is not imminent, a dam ownershould consult a professional engineerexperienced in dam safety. Quickreaction to questionable conditionswill ensure tbe safety and long life ofa dam and possibly prevent cosUyrepairs.

Crucial Inspecrion Times - Thereare at least five special times wben aninspection is recommended regard­less of the regular scbedule.I. Prior10 a predictedmajor rainslonn

or beavy snow melt; cbeck spill­way, ouUet cbannel, and riprap,

2. During or after a severe rain­stonn; cbeck spiJlway, outletcbannel, and riprap,

3. During or following a severewindslorm; cbeck riprap perfor­mance during the storm (if pos­sible) and' again after the stormhas subsided,

4. Following an earthquake in thearea; make a complete inspectionimmediately after the event andweekly inspections fot the nextseveral months to detect anydelayed effects,

5. During and inunediately after thefirst reservoir filling; schedule aregular program of frequent corn­plete inspections during the perioda reservoir is flISt being filled toassure that design and site con­dilions are as predicted. In moststates, an inspection and filling

schedule are presenl>ed by thedesign engineer and approved by!be stale engineer.

5.3 EMBANKMENT DAMSAND STRUCTURESEmbankment dams constitute themajority of structures in place in theU.S. Table 5. I presents a generaldirectory of embankment features 10be inspected and the conditions 10look for. The major features include:

• Upstream slope• Downstream slope• Crest• Seepage areasMany of the principles and guidelinespresented in this, section are alsoapplicable to concrete structures.

5.3.1 Upstream Slope - Typically,major problems encountered on anupstream slope are:

• Cracks• Slides• Cave-ins or sink holes

.• Severe erosionThe flISt three conditions may indi­cate serious problems within theembankment Severe erosion obvi­ously can weaken the structure. Anupstream slope should receive aclose inspection because riprap andbigh water levels can bide problems.(When walking on riprap, cautionsbould be used to avoid personalinjury.) When a reservoir is emptied,the exposed slope should'be thorough­ly inspected for - settlement areas,rodent activity, sink boles, or slides.Also, the reservoir basin (bottom ofthe reservoir) should be inspected for

• cave-ins or sink boles.Again,' most importantly, a criss­cross path should be used wheninspecting the slope so that cracksand slides can be easily identified. Inmany instances, sighting along thewater line alignment will indicate achange in the uniformity of the slope;an inspector should stand at one endof the dam and sight along the waterline checking for straightness anduniformity. If a crack is seen, thecrest and downstream slope in itsinunediate area should be carefullyinspected.Cracks indicate possible foundationmovement, embanbnent failure, or Ii

surface slide. Locating them can bedi/liculL Cracks can be less than aninch in width, but still several feetdeep. Cracks I foot deep usually are

23

not produced by drying and usuallyare cause for concern. A line ofrecenUy dislodged riprap onimupstream slope could indicate acrack below the riprap.Slides can be almost as difficult todetect as cracks. When a dam is con­structed the slopes may not be uni­formly graded. Familiarity with theslope coilfiguration at the end of con­struction can help identify subse­quent slope movements. Moreover,the appearance or slides may be sul>­Ue; for example, they may produceonly about 2 feet or settlement orbulging in a distance of 100 feet ormore, yet this would still be a signifI­cant amount of setUement. Datedphotographs are particularly helpfulin detecting such changes.Sink holes or cave-ins result frominternal erosion of the dam - a veryserious condition for earthen ern­bankments. The internal erosion, orpiping, may be reflected by turbidseepage water on exit Surface soilmaterials may be eroded by waveaction, rain runoff, and burrowactivities. IT aUowed to continue, theembankment thickness can be reducedand the structure weakened.

5.3.2 Downstream Slope - Adownstream slope should be inspect­ed carefully because it is the areawhere evidence of developing prol>­lems appears most frequently~ Toassure adequate inspection" this areashould be kepi free from obscuringweeds, brush, or trees.When cracks, slides or seepage arenoted in the downstream slope, thedesignated dam safety authoritiesshould be notified inunediately.On the downstream slope, some ofthe more threatening conditions thatcould be identified are: •

~ Cracks• Slides• SeepageCracks can indicate setUement, dry­ing and shrinkage, or the develop­ment of a slide. Whatever the cause,cracks should be monitored andchanges in length and width noted.Drying cracks may appear and disap­pear seasonally and normally will notshow vertical displacement as willsettlement cracks or slide cracks.Slides require inunediale detailedevaluation. Early warning signsinclude a bulge in the embankmentnear the toe of a dam or vertical dis-

placement in the upper portion ofan embankmenLSeepage is discussed separatelybelow.If any of these three conditions areSeen or suspected, the state engineer'soffice should be notified immediately.If a downstream slope is coveredwith heavy brush or vegetation, amore concerted search must bemade.

5.3.3 Crest - A dam's crest usuallyprovides the primary access for in­spection and maintenance. Becausesurface water will pond on a crestunless that surface is well maintained,this part of a dam usually requiresperiodic regrading. However, prob­lems found on the crest should not besimply graded over or covered up.When a questionable condition isfound, the state's dam safetyengineers should be notifiedimmediately.

On the crest, some of the morethreatening conditions that may beidentified are:

• Longitudinal cracking• Transverse cracking• Misalignment

Longitudinal cracking can indicatelocalized instability, differential set­Uement, and/or movement betweenadjacent sections of the embank­menL Longitudinal cracking is typ­ically characterized by a single crackor a close, paraDel system of cracksalong the crest in a direction more orless parallel 10 the axis of the dam.These cracks, which are usually con­tinuous over their length and areusually greater than I foot deep, canbe differentiated from drying crackswhich are usually intermittent, erraticin pattern" sballow, vel}' narrow,and numerous.

Longitudinal cracking may precedevertical displacement as a damaltempts 10 adjust to a position ofgreater stability. Vertical dis­placements on the crest are usuallyaccompanied by displacements onthe upstream or downstream face ofadam.

Transverse cracking can indicate dif­ferential settlement or movement be­tween adjacent segments of a dam.Transverse cracking is usually asingle crack or a close, parallel sys­tem of cracks which extend acrossthe crest in a direction more or lessperpendicular to the length of a dam.

This type of cracking is usuallygreater than I foot in depth.Transverse cracking poses a definitethreat to the safety and integrity of adam. If a crack should progress to apoint below the reservoir water sur­face elevation, seepage could pro~

ress along the crack and through theembankment causing severe erosionand ifnot corrected, leading to failureof the darn.Misaligrunent can indicate relativemovement between adjacent portionsof a dam - generaDy in directionsperpendicular to the axis of the dam.Excessive settlement ofdam materialand/or the foundation can also causemisalignmenl Most problems areusually detectable during close in­spection. Misaligrunent may, how­ever, only be detectable by viewing adam from either abutmenL Ifon closeinspection, the crest appears to bestraight forthe length of the structure,alignment can be further checked bystanding away from the dam on eitherabutment and sighting along theupstream and downstream edges ofthe cresL On curved dams, aligrunentcan be checked by standing at eitherend of a short segment of the dam andsighting along the crest's upstreamand downstream edges, noting anycurvature or misaligrunent in thatsection.

5.3.4 Seepage areas - As discussedpreviously, although all dams havesome seepage, seepage in any area onor near a darn can be dangerous, andall seepage should be trealed as apotential problem. Wet areas down­stream from dams are not usuallynatural springs, but seepage areas.Seepage must be controlled in bothvelocity and quantity. High velocityflows through a dam can cause pro­gressive erosion and, ultimately,failure. Saturaled areas of an em­bankment or abutment'can move inmassive slides and thus also leadto failure.

Seepage can emerge anywhere on thedownstream face of a dam, beyondthe toe, or on the downstream abut­ments at elevations below normalreservoir levels. A potentiaDy dan­gerous condition exists when seepageappears on the downstream faceabove the toe of a dam. Seepage onthe downstream slope can cause aslide or failure of the darn by internalerosion (piping). Evidence of seepagemay vary from a soft, wet area to a

flowing spring, and may appearinitially as only an area wherevegetation is lush and dark greeri incolor. Cattails" reeds, mosses, andother marsh vegetation often becomeestablished in seepage areas. Down­stream abutment areas should alwaysbe inspected closely for signs ofseepage, as should the area ofcontactbetween an embankment and a con­duit spillway;drain, or other appurte­nant structures and outlets. Slides inthe embankment or an abutment maybe the result of seepage causing soilsaturation and high pore pressures.Since seepage can be present but notreadily visible, an intensive searchshould be made of all downstreamareas where seepage water mightemerge. Even in short grass cover,seepage may not be visible and mustbe walked on to be. found. Ideally, aninspection for seepage should bemade when a reservoir is fuJI.

5.4 CONCRETE DAMS ANDSTRUCTURESFrom a safety standpoint, the prin­cipal advantage of concrete darnsover earth dams is their relative free­dom from failure by erosion duringovertopping as weD as from embank­ment slides and piping failures.Although concrete dams comprise aminority of all darns, they are com­monly of greater height and storagecapacity than earth structures. Thus,they often represent a potentiallygreater hazard to life and property. Itis important that concrete damownen be aware of the principalmodes of failure of such dams andthat they be able to discern betweenconditions which threaten the safetyof the dam and those which merelyindicate a need for maintenance.Concrete dams fail for reasonS thatare significantly different from earthdams. These include:

• Structural cracks. • Foundation and abutment

weakness• Deterioration due to alkali-

aggregate reaction

Should any of these conditions bediscovered during inspection, anowner should obtain engineeringassistance immediately.

Structural cracks occur when por­tions of the dam are overstressed andare the result of inadequate design,poor construction or faulty materials.Structural cracks are often irregular,

may run at an angle to the major axesof the dam and may exhibit abruptchanges in direction. These crackscan also have noticeable radial,transverse, or vertical displacemenL

Concrete dams transfer a substantialload to the abutments and founda­tion. Although the concrete of a dammay endure, the natural abutments orfoundation may crack, crumble, ormove in a massive slide. If thisoccurs, support for the dam is lost,and it fails. hnpending failure of thefoundation or abutments may be dif­ficult to detect because initial move­ments are often very smaiL

Severe deterioration can result froma chemical reaction between alkalipresent in cements and certain formsof silica present in some aggregales.This chemical reaction producesbyproducts of silica gels which causeexpansion and loss of strength withinconcrete. Alkali reaction is charac­terized by certain observable con­ditions such as cracking (usually arandom pattern on a fairly largescale), and by excessive internal andoverall expansion. Additional indica­tions include the presence of agelatinous exudation or whitishamorphous deposits on the surface,and a chalky appearance of freshlyfractured concrete.

The alkali-aggregate reaction takesplace in the presence of water. Sur­faces exposed to the elements ordampened by seepage will deterioratemost rapid/yo Once suspected, thecondition can be confirmed by aseries of tests performed- on coresamples drilled from a dam. Althoughthe deterioration is gTadual, alkali­aggregate reaction cannot be eco­nomically corrected by ally meansnow known. Continued deteriorationmay require total replacement of astructure.

Inspection of a concrete dam issimilar to that of an earth darn.However, the foUowing additionalitems should be considered:

• Access and safety• Monitoring• Oullet system• Cracks at construction and

expansion joints• Shrinkage cracks• Deterioration due 10 spalling• Minor leakageAccess and safety are importanlbecause the faces of concrete damsare often nearly vertical, and sites are

commonly steeJ>-walled rock can­yons. Access to the downstreamface, toe area. and abutments of suchdams may be difficult and requirespecial safety equipment such assafety ropes, or a boatswain's chair.Concrete dams pose a special prob­lem for the dam owner because ofthedifficulty in gaining close accesS tothe steep surfaces. Regular inspec­tion with a pair of powerful binocularscan initially identify areas wherechange is occurring. When thesechanges arc noted, a detailed closeup inspection should be conducted.Oose inspection of the upstream facemay also require a boatswain's chairor a boaL

Monitoring helps detect structuralproblems in concrele dams such ascracks in the dam, abubnents, orfoundation. Cracks may developslowly at first, making it difficult todetermine if they arc widening orotherwise changing overtime. If astructural crack -is discovered, itshould be monitored for changes inwidth, length, and offset, and a mon­itoring network of instruments shouldbe installed and read on a regularbasis.Outlet system deterioration is a prob­lem for all dams but the frequency ofsuch damage may be higher in con­crele dams because of their gTeateraverage hydraulic pressure. Thus,outlet system inspection should beemphasized for large concrete darns.Cracks at construction joints existbecause concrete dams are built insegments, while expansion joints arebuilt into darns to accommodatevolumetric changes which occur inthe structures after concrete place­menL The latter are referred to as..designed" cracks. These joints aretypically constructed so that no bondor reinforcing, except non-bondedwaterstops and dowels, ~xtend acrossthe joints.Shrinkage cracks often occur when,during original construction, irreg­ularities or pockets in the abutmentcontact are filled with concrete andnot allowed to fully cure prior toplacement of adjacent portions of thedam. Subsequent shrinkage of theconcrete may lead to irregular crack­ing at or Dear the abutmenL

Shrinkage cracks are also caused bytemperature variation. During wintermonths, the upper portion of a dammay become significantly colder than

25

those portions which arc in directcontact with reservoir water. Thistemperature differential can result incracks which extend from the crestfor some distance down each face ofthe darn. These cracks will probablyoccur at CQnstruction or expansionjoints, if these are provided.

Shrinkage cracks can.be a sign thatcertain portions of the dam are notcarrying the design load. In suchcases, the total compression loadmust be carried by a smaller percen­tage of the structure. It may benecessary to restore load-carryingcapability by gTouting affected areas.This work requires the assistance ofan engineer.

SpaDing is the process by which con­crete chips and breaks away as aresult of freezing and thawing.Ahnost every concrete dam in colderclimates experiences continued minordeterioration due to spaDing. Becauseit usually affects only the surface of astructure, it is not ordinarily con­sidered· dangerous. However, if al­lowed "to continue, spaDing can resultin structural damage, particularly if adam is of thin cross section. Also,repair is necessary when reinforcingsteel becomes exposed. The methodof repair of spalled areas dependsupon the depth of the deterioration.In severe situations, engineeringassistance is required

Minor leakage through concretedarns, although unsightly, is not

-usually dangerous, unless accom­panied by structural cracking. Theeffect may be to promote deteriora­tion due to freezing and thawing.However, increases in seepage couldindicate that, through chemical action,materials are £>eing leached from thedam and carried away by the flowingwater. Dam owners should note thatdecreases in seepage could alsooccur as mineral deposits are formedin portions of the seepage channel. Ineither case, the condition is nolinherently dangerous and detailed-study is required before it can bedetennined if repair is necessary forother than cosmetic reasons.

26

5.5 SPILLWAYSAs detailed in Chapter 2, the mainfunction of a spillway is to provide asafe exit for excess water in a reser­voir. If a spillway is of inadequatesize, a dam could be overtopped andfail Similarly, defects in a spiDwaycan cause failure by rapid erosion. Aspillway sbould always be kept freeof obstructions, have the ability toresist erosion, and be protected fromdeterioration. Because dams repre­sent a substantial investment andspiUways make up a major part ofdam costs, a conscientious annualmaintenance program should be pur­sued nol only to protect the publicbut also to riUnimize costs as weD.

The primary problems encounteredwith spillways include:

• Inadequate capacity• Obstructions• Erosion• Deterioration• Cracks• Undermining or spillway ouUetInadequate capacity is delerminedby several factors, such as drainagearea served, magnitude or intensityof storms in the watershed, storagecapacity of the reservoir, and thespeed with which rain waler nowsinto and fills the reservoir. An inade­quate spillway can cause the waler ina reservoir to overtop the dam.Obstructions of a spillway may resultfrom excessive groWth of grass andweeds, thick brush, trees, debris, orlandslide deposits. An obstructedspillway can have a substantiallyreduced discharge capacily whichcan lead to overtopping of the dam.Gtass is usuaDy not considered anobstruction; however, tall weeds,brush, and young trees should beperiodically cleared from spillways.Similarly, any substantial amount ofsoil deposited in a spillway ­whether from sloughing. landslide orsediment transport - should beimmediately removed. Timely re­moval of large rocks is especiallyimportant, since they can obstructflow and encourage erosion.Erosion of a spillway may occur duroing a large storm when large amountsof water now for many hours. Severedamage of a spillway or. completewash-out can result if the spillwaycannot resist erosion. If a spillway isexcavated out of a rock formation orlined with concrete, erosion is usuallynol a problem. However, if a spillway

is excavated in sandy soil, deteri­orated granite, clay. or sih deposits,erosion protection is very important..GeneraJly, resistance to erosion canbe increased ifa spillway channel hasa mild slope, or if it is covered with alayer of grass or riprap with bed­ding material.A spillway cannot be expected toperform properly if it has deteriora­ted Examples include: collapse ofside slopes~ riprap~ concrete lining"approach section, the chute channel,the stilling basin, the discharge chan­nel~ or protective grass cover. Theseproblems can cause water to nowunder and around the protectivemateriaJ and lead to severe erosion.Remedial action must be taken assoon as any sign of deterioration hasbeen detected.Drying cracks in an earth spillwaychannel are usually not regarded as afunctional problem. However, miss­ing rocks in a riprap lining can beconsidered a "crackn in the protec~

tive cover, and must be repaired atonce. Cracks in concrete lining of aspillway are commonly encounteredThese cracks may be caused byuneven foundation selUement, shrink­age, slab displacement, or excessiveearth or water pressure. Large crackswill allow water to wash out finematerial below or behind the con­crete slab, causing erosion, morecracks, and even severe displacementorthe slab. The slab may even be dis­lodged and washed away by the now.A severely cracked concrete spillwayshould be examined by and repairedunder the supervision of an engineer.Undermining of a spillway causeserosion at a spillway ouUet, whether itbe a pipe or overUow spillway, is oneof the most common spillway prob­lemS. Severe undermining of the ouUetcan displace sections of pipe, causeslides in the downstream embank­ment of lhe dam and eventually leadto complete failure of a dam. Watermust be conveyed safely from thereservoir to a point downstream of thedam without endangering the spillwayitself or the embankment. Often thespillway ouUet is adequalely protec­ted for normal now conditions, but notfor extreme nows. It is easy to mis­estimate the energy and force of now­ing water and the resistance of outletmaterial (earth, rock, concrete, etc).The required level of protection is dif­ficult to establish by visual inspectionbut can usually be determined by hy-

draulic calculations performed by aprofessionaJ engineer.

Structures that provide complete ero­sion control at a spillway ouUet areusually expensive, but often neces­sary. Less expensive protection canalso be effective, but require exten­sive periodic maintenance as areas oferosion and deterioration develop.The following four factors, ofteninterrelated, contribute to erosion atthe spillway oullet:J. Flows emerge from the ouUet are

above the stream channel. IfouUet nows emerge at the correctelevation, tailwater in the streamchaimel can absorb a substantialamount or the high velocity, nowand the hydraulic energy will becontained in the stilling basin.

2. Flows emerging from the spillwayare generally free ofsediment andtherefore have substantial sediment­carrying capacity. In obtainingsediment, moving water will scoursoil material from the channel andleave eroded areas. Such erosionis difficult to design for andrequires protection of the ouUetfor a safe distance downstreamfrom the dam.

3. Flows leaving the ouUet at highvelocity can create negative pres­SUIeS that can cause material to beloosened and removed from thenoor and walls of the outlet chan­nel. This action is called Ucavita.tion" when it occurs. on concreteor metal surfaces. Venting cansometimes be used to relieve

negative pressures.

4. Water leaking through pipe jointsand/or .nowing along a pipe fromthe reservoir may weaken the soilstructure around the pipe. inade­quate compaction adjacent. tosuch structures during construc­tion can compound this problem.

Procedure for inspection - Spillwayinspection is an important part of adam safety program. The basicobjective of spillway inspection is todetect any sign of obstruction, ero­sion, deterioration, misalignment,or cracking.When inspecting an earth spillway,one should determine whether sideslopes have sloughed, whether thereis excessive vegetation in the chan­nel; and one should look for signs oferosion and rodent activity. Oneshould also use a probe to delenninethe hardness and moislure conlent of

the soil, note the location of par­ticularly wet or soft spots, and see ifthe stilling basin or drop structure isproperly protected with rocks or rip­rap. Because some erosion is un­avoidable during stiJJing. an ownershould also determine whether sucherosion might endanger the embank­ment itself. If the spillway is installedwith a sill, a dam owner should alsodetermine if there are any cracks ormisalignment in the siJJ and check forerosion beneath or downstream ofthe sill.

Commonly encountered defects ofconcrete spiJIways and general in­spection procedures for cracks, spall­ing. drains, joints, and misalignmentare summarized in the. followingparagraphs.

Hairline cracks are usually harmless.Large cracks should be carefullyinspected and their location, width.length. and orientation noted. Deter­ioration should be determined andexposure of reinforcing bars shouldbe watched for.

Spillway surfaces exposed to freeze­thaw cycles often suffer from surfacespaJling. Chemical action, con­tamination, and unsound aggregatescan also cause spaDing. If spalling isextensive, the spalled area should besketched or photographed. showingthe length, width, and depth of thearea The problem should be exam­ined closely to see if the remainingconcrete has deteriorRted or if rein­forcing bars are exposed. The con­crete should be tapped with a"honker" or rock hammer to deter­mine if voids exist below the surface.Shallow spalling should be examinedfrom time to time to determine if it isbecoming worse. Deep spaDing shouldbe repaired as soon as possible by anexperienced contractor.

Walls ofspillways are usually equippedwith weep (or drain) holes. Occa­sionally spillway chute slabs are alsoequipped with weep holes. If all suchholes are dry, the soil behind the wallor below the slab is probably dry. Ifsome holes are draining while othersare dry, the dry holes may be pluggedby mud or mineral deposits. Pluggedweep holes increase the chances forfailure of retaining walls or chuteslabs. The plugged holes should beprobed to determine causes of block­age and soil or deposits cleaned outto restore drainage. If this work is notsuccessful, rehabilitBtion should beperformed as soon as possible under

the supervJSlon of a professionalengineer.Spillway retaining walls and chuteslabs are normally constructed insections. Between adjoining sections.gaps or joints must be tightly sealedwith nexible materials such as tBr.epoxies, or other chemical com­pounds. Sometimes rubber or plasticdiaphragm materials or copper foilare used to obtain watertightness.During inspection. one should notethe location. length. and depth of anymissing sealant. and probe open gapsto determine if soil behind the wall orbelow the slab has been undermined

Misalignment of spillway retainingwalls or chute slabs may be causedby foundation settlement or earth orwater pressure. The inspector shouldcarefully look at the upstream ordownstream end of a spillway nearthe wall to determine if it has beentipped inward or outward. Relativedisplacement or offset between neigh­boring sections can be readily iden­tified at joints. The horizontal as wellas vertical displacement should bemeasured A fence on top of theretaining wall is usually erected in astraight line at the time of construc­tion; thus any curve or distortion ofthe fence line may indicate walldeformation.

At the time ofconstruction. the entirespillway chute should form a smoothsurface. Thus, measurement of rela­tive movement between neighboringchute slabs at joints will give a goodindication of slab displacement. Mis­alignment or displacement of waDs or'.the slab is often accompanied bycracks. A clear description of crackpatterns should be recorded orphotos taken to help in understandingthe nature of the displacement.

27

5.6 INLETS, OUTlETS, ANDDRAINSA dam's inlet and outlet works.including internal drains, are essen­tial to the operation of a dam. Itemsfor inspection and special attentioninclude:

• Reservoir pool levels• Lake drains and internal drains• Corrosion• Trash racks on pipe spillways• CavitationThe topics discussed above forspillways also are relevant.

Reservoir pool levels - Reservoirpool levels are controlled by spiUwaygates, lake drain and release struc­tures, or. nashboards. Flashboardsare sometimes used to permanentlyor temporarily raise the pool level ofwater supply reservoirs. Flashboardsshould not be installed or anowedunless there is sufficient freeboardremaining to safely accommodate adesign nood. Pool level draw downshould not exceed about I foot perweek for slopes composed of clay orsilt materials except in emergencysituations. Very nat slopes or slopeswith free-draining upstream soilscan, however, withstand more rapiddraw down rates. Conditions causingor requiring temporary or permanentadjustment of the pool level include:

• Development of a problem whichrequires that the pool be lowered.Drawdownis a temporary solu­tion until the problem is solved

• Release of water downstream tosupplement stream now duringdry conditions.

• Auctuations in the service area'sdemand for water.

• Repair of boat docks in the winterand growth of aquatic vegetationalong the shoreline.

• Requirements for recreation, hy­dropower, or water fowl andfish managemenl

Lake drains - A lake drain shouldalways be operable so that the poollevel can be drawn down in case of anemergency or for necessary repair.Lake drain valves or gates that havenot been operated for a long time canpresent a special problem for owners.Hthe valve cannot be closed after it isopened. the impoundment could becompletely drained. An uncontrolledand rapid drawdown could also causemore serious problems such as slidesalong the saturated upstream slope ofthe embankment or downstream

21

nooding. Therefore, when a valve orgate is operaled, II should be Inspect­ed and all appropriate parts lub­ricated and repaired. It is alsoprudent to advise downstream resi­dents of large and/or prolongeddischarges.

To lest a valve or gate without riskingcomplete drainage, one must phys­icaUy block the drain inlet upstreamfrom the valve. Some drains havebeen designed with this capabiJiIyand have dual valves or gates, or slotsfor stoplogs (sometimes called bult­heads) upstream from the valve.Otherwise, divers can be hired toinspect the drain inlet and may beable to construct a temporary blockat the inleL

Other problems may be encounteredwhen operating a late drain. Sedi­ment can build up and block the draininlet, or debris can enter the valvechamber, hindering its function. Thelikelihood of these problems isgreatly decreased if the valve orgate is operated and maintainedperiodically.

Corrosion - Conosion is a commonproblem of pipe spiUways and otherconduits made ofmetal Exposure tomoisture, acid conditions, or salt willaccelerate corrosion. In particular,acid runoff from strip mine areas willcause rapid corrosion of steel pipes.In such areas, pipes made of n0n­

corrosive materials such as concreteor plastic should be used. Metalpipes which have been coated toresist accelerated corrosion are alsoavailable. The coating can be ofepoxy, aluminum, zinc (galvaniza­tion), asbestos or mortar. Coatingsapplied to pipes in service aregenerally not very effective becauseof the difficulIy of establishing abond. Similarly, 'bituniinous coatingcarmot be expected to last more thanone to two years on nowways. orcoun;e, corrosion of metal parts ofoperating mechanisms can be effec>­tively treated and prevented bykeeping those parts greased and/orpainted

Corrosion can also be conlroUed orarrested by installing cathodic pr0­

tection. A metallic anode made out ofa material such as magnesium isburied in the soil and is connected tothe metal pipe by wire. An electricpotential is established which causesthe magnesium to corrode and not thepipe.

Trash on pipe spillways - Manydarns have pipe and riser spillways.As with concrete spillwsys, pipeinlets that become plugged with deb­ris or trash reduce spillway capaciIy.As a result. the potential for overtop­ping is greatly increased, particularlyif there is only one outleL If a damhas an emergency spillway channel,a plugged principal spiUway willcause more frequent and greater thannormal now in the emergency spill­way. Because emergency spiUwaysare generally designed for infrequentnows of short duration, seriousdamage may resuIL For these reasonstrash collectors or racks should beinstaIIed at the inlets 10 pipe spillwaysand late drains.A weIl-designed trasbrack will sloplarge debris that could plug a pipe butallow unrestricted passage of waterand smaller debris. Some of the mosteffective racks have submerged open­ings which allow water to passbeJ;lCath. the trash into the riser inletas the pool level rises. Openings-thatare too small wiD stop smaU debrissuch as twigs and leaves, which inturn will cause a progression of largeritems to build up, eventually c0m­

pletely blockinll the inleL Trasbrackopenings should be at least 6 inchesacross regardless of the pipe size.The larger the principal spiUway con­duit. the larger the trasbrack openingshould be. The largest possibleopenings should be used,' up to amaximum of about 2 feeLA trashrack should be properly'attached to the riser inlet and strongenough to withstand the forces offast-nowing debris, heavy debris, andice. If the riser is readily accessible,vandals may throw riprap stone intoiL The size of the trashrack openingsshould not be decreased to preventthis. Instead rock that is larger thanthe trasbrack openings or too Iarge tohandle should be used for riprap.

Maintenance should include periodicchecking of the ract for rusted andbroken sections and repair as needed.The Irasbrack should be checked fr~

quently during and after storms toensure that it is functioning properlyand to remove accumulated debris.

Cavitation - Wheo water nowsthrough an outlet system and passesrestrictions (e. g.., valves), a presswedrop may occur. If localized waterpressures drop below the vapor pres­sure of water, a partial vacuum is

created and the water actually boils,causing shockwaves which can dam­age the outlet pipes and controlvalves. This process can be a seriousproblem for large dams where dis­charge velocities are high.

Testing the outlet system - Allvalves should be fully opened andclosed at least once a year. This notonly limits corrosion buildup on COn­trol stems and gate guides, but alsoprovides an opportuniIy to check forsmooth operation of the system.Jerky or erratic operation couldsignal problems, and indicate theneed for more detailed inspection.

The full range of gate settings shouldbe checked. The person performingthe inspection should slowly open thevalve, checking for noise and vibra­tion - certain valve settings mayresuk in greater turbulence. He orshe should also listen for noise whichsounds lite gravel being rapidlytransported through the system. Thissound indicates that cavitation occur­rins, and these gate settings should beavoided The operation of all mecb­anical and electrical systems, backupelectric motors, power generaton,and power and lighting wiring associ­ated with the outlet should also bechecked.Inspecting the outlet system ­Accessible portions of the outlet.

.such.as the outfall structure and con­trol, can be easily and regularlyinspected However, severe prob­lems are commonly associated withdeterioration or failure of portions ofthe system which are either buried inthe dam or normally under water.

Areas to be inspected include:

• Outlet pipes 30 inches or greaterin diameter can be inspected inter­naUy, provided the system has anupstream valve allowing the pipeto be emptied Tapping the c0n­

duit interior with a hammer canhelp locate voids behind the pipe.This Iype of inspection sbould beperformed at least once a year.

• Small diameter outlet pipes canbe inspected by remote TVcamera if necessary. The camerais charmeled through the conduitand Iransmits a picture back to anequipment truck. This Iype ofinspection is expensive am usuallyrequires the services of an eo­gineer. However, if no othermethod of inspection is possible,inspection by TV is recommendedat least once every live years.

• .Outlet intake structures, wetweDs, and outlet pipes with onlydOWllStream valves ore the mostdiJlicult dam appurtenances to

" inspect because they ore usuaUyunder water. These should beinspected whenever Ibe reservoiris drawn down or at fIVe yearintervals. H a defmite problem issuspect.... or if the reservoirremains full over exteoded per­iods, divers should be hired to per_form an underwater inspection.

5.7 OTHER AREASOther areas requiring inspectioninclude:

• Mechanical and electricalsystems

• Restrvoir surface and shoreline• Upstream watershed• Downstream DoodplainsMecJumical equipment includes spill­way gates, sluice gates or valves forlake drains or water supply pipes,stoplogs, sump pumps, Dashboards,retief weDs, emergency power Sour­ces, siphons, and other devices. Allmechauical and associated electricalequipment should be operated atleast once a year and prefera.bly mOreoften. The test should cover the fuJIoperating range of the equipmentunder actual operating conditions.Each operating device should be per­manently marked for easy identifica­tion, and all operating equipmentshould be kept accessible. All cOn­trols should be checked for propersecurity to prevent" vandalism, andfmal1y, all operating instructions'should be checked for clarity andmaintained in a secure, but readilyaccessible location.

•

29

The reservoir surface and shoretineshould be inspected to ideotify poss,i­ble problems away from the actualstructure. Whirlpools can indicatesubmerged outlets. Large land stidescoming into the reservoir could causewaves overtopping the dam.Floods arise from the upstreamwatershed Therefore, chnracterislicsof the watershed, such as imperviousareas (e.g. parking lots), relate direct­ly to the magnitude of a Dood. Urbandevelopment in a watershed Canincrease the size of Dood peaks andthe volume of runolf, thereby makinga previously acceptable spillwayinadequate. Awareness of upstreamdevelopment and other factors whichmight inDuence reservoir inOows isimportant in order to anticipate p0s­

sible problems and necessary ormodifications in the dam.

Development in downstream Oood­plains is also very important to the

"dam owner as the extent of devel-opment and Dood preparedness relatedirectly to loss of life and damagessbould the dam fail.

— blank —

" "GURIS 5.3.1INSPECTION GUIDIUNIS •EMBANKMINT UPSTllIAM $l,OPI

PROBLEM

SINKHOLE

LARGE CRACKS

SLIDE, SLUMP OR SLIP

SCARPS. BENCHES,OVERSTEEP AREAS

PROBABLE CAUSE

Piping or inlemal erosion of embankmenlm.~,rills or foundAlion CIUUS • sinJl.hole.The cave-ill of.." eroded cavern can result in• sink hole, A small hoi, in lh" wall of anoutlet pipe: can deYlllop a sink hole. Ditty......ter 11 tho Cllit indicate! eto.ion of !hIdam.

A portion or th, e:mblnaltlll:nl hal movedbee.IllO o( 1011 of .uonlth, or the found.tionmay hive moved, <:llIIin. embanJun<lnlmovtmanL,

Earth or rocu movl down the .Iop' 1I0nlaJlippll' .lolrl'.c:e becallli ohao a'clp I.lopcl,or the foundation mavil. Alia, look. for.lidt. mov,mtm ill rlll"oir buin.

Wave Iction, locll ..ttJem.nt, or ice IctionCllol.tl $Oil and rock to lrod. and .lide to thelowllr pin of Ule .lope fonninl I bench.

POSSIBLE CONSEQUENCES

HAZARDOUSPipi", can (Imply' reurvoir through. 'maUhole in the wLlI or can Iud La (allure of •dim ... loil pipe, ,rod, throuih th, {oWld...lion or I pCl'YiO\l' pal1 or Lh, dam.

HAZARDOUSlndh:.r.ca on.et or m.ujYll IUdl or 'Ittl..m~n' C:llolKd by foundation faillol....

HAZARDOUSA "rill of IUd" can lead to ob.tructiou ofthe ololtillt or faUun at Lbt dam.

Ero.ion I....nl the width and pouibleheiaht of Ih. embankment .nd could lead toInc:rcucd ..eplp or Ovel1oppln' of tilldam.

RECOMMENDED ACTIONS

Inspect other plru of the dam (or seep,"e ormore ,ink holes. Identify exact CIUSll of sink.hole.. ChllClr. ,,,pllll and l,wlG outtlo..... ,rot dirty Wltlt. A qualifiod '"Piller shouldin.pect the c;ondltlort.l and l'tconvnendfurther action. to be lUen•ENOll'lEER REQUIRED

Depclndinl on embanknumt Involved, dr,wI'CI4lr'Yoir level down. A qulltled engln"rJhould inl~ct the conditionJ and recom­mend further Ictlan. to be tlkln;ENOll'lEER REQUIRED

Evaluate tl..l-nt or the .lIdL Monitor .Ud.,(See Cbapter 6.) Draw the rllinoif' Itveldown It .&flty of dam I. thttltened. Aqullmed engin.er should in.pelOt the eon·diOon. and rccorNnond further actlon. to betuen.ENGll'IEER REQUIRED

Delennine ..ICt clun of ,cup.. DonlCllU1IY eanllwork, fC,lort; embankmentto orilln.1 slope and provide adequale pro­teGtlon (beddlnl and I"iprlp), Sot Chlpter7.

" PROBLEM

BROKEN DOWNMISSING RIPRAP

EROSION BEHINDPOORLY GRADED RIPRAP

Flgur•• 5.3.::lnlpectlon Guld.Unn •Downl'r.am $lope

SLIDE/SLOUGH

PROBABLE CAUSE

Poor quaLity riprlp hu deteriorate:d. WI"'.acuon or iell Iction hu dilplacad ripr.p.RoW'ld IIld IimilaNite:d roc:kI have rollllddewoNU.

Similar-.lud rock, allow ..... IVU to pin be-­tw.," tham and .rodt small grlvol pll1Jcl'land 'Oil.

."

\.,",

I. Lick or or 10•• or Itrll"1th of embank­manl materiLl.2. Loll or Itrcnlth can be attributed 10Inliltntion of waltir lnl.O!.he embanJunent orlou or support by the roWldatiolt.

POSSIBLE CONSEQUENCES

Wave Icuon '&&1nlllhellll unpltlt.lctlld ....ud.cr..~.. tmbanimC"l width.

Soil J. 'rvdcd .way (rom bclWld the riprlp.nu, Lliowl riprap to ..a1:s. provldin. I...prQl.oGtion and dtcruHd tmbinlmtm. wK1lh.

HAZARDOUSMUlive 'lide cUll lhroua!t crnt or up­Itream Ilope rcduclnl ","board and CnJU,cetlon. Stnlclutll coUap.. or oyenoppingCIJl re,ull,

RECOMMEND ACTIONS

Ro-."Llbli.h normal Ilope. PI"l1 baddin,and c;;omptltlnt ripr.p. (St. Chapter 7.)

ao-••tablilh ,tracY"1 slope! pltI~cuon.

Place bedc1in. mwriaj, ENGlNEER RE·QUUlED (or d••I&n (or pad,l.Ion and li~.rot l'Ol:i ror btddln& and riprlp. A quaJUltdIn&in'" .hould in,pea the condillons andrttVOmmcnd l\uthor laian. 10 b4l laken,

I. Mea.Ute o,;tcnl Illd dilplaccmenl of.lIdo.2. It continued moyement U seen. bo~n

lowering wal.Or level unal movement SlOps.J. Havel quaJined C1n~cer il'\$pcct the eon·dition and rcconvnend further Iction.ENQINEER REQUIRED

.,PROBLEM

TRANSVERSE CRACKING

CAVE IN/COLLAPSE

LONGITUDINAL CRACKING

SLUMP(LOCALIZED CONDITION)

PROBABLE CAUSE

t>itrlln:ntlal settlement of the cmban&menlalao Iuds to ttlllYerse crackina (e.J., "nterulttlcs morll than Ibutmenul.

I, LIck or adequate comp.euon.2. Rode"' hoi. below.J. Pipinl ttuolllb embankment or foWld.allon.

I. DryitIIII1d altrin.kl&ll of surface maleri,1.2. DoWNllcun movement 0( .,ttl,mentolcmbanim,nL

Preceded by erosion unden::uttins I portionor thll slope. Can &Iso be round on .tlllP,lopu.

POSSIBLE CONSEQUENCES

HAZARDOUSSettl~menl or slvink.lll c,.ck~ un Iud to'UP"11 of rlllll'Voir wiler throush lhll dam.SluiI'lkl'lI crick....Uo.... luter 10 enter theembanJonenL nul promolet .INT.tion andinereuc. (r":r.t·thaw "tion.

HAZARDOUSlIldicllCI. pouibll wub out of embankmcmt.

I. Can be an culy wuninl of I pol.cntialslide.2. Shrinklp crlCU Iilow water to c,"LIlr tnllemblnkment Irld r""Iin, will lw,r «ll'1cklh, ernbankmGlLJ. SettJement or sUde IhowinS 10" orItlellllh in embankment I;an Iud to lLilu,..

Can UpO.tll Impervious zona 10 erolion IDdIud to ful1hu Ilumpll.

RECOMMENDED ACTIONS

I. (f ",ceSl&r)'. plus upstrllm lind of crier.to prevent now. from the rlSlIr'Volr.2. A qutlUled ,n&innT should inspect thecondilton, and 'llconvn,nd l\uthn IcYan,tobe talton.ENGINEER REQUIRED

1. In.peel for and lmmodlatelY rePlIr rodllothollIS. ConlTOl rodenu to preYent fuNredam'I"2. HIYtl .. quaW1lld anJ,in,., in,peel the can·dillon U1d recommlnd further awan,ENGINEER REQUIRED

I. If crac:lu are from d1yinlo dre" ..... withwIII..complc:ted mlLllriaJ to Ir.lllP furflC,wltor oul and nllura! moi.turl in.1., U crlCu UI 'ILenslvl, I qu.lilledenlineer should IlIIptet the condiUolII andrecommend lurther IcLioD' 10 be l&ken.ENGINEER REQUIRED

I. [n.peC! lrea ror seepale.2, Monitor ror progrenivll raJJure.J. Hive I qualified eni!ne,r inspect the con­dition and retonvnlnd rul1her action.ENGINEER REQVIRED

,. PROB~EM

EROSION

TREES/OBSCURING BRUSH

RODENT ACTIVITY

~IVESTOCKICATT~E TRA,fFIC

PROBAB~E CAUSE

Water (rom in'cn•• rainstorms or sno....·melt.curiq .\ufacc maleriaJ down lb., .Iopo.""WUAI in conLinuoUl tnlu&hl.

Ov,r·.bw1d&nIOO of rodenu. Hoi... tl.lnn,1sand elYImi let cau.ed by AnUnal blln'Ow­inp. Certain IlIbiLaulik, c:att&il trpt pllnlland II." clo.. wLb, fC'Cl'Voir 'OCOurl"th... lnima1l.

EICClljVI travel by livmock 'Ipc<:iallyharmful ~ ,lop' when wcL

POSSIB~E CONSEQUENCES

Can be hUlldoul if allowed 10 continue.Ero,ion can lead 10 eventual dcl,rior,tion oflit. dowrutrum slop. and (lihue of the,weN....

Lule Ir'lI I'OOli can ernUl 't'piSD path•.BUlh•• can obICUAI ri.ual ulIPll:tion andhubor rod.nu.

. Can reduce lenith o{ lI11p.,e P.th. and Iudto pipinl {ailure. I( tUMel Illl.lI throudlmOlt or Ui, d"". it can I",d to rallurl ofthe dam.

Crcalel UIU bue o{ ero.ion prote~tion inaI:IU." erolion channell. AJlowI ......'0' to.\.Ind. Ast. IUlc:opublo to dl')'inll:raclt••

RECOMMENDED ACTIONS

I. The prcr,n,d method to protect erodedare., i.I nx:lr. or "plap.2. Re-'ltabUliung PrQlAlctiYl ,,"u... can baadcqUI,1 il th. problem i. dllectcd urI)'.

I. Remove ,II IUi_, deep-rooled (feu and.twbt on or nut the embankment. Prop"i)'bK1cfU1 void. (S.. ChapLet 1,)2. Contltll VI,ltlUon on the embankmentthat obtaii''' vi.u.alln.poctien. (5,. Chip'"Lor 7.)

I. Cootn3l rodln... itt prwYln, morw dam"l•2. Backll.lI nJ.unl rodent hoili.J. RMnOY, rod,nll. OtLonnin. u.ct loc.·don or diuinl LDd IIllocnt or NM.Iin&.RomeY, habi",t and repair damap•. (5'1Chapter 7,)

I. Fencll lJVll:l~k out.ldo cmbWmentU'L2. R.cpair IIro.ion ·prolllcUon, I.e.. riptep,&lUI,

J5 . FI loire. 5.3.3In'I:3-O"O" Guldelln•••Imbclnkmenl ere"

PROBLEM

LONGITUDINAL CRACK

VERTICAL DISPLACEMENT

CAVE·IN ON CREST

PROBABLE CAUSE

I. Uneven .ettlemenl between adjacenl sec_tion. or zones within thl emb'anXmenl.2.Found.l.ion f&.iluOl clusing loIS of supportto embM.nkmenLJ. Initial ILlpl of embankment I~de.

I. v.rtieal mov.ment btlwee" adjlOlnt ,,'"lio"" or Ib, ImblRkm.nL2. Structural ddonnllion or.f.i1urll c:au.edby ItJ'Uc:Nral .tlllI or I",,\lbiliC)', or byfailure of tbl rOWldation.

I. Rodenl activity.2. Hole In outJet conduit i, CIUSInI erosionor .mbanlan.nt malerial,3. Intemal erolion or pipinl of 11mbankmentmaterial by I'lpap.•. Breakdown o( di.penive clay. withinembilWn,nt by J"pl'lII waten:.

POSSIBLE CONSEQUENCES

HAZARDOUSI. CI'llIUS local Ire. of low strength withinembanlunlnt, Could 1M the point of inhi.tionof fuNre stnl<:Nral movement, defonn.tion,or failure.2. Prnvidelentrance point ror surflce run-otl'into Imbankmlnl.. aUowlns Slturl\lion oradja,enl embankment uea. and poaaiblelubril;llion wtti,h r;ould Ilid 10 localizedrailure,

HAZARDOUSI. Provide. 'o;al arll of low .tnn;th withinembankmenl which could elUH IUNr.movem.nL2, Leads to stnlctl.lral lnSl.lbility or fLiJuflI.J. Providll entrance point for surflCe walerthai could further lubricate railure planll.4, R,duc:e~ availlbl. embankment Crollsletion. .

HAZARDOUSI. Void wilbin dam could clu.e localizedclvinio sloughinl, In.l.ability, or reduced11mblnkment croll section.Z, Entranee point Cor aurft!;:o wlter,

RECOMMENDED ACTIONS

I. Insplct crick and carerully record 1001­tion. I.nlth. d.pth, widUl, a1icnm.nl, andother peRinllnt physical features. lmmedi­Ilely stake out limiu of cra,king. Monitorfl"equenlJy,2. En~neer should d.tennine elUSI oreTickinl and supemlll sl.p. nllC.llary tore<!u,. danpr to dam and comet condition.J. ElT"tivlly seal the cracks It Ih. ,rest'ssurfac. to prev.nt inllltnrJon by .wiaeewltIlr.4. Continue to routinely monitor crest forevidence or ful'thllr cracitin"ENGINEER REQUIRED

I. Carefully Ul.peetdi.plaeemllnland rer;ordiu location. vertical and neNonlal d.ilplace~

ment, lenath. and other phy,ical rllt\lres,lmmedlately .taltl out Umits of crlckina:.2. Engineer Ihould de"nninCl ClUte of di..placllmenland supervi.. all stop, n.cII.aryto reduce dangllr to dam and cometcondition.J. EXClvate lreato ttl. bottom ofthe dispiaco­ment. Backfill exclvalion u.inl ,0mpelCnlmil.rial and conectcon.truclion technique I,and under supervision of ,nainnr.4, Continu. to monitor arou routinely rorevidence or fuNre crac:kinl or movement.(See ChaplOr 6.)ENGINEER REQUIRED

I. Car.fully tnspect and record locltion andphysical charlc;t.ori,tie, (deplb. widlh. !enith)of eav. in.2. Enlineor should detllrminll cau.. or Clvein and supervi.. all.t.p. nl"SlIl)' to rtduellthrllt to dam and comet condition.J. Exc.vate eaVll in. slope .id.. of nc.vl­tion. and baeldlll hole with competontmaLerial u.in, proper con.tr\lction ltch-­niques, (S.. Chlpl., 7.) Thi••hould belupervi.ed by enpneer.ENGINEER REQUIRED

"PROBLEM

CREST MISALIGNMENT

LOW AREAIN CREST OF DAM

PROBABLE CAUSE

I. Uney,n movement betwnn .djacent"gmlnu of th, ambankm.nt.2. Ddonnation "'ll.ed by IlnicturaJ .trcUor in.lability.

I. Movlmlnl bltwoon .djacent pans orlb, '''''CNn!.2. Ufllven dtn"tion or dam WIder loadlnlby r"lrvoir.J, Structural "ronnalion or raiJUR nluu •• of mi,allpVnlnt.

I, EXClllivlI ~ottlcmonl in the embanJunentor rOlUldation di",;t1y tanlilb !hili low Ifcain Ib, CA,L2. lDtemaJlm.ion or embankmenl m.llnal.J. POWld,lJon IPreadln, to Up'U'lun indio,down.tRun ditte:tJOfL4. Prolonled wind ero.lon o( Cl'1l.t un.$, lmpropolr f10aJ iJ'1din1 roUowina ;on~

.tN;lJon.

POSSIBLE CONSEQUENCES

HAZARDOUSI. c~ provid. I IMth for "'p'I' throulhthe lImbanluncnt Ctol. nction.2. ProvidN local 're. of low 'b"Clngtn withinembankment, Futur••tNeturaJ moYenta"t.d,ronnauon or f.i1ure could bllin.J. Provide. ,nulIlc. point for .urf", NIlotrlo cnlcr ,mbankm,nL

I, Area of millJ.ipunent i. u.u..Uy .ccom­panied by loW uea La cre.t which rtGuI;Ufreeboln1.2. Can produce locaJ ucu allow emblUlk·menl strenilh which may 1.1Ii 10 railure.

~UCCI I'eeboard av.iI.bl. to pUt noodOow, niely throu'" .pillw.y.

RECOMMENDED ACTIONS

I. wpal:t crack U1d IOuefuUy l'lcord eraelr.loc.IIlJgn.lenph, depth, wldUl. and other per­!.ina"t physical r...Nt'II'. Stab out limiuof crac:k.ina.2. Enline" should dell.min. UlUC ofc;rIClr.in, &lid luptrvl•• &1I.tep. "_Ciliary '-0~uc. d....aor io dam and eonm condition.J. Exe'YlLt cre.t alonl crick 1.0 I pointbelow the boUom ofUlI go,ell;. Then b.ckliU·Ul' ....c.vnlon LUinl competent m.lArial andIXllT,e:t C(lRltn,ll:;:tion Ilc;hniquCl. Thl. willsaal tho crack .pin.t "'P"I and 'Urf'CIrunoff. (So. Chap'-, 7,) Thl••hould bIsuperviMd by lolin.lr.... Coatlnul to monilor mst routinely (orIvidfnGl or futun!,uack.i.alo (Stl, Ch.pler6.)ENGINEER REQUIRED

I. "Ell.I.bU.h monwnenL1 across crill todetennifll IX&e:t amount. lcx:.tlon. &ndClitenl or mil&IJlMlenL.2. Enlin..r Ihould dlllnnlni nuu of mil­a.li&MIen~ IIld IUlMrYi'1 all .Iep. nte"....yto r,du;, !.hr,ac 10 dun &nd corrtetcondition.J. Monitor cre.l monwnenL1 on ••chcdulodbui. roUowinl rcmediaJ .;tion to dete;tponiblo "'tur. movlllmlllnL. (SCI Chapler6.)ENGINEER REQUIRED

1, ulIbli,h monwnenu tlonslonS'h of ;flltto deunnin. exact amown. location. Indoxlent of IIttiament in ;fl1L.2. En&int" .hould dOllrmino CIUU or lowuea IlId .upe",bl a.l.l IWpl n,c"luy tol'1lduel pollibll Wilt Of. tA, dun and ~"lCtcoDditJon.J, Ro-ell.l.blith wWonn Cnllt elevltion overcrllt Itnjth by pllC!nl nil In low u .. 1I.1n1proper I;Onttrl.l':uon tocltniqullI. Thl••houidbe IlIptrvl,ed by OIl&1necr.4. Rt-lI.tabu.b monum,nl.l Krotl cml ordam and monll.or RlOnumlinti on , routinobuil to dltlci pouibl. tutu", aolT,l,mtnLENGINEER REQUIRED

" PROBLEM

RODENT ACTIVIIT

GULLY ON CREST

RUTS ALONG CREST

PROBABLE CAUSE

Ne&iec:~ of dam and lack of proper main·lenance proC;:lduru.

I. Poor p'ldlnl X.ad improper drain.se o(CfUI. lmproP4r drain'lI nUllls surflceNnotr to coUect and drlln of cre.t .t lowpoinl in upstream or dOWftlU"1Il1 .houIdu.2. InadeqUlto .pillw.y cap.cily which huclusld dam to avenal'. .

Heavy vehicle tumc without adequltlS orproper maintenance or proper CRlllwf.cInc.

POSSIBLE CONSEQUENCES

I. Obscures larll paN of the dam, prllvent·ln, Idequllcl. IC:a1ratl vl'uII inspection ofall palU of th. dun. Problem. whichthreaten \h. intlpity olth, dam elll developU1d ....m.in undllilcted until thlY prop1l11 to• poinl that WlIllnl tho dam', ,&fllty.2. Ancel.lAd root system. d,vt'lop andpeneltlte inlo the dam', Croll .,won. Whenlhll vllliation dill, the dec,yin, root 1)'5­tem. can provide pa\.hl for I.tpap. lbi.rllducll. the etrective 'I,pl,e PIth lhroUlhthe Imbsnkmcnl and could Iud to pOlliblapipinl ,ltua!.ion•.3. PfllfCnU: IUy ace.1I to aU palU rJ thodam for opo...Licn. mUlleinan", andin'pection.4, Providlu habitat fOf rod,nU.

I, Enlrance point for .urfac, 1'\lnolf to enLerdam. Could latur.t.t aetlacent portion. ofthe dam.2. E.pcci.Uy danprou. if hole pcnctr.14.dam belo.... phreatic Unl. Durinl penodJ ofhl5h .Iorlle, .eep'I' p.lb throuih t!le damwould be IP'Cllly reduc:ed and ,pipifll.itu'.tion could develop.

1. C&n reduce i1.ble rn:eboard.2. Reduce. c:ro ection.1 an. 0( dam.J, IMibitl Icce" to all pllU of the crestand dun.4. Can re.ult in a haurdOUI wndilion ifdlloto oYtrtoPPinio'

I. Inhibits ouy 'C~ISU to .11 parts orcrest.2. Allow. continllod developmenl or rolling.J. Allowa lIandin, ""'It" to c:oUect IndnNrlte crllt or dam.4, 0iKrltUllllld m.unlnlnCI ...ehich~1 canlit INck.

RECOMMENDED ACTiONS

I. R.mov. IU damqinl &ftIwth from thldam. nu. wowd lnclw. R1movll of ltOCli.bUlh". bnI./I. mf,n, and P"Owth othorthan 11'11'. Qru••hawd bt oncallupd onIII ugmenu ortho dam to prevent erotion byIUrl.C. runoff'. Rooi .y.lem••hould aI.o beremoved to tJlll mulmum pracucal Cltent,The void which n1lulll (rom removlnl tJloroot sylttm .hould bt backlllled withwellcompettnt, wtll-eomplctld milirili.1. Puture u.nd"irabl, P"QW1.h .hould boremoved b, cutt.lnlor .prayinlo u part of anannual ma&nllauot PfOP'IIT1o ($" Chap.IIr 1.) .J. All cut1Jn1 Of debri. ""ultln&: from thev'lIltaliv, Nmovll .houkl be lmmedl..ttlyt&i.en from th, dam and properly dI.potIed ofoullide thl reslrvoir buin.

I. Complltely bacldliU !,hI hall with QomPll"lent. welkomp.C1od m'lenal.2. lnitato • rodent c:onlrol propam to reducethl bUfTOwitll anlmal population ancIlO pre­Yllnt futu" dam.p to !.he dun. (See Ch.pter7,)

I. RalDro freeboard to dun by Iddin& flUmatlrial in low WI" ulina proper c:on.We­tion IecMiqulII. (Seo Chaplet 7.\2, Rearadin& cresl to provide propc,r drainl;aof SUrflCO ninofl'.J. If IlIlIy was c.lI.ed by OYlrtoppin", pro­vide adeqlllllI spillw.y which meeu curnntdCllp ltandanll. Thl, Ihould be done byengineer.4. Ro-e"lbU.~ pfOlee:tlvo cover,

I, Drain .tAndin, WIlllr rrom NUl.2. RelP'adt and Ncomplcl crest 10 rellor.inlel'ilY and provide propelr dllin.p toIIpltrum slopel. (St. Chapt" 7.)), Provido 11'11111 or ro.dbue mlteri,1 toIccommodltcl tramc.4. Do pcriodlo mainle",",", V1d nuadinlloprevent r,ronnltion or nau. .

------- - ---

.. PROBLEM

PUDDLING ON CI\EST·POOR DP.AINAGE

DRYING CP.ACKS

PROBABLE CAUSE

I. Poor P-adinl and improper drain_go ofQllt.

1. Localiud c:onaoUd.!.ioa or ,cWlm,nl 0110crG.l allow. puOdJCII to dlv,lop.

Material 011 the cr," of d&m IllplJld. &AdcontJ'aetI with al'_maLi wlttia, IUId dryiDlof WuLll.lllr eyeI... Dryjaa c:rac:1u &nI uI"'Uy,bort, Iballow, n&m:IW, ud many.

POSSIBLE CONSEQUENCES

I. C.uu loca!iud 'INt,tion or tha crOlL2, lnhibitJ ACCC" kJ aU putl or lb. damand erul.J, Becom" p~lI"CI.ivcly worn it noloor".;WJ.

Provide. point of entrlllco (or .wfiCI l'Wlotrand surf.ce moilture, CIU.in, oILlNlluon ofad,iIC.ot emblAkment UlU. Thit ll.l1.Ua­tion. and Iller dl'yinlofth. dam. could C'lUlfurther c:rac;lin"

I\ECOMMENDED ACTIONS

I. Drain ,Landin, wIl.Ilr (rom puddlea.2. R.llP'ad. aIId rICQmp.~ cr••t 10 flltor,inllpit)' and provid' proper drain", toupltre&al.1apCI. (5•• Chapler 7.)J. Proyjdli pI"el or roarJbut mmnal toIGCOINIIodat. tr&I1\c:.4. Do period.ic m-tDullw:lCC and rtplcW1' toprl"nt rtronn.Llon of low aRU. .

I. Sui ,wi_ell of <:rlclu wiUl • altll.. impol'·viou. m~rial. (Scle Chapter 7.)2. RouUo.1y pade Cl"llil to Pfovid. properdraJ.aap aDd fill f;n,lu. -OR3. Conr IO",at with non-plutiIO (nol lOllY)m&lClriaJ to pr.vant lUI' moiaNra lOOnt.&D~

variatiolU,

" Flgur•• S.3AInspecllon CiUldeUn•••ImlKlnlnnonl Soopago Noaa

PROBLEM

EXCESSIVE OUANTITYANDIOR MUODY WATEREXITING FROM A POINT

STREAM OF WATEREXITING THROUGH CRACKSNEAR THE CREST .

SEEPAGE WATEREXITING AS A BOILIN THE FOUNDATION

PROBABLE CAUSE

I. Waler hu crealed an open pathway,channel. or pip, lhrou&h thl dam. Th, Wilif

i. ,rodin, and clt1')'in••mbanlcment m.~

terilJ.2. I...&ra. amoWiU o(wllAIr hav" accumulatedin thl down.tream dope. Wiler andemb.nlun-nt mlterial. are llxiting It onepoint. SUlfI'e qltlc.ion may bt !;:autin, th.muddy w,I.I'.J. RDdeoli. (roat leUoo or poor con.lnIctionhave allowed wlter to CAW! aq openpathway or pip' l.brou&h the cmbaakmlat.

1. S,v,,, dryinl nu cauH4 .hrinka,o ormbankmlnl malarial.:z. SeCLI.mtnt In thl embankment or found..lioa il cau.lo. th. trIOIVIII"O Cnlcia.

Som, part of lb. roundation mallrial il ,up­plyin,1 now pith. 1'1U, c:ould be clU'od by.,and or plvel I,yer in the fOWld,lion.

POSSIBLE CONSEQUENCES

HAZARDOUSI. Continued now. can uluralAl puu of theembankment Md Icad to ,'idell in th,u ••2. Continued now, can further erodeembllWncnt mlt.eriaJ. and Iud to failure ofthe dam.

HAZARDOUSPlow throu,"" l.ho crack can cause railu... orlho dam.

HAZARDOUSlnl:llIued floWil can lead to ,ra.lon of Ulll(ouod,lion and failure of tho dam.

RECOMMENDED ACTIONS

I. Belin meuurin. ouQ'low quanuty &ndutabliahin. whether wiler i. ,euinl mud-­diu••t.lyllI, the nmc. or cilluini up.2. IfquantitY of now i. !.nc::r,ui.n,lhe wlterlevel iQ the relervoir .hawd bllowered \IllUlth' now .tabilizil or slOpt.J. S,U'CiI for opanlnl on up.tI'um 'ld' IDliplUI it pouibl,.4. it. ql,LlliRlld engineer .houJd in.PlC! !.h'Q)ndiuoo and rcwmnlllnd furth,r ae:tJoQl tobe Ukcn.ENGINEER IlEQUlIlED

I. Plu,lb, upltrum .id, oflh, crKk ID 'lopthll now.2. Thll wIlir Illvelin h' re,e""oir 'hould belower,d \lOti! it 11 below the l,v,1 or thecraclu.J. it. ql,Lllifilld ,n;ineer .hould in.pec~, tnllloonditioa and rt;oRUncnd f'ur1ber ac1JORI IDbo lUo" .

I. Examin. \he boil (or ttan.portllion oftoundllioQ material••2. It soli pllUfi:lo. Ill! movin, down'trum,.andba.. or earth .nould be \I11d to crutl •c1ik4I IIOURd the boil: Th, p"'''\Inll cl'lalldby the wlttr l,v,1 within the dike may eon·trol now v,lociUea and lllmporarily pn:vlnlfurther era. ion.J. U 'fOIion i. becominlll'ut,r. the rlllllr·voir l,v,1 .hould be IowIl"ld.4. A ql,LlWl,d ,nlin'" .I\ould Inspect thecondition IIId ",commend fur1bllr aclion. tobe tUliln.ENOINEER IlEQUIIlED

.. PROBLEM

SEEPAGE EXITING ATABUTMENT CONTACT

LARGE AREA WET ORPRODUCING FLOW

MARKED CHANGEIN VEGETATION

BULGE IN LARGE WET AREA

PROBABLE CAUSE

I. W.l.Ir nOW'inl UutJu&b PlthwIY& iD. UlCabuU'ntnl.2. WI"'t nowilll tMlup the C1mblllkmlnl.

A IlICpI'll path hu devGloptd lhroua,h theabutment or Clmbankment m....rial. &nil(ailW1l of the dam CUI occur.

I. Emblllokmea( material UI supplying nowlPIlJu:.z. N.twa! aeediAl by wind.J. CbMlllII ••ed t)1)'I durinl urly poat COQ­

struccJ~ .eoc1iA",

Down,tRam embankment mar.cria.l. havebllWI ~ movt.

POSSIBLE CONSEQUENCES

HAZARDOUSCan Iud to Il"Otion ol.mbankmcn~ mll.Criwand flillllo of 1M dam.

HAZARDOUSI. lnereued now. c:ould load to ervaion QfembWm.at mllCrial uxi· (ailuRI of thedam.2. Saturation of the embankment can Iud toloc&.l llidlll wh.i..h l:Ould elUl. failurl ofWI dam.

CLlIo ~how ...tufl~d If'llL

HAZARDOUS'Failurl ot th. Imbankm,n( relult frommu.ivI slidinl ean rouow !hI" Iulymov,manU.

RECOMMENDED ACTIONS

I. Study luka" ..... Lo dl.t.nnin, quantityof now and er.&ln( of IlNraUon.Z. In.PC~ daily (or dt....lopUll .l~•.J. W,14t I.nll" r...rvolr mlY R.ed 10 btlowcrtd to UI\Ilt Ul' .arlty ollh' .mbW­....e4. A qualified laii,netr 'bauJd in.pcct !.heoondlUoGl ud recommend~.r I ..donl ~bo ......BNGINBBR REQUIRED

1. Stu.. out !.hI .alutltod un &ad monil,Qr(or gowtb or Ihrinkin&o2. Mtu""'t Ill)' Qu1JlOWt ...C:......,I1IIly IIpOllibl••3. Ruervoi, livol m.y n.ed to tit lowned IflaNratod "1.. iDc;rI..1 in ,b., It I ftud'ICflp Iev.1 0' it flow Ine"I1'"4. It. qu..un,d _,nliA,.r .hould iJuPf~ thecooditio.a IDd ~l:Onun.nd fuM" IIOUoni tobI taicc.BNGINBBR REQUIRED

I. U.. prob, LlIod .hoval to ntlbU,h if lbam&terills in WI .vI' .... W'Ue' than ,u,­I'OUAliinI anu.2. UUI...how. w,mln. when lurroWldina:.,111 do not, .. quaUfi,d ,nlin." IhouldIn'ple, tho eondilJon and ftconun,nd l\atIhnactiOnl 10 bI l.Lk,n.~OINBBR REQUIRED

1. Compan lImb.nkm,n( erou nelion tothe ,nd or C'oONiltUction c:ondition (0 '" I(ob.,rvod condition may "flClet C1nd orconall\lGtlon.2. Stlb OUl IiTcelcd &rU and ,"ur.telymaUUrll oull1ow.J. A qu.UO.d ,nain." .hould in.peet !hI!condition 11'111 ~CQnunlnd further aetlon. tobe tAken.BNGINB~R REQUIRED

" PROB~EM

TRAMPO~INE EFFECTIN LARGE SOGGY AREA

~EAKAGE FROM ABUTMENTSBEYOND THE DAM

WET AREA INHORIZONTA~ BAND

LARGE INCREASE IN F~OWOR SEDIMENT INDRAIN OUTfA~~

PROBAB~E CAUSE

I. Waur mavin, rapidly lhroul,h th~

ImbanJunlnt or foundauon i. bam! can­ltolled or conlain,d by • w,U'llIL1bli,h,dtwf root Iy,tem.

WllA, mavin, tJwuih clieu and auures inthe .bub:lllnl maceriall.

Prolt I.yar or layer ~ .andy mltoriaJ inori&inal c:oaItNCUol\o

A .nortlned "Ipap pith or InCTcued.torap lovII..

POSSIB~ECONSEQUENCES

Condition 3howl ,,"cusive seep'IO in the1Ie1. If conlrol laye' of lurf is destroy,d.rapid erolian of foundation materi.l, could,,,ult in rallul. or the dam.

Can Iud to rapid erosion of _bulmen! andevacuation of tho rlllef\'olr. Can lead lOmu,iVtl sUd" nllt or down.tRam fromtho dam.

HAZARDOUSI. W,tlinl of V1U below lb, area orIxcc'live "Cpl" CUI I,d to IocI1lz.edIn'lablllty or the cmblnkmenL (SUDES)2. EXC4Iujvt I1pwl Clan lead to accel,rated,rollon orembankment mlteril1. and raill.ll'Clof the dam.

HAZARDOUSI. Hlprnk)cicy flow. can causeerOlion ofdrain then emblUmenl mawri,l..2. Can lead to Iliplnl failure.

RE.COMMENDED ACTIONS

I. Carefully inlpect the arn for out!lowquantity and any transported maLfriaJ.2. A qUIUfi,d ,n&ineet .hawd in.peel thocondilion and rKOnvftond l\l.r\b.r le110n. r.obe laken.ENGINEER REQUIRED

I. C....NUy in.PCet. the AtCli to delerminllquantity at now and unount of trwponcdmateriaL2. A qu.Uficd engineer or loololl.t Ihouldlrllpect tbt condition and I1commond ful1herIctionl to bf t&ll.on.

i. Determine u cio..l)' u pouible the nowbeinillrodl.lced.2. U'l1ow lnc:nu", r...rvolr level should 1Mreduced until now ltabillz:e. or .top••J. St&k8 OUI the exact un involved4. Ulinl hand too13. try to idenufy tnemltcri_1 aUowinl the now.,. A qualified enlineer should Lnapecl tnecondition and rocommend li.Irthor aCUOnll.obe l&kln.ENGll'!EER REQUIRED

1. Accurately meuurel outllow quantityand detemlne tnlOWIt or Inonut ovtr pre­vlOUI now..1. CoU'dJar .UJlplc. to comparo NriJidiry.J. U ,Ithor qUlnulY Of turbidity hulncreulld by 2'%. I qualmod enlinc.,loould evaluate: the condition and; recom­mend further ac:tion•.ENGINEER REQUIRED

•• "gur•• SAIftipecUon Gulden,... •concr.t. U",tream Slope

PROBLEM

CRACKED DETERIORATEDCONCRETE FACE

CRACKS DUE TO DRYING

Plgur•• S.S'nopeatlon Quld.llnn •Splllw......

EXCESSIVE VEGETATIONOR DEBRIS IN CHANNEL

ip'~.~---...;.

PROBABLE CAUSE

Concratt: downeraLed nliultiD& (rom weath­OM" JOLIU lUI., d,wio...1.Od or di.placoed.

n, lClill~•• 11l moi.uul &lid ,hrinlu., uu.~In, ;JacU. NOTE: U.u&!Jy "'0 oa ""IlAd downauum .loplilTlOluy.

AexwnuJ.don of .lidc mltarial., dead Irec.,".:....ive vcptlLivo pvW\h, ou::.,la .piUw.y~&Mol.

POSSIBLE CONSEQUENCES

Soil Is "oded bllWld tM (aca andcavems canbe fonnld. URiUpporttd HcUOGJ of COR".t,criCk. I... ""00 may w.pl,'" conc"'••

Heavy rlias can fill up crlC:U and caUlIsmall paN d f.ft'IbaAlua.Df. ~ move a10nlinUimaJ ,Up IU"""

Raduced di.lOhllle capacity: overllo..... of.pillway; ovenoppinl of dun. Prolon&cdQVOItOpPUl& <:ID ,.WI faiJW't of thll dll11.

RECOMMENDED ACTIONS

Oct'nnw_ c......e. Either pateh with ~Ul orcontld ,nliA'., (or plnnanlnt r"Palrmethod.2. U daml,1 1a u.a.osl"I, I qu&JiIlcdftIPn"r should Wptct u.. CQnditJol1l I.lIdraGCImmand Cwtb., action. 10 be lLUn.ENOINEER REQUIRED

1. MoDilor c:r.cu rOt UIl.rau.. la widl.h.dtpth" or le"ath,1. A qualllled ,nliDeer .hawd In.pect thoconditio. uad n1commlnd li.arth., KUon. 10be t&Un.ENOINEER REQUIRED

Clean out debris pariod.ically: contn:ll vele­Lldve ifOwUI in spillw.)' channel. wtaU 101boom ia (ront ot .piU......)' entnnlOO to inter­lOIlpt d.bli••

... PROBLEM

EROSION CHANNELS

EXCESSIVE EROSIONIN EARTH· SLIDE CAUSESCONCENTRATED FLOWS

END OF SPILLWAY CHUTEUNDERCUT

WALL DISPLACEMENT

PROBABLE CAUSE

Surflce runolT from intl"u r&inltomu orflow from .pill....y camn ,unlel materialdown lb' .lopel. r.,ultin, In t;Ontinou.tlOU~. Uv,nocK traffic: Cl"1114 ilolllie.where now coocentrlt.. vari,a.

O!u:hUII velocity too hi~ bottom and.Iopt mlLiriai 100•• or delerionlOd.; c:hlW'leland ba.a.k ,Iopl' too steep; bill .ouunprotected: poor con.sltUalon protlc:tivi,wfac:e: rliJed.

Poor wnftl\lratioD of luUin. buiD unI-UIhIY ,rol1.ible maltrill•• Abacn" of ~totrwill I' 'Dd of c:huLi.

Poor workman.hip; WIG""" settlement offoundation:: Ixc.uive ..nh and ""Iter prea­IlIre: in'lIIfIcent .teel bu rtlnforeement ofconer,t•.

POSSIBLE CONSEQUENCES

Unabated erosion c&l1lud to .Udes. ,lump.or ,lip.....hlch can mull in nsdUl:ld .piUwl)'clpacity. bladequ&lI .pillwlY cipacity canIud to embankmenl oveMppinlllld ,Clultin dun f&ilunl.

Di.turbed now plnem; lou of material.inCTllulld ,oditrulnt load down.trnm; col·I.!»e of banJu; failure of .piUwlY: can leadto r.pid .v.eu.tion of the rtlervoir lhroudJlb, $,v,~ly eroded .pi!Jway.

HAZARDOUSSlJ\Icturll damal' to spiUway structure;ooUapat of .l.b and wall Iud to coltl)'l"fPalr,

Minor dilplacemGnt wiJl crllte eddin .ndtw"bulcnce in the now, cIII,inl oro.ion of lbesoil b,lUnd the will. Major di,placement wiUcause .evtre criCks ud ",n\\l11 fallure 0(th' .lJ\IeNIlJ.

RECOMMENDED ACTIONS

PhOIOPlph condition. Repair dam'led"'au by repllcln. ,rod'd malerial withcomplcted nu. Protect. UfU llain.t fUNr,ero.ion by In.lJJlln, Iuilabl, nx:k riprap,R.cveletlll!lll1la it Ipproprlalo. BM' eondj.tion to tho attention of th, ongln"r dUM,nut Irupee:tJon.

Minimizo now vGlo<:it)' by proper design.Un lOund malonal. Keep ehannellUld blnlr;slopel mild. Encour.ge p;rowth of IVU. on.oil surface. Con.lnIct smooth and weU.completed surfKtI. Prolect .urfael' withnprlp, uphall, or eonerele. Rlpair erodedpart \Yin••ound eon.lJ\Ieuon praf;.Liect.

Dew.wr aft'ee~d area: clean out eroded 1111IUld properly b.cklUl. Improve aueam chan.n,1 below chUte'. provld, properly Ilud rip­...p ia .ti!lln. buia un. wu.u eutot!'wall.

Rlcon.truction .hould be dono lecordina: tosound onlinoorinl practico., Poundationshould bt cUllfully pRplflld. Adequllllweep hoi.. Ihould be In.talled to relievow.ter proUUfG bclhlnd waU. U" enoushr.infon:llm.nt In the eoncreta. Anchor WillI

to provenl furtner diaplacement" ',lnst.UslnlU between spillway wllb II ncedod.Clean out and b.ckllush drains 10 luurtlproper op"llion.. Con.ull All en&lnellrbefore Iclion. are taken.~NGIN~~R REQUIRED

..PROBLEM

LARGE CRACKS

OPEN OR DISPLACED JOINTS

BREAKDOWN AND LOSSOF RIPRAP

MATERIAL DETERIORATlON·SPALLINGAND DISINTEGRATION OF RIPRAP,CONCRETE. ETC.

PROBABLE CAUSE

Con.truction deface local cQI:lI;,ntr.t.edItt...; local mit.';'" delerior,tion; (ound,·\.ion failure. lllic.uiv. bl,kIIU pliny".

E:tcII.lvl and un,ven lattl,mcnt of foun.dation; .Iklinl of concret, ,I&b; con.tnIctionjolllt too wid. and 11ft WII.al.d. StaJanld'lAriOl"ced and wuh,d 'w:.y.

Slope too Iteep; melenal poorly Indectfailurt of Illbpad.: flow vel~ity too high:improper pllcoment of mlLllnll; bcddin;m....rial Of foundation wuhcd ,wly.

Un of unsound or defcl:livi materials; SlNc;.tur...ubjeC:l to frun-th.w c~cllll: ImpropermainlenlRGI pnCUetOJi harmful l:h.miub.

POSSIBLE CONSEQUENCES

HAZARDOUSOi.tUrbUlc, La flow plt1clm.; crosion of(OllAdatioa Illd blclUIU; noontuaJ COUI",'of ,tnu;tu....

HAZARDOUSEro.ion o( (ound.tion malarial may Wluen,uppen ud CIILI' further craW: p,..aur•.induced by wlter flowS over di.pl",djOLnU may \IIuh Iway wall or .llb, or ClU"u;tca.ivo u.adcnninitl"

HAZARDOUSErolion of l:h&Mcl bottom and bank.,;railura of IpillwlY.

Strul:ture life will bI Jhonenect prematuref.ilwe.

RECOMMENDED ACTIONS

Lull cl'lck. wil.houl IUICI dl.plac,mcnt.hould br n1paind by patchin"

Surroundial &rIU .bauld ~ IOlunld or cutoul breCOnl pll.clUna mal.rlal i. applied.. (S"Cbapw, 7,) lnIl.IJJ'l.ion of weep holel oroUi., ""ca. any til a,eded.

Coa.tnll:tlon john .hould blI no wider r.han1/2 Inch. AU JOlall .hould bI ..&I.d withuphill or othlr Oexibl. matlnab. W.ler.'lopt ,liquid hi uaed where (Iuibl.. Clul1the joint. relJl.1CI uod,d mat4rial', &lid tealthe joinL found&lion' 'hould be properlydriUncd and prcplRd. Undllnidc of l:hllLt,I'ba Ihould h". ribe of cnoll&n dcplh 1.0prennt IUlIin" Avoid It,cp c:hu" slope.ENGINEER REQUIRED

Oesilll • subia slope for l:hlMel bottom &lidbanlt. Ripr.p mltlrial should be well&TIded (th, mittNI should l:onWn smlU.mccilwn, and lar,. pWCIII). Sub-gad.'hould be proptrlt ptlpared befora pllC:o­men1 or ripr,P. lnmll llI\er fabric; ifne""ary. Control now velocity in !ha,plllw.y by proper dt,liM. Ripr.p ,hould bopl.c:cd Ie<:Ordin. 10 ,pocillcauon. Scrvic:..o( lUI cnlinc., lie rel:Ommcnded.ENGINEER REQUIRED

Avoid win; shalo or ,&Pd.tonc for riprap,Add alr.entrllnln. lalnt wh," mixlo; can·l:I'tle. U.. oNY l:M:an aood qlllUty 'iif1lllttain the concrete. Ste.1 bll1 ahould have .tloaM I ilK:h 01 c:onetlw l:OVoc. ConlilcllUe.hould be kopt w,t and prottl;1&d (rom fra,;·ina dunnll:urin" Tlmblc .hould bot trllttdbofore u.ln" '

POOR SURFACE DRAINAGE

CONCRETE EROSION,ABRASION, AND PRACTURING

LEAKAGE IN OR AROUNDSPILLWAY

TOO MUCH LEAKAGE FROMSPILLWAY UNDER DRAINS

PROBABLE CAUSE

No weep hole.: no drainlP facility; pluUClddrain••

Plow velocity too hilll (uluilly OCCUl"I IIlower ilInd of c:huta In llJih dam.);'. rollinl orpnel and roclu down !.he chull: cavitybehind or billow c:oncrlte .llb.

I. Cr.~1u and joinu: In IlIIololic: (onnauon ItIpillwlY an pcnnitUn, IIlIIpa,I.2. Gr.....1or land lay,,, It IpijlwlY aro pcr·m.iCUnII..P·..•

Drain or cutoff may havtl failed.

POSSIBLE CONSEQUENCES

Wet r~und.tion.hu lower JUpportina capa­city: uplift prellUA! relullin, from HIPlPwlter may C.UI. dAmap 10 spillway chute;accumulation of Wile, may abo i"(reu.tolal pnluur. on spillw.y WIU. and CIII,.dam....

Pock maru and spallinl of concrolllsurfaceinay progrelli,ely become wone: small holemay c;aus.. W'ldcnnWnl of foWJdIUon. Iud-­inllo fallure of Ilnlc:turl.

HAZARDOUSI. Could I,ad to nc:ouivo 1011 of .laredwater.',2. Could Iud to I progrouive f.lIure itvolocidea are hilh enoup 10 C.UI" erosionof n.tural m'len.".

HAZARDOUSI. EIG...h, now. under Lh••pillway couldIud to ol'Ollon of lOundaLlon mlllri.1 andCOUlPSO of Plru of Lho .plll.lY.2. Uncontrolled now. could lead 10 lou ofllored wlter.

RECOMMENDED AcTIONS

Inllall "'up boln on .pillway waU•• werendortlOl,lhouid bllurrounded and pac:kadwilh II'tded Rllarin, m•.,rial, lnttaU drainIf.tam under ,pillway nlu downJU't1mand. elfin out ,ai.una Wllfp 1101". Blck·nUib Ind nil.bliltace draln 'Y'llIm und., th.supervi.lon of an onsinlle,.ENGINEER REQUIRED

RAimo.... rock. and "'.....Is from .pillwaychutl berMe flood lOuon. Rai•• wlt.r levelin .ullln, buin. UII &oed quality concrotCl,Amari c:onc:nle .urfiCCI II .mooth.ENGINEER REQUIRED

I. Examine exit .rea to sell ir type ormaterial can explain leakage.2. MUlur, now quantiry and chick (or lifO­lion or n.tural m.teri.ls,J. Unow rile or amount of IIroded materials"inmues rapidly. roservoir 11'01 should belowClred Wltil now .t.abi1i:tCI Of .lop•.4. A qualified en&ineer should inspect thecoodition and ...commend furthor Iction. tobe lakeR.ENGIN~ER REQUIRED

Sam. u aba'lIl.

.. PROBLEM

SOOPAGO FROM ACONSTRUCTION JOINT ORCRACK IN CONCRETOSTRUCTURO

fig"," 5.6InlpK.lon Guld.lln... ,Inl.... Oull... and C,alM

OUTLOT PIPE DAMAGE

CRACK

JOINT OFFSET

CONTROL WORKS

UNTJRNOIi.:S r

("UNTMUl. STUI

BHClIi.:NI""~."I.'oriI;

sn;M la'lIn',s'

/

I,' ,

PROBABLE CAUSE

WaLer it collectina bctund Itnlcturll becaunof in.umc;icn~ drainl,e or ,IQUlld weepholn.

Settlement; impact.

Ruu (It.,1 pip')Erolion (cClncrc\O pipe)CaviaLion

Settlement or POO' 1;0nsl;N..:Unn prl",ul;e.

I. BROKEN SUPPORT BLOCKCon",'" detllnortuon. Exccnive fo,,"uel1ed. Oil dJlltrol I\lm by uYinl lO open1'\1 ....h.n it wu jammed.

2. BENT/BROKEN CONTROL STEMRUlt. Ex"" .. (arce used 10 open or clollp ..... lnadequatp or broken Item lIIidn.

J. BROKEN/MISSING STI:MGUIDES

Rull. lrtadtqua.... lubncallon. EllCOI. (orce\lied. to open or ",10.. pta when it w...jllMltd.

POSSIBLE CONSEQUENCES

I. CUI c,un wall,lo tip in and over, flowllhrou&h concrete can lead to rapid deteriora·tion from wulherinio2. I( the .pUlwIY i, locl~d wil.hin theembanJunlnt. rapid tn)I'on can I'ld toraUure or the dam.

Exccuiv, seep,p, pouiblc in\.lmal erosion.

HAZARDOUSExccuive seep'ie, pouiblc Inlemalcrosion,

HAZARDOUSProvidel p.l..p .....y for w.LI, to 'lUt oren'Ir pip'. rnultina in lro.ion or intimalmaterial. of the d&m.

CIIJICI ,0ntrolluppeR block to tile. controlstem m.y bind. Control beld woru rna)' lit­tl•. 0,1.1 may not aPln ,11th, way. Suppol1clock may fa.ll ~mpICltely, llivini outlotinoperable,

HAZARDOUSOutlet Is Inoplrable.

to.. of .upport (or ,ontloillom. Stem mtybu,kJ. and bAlu. under Iven nonnal \lI', (uin UU, ",ampl,).

RECOMMONDED ACTIONS

I. Chick Ula bthind WIU for puddUn, oflunlCa waur.1. eh,ci and clean u nccd~ dr.in OUlllll"flulh linn. and we.p nol...J. 1t conc1itkln penilt.l I qualified cnlin••rIhould in.plc:\ Ih, condition and Bcomm.ndfurthlt acUen. io bI lUln.

Check for ,,,idenelll of wlter either cnlArin,or C:dUnI pi~ It crlck/holG/ctc.

Tap pipe! in vicinity of d&mlled un. Ii. len­inC for hollow ,ound ....hlch shaWl I void huformed &lonl lohe Quuide 01 Ihe ..:onduir..

If a provellive failure i. lu.poet.ed, nquuIeniin"nnl advice.

Any of thOlO ",ondltionl can mean the ",on­trol i. eithor inoperablo or It best par\Jyoplrabll!. UIO or tho Iyltem lhould bomlnimi:r.ed or dilcontinuld. If thl outlet 1)'1'l&m has , second concrol valvo. ",onsiderusinl it to regul,1.e releu" until ropurl cantill made. Engine'Rna help il recommlnded.

" PROBLEM

FAILURE OF CONCRETEOUTFALL STRUCTURE

OUTLET RELEASES E'RODINGTOE OF DAM

f&ft?)\~) ;/~VALVE LEAKAGE

DEBRIS STUCK UNDER GATE

.~~.~.>,., ..'1',LOa"":"""//J;),0Jii F

CRACKED GATE LEAF

DAMAGE GATE SEATOR GUIDES

/,. "IRVENT, '/

SEEPAGE WATER EXITINGfROM A POINT ADJACENTTO THE OUTLET

PROBABLE CAUSE

Exceuivi side prelluru aD DOrll'lialo~C1

c:oac;ntl.tnI.;N". Poor CQo"clo quility.

Outlot pipe too .1Iort. Lack or 'D''1J'~dluip.ti.a. pool or .tnIl:CW'W It dcnrmlnun_ of ooadWL

Ice .ction. rult. atrec1 vibraUon. or .tlelSmullinl frons (Cftilll P.ilI l:lwtd wh," i~

.J........

Ru.l., efOlio", cavit.auon, vibr.tioD.' or.ur,

1. A brni in the outlet pipe.2. A p.lJI ror ~ow hu developed alonglJleouuide or the oullet pipe.

POSSIBLE CONSEQUENCES

HAZARDOUSLot:, 01 olltraU .CNcturll upotn ,mow­D1WC to .~,iOD by 0l&1I.~ ",11"u,

HAZARDOUSElQ,iw of toe O'lenteepen. downatrcam.Iope, C~Io, propu.i" .Joulhina.

G.~ wiU not clo••. aiLe or Ilom may bedam.1td !II ofron to clo•• plO.

Gate-I'll' maiD (aU l:Omplel.ely. eYKuaUngrtlll'¥Oir.

Leak.g, and 10.. or .upport (or pte leal.Gate may bind ill lLIid.. and becomeInoperable.

HAZARDOUSCOtIanued Ro.... can le.d to raid erosion orembanlunont m.toria1l and railure or thed....

RECOMMENDED ACTIONS

I. Check for prosnui"l (ailWll by monJto....In, typh;:&! dlmllUion, ludl AI "0" ,bawula "gu....2. Repair by patottiAg crub IDd lupplyitllWaUllp vouod concnle .tnICCWli. Tot&.ltlpllQtmloC of ouliall .CIWRU'O maybeD'odod.

I. Eltend pipe t.yond toe (UN' pipe of,amo.WI aDd mal4lnll, aad (orm WllerUl!:llcoa.alction to oz.i,tia, coaduJt).2. Proc.e:t cmbll1bnlDI with ripr.p ovu l\Iit,...blt beddl..ta"

RI.i•• lAd lower ,.to .lowly untJJ debri. i.looIened aad fiolu pale val". When rlll"r.voir 1.1 lowered, ropalr or rwrXlCI tJuhnck.

UII nlYe only in fully 0Pfln or clo.ed po.i­Lion. Minimize uso OrYalv, unLillea{ can berepa.ir 01 replaced.

Minimize uae o( v.lve until ruidu/'lili canbI repa.ired. IfcaYit&Uon .. the caUII, check1.0 see II' air vent pipe u.i.l, Uld i.unobltNcted.

I. ThomuihlY invlltig.te tha lrea by prob­Ing and/or .hoy,Ulrt,l.o'u if Uta cau.lll:1nbI dewnnlned.2. Odennin. if lukall water I. c:llT'Yinl soilpartiel...J. Determine quantity of flo"'.•. If now increull. or I. clJTYin; embank­ment materials, tllCl'¥Oir lev,1 should belowered until leu.p ltop.l.,. A ql!.Ulied engineer should' In.pecl ll1acondition and n1commtnd further ilOtion. tobe taJl.en.ENGINEER REQUIRED

— blank —

49TABLE 6.1INSTRUMENTATION AND MONITORING

GUIDEUNES DIRECTORY

MEANS OFPROBLEMDETECTION

Table 6. J lists ftaturrs to be observed at adam" and the suggesled irutromrnts or obser­vation technique to be used Tht sp«i/ic stt­rions ofthis manual whtrr an instrument orobservation technique is disnned arr alsoindicoted.

X

-i!

----- ;;

i

)\,1--,

;

Ii

! ~=-I- I - .

"L,

iI!,

x-~-

IL-1--,

X

J--i

I

I_fii

__I

iIj--r-

1­-j­

J

J--,___ I

--){- X,---x

i - -

Ir

X-1-_

-I-J' --- L!-

~--- 1-

j

-- ;

- f-

I

-- X

x

-T ]-1 --

I I I! 1--- I X -- -X ~ _ Jt. X - --I'f- ;(-- I i X--!

t+F+=l~F-lI ' I !

~ -j I X J J ,(i ,c- -*--- X--XX I 1--- x--Ji:! Jf X X X

-- I ~

1---

X-

lXX

Jf­X

I,-----

II

x-I,

I

•X

J,I

1-

XII.I

1

I*XXXX-t ---II,XX~X

XI

I

II

X--- X

1II

i --

1II

-- *----x-x!

X

-1-

!XX-­X-

IX ---

X ---1'~- --x- x

~------I

I

i I

I Ix- *x-- x-x--- -i.--­X ---X-

xx-­),{-

*XXX

i;

XXXJiX

1 _2-Ix--

I,,

CONCRETE DAMSUpstream SlopeDownstream SlopeLeft/Right AbutmentsCrestInternal Drain. SystemRelier DrainsGalleriesSluiceways/ContrQls

SPIUWAYSApproach ChannelJnleiJoutJet structureStilling BasinDischarge conduiVChannel

Control FeaturesErosion ProtectionSide Slope.

FEATURE

EMBANKMENT DAMUpstream SlopeDownstream SlopeLeft/Right AbutmentsCrestInternal Drainage Sys.Relier DrainsRiprap & Slope

Protection

OUTLETS. DRAINSlnJeVoutJel structureStilling BasinDischarge Ch~elTrashrackJDebris Control _Emergency Systems

GENERAL AREASReservoir SurfaceMechlelect_ systemsShorelineUpstream WatershedDownstream Channel

CHAPTER 6INSTRUMENTATION AND MONITORINGGUIDELINES

6.0 GENERAL"Instrumentation of a dam furnishesdata to detennine if the completedstructure is functioning as intendedand to provide a continuing sur­veillance of the structure to warn ofany developments which endanger itssafety" (ICOW. 1969).The means and methods available tomonitor phenomena that can lead todam failure include a wide spectrumof instruments and procedures rang­ing from very simple to very com­plex. Any program of dam safetyinstrumentation must be properlydesigned and consistent with otherproject components. must be basedon prevailing geotechnical conditionsat the dam. and must include con­sideration of the hydrologic -andhydraulic factors present both beforeand after the prQject is in operation.Instruments designed for monitoringpotential deficiencies at existingdams must take into account thethreat to life and property that thedam presents. Thus. the extent andnature of the instrumentation dependsnot only on the complexity of thedam and the size of the reservoir. butalso on the potential for loss of lifeand property downstream of thedam.

An instrumentation program shouldinvolve instruments and evaluationmethods that are as simple and

.straightforward as the project willallow. Beyond that. the dam ownershould make a definite commitmentto an ongoing monitoring program orthe installation of insl{Uments prob­ably will be wasted

This chapter discusses deficiencies indams that maybe discovered and thetypes of instruments that may beused to monitor those deficiencies.Table 6. I describes deficiencies.their causes and generic means fordetecting them. Increased knowledgeof these deficiencies acquired througha monitoring program is useful indetermining both Ihe .cause of thedeficiency and the necessary remedy.

Sf

Involvement ofqualified personnel inthe design. installation. monitoring.and evaluation of an instrumentationsystem is of prime importance to thesuccess of the program.

6.1 REASONS FORINSTRUMENTATIONInstrumentation and proper monitor­ing and evaluation are extremelyvaluable in determining the perfor­mance of a dam. Specific reasons forinstrumentation include:

• Warning of a Problem - Often.instruments can detect unusualchanges. such as water fluc­tuations in pressure that are notvisible. In other cases. gradualprogressive changes in say see~

age flow. which would go unnoticedvisually. can be monitored regu­larly. This monitoring can warn ofthe development of a seriousseepage problem.

• Analyzing and Defining a Prob­lem - Instrumentation data isfrequently used to provide en­gineering information necessaryfor analyzing and defining theexte·nt of a problem. For example.downstream movement of a dambecause of high reservoir waterpressure must be analyzed todetermine if the movement isuniformly distributed along thedam, whether the movement is in.the dam. the foundation. or both.and whether the movement is con­tinuing at a constant. increasing ordecreasing rate. Such informationcan then be used to design correc­tive measures.

• Proving Behavior Is as Expected- Instruments installed at a dammay infrequently (or even never)show any anomaly or problem.However. even this information isvaluable because it shows that thedam is performing as designedand provides peace o( mind to anowner. Also, although a problemmay appear 10 be happening orimminent, instrument readingsmight show that the deliciency

52

(say increased seepage) is nonnal(merely a result of higher thannormal reservoir level) and wasforeseen in the dam's design.

• Evaluating RemedialAction Pel'­formance - Many dams, par­ticularly older darns, are modifiedto allow for increased capacity orto correct a deficiency. Instru­ment readings before and after thechange allow analysis and evalu..tion of the performance of themodification.

action, expansion resulting from tem­perature change, and heave resultingfrom hydrostatic uplift pressures.They can be categorized by direc­tion:• Horizontal Movement - Horizon­

tal or translational movementoonunonIy happens in an upstream­downstream direction in bothembankment and concrete dams.It involves, the movement of anentire darn mass relative to its

/

.... MIN1MUM

-.

I- REBAR

mU.n \\ URKS

J~~' ---r~r ~_~___ STATION

AXIS ~F DA\M LLo -1_ /

..,-~~,...:=:==;o~~~~~-- ~

~ ! ~~ -- ~- - ...

~:r.~I&:~ar:~~

Figure 6.1 b - Plan of Alignment Syslem

Figure 6.1a - Inslallallon of Permanent Points

6.2 INSTRUMENT TYPES ANDUSAGEA wide· variety of devices and pr~

cedures are used to monitor dams.The features of dams and dam sitesmost often monitored by instru­ments include:• Movements: (horizontal, verti­

cal, rotational and lateral)• Pore pressure and uplift pres-

sures• Waler level and now• Seepage now• Waler quality• Temperalure• Crack and joint size• Seismic activity• Weather and precipitation• Stress and slrainA listing of manufacturers and sup­pliers for the various instrumentationdevices is pr~vided in a rePort byDunnicliff () 98) ). Details of theinstallation, operation, and mairi­tenance of each device Bie describedin U.S. Bureau of Reclamation(J986).

6.2.1 Visual observations - As dis-. cussed in Chapter S, visual obser­

vations by the dam owner or theowner's representative may be themost important and effective meansof monitoring the performance of adam. The visual inspections shouldbe made whenever the inspectorvisits the dam site and should consistof a minimum of walking along thedam alignment and looking for anysigns of distress or unusual con­ditions at the dam.6.2.2 Movements - Movementsoccur in every dam. They are causedby Slresses induced by reservoirwater pressure, unstable slopes (lowshearing strength), low foundationshearing strength, settJement (c0m­pressibility of foundation and dammaterials), thrust due to arching

$3

abutments or foundation. In anembankment dam, instrumentscommonly used for monitoringsuch movement include:

• Extensometers• Multi-point extensometers• Inclinometers• Embankment measuring

points• Shear strips• Structural measurinl points

Installation of simple meaSurinapoints is illustrated iD Ape 6.], aand b, a simple crack monitoring sys­tem is shown in Figure 6.2, andinclinometer systems IIDd plots areshown in Figure 6.3.c.For a concrete dam, instruments formonitoring horizOntal movementsmay include:

• Crack measuring devices• Extensometers• Muhi-point extensometen• Inclinometers• Structural measuring points• Tape gauges.• Strain meters• PJumb lines• Foundation deformation gauges

CARPENTER'S UVEL(Spirfl Lntl)

YMINIMUMEMBWMENT

"OR"O,"I \ I.mS1'1 \C • \1.·'·1

•41n1tW)

~;..;exozou~ -L__-L_-\-_-,,-4

SECOND Rf.ADlNGn'"'''' :1_ --r--r ~=:gc::z::»~~,.

b(Sa........)

Figure 6.2 Monitoring Cracks on Embankment

+1.1

1ST READING•:-2ND READING,,

•,

•

,,I1.,,

-u

...wWl&.

Z

:z::Ii:wo

8- DIRECTION

+1.1

I 1•,•, 5,,,

,i,

I/

1

•

-uDEFUCTION IN INCHES

Figure 6.3b - Plot of tncllnomet... Readings

1ST READING +--..,

2ND READING

B-..-

INCLINOMETER

tnctlnomet... Syst.ms and Plots are Shown In Figure 6.3~c.

A • DIRECTION

A+- -A-

Figur. 6.3a - IncDnom.ter....D.tall at surfac.

A­

Figure 6.3c Incllnom.t.r and Casing

In a concrete dam. vertical move­ment monitoring devices mayinclude:

• Settlement sensors• Extensometers• Piezometers• Structural measuring points• Foundation deformation

gauges• Rotational Movement - Rota­

tionaJ mo··ernent is commonly aresuh nf high reservoir water pres­sure in combination with lowshe:>rin1- strength in an embank­ment or fowldalion and may occurin either component of a darn.This kind of movement may bemeasured in either embantmentor concrete dams by instrumentssuch as:

• Extensometers• I ndinomeh:rs• liltmeters• Surface measurement points• Crack measurement devices• Piezometers• Foundation deformation

gauges• Plumblines (concrete only)

• Lateral Movement - LateraJmovement (parallel with the crestor a dam) is common in concretearch and gravity dams. The struc­ture 01 an arch dam causes reser­voir water pressure to be translatedinto a horizontal thrust againsteach abutment Gravity damsalso exhibit some lateral rnove­ment because or expansion andcontraction due to temperaturechanges. These movements maybe detected by:

• Structural measurementpoints

• liltmeters• Extensomcters• Crack measurement devices• Plumblines• Strainmeters• Stressmeters• Inclinometers• Jointmeters• Thermometers• Load cells

6.2.3 Pore pressure and uplift pres­sure: As discussed in Chapter 2. acertain amount orwater seeps through.under. and around the ends 01 alldllJJlS. The water moves throughpores in the soil, rock. or concrete asweU as through cracks, joints. etc..The pressure of the water as it moves

movements may be monitoredby:

• Settlement plates/sensors• Extcnsometen• Piezometers• Vertical Internal movement

devices• Embankment measuring

points• Structural measuring points• Inclinometcl' casing mea­

surements

Ib) STRAIGHT EDGE AND TAPE. PLUS REFERENCE POINTS

PLUMB BOB OR WEIGHT

STRING OR TWINE

~s

STEEL TAPEI

---:'~"~'~'=.~.'~.. ~.-.~:=.~>~.Fr.~.~..=...~..~....=..=.~=.~I:":V~ERT1CAL DISPLACEMENT.:'. ~ ..

WALL

STRAIGHT EDGE

•

Ca. STRAIGHT EDGE AND TAPE

LOOK FOR CHANGES

HERE ll-sun TAPE?-l

LOOK FOR CHANGES HERE

Ie) PLUM. Boa

STRUCTURAL _./CRACK oF.

SIDE OF >.

CONCRETE •... t:SPILLWAYWALL

Cd) MORTAR MARKER

LOOK FOR CRACKINGTHROUGH PATCH

Figure 6.4 - Measuring Displacements

..ExlilDples of monitoring of c:oocretestructure movements are shown inFigure 6.4.• YeTtkaI Movement - VerticaJ

movement is c:ommOoly a resultofc:onso6dation of embanlment orfoundation materials rmdting insettlement of the dam. Anothercause is heave (particularly at thetoe of • dam) caused by hyd~static uplift pressures.

In an embankment.da~ verticaJ

acts uniformly in all planes and istermed pore pressure. The upwardforce (caDed uplift pressure) has theeffect ofreducing the effective weightof the downstream portiOn of a damand can materially reduce damstability. Pore pressure in an em­bankment dam. a dam foundation orabutment. reduces that component'sshearing strength. In addition, excesswater, if not effectively channeled bydrains or filters. can result in pro­gressive internal erosion (piping) andfailure. Pore pressures can be m0n­

itored with the following equipment• Piezometers

electricalopen weDpneumatichydraulicporous tubeslotted pipe

• Pressure meters &. gauges

• Load cellsSimple piezometers may be as illus­trated in Figure 6.5, while a basicobservation weD ~ shown in Figure6.6.

6.2.4 Water Level and Flow· Formost dams, it is important to monitorthe water level in the reservoir andthe downstream pool regularly todetennine the quantity ofwater in thereservoir and its level relative to theregular outlet works and the emer­gency spillway. The water level isalso used to compute water pressure .and pore pressure; the volume ofseepage is usuaRy directly related tothe reservoir level. It is also impor­tant to establish the normal or typicalDow through the outlet works forlegal purposes.Water levels may be measured bysimple elevation gauges - either staffgauges or numbers painted on perma­nent, fixed structures in the reservoir- or by complex water level sensingdevices. Flow quantities are oftencomputed from a knowledge of thedimensions of the outlet works andthe depth offlow in the ouUet channel·or pipe.

55

6.2.5 Seepage flow - Seepage mustbe monitored on a regular basis' todetermine if it is increasing. decreas­ing. or remaining constant as thereservoir level fluctuates. A flow ratechanging relative to a reservoir waterlevel can be an indication of aclogged drain, piping. or internalcracking of the embankmenL Seepagemay be measured using the followingdevices and methods:

• Weirs (any shape such as V­notch, rectangular, trapezoidal,etc.)

• Flumes (such as a Parshallnume)

• Pipe methods• Timed-bucket methods• Flow metersExamples ofweirs. flumes, and buck­et measuring installations are ilJus.­trated in Figures 6.7. 6.8, and 6.9.6.2.6 Water quality - Seepagecomes into contact with variousminerals in the soil and rock in andaround the darn. This can cause twoprOblems: the chemical dissolution ofa natural rock such as limestone. orthe internal erosion of soil.

STANDPIPE

CONCRETE OR GROUT

•Figure 6.6 - Typical Observation wen Installation

OVERBURDEN

J-MINIMUMDIAMETERBORING

YNEUMATICTRANSDUCER

POROUS ----Ie.fiLTER

POROUS STONE SENSING UNIT

C;?~it:Uj~ndow.)

~~W.ln ~nltn htrt; prtssvrt is tlItf1td on adi.pltralrM al IItt tn. of Iht wnshtlr vnll.

TO PORE PRESSURE TERMINAL

INSTALLATION DETAIL(TYPICAL)

Figure 6.5 - Porous Stone Piezometer

56

Dissolution of minerals can often bedetected by comparing chemicalanalyses of reservoir water'andseepage water. Such tests ate sitespecifIC; for example, in a limestonearea. one would look for calcium andcarbonates, in a gypsum area, cal­chun and sulfates. Other tests, suchas ph can also sometimes provideuseful· information on chemicaldissolution.Internal erosion can be detected bycomparing turbidity of reservoirwater with that of seepage water. Alarge increase in turbidity indicateserosion.

6.2.7 Temperature - The internaltemperature of concrete dams iscommonly measured both during andafter construction. During construc­tion, the heat of hydration of freshlyplaced concrete can create highstresses which could result in latercracking. After construction is com­pleted and a dam is in operation, it isnot uncommon for very significanttemperature differentials to existdepending on the season of the year.For example, during the winter, theupstream face of a dam remainsrelatively wann because of reservoirwater temperature, while the down­stream face of the dam is reduced to acold ambient air temperature. Thereverse is true in the summer. Tem­perature measurements are impor­tant botIt to determine causes ofmovement due to expansion or con­traction and to compute actual move­menL Temperature measurementscan be made by using any of severaldifferent kinds of embedded ther­mometers or by making simultaneoustemperature readings on devices suchas ~tressand stram meters which pro­vide means for indirectly measuringtemperature of the mass.·6.2.8 Crack and joint size - Aknowledge of the locations andwidths of cracks and joints in con­crete dams and in concrete spillwaysand other concrete appurtenances ofembanbnent dams is importantbecause of the potential for seepagethrough those openings. Even more,it is important to know if the width ofsuch openings is increasing or de­creasing. Various crack and joint·measuring devices are available. andmost allow very accurate measure­menL Some use simple tape or dialgauges, while others use complexelectronics to gain measurements.

BULKHEAD

SEC. A-A

DEPTH OF FLUME

DEPTH INDICATOR

METAL STRIP.

'\.~----T

METAL SfRIP

~

,..: V-NOTCH WEIR

•

BULKHEAD

W~TER SURFACE

~JH

(H EIGHT OF WATERABOVE CREST

PARSHALL FLUME(Installation and I10w measunmenl

aceordinllo manufaaurcr's instr1lClions)PanMJlfIurM

Tllr..., Sbippinc Intate <mtalR.ln! Capacity W""h Dept'" We.... W"'" Lnol'itds. JPIIt. lin.) (ift.) (Ibs.) G.... (ilL) (ft_....)

.on )2 , 6 n 16 ,..,.. r· ," •..... 21O 2 1O 2S ,r- S"I.. T·roW

.64 2'7 ) 12 ~~ 12 iOJ,. )"·r'-134 ~ ) IS .1 16 10". )"·r

(HEIGHT OF WATEP L B_U_L_K_H_E_A_D ..."BOVE CREST

WAUR SIJRFACE

RECTANGULAR WEIR

"

ItI',I

". !I-ALTERNATIVE DEPTHINDICAJOR ,PLACEON UPSTREAM FACE>F BUUtHEAD)

Figure 6.7 - standard Weirs

FI9",e 6.1 Parshall Flume

_, \ \ \\\ W ,~~ \\/,\1.:' !r. '~fffl} ifIll

-----e------- -..., ~RECORD TIME iIT TAXES TO FILL COU.ECnONCONTAINER 7 onCH

DIXE TO CONTROLFLOW

Figure 6.9 Bucket and Stopwatch Method

57

6.2.9 Seismic activity - Seismicmeasuring devices record the inten­sity and duration of large-scale earthmovements such as earthquakes.Many federal and state dams usethese instruments because they arepart of the U.S. Geological Survey'snetwork of seismic recording stations.It ~ay or may not be necessary for apnvate dam to contain any seismicdevices depending upon whether it isin an area of significant seismic risk.Seismic instruments can also be usedto monitor any blasting conductednear a dam site.

6.2.1.0 'Yeather and precipitation­MODltonng the weather at a dam sitecan provide valuable informationa~ut both day-t~day performanceand developing problems. A raingauge, thermometer, and wind gaugecan be easily purchased, installedmaintained and monitored at ~dam site.

6.2.11 Stress and strain - Measwe-_ments to determine streSs and/or

strain are common in concrete damsand to a lesser extent, in embank­ment dams. The monitoring devicespreviously listed for measuring dammovements, crack and joint size andtemperature are also appropriate formeaswing stress and strain. Monitor­ing for stress and strain permits veryearly detection of movemenL

6.3 FREQUENCY OFMONITORINGThe frequency of instrument readingsor malting observations at a damdepends on several factors including:

• Relative hazar~ to life and prop­erty that the dam represents

• Height or size of the dam ,• Relative quantity of water im­

pounded by the dam• Relative seismic risk at the

site• Age of the dam• Frequency and amount of water

level nuctuation in the reservoirIn general, as each of the above fac­tors increases, the frequency of mon­itoring should increase. For example,very frequent (even daily) readingsshould be taken during the first fillingof a reservoir, and more frequentreadings should be taken during highwater levels and after significantstorms and earthquakes. As a rule ofthumb, simple visual observationsshould be made during each visit tothe dam and not less than monthly.Daily or weekly readings should bemade during the flrst filling. im­mediate readings should be takenfollowing a storm or earthquake, andsignificant seepage, movement, andstress-strain readings should ~ably be made at least monthly.

59TABLE 7.1MAINTENANCE GUIDEUNES

DIRECTORY

~~Or-:~-::c ....~~REQUIRED -< :«

MAJNTENANCE---.. 1J1~

Tobit 7.1 lis's i'tms to bt moin,ointd at adam and Ilrt mainltnona lasks la lit ptr­formtd. T1rt sp«jfic s«'wns wlrert 1M ma;~

tenanu 'asks art diseusstd art also '101M

X

x

XX

~,!

IIIX ,--

I -L ---.-I __ I JI -,-- ~ ---

t-- ,-------j-- - 1-: --.- :----. X--X

-X i -)( x-----i

I r i- i

! I ! If X X-----

j_._". Ii-. ----I---.f------­i- _-~= - -- .!- -- *----- *-. -I'.- -~ ------ -I-'~-== ~

-- 1--- X - i- X _._--.!I X- l-- -~---- f-~-X

I ... ,--.1--1- i---t1--- x--- Jf. .-- -- X-'--'*.-j - I--. I - x-- -- x·· ---- --I t 1 * f -- fl-*j,:----.--Jf,.--i-- *·~~rX -- - --- '--'----·'-1-- x---

I I t I· - I-T---:--'1-'- ~_ -.~ I -~--=l1- -- x-- x- -~-

11==-i I=·=-~II ~ .. ~ ..--;:'·-31_ . --- . J~-=-*.~~ -- !--~

I i I-- x---x·--_·

X

xXXX

Xi

X

XX

I

I:

X

x

•X

I

x

XXXX

X

x,-i

XX-I,,

x

X

X

XXXX

x

X,

XX

x

XX

X

X

xI

X

x

XX

·X

XX

xXXX

X

IXX

.I

IIIIXI

x

SPIUWAYSApproach ChannelInlet/outlet structureStilling BasinDischarge conduit!Channel

Control FeaturesErosion ProtectionSide Slopes

CONCRETE DAMSUpstream SlopeDownstream SlopeuNRight AbutmentsCrestInlernal Drain. SystemRelief DrainsGalleriesSluiceways/Controls

FEATURE

EMBANKMENT DAMUpstream SlopeDownstream SlopeLeNRight AbutmentsCrestInternal Drainage Sys.Relief DrainsRiprap & SlopeProtection

GENERAL AREASReservoir SurfaceMech/elect. syslernsShorelineUpstream WatershedDownstream Channel

OUTLETS. DRAINSInlet/outlet structureStilling BasinDischarge ChannelTrashracltlDebris ControlEmergency Systems

CHAPTER 7MAINTENANCE GUIPEUNES

7.0 GENERALA good maintenance program willprotect a dam against deteriorationand prolong its life. A poorly main­tained dam will deteriorate and canfail Nearly aD the components of adarn and the materials used for damconstruction are susceptible to dam­aging deterioration if not properlymaintained A good maintenanceprogram provides not only protectionfor the owner, but for the generalpublic as wen. Moreover, the cost ofa proper maintenance program issmaJl compared to the cost of majorrepairs, Joss of life and property andresultant litigation.A dam owner should develop a basicmaintenance program based primarilyon systematic and frequent inspec-­tions. Inspections, as noted in Chap­ter S, should be done at least monthlyand after major nood or earthqualeevents. During each inspection, achecklist of items calling for main­tenance should be used.

7.1 MAINTENANCEPRIORITIESMaintenance is a task which shouldnever be neglected. If it is, severalareo ultimately wiD need attention­some of greater concern than others.The foUowina outline lists, by rela­tive priority, the various problems orconditions that might be encounteredin • deteriorated darn7.1.1 I mmediate maintenance -Thefollowin, conditions are critical andcall for immediate attention:..• A darn about to be overtopped or

being overtopped

• A darn about to be breached (byprqgressive erosion, slope failure,or other circwnstances)

• A dam showing signs of piping orinternal erosion indicated byincreasingly cloudy seepage orother symptoms

• A spillway being blocked. orotherwise rendered inoperable, orhaving normal discharge re­stricted

6t

• Evidence of excessive seepageappearing anywhere at the damsite (an embankment becomingsaturated, seepage exiting on thedownstream face of a dam)increasing in volwne.

Although the remedy for some criti­cal problems may be obvious (suchas clearing a blocked spillway), theproblems listed above generally

. require the services of a ProfessionalEngineer familiar with the construc­tion and maintenance of dams. Theemergency action plan (discussed inChapter 8) should be activated whenany of the above conditions arenoted.7.1.2 Required maintenance atearliest possible date - The follow­ing maintenance should be com­pleted as soon as possible after thedefective condition is noted:

• All underbrush and trees shouldbe removed from the dam. and agood grass cover should beestablished

• Eroded areas and gullies onembankment dams should be re­stored and reseeded

• Defective spillways, gates. valves.lind other appurtenant features ofa darn should be repaired

• Deteriorated concrete or metalcomponents of a darn should berepaired as soon as weatherpermits

7.I.j Continuing maintenance ­. Several tasks should be perfonned on

a continuing basis: .

• Routine mowing and generalmaintenance .

• Maintenance and filling of any. cracks.and joints on concrete

dams

• Observation of any springs orareas of seepage

• Inspection of the dam (as dis­cussed in Chapter 5)

• Monitoring of development inthe watershed which wouldmaterially increase runofffrom storms

62

• Monitoring of developmentdownstream and updating theemergency notification plan toinclude new homes or otheroccupied structures within thearea

7.2 SPECIFIC MAINTENANCEITEMS7.2.1 Earthwork Maintenance andRepair - Deterioration of the sur­faces of an earth dam may occur forse~ral reasons. For example, waveaction may cut into the upstreamslope, vehicles may cause rots in thecrest or slopes, or runoff waters mayleave erosion gullies on the down­stream slope. Other special pro~

lems, such as shrinJtage cracks orrodent damage, may also occur.Damage of' this nature must berepaired on a continuing basis. Themaintenance procedures describedbelow are effective in repairing minorearthwork problems. However, thissection is not intended to be a techni­cal guide, and the methods discussedshould not be used to solve seriousproblems. Conditions such as em-

:b~ent slides, structural cracking,and sinkholes threaten the immediatesafety of a dam and require immediaterepair under the direction of an

. engineer.

The material selected for repairingembankments depends upon the pur­pose of the earthwork. Generally,earth shou~d be free from vegetation(Jrganic materials, trash, or larg~rock. Most of the earth should befine-grained soils or earth clodswhich easily break down whenwork.ed wi~ compaction equipmentThe IDtent IS to use a material whichwhen compacted, fonns a finn, solidmass, free from excessive voids.If Oow-r~sistant portions of anemb~ent. are being repaired,n;tatenals which are high in clay orslh content should be used. If thearea is to be free draining or highlypenneable. (i.e., riprep bedding, etc.)the matenal should have a higherpercentage of sand and gravel. As ageneral rule, it is usually satisfactoryto. repl~ce ?'" repair damaged areas~th sods Similar to those originallym place.

An important soil property affectingcompaction is moisture content.Soils which are too dry or too wet donot compact well. One may roughlytest repair material by squeezing it

into a tight ball. If the sample main­tains its shape without cracking andfalling apart (which means it is toodry), and without depositing excesswater onto the hand (which means itis too wet), the moisture content isprobably near the proper levelBefore placement of earth, the repairarea must be prepared by removingall inappropriate material. Vegeta­tion such as brush, roots, and treestumps must be cleared and any largerocks or trash removed. Also, unsuit­able earth, such as organic or loosesoils, should be removed, so that thework surface consists ofexposed fmnclean embankment material.

Following cle~up, the affected areashould be shaped and dressed, so thatthe new fiU can be compacted andwill properly tie into the existing fiU.If possible, slopes should be trimmed.and surfaces roughened by scarifyingor plowing to improve the bond be­tween the new and existing fi)) and toprovide a good base to compactagainst. ..'

Soils should be placed in loose layersup to 8 inches thick and compactedmanually or mechanically to fonn adense mass free from large rock ororganic material. Soil moisture mustbe maintained in the proper range.The fiU should be watered and mixedto the proper wetness or scarified andallowed to dry if too wetDuring backfilling, care should betalen that fiU does not become too­wet from rainstonn runoff. Runoffshould be directed away from thework area and repair areas should beoverfilled so that the fiJi maintains acrown which will shed water...As mentioned eariler,. occasionallyminor cracks will fonn in an earthdam -b«ause of surface drying.These are called dessication (drying)cracks and should not be confusedwith structural or settlement cracks.Dryingqacks are usually parallel tothe main axis of the dam, typicallynear the upstream or downstreamshoulders of the crest These cracksoften om intennittently along thelength of the dam and may be up to 4feet deep. Drying cracks can be dis­tinguished from more serious struc­tural cracks because the former areusually no wider than a few inchesand have edges that are not offsetvertically.

As a precaution, suspected dryingcracks should initially be monitored

57

with the same care used for structuralcracks. The problem area should bemarked with swvey stakes. andmon­itoring pins should be installed oneither side of the crack to allowrecording of any changes in width orvertical offsel Once satisfied that

. observed cracking is the result ofshrinkage or drying. an owner maystop monitoring.However, these cracks will close asclimatic or soil moisture conditionschange. If they do not, it may benecessary to backfiD the cracks toprevent entry of surface moisturewhich could resuh in saturalioD of thedam. 1be cracks may be simply fiUedwith earth that is tamped in placewith hand or tools. It is also re~mended that the crest of a dam begraded to direct nmoff waten awayfrom areas damaged by dryingcracks.

As Chapter 5 suggests, erosion is oneof the most common maintenanceproblems at embanbnent structures.Erosion is a natural process, and itscontinuous forces will eventuallywear down almost any surface orstructure. Periodic and timely main­tenance is essential to prevent con­tinuous deterioration and possiblefailure.Sturdy sod. free from weeds andbrush, is an effective means of pre­venting erosion. Embankment 'slopesare nonnally designed and construct­ed so that surface drainage will bespread out in thin layers (sheet now)on the grassy cover. When embank­ment sod is in poor condition or Oowsare concentrated at any location, theresuhing erosion will leave rills andguJJiesin the embankment slope. Anowner should look for such areas andbe aware of the problems that maydevelop. Eroded areas must bepromptly repaired to prevent moreserious damage to the embanbnent.RiDs and gullies should be fdled withsuitable soil (the upper 4 inchesshould be top soil, if possible,) c0m­pacted, and then seeded. A local SoilConservation Service Officer can bevery helpful in selecting the types ofgrass to use for dam surface prote<rtion. Erosion in large gullies can beslowed by stacking bales of hay orstraw across the gully until penna­nent repainl can be made.Not only should eroded areas berepaired, but the cause of the erosionshould be found to prevent. rontinu­in& maintenance problem. Erosion

~ght be caused or aggravated byimproper drainage, settlement.. ped­estrian traffic, animal burrows. orother factors. The cause of the ero­sion will have a direct bearing on thetype of repair needed

Paths due to pedestrian or two-wheeland four-wheel vehicle traffic are aproblem on many embankments. If apath bas become established. vegeta­tion will not provide adequate protec­tion and more durable cover will berequired unless traffic is eliminated.Small stones, asphalt, or concretemay be used effectively to cover foot­paths. In addition, railroad ties orother treated wood beams can beembedded into an embankment slopeto form an inexpensive stairway.Erosion is also common at the pointwhere an embankment and the con­crete walls of a spillway or otherstructure meel Poor compactionadjacent to such a wall during con­struction and subsequent settlementcan result in an area along the walllower than the grade of the embank­ment. Runoff, therefore, often con­centrates alon~ these structures,resulting in erosion. People also fre­quently walk along these walls. wear­ing down the vegetal cover. Possiblesolutions include regrading the areaso that it slopes away from the wall,adding more resistant surface protec­tion, or constructing wooden steps.Adequate erosion protection is alsoneeded along the contact between thedownstream face of an embankmentand the abutments. Runoff from rain­fall can concentrate in gutters con­structed in these areas and can reacherosive velocities because ofrelativelysteep slopes. Berms on the down­stream face that collect surface waterand empty into these gutters add tothe runoff volume. Sod-surfaced gut­ters may not adequately prevent ero­sion in these areas. Paved concretegullers may not be desirable eitherbecause they do not slow the waterand can be undermined by erosion.Also, small animals often constructburrows underneath these guttersadding to the erosion potential.

A weD- graded mixture of rocks up to9 to 12 inches in diameter (or larger)placed on a layer of sand (filter)generally provides the best protec­tion for these gutters on small dams.Riprap slushed with a thin concreteslurry has also been successful inpreventing erosion on larger damsand should be used if large stonematerial is not available.

As with erosion around spillways,erosion adjacent to gutters resultsfrom improper construction or a poordesign in which the finished gutter istoo high with respect to adjacentground. This condition preventsmuch of the runolf water from enter­ing the gutter. Instead. the flow con­centrates along the side of the gutter,erodes and may eventuany under­mine the gutter.Care should be taken when replacingfailed gutters or designing new gut­ters to assure that:

• The channel has adequatecapacity

• Adequate erosion protection anda satisfactory filter have beenprovided

• Surface runoff can easily enter thegutter

• The outlet is~equatelyprotectedfrom erosion

7.2.2 Riprap maintenance andrepair - A serious erosion Proble111called "beaching" can develop on theupstream slope of a dam. Wavescaused by high winds or hi~speedboats can erode the exposed face ofan embankment by repeatedly strik­ing the surface just above the poolelevation. rushing op the slope. thentumbling back into the pool. Thisaction erodes material from the faceof the embankment and displaces itdown the slope, creating a "beach."Erosion of tmprotected soil can berapid and. during a severe stonn,could -lead to complete failure of adam.The upstream face of a dam is com­monly protected against wave ero­sion and resultant beaching byplacement on the face of a layer ofrock . riprap over a layer or filtermaterial. Sometimes. materials suchas steel. bitwnmous or concrete fac­in~ .bricks or concre~ blocks areused for this upstream slope protec­tion. Protective beaches are some­times actually ·blblt into smaU damsby placing a berm (8 to 10 feet wide)along the upstream face a short dis­tance below the normal pool levelthereby providing a surface on whichwave energy can dissipate. Generally,however, rock riprap provides themost economical and effectiveprotection.Nonetheless, beaching can occur inexisting riprap if the embankmentsurface is not properly protected by afilter. Water running down the slope

under the riprap can erode theembankment. Sections of rip-rapwhich have slwnped downward areoften signs of this kind of beaching.Similarly, concrete facing used toprotect slopes may fail becausewaves wash soil from beneath theslabs through joints and cracks.Detection of this problem is difficultbecause the '1oids are hidden andfailure may be sudden and extensive.Effective slope protection must pre­vent soil from being removed fromthe embankmenlWhen erosion occurs and beachingdevelops on the upstream slope or adam, repairs should be made as soonas possible. The pool level should belowered and the surface or the damprepared for repair. A small berm or"bench" should be built across theface of the dam at the base ofthe newlayer of protection to help hold thelayer in place. The size of the benchneeded depends on the thickness ofthe protective layer.A riprap layer should extend aminimum of 3 feet below the lowestexpected normal pool level. Other­wise, wave action during periods oflow lake level will undermine anddestroy the protection.If rock riprap is used, it should con­sist of a heterogeneous mixture ofirregular shaped stone placed over asand and gravel filter. The largestrock must be .Iarge enough In bothsize and weight to break up theenergy of the maximum expectedwaves and hold smaller stones inplace. (An engineer may have to beconsulted to determine size.) Thesmaller rocks help to fill the spacesbetweenthe larger pieces and to forma stable mass. The filter prevents soilparticles on the embankment surfacefrom being washed out throuBh thespaces between the rocks in the rip­rap. H the filter material itselfcan bewashed out through these voids andbeaching develops, two layers offilters may be required. The lowerlayer should. be composed or sand orfilter fabric to protect the soil surfaceand the upper layer should be com- .posed of coarser materials.A dam owner should expect someriprap deterioration because ofweathering. Freezing and thawing.wetting and drying. abrasive waveaction and other natural processeswill eventually break down thematerial. Therefore. sufficient main­tenance funds should be allocated forthe regular replacement of riprap.

64

The useful life of riprap variesdepending on the characteristics ofthe stone used. Thus. stone for riprapshould be rock that is dense and wellcemented. When riprap breaks down,and erosion and beaching occur moreoften than once every three to fiveyears, professional advice should besought to design more effectiveslope protection.

7.2.3 Vegetation maintenance- Theentire dam should be kept clear ofunwanted vegetation such as brush Ortrees. Excessive growth may causeseveral problems:

• ]t can obscure the surface of anembankment and prevent a thor­ough inspection of the darn

• Large trees can be uprooted byhigh wind or erosion and leavelarge holes, that can lead tobreaching of the dam

• Some root systems can decay androt. providing passageways forwater, and thus· causing erosion

• Growing root systems can liftconcrete slabs or structures

• Weeds can prevent the growth ordesirable grasses

• Rodent habitats can developWhen brush is cut down, it should beremoved from a darn to permit a clearview of the embankment Followingremoval of large brush or trees, theleft over root systems should also beremoved if possible and the resulting

·holes properly rtJled In cases wherethey cannot be removed, root sys­tems can be treated with herbicide(properly applied) to retard furthergrowth. After the removal of brush,cuttings may need to be burned. Ifthis is done, dam owners shouldnotify the local fire ~epartment,

forest service. or other agency re­sponsible for flTe control.

If properly maintained. grass is notonly an effective means ofcontrolJmgerosion. it also enhances the appear­arice of a dam and provides a surface'that can be easily inspected Grassroots and stems tend to trap fme sandand soil particles, forming an erosion­resistant layer once the plants arewelJ established Grass is least effec­tive in areas ofconcentrated runofforin areas subjected to wave action.

7.2.4 Livestock control - Livestockshould not be allowed to gaze on anembankment surface. When soil iswet. they can damage vegetation anddestroy the uniformity of the surface.

Moreover, livestocl tend to wall inestablished paths and thus can pro­mote severe erosion. Such pathsshould be regraded and seeded, andthe livestock should be permanentlyfenced out of the area.

7.2.5 Rodent damage control ~

Rodents, such as groundhogs (wood­chucks), muskrats, and beavers arenaturally attracted to the habitatscreated by dams and reservoirs andcan, by their behavior, endanger thestructural integrity and proper perfor­mance of embankments and spillways.Groundhog and muskrat burrows canweaken embankments and can serveas pathways for seepage. Beavers canplug a spilJway and raise the poollevel. Rodent control is essential tothe preservation of a darn.

The groundhog is the largest memberof the squirrel family. Its coarse fur isa typically grayish brown with a red­dish cast Occupied groundhog bur­rows are easily reCognized in thespring because of the groundhog's_habit of keeping them "cleaned out"Fresh soil is generally found at themouth of such active burrows. Hatr­round mounds, paths leading from theden to nearby ftehls, and clawed orgirdled trees and shrubs also indicateinhabited burrows and dens.

When burrowing into an embank­ment, groundhogs stay above thephreatic surface (upper surface ofseepage or saturation) to stay dry.The burrow is rarely a single tunnel. Itis usually forked, with more than oneentrance and with several side pas­sages or rooms from I to 12 feet inlength.

Controls should bC implemented dur­ing early spring when active burrowsare easy to fmd, young groundhogshave DOl yet scauered. and there isless likelihood of damage to otherwildlife. In summer, faU, and winter.game animals may scurry..into gr0und­hog burrows for brief protection andmay even take up permanent residenceduring the period of groundhogtu"bemation.

Groundhogs can be controlJed withfumigants or fIrearms. Fwnigation isthe most practical method althougharound buildings or high fire hazardareas, .shooting may be preferable.Gas cartridges for fumigation may bepurchased 8t local farm exchanges,fann supply centers, and many countyextension offices.

. Groundhogs will be discouraged frominhabiting an embankment ifthe grasscover is kept mowed.

The mushat is a stocky rodent with abroad head, short legs, small eyes,and rich dark brown fur. Muskrats arechieOy nocturnal and can be foundwherever there are marshes, swamps,ponds. lakes, and streams havingcalm or very slowly moving waterwith vegetation in the water and along.the banks.

Barriers, such as properly construct­ed riprap and filter layers, provide themost practicaJ protection from musk­rats by preventing burrowing. As amuskrat tries to construct a burrow,the sand and gravel ofa mter layer willcave in and discourage den building.Filter layers and riprap should extendat least 3 feet below water line. Heavywire fencing laid Oat against a slopeand extending above and below the

.waterline can also be effective. Elim~nating or reducing aquatic vegetationalong a shoreline will also discouragemuskrat habitation. Trapping withsteel traps is normally the most practi­cal method of removing muskrats thathave already inhabited a pond.The easily recognized beaver, if in­habiting an area around a dam. will tryto plug the spillway with their cut­tings. Routinely removing the cuttingscan aJleviate the problem or an elec­trically charged wire or wires can beplaced around the spillway inlet.Beaver may be trapped during theproper season and sometimes a localfur trapperwill perform the work at lit­tle or no expense to the owner.

Methods of repairing rodent damagedepend upon the nature of the damage.but in any case. extermination of therodent population is the required firststep. If the damage consists mostly ofshallow holes scattered across anembankment. repair may be necessaryto maintain the appearance or thedarn, to keep runoffwaters from infil­trating the dam, or to discouragerodents from subsequently returningto the embankment In these cases,tamping of earth into the rodent holeshould be sufficient repair. Soil shouldbe placed as deeply as possible andcompacted with a pole or shovelhandle.

Large burrows on an embankmentshould be ftned by mud-packing. Thissimple, inexpensive method involvesplacing one or two lengths of met21stove or vent pipe verticaJly over theentrance of the den with a tight seal

behteen the pipe and den. A mud­pack mixture is then poured into thepipe until the burrow and pipe arefilled with the earth-water mixture.The pipe is removed and additionaldrY earth is tamped into the entr8l)ce.The mud-pack mixture is made byaddingwater to a 90 percent earth and10 percent cement mixture until 8

slurry ofthin cement is attained. Allentrances should be plugged withweD-compacted earth and vegetationre-established. Dens should be elim­inated promptly because one btmowcan lead to failure of a dam.

Different repair measures are neces­sary if a dam has been damaged byextensive small rodent tunneling or by

. beaver or muskrat activity. )n thesecases, :t may be necessary to excavatethe damaged area down to competentsoil and repair as described in Sec­tion 7.2.1.Occasionally, rodent activity willresult in passages which extendthrough the embankment that couldresult in leakage of reservoir water,piping. and, ultimately, failure. Inthese cases, the downstream end ofthe tunnel should not be pluggedsince this wiD add to the saturation ofthe dam. Tunnels of rodents orground squirrels will nonnaUy beabove the phreatic surface withprimary entrance on the downstreamside of the dam. while those of beaverand muskrat nonnally exist below orat the water surface with entrance onthe upstream slope. H8 rodent hole isfound that extends through the dam.the best procedure is first to locatethe upstream end of the passage. Thearea around the entrance should beexcavated and then backfilled withimpervious material. This places 8

plug or p'atch at the passage entranceso that reservoir water is. preventedfrom saturating the interior of thedarn. This should be considered atemporary repair. Excavation andbackfilling of the entire tunnel or fill­ing of the tunnel with cement groutare possible Iong-tenn solutions, butpressure cement grouting is anexpensive and sometimes dangerousprocedure. Indeed, pressure exertedduring grouting can cause additionaldamage to the embanlment in theform of hydraulic fracturing (anopening of cracks by high pressuregrouting). Thus, grouting should beperformed only under the direction ofan engineer.

1.2.6 Traffic damage control - Asmentioned eariler. vehicles drivingacross an embankment dam cancreate ruts in the dam crest if thecrest is not surfaced with roadwaymaterial. The ruts can then collectwater and cause saturation and sof­tening of the dam. Other ruts may beformed by vehicles driving up anddown a dam face. These ruts cancollect runoff and result in severeerosion. Vehicles should be bannedfrom darn slopes and kept out by fen­ces or barricades. Any ruts should berepaired as soon as possible using themethods outlined in Section 1.2.1.1.2.1 Mechanical maintenance ­Proper operation of a dam's outletworks is essential to the safe andsatisfactory operation of a dam.Release of water from a dam is nor­mally a frequent or ongoing function.However, on some reservoirs usedfor recreation. fish propagation. orother pwposes that do nol requirecontinual release of· water, an oper­able outlet· provides the only means _for the emergency lowering of the·reservoir and is therefore, essentialfor the safety of the dam.

If routine inspection of the outletworks indicates the need for main­tenance, the work should be com­pleted as soon as access can begained. Postponement of main­tenance could cause damage to theinstallation. significantly reduce theuseful life of the structure, and resultin more extensive and more costlyrepairs when finally done. Moreimportantly. failure to maintain anoutlet system can lead directly tofailure of the dam.

The simplest procedure to insure thesmooth operation of outlet gates is tooperate all gates through their fullrange at least once and preferablytwice annually. Many gate manufac­turers recommend operating gates asoften as four times a yeh. Becauseoperating gates under fuJI reservoirpressure can result in large outlet dis­charges, gate testing should bescheduled during periods of lowstorage. If this cannot be done, theyshould be operated during periods oflow stream now. If large releases areexpected, outlets should be testedonly after coordinating releases withwater administration officials andnotifying downstream residents andwater users.

65

Operation of the gates minimizes thebuildup of rust in the operati~g

mechanism and therefore, the likeli­hood of seizure of the operatingmechanism. During this procedure.the mechanical parts of the hoistingmechanism - including drive gears.bearings, and wear plates - should bechecked for adverse or excessivewear, all bolts. including anchorbolts, should be checked for tight­ness, worn and corroded parts shouldbe replaced, and mechanical andalignment adjusbnents should bemade as necessary.

The way the gate actually operatesshould also be noted. Rough. noisy.or erratic movement could be the firstsigns of a developing problem. Thecause ofoperational problems shouldbe investigated and correctedimmediately.

Excessive force should be neitherneeded nor applied to either raise orlower a gate. Most hoisting mech­anisms are designed to operate satis­factorily with a maximwn force of40pounds on the operating handle orwheel. Ifexcessive force seems to beneeded, something may be bindingthe mechanical system. The applic.tion of excessive force may result inincreased binding of the gate ordamage to the outlet works. H theredoes seem to be undue resistance, thegate should be worked up and dowDrepeatedly in short stroke~ until thebinding ceases, and/or the cause ofthe problem should be investigatedor course. the problem should becorrected as soon as possible toassure the continued operability ofthe gate.n a gate does not properly seal "t!henclosed; debris may be lodged underor around the gate leafor frame. Thegate should be raised at least 2 to 3inches to nush the debris. and theoperator should then attempt toreclose the gate. This procedure

. should be repeated until proper seal­ing is achieved However. if thisproblem or any other problem per­sists, a manufacturer's representativeor engineer experienced in gatedesign and operation should beconsuhed.

An outlet gate operating mechanismshould always be well lubricated inaccordance with manufacturer'sspecifICations. Proper lubricationwiD not only reduce wear in themechanism, but also protect itagainst adverse weather. Gates with

66

oil-filled stems (i.e.• stems encased ina larger surrounding pipe) should bechecked semiannually to assure the

. proper oil level is maintained If suchmechanisms are neglected. watercould enter the encasement pipethrough the lower oil seal and couldcause failure of the upper and/orlower seals which in tum could leadto the conosion ofboth the gate stemand interior of the encasementpipe.The metal used in gate seats isusually brass. stainless steel. bronze,or other rust-resistant alloys. Okleror smaller gates may not be fittedwith seats, making them susceptibleto rusting at the contact surfaces be­tween the gate leaf and gate frame.Operation of gates should preventexcessive rust buildup or seizure.

For satisfactory operation, a gatestem must be maintained in properalignment with the gate and hoistingmechanism. Proper alignment andsupport is supplied by stem guides insufficient number and properly spacedalong the stem. Stem guides arebrackets or bearings through which astem passes. They both preventlateral movement of the stem andbending or buckling when a stem issubjected to compression as a gate isbeing closed.

The alignment of a stem should bechecked during routine inspections.Alignment milY be checked by sight­ing along the length of the stem, ormore accurately by dropping aplumbline from a point near the topof the stem to the other end. The stemshould be checked in both anupstream/downstream direction aswell as in a lateral direction to ensurestraightness. While checking align­ment, aU gate stem guide anchors andadjusting bolts should be checked fortightness. A loose guide provides nosupport to the stem and could causebuckling of the stem at that poinL

Ifd!lring normal inspection. the stemappears out of alignment, the causeshould be repaired. The gate shouldbe completely lowered and an ten­sion or compression taken ofT thestem. Any misaligned stem guidesshould be loosened and made tomove freely. The hoisting mechanismshould then be operated to put ten­sion on the stem. thereby straighten­ing it, but the gate should not beopened The affected guides shouldthen be aligned and fastened so thatthe stem passes exactly throughtheir centers.

Many outlet gates are equipped withwedges that bold the gate leaf tightlyagainst the gate frame as the gate isclosed, thus causing a tight seal.lbrough years ofuse, gate seats maybecome worn, causing the gate toleak increasingly. If an installationhas a wedge system, the leakage maybe substantially reduced or eliminatedby readjusting the wedges.Because adjustment of these gates iscomplicated, inexperienced person­nel can cause extensive damage to agate. Improper adjustment couldcause pl"emature seating of the gate.possible scoring of the gate seats,binding or the gate. gate vibration,leakage, uneven closing of the gate,or damage to wedges or gate guides.Thus, only experienced personnelshould perform adjustments, and· agate supplier or manufacturer shouldbe consulted to obtain names ofpeo­ple experienced in such wort.

Ice can exert great force on and causesignificant damage to an outlet. &at~leaf. Storage levels in a reservoir dm­ing winter should be low enough thatice cannot form behind a gate. Toprevent i~e damage. the winter waterlevel should be significantly higherthan the gate if storage is maintainedthrough the winter or, if the reservoiris to remain empty over the wintermonths, the outlet should be left. fullyopen. Ifoperations caU for the waterlevel to move across the gate durin"gthe winter, a bubbler or other anti- .icing system may be needed.

7.2.8 Electrical maintenance ­Electricity is typically used at adam to:

• Provide lighting• Operate outlet gates• Operate recording equipment

. • Operate spillway gates• Operate other' miscellaneous

equipmentIt is important that an electrical sys­tem be well maintained. Main­tenance should' include a thoroughcheck of fuses and a test of the sys­tem to ensure that all parts are pr0p­erly functioning. The electrical systemshould be free from moisture and dirt,and wiring should be checked for cor­rosion and mineral deposits. Anynecessary repairs should be com­pleted immediately. and records ofthe repair work should be kept.Generators used for auxiliary emer­gency power must also be main­tained This work includes changingoil, checking ba"eries and antifreeze

and ensuring that fuel is readilyavailable.7.2.9 Cleaning - As already sug­gested. the proper operation ofspill~ays. slui~ways, approachchannels, inlet!outlet structures. stiD­ing basins, discharge conduit, damslopes, trashracks. and debris controldevices require regular and thoroughdebris reinoval and cleaning. Clean­ing is especially important afterupstream storms which tend to sendmore debris into the reservoir.

7.2.10 Concrete maintenance ­Also as mentioned, periodic main­tenance should be performed on allCODa-ete surfaces to repair deteri­orated areas. Concrete deteriorationshould be repaired inunediately whennoted; it is most easily repaired in itsearly stages. Deterioration canaccelerate and. if left unattended, canresult in serious problems or dam

. failure. An experienced engineershould be consulted to determineboth the extent of deterioration andthe proper method of repair.

7.2..11 Metal component main­ttnanee - AU exposed. bare ferrousmetal on an outlet installation,whether submerged or exposed to air,will tend to rusL To prevent corro­sion, exposed Cerrous metals musteither be painted or heavily greased.H painted, the paint should beappropriate and applied·foUowing thepaint manfacturefs directions.When areas are repainted, stepsshould be tak~n to' assure that paintdoes not get on gate seats, gatewedges, or gate stems where thestems pass tlvough the stem guides,or on other friction surfaces where

. paint could cause binding. Heavygress·c should be used on surfaceswhere binding can occur. Becauserust is especiaUy damaging to contactsurfaces, existing rust should beremoved before the periodic applica­tion of greaSe.

Ta~ 8./ is Q nif~renc~ dirrcrory ofoC'C"llrrrn- TABLE 8.167

en and ~m~rg~lICY acriolU 10 ~ rak~" if EMERGlHCY ACnONlIudrdGUIOEUHES DIRECTORY

0 ...~Z 0

ffi~Z ~Z b.J b.Jo ...0:~ 0 ~~ >-1: ~~ Z0. Z

t~ 0 <::> ~III0 0~~

Zm ~~ ~u ~~. O~t 11I- O~ ..J::> m~ ..J~>m =0 !:)d (l)Q =::> ..Ju =1: ~::>III<~ ~g ~~> ;::;:-

~a 0:< ~b.J g~OCCURRENCE .. 0 ~b.J b.J~ u:l~ O~ b.J{I) (I) = u:l{l)

EMERGENCY ACTIONII

HYDRAUUC iLower water level X k X X X X X X .~Increase outlet Rows X I i

X X iControlled Breach X X ISandbags (increase X Xfreeboard) I

!Plug leak entrance X X XClose outlet X . i. IEROSION CONTROl i. IiSandbags X- X X . __ .. 'iRiprap X r XWeight toe area i

X X I :.. ·1I I II I !! I ~ IOPERATIONS I ! i..... __ .~Inspect X X X X X ! . X

Monitor X ! X X X X X I. X ···--ij-

Repair &:. maintain I ! X X x- .... ,:._-- ki ' .

Emergency notification X. I

X , fC -- ._-- ---- _.. rOperate at reduced X X X X X X X··· ·_--xlevel

...

CHAPTER 8EMERGENCY ACTION PLAN GUIDELINES

8.0 THE EMERGENCY ACTIONPlANAlthough most dam owners have ahigh level or confJdence in the struc­tures they own and are certain theirdams will not fail. history has shownthat on occasion dams do fail andthat often these failures cause exten­sive property damage and de aths. Adam owner should prepare for thispossibility by developing an- emer­gency action plan which provides asystematic means to:

• Identify emergency conditionsthreatening adam

• Expedite effective response ac­tions to preve~t failure

• Reduce .loss or life and propertydamage sbouJd failure occur -

A dam owner is responsible· for pre­paring a plan stating the above pur­poses and listing actions that theowner. the operating personnel andlocal government authorities shouldtake. A plan should include sectionson:Purpose: (indicated above)Situation:• A list of problem indi~ators (see

the checklist included in Table8.3)

• A sununary ofcommunities in thepotential inundation zone andOood travel times

•

69

• A list of anticipated failure situa­tions that can be used as a guidefor appropriate responses suchas:

• Failure pending - structure canlikely be saved with inunediateremedial action

• Failure imminent - structuremay possibly be saved withimmediate remedial action

• Failure in progress - no chanceto save the structure

• Flooding expected or in pro­gress upstream from the damsite

• Any other conditions peculiarto this dam

Execution:• A list of remedial actions to pre­

vent failure (see Section 8.2.)

• A plan for notification of down­stream communities that allowsthe greatest possible time to warnand evacuate residents shouldfailure occur and a Jist or te~

phone numbers or emergency pre­paredness officials in eachcommunity (There is an impor­tant distinction between notifica­tion and warning. Notification isthe responsibility of the damowner. he or she must notify com­munity emergency officials ofimpending failure. These officialsmust then warn the public andevacuate them from the inunda­-tion zone if necessary. Publicwarning processes need not befully specified in the dam owners'"emergency action plan.)

Resources and CoordinatingInstructions:• A list of those who can be ofassis­

tance, related telephone numbers.and radio call signs

• A list of materials for use inremedial action; for example,sandbags, high intensity lightingfor night repairs

TABLEa.2POTENTIAL PROBLEMS

AND IMMEDIATE RESPONSE ACTIONS

OVERTOPPING BY FLOOD WATERS• OpeD outlet to its maximum safe capacity• Place sandbap aJona the crest to incTease freeboard aDd force more water throop the

spillway and outlet• Provide erosio&-resistant protectioa 10 the dowDstream slope by placiDa plastic sheets

or odter materials over erodiDa aieas• Di-rert flood waten arowxt the reservoir bum if possible• Creale 8dditionaI spiUway capacity by makinc a cootroDed breach ma Jow embank-

ment 01' dike see:tioa where the foundation inaterials are erosion resistantLOSS OF FREEBOARD OR DAM CROSS SECTION DUE TO STORMWAVE EROSION• Place additiooaJ riprap or saodbap in damaged aRas to preveDt fuJ1bei-

embllDlmeDt erosion• Lower the water level to aa elevaOOo below the damazed area• Restore &eeboardwitb sandbap or euth and rockfiU• Continue close inspection or the damaged area until the storm is overSLIDES ON THE UPSTJlEAM OR DOWNSTREAM SLOPE OF THEEMBANKMENT• Lower the water level at a rate and to an ele.,.tion eoasidered safe liveD the slide COD­

ditioa. H the outlet is damllled or bIoct~pumpiDs. sipboDiDs. 01' a CODb'oIIed breachmay be required

• Restore lost freeboard if required by p1acins sandbap 01' rl1lin& ill the Ic?P or theslide ,

• Stabilize slides 011 the downsbam slope by weiBbtiDs the toe area with additiooal soil.rock, 01' sravel

EROSIONAL FLOWS THROUGH TIlE EMBANKMENT, FOUNDATION.OR ABUIMENTS• PluS die Dow with whatever material is available (hay bales. beDtoaite. or plastic

lbeetioa if the entrance to the leat is ill the reservoir bum)• Lower the water level uutiJ the I10w decreases "to a aoa-erosive velocity oc uutil it

~ '_1_·• Place a protective sand and gravel filter over the exit area to bold materiau 1D

place• ContiDue Iowerina the water level until a safe elevation is reached• Continue operatins at a reduced level uutil repain can be made .

10

A dam owner should male full use orother persons who we c:oocemedwith dam safety. Cooperative plan­ning cm peatly benefit all partjesand result in a more concrete,intepated, plm. People and organi­zations with whom a dam ownershould coordinate emergency~nina inc~WCAL PARTICIPANTSThe dam's owners, shareholders, aDd

beneficiariesOfficials ornearby downstream cities

and townsLocal police, county sheriff .local emergency officialsLocal fare departmentCounty highway departmentLocal construction companiesNews media serving the area (radio,

TV, newspaper)Nearby engineering finDsProfessional diving servicesHelicopter servicesHospital and'or ambulance services

STATE AGENCIESState Engineers office

State EDJineerDam Safety BranchLocal water commissionerDivisioa enPoeer

State offICe responsible for disasteremergency servicesState Highway Patrol

Department or highwaysDep~ent of health

FEDERAL AGENCIESBureau of ReclamationU.S. Forest ServiceNational Park ServiceU.S. Army Corps of EngineersFederal Bureau of InvestigationFederal Emergency Mma,eDJent

Agency"Federal EnerlY Regulatory

CommissionUnited States <koIogicaJ Survey

A checklist to assist in the develop­ment of an emergency action plUlisprovided at the end of this chapter. Adam owner should use this Jist todevelop a plan and to update the planperiodically thereafter as conditionschange (see Table 8.3).

8.t IDENTlFICAnON OFEMERGENCY CONDlnONSAND INITIATION OFEMERGENCY RESPONSEACnOHSAs discussed in earlier chapters, adam owner should observe a damstructure and the dam site OD aregular basis. Failure 1s most oftencaused by overtopping, water nowin&through a dam's key components,and weaknesses in the foundationand outlet works. As discussed inChapters S and 6, a nwnber ofindicators can signal the beginnin& ofproblems that might cause failure.

At a minimum, a dam owner shouldinclude in the II Situation" portion ofthe plan a reminder to check the his­tory and location or hazards whichcould lead to overtopping or otheracute problems. These are discussedin detail in Chapter 3 and include:

• Earthquakes and active faults• Flooding, storms, SDOW melt

runolf

• LandslidesReporting a Dam Safety Incident­WbeD reportin& a dun incident, aDdirections for example ·'left of" or"right from") are from the point ofvie,!, of an observer facing down­stream.

When an "indicator" or dangerouscondition appears, a dam owner orresponsible agent must tale immed­iate action. Ir failure is possible, thatperson should report the situation tostate and local dam safetyautboritiesimmediately. The report shouldinclude:

• The name of the pem>o makingthe report and how he or she canbecODtacted

FAILURE OF APPURTENANT STRUCTURES SUCH AS OUTLETS ORSPILLWAYS• JmpJement temporal}' measures to protect the damaged stnJctwe, such as closing aD

outlet or providiq temporary pmtedioo for a dam-sed spillway• Employ experienced professional divers if DeCeSSuy to assess the problem an4 0

possibly impIemeDt ~pair

• Lower the water level to a safe devation. H the outlet is inoperable, pumpiD&, sipboD-ins. or a cootroIIed breach may be required

MASS MOVEMENT OF mE DAM ON ITS FOUNDATION,(SPREADING Ok MASS SUDING FAILURE)• hnmediately lower the ....ter lenl UDti1 esc:essive JDOYcmenl stops• CootiDue loweriDa the water until a safe level is ~ached

• Continue operatiDg at a reduced level UDtiJ repairs CaD be madeEXCESSIVE SEEPAGE AND HIGH LEVEL SATURATION OF THEEMBANKMENT• Lower the water to a safe level• Cootinue frequent monitoring for signs of slides. cracking or concentrated seepage• Cootinue operation at • mtuced lnel uutil repairs CaD be madeSPILLWAY BACKCUTTING mREATENING kESERVOIREVACUATION• Reduce the now over the spillway by fuJly openina the maiD outlet• Provide temporary protectioo at the point of erosion by placinl sandbags. riprap

materials, or plastic sheets weighted with saDdbap• WIlen inDow subsides, lower the water to • safe level• Continue operating at a low water level in Older 10 minimize spillway DowEXCESSIVE SEITLEMENT OF THE EMBANKMENT• Lower the water level by ~leasiDgit tbroup the outlet or by pwnpin.. siphoning. Or a

CODtroUed breach• H necessary, ~sto~ littboard, preferably by placing saudbap• Lower water to a safe level• Continue opelating at a reduced level uutil repairs CaD be madeLOSS OF ABUTMENT SUPPORT OR EXTENSIVE CRACKING INCONCRETE DAMS• Lower the water level by releasing it through the outlet• Implement notification procedures• Auempt to block water movement throop the dam by placiDg plastic sheets on the

upstream face

• Lowering water to a safe level

• The name of the dam. lake orreservoir, and river, stream. ortributary the dam is located on

• The location of the dam by thenearest highways. roads or townsand by township and section, andrange and principal meridian, ifknown

• A description of the problem (forexample, excessive leakage,cracks, sand boils, slides, wetspots, etc.)

• The location of the problem areaon the dam relative to embank­ment height (for example. "about1/3 up from the toe") and relativeto the dam's crest (for example.100 feet to the right of the outletor abutment) and in terms of whatpart or the dam is actually affected(for example, upstream slope,crest, or downstream slope)

• A description of the extent of theproblem area

• An estimate of the °quantity ofunusual Dow as weD as 8 descrip­tion of flow quality (clear,cloudy, muddy)

• A reading of the water level in thereservoir relative to· the dam'screst, spillway 8JWJ/or the gaugerod

• An indication of whether thewater level is rising or falling

• An indication of whether thesituation appears to be worsenin&

• An indication of whether theproblem appears to be conw.able or is an emergency

• The cunent weather CODditions atthe site

• Anytiling else that seemsimportant

7t

A reporting form is included inAppendix B of this manual Ownersshould use it as a guide and supple­ment it with additional site-specificdetails.AdditionaDy. the items on the reportform should be periodically reviewedby owners and operators who ~quentiy visit the dam site. An u~to­

date report fonn and accurate reportwill permit intelligent assessment ofaproblem situation and proper imple­mentation of an emergency actionplan.

Immediate Response Actions ­Response actions should be listed inthe o"Execution" section of theemergency action plan according tothe problem or indicators beingaddressed (as in Table 8.2).

8.2 GUIDEUNES FOREMERGENCY NOnFICAnONAn essential part of the "Execution"Section of an emergency ac:tion-pipis • list of ageocies/persoDs to benotified iI. the event of a potentialfailure. Names for this list should beobtained from and coordinated withlocal law enforcement agencies BOdlocal disaster emergency servicesoff'JCes. The list should include keypeople or agencies woo can activatewarning and evacuation proceduresfor the public or who might be able toassist a dam owner in delaying orpreventing failme. "The foUowinJagencies can offer emerxency assis­tance if faiJure ofa dam appearsimminent:• Local sheriff. police, and/or

rare departments• Local disaster emergency agency• County engineer• State department responsible

for dam safety• State disaster emergency serv-

ices officeA copy of the notification list shouldbe posted in a prominent, accessiblelocation at the dam - near •telephone and/or radio transmitter, ifpossible. It should be periodicaUy(once or twice a year) verified andupdated as necessary. It shouldinclude individual names and titles,locations, office and home telephonenumbers, and radio frequencies andcall signals if appropriate. Specialprocedures should be developed fornighttime, boliday, and weekendnotification and for notification dur­ing a severe storm when telephones

72

may not be working or highways maybe impassable. . .

The notification element or anemergency action plan should bebrief, simple. and easy to implementunder any conditions. Notification ofimpending failure is the filst step inthe process that leads to public warn­ins. A dam owner should be carefulto quickly notify the key official re­sponsible for warning and evacuatingthe public. NormaUy, this is thecounty sheriff or city police chief.

• Notification or that official is theclear responsibility of the dam ownerwho should toow the roles and re­sponsibilities or both the official andthe agency that will cany out publicsafety actions. Often. if a reservoir islarge, the potential inundation zonewiD extend for many miles, andfailure will threaten several c0m­

munities and counties. A dam ownershould include the proper official foreach jurisdiction in the notificationplan, so all can be notified as quicklyas possible, (usc position· titles forofficials SO that the plan does notrequire updating every time a personchanges jobs). n

Certain key information must beincluded in every notification planincluding information about potentialinundation areas and travel times forthe breach (flood) wavc. Inundationmaps showing potential areas offlooding from a dam failure areespeciaUy useful in local warning andevacuation planning. Detailed infor­mation about the identification ofinundation zones and the develop­ment of maps can be found by con­tacting a state engineer's office orlocal planning office.

TABLE 8.3. CHECKLIST FORDAM EMERGENCY

PLANS

J. Development of Plan

IL Overview: Use format suggestedin paragraph 8.0.

I. Are reportinl procedulesclear in showinl what datamust be collected and whatinformation shOuld be re-·ported?

2. Are terms in the plan definedso that useR will have DO

questions about the natUre ofthe situation?

L failure vs. impendinlfailure

b. emergency situation vs.potential problem

c. rapidly vs. slowly devel­opinl situation

B. Problem Identification

I. Are all indicatOR of poten­tial failure covered in theplan?

L Siumpin&lsloughin,b. Erosionc. Riprap displacementd Slides on dam or abul­

mente. Increased amount of

seepager. Cloudy or dirty seepageg. Boilsh. Pipingi Whirlpools 1vortices)

. j. SettlementIt. CracksI. Bogsm. Sinkholesn. Abnormal instrument.

tion readings0. Failure of operating

equipmentp. Water in the intake towerq. Other

2. Are all emergency situationscovered in the plan?

L earthquakesb. floods •c. stormsd massive landslidesCo vokani<: eruptionsr. firesg. civil disturbanceh. sudden water releasesi. other potential disasteR

3. Does the problem identific.lion section list all the possi­ble ~ations of a problem?

4. Are the above elements.indicators and events suf­f-eentJy defmed so that theuser can understand them?

s. Does the plan identify th~cause or the problem?

6. Can the user ascertiin theseriousness of the problem?(i.e.• when: the problem be-­comes an emergency)

7. Can the user determine whataction is needed?

8. Can the user ascerbm exact­ly when to notify localoffICials and which ~al

offICials to notify dependingon the D8tuR oflhe problem?

9. Can the user determine whatequipment or supplies areneeded fOl' each type ofproblem?

10. Does the format of the planeasily lint· problem iden­tifICation with the action totake, notification to make.and equipment and suppliesto use?

II. Does the plan include a listof historical problems ormost common problems forthe type crdam ill questioo?

C. Notification

I. Does the plan contain • listof key agency personneland show:

L their office and 24-hourtelephone number

b. the name of their alter­nate

c. which officials to callflTSt

d. responsibilities cr theoff"lCials

2. Does the plan show the damtender or p~ect managersresponsibility in the event ofa total loss of communic.tions?

3. Does the plan's format allowthe user to fmd the name ofthe primary con~ets quick­ly? Has the order ofnotific.tioa been prioritized?

4. Does the plan·s list of localofficials in cbarge of evacua­tion include:

L otrlCe and 24-hour tele­phone number

b. names of alternatesc. which officials should be

. contacted ramd at what point offICials

should be called. "C. how messages should

be worded

S. Does the plan descn"be thecommunication system?

L under normal conditionsb. when backup is neces­

saryc. Are radio call numbers

and frequencies included___ for own radios

for those tobe notifaed

6. Does the plan include pr0­

cedures for downstreamnotification?

L downstream operatorsb. other damsc. industriesd. other agenciese. recreational users

D. local Coordination

I. Was the development of theplan coordinated with localoffICials?

a. did agencies contributeb. wa. the plan integrated

into the local plan

2. Do inundation maps providesufficient infonnation andexplanation?

L is language understand-able

b. are terms explainedc. is map usage explainedd. are criteria explainede. is travel time shownr. are hazardous elevations

shown~ is Oood plain infonnation

available

E. ~sources

I. Are resources adequatelyidentified? Does the planindicate how to locate emer­gency equipment?

L are equipment and sour­ces specifically deS­en"bed with the contactname and telephonenumber included

b. are supplies and sup­pliers specifically·des­cribed with the name ofthe contact and tele­phone number included

c. are repair material anderosion protection mater-.ial described

d. are memos of under­standing to share resour­ces with governmententities described

F. Review

I. Was there a comprehensivereview of the plan at the timeit was developed? Was it:

L technically accurateb. workablec. in compliance with cri­

teria• d. sufficiently comprehen-

sivee. presented effectively

II.Implementation of Plan

A. I..ocal Coordination

I. Were emergency plans (in­cluding notification lists andinundation maps) sent to aUappropriate officials? Is thelist maintained?

2. Have local officials had abriefmg or other explanationof the plan? Is a record ofsuch briefmg maintained?Did the briefmg explain:

a. basic project datab. mapsc. communication networksd. points of contacte. notifICation procedures··

3. Have effective lines of com­munication for critical c0n­

ditions been set up?

4. Have the dam owner andlocal officials aueed on theirrelationship, roles and re­sponsibilities during a damfailure. Is the agreement inwriting?

5.· Has the dam owner reviewedlocal evacuation plans anddiscussed them with localo.ncials?

B. Training

I. Has a plan for exercising theplan been developed?

2. Have exercises been conduc­ted? Is a schedule of exer­cises maintained'?

3. Have the foUowing elementsof the plan been exercised?

L problem identificationb. emergency scenariosc. notir~ation of dam owner

and operating stalfd. notification of otherse. communication systemf. resource list

4. Were aD appropriate person­nel involved in tbe test?

Ii- owner"s personnelb. dam safety personnelc. maintenaoce personneld. support staffe. local officialsr. contractors and suppliers .

73

C. Personnel and Resource Readi­ness

I. Are aD appropriate employ­ees familiar with theemer­gency action plan?

2. Do aU appropriate employeeshave access to the plan?

3. Have aU appropriate person­nel received training in thefoUowing?

a. how to use the planb. identifying a problemc. identifying the severity of

a problemd. using the communication

equipmente. using the notification

subplanf. overall dam safety

4. Are Itey personnel available24 hours a day?

5. Is the division of personnelinto emerceocy responseteams appropriate?

6. Do employees understandtheir roles during emergen­cies?

7. Do key employees haveaCcess to the dam duringemergeocies?

8. Are resources ready?

a. equipmentb. list of contractorsc. supplies on hand or read­

ily available

D. Updating and Reviewing

1. Is the plan reviewed atleast annually?

2. Are notification proceduresregularly updated?

L names and telephonenumbers of Itey staff

b. names and telephonenumbers of local off~

cialsc. names and telephone

nmnbers of contractors

3. Is the plan reviewed to makesure that:

a. exercises are conductedb. personnel are trainedc. communication equip-.

ment is maintainedd other equipment is

maintainede. the downstream warning

system is in place andoperational

r. any new problems areincluded

~ inundation maps are stiDcurrent

CHAPTER 9OPERATIONS GUIDELINES

9.0 GENERALAn operations plan details each ofthe safety program componentsoutlined in Chapter 4. and detailed inChapters 5 through 8. The extent ofan operations plan depends on thecomplexity ofthe dam itself- factorssuch as dam size, number and type ofappurtenances and operating mech­anisms.The operation of a dam may involveadjusting the reservoir level. control­ling debris by opening and closingvalves. keeping records, and, ingeneral. ensuring public safety. Prop­er operation procedures is extremely'important for miUntaining a safestructure. Many small dams do notneed a full-time operator. but shouldbe checked regularly. Specialopera­tional procedures to be followed dur­ing an emergency should be posted,particularly if the owner/operator isnot always available.

9.1 OPERATIONS PLAN. GUIDEUNESEstablishing an operations procedureor plan calls for detailed documenta­tion of the following:

• Dam and reservoir physicalcharacteristics data

• Descriptions of dam com­ponents (Chapter 2)

• Operations instructions foroperable mechanisms (Chap­ter 9)

• Inspection guidelines (Chapter5)

• Instrumentation .and monitor­ing guidelines (Chapter 6)

• Maintenance operations guide­lines (Chapter 7)

• Emergency operations guide­lines (Chapter 8)

• Bibliographical information(Appendix D)

As recommended in Chapter 4.collection and review of existinginfonnation on the dam design, con­struction and structural character­istics is the first step in developing adam safety program. Guid~lines for

75

inspections, monitoring. main­tenance, and emergency action plan­ning are presented in the otherindicated chapters.The operation plan should haveseveral seperate sections:Section A: Background Data

1. Vital dam statistics2. Description of appurtenances

Section B: Operations Instructionsand Records

1. Operating instructions for oper­able mechanisms

2. Inspection instructions andfoons

3. Monitoring instructions andforms

4. Maintenance instructions andforms

5. Biblography6. Telephone list

Section C: Emergency WamingSystemSections A and B are describedbrieny below and a schedule ofroutine tasks is included. Instructionsare included for frequent inspections,monitoring. and follow-up main­tenance. The Emergency WarningSystem plan is discussed in Chapter8.9.].] Background Data]. Vital dam statistics include:a. General

-. Type of dam• Height of dam• Length of crest• Width of crest• Angle of upstream slope• Angle of downstream slope• Available freeboard• Capacity tables for

reservoir• Top of dam elevation• Capacity tables of inflow

and outflow works• County location• Township location• Stream name• Year completed• Hazard classification

b. Spillway

• Type of spillway• Length of spillway• Spillway channel elevation• Normal pool elevation• Available freeboard• Maximum observed flow

and date ofoccurrence• Discharge tables for

spiDwayCo Outlet

• Size. configuration andtype of outlet

• Size and type of outletcoatrol device

• Discharge tables for outlet• Inlet invert elevation• Outlet invert elevation• Drainage systems'and

drain locations

9.1.2 Operations Instructions andRecords

Operoting instTuctions fOr operoblemechanisms - The plan should pr0­vide complete. clear. st~by stepinstructions for operating aD mecha­nisms associated with a dam includ­ing the outlet control valve andspillway gates. Proper sequencesshould be emphasized and sketches,drawings. and photographs to aid inidentifying specific handles, crmb.buttons, etc should be includcd.. Thecorred method of opening and clos­ing pard gates. gate usage duringlow and high flow. openings at whichexcessive vibrations are experienced,and operating problems peculial'to •specifIC gate should also be listed.For hydraulic and electric gates. aschematic diagram should be pr0­vided showing eacb component (in­cluding back-up equipment) and itsplace in the operating sequence.

Instructions on the general operatioaoftbe reservoir. including the regula­tion of inflow and outlet ditches.should be given. These should statethe maximum pool levels to beallowed at different times of the year,maximum and/or minimum carryover storage. maximum and/or mini­mum permissible outlet releases.They should also descn"be operatioaof the outlet to limit or. preventexcessive spillway flow, and themethod for periodic drainage of thereservoir to permit thorough outlet orupstream slope inspectioa.

l~ct;on and ;nstTumentatioll - Aclear. step-by-step set of instructionsfor conducting a comprehensive

inspection of the dam and its sur­roundings should also be provided.Forms. for re~ding data such asthose in Appendix A. should be usedand copies of all completed~tion records should be kept.

Monitoring instTuctions - Clearinstructions on how to use monitor­ing instruments and how to takemeasurements at monitoring pointsshould be prepared, a map identify­ing each instnunent and monitoringpoint should be mcluded, and formsfor recording the data shou_1eI be p~vided. The monitoring points them­selves, plus any seepage or otherareas needinl special attention shouldbe kept clear ofobscuring growth andbe permanently marked, so they canbe found during inspection. The helpof • qualified engineer will be usefulin developing this section.

Monitoring can only be beneficial ifthe observations are recorded in anorderly way and form a clear perfor­mance record. Thus, plotting orcharting some of the readings will benecessary. Instructions on how to.make and record each measwementor observation must be provided. Ifthe owner's engineer is not going toplot or chart the data, instructionsand forms should be developed toallow owneR. operators. or main­tenance penonnel to do this work.An experienced consulting engineermay be helpful in preparing theneeded formats.

Maintenance instructions - instruc­tions for performing periodic main­tenance should be given in detail. sothat new penonnel can understandthe task and experienced personnelcan verify that they have completedthe wort properly. AU needed main­tenance work should be .identifiedand listed. This list includes the tasksdescribed in Chapter 7 sucb as:

1. Removing brush and trees2. Removing debris· .3. Regrading the crest ud/or access

roads4. Removing harmful rodentsS. Operating and lubricating gates6. Addina riprap when needed7. Sealingjoints in concrete facings8. Oeaning drainpipes and outlets9. Maintaining monitoring points

10. Maintaining security of operat­ing equipment

Bibliography - All available referencematerial should be cataloged in asingle Iisl Other title. aUthor oragency responsible for publication.date and place ofpublication or briefdescription. and the permanent 1oca­tion of the material (for example fi1­ing cabinet in basement) should beincluded. Even materials withouttitles or authors. sucb as photographsand maintenance information, shouldbe listed.

Telephone List - A comprehensiveu~t<HIate listing of important tele­phone numben should be maintainedand include:

• The owner/operator (home andoffice) phones

• Employees actively involved withthe dam

• The local emergency manage­ment agency

• State police• The local police and fire depart­

ments• ]be state agency responsible for

dam safety• Qualified local engineering c0n­

sultants• Downstream residents

9.2 SCHEDULE OF ROunNETASKSA schedule should be establishedthat includes both day-to day tasksand tasks performed Jess frequentlyduring the year. Such a scheduleserves to formalize inspection andmaintenance procedures and makesit easy to determine when a tastshould be done. As suUested inTable 9.1. The frequency of arequited task is often dependent uponthe hazard classification of the dam(See Chapter 3).

9.3 RECORD KEEPING .As already suggested, operating adam should mclude keeping accuraterecords of:I. Observations: All observations

should be recorded. Periodicobservation of seepage is par­ticularly important. Again, phot~graphs are valuable for recordingobservations and documentingchanges.

2. Maintenance: Written records ofmaintenance and major repainare important for evaluating thesafety of a dam.

3. Rai1ffaH and Water Lnelr Arecord of the date, time. BDd JDaX­immn elevation of utremely highwater and associated rainfall orrunoff b espcciaDy helpful inevaluating the performaDCe of 8

dam aDd its spillway system. Inparticular, records should be keptfor reservoirs that haVe widelyfhK:tuatio& water levels.

4. Drawdown: A record should bekept or the amount. rate, andreason for pool level drawdown.

S. Other Procetlurrr A completerecord or all operating procedw"esshould be maintained

,

77

TABU 9.1OPERATION PLAN SCHEDULE OF ROUTINE TASKS

Hazard OassificatioDs

Category I Cate~ory 2 Category 3Higb Huard Sipiflcant Low HazardMany lives lost. Few lives lost. No lives lost.

FmpleDC)' Excessive damage Appreciable damage Minimal damage

(Minimum)Daily SurveiUanc:e.Weekly Monitor seepage. SurveiUanc:e.MoathIy CoIIec:t and examine Collect and examine SurveiUanc:e.

observation weD data. observation weD data. Monitor seepage.Collect and eIamineobservation weD data.

Quarterly Inspect visuaUy. Inspect visually.Bi annually Test outlet and

spillway components.Annually Inspection by Inspection by Visual inspection.

engineer. engineer. Test outlet.Cbed alignments Test outlet and spill-and movemeDts.. way components.

Check alignmentsand movements.

Asrequiml Routine maintenance Routine maintenance Routine maintenanc:elIDCI additional and additional and additionalinspections. inspections. inspections.

Check aliptmentsand movements.

Immediately Additional Additional Additionalafter Doods inspections. inspections. inspectionslIDCIe~

quakes

..

CHAPTER 10REDUCING THE CONSEQUENCESOF DAM FAILURE

10.0 SUPPLEMENTS TO ADAM SAFETY PROGRAMThis manual has stressed safety asboth a fundamental need and a primeresponsibility or the dam owner.Developing an effective dam safetyprogram is the single most importantmeasure a dam owner can take toreduce the possibility or consequen­ces of dam failure. However, on anational scale, an acceptable level ofdam safety is stiD far from beingachieved. Losses are continuing toincrease and may intensify as pap­ulation growth and migration con-.tinue. From both the perspective ofthe nation and the dam owner, othersteps must be taken to reduce loss oflife and property and subsequentliability.Uabilities which are determinedfolJowing a dam failure stronglyaffect bOth organizations and people,governments and dam owners. De­termination of liability is the legalmeans developed by society torecover damages due to a "wrong"(in this case, lack of dam safety) andis another aspect of the dam safetyproblem. A thorough understandingof this legal process can help the damowner decide the steps to be taken toreduce liability.A discussion of liability and its rela­tion to a dam owner is presentedbelow, followed by a discussion ofthree important measures beyondt,hat of individual dam safety· thatdam owners can promote to reduceliability - the use cf insurance, theprovision or governmental assis­laDce, and the use of consultants.

10.1 LIABILITYThe following discussion reviewsgeneral principles concerning liabilityand the operation or reservoirs.Uability in specifIC instances, how­ever, very much depends upon thedam. the accident, the owner and thejurisdiction in which the reservoiris located.The liability of an owner or a reser­voir is considered general civil

79

("tort") liability, A tort is simply acivil wrong for which an injured partymay recover damages from the re­sponsible party. In most circumst.an­ces, simply causing damage is notsufficient basis for the imposition ofliability. Negligence must accom­pany the injury before liability isincurred However, negligence is not·a fued concept; it has been modifiedand changed by court decisions overthe years. In simplest terms, it hasbeen described as the violation of aduty to act as a reasonable and pru­dent person would act; a violationwhich directly results in damage toanother.The questions of what "duty" isimposed by society and what stan­dard or reasonable care is imposedby the duty have undergone enor­mous scrutiny and changes over thepast 25 years. In many instances theduty to make a product safe or theduty to insure that one's propertydoes not pose a danger to others, hasbeen significantly increased.While the concept of negligence hasbeen subs~tially broadened, changesin the limits of negligence do notdirectly affect dam owners because aseparate basis of liability has longbeen imposed upon them. This stan­dard is one of "strict liability." Strictliability is not based upon fault ornegligence, rather it is based solelyupon resulting damage, regardless offautt. Strict liability is generallyapplied to those activities which aredeemed "ultra-hazardous" aDd Dotcapable ofbeing rendered reasonablysafe.

The whole concept of strict liabilitywas fIrSt established in a case involv­ing a reservoir - the 1866 Englishcase, Fletcher vs. Ryfands, LR J,Ex. 265. A reservoir was built in thevicinity or abandoned coal mines; thewater from the reservoir found itsway into the abandoned shafts andfrom there into active shafts andcaused damage. ·Under present legalthought, the basis of liability for suchan occurrence may well be negligentdesign (i.e., failure to adequately

UIF WATER ESCAPES FROM A DAM,REGARDLESS OF FAULT, THE OWNERIS RESPONSIBLE FOR ALL DAMAGESSUSTAINED:'

10

investigate the surrounding cir­cumstances at the time the reservoirwas built). However, in the actualdecision, it was assumed that no onecould have known the abandonedmine shafts existed and specificallydecided that the owner was notnegligent. Nonetheless, the EnglishCourt established the concept ofstrict liability for reservoir owners,and the owner of the reservoir wasfound to be liable for the escape ofwater from the reservoir regardless offault.

Fletcher vs. Rylands has subse­quently been adopted by most U.S.courts and has been cited whensimilar circumstances are con­sidered. It is the basis for imposingliability on the owner of a reservoirfor all damages caused, regardless offauk and without need to provenegligence.

Thus, with a very limited number ofexceptions, the general statement ofliability for the owner or operator ofareservoir is:

It should be noted however, that allof the discussion concerning rom­pensation for damages due to releaseof water from a reservoir deal solelywith water that has previously beenstored. In all circumstances to date,and in most states by specific statute,a reservoir oWner may pass on allnatural flood waters without incur­ring any liability downstream.Strict liability has two relativelynarrow exceptions: acts of God, orintentional acts of third parties, overwhom the owner had no control.While acts of God are recognized asa defense, this does not include allnatural occurrences over which theowner had no control, but is morenarrowly limited to those events overwhich the owner had no control andalso which the owner could not, usingavailable expertise, have anticipated.The other exception - intentionalacts ofthird parties - was established·by the Wyoming Supreme Court inthe Wheatland case. The WheatlandIrrigation District asserted that theirreservoir had been damaged bysaboteurs, and the Wyoming Su­preme Court recognized that illegal,

intentional acts by third partieswhich the owner could not protectagainst or anticipate were a viabledefense to strict liability.Still, where there is no remediallegislation, the circumstances inwhich a reservoir owner is not liablefor all damages caused by the leakingor breaking of his dam are severelylimited.While the standard of liability im­posed on a reservoir owner affordsextremely limited relief, severalstates have enacted legislation whichlimits, in certain circumstances lia­bility for damages. In many otherstates, by statute or common law, theowner of a reservoir is entitled to util­ize (i.e., release water to) the "nor­mal high water line" of a streamwithout incurring liability for prop­erty damaged within the "normal"flood area. However, the definition ofthe limits within which no liability isimposed vary from place to place andmay not be clearly designated. of!maps. Nonetheless, the right to titil-

ize dermed or "historic" floodplainregions downstream of a reservoircan provide substantial relief from

·strict liability for a reservoir owner.With the recent insurance crisis andsoaring Iiabililty insurance rates,many states are considering legisla­tion which would limit either thebasis of liability or the amount ofliability that can be imposed on areservoir owner. Some states, forexample. are considering legislationwhich would change the standard ofliability for a reservoir owner from astandard of "strict liability" to one ofproven negligence.If coupled with a redefinition ofnegligent actions, statutory modifica­tion of the basis of a reservoirowner's liability could have a signifi­cant effect. However, as notedabove, the trend during the past 25years has been to broaden, notnarrow, the scope of negligent be­havior by imposing broad expec­tations of prudence and foresight.Even if standards of "strict liability"are replaced by standards of "negli­gence," in the case of a reservoirowner, because the criteria of reason-

able care and foresight are broadlyinterpreted, the change may notgreatly affect the actual standard ofliability imposedIn summary, existing law holds areservoir· owner to the highest stan­dard of care. Pending legislation maylimit liability in certain circumst2Jl­ces, however the general statementremains unchanged: the owner is lia­ble for all damages caused by waterescaping from a reservoir - despitethe best efforts of the owner.

10.2 MEASURES TO REDUCETHE CONSEQUENCESOF DAM FAILUREA dam owner can directly andindirectly influence the introductionand use of a variety of measures thatwill reduce the consequences of damfailure. Insurance can be purchasedthus, spreading costs from a singledam owner to others. Land usemeasures, although difficult to insti­tute, can be an even better means ofmitigating future disasters. (If peopleare restricted from living in inunda­tion zones, safety is obviously radi­cally improved.) Increasing publicawareness and governmental plan­ning are also measures that canreduce the consequences of damfailure.A dam owner can obtain insurancedirectly and should do so. The othermeasures discussed here: land use,public awareness and preparednessplanning. are essentially controlledby local governments. Therefore,dam owners would be wise to toencourage as strongly as possibleawareness and action in the publicsector. Finally, a dam owner mayalso wish to hire consultants from thepriv"ate sector when the informationneeded for prudent decisions exceedstheir expertise.

10.2.1 Insurance - Insurance canprovide liability and asset protectionand thus, is important for damowners. In many states a minimumlevel of insurance coverage is man­dated by law; in others it is not. Ineither case, the level of insurancecarried should be based on: state law,value of facilities at risk, potentialdownstream impacts,· condition andage of the dam, likelihood of an in~i­dent occurring and the cost of avaIl­able of insurance. Insurance spreadsrisk among a large group of peopleand can not only provide protectionfor the person or organization owningthe dam, but also for employees and

Table10.1 :Comparison of warning success for selected dam failures

and nash floods

Early Potential Actual loss Fablit)'Event • direction loss or life or life rate (%)

&: wamina

Bil Thompson. Colo. No 2,500 139 S.6(Rash Flood)

Laurel Run Dam, Pa. No ISO 39 25.0Kelly Barnes Dam, Ga- No 200 39 20.0Buffalo Creek, W. Va. Some 4,000 125 3.1Teton Dam, Idaho Yes 3S,000 II <0.1Southern Conn. Yes Unknown 0 0June 1982(20 dams r.iJed)

Lawn late, Colo. Yes 4,000 3 <0.1D.M.AD, Utah Yes 500 1 0.2Source: Graham, 1983.

governing boards who may be heldpersonally liable. Types or coverage,availability and cost will vary fromtime to time, so it is, advisable to seekprofessional advice when consideringthe purchase of insuranCe. Someinsurance companies and brokersspecialize in issues related to damfailure. Recommendations of insurerscan normally be obtained frominsurance industry representatives orfrom the state agency responsible fordam safety. Nol only can damageand liability be covered. the cost ofbusiness interruption, lost income,and workmen's compensation canalso be provided.

Insurance can spread and reducepotential loss and as such should bean accepted cost of doing business.Many persons have avoided this costand have paid severely for theirshortsightedness.

10.2.2 Governmental assistance ­One of the fundamential functions ofgovernment is to protect citizensfrom threats to their health, safety,and general welfare. Reducing theconsequences of dam failure isclearly a duty of federal, state andJocal governments which have jointand separate responsibilities to thepublic concerning dam safety.

Land use planning. public awarenessprograms, and emergency prepared­ness pJaruiing are typically conduct­ed at the local level - the level ofgovenunent most immediate and re­sponsive to the dam owner. Federalagencies have technical expertiseand can normally provide technicalassistance when requested. but ulti­mately, each state is responsible forits own dam safety program.

Localgovemment roles - Populationsettlement pattern and populationgrowth strongly affect the costs ofdam failures. More simply, if no onewere allowed to settle in hazardousareas, few, if any, lives would be lostand little property damaged. Con­versely, as settlement continues neardams and in inundation zones, thepotential for disaster increases com­mensurately. "Low-hazard" damsare continually being transfonnedinto "significant hazard" and "highhazard" dams as this settlement con­tinues. Increased losses are inevit­able unless significant land usemeasures are enacted to restrict theuse of land in inundation zones. Thestrategjes used will reflect federal,state, and local efforts, but localgovernment must make the critical

decisions and only rely on state andfederal government for support. All.elements of mitigation planning arebased upon or affected by the way inwhich the affected land is used.

If the land has not been developed,the establishment of open spaceareas in potential inundation zones isa particularly effective way to reducefuture costs of dam failure. Indeed,this is the best mitigation strategy toreduce future loss. Despite thisutility, organized programs or strat­egies of land acquisition or settle­ment restriction exist in few states ­usually because of strong oppositionamong developers and land owners.

If land is already under development,zoning measures to limit high popul.tion density can be useful. Also, theestablishment of "green areas" ­parks or golf courses - can be lowcost means of limiting senlemeot ininundation zones. In some fullydeveloped areas, nood proofingdevices (walls, barriers) may proveuseful.

In much of the nation, land hasalready been developed and residen­tial construction in inundation zonesis already in place. People that live insuch 8Jeas may have a false sense ofsecurity and not be aware that ahazard even exists.Experience bas clearly shown thatsimple warning and evacuation pr~

cedures can save a significant num­beroflives. Table 10.1 demonstratesthis success and the correspoodin&failure wben c8Jly detection andwarning are not available. Oe8Jly,communities downstream from adam should establish an early n0tifi­cation and warning system.

a,The stimulation or public awarenessofthis hazard and the development ofwarning aDd evacuation plans isclearly the responsibility of localgovernment The utility of sUchefforts cannot be overlooked; theaggregate·retum will be large over thelong term.Existing levels of awareness varyacross the nation. Some people arefully aware of their exposure to thiShazard while many do not even real­ize that they reside in an inWldationzone. Obviously, tourists are usuallyless aware than pennanent residents;camp grounds for ex ample, are notnormally posted with signs that pOintout the existence of a dam hazard.Oearly. awareness is the fIrSt step inmitigating the hazard and increas­ing safety.

Thus, counties, cities, towns andsmaller unincorporated communitiesurgently need:

• To develop programs to inCreaseawareness of CJlisting dam fai~

ure hazards, aod more specifi~

ally, of who is in danger.• To de'felop plans for warning

and evacuating the population,• To increase public familiarity

with plans through publications,well publicized exercises andother means.

UsuaUy, a public awareness programwiD be well received and generateconfidence in government Media ­television, and newspapers - radioare potentiaDy the most effective wayto educate people. Dam ownersshould encourage pub6c awarenessas weD as warning and evacuationplanning.

12

State government roles - Most stategovernments have actively attemptedto reduce the possibility of and con­sequences ofdam failure through anyof several major programs.

While some local public and privateorganizations may capable of super­vising dam safety, the authority and .responsibility for such measures restwith state agencies that approveplans and specifications for thedesign and construction ofdams, andconduct of inspections of existingdams. In most states, dam safety ismonitored by the department ofwater resources, state engineersotrlCe. or an equivalent agency in theexecutive branch of government1bese. agencies often determine therules and regulations governing thedesign, construction, and main­tenance of dams.1be state office of emergency pre­paredness is also concerned withdam safety. However, it deals mainlywith planning for the protection ofpeople - awareness, warning andevacuation planning. Disaster (in­cluding dam failure) response andrecovery efforts are part of thisprogram.

Federal government roles - TheFederal Emergency ManagementAgency (FEMA) develops and main­tains guidelines for dam safetypolicy, as well as programs for pre­paredness, emergency response andrecovery planning and mitigationplanning. FEMA coordinates allfederal dam safety programs, andotherwise promotes both federal andnonfederal programs to reduce thehazard posed by unsafe dams.The Federal Energy RegulatoryCommission (FERC) supervises thedam safety program mandated by theFederal Power Act It issues rulesand regulations to ensure that licensedprojects are adequately construct~

operated and maintained to protectlife, health and property. FERC"sjurisdiction includes dams at hydr<>­electric prqects on navigable streamsor on federally owned land projectsusing surplus water or waterpowerfrom federally owned dams; anddams affecting interstate or foreigncommerce.

The Department of the Anny, Corpsof Engineers, is authorized by theFederal Water Pollution Control Actof 1972 and the River and HarborAct of1899 to issue permits for workinvolving the nation's waterways.Under the National Dam Safety Actof 1972, the Corps, working withindividual states, inventoried 68,153dams, inspected 8,818, and estab­lished a list of hazard criteria.Five agencies within the DepartmentofAgricuhure are involved with noD­federal dams. These include theAgricultural Stabilization and Con­servation Service (ASCS)~ theFarmer's Home Administration(FMHA), the Forest Servker theRuraJ ElectrifICation Administration(REA) and the Soil ConservationService (SCS). Technical engineer­ing is the responsibility of the SoilConservation Service.The U.S. Department of tile Interior,Office of Surface Mining (OSM)provides support to state regulatoryagencies that conduct dam inspection.and monitoring as it relates to surfacemining. The Department's Bureau ofReclamation also manages a pr<>­gram or water development whichincludes providing water for irriga­tion, the hydroelectric power indus­try, and recreation.10.2.3 Consultants role in damsafety - A dam is a special kind ofstructure which is conceptually sim­ple but made or many complicated"components. Several engineeringskiDs are needed to design, build,inspect and repair a dam, and it isuncommon that a dam owner has aDof these technical skins. Even if thedam owner did have these skiDs, it isunlikely that an owner .could devote

•

the time and effort necessary to dothe work properly. Thus, private con­suhants can play an important role ina dam safety program, and ownersshould consider contracting withconsuhing firms for assistance.When hiring a consultant, certainsteps will insure that an ownerobtains what is really needed Theinitial screening of possible c0n­

sultants should be based on pr<>­fessional qualifications. A Jist ofconsultants who have experiencewith dams may be available from thestate office managing dam safety.The owner should then investigatethe background and experience oftilecompany and the specific experienceof the individuals who will do thework.

The owner should be sure to defme asclearly as possible the wort to bedone. Although some ownen select aconsulting fum based on qualiflCa-

. tions and then work with the fmn todefine the work to be done, an ownercan often define the scope or workhimself, and then receive bids andproposals from several consultants.This latter arrangement usuallyresults in the lowest cost for • givenpiece of wort.H many of the items discussed in thisguidebook are new and unfamiJiar toa dam owner, a consultant should becontacted immediately. Professionalconsultants help conduct a properand safe evaluation ofa dam, ·and canhelp develop and execute an effectivedam safety program. Of course. adam owner should· have confidencein the consultant he hires. When aconsultant makes recommendations,they must be taken seriously.

APPENDIX AINSPECTION FORMS

•

13

INSPECTION D TE:NAME OF DAM: A

EMBANKMENT CHECK ( )ACTION

Q 1 of 2 NEEDED

il '" e",0 g '"z c:oHDmON OUIIVATlONS -:II Z~~ ~

~0 :l2 _CI

I SUIU'ACE CMCKING

% CAVIl IN. ANIMAL BUJUl.OW

3 LOW AJ\.EAlS)

B4 HOlUZONTALAUGNMENT, RUTS ANDiOR PUDOLES

6 VIlGETAnON CONomON

7

•9 SUDE. SLOUGH. SCARP

10 SLOPE PROTEcnON

! II SINKHOLE, ANIMAL BURROW

U EMB.·ABUT. CONTACT

I q EROSION

14 VIlOETAnONCONomON ..13

16

AD0l110NAL COMMENTS: REFER TO ITEM NO. IF APPUCABLE.

INSPECTION DATENAME OF DAM: :

EMBANKMENT CHECK ( )ACTION

Q 2012 NEEDED

i§=I ,

i i= ~ =CONDITION OBSERVATION - -~

Z ~~ ::0 ~I: :s ~O =17 WET A.REA(S) (NO PLOW)

18 SEEPAGE

!19 SLIDE, SLOUGH, SCARP

20 EMB.·ABUT. CONTACT

! 21 CAVE IN, ANIMAL BURROW

=22 EROSION

! 23 UNUSUAL MOVEMENT

24 VEGETATION CONTllOL•

2$

26 .27 PIEZOMETEIWOBSERV. WEU.S

,28 STAPP GAUGE AND RECORDER

i 29 WEIRS

30 SUaVEY MONUMENTS \

31 DRAINS:I~

PREQUENCY OP READINGSi 31

33 LOCATION OP RECORDS

343S

ADDITIONAL COMMENTS: UPER TO ITEM NO. IP APPLICABLE.

NAME OF DAM' INSPECTION DATE:

COWNSTREAM AREA CHECK ( )

AND MIse. ACTIONa NEEDED

i§ 1 of 1al:i ~ s ..:.

I- al:CONDITION ONERVATIONS - ~lU -:z lUI- 0(

~ 0 >0( c..\I,l

2 ~O al:

36 ABUTMENT LEAKAGE

is 37 POUNDAnON SEEPAGE

=38 SUD£. SLOUGH. SCARP

I39 DRAINAGE SYSTEM

40

4\

42 DOWNSTREAM HAZARDDESCIUPTtON

43 DATE Of LAST UPDATE OFEMERGENCY AcnON PLAN

44 RESERVOIR SLOP~S

.. 4.5 ACCESS ROADS

I46 SECURITY DEVICES

,.

47

48

49 ' ,

30

ADDITIONAL COMMENTS; UPER TO ItEM NO. If APPLICABLE.

NAME OF DAM: INSPECTION DATE:

SPIUWAYS CHECK ( )ACTION

a 1 of 1 NEEDED

i§cCi .

0 g - cCI-z CONDITION OBSERVATIONS 't)1oI.I -::E :z I0I.l1- <0.

l.I.I 0 >< loI.Il: ~ ~C1 '"~I SLIDE. SLOUOH. SCARP

~2 EROSION:I".1 jJ VEOETATION CONDmON-%

~8 ~4 DEBRIS

~~

~61I

571 SIDEWALLS

.181 CHANNEL FLOOR

:I S9! UNUSUAL MOVEMENT

-.. 601 APPROACH AREA§i611 WEIR OR CONTROL

j~ 62! DISCHAROE AREA

6JI

64

65 DirrAXE STRUcnJRE

5 66 TRASHRACK!

67 STILLING BASIN

I 68

69

ADDITIONAL COMMENTS: REfER TO ITEM NO. If APPUCABLE.

",

INSPECTION DANAME OF DAM: TE:

OUTLET WORKS CHECK ( )ACTION

Q 1 of 1 NEEDED~i=

=1 l:G~d § l:Gz CONDInON OBSERVATIONS '" -:ll :z: ~~ <

0 ..'" :;jt:: ~ ~r.:I

70 INTAKE STRUCTURE

71 TRASHRACK

n Sl1LLlNG BASIN

73 PlUMA.RY CLOSURE

74 SECONDARY CLOSURElit

" CONTROL MECHANISM~0 76 OUTLET PIPE~

; 77 OUTLET TOWER

78 EROSION ALONG DAM TOE

79 SEEPAGE

80 UNUSUAL MOVEMENT

81

82

83 ..ADDITIONAL COMMENTS: REFER TO ITEM NO. IF APPLICABLE.

INSPECTION DATENAME OF DAM: :

CONCRETE/MASONRYCHECK ( )DAMS ACTION

Cl NEEDED

~~ 1 of 1=:; '" .:.! 0 0

t:: ... '"z CONDITION OIl$ERVATIONS [21>.1 -::s z <0 ~~

..'" ~t: ::E _t.7

8<1 SURFACE CONDITIONS

8S CONDITION OF JOINTS

;g 86 UNUSUAL MOVllMENT

87 ABUTMENT-DAM CONTACTS

88:)

89

90 SURFACE CONDITIONS

91 C,ONDITION OF JOINTS •

~92 UNUSUAL MOVEMENT

93 ABUTMENT-DAM CONTACTS

SU 94 DRAINSj~

9S LEAKAGEg96

97

98 SURFACE CONDITIONS

99 HORIZONTAL ALIGNMENT

Ii; VIlRTlCAL ALIGNMENT

~ CONDITION OF JOINTS

UNUSUAL MOVEMENTS

ADDITIONAL COMMENTS: REFER TO ITEM NO. IF APPLICABLE.

APPENDIX BREPORT FORM

•

95

DAM INCIDENT REPORT FORM

DATE TlME _

NAME OF DAM --'----

STREAM NAME _

WCATION _

COUNTY _

OBSERVER _

OBSERVER TELEPHONE _

NATURE OF PROBLEM _

WCATION OF PROBLEM AREA ~ _(Looking Downstream)

EXTENT OF PROBLEM AREA .:..- _

FLOW QUANTITY AND COLOR _

WATER LEVEL IN RESERVOlR _

WAS SITUATION WORSENING ~-------------------

EMERGENCY STATUS _

CURRENT WEATHER CONDITIONS _

ADDITIONAL COMMENTS: -'-- _

APPENDIXCGLOSSARY

99

ABUTMENTThat part of a valley side against which a dam is constructed. An artificial abut­ment is sometimes constructed as a concrete gravity section, to take the thrust ofan arch dam where there is no suitable natural abutment. Right and left abut­ments are those on respective sides of an observer looking downstream.

ACTIVE STORAGEThe volume of a reservoir that is available for power generation, irrigation, noodcontrol, or other purposes. Active storage excludes nood surcharge. It is thereservoir capacity less inactive and dead storages. The terms "useful storage,""unable storage," or "working storage" are sometimes used but are notrecommended.

AIRVENT PIPEA pipe designed to provide air to the outlet conduit to reduce turbulence duringrelease of water. Extra air is usually necessary downstream of constrictions.

APPURTENANT STRUCTURESAncillary features of a dam, such as the outlet, spillway, powerhouse,tunnels, etc.

AQUEDUCTAn artificial channel for conveying water, i.e., a canal, pipe, or tunnel; hence theterms "connecting aqueduct" and "diversion aqueduct."

ARCH DAMA concrete or masonry dam that is curved so as to transmit the major part of thewater pressure to the abutments.

Double Curvature Arch DamAn arch dam that is curved vertically as well as horizontally.

Arch BuHress DamSee Buttress Dam.

Arch Gravity DamSee Gravity Dam.

AUXIUARY SPillWAYSee Spillway.

AXIS OF DAM •A plane or curved surface, arbitrarily chosen by a designer, appearing as a line ina plan or cross section to which the horizontal dimensions of the dam canbe -referred.

BACKWATER CURVEThe longitudinal profile of the water surface in an open channel where the depthof now has been increased by an obstruction, an increase in channel roughness, adecrease in channel width, or a nattening of the bed slope.

BASE WIDTH (Base thickness)The maximum width or thickness of a dam measured horizontally betweenupstream and downstream faces and nonnal to the axis of the dam but excludingprojections for outlets, etc.

BERMA horizontal step or bench in the sloping profi!e of an embankment darn.

tOO

BLANKET

Drainage BlanketA drainage layer placed directly over the foundation material.

Grout BlanketSee Consolidation Grouting.

upstream BlanketAn impervious layer placed on the reservoir floor upstream of a dam. In thecase of an embankment dam. the blanket may be connected to the imperme­able element in a dam.

BunRESS DAMA dam consisting of a watertight upstream face supported at intervals on thedownstream side by a series of buttresses.

Arch Buttress Dam (Curved Buttress Dam)·A buttress dam that is curved in plan.

Multiple Arch DamA buttress dam whose upstream part comprises a series of arches.

CofferdamA temporary structure enclosing all or part of a construction area so that con­struction can proceed in a dry area. A udiversion cOfferdam" diverts a riverinto a pipe, channel, or tunnel.

CONCRETE unIn concrete work the vertical distance between successive horizontal construc­tion joints.

CONDUITA closed channel for conveying discharge through or under a dam.

CONSOUDATION GROUTING (Blanket Grouting)The injection ofgrout to consolidate a layer ofthe foundation, resulting in greaterimpermeability and!or strength.

CONSTRUCTION JOINTThe interface between two successive placings or poUr~ of concrete where abond, not permanent separation is intended.

CORE WAllA waD built of impervious m.aterial, usua))y concrete or asphaltic concrete, in thebody of an embankment dam to prevent leakage.

CREST GATESee Gate.

..

CREST LENGTHThe length of the top of a dam, including the length of spillway, powerhouse,navigation lock, fish pass, etc. where these structures form part of the length of adam. If detached from a dam, these structures should not be included

CREST OF DAMThe crown of an overflow section of a dam. In the United States, the term "crestofdam" is often used when "top ofdam" is meant.. To avoid confusion, the terms"crest ofspillway" and "top ofdam" may be used to refer to the overflow sectionand the dam proper, respectively.

CRIB DAMA gravity dam built up of boxes, cobs, crossed timbers, or gabions and filled withearth or rock.

CULVERT(a) A drain or watenvay builtlransversely under a road, railway, or embank­ment, usually consisting of a pipe or covered channel of box section. (b) Agallery or waterway constructed through any type ofdam, which is normally drybut is used occasionally for discharging water, hence Ibe terms "scour culverl,"·udrawofT culvel\" and Uspillway culvert."

CURTAINSee Grout curtain

CURVED BUTTRESS DAM (Arch Buttress Dam)See Buttress Dam.

CURVED GRAVITY DAMSee Gravity Dam.

CUTOFFAn impervious construction or material which reduces seepage or prevents itfrom passing through foundation material. .

CUTOFF TRENCHAn excavation later to be fined wilb impervious material to form a cutoff. Some­times used incorrectly 10 describe Ibe culoff itself.

CUTOFF WALLA wall of impervious material (e.g., concrete, asphaltic concrete, steel sheetpil­ing) built into Ibe foundation .to reduce seepage under Ibe dam. .

DAMA barrier built across a watercourse for impounding or diverting Ibe flow ofwater.

DEAD STORAGEThe storage Ibatlies below Ibe invert ofthe lowest ouUet and Ibal, Iberefore, can­not be wilbdrawn from Ibe reservoir.

DESIGN FLOODSee Spillway Design Flood.

DIAMOND HEAD BUnRESS DAMSee Buttress Dam.

DIAPHRAGMSee Membrane.

DIKE (Leve.)A.long low embankment whose height is usually less Iban 4 to 5 meters andwhose length is more Iban 10 or IS times Ibe maximum height Usually applied10 embankments or structures built to protect land from flooding. lfbuilt ofcoD­crete or masonry Ibe struclore is usually referred to as a Dood wall. Also used todescribe embankments Ibat block areas on a reservoir rim Ibat are lower Iban Ibelop oflbe main dam and Ibat are quite long. In Ibe Mississippi River basin, wherethe old F,encli word levee has survived, the term now applies to flood protectingembankments whose height can average up 10 10 to IS meters.

DIVERSION CHANNEL CANAl. OR TUNNELA walerway used 10 divert water from its natural course. These lerms aregenerally applied 10 temporary structures such as Ibose designed to bypass wateraround a dam sile during construction. "Channel' is normally used instead of"canal" when the walerway is short OccasionBlly these terms are applied topermanent structures.

DRAINAGE AREAAn area that drains naturally 10 a particular point on a river.

tDt

t02

DRAINAGE lAYER OR BlANKETA layer of penneable material in a dam to relieve pore pressure or to facilitatedrainage of ftIl.

DRAINAGE WELlS (Relief WelOA vertical well or borehole, usually downstream of impervious cores, grout cur­lains, or cutoffs, designed to collect and direct seepage through or under a dam toreduce uplift pressure under or within a dam. A line of such wells fonDS adrainage curtain.

DRAWDOWNThe lowering of water surface level due to release of water from areservoir.

EARTH DAM OR EARTHFill DAMSee Embankment Dam.

EMBANKMENTA slope of fill material, usually earth or rock, that is longer than it is high. Thesloping side of a dam.

Embankmenl Dam (Fill Dam)Any dam constructed of excavated natural materials or of industrialwaste materials.

Earth Dam (Earlhflll Dam)An embankment dam in which rnore than 50,*, ofthe total volume is formed ofcompacted fine-grained material obtained from a borrow area.

Homogeneous Earthflll DamAn embankment dam constructed ofsimilar earth material throughout, exceptinternal drains or drainage blankets; distinguished from a zoned earthfJlIdam.

Hydraulic Fill DamAn embankment dam constructed of materials, often dredged, that are con­veyed and placed by suspension in flowing water.

Rocldlll DamAn embankment dam in which more than 50% of the total volume comprisescompacted or dumped pervious natural or crushed rock.

Rolled Fill DamAn embankment dam of earth or rock in which the material is placed in layersand compacted by using rollers or rolling equipment.

Zoned Embankment DamAn embankment dam, of which is composed of zones of selected materialshaving different degrees of porosity, permeability, and density.

EMERGENCY ACTION PlANA predetennined plan of action to be taken to reduce the potential for propertydamage and loss of lives in an area affected by a dam break.

EMERGENCY GATEA standby or reserve gate used only when the normal means ofwater control arenot available.

EMERGENCY SPIllWAYSee Spillway.

ENERGY/DISSIPATING VALVEAny device constructed in a waterway to reduce or destroy the energy of fast­"owing water.

103

4 EPICENTERThe point on the earth’s surface directly above the focus of an earthquake.

FACEThe external surface of a structure, e-g, the surface of a wall of a dam.

FACINGWith reference to a wall or concrete dam, a coating of material, masonry orbrick, for architectural or protection purposes, e.g., stonework facing, brickworkfacing With reference to an embankment dam, an impervious coating or face onthe upstream slope of the dam.

FAILUREThe uncontrolled release of water from a dam.

FILTER (Filter Zone)A band or zone of granular material that is incorporated into a dam and is graded(either naturally or by selection) so as to allow seepage to flow across or downthe filter without causing the migration of material from zones adjacent tothe filter.

FLASHBOARDSA length of timber, concrete, or steel pl aced on the crest of a spi llway to raise theretention water level el but that may be quickly removed in the event of a flood .either by a tripping device or by deliberately designed failure-of the flashboard orits supports.

FLOODPLAINAn area adjoining a body of water or natural stream that has been or may becovered by flood water.

FLOODPLAIN MANAGEMENTA management program to reduce the consequences of flooding - either bynatural runoff or by dam failure - to existing and future properties in a flood-plain.

FLOOD ROUTINGThe determination of the attenuating effect of storage on a flood passing througha valley, channel, or reservoir.

FLOOD SURCHARGEThe volume or space in a reservoir between the controlled retention water leveland the maximum water level. Flood surcharge cannot be retained in the reser-voirbut will flow over the spillway until the controlled retention water level isreached. (The term “wet freeboard” for describing tbe depth of flood surchargeis not recommended; see Freeboard),

FL OOD WALLA concrete wall constructed adjacent to a stream for the purpose of pieventingflooding of property on the landward side of the wall; normally constructad inlieu of or to supplement a levee where the land required for levee construction isexpensive or not available.

FOUNDATION OF DAMThe natural material on which the dam structure is placed.

FREEBOARDThe vertical distance between a stated water level and the top of a dam. “Netfreeboard,” “dry freeboad, ” “flood freeboard,” or “residual Freeboard” is thevertical distance between the estimated maximum water level and the top of adam, “Gross freeboard” or “total freeboard” is the vertical distance between themaximum planned controlled retention water level and the top of a dam. (Thatpart of tbe “gross freeboard” attributable to the depth of flood surcharge is some-times referred to as the “wet freeboard,” but this term is not recommended; it ispreferable that freeboard be used with reference to the top of the dam

tot

GAWRY(a) A passageway within the body of a dam or abutment; hence the tenns "grout­ing gallery," "inspection gallery," and "drainage gaDery." (b) A long and rathernarrow hall; hence the following terms for a power plant "valve gallery,"·"transfonner gaDery," and "busbar gallery."

GATEA device in which a leafor member is moved across the waterway from an exter­nal position to control or stop the now.

Bulkhead GoteA gate used either for temporary closure of a channel or conduit to empty it forinspection or maintenance or for closure against nowing water when the headdilTerence is smaD, e.g., for diversion tunnel closure. Although a bulkhead gateis usually opened and closed under nearly balanced pressures, it neverthelessmay be capable of withstanding a high pressure dilTerential when in theclosed position.

ere.t Gote (Spillway Gote)A gate on the crest of a spillway to control overflow or reservoir waterlevel.

Emergency GateA standby orreserve gate used only when the nonnal means ofwater control isnol available.

Fixed Wheel Gate (Fixed Roller Gate, Fixed Axle Gate)A gate having wheels or rollers mounted on the end posts of the gate. Thewheels bear against rails fIXed in side grooves or gate guides.

Flap GateA gate hinged along one edge, usually either the top or bottom edge. Examplesof bottom-hinged nap gates are tilting gates and belly gates, S<H:aDed due totheir shape in cross section.

Flood GoteA gale to control flood release from a reservoir.

Guard Gate (Guard Valve)A gate or valve that operates fully open or closed It may function as a second­ary device for shulling off the now ofwater in case the primary closure devicebecomes inoperable, but is usually operated under balanced pressure, no­flow conditions.

outlet GoteA gate controlling the oulOow of water from a reservoir.

RadIal Gate (Talntlll Gote)A gate with a curved upstream plate and radial arms hinged to piers or othersupporting structures.

Regulating Gote (RegUlating Valve)A gale or valve that operates under fuJI pressure and flow conditions to throttleand vary the rate of discharge.

Slide Gote (SluIce Gote)A gate that can be opened or closed by sliding il in supporting guides.

GRAVITY DAMA dam constructed of concrete and/or masonry that relies on its weight forstability.

Arch Gravity DamAn arch dam in which part of the water pressure is transmitted to the abut­ments by horizontal thrust and part to the foundation by cantileveraction.

Curved Gravity DamA gravity dam that is curved in plan.

Hollow Gravity Dam (Cellular Gravity Dam)A dam that has the outward appearance of a standard gravity dam but that is ofhoUow construction.

GROSS STORAGE (Reservoir Copaclty (Gross Copaclty 01 Reservoir)The gross capacity of a reservoir from the river bed up to maximum controlledretention water level. It. includes active, inactive, and dead storage.

GROUT BlANKETSee Blanket.

GROUT CAPA concrete pad or waD constructed to facilitate pressure grouting of the groutcurtain beneath it. .

GROUT CURTAIN (Grout Culofl)A barrier produced by injecting grout into a vertical zone, usually narrowhorizontally, in the foundation to reduce seepage under a dam.

HEIGHT ABOVE LOWEST FOUNDATIONThe maximum height from the lowest pointofthe general foundation to the topofthe darn.

HYDRAUUC HEIGHTThe height to which water rises behiod a dam and the difference between thelowest point "in the original streambed at the aXis of the dam and the maximumcontrollable water surface.

HYDROGRAPHA graphic representation of discharge, stage, or other bydraulic property withrespect to time for a particular point on a stream. (At times the term is applied tothe phenomenon the graphic representation describes; bence a flood bydrograpbis the passage of a llood discharge past the observation point.)

INACTIVE STORAGEThe storage volume of a reservoir measured between the invert level of thelowest ouUet and minimum operating level •

INCUNOMETER (tnclomeler)An instrument, usually consisting ofa metal or plastic lube inserted in a drill boleand a sensitized monitor either lowered into the lube or flIed within the lube.This measures at different points the tube's inclination to the vertical. By integra­tion, lhe lateral position at different levels of the tube may be found relative to apoint, usually the top or bottom ofthe lube, assumed to be flIed. The system maybe used to measure setUement.

INTAKE.Any structure in a reservoir, darn, or river through whicb water can be drawn intoan aqueduct.

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INTENSITY SCAlEAn arbitrary scale used to descn"be the severity ofearthquake-induced shaking ata particular place. The scale is not based on measurement but on direct observa­tion. Several scales are used (e.g., the Mndified Mercalli scale,the MSK scale)all with grades indicated by Roman numerals from I to XIL

INTERNAL EROSIONSee Piping.

INUNDATION MAPA map delineating the area that would be inundated in the event of a darnfailure.

lEAKAGEUncontrolled loss of water by flow through a hole or crack.

UNINGWith reference to a canal, tunnel, shaft, or reservoir, a coating of asphaltic con­crete, reinforced or unreinforced concrete, shotcrete, rubber or plastic to providewatertightness, prevent erosion, reduce friction, or support the periphery of thestructure. May also refer to lining, such as steel or concrete, of outlet pipeor conduit.

UVE STORAGEThe sum of active. and inactive storage volumes. When there is no inactivestorage, as in some irrigation reservoirs, the tenns "live storage" and lI'activestorage" are equivalent. -

lOW lEVEl OUTlET (Bottom outlet)An opening at a low level from a reservoir generally used for emptying or forscouring sediment and sometimes for irrigation releases.

MAGNIWDE (see also RIchter SCale)A rating of an earthquake independent of Ibe place of observation. It iscalculated from seismographic measurements and is properly expressed inordinary numbers and decimals based on a logarithmic scale. Each higher num­ber expresses an amount of earthquake energy that is 10 times greater than thatexpressed by the preceding lower number, e.g., a magnitude 6 earthquake has 10times more energy than a magnitude S.

MASONRY DAMA dam constructed mainly of stone, brick, or concrete blocks that mayor maynot be joined wilb mortar. A dam having only a masonry facing should not bereferred to as a masonry dam.

MAXIMUM CREDIBlE EARTHQUAKE (MeaThe severest earthquake that is believed to be possible at a site on the basis ofgeologic and seismological evidence. It is determined by regional and localstudies including a complete review of all historic earthquake data ofevents suf­ficiently nearby to ~ct the site, all faults in the area, and attenuations due tofaults to the site.

MAXIMUM CROSS SECTION OF DAMA cross section of a dam at the point of maximum height of the dam.

MAXIMUM WATER lEVELThe maximum water level, including flood surcharge, Ibe darn is designedto withstand.

MEMBRANE (Diaphragm)A sheet or thin zone or facing made of a flexible material that is sometimesreferred to as a diaphragm waIl or diaphragm.

MINIMUM OPERATING UVELThe lowest level to which the reservoir is drawn down under nonnal operating

.conditions.

MORNING GLORY SPILLWAYSee Spillway.

NORMAL WATER UVELFor a reservoir with a fIXed overflow sill the lowest crest level oCthat sill. For areservoir whose outllow is controlled wholly or partly by movable gates, siphonsor other means, it is the maximum level to which water may rise under normaloperating conditions, exclusive oC any provision Cor llood surcharge.

OPERATING BASIS EARTHQUAKEA hypothetical earthquake used Cor design purposes. A more moderate standardthan the Maximum Credible Earthquake·(see), it is based on regional and localgeology and seismology studies and is considered likely to occur during the liCe oCthe dam.

ONE-HUNDRED YEAR (100·Year) EXCEEDANCE INTERVALThe Dood magnitude expected to be equalled or exceeded on the average ofonCein 100 years. It may also be expressed as an exceedance frequency with a per­cent chance of being exceeded in any given year.

ounnAn opening through which water can be Creely discharged Crom a reservoir.

OVERFLOW DAM (Overtoppable Dam)A dam designed to be overtopped

PARAPnWALLA solid wall built along the top of a dam Cor ornament, Cor the safety oC vehiclesand pedestrians, or to prevent overtopping.

PEAK FLOWThe maximum instantaneous discharge that occurs during a llood. It is coinci­dent with the peak of a Dood hydrograph.

PERVIOUS lONEA part of the cross section oC an embankment dam comprising material oChigh penneability.

PHREATIC SURFACEThe Cree surface oC groundwater at atmospheric pressure.

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PIElOMmRAn instrumentconcrete.

Cor measuring pore water pressure within soil, rock. or

•

PIPINGThe progressive development of internal erosion by· seepage, appearingdownstream as a hole or'seam discharging water that contains soil particles.

PORE PRESSUREThe interstitial pressure oC water within a mass of soil rock. or concrete.

PRESSURE CELLAn instrument Cor measuring pressure within a mass ofsoil, rock. or concrete orat an interface between one and the other. .

PRESSURE REUEF PIPESPipes used to relieve uplift or pore water pressure in a dam Coundation or in thedam structure.

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PROBABLE MAXIMUM FLOOD (PMF)A flood that would result from the most severe combination of criticalmeteorologic and hydrologic conditions possible in the region.

On.Hol. PMFA flood with a peak flow equal to one-halfof the peak flow ora probable max-imum flood. .

PROBABLE MAXIMUM PRECIPITATION (PMP)The maximum amount and duration of precipitation that can be expected tooccur on a drainage basin.

PUMPED STORAGE RESERVOIRA reservoir filled entirely or mainly with water pumped from outside its naturaldrainage area.

REGUlATING DAMA dam impounding a reservoir from which water is released to regulate the flowin 8 river~

REUEF WEllSee Drainage Wen.

RESERVOIR AREAThe sunace area of a reservoir when fined to controlled retention waterlevel.

RESERVOIR ROUTINGThe computation by which the interrelated effects of the inflow hydrograpb,reservoir storage, and discharge from the reservoir are evaluated.

RESERVOIR SURFACEThe sunace of a reservoir at any level.

RICHTER SCALEA scale proposed by C.F. Richter to descnoe the magnitude of an earthquake bymeasurements made in well-dermed conditions and with a given type of seis­mograh. The zero of the scale is fixed arbitrarily to fit the smallest recordedearthquakes. The largest recorded earthquake magnitudes are near 8.7 and arethe result ofobservations and not an arbitrary upper limit like that of the intensityscale. .

RIPRAPA layer of large uncoursed stones, broken rock, or precast blocks placed in ran­dom fashion on the upstream slope of an embankment dam, on a reservoir shore,or on the sides of a channel as a protection against wave and ice action. Verylarge riprap is sometimes referred to as armoring.

RISK ASSESSMENT •As applied to dam safety. the process of identifying the likelihood and conse­quences of dam· failure to provide the basis for informed decisions on •course of action. .

ROCKFill DAMSee Embankment Dam.

ROllCRETEA no-slump concrete that can be hauled in dump trucks, spread with a bulldozeror grader. and compacted with a vibratory roller.

SEEPAGEThe interstitial movement of water that may take place through a dam, its foun­dation, or its abutments.

SEEPAGE COUAIA projecting collar, usually ofconcrete, built around the outside of a pipe, tunnel,or conduit under an embankment dam, to lengthen the seepage path along theouter surface of the conduit

SIll(a) A submerged structure across a river to conlrolthe water level upstream. (b)The crest of a spiDway. (c) A horizontal gate seating, made ofwood, stone, con­crete or metal at the invert of any opening or gap in a structure, hence theexpressions "gate siD" and "stoplog sill:'

SlOPE(a) The side of a hill or mountain. (b) The inclined face of a cutting or canal orembankment (c) Inclination from the horizonia!. In the Untied States, it ismeasured as the ratio of the number ofunits ofhorizontal distance to the numberor corresponding units or vertical distance. The term is used in English for anyinclination and is expressed as a percent when the slope is gentle, in which casethe tenn "gradient" is also used. .

SLOPE PROTECTIONThe protection of a slope against wave action or erosion.

SlUICEWAYSee low-level outlet

SPillWAYA structure over or through which nood nows are discharged. H the now is con;trolled by gates, it is a controlled spillway; if the elevation or the spillway crest isthe only control, it is an uncontrolled spillway.

AUXiliary Spillway (Emergency Spillway)A secondary spiDway designed to operate only during exceptionally largennods.

Fuse Plug SpillwayAn auxiliary or emergency spillway comprising a low embankment or anatural saddle designed to be overtopped and eroded away during a very rareand exceptionally large flood.

Primary Spillway (PrincIpal Spillway)The principal or rust-used spillway during nood flows.

Shan Spillway (Momlng Glory Spnlway)A vertic"a1 or inclined shaft into which flood water spills and then is conductedthrough, under, or around a dam by means of a conduit or tunnel; If the upperpart of the shaft is splayed out and terminates in a circular horizonial weir, it istermed a "bellmouth" or "morning glory" spillway.

Side Channel Spillway •A spillway whose crest is roughly parallel to the channel immediatelydownstream of the spillway.

Siphon SpillwayA spillway with one or more siphons built at crest level. This type of spillwayis sometimes used for providing automatic surface-level regulation withinnarrow limits or when considerable discharge capacity is necessary within ashort period of time.

SPillWAY CHANNEL (Spillway Tunnel)A channel or tunnel conveying water from the spillway to the riverdownstream.

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SPillWAY DESIGN FLOOD (SDF)The largest flood that a given project is designed to pass safely. The reservoirinflow-discharge hydrograph used to estimate the spillway discharge capacityrequirements and corresponding maximum surcharge elevation in thereservoir.

mWNGBASINA basin constructed to dissipate Ibe energy of fast-flowing water, e.g., from a

spillway or bottom outlet, and to protect the river bed from erosion.

STOPLOGSLarge logs or timber or steel beams placed on top of eacb other wilb their endsheld in guides on each side of a channel or conduit providing a cbeaper or moreeasily handled temporlll}' closure than a bulkhead gate.

STORAGEThe retention of water or delay of nmolf either by planned operation, as in areservoir, or by temporlll}' fIlling of overIJow areas, as in the progression of aflood crest through a natural stream channel.

STORAGE RESERVOIRA reservoir that is operated with cbanging water level for the purpose of storingand releasing water.

TAILRACE .The tunnel, channel, or conduit that conveys the discharge from the turbine tothe river; hence the terms "tailrace- tunnel" and Utailrace canal.'"

TAILWATER LEVELThe level ofwater in the tailrace at the nearest free surface to Ibe turbine or in thedischarge channel immediately downstream of the dam.

TOE OF DAMThe junction of Ibe downstream face of a dam with the ground surface, alsoreferred to as downstream toe. For an embankment dam the junction of theupstream fac~ with ground surface is called the upstream toe.

TOP OF DAMThe elevation of the uppermost surface of a dam, usually a road or walkway,excluding any parapet wall, railings, etC.

TOP THICKNESS (Top Width)The thickness or width of a dam at the level of the top of the dam. In general, theterm "thickness" is used for gravity and arcb dams and "width" is used foroIherd~ ~

.TRANSmON ZONE (SemlpervioUi Zone)A part of the cross section of a zoned embankment dam comprising material ofintermediate size between that of an impervious zone and that of apermeable zone.

TRASH RACKA screen located at an intake 10 prevent the ingress of debris.

TUNNELA long underground excavation usually having a uniform cross section. Types oftunnel include: headrace tunnel, pressure tunnel, collecting tunnel, diversion tuR­nel, power tunnel, tailrace tunnel, navigation tunnel, access tunnel, scour tunnel,drawofT tunnel, and spillway tunnel.

UNDERSEEPAGEThe interstitial movement of water through a foundation.

UPLIFTThe upward pressure in the pores of a material (interstitial pressure) or on thebase of a structure.

UPSTREAM BlANKETSee Blanket

VALVEA device filted to a pipeline or orifice in which the closure member is eitherrotated or moved transversely or longitudinally in the waterway so as to controlor stop the flow.

WATERSHED DIVIDEThe divide or boundary between catchment areas (or drainage areas).

WATERSTOPA strip ofmetal, rubber, or other material used to prevent leakage through jointsbetween adjacent sections of concrete. .

WEIR(a) A low dam or waD built acro" a stream to raise the upstream water level,tenned filled-crest weir when uncontroDed. (b) A structure built across a streamor channel for the purpose ofmeasuring now, sometimes called ameasuring weir .or gauging weir. Types of weir include broad-crested weir, sblUJH'rested weir,drowned weir, and submerged weir.

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APPENDIX DSELECTED BIBLIOGRAPHY

STATE MANUALS

Arkansas Soil and Water Conservation Commission (1980) Safely Evaluationof Small Earth Dams LillIe Rock, Arkansas.

Colorado State Engineer's Office, Division of Water Resources (1983) DamSafely Manual Denver, Colorado.

State of minois Department of Water Resources (1980) Guidelines and Formsfor Inspection of minois Dams, Springfield, Illinois.

Kentucky Natural Resources and Environmental Protection Cabinet, DivisionofWater Resources (1985) Guidelines for Maintenance and Inspection ofDamsin Kentucky.

Michigan Edition, STS Consultants, Dam Safety Guidebook.

North Carolina Department of Natural Resources and Community Develop­ment, Division of Land Resources, Land Quality Security Dam OperationMaintenance and Inspection Manual.

North Dakota Dam Design Handbook, North Dakota State Engineer.

Ohio Department of Natoral Resources (1983) Operation, Maintenance, andInspection Manual for Dams, Dikes, and Levees.

Pennsylvania Department of Environmental Resources, Division ofDam Safety(1986) A Manual for the Inspection, Maintenance, and Operation of Damsin Pennsylvania.

Virginia State Water Control Board, Bureau of Water Control Management(1983) Safety Evaluation ofSmalJ Earth Dams, Information Bulletin 549, Rich­mond, Virginia.

Wyoming Disaster and Civil Defense Office (1984) Dam Safety: A Manual forPrivate Dam Owners.

Selected BIbliographyAmerican Society of ,Civil Engineers (ASCE)/U.S. Commission on LargeDams (USCOLD) (1975). Lessons from Dam Incidents, USA NewYork: ASCE.

American Concrete Institute (ACI) (1968). "Guide for Making A ConditionSurvey of Concrete In Service", Journal of the American Concrete Institute,Vol. 65, No. I I: ACI.

(1982). "Materials and General Properties of Concrete." In ACI Manual ofConcrete Practice, Part J. Detroit: ACI.

Bartholomew, C.L, et al (1986). Embankment Dam InstrumentationManual U.S. Bureau of Reclamation, Washington, D.C., GoverrunentPrinting Office.

(1987). (To be published) Concrete Dam Instrumentation Manual, U.S.Bureau of Reclamation, Washington, D.C., Government Printing Office.

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Chiefof Engineers (1915). "Recommended Guidelines for Safely Inspection ofDams." National Program of Inspection of Dams, Vol. I, Appendix D,Washington, D.C., Department of the Army.

Concrete Construction Publication, Inc. (1983). "Four Steps to SuccessfulConcrete Repair." Vol. 28, No. I. Addison, Illinois: Concrete ConstructionPublication, Inc.

(1985) "Crack Repair." Vol. 30, No.1. Addison,lUinois: Concrete ConstructonPublication, Inc.

Dunniclilf, J. (1981). Measurements Commitee Report, U.S. Committee onlarge Dams Section VI, Inventory of Geotechnical Instruments, Manufacturersor Suppliers.

Golze, A.R., ed (1911). Handbook of Dam Engineering, Van NostrandReinbold Co., New York.

Graham, W.J. (1983). Dam Failure Warning EfTectivness, Denver,Colorado, U.S. Bureau of Reclamation. Unpublished report.

Interagency Committee on Dam Safely, Subcommittee on Emergency ActionPlanning (1985). Emergency Action Planning Guidelines fnr Dams,Washington, D.C., Federal Emergency Management Agency.

Interagency Committee on Large Dams (ICOID) (1-969). General Con­siderations Applicable to Instrumentation for Earth and Rock/ill Dams, Com­mittee on Observations of Dam and Models, Bullelin, No. 21, Boston,Massachusetts.

(1981). Automated Observation for Instantaneous Safety Control of Damsand Reservoirs, Bulletin No. 4 I, Boston, Massachusetts.

International Conference of Building Officials (1919). Uniform BuildingCode, 1919 Edition, Whittier, California.

Jansen; R.B. (1968). A Prescription for Dam Safely - Instrumentation andSurveillance, Conference of CoDege of Engineering, Uuiversity of Califor­nia, Berkeley.

(1980). Dams and Public Safely, U.S. Bureau of Reclamation, GovemmentPrinting Office, Washington, D.C.

Mine Safely and Health Administration, Mine Waste and· GeotechnicalEngineering Division (1984). Construction Inspection of Dams and CoalRefuse Embankments, BrucetOn Mills, Pennsy~vania.

National Association of Conservation Districts "Dam Safely - Who is Respon­sible?" Slide shnw produced by National Association of Conservation Districts,Washington, D.C. .

•National Researc.h Council (1982). Geotechnicallnstrurnentation for Monitor­ing Field Performance, Washington, D.C., National Academy Press.

National Research Council, Committee on the Safely of Existing Dams (1983).Safely of Exisling Dams, EvaIuation and Improvement, Washington, D.c.,National Academy Press.

National Research Council, Committee on Safely Criteria for Dams (1985).. Safely of Dams Flood and Earthquake Criteria, Washington, D.C., National

Academy Press.

National Research Council, Committee on Safety of Non-Federal Dams(1982). Safely of Non-Federal Dams: A Review of the Federal Role,Washington, D.C., National Academy Press.

Sharma and Raphael (1979/1981). General Considerations on ReservoirInslrumenlation, Committee on Measurements, USCOLD, Boston, Massa­chusetts.

Sowers, G.F. (1961). "The Use and Misuse of Earth Dams," ConsultingEngineering, New York.

Truby, Jack, Hagan, Pat (1985). The Dam Failure Hazard; Awareness and Pre­paredness, Golden, Colorado, Colorado Division Of Disaster EmergencyServices.

Tschantz, Bruce A. (1972). The Inspection and Maintenance of PrivatelyOwned Dams in Tennessee, University of Tennessee, Knoxville, Tennessee..

Federal Emergency. Management Agency (FEMA) (1984). Updated ReviewSummary of State Non·Federal Dam Safety Programs, Washington, D.C.

U.S. Army Corps of Engineers (1971 and 1976). Inslrumenlation of Earth andRocklill Dams, Parts I and 2, August 1971 and November 1976,Washington, D.C.

(1980a). Flood Emergency Plans, Guidelines for Corps Dams, HydrologicEngineering Center, Davis, California.

(1980b) Instrumentation for Measurement of Slruclural Behavior of ConcreteSlruclures, Washington, D.C.

(1982) National Program for Inspection of Non·Federal Darns· Final Reportto Congress, Washington, D.C.

U.S. Committee on Large Dams (USCOLD) (1983). Guidelines for Inspec­tion of Dams Following Earthquakes, Washington, D.C., Government Print­ing Office.

(1986). General Considerations Applicable to Performance Monitoringof Dams, U.S. Committee on Large Dams, Boston, Massachusetts.

U.S. Dept of Agriculture (1980). Forest Service and Soil Conservation Service,Guide for Safety Evaluation and Periodic Inspection of Existing Dams,Washington, D.C.

U.S. Department of the Interior, Bureau of Reclamation (1974). Earth Manual,2d ed., Washington, D.C., Government Printing Office.

(1975). Concrete Manual, A Water Resource Technical Publication,Washington, D.C. Government Printing Office.

(1976). Design of Gravity Dams, Washington, D.C., GovernmentPrinting Office.

(1977). Design of Arch Dams, Washington, D.C., Government Print­ing Office.

(1985). Design of Small Dams, Washington, D.C., Government PrintingOffice. ~

(1982). Operation and Mainlenance Guidelines for Small Dams, Wash­ington; D.C., Government Prinling Office.

(1983). Safely Evalualion of Existing Dams, (Seed Manual), Washington,D.c., Government Printing Office.

(1984). Waler Measurement Manual, Washington, D.C., GovernmentPrinting Office.

U.S. Department ofthe Interior, GeolOgical Survey (1985). Floods From DamFailures, Denver, Colorado.

Wilson, S.D. (1973). "Deformamtion of Earth and Rocklill Dams", Embank­ment Dam Engineering Casagrande Volume, New York, John Wiley &Sons.

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APPENDIX ESTATE BACKGROUND AND PERSPECTIVE

(Each slale ;s encouraged 10 include this ;Tfformation prior 10 disseminalion of themanual.)

NE.W YORK STATE DEPAR'IMENT OF ENVIRONMENTI\L CONSERVATION

EnvirolllTEntal Conservation Law, Article 15-050315-0507

Dam Safety Regulations, 6NYrnR 673January 1986

Guidelines for Design of DamsJanuary 1985

Guidelines for Developnent of a Dam, Emergency Action PlanFebruary 1982

SOIL CONSERVATION SERVICE: U. S. Dept. of Agriculture

Earth Dams and Reservoirs, Teclmical Release No. 60Revised Aug. 1981

National Engineering Handbook; August 1972Section 4, Hydrology

N?\TIONAL OCIWUC /; A'IHJSPHERIC J\llIIINISTRATIONNATIONAL WEATHER SERVICE: U. S. Dept. of CcmJErce

Hydraneteorological Report 33: April 1956"Seasonal Variation of the Probable Max:iJnun Precipitation Eastof the 105th Meridian for Areas fran 10 to .1000 Square Miles andDurations of 6, 12, 24 and 48 Hours"

Hydraneteorological Rep:>rt 51: June 1978"Probable Max:iJnun Precipitation Estimates, United States East of the:105th-Meridian"

•Teclmical Paper 40: May 1961

"Rainfall Frequency Atlas of the United States for Durations fran 30Minutes to 24 Hours and Return Periods fran 1 to 100 Years"

DAMBRK; 1980"The NWS Dam-Break Flood Forecasting Medel"

SMPDBK"The NWS Simplified Dam Break Flood Forecasting Model"

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Technical Paper 49; 1964"'l'wcrto Ten-Day Precipitation for Return Pericds of 2 to 100 Years inthe Contigu:lUs united States"

CORPS OF ENGINEERS, U. S. Anny.

Hydrological Engineering Center1ID2-1 F10cd Hydrograph Package; 1981

ETL 1110-2-256, June 1981Sliding Stability for Concrete Structures

EM 1110-2-1902, April 1976Stability of Earth and Rock-Fill Dams

A!'IERICAN SOCIETY OF CIVIL ENGINEERS (A...c:eE)Proceedings of the Engineering Foundation Conferenceat Asilanar Conference GrOUJrls, Pacific Grove, California

Inspection, Maintenance and Rehahilitation of Old DamsSepteml::er 1973

Responsibility and Liability of Public & Private Interest..; on DamsSepteml::er 1975

The Evaluation of Dam Safety. Noveml::er 1976

Proceedings of the Engineering Foundation Conferenceat Herkirrer, New Hampshire

Safety of Small DamsAugust 2974

A/1ERICAN SOCIETY OF CIVIL ENGINEERS

Current Trends in Design and Construction of flnbankIrent Dams1979 •

, .