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NATIONAL DAM SAETY PORAM. MSTEAD LAKE DAM (INVENTORY NUMB--ETCUl AUG 81 E O'BRIEN DACW51-1C-00 UNCLASSIFIED NL E h hGhh h-ET hmhhhhahhhh7 II IIIEEEI2t
NATIONAL DAM SAETY PORAM. MSTEAD LAKE DAM (INVENTORY NUMB--ETCUlAUG 81 E O'BRIEN DACW51-1C-00
UNCLASSIFIED NLE h hGhh h-EThmhhhhahhhh7
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2~' LEWEI
LONG ISLAND BASIN
HEMPSTEAD LAKE DAM
0NASSAU COUNTY, NEW YORKI INVENTORY NO. N.Y. 108
I PHASE I INSPECTION REPORT
I NATIONAL DAM SAFETY PROGRAM
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gl DTICAPPROVED FOR PUBLIC RELiJA E-ECTEI OfTRR1uTIONUMiTEi OCT 20 1981.
I DI NEW YORK DISTRICT CORPS OF ENGINEERS
JULY 1981
10 10 19
DISCLAIMER NOTICE
THIS DOCUMENT IS BEST QUALITYPRACTICABLE. THE COPY FURNISHEDTO DTIC CONTAINED A SIGNIFICANTNUMBER OF PAGES WHICH DO NOTREPRODUCE LEGIBLY.
s.. . . . .
sgCuemvr CLAJIUV3CATIOI4 0F THIS PAGM ("~W Od 04.t00Vd)
REPORT DOCUMENTATION PAGE REDISRUTOS
I.REOR UMI& 1.GOVr ACCESSIO6 140. 3. atPU E &E -.- ffl-Wa ion-Report . Phaelvse I Insection Report
siptead Lake )Dani.. .. ationaL Dam Safety Prograa*Long Island*Basin, Nassau County, N.Y. W* *U msInventory No. 108
UGENE/ Brieni IDAClW51-81 -C-# 68
19.-PIRpOR4fgG ORGANIZATION NAME AN#D ADORESS * 0.POR4E.MVPOSCT. TASX(
Tippet ta-Abbe t t-bNcCarthy-Strat ton -(,i..7r,:The TAMS Building toC .. 7/IL655 Third Aucantio mewYol New Ynrk 1flfl7 _______________
I 11.. Co-4.tTRj.LUHC OFFICE HNK ANU A6DRESS______
* Departne nt of the'AmrnyU 5 ute4 1* 26 Federal Plaza A-gew York. Diitrict, CofE 1
'I Ne'Nr.1ew York 102787 ac. . R AS...hDaf -
14.HITRN AGENCY NfAME & A6R~~rn3mm -mu"4ofc)-SDepartment of tbe Army26 Federal Plaza New York District, CWE UCASFENewi York, .WfY 10287 .IS.. DiCLASSFICATI,4OuDoPGoAoI'a
IS. DISTRISUTIO.4 STATS.4t.T (of ih02 P-por-*
A D r o,/ d if cr . rei .aize; -Distribution ucli-.ited-fp
/ ational Dm safety Program. lstadLkam(Inventory Number 4% 108), Long Island
Basing Nassau County, New York. Phise I
S-. - Inspection Reports--
I. Y. x .f S 33 ( X..- AJ-* byj n .c
Dam~ Saeo: ro-yn Hempstead Lake Damn?:a3 i.-al I n s fetyn %,a : Nassau County
LL~t~l Inpecton .Lung Island BasinH yd.3'.:L3y, Structu-IralS:b iy
h!-- eeport provides *L> *:on and a-,al,:r.?hstc.L of the!::~ of the report da:-,.. iaormacion an-d -.. are based vt .-- a
4 1%;,--Inn ^f rl r;m -. * nerforingo~"3The examination of document',s and the visual inSpaption)
~J of Hempstead L~ake Dam did -not reveal conditions which constitute-and immxediate ation. mnlieo poety oevr hdam has some deficiencies which require further investigation
LASS,$#C %j-3VrfCW V Tht . W.. .. f
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SECUPUTY CLASSIFICAT 10?4 OF TIS pASe(W'ten 08(4 KeaIrieo
Using the Corps of Engineers screening criteria forreview of spillway adequacy, it has been determined that thedam would be overtopped for all storms exceeding approximately2. percent of the PMF. The overtopping of the dam could causethe erosion of both abutments and the downstream face of thedam resulting in dam failure, thus significantly increasing~the-hazard to the loss of life downstream. The spillway istherefore adjudged as "seriously inadequate" and the dam isassessed as unsafe, non-emergency.
The classification of "unsafe" applied to a dam becausebf a "seriously inadequate" spillway is not meant td connotethe same degree of emergency as would be associated with anounsafe" classification applied for a structural deficiency.It does mean that there appears to be a serious deficiency inspillway capacity and if a severe storm were to occur, over-topping and failure of the dam could tak6 place, significantlyincreasing the hazard to loss of life downstream of the dam.
It is therefore recommended that within 3 months of not-ification to the owner, detailed hydrologic/hydraulic investigationsof the structure should be undertaken to more accurately determinethe site specific characteristics of the watershed and their affectupon the overtopping potential of the dam. The results of theseinvestigations will determine the appropriate remedial measureswhich will be.required to achieve a spillway capacity adequate-to discharge the outflow from at least the one-half PMV. .Within12 months of the date of not'ificati.on to the owner, modificationsto the structure, dcic ud necess ;ry as a rcsult of studies, shouldhay,. I'een completed. In the intcrim, a dc.-etailed emergency action
:Iust h evI opcf. and imlipi ' cn Lcd during periods of unusually1J,_''evy prcvJ p 4t *: .l.];c, aD: 11-(1 ie-clt,- surve ilIance of thestructure r:u,;t be provi ded dui .eC. these rio,3.
Accession ForNTIS GRA&I
DTIC TAB 0Unannounced 0______ [ DTICJustification
Distribution/ _ OCT 20 1981Availability Codes
Avail and/orDist Special D
X&CURITY VLAS!Ar* 1CA 710h1 OF INIS PAGrP' .n Pala I.tr~d)
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LONG ISLAND BASIN
I HEMPSTEAD LAKE DAM
NASSAU COUNTY, NEW YORKINVENTORY NO. N.Y. 108
IPHASE I INSPECTION REPORT
NATIONAL DAM SAFETY PROGRAM
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S[ NEW YORK DISTRICT CORPS OF ENGINEERS
= JULY 1981
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3 PWWEACE
This report is prepared under guidance contained in theRecommended Guidelines for Safety Inspection of Dams, forPhase I Investigations. Copies of these guidelines may be ob-tained from the Office of Chief of Engineers, Washington, D. C.,20314. The purpose of a Phase I Investigation is to identifyexpeditiously those dams which may pose hazards to human lifeor property. The assessment of the general condition of the damI is based upon available data and visual inspections. Detailedinvestigations, and analyses involving topographic mapping, sub-
surface investigations, testing, and detailed computational eval-uations are beyond the scope of a Phase I Investigation; however,the investigation is intended .to identify any need for such studies.
In reviewing this report, it should be realized that thereported condition of the dam is based on observations of fieldconditions at the time of inspection along with data availableto the inspection team. In cases where the reservoir was loweredor drained prior to inspection, such action, while improving thestability and safety of the dam, removes the normal load on thestructure and may obscure certain conditions which might other-wise be detectable if inspected under the normal operating environ-ment of the structure.
It is important to note that the con4ition of a dam dependson numerous and constantly changing internal and external con-ditions, and is evolutionary in nature. It would be incorrectto assume that the present condition of the dam will continue torepresent the condition of the dam at some point in the future.Only through frequent inspections can unsafe conditions be de-tected and only through continued care and maintenance can these[ conditions be prevented or corrected.
Phase I inspections are not intended to provide detailedii hydrologic and hydraulic analyses. In accordance with the
established Guidelines, the Spillway Test flood is based on theestimated "Probable Maximum Flood" for the region (greatest rea-sonably possible storm runoff), or fractions thereof. Becauseof the magnitude and rarity of such a storm event, a findingthat a spillway will not pass the test flood should not be in-O: terpreted as necessarily posing a highly inadequate condition.The test flood provides a measure of relative spillway capacityand serves as an aid in determining the need for more detailedhydrologic and hydraulic studies, considering the size of thep dam, its general condition and the downstream damage potential.
1
NATIONAL DAM SAFETY PROGRAM
HEMPSTEAD LAKE DAMI.D. NO. N.Y. 108D.E.C. NO. 193LONG ISLAND BASINI NASSAU COUNTY, N.Y.
i CONTENTS
Page 4
No. s- ASSESSMENT
- OVERVIEW PHOTOGRAPH
1 PROJECT INFORMATION
L1.1 GENERAL
a. Authority 1b. Purpose of Inspection 1
1.2 DESCRIPTION OF THE PROJECT 1
I a. Description of the Dam andAppurtenant Structures 1
b. Location 2[ c. Size Classification 2d. Hazard Classification 2e. Ownership 2f. Purpose of Dam 2g. Design and Construction History 2h. Normal Operating Procedure 2
1 1.3 PERTINENT DATA 2
a. Drainage Area 2b. Discharge at Damsite 2c. Elevation 2d. Reservoir 3
I e. Storage 3f. Dam 3g. Spillway 3h. Reservoir Drain and Pipelines 3
2 ENGINEERING DATA 5
I2. GEOLOGY 5
2.2 SUBSURFACE INVESTIGATIONS 5
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n 2.3 DAM AND APPURTENANT STRUCTURES 5
2.4 CONSTRUCTION RECORDS 5
n 2.5 OPERATION RECORDS 5
3 2.6 EVALUATION OF DATA 5
3 VISUAL INSPECTION 6
S3.1 FINDINGS 6a. General 6b. Dam 6c. Spillway 6d. Outlets and Pipeline 6e. Abutments 7f. Reservoir Area 7
3.2 EVALUATION OF OBSERVATIONS 7
1 4 OPERATION AND MAINTENANCE PROCEDURES 8
i 4.1 PROCEDURES 8
4.2 MAINTENANCE OF THE DAM 8
4.3 WARNING SYSTEM IN EFFECT 8
4.4 EVALUATION 8
1 5 HYDROLOGIC/HYDRAULIC 9
5.1 DRAINAGE AREA CHARACTERISTICS 9
5.2 ANALYSIS CRITERIA 9
5.3 SPILLWAY CAPACITY 9
5.4 RESERVOIR CAPACITY 10
5.5 FLOODS OF RECORD 10
5.6 OVERTOPPING POTENTIAL 10
5.7 EVALUATION 10
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6 STRUCTURAL STABILITY 11
1 6.1 EVALUATION OF STRUCTURAL STABILITY 11
a. Visual Observations 11b. Design and Construction Data 11c. Operating Records 11d. Post-Construction Changes 11e. Stability Analysis 11f. Seismic Analysis 11
7 ASSESSMENT/RECOMMENDATIONS 12
7.1 ASSESSMENT 12
a. Safety 12b. Adequacy of Information 12c. Need for Additional Investigations 12d. Urgency 12
7.2 RECOMMENDED MEASURES 13
IAPPENDICESJ A. DRAWINGS
a. Vicinity Mapb. Topographic Mapc. General Location PlanJ. Cross Section
B. PHOTOGRAPHS
C. VISUAL INSPECTION CHECKLIST
D. HYDROLOGIC DATA AND COMPUTATIONS
E. REFERENCES
F. OTHER DATA
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PHASE I INSPECTION REPORT
I NATIONAL DAM SAFETY PROGRAMA
3J
NAME OF DAM Hempstead Lake Dam, NY 108
j STATE LOCATED New York
COUNTY LOCATED Nassau
I STREAM Mill River
BASIN Long Island
DATE OF INSPECTION March 13, 1981
LASSESSMENT
The examination of documents and the visual inspectionof Hempstead Lake Dam did not reveal conditions which constitutean immediate hazard to human life or property. However, thedam has some deficiencies which require further investigationand remedial action.
Using the Corps of Engineers screening criteria forreview of spillway adequacy, it has been determined that thedam would be overtopped for all storms exceeding approximately2 percent of the PMF. The overtopping of the dam could causethe erosion of both abutments and the downstream face of thedam resulting in dam failure, thus significantly increasingthe hazard to the loss of life downstream. The spillway istherefore adjudged as "seriously inadequate" and the dam isassessed as unsafe, non-emergency.
The classification of "unsafe" applied to a dam becauseof a "seriously inadequate" spillway is not meant to connote 3
the same degree of emergency as would be associated with an I[ "unsafe" classification applied for a structural deficiency.It does mean that there appears to be a serious deficiency inspillway capacity and if a severe storm were to occur, over-topping and failure of the dam could take place, significantlyincreasing the hazard to loss of life downstream of the dam.
It is therefore recommended that within 3 months of not-ification to the owner, detailed hydrologic/hydraulic investigationsof the structure should be undertaken to more accurately determinethe site specific characteristics of the watershed and their affectI
I
upon the overtopping potential of the dam. The results of these -'
investigations will determine the appropriate remedial measureswhich will be required to achieve a spillway capacity adequateto discharge the outflow from at least the one-half PMF. Within12 months of the date of notification to the owner, modificationsto the structure, deemed necessary as a result of studies, shouldhave been completed. In the interim, a detailed emergency actionplan must be developed and implemented during periods of unusuallyheavy precipitation. Also, around-the-clock surveillance of thestructure must be provided during these periods.
In addition, the dam has a number of problem areas which,if left uncorrected, have the potential for the development ofhazardous conditions and must be corrected within one year.These are:
1. The gates for the low level outlets should be re-paired and made operable.
2. The brush, saplings and debris should be removed fromthe downstream slope. All coniferous trees should be removedwhile larger hardwood trees should not be removed, but shouldbe inventoried and their condition monitored. If a tree dies,the area around the tree should then be monitored for possible
seepage. A program of periodic mowing and cutting should beprovided.
3. All trees and brush on the upstream face should beremoved and periodic mowing and cutting provided.
4. Slope paving stones missing from the upstream faceshould be replaced.
5. The aqueduct and outlet pipelines should be carefully
inspected and their capacity confirmed.
6. Provide a program of periodic inspection and mainte-nance of the dam and appurtenances including yearly operation andlubrication of the reservoir drain sytem. Document this informa- 4tion for future reference. The emergency action plan describedin section 7.1d should be maintained and updated periodicallyduring the life of the structure.
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Eugene 'Brien, P.E.New YoQ No. 29823
Approved by: rZ651. W.M.Smti.
Ci'New York,?trh /gineer
Date: i
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PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM
HEMPSTEAD LAKE DAMI.D. NO. N.Y. 108I D.E.C. NO. 193LONG ISLAND BASIN
NASSAU COUNTY, N.Y.
SECTION 1 - PROJECT INFORMATION
1.1 GENERAL
I a. AuthorityThe Phase I inspection reported herein was authorized
by the Department of the Army, New York District, Corps of Engi-neers by Contract No. DACW 51-81-C-0008 dated 14 December 1981in fulfillment of the requirements of the National Dam Inspec-tion Act, Public Law 92-367, 8 August 1972.
I b. Purpose of InspectionThe inspection was conducted to evaluate the existing
I conditions of the dam, to identify deficiencies and hazardousconditions, to determine if these deficiencies constitute hazardsto life and property, and to recommend remedial measures whereI required.
1.2 DESCRIPITON OF THE PROJECT
a. Description of the Dam and Appurtenant StructuresThe Hempstead Lake Dam is composed of an approxi-
mately 1,200 foot long earth embankment. The crest of the dam( is 74 feet wide and its maximum height above the river is 24
feet. The upstream face of the dam is paved with stone and theupper part of the dam has a slope of IV:lH, while the lower part
r of the dam has a slope of IV:3H. The downstream slope of thedam varies non-uniformly due to highway embankment fill whichhas been placed over the years.
An intake tower located to the left of the centerof the dam contains five gated openings at three different ele-vations. These intakes supply two 36-inch cast iron pipes whichsupply a horseshoe-shaped (6' Wide x 5" High) water supply aqueductwhich passes under the dam. The gates are controlled from a houselocated at the top of the intake tower. Located below the gate-
rhouse within the tower are four uncontrolled spillway openings(6' Wide, 2'-2" High) which discharge into the same aqueduct asthe low level water supply intakes.
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,!1 Ii I b. Location
3 b Hempstead Lake Dam is located on the Mill River inHempstead Lake State Park near the Village of Rockville Centre,New York. Lake Drive near its intersection with Peninsula Boule-vard, passes over the top of the dam.
c. Size ClassificationThe dam is 24 feet high and has a reservoir with a
maximum storage capacity of 2,300 acre-feet and therefore isclassified as an intermediate dam (storage capacity >1,000acre-feet, <50,000 acre-feet).
d. Hazard ClassificationThe dam is in the "high" hazard potential category
because of its location within a developed suburban area andthe close downstream proximity of major highways and residences.
e. OwnershiHempste Lake Dam is owned by the New York City
Bureau of Water Supply. The person to contact is Mr. EdwardConway, Acting Borough Engineer, Queens at 119-45 Union Turn-pike, Forest Hills, New York, 11375, Telephone Number (212)520-3467.
f. Purpose of DamThe dam impounds water as part of the New York City
Water Supply. The water has not been used for this purpose,however, in several years.
g. Design and Construction HistoryThe dam was designed and constructed in 1873 for
the Brooklyn Water Company. The designer and constructorsare not known.
h. Normal Operating ProcedureThere is no normal operating procedure nor records
of past operating procedures.
1.3 PERTINENT DATA
a. Drainage Area, Square Miles 14.9
b. Discharge at Damsite, cfsUngated Spillways InletsMaximum Capacity - Two 36-InchCI Pipes 320
Total Discharge Maximum Pool 320
c. Elevation, Feet Above MSL,USGS DatumTop of Dam 34.0Maximum Pool 34.0
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ISpillway Crest 29.0Invert Water Supply Intake 1 18.0Invert Water Supply Intake 2 18.0Invert Water Supply Intake 3 13.9Invert Water Supply Intake 4 12.5Invert Water Supply Intake 5 12.5
I d. ReservoirLength of Normal Pool (Feet) 5000Surface Area of Maximum Pool(Acres) 183.3
Surface Area of Normal Pool(Acres) 149.4
e. Storage, Acre-FeetReservoir at Spillway Crest 1400Reservoir at Maximum Pool 2300
f. DamType Earth EmbankmentLength (Feet) 1,200Upstream Slope Paved with Stone
Upper lV:IHLower IV:3H
Downstream Slope Varies Non-uniformlyCrest Elevation (MSL) 34Crest Width (Feet) 74Grout Curtain None
Ii Cutoff "Puddled" to El -13(unknown material)
i g. SpillwayType Uncontrolled Overflow
Slots into Outlet WorksSize 4 @ 6 ft wide x.2'2" hichCrest Elevation (MSL) 29Upstream Channel NoneDownstream Channel Horseshoe Aqueduct
6" wide x 5' hiqh
i h. Reservoir Drain and PipelinesUpstream - An intake tower is located on the up-stream face of the dam slightly to the left ofcenter of the dam. There are five intakes at threedifferent elevations (see Table ) which eventuallysupply a horseshoe-shaped aqueduct with a six footwide base and a maximum height of five feet.
Dimensions Invert Elev.Water Supply Intake 1 2'9" W x 3'3" H 18' MSLWater Supply Intake 2 2'9" W x 3'3" H 18' MSLWater Supply Intake 3 2'9" W x 2'9" H 13.9' MSLWater Supply Intake 4 2'9" W x 2'9" H 12.5' MSLWater Supply Intake 5 2'9" W x 2'9" H 12.5' MSL
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1The intake discharges into a common chamber 6 feetx 20 feet. From the chamber, two 36-inch diametercast iron outlet pipes about 38 foot long joint and
K i enter a brick horseshoe-shaped aqueduct. The5, aqueduct can provide discharges into either the
NYC Water Supply System or into South Pond locatedI about 1/4 mile downstream
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5 SECTION 2 -ENGINEERING DATA
3 2.1 GEOLOGY
The records of the owner contain no data on site geology.i However, there is data available in the literature on the gen-
eral geology of the area. The Hempstead Lake Dam is locatedin the northeast portion of the Atlantic Coastal Plain Physio-graphic Province. This province is characterized by sedimentswhich lack a definite coherence. The area around HempsteadLake Dam is characteristic of the south shore of Long Islandexhibiting topography of very low relief and consisting ofglacial outwash plain sediments of clayey sand, sand and graveldeposits. These Quaternary deposits overlie the Magothy Form-ation of the Upper Cretaceous. These are also primarily clayeysand, sand and gravel.
2.2 SUBSURFACE INVESTIGATIONS
jl There are no records of subsurface investigations car-ried out at the site. It is known that the surficial soils inthe vicinity of the Hempstead Lake Dam are glacial outwash plainclayey sands, sands and gravels.
2.3 DAM AND APPURTENANT STRUCTURES
1There are no records or drawings available withregard to the original construction of the dam in 1873.I. There is only a sketch of a typical section and some propertyownership plans. No records are available of the subsequentchanges to the crest width.
2.4 CONSTRUCTION RECORDS
No information has been located in relation to theconstruction of the project. The name(s) of the contractor(s)is (are) unknown.
f 2.5 OPERATION RECORDS
In recent years there has been no regular operation ofthe dam and no records are kept of reservoir operation. Thedam is monitored and routine maintenance is carried out by theLong Island State Park Commission (LISPC). No systematic moni-toring of the performance of the dam is in effect.
2.6 EVALUATION OF DATA
There is sufficient data available to support a PhaseI evaluation of the dam.
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SECTION 3 - VISUAL INSPECTION
I!3.1 FINDINGS
I a. GeneralThe vsual inspection of the Hempstead Lake Dam[ was made on 13 March 1981. The weather was clear and the
temperature was in the low fifties. At the time of the in-spection, the lake level was at two uppermost lowlevel watersupply inlets, El 18, about 11 feet below the spillway crest.
b. DamThe earth embankment appears to be in good condi-
tion. The vertical and horizontal alignment of the crestappears to be good (see Photograph 2 ). The crest width ofthe dam has been widened (to 74 feet) from the original designf width (24 feet) to accommodate a highway.
The upstream slope shows no signs of erosion ordistress. The stone paving is in good condition withonly a few stones missing and some small (3-inch) trees grow-ing near the crest through joints. Additionally, there issome minor sediment buildup on the upstream face near the leftabutment.
The downstream slope of the dam has been alteredas a result of the widening of the crest. The resultingslope is non-uniform with its steepest section on the upperportions of the dam. The downstream slope is completely over-grown with undesirable brush and tree growth with trees of upto 18 inches in diameter. There is no sloughing or subsidence,although local depressions exist due to surface runoff alongvarious footpaths perpendicular and parallel to the slope.No seepage was evident on the downstream slope.
There is no emergency action plan for the project.
c. SpillwayThe visible portion of the overflows and tower which
serve as a spillway are in good condition; it was not possible,however, to ascertain the condition of the tailraces.
d. Outlets and PipelineThe upstream regulating gates of the water supply
intakes and the reservoir drain are not in operating condition.The gates are rusted in position, the two upper gates are openedabout six inches and the other three gates are rusted closed.The operating mechanisms are not operable. It was not possibleto ascertain the condition of the outlet pipes or the brickaqueduct.
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e. AbutmentsThe abutment contacts and the abutments are in good
condition. There does not appear to be any portion of theabutments lower than the crest elevation of the dam.
f. Reservoir AreaThe reservoir area is located within the park bor-
dered on its northern end by the Southern State Parkway. Itis relatively flat land. There are neither slides, rockfallsor sloughing around the reservoir. There are only minor sedi-I: mentation problems visible.
3.2 EVALUATION OF OBSERVATIONS
Visual observations made during the course of the in-spection did not indicate any serious problems which wouldadversely affect the adequacy of the dam and appurtenantfacilities. The following is a list, in order of importance,of problem areas encountered which should be corrected beforefurther deterioration results in a hazardous condition. Appro-
I priate remedies are also included.
1. The gates for all outlets, which are rusted closed,j and are inoperable, should be repaired.
2. Clear all brush, saplings and debris from the down-stream slope. All coniferous trees should be removed whilelarger hardwood trees should not be removed, but should beinventoried and their condition monitored. If a tree dies,the area around the tree should then be monitored for possibleseepage. A program of periodic mowing and cutting should beseprovied. porm proi
3. All trees and brush on the upstream face shouldbe removed and a program of periodic cutting provided.
4. Slope paving stones missing from the upstream faceshould be replaced.
5. The aqueduct and outlet pipelines should be care-I fully inspected and their capacity confirmed.
6. Develop an emergency action plan for the project.
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5 SECTION 4 - OPERATION AND MAINTENANCE PROCEDURES
4.1 PROCEDURES
No written operation and maintenance procedures existfor the project. There is no normal operation of the project.
4.2 MAINTENANCE OF THE DAM
There is no regular maintenance schedule for the dam.The responsibility for day-to-day maintenance of the dam re-portedly belongs to the Long Island State Park Commission Staff.
4.3 WARNING SYSTEM IN EFFECT
No warning system is in effect or in preparation.
4.4 EVALUATION
The overall maintenance of the Hempstead Lake Reservoiris considered inadequate in the following areas:
1. The reservoir outlets are inoperable due to an absenceIof operation and maintenance.
2. Control of trees and vegetation on the downstreamface and to a limited extent on the upstream face.
3. No formal operation and maintenance manuals exist
U for the project.
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II SECTION 5 - HYDROLOGIC/HYDRAULIC
5.1 DRAINAGE AREA CHARACTERISTICS
Hempstead Lake is located in the town of Hempstead,Nassau County, the State of New York (Hydrologic Unit Coder02030102). It is situated in the Hempstead Lake State Parkjust south of the Southern State Parkway. The Hempstead Lakedrainage area, as can be outlined on the USGS quadrangle map, is14.9 square miles. However, as in the adjacent tMeadow BrookI- which has a similar drainage area as the Hempstead Lake basin,it is estimated that only 9.8 square miles of the basin con-tributes to the storm runoff at the lake. The remaining 5.1square miles north of the Northern State Parkway consist mainlyof largely forested estates, and all the precipitation in thisarea, even during intense storms, infiltrates into the highlypermeable sandy ground.
It has been estimated that in the "effective drainagearea", some 32 percent of the area is impervious due to theroads, buildings, etc. &nd that the construction of storageponds, for aquifer recharge, accounts for about a 15 percentrainfall loss. This "effective drainage area" is almost 100percent urbanized and is drained by a number of storm-sewersub-basins, which may or may not discharge within the basin.The detailed evaluation of the impact of these storm-sewers
f on the flood hydrographs is outside the scope of this Phase Iinvestigation.
5.2 ANALYSIS CRITERIA
The Hempstead Lake drainage basin is ungauged. However,the adjacent East Meadow Brook basin is gauged and a unit hydro-graph has been developed for the 10 square mile Hempstead sub-area. It is assumed, for the purposes of this study, that thebasin characteristics are similar enough to transfer this unithydrograph without any alterations. Loss parameters were estimatedinaccordance with U.S.G.S. Professional Paper 627-F (Ref.l) to reflectthe high infiltration capacity of the pervious soil found in this basin.(Initial loss 2.2 inches; constant loss 0.24 inches per hour.) The proba-ble Maximum Precipitation (PMP) was taken fran the National Weather ServiceRyd erological Report No. 33. In accordance with the "RecmuanedGuidelines for Safety Inspections of Da", the adequacy of the spillwayI was analyzed using the Probable Maximum Flood (PHF). A multi-plananalysis was perfomed to test the spillway under the full, 0.75, 0.50and 0.25 PMF.
5.3 SPILLWAY CAPACITY
The spillway at Hempstead Lake is included as part ofthe inlet tower works. The spillway consists of four arched
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openings six feet wide with a maximum height of 26 inches.The four openings have an invert elevation of 29 feet. Thecapacity of the spillway is limited to the capacity of thetwo 36-inch low level outlet pipes (323 cfs).
5.4 RESERVOIR CAPACITY
The normal capacity of the Hempstead Lake is listed as2,700 acre-feet (117.65 million gallons). However, it is esti-mated that the present capacity is about 1,400 acre-feet sincethe construction of the Southern State Parkway, which crossesthrough the original storage area. The computed surchargestorage between the spillway crest elevation (29.0 feet) andthe top of the dam is 140 acre-feet, which is equivalent to
Il approximately 0.17 inches of runoff over the "effective"drainage area.
1 5.5 FLOODS OF RECORD
There are no records available of floods of maximumlake elevations. However, it is reported that the dam hasnot been overtopped in the last 20 years.
5.6 OVERTOPPING POTENTIAL
The potential of the dam being overtopped was investi-gated on the basis of the spillway discharge capacity and theavailable surcharge storage to meet the selected design floodinflows.
The analysis was performed assuming that the lake levelwas at spillway crest elevation (29.0 feet) at the start of theflood event. The computed inflow peak (PMF) is 15,460 cfs. TheHEC-lB computer analysis indicated that the spillway is capableof passing about 2 percent of the PMF without the dam beingovertopped. A summary of the results are as follows:
RATIO (F PF PEAK INFLOW PEAK 0i7TELG OVERIOPPING
1.00 15,460 cfs 15,370 cfs 2.54 ft0.75 11,600 cfs 11,520 cfs 2.09 ft0.50 7,730 cfs 7,610 cfs 1.57 ft0.25 3,870 cfs 3,700 cfs 0.94 ft
5.7 EVALUATION
The dam does not have sufficient spillway capacity topass either the PMF or one-half (1/2) PMF, without overtoppingthe dam. The overtopping of the dam could cause the failure ofthe dam, thus significantly increasing the hazard for the loss oflife downstream. The spillway is, therefore, assessed as "seriouslySlJ inadequate" and the dam is assessed as unsafe, non-emergency.
S-10-
_____ _____ ____
SECTION 6 - STRUCTURAL STABILITY
6.1 EVALUATION OF STRUCTURAL STABILITY
a. Visual ObservationsVisual observations did not indicate any structural
problems with the embankment or appurtenant structures with thereservoir at its present level. There seems to be no adverseconditions which would affect the stability of the dam at the[ present time.
b. Design and Construction DataDesign and construction data is limited to a sketch
of a typical original cross section of the dam. There are nodesign calculations or construction data available.
On the basis of performance, visual inspection aswell as engineering judgment, the embankment and appurtenantstructures appear to be adequate with the reservoir at its pre-sent level.
c. Operating RecordsThere are no operating records kept or available.
There are no records or reports of any operational problemswhich would effect the stability of the dam.
d. Post-Construction ChangesIt is reported that the dam was constructed in 1873 U
as shown on the sketch included in the drawings. Subsequentto the construction, at some unknown date, the crest was widenedto 74 feet. Details of the changes are not available.
Visual observations, performance and engineeringjudgment indicate that the changes do not adversely effect thestability of the dam with the reservoir at its present level.
e. Stability AnalysisThere is no concrete gravity structure, therefore the
recommended Phase I guidelines do no warrant a structural stabil-3 ity analysis.
f. Seismic StabilityThe dam is located in Seismic Zone I and in accor-
dance with recommended Phase 1 guidelines, does not warrantseismic analysis.
I
I -11-
I
A!
3 SECTION 7 - ASSESSMENT/RECOMMENDATIONS
3 7.1 ASSESSMENT
a. SafetyExamination of available documents and a visual
inspection of the dam and the appurtenant structures did notreveal conditions which constitute an immediate hazard to humanlife or property. However, the dam has some deficiencies which
i require further investigation and remedial action.
Using the Corps of Engineers screening criteria forreview of spillway adequacy, it has been determined that thedam would be overtopped for all storms exceeding approximatelytwo percent of the PMF. The overtopping of the dam could causethe erosion of the abutments and the downstream face of theI dam resulting in dam failure, thus significantly increasingthe hazard for loss of life downstream. The spillway is there-fore adjudged as "seriously inadequate" and the dam is assessedas unsafe, non-emergency.
The classification of "unsafe" applied to a dam be-cause of a "seriously inadequate" spillway is not meant to con-note the same degree of emergency as would be associated withan "unsafe" classification applied for a structural deficiency.It does mean, however, that based on an initial screening andpreliminary computations, there appears to be a serious defi-ciency in spillway capacity so that if a severe storm were tooccur, overtopping and failure of the dam would take place,significantly increasing the hazard to loss of life downstreamfrom the dam.
b. Adequacy of InformationThe information and data available were adequatefor performance of this investigation, except as noted in Sec-I tion 6.1c.
c. Need for Additional InvestigationsSince the spillway is considered to be "seriously
inadequate", additional hydrologic/hydraulic investigationsare required to more accurately determine the site specificcharacteristics of the watershed. After the in-depth hydrologic/
£ hydraulic investigations have been completed, remedial measures* must be initiated to provide spillway capacity sufficient to
discharge the outflow from the one-half (1/2) PMF event.
11 d. UrgencyThe additional hydrologic/hydraulic investigations
which are required must be initiated within 3 months from thedate of notification. Within 12 months of notification, remedialmeasures as a result of these investigations must be initiated,
-12-
I"
with completion of these measures during the following year.In the interim, develop an emergency action plan for the noti-fication of downstream residents and proper governmental auth-orities in the event of overtopping, and provide around-the-clock surveillance of the dam during periods of extreme runoff.The other problem areas listed below must be corrected withinone year from notification.
7.2 RECOMMENDED MEASURES
1. The gates for all low level outlets should be madeoperable.
2. Clear all brush, saplings and debris from the down-stream slope. All coniferous trees should be removed, whilelarger hardwood trees should not be removed but should be in-
ventoried and their condition monitored. If a tree dies, thearea around the tree should then be monitored for possibleseepage. A program of periodic mowing and cutting should beprovided.
3. All trees and brush on the upstream face should beremoved and periodic mowing and cutting provided.
4. Slope paving stones missing from the upstream faceshould be replaced.
5. The aqueduct and outlet pipeline should be carefullyinspected and their capacity confirmed.
6. Provide a program of periodic inspection and mainte-nance of the dam and appurtenances including yearly operationand lubrication of the reservoir outlet system. Document thisinformation for future reference. The emergency action plan
Idescribed in Section 7.1d should be maintained and updated
IIperiodically during the life of the structure.
I,I
'1 -13-
I
[i5
rI
I
I DRAWINGS
iI
[
I
• II APPENDIX A
IlI II I I l I lii I;i ll -
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aren
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all
rk.ep
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oil
V3
7.
-Js
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S .LYU IOOK, N.Y. QUADPREPORT, N.Y. QUADarIcK SILLE, N.Y. QUADSEA CLIFF, N.Y. QUAD
~TOPOGRAPHIC M4AP
HEMSPSTEAD LAKE DAM4
ab
0
II,
001, N.Y. QUADOfRT, N.Y. QUADVILLE, N.Y. QUADLIPT, N.Y. QUAD
TOPOGRAPHIC MAPSTEAD LAKE DAM
'04
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i
II
PHOTOGRAPHS!i!I
*II.APPENDIX B'
7.
2.VEIFCET OKN OADRIHIBUMN
Fl
1 23. VIEW OF CPSREMSD OOKN TOAD
Iv
I
I
UJ
II
II
I.Ii[
{[5. VIEW OF UPSTREAM FACE LOOKING TOWARDS2
LEF ABUMEN FRoM GATEoUsE
I a,
I
IJ
I
6. VIEW OF DOWNSTREAM FACE OF DAM
I,
7. OUTLET OF AQUEDUCT FROM HEMPSTEAD LAKE
AT SOUTH POND
.1 *
:1:
1 8. VIEW OF GATE-HOUSE SHOWINGEMERGENCY SPILL-f OVER INLETS
VI
i
I
II1
fi 9. VIEW OF SPILLOVER INLETS AND INTERIOR OF
i INTAKE STRUCTURE
I . . . . ll l
I[
1
10. CONTROL VALVES FOR GATES (TWO RIGHT GATES)
Ii
} 11. CONTROL VALVES FOR GATES (TWO LEFT GATES)
itt'-it' - - 4 *& -K'-
I
II
I Lj
1I1III
12. TWO UPPERMOST LOW LEVEL WATER SUPPLY INLETS
IIII-r[I
1~rIi
I
I..,
IIII
•i
I VISUAL INSPECTION CHEcKLIsT
I
II.
I. APPENDIX C
I
' - a T" . .. . K ,3 I ' VISUAl. INSM'rC I rON mCi Kr.TST
Basic Data
a.. General
Name of Darn /anoe-I-Fed.I.D. DEC Dam No. 234' /9 3
River Basin L0114 rs/'t/
ILocation: Town lfg4gjlllle Citre county F4 .ssd.LL
Stream Name , I
Tri Aary of ----------
Latitude (N) 7'-4'A V Longitude (W) 73- 3B,
Type of Dam Zar_
I Hazard Category /, H ,
Date(s) of Inspection /I rcI A /3, /?9/
Weather Conditions t ,l J - T"n,/. /v ,. t-
I .Reservoir Level at Time of Inspection
b. Inspection Personnel /1-1V:ev - - rt 7-e n
[ e.. Persons Contacted (Including Address & Phone No.) i ,4 r 47- So.
Al 5-2 / Co.'7v V/
I c. History:
Date Constr.'...tcd JX S r1 Date(s) licconstructed________
Constructed by .kJn+ knJ.. r,
Ov'er a J rcJork C;,,+Sheet I
r tlankm(nt
a. Characteristics
(1) nbankment /aterial "fa f) Wdl(
(2) Cutoff Type Lk eii4,16A /rnevr/ W-1 9,'~k7 ,J"
()Impervious Core A&Y o
[ (4) Internal Drainage System 4 e.
-)Miscellaneous. -
b. Crest
(1) Vertical Alignment '.f , /
(2€ ) _ _" _ _ _ __-_ _,_e()Horizontal Aligniment _ _______
(3) Sur a 'OeaS . Az' n/6/e
(4) Miscellaneous (re( A*/? 'rf7f-,k, .
0 C.: Upstream Slope
(1) Slope (Estimate) (V:11 9,2124-cr h /Y,' Zw"O f- /.':(2) Undesirable *Growth or Debris, Animal Burrows
(3) Sloughing, Subsidence or Depressions AID -- n..EWle
She
11I I-
I (4I) Slope Ptotcction , e-'/ /
* .I -jeg "a O1 y0;L
(5) Surface Cracks or Movement at Toe
4. Downstream Slope
(1) Slope (Estimate - V:H) .
Udesirab].e Growth or Debris, Aninal irrows FI ez&a&fO)I r ~Wjk bru ,.
(3) Sloughing, Subsidence or Depressions j /au A, or n--/c ..
4 *-* I a
(iSurface Cracks or Movement at -Toe _____________________
I"5) Seepage ,A/ e A
I.(6) External Drainage System (Ditches, Trenches; Blanket)
(7) Condition Around Outlet Structureo7 o . -/., .-
(8) Seepage Beyond Toe A/C.P- 'ed/deW "
e. Abutments -Embankmcnt Contact
il"Sheet 3
1 (1) Erosion at Contact _______________________
(2) Seepage Along Contact _ J _ __ __-_
II
- I3) Drainage System
a. Description of System AImi1 o
[ b. Condition of System _ __0___--_
c a. Discharge from Drainage System AJ 'o -.
[ 4) Instrumenttion (omrunentation/Surve'ys, Observation Wells, Weirs,Piezometers, Etc.) A _ 1 _ _ _ _ _ -e__
Shoot 4
i
a. Slopes leey /W.'j I re-/l,, In e* ge; - A'/r &~
b. Sedimentation d.-e.. 4.eS~"/~ ,00
a.Unsul onditions Which Affect Dwn Info& /
6)Area Downstrean 'of Dam
a.* Downstream HIazard (No. of Homes, W ighwzys,.etc.) /,'k~D*,-
b. r7A
c.* Evidence of Movemn.ent B~eyond Toe of Dam Ar7~..
d. Coudition of Dovnstrearrn Channel Az4 1 Miri
[7) S1 4llwav(s) _(Includinr flischnr~e Convevance Channel)
d1_5 f.~ .- ',i X0 w<e& Z.rA 4 ee
1 *. Gcneral C a1A;7; ,P/O e-6-14 lrel,?/.J
b. Condition, of Sprvice Spillway 4- kP C3
SheetS5
" M
e . Condition of Auxiliary Spillway AIef
IId.' Condition of Discharge Conveyance Channiel td /6,/,
-P 41 Sg' 4 .VI
Reservoir Drain/Outlet
Type: Pipe ______Conduit ______other
Material:* Concrete Metal Other ___rc______
S size.:. /# 'Y/1/,WLength ttik,,,C,,)x', Lr : Y&M I/ rn n, ro
Invert Elevations: Entrance -- ' -/0,4r7) Exit 25 '
I Physical Condition (Describe): Unobservable
Material.: 0k1 5 I/'S;A /e
Joints: Alignment
[ Structural Integrity: _____________________
I. Hydraulic Capability: _____________________
Means, of C<,.t,.olG.t , Gate ..
Mean ofCo'lro: ~Vale- Uncontrolled _
[ Operation: Opcrnblc ____ Inolpcrnblc i Other _____
Present Condition (Dcscribe): 600.,, .o e oM ,, , ,4,.'rods ,'',s,.-j. eA4.. , o= ,+ .. i
II . Sheet 6
r4. " "77 l
.9) Stmichmal. .
C Concrete Surfaces WAe gk~ 7 vd -
b. Structural Cracking s''e I 7, t%_ _ _
a. Movemcnt- Horizontal & Vertical Alignent (Settlement) ,_ __
d. Junctions with Abutmn.n s or Dr.!nkmt.its , __
I. .
e . Drains - Foundation, Joint, race_________________
f. Water Passages, Conduits, Sluices S ._________I
[
Seepage or Leakage 'r '
iiS* .. S *.•~t
0* _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
• See:'
_ -. v . , - .,
f Joints- Constriction, etc. 7;.j ameY -
1. Foundation ,IJO-
I
j.Abutments'
[k. Control Gates _-- ,t,',. ,
1. Approach & Outlet Channcls ._, • c cxs4!
in. Ener Dissipators (Plunge Pool, etc.) ;/__ _ _
Uln. Intake Structurcs ' -e Ito .-S C A o-AA.I I
Ii
Io. Stability . ,] r'
p. Miscellameous •N-1__
ia•. . Shet 8 ,
S..
I 10) Ap rtenant Structures (Powerhouse,Lock,GatehouseOther)
a. Description and Condition J/et, re a .
I
I
I .I.I1
i
IiiI"1#
I. / )g.rIA fW.•
i,.," I m e i iII II IW
II
[S [
HYDROLOGIC DATA AND COMPUTATIONS
I.
I APENI D
CHECK LIST FOR DAMSHYDROLOGIC AID IIYDIAULIC
ENGINEERING DATA
LAREA-CAPACITY DATA:
I Elevation Surface Area Storage Cipacity(ft.) (acres) (acre-ft.)
1 1) Topof Dami *3 0 7.3r 2) Design High Water
(Max. Design Pool)
3) Auxiliary Spillway
4) Pool Level with .1Flashboards _ __--_ _
5) Service Spill-ayCrest + . 0 P-Is HOO
DISCHARGESVolume-(cfs)
1) Average Daily n knr u.v
I. 2) Spillway @ Maximum High Water
[ . ) Spillway @ Design High Water knp0u-own
4) Spillway @ Auxiliary Spillway Crest Elevation LA-^k,__, _
75) Low Level Outlet WV-k rm ,
6) Total (of all facilities) @ Maximum High Water Q.1,H o., - + ."' B Mximum Known Flood _L,.Aleft0 toY
[ 8) At Time of Inspection
I
CREST: ELEVATION:- 3_ _
I ~Type: ~2~ ~~~ct
[ Width: '7V -6Lengtil: /D
$pllover. ?4 je r O-TL. T (WO0RK
I Location TDTi -' eA-
I SPILLWAY:
SERVICE AUXILIARY
(6 A&J Elevation - zqD
____________________ Type 4 ~ 'Ce/e
Width . X /
Type of Control
I Uncontrolled _
Contro led:
_Type
(Flashbcards; gate)i Number
Size/Length
Invert Material
Anticipated Lengthof operating service
_ _.. .. _ Chute Length M +6-- KP1 o c./Y
Height Between Spillway Crest _--/_" _"
( .& Approach Channel Invert
I; (Weir Flow)
I .
ii
- "
HYDROMETEROLOGICAL GAGES: )jo V 44..i , 0 r , cJc.L.
Type
1Location:Records: 0)o0,N UAIL AQ'.
Date -
Max. Reading -
I FLOOD WATER CONTROL SYSTEM:
" Warning System: __
Method of Controlled Releases (mechanisms):
Lo. Le,e A o tx-I'J Is TowTer-- ,v't tA
II.i.
ill]..
DRAINAGE AREA: _____________________________I DRAINAGE BASIN RUNOFF CHARACTERISTICS:.
' I Land Use - Type: ___ ....
'[ Terrain R'elief: F!-+
Surface -Soil: - ' Ii "pr,-cJ l 'I7, a- 0;/
Runoff Potential (existing or planned extensive alterations to existing(surface or subsurface conditions)
Jy SuiA f4 Al ~ e ~ ~ ~ n
Potential Sedimentation problem areas (natural or man-made; present or future)
1 Potential Backwater problem areas for levels at maximum storage capacityIncluding surcharge storage:
I .VkLOC J, 4c s4iaa LLCer S e r u 0 0 ILI
+K, We oseu
Dikes Floodwalls (overflow & non-overflow ) - Low reaches along theReservoir perimeter: S
Loca tion:
Elevation: . .. ..
I "" Reservoir:
" Length e Maximum Pool (i l O eiles)
Length of Shoreline (@ Spillway Crest) 2.7 (Nles) ,
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II REFERENCES
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APPENDIX E
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References
1 1. "Summary of the Hydrologic Situation on Long Island, NewYork, as a Guide to Water-Management Alternatives", AU.. S. Geological Survey Professional Paper 627-F, 1972.
2. "Seasonal Variation of the Probably Maximum Precipitation,East of the 105th Meridian for Areas from 10 to 1,000Square Miles, and Durations of 6, 12, 24, and 48 Hours",Hydrometeorological Report No. 33. Weather Bureau, U. S.Department of Commerce, April 1956.
3. "Effects of Urban Development on Direct Runoff to EastMeadow Brook, Nassua Coutny, Long Usland, New York",U. S. Geological Survey Professional Paper 627-B, 1969.
4. "Flood Hydrograph Package (HEC-1) Users Manual for DamSafety Investigations", U. S. Army Corps of Engineers,Hydrologic Engineering Center, September 1979.
5. "Lower Hudson River Basin Hydrologic Flood Routing Model",for New Yoek District Corps of Engineers, Water ResourcesEngineers, Inc., January 1977
6. "Standard Project Flood Determination", EM-1110-2-1411,Army Corps of Engineers, Washington, D.C., Rev. 1965
7. "Probable Maximum Precipitation Estimates, United StatesEast of the 105th Meridian", Hydrometeorological ReportNo. 51, National Weather Service, June 1978.
8. "National Program of Inspection of Dams", Vol.3, Depart-ment of the Army, Office of the Chief of Engineers, 1975.
9. "Flood Hydrograph Analyses and Computations", EM-1110-2-
1405, U. S. Army Corps of Engineers, August 1959
10. "Recommended Guidelines for Safety Inspection of Dams",Department of the Army, Office of the Chief of EngineersAppendix D.
11. "Water Resources Data for New York, Vol. 1" 1979. U. S.Geological Survey Winter-Data Report NY-79-1.
12. The University of the State of New York, The StateEducation Department State Museum and Science ServiceGeological Survey - MAP and Chart Serves No. 5, GeologicMAP of New York 1961, Lower Hudson Sheet.
13. Schuberth, Christopher J., The Geology of New York City[and Environ., a968, The Natural History Press, N.Y.
I 1
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11
IIII OTHER DATA
ii
III[III S
~APPENDIx F
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*Ij PA Cit: /%, PA. NO.; E2.: USE)
* 1j11s1Xtf S~'W.:yr-1 ;(,os.try ofj
Ij SC LLIC:-%!IL n .Cr~lcks Df IccLlZons
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l ' '' ' "" " 1"95 L U '
S "'STATE OF NEW YORK
DEPARTMENT OF "
"tate Enuiurrr a)ti . rurgt or.1"ALBAINY
[ Report of a Structure Impounding Water
[ -.To assist in carrying out the provisions of Section 22 of the Conservation Law, being Chapter LXV of the
- Consoldated Laws of New York State, rclating to safeguarding life and property and the crection, rcconstruction,
I or maintenance of structures for inpounding water. owncrs of such structures are requested to fill out as completely
as possible this report form for each such dam or reservoir owned within the State of New York for which no plans
or reports relative thcrcto arc on file in this Department, and to return this rTp ort form, together wth prints or
photograplas explanatory tlcrrof to this dcpartment. I"- 11.Zps't01ak Stora-e Reservoir
z. The structure is on.Iie pstes&...td..e ..... ... flong ................ :.in the
T o w n o . . .e . t e d ... . . . . . ... ..... ... .C o u n t y o f .. .. . .. .I .. .. .. ... 2. .. ...... ...... ............... .. 3. .. ... . N ~ .: . .y . ..... .. .. .. .. ...... . .,
... halfw.y bet.een Rocville Center and .e.sted................(Give exact dstance and ditc ..n iron a wll-kn.v.n bndage. dam. 'illa^ main r., wr..,ik ,a nw-th d a tr.m)
2. Is any part of the structurc built upon or does its pond flood a,,y State lands? ........ ].]...t .................................... .
3. The name and address of the ownecr is ..The.. Ci.ty of llel York.............. ........... ... .......................... ... . .......................... .............
4. The structure is used for.i-mp und.in ,wat e r ..for. .v-t.r upp-. ..
. 5. The material of the right bank. in the direction with the current, is ........ . ...... ........... ;at the
spilhay crest elevation this material has a top slope of ......... inches vcrticiil to a foot horizontal on the
IT center line of the structure, a vertical thickness at this elevation of ..................... .ect, and the top surface extenels
for a vertical height of ............................ fet above the sjiillway crefl.
[ 6. The material of the left bank is ............................. ........ _; has a top slopc of ........................... inches
to a foot horizontal, a thicknuss of ....................... fet and a height of ................... feet.
7. The natural maltcrial of tle be on which tlte stntetuare rests is (cl!,y. %aMd. gravel. 1%irs I', granite, shale.
slate, limcstone. etc.).. .. nd ind gravel ........ .............................................
rill. °.. .o...o...o... ... ........... o ... .. . ........... ° . ooo..... . o...o.. o . .. .. . .... .. o.. ... .. ..... .... .... ......... ..
. ................ ...................... . .....................
L . State the c'racter (if the be and th banks in nrespect to the har-lated &wrvimusncis. water bearing.of exposure to air and to water. unifurnity. etc -.-- . ... ..
... ..
4r' m,=,m
" • - If the bed is in layers. die layers horizontal or inclinedl ...... If inclined what is the
direction of the horizontal outcropping relative to the axis of the main structure and the inclination and direction
cithe iayers in a plane perpendicular to the horizontal outcrupping?. ..... .
. .. .. . .. ......
o. What is the thickness of the layers'.........-......
it. 'Are there any porous scams or ............. ...... ... . .............
.s The watershed at the above structure and draining into the pond formed thereby is.......... square miles.
z3. The pond area at the spillway crest elevation is.... !.........acres and the pond impounds... 4 7 .... 4 .7 OC 9
'cubic feet of water.
14. The maximum known flow of the stream at the structure was.._ __...............cubic fct per second on! -i.iS. 'Has the spillway capacity evcr been exceeded by a high flow? _.................
Can anypossible flood flow.rom the pond otherwise than through the wastes noted under 17 and i8 of this
j repo ?.. .... .If so, give the Iccation, the length and the e!c.ation relative to the spillway crest and the
character and slopes of the ground of such possible wastes ............................................................
....................-.................- - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
6. State if any damnage to life or to any buildings, roads or other property could he cau.ed by any .4dkfailure of the above structure. Describe the location, the character and the use tf buildings bel-ow the structurewhich might be d.r.agcd by any failure of the structure; of roads adjacent to or crossing the stream bc!ow te
' structure, giving the lowest clevation of the roadway above the stream bed and giving the shape, the heilgh and thewidth of stream openings; and of any emliankments or steep slopes that any flocxl could pas.s over. Also indicate
the character and use macc of the ground below the structure.......... ........ ................ ....
.Ifthe dam should fail considerable damage.would be done to '.he
Long...Island Railroad to t ie City.!s...pipe lines. and to ...t."I .h.elo r. parts ....
of..Rq.kvi.l.e.. C.enter... ... .. ... ........................ ......... ......
...... . . ................................ ................ .................. ..o .................. .................................................................. ...........
&7. WAST'S. The spillway of the :lovc strueture is ............... feet lom:g in the rl,; Llic waters atc
. old at the right end by ...................... ......... the top of which i ............... f.. L al'ove Ot, SpiliwayMot and has a tup width of ................ ft and at t left end by -L ............. ...... the
top of which is_... .fcct above the spillway crest, and has a top width of ............ .-... fcet.
IlL Tlher'is alsio for flooildischarge a pe.. . ... italihtle din' jt. "r)n4.thc lxitto an is .. ............
feet below the spilhway crest; awl a (sluice, gate oulCL). ............... t wid in the cle-r by...................................... . ..... •.......
feet high, and the bottom i .. . Jco t below the spillway crest. ". .. "
....
i ] ,. -
no9. ArOaN. Delow the spillway Ihere is z apron bilt of .................................................
feet widc and....................... feet thick. The downstream side of the apron has a thickness o.feet
*for a width nf.... ...................... fcqt.
2o. Ias the structuri' af w*venkti.e.sLs which are liable to cause its failure in high flows? ......
2a. SKc(Iesi. On te bgwk (of tI'i rt|port makc a sketch to scalc for each different cruss-setion of the above
structure ithe grvtc:t-'t dlth: riih: w h-iglt an the dkq~ti fnmi the smifam' ti tie f.,ndnt iom. the bttomn width,
tile t widilh (fur t .'-rf i ,,r i n:, ,iry .%I iilway at two fort I el,,w tlw er-..). the r!,vaiti,it tif the top in rurc, ice
to the spillway crrst, the I.caijth of tile .'ctiti'u, and tilL material of vhich the s.ct itu i:; cmstructed; on the spillway
s' cction show a cross sictio(n, f the :proi., giving its width, thickness and matcrial, and show the abutment or -vash
'mall at the end if the spifway, giving.- its lIrihts and thickness. Mark c:,ch secticin with a capital letter. Also
sketch a plal; show the alo-c nctilm 1,3- thcir top lines. giving the mark and the entgth of m ch; the opening,' by
their horizontal dinunsiis; the nlutnmits lv thi.r top width and to) k.,,.ths from the rpstrvam face of the spill-
way section; and outline the apron. Also sketch in elf:vation of each end of t.-c structure with a crosS section .of
the banks, giving the dtpth and width exca'ateu, into the banks.
22. WATER SU'P'P.'. Th'. Wts impounded by the above structure hnvc £e€ been used for a public water
supply since .... 1y........... t.Ci ty ..o._ew...York ..................................................ii 4
!..
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.-.. oU, . 6... .
.. .... .... .... ... ... .. .. ". .. .. " " .. .".. ... . .... ......................... .... ......... .... ..
J " , •• :
7
For profiEs of the.&dnu of the Hempstead Reservoir see print attached
Tb'aoe nfwatoni crrc t tebet fmykn~ euev see prI attied
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I ?Lncpa u dn Ie/ok* eWruary 192°5 Chief i ngincer Bureau of Water Supp'.
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