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+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

* MCP Application Notes: * * * * 1. Character(s) preceded & followed by these symbols (.-) or (+,) * * are super- or subscripted, respectively. * * EXAMPLES: 42m.3- = 42 cubic meters *

* CO+2, = carbon dioxide * * * * 2. All table notes (letters and numbers) have been enclosed in square* * brackets in both the table and below the table. The same is * * true for footnotes. *

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

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ACI 210.1R-94

Compendium of Case Histories on Repair of

Erosion-Damaged Concrete in Hydraulic Structures

Reported by ACI Committee 210

Stephen B. Tatro

Chairman

Patrick J. Creegan Angel E. Herrera James E. McDonaldJames R. Graham Richard A. Kaden Ernest K. Schrader

This report is a companion document to ACI 210R. It contains a series of

case histories on hydraulic structures that have been damaged by erosion from

various physical, mechanical, and chemical actions. Many of these structureshave been successfully repaired. There were many examples to select from;

however, the committee has selected recent, typical projects, with differing

repair techniques, to provide a broad range of current experience. These

case histories cover only damage to the hydraulic surfaces due to the action

of water, waterborne material, or chemical attack of concrete from fluidsconveyed along the hydraulic passages. In addition to repairs of the damaged

concrete, remedial work frequently includes design modifications that are

intended to eliminate or minimize the action that produced the damage. This

report does not cover repair of concrete damaged by other environmental

factors such as freeze-thaw, expansive aggregate, or corroding reinforcement.

Keywords: abrasion; abrasion resistance; aeration; cavitation; chemical

attack; concrete dams; concrete pipes; corrosion; corrosion resistance;

deterioration; erosion; grinding (material removal); high-strength concretes;

hydraulic structures; maintenance; outlet works; penstocks; pipe linings;

pipes (tubes); pittings; polymer concrete; renovating; repairs; sewers;

spillways; tolerances (mechanics); wear.

CONTENTS

Chapter 1 - Introduction

Chapter 2 - Cavitation-erosion case histories

Dworshak Dam

Glen Canyon Dam

Lower Monumental Dam

Lucky Peak DamTerzaghi Dam

Yellowtail Afterbay Dam

Yellowtail Dam

Keenleyside Dam

Chapter 3 - Abrasion-erosion case historiesEspinosa Irrigation Diversion DamKinzua Dam

Los Angeles River Channel

Nolin Lake Dam

Pine River Watershed, Structure No. 41

Pomona Dam

Providence-Millville Diversion StructureRed Rock Dam

Sheldon Gulch Siphon

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Chapter 4 - Chemical attack-erosion case histories

Barceloneta Trunk Sewer

Dworshak National Fish Hatchery

Los Angeles Sanitary Sewer System and

Hyperion Sewage Treatment FacilityPecos Arroyo Watershed, Site 1

Chapter 5 - Project reference list

o ACI 210.1R-94 became effective Nov. 1, 1994.o Copyright 1994, American Concrete Institute.

o All rights reserved including rights of reproduction and use in any form

or by any means, including the making of copies by any photo process, or by

any electronic or mechanical device, printed, written, or oral, or recording

for sound or visual reproduction for use in any knowledge or retrieval system

or device, unless permission in writing is obtained from the copyrightproprietors.

ACI Committee Reports, Guides, Standard Practices, and Commentaries are

intended for guidance in designing, planning, executing, or inspecting

construction and in preparing specifications. Reference to these documentsshall not be made in the Project Documents. If items found in these documents

are desired to be part of the Project Documents they should be phrased in

mandatory language and incorporated into the Project Documents.

CHAPTER 1 - INTRODUCTION

This compendium of case histories provides information on damage that hasoccurred to hydraulic structures and the various methods of repair that have

been used. ACI Committee 210 has prepared this report to help others

experiencing similar problems in existing work. Knowledge gained from these

experiences may help avoid oversights in design and construction of hydraulic

structures and provide guidance in the treatment of future problems.

Erosion of concrete in hydraulic structures may occur as a result of

abrasive action, cavitation, or chemical attack. Damage may develop rapidly

after some unusual event such as a flood or it may develop gradually during

normal continuous operation or use. In most cases where damage has occurred,

simply replacing the eroded concrete will ensure immediate serviceability,but may not ensure long-term performance of the structure. Therefore, repair

work usually includes replacing eroded concrete with a more resistant

concrete and additional surface treatment, modifying the design or operation

of the structure to eliminate the mechanism that produced the damage, or

both. A detailed discussion of mechanisms causing erosion in hydraulic

structures, and recommendations on maintenance and repair, is contained inACI 210R.

When damage does occur to hydraulic structures, repair work poses someunique problems and is often very costly. Direct access to the damaged area

may not be possible, or may be limited by time, or other constraints. Insome cases, such as repair to spillway stilling basin floors, expensive

bulkheads and dewatering are required. It may not be possible to completely

dry the area to be repaired or maintain the most desirable temperature. A

great deal of planning and scheduling for repair work are normally required,

not only for the repairs and access, but also for control of water releases

and reservoir levels. If time permits, extensive investigation usuallyprecedes planning and scheduling to determine the nature and extent of

damage. Hydraulic model studies may also be necessary to evaluate possible

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modifications in the design or operation of the facility.

This compendium provides the history on 21 projects with hydraulic erosiondamage. They vary in size and cover a variety of problems: 8 with cavitation

damage, 9 with abrasion-erosion damage, and 4 with erosion damage from

chemical attack. Table 1.1 summarizes the projects. Each repair was

slightly different. Each history includes background information on the

project or facility, the problem of erosion, the selected solution to theproblem, and the performance of the corrective action. Histories alsocontain references and owner information if further details are needed.

CHAPTER 2 - CAVITATION-EROSION CASE HISTORIES

DWORSHAK DAM

North Fork, Clearwater River, Idaho

BACKGROUND

Dworshak Dam, operational in 1973, is a straight-axis concrete gravity dam,

717 ft high, 3287 ft long at the crest, and contains 6,500,000 cubic yards of

concrete. In addition to two gated overflow spillways, three regulatingoutlets, 12 ft wide by 17 ft high, are located in the spill-way monoliths.

The inlet elevation for each regulating outlet is 250 ft below the maximum

reservoir elevation. Each outlet jet is capable of a maximum discharge of

14,000 ft.3-/s.

Outlet surfaces are reinforced structural concrete placed concurrently with

adjacent lean, large aggregate concrete. Coatings to the outlet surfaces

were applied during the original construction. In Outlet 1, the wall and

invert surfaces from the tainter gate to a point 50 ft downstream are coated

with an epoxy mortar having an average thickness of 3/8 in. The same area of

Outlet 2 was coated using an epoxy resin, approximately .05 in. in thickness.Outlet 3 was untreated.

The outlets were operated intermittently at various gate openings for a

period of 4 years between 1971 and 1975, resulting in a cumulative dischargeduration of approximately 10 months. The three outlets were not operatedsymmetrically; outlets 1 and 2 were used primarily.

PROBLEM

Inspection in 1973 showed minor concrete scaling of the concrete wall

surfaces of Outlets 1 and 2. One year later, in 1974, serious erosion had

occurred at wall surfaces of both outlets immediately downstream of the wall

coatings, 50 ft from the tainter gate. Part of this wall area had eroded toa depth of 22 in., exposing and even removing some No. 9 reinforcing bars.

In the wall surfaces downstream of Outlet 1 medium damage, up to 1 in. depth

of erosion, also occurred in over 60 square yards of surface, bordered by

lighter erosion. Every horizontal lift joint (construction joint) along the

path of the jet, showed additional cavitation erosion.

SOLUTION

Repairs were categorized as three types:

o Areas with heavy damage, with erosion greater than 2 to 3 in., were

delineated by a 3-in. saw cut and the interior concrete excavated to aminimum depth of 15 in. (Fig. 2.1 and 2.2). Reinforcement was re-

established and steel fiber-reinforced concrete (FRC) was used as the

replacement material.

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o Areas with medium damage, where the depth of erosion was less than 1 in.,

were bush-hammered to a depth of 3/8 to 1 in. and dry-packed with mortar.

The mortar, if left untreated, would easily have failed when subjected tothe high velocity discharge.

o Areas with minor damage, surfaces showing a sandblast texture, were not

separately treated prior to polymer impregnation. The entire wall

surfaces of Outlet 1 were then treated by polymer impregnation from thedownstream edge of the existing epoxy mortar coating to a distance 200 ftdown-stream.

TABLE 1.1

SUMMARY TABLE OF PROJECTS COMPRISING THIS REPORT

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))))))))))))))))))))))))))))))

Year

Reference

Project name completed Type Location Owner Problem

Repair type page

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Dworshak Dam 1974 Gravity dam Idaho Corps of

Cavitation Polymer 210.1R-2

Engineers

impregnation

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Glen Canyon Dam 1964 Arch dam Arizona Bureau of

Cavitation Aeration 210.1R-5

Reclamation

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Lower Monumental 1969 Navigation Washington Corps of

Cavitation Epoxy 210.1R-6

Dam lock Engineers

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

Lucky Peak Dam 1956 Outlet Idaho Corps of

Cavitation Various 210.1R-8

structure Engineers

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Terzaghi Dam 1960 Outlet British B.C. Hydro

Cavitation Hydraulic 210.1R-9

structure Columbia Authority

redesign

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))))))))))))))))))))))))))))))

Yellowtail 1966 Stilling Montana Bureau of

Cavitation Various 210.1R-11

Afterbay Dam basin Reclamation

overlays

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))))))))))))))))))))))))))))))

Yellowtail Dam 1966 Stilling Montana Bureau of

Cavitation Aeration and 210.1R-11

basin Reclamation

overlays

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Keenleyside Dam 1968 Outlet British B.C. Hydro

Cavitation High-strength 210.1R-12

structure Columbia Authorityconcrete

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))))))))))))))))))))))))))))))

Espinosa 1984 Diversion dam New Mexico Soil Conser-

Abrasion Steel plate 210.1R-13Irrigation vation

armor

Diversion Dam Service

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))))))))))))))))))))))))))))))

Kinzua Dam 1965 Stilling Pennsylvania Corps ofAbrasion Silica fume 210.1R-15

basin Engineers

concrete

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))))))))))))))))))))))))))))))

Los Angeles River 1940s Channel California Corps ofAbrasion Silica fume 210.1R-17

Channel Engineers

concrete

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))))))))))))))))))))))))))))))

Nolin Lake Dam 1963 Stilling Kentucky Corps ofAbrasion Hydraulic 210.1R-18

basin Engineers

redesign

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Pine River Proposed Channel Colorado Soil Conser-

Abrasion High-strength 210.1R-19

Watershed, vation

concrete

Structure No. 41 Service

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Pomona Dam 1963 Stilling Kansas Corps of

Abrasion Various 210.1R-20

basin Engineers

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Providence- 1986 Diversion dam Utah Soil Conser-

Abrasion Surface 210.1R-22

Millville vation

hardener

Diversion ServiceStructure

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))))))))))))))))))))))))))))))

Red Rock Dam 1969 Stilling Iowa Corps of

Abrasion Underwater 210.1R-23basin Engineers

concrete

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Sheldon Gulch 1991 Syphon outlet Wyoming Soil Conser-

Abrasion Polymer- 210.1R-25Siphon vation

modified

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Service

mortar

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Barceloneta Trunk 1976 Pipeline Puerto Rico Puerto Rico

Chemical PVC lining 210.1R-25

Sewer Aqueduct & attack

SewerAuthority

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))))))))))))))))))))))))))))))

Dworshak National 1960s Concrete Idaho Corps of

Chemical Linings 210.1R-26

Fish Hatchery tanks Engineers attack

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

))))))))))))))))))))))))))))))

Los Angeles Varies Sewerage California City of Los

Chemical Shotcrete and 210.1R-27

Sanitary Sewer structures Angeles attack

PVC linersSystem and

Hyperion Sewage

Treatment Facility

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))))))))))))))))))))))))))))))

Pecos Arroyo 1988 Outlet New Mexico Soil Conser-Chemical HDPE liner 210.1R-30

Watershed, Site 1 conduit vation attack

and

Service

hydraulic

redesign

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))))))))))))))))))))))))))))))

Damage to the epoxy mortar was minimal and located near the outlet gate.This area was repaired with new epoxy.

The polymer impregnation process involved drying all the surfaces to a

temperature up to 300 F to drive off water and then allowing the surface to

cool to 230 F. Monomer was then applied to the surface using a verticalsoaking chamber. Excessive monomer was drained and the surface was

polymerized by the application of approximately 150 F water.

PERFORMANCE

Operation of the outlets from the time of repair in 1975 until 1982 hasbeen minimal, averaging 1400 ft.3-/s per outlet with peak discharges of 3600

ft.3-/s per outlet. Durations of usage are not known. After 1982 outlet

discharges increased, with durations exceeding 50 days.

Inspections performed in 1976, the year after the repairs, showed noadditional concrete damage except for some minor surface spalling adjacent to

a major pre-existing crack in an area of drypacked mortar. The spalled area

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Fig 2.1-Dworshak Dam. Detail showing depth of erosion behind reinforcing steel

Fig. 2.2-Dworshak Dam. Extent of outlet surface preparation prior to concrete & mortar placements

was patched with epoxy paste, except that the epoxy paste did not bridge the

crack this time. Epoxy resin coating repairs applied to Outlet 2 showedsome failures.

Inspections in 1983 and 1988 showed that epoxy mortar coatings in Outlet 1

continued to perform well. Small areas of damage, typically spalls, are

periodically repaired with a paste epoxy. Epoxy resin coatings in Outlet 2

are repaired more frequently but are performing adequately. Surfaces

repaired with FRC and mortar and subsequently polymer-impregnated showednegligible damage. Polymer-impregnated parent concrete shows a typical

matrix erosion around the coarse aggregate to a depth of 1/4-in., and lift

joints exhibit pitting up to 3/8-in. deep. Surfaces along lift joints not

polymer-impregnated show erosion up to 3/4-in. in depth and a general

surface pitting greater than the companion polymer-impregnated surfaces.

DISCUSSION

Because of variation in the operation of these outlets, both in flow rate

and duration, exact time-rate erosion conclusions are difficult to make.

Recent outlet discharge has fluctuated annually from moderate flows to none.In general, surfaces that received replacement materials and were

subsequently polymer-impregnated have performed well. Original concrete and

new polymer-impregnated concrete is showing evidence of deterioration, but at

a rate that is less than the unimpregnated surfaces. The best performance

was by the original epoxy mortar coating. The epoxy mortar in Outlet 1

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continues to display an excellent surface condition, with no cavitation-

generated pitting. The epoxy resin coating in Outlet 2 displays good

performance.

In 1988, outlets were modified by adding aeration deflectors, wedges 27 in.

wide by 1.5 in. high, to the sides and bottom of each outlet. These

deflectors were designed to increase the aeration of the discharge jet and

further reduce the cavitation erosion of the outlet surfaces. Subsequentdeterioration of the outlet surfaces has not been observed.

The polymer impregnating of the concrete surfaces of the outlets was a very

complex system of operations. Success requires continual evaluation of

application conditions and flexibility to react to changes in those

conditions. Issues relating to safety, cost, and field engineering addsignificant challenges to a polymer impregnation project. It is doubtful

that this process would be attempted today under similar circumstances. It

is more likely that the aeration deflectors would be the first remedy

considered since they provide a positive solution to the problem without the

higher risks of a failure inherent in the polymer impregnation process.

REFERENCES

Schrader, Ernest K., and Kaden, Richard A., "Outlet Repairs at Dworshak

Dam," The Military Engineer, The Society of American Military Engineers,

Washington, D.C., May-June 1976, pp. 254-259.

Murray, Myles A., and Schultheis, Vern F., "Polymerization of Concrete

Fights Cavitation," Civil Engineering, V. 47, No. 4, American Society of

Civil Engineers, New York, April 1977, pp. 67-70.

U.S. Army Engineer District, Walla Walla, "Polymer Impregnation of Concreteat Dworshak Dam," Walla Walla, WA, July 1976, Reissued April 1977.

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Reports No.

6, 7, and 8, Dworshak Dam and Reservoir," Walla Walla District, Jan. 1985.

CONTACT/OWNER

Walla Walla District, Corps of Engineers

City-County Airport

Walla Walla, WA 99362

GLEN CANYON DAM

Colorado River, Northeast Arizona

BACKGROUND

Glen Canyon Dam, operational in 1964, is a concrete gravity, arch

structure, 710 ft high with a crest length of 1560 ft. The dam is flanked on

both sides by high-head tunnel spillways, each including an intake structure

with two 40- by 55-ft radial gates. Each tunnel consists of a 41-ft diameter

section inclined at 55 percent, a vertical bend (elbow), and 985 ft of nearhorizontal length followed by a deflector bucket. Water first flowed through

the spillways in 1980, 16 years after completion of the dam.

PROBLEM

In late May 1983, runoff in the upper reaches of the Colorado River wassteadily increasing due to snowmelt from an extremely heavy snowpack. On

June 2, 1983, the left tunnel spillway gates were opened to release 10,000

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ft.3-/s. On June 5 the release was increased to 20,000 ft.3-/s. On June 6

officials heard loud rumbling noises coming from the left spillway.

Engineers examined the tunnel and found several large holes in the invert ofthe elbow. This damage was initiated by cavitation, triggered by dis-

continuities formed by calcite deposits on the tunnel invert at the upstream

end of the elbow. In spite of this damage, continued high runoff required

increasing the discharge in the left spillway tunnel to 23,000 ft.3-/s by

June 23. Flows in the right spillway tunnel were held at 6000 ft.3-/s tominimize damage from cavitation. Spillway gates were finally closed July 23,and engineers made a thorough inspection of the tunnels.

Extensive damage had occurred in and near the left tunnel elbow (Fig. 2.3).

Immediately downstream from the elbow, a hole (35 ft deep, 134 ft long, and

50 ft wide) had been eroded in the concrete lining and underlying sandstonefoundation. Other smaller holes had been eroded in the lining in leapfrog

fashion upstream from the elbow.

SOLUTION

The repair work was accomplished in six phases: 1) removing loose anddefective concrete lining and foundation rock; 2) backfilling large cavities

in sandstone foundation with concrete; 3) reconstructing tunnel lining; 4)

grinding and patching of small defective areas; 5) removing about 500 cubic

yards of debris from lower reaches of tunnel and flip bucket; and 6) con-

structing an aeration device in the lining upstream of the vertical elbow.

Sandstone cavities were filled with tremie concrete before the lining was

replaced. About 2000 cubic yards of replacement concrete was used. The

aeration slot was modeled in the Bureau of Reclamation Hydraulic Laboratory

to ensure that its design would provide the performance required.

The aeration slot was constructed on the inclined portion of the tunnel

approximately 150 ft upstream from the start of the elbow. A small 7-in.

-high ramp was constructed immediately upstream of the slot. The slot was 4

by 4 ft in cross section and extended around the lower three-fourths of the

tunnel circumference (Fig. 2.4). All repairs and the slot were completed in

the summer of 1983.

PERFORMANCE

Because of the moderate runoff in the Colorado River since completion of

the tunnel repairs, it has not been necessary to use the large spillwaytunnels.

Fig. 2.3-Glen Canyon Dam. Erosion of spillway tunnel invert & sandstone foundation rock

downstream of the elbow

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However, shortly after completion of the work, another high runoff period

permitted performance of a field verification test. This test lasted 72 hr

with a maximum flow during that time of 50,000 ft.3-/s. The test wasconducted in two phases with several interruptions in each for examination of

the tunnel. Offsets were intentionally left in place to evaluate whether the

aeration slot would indeed preclude cavitation and attendant concrete damage.

The tunnel repairs and air slot performed as designed. No sign of cavitation

damage was evident anywhere in the tunnel. Aeration has decreased the flowcapacity of the spillway tunnels by approximately 20 percent of the originalflow capacity.

REFERENCES

Burgi, P.H., and Eckley, M.S., "Repairs at Glen Canyon Dam," ConcreteInternational, American Concrete Institute, MI, V. 9, No. 3, Mar. 1986, pp.

24-31.

Frizell, K.W., "Glen Canyon Dam Spillway Tests Model -- Prototype

Comparison," Hydraulics and Hydrology in the Small Computer Age, Proceeding

of the Specialty Conference, Lake Buena Vista, Florida, Aug. 12-17, 1985,American Society of Civil Engineers, New York, 1985, pp. 1142-1147.

Frizell, K.W., "Spillway Tests at Glen Canyon Dam," U.S. Bureau of

Reclamation, Denver, CO, July 1985.

Pugh, C.A., "Modeling Aeration Devices for Glen Canyon Dam," Water forResource Development, Proceedings of the Conference, Coeur d'Alene, Idaho,

Aug. 14-17, 1984, American Society of Civil Engineers, New York, 1984, pp.

412-416.

CONTACT

U.S. Bureau of Reclamation

P.O. Box 25007, Denver Federal Center

Denver, CO 80225

LOWER MONUMENTAL DAM

Snake River, Near Kaloutus, Washington

BACKGROUND

Lower Monumental Dam, operational in 1970, consists of a concrete gravity

spillway and dam, earthfill embankments, a navigation lock, and a six-unit

powerhouse.

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The 86-ft wide by 675-ft long navigation lock chamber, with a rise of 100

ft, is filled and emptied by two galleries or culverts, landside and

riverside of the lock structure. The landside culvert, which supplies fivedownstream laterals, crosses under the navigation lock to discharge into the

river. The riverside culvert supplies and discharges water to the upstream

five laterals. Each lateral consists of 10 portal entrances approximately

1.5 ft wide by 3 ft high. Flow velocities in excess of 120 ft/s occur in

several of the portals entrances. A tie-in gallery exists between the twomain culverts, near the downstream gates, that equalizes the pressure betweenthe two culverts.

PROBLEM

Inspections as early as 1975 revealed that the ceiling concrete of thelandslide culvert was spalled at some monolith joints to depths of 9 in.

This may have been initiated by differential movement of adjacent monoliths

when the lock chamber was filled and emptied. Damage to the invert, at

several locations, was irregular, with erosion a maximum of 18 in. deep at

the monolith joint, decreasing to 1 in. at a point 10 ft upstream of the

joint. Reinforcing steel was exposed. Other areas of erosion in the invertand on wall surfaces were observed, measuring 2 ft square and 2 in. deep.

Later inspections revealed that portal surfaces nearest the culverts of the

most downstream laterals were showing signs of concrete erosion (Fig. 2.5).

By 1978, the portal walls, ceiling, and invert had eroded as deep as 3 in.

over an area of 5 square ft, exposing reinforcing steel.

All four corners of the tie-in gallery experienced obvious cavitation

damage. The damage varied from minor pitting to exposure and undercutting of

the 1-1/2-in. aggregate.

SOLUTION

In 1978, the navigation lock system was shut down for two weeks for

repairs. The major erosion damage to the landslide culvert was repaired by

mechanically anchored steel fiber-reinforced concrete. The smaller areas of

damage received a trowel application of a paste epoxy product. Ceilingdamage was backfilled with dry-mix shotcrete. Portal and tie-in gallery

surfaces received application of a paste epoxy, troweled to a feather edge

around the perimeter.

PERFORMANCE

The mechanically anchored fiber-reinforced concrete has performed well to

date. No additional erosion has been observed. Shotcrete patches to the

ceiling adjacent to the joints show continued spalling, but to a lesser

extent than prior to repairs.

The repairs to the portal surfaces and tie-in gallery surfaces performed

poorly. After 1 year of service, approximately 40 percent of the epoxy paste

had failed; and after 3 years, nearly 100 percent has failed. Concrete

erosion in these areas has subsequently increased to depths of 6 to 8 in. in

the tie-in gallery and up to 5 to 6 in. on the two most downstream portalsurfaces.

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Fig. 2.5-Lower Monumental Dam. Cavitation erosion of navigation lock portal surface

DISCUSSION

Recent inspections have shown that the rate of erosion has decreased. Theaccumulated erosion of concrete from certain surfaces is significant;

however, subsequent erosion is almost negligible. Consequently, repair

schedules are not critical.

Paste epoxy was applied to the concrete surfaces transitioning to featheredges along the perimeter of the patches. Cavitation eroded the concrete

adjacent to the feather edges as well as eroding the thin epoxy edges (Fig.

2.5). These new voids undermined the new, thicker epoxy, and at some point

caused another failure of the leading edge. As the leading edge void

increased in size, the failure progressed until little epoxy was left in therepaired area. After erosion of the epoxy patch material, no furtherconcrete erosion has occurred. It appears that the eroded configuration of

the surface is hydraulically stable.

Patch-type repair procedures are not sufficient for this structure because

erosion is initiated at the edge of the new patch. Eventual repairs willreplace larger areas of the concrete flow surfaces and will include

substantial anchoring of new materials.

REFERENCES

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Report No.6, Lower Monumental Lock and Dam," Walla Walla, WA, Jan. 1977.

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Report No.

7, Lower Monumental Lock and Dam," Walla Walla, WA, Jan. 1981.

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Report No.8, Lower Monumental Lock and Dam," Walla Walla, WA, Jan. 1983.

CONTACT/OWNER

Walla Walla District, Corps of EngineersCity-County Airport


LUCKY PEAK DAM

Boise River, Near Boise, Idaho

BACKGROUND

Lucky Peak Dam, operational in 1955, is 340 ft high with a crest length of

2340 ft. The dam is an earth and rockfill structure with a silt core, gradedfilters, and rock shells. The ungated spillway is a 6000-ft-long ogee weir

discharging into an unlined channel. The outlet works consists of a 23-ft-

diameter steel conduit that delivers water to a manifold structure with six

outlets. Each outlet is controlled by a 5.25-ft by 10-ft slide gate. Indiv-

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idual flip lips were constructed downstream from each slide gate. Downstream

of the flip lips is the plunge pool, excavated into the basalt rock, with

bottom areal dimensions of 150 by 150 ft. The outlet alignment and designwere determined by hydraulic modeling. The six outlets operated under a

maximum head of 228 ft with a design discharge of 30,500 ft.3-/s and a

maximum discharge velocity ranging between 88 ft/s and 124 ft/s.

PROBLEM

The steel manifold gates have a long history of cavitation erosion

problems. The original bronze gate seals were seriously damaged by

cavitation after initial use. Flow rates across the manifold gate frames in

excess of 150 ft/s for many days were common. The gate seals were replaced

with new seals made of stainless steel and aluminum-bronze. The cast-steelgate frames required continual repair of cavitated areas. In 1975 alone,

over 2000 pounds of stainless steel welding rod was manually welded into the

eroded areas and ground smooth. Neat cement grout was pumped behind the gate

frames to reestablish full bearing of the gate frames with the concrete

structure.

The concrete invert and side piers, which separate each of the six flip

lips, suffered extensive erosion soon after the start of operations in 1955

(Fig. 2.6). 3/4-in.-thick steel plates were anchored to the piers and invert

areas just downstream of the manifold gates. These steel wall plates became

severely pitted, as did the downstream concrete flip lip invert surfaces. In

1968, the damaged plates were again repaired by filling the eroded areas withstainless steel welding, and grouting behind the plates. Deteriorated con-

crete on the flip lips was removed and additional steel plates were installed

over those areas. This also failed and repairs commenced again. Deep areas

of cavitation damage in the invert and piers were filled with concrete. New

1/2-in.-thick plates were installed. These were stiffened with steel beams,welded on 5-ft centers in each direction. Deep anchor bars were welded to

the plate material to hold them in place. Again, the voids under the plates

were grouted. But during the next two years, these repairs also failed.

In 1974, it was recommended that the outlet be restudied hydraulically.

That year, remaining plate material was removed. Cavities were foundpenetrating the invert and through the piers and into the adjacent outlet

invert. These voids were crudely filled with FRC in a "field expedient"

manner. Much of this FRC was placed in standing water with little quality

control, while adjacent bays were discharging.

SOLUTION

The side piers were redesigned and replaced to provide vents that would

introduce air to the underside of the jet just downstream of the gates. This

modification was intended to prevent additional invert erosion. However,

major modifications to the gates and gate frames were necessary if cavitationerosion was to be eliminated. These modifications were not made since future

power-house construction would reduce and nearly eliminate the need to use

the outlet, reserving the structure for emergency and special operations use

only. Steel lining on the piers was strengthened and replaced. Stiffened

steel plates, 1-1/4 in. thick, were installed on the piers and invert.Mortar backfill was pumped behind the invert plates and new concrete placed

between pier plates.

PERFORMANCE

After one year of above average usage on bays 3 and 4, cavitation was againobserved. The side piers just downstream of the gates showed areas of 1 to 2

square ft that had eroded through the steel plate and into the concrete about

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6 in. No erosion of the invert plates or the "field expedient" FRC occurred.

Use of these bays has almost stopped since the new powerhouse became

operational.

DISCUSSION

The introduction of air beneath the jet appears to have cushioned the

effects of cavitation on the flip lip invert. However, pier walls continueto erode at an extraordinary rate. The cause lies with the design of thegates and gate frame. It is evident that satisfactory performance of the

structure can never be achieved until the gates and frames are redesigned and

reconstructed to eliminate the conditions that cause cavitation.

Fig. 2.6-Lucky Peak Dam.Cavitation erosion of flip lip surface

REFERENCES

U.S. Army Engineer District, Walla Walla, "Lucky Peak Lake, Idaho, Design

Memorandum 12, Flip Bucket Modifications," Supplement No. 1, Outlet Works,Slide Gate Repair and Modification, Walla Walla, WA, July 1986.

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Report No.

6, Lucky Peak Lake," Walla Walla, WA, Jan. 1985.

U.S. Army Engineer District, Walla Walla, "Periodic Inspection Report No.7, Lucky Peak Lake," Walla Walla, WA, Jan. 1989.

CONTACT/OWNER

Walla Walla District, Corps of EngineersCity-County Airport


TERZAGHI DAM

Bridge River Near Lillooet, British Columbia, Canada

BACKGROUND

Terzaghi Dam, operational in 1960, is 197 ft high with a crest length of

1200 ft. The earth and rockfill embankment consisting of an upstream

impervious fill, clay blanket, sheet pile cutoff, and multiline groutcurtain, is founded on sands and gravels infilling a deep river channel. The

dam impounds Bridge River flow to form the Carpenter Lake reservoir, from

which water is drawn through two tunnels to Bridge River generating stations

1 and 2, located at Shalalth, B.C., on Seton Lake.

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Terzaghi Dam discharge facilities are composed of a surface spillway

consisting of a 345 ft long free overflow section; and a gated section with

two 25 ft wide by 35 ft high gates. Two rectangular low level outlets (LLO),each 8 ft wide by 16 ft high are subject to a maximum heat of 169 ft. These

outlets were constructed in the top half of the concrete plug in the 32 ft,

horseshoe-shaped diversion tunnel.

Fig. 2.7-Terzaghi Dam. Downstream detail of constrictor ring

PROBLEM

The LLOs were operated in 1963 for about 23 days to draw down Carpenter

Lake to permit low-level embankment repairs. Severe cavitation erosion of

the concrete wall and ceiling surfaces downstream of bulkhead gate slots was

observed in the north LLO after the water release.

Dam safety investigations in 1985 identified that the LLO's were required

to permit emergency drawdown of Carpenter Lake for dam inspection and repair,

and to provide additional discharge capacity during large floods.

SOLUTION

The repair consisted of three main categories of work -- repair of damage,

improvement to reduce cavitation potential, and refurbishing gates and

equipment.

Repair of cavitation damage in the north LLO included repair of the walls,

crown, and gate slots.

Improvements to reduce cavitation potential included 1) installing 9-in.

deep rectangular constrictor frames (Fig. 2.7) immediately downstream of the

operating gates to increase pressures in the previously cavitated area, 2)backfilling old bulkhead gate slots and streamlining the existing LLO invert

entrances, and 3) installing piezometers in the north LLO to provide

information on flow characteristics of the streamlined LLO during discharge

testing.

Refurbishing gates and equipment included 1) replacing leaking gate seals

on closure gates; 2) sandblasting and repainting gates, guides, head covers,

and air shafts; 3) cleaning gate lifting rods and replacing bonnet packings;

4) replacing ballast concrete in north LLO gates and installing ballast cover

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plates on all gates; and 5) refurbishing hydraulic lifting mechanisms of

gates.

Repair concrete was designed to fully bond with existing concrete. Surface

preparation included; saw cutting around the perimeter of the damage, chip-

ping to expose rebar, and installation of grouted dowels. Latex-modified

concrete was used for all repair work, with steel fiber reinforcement for the

cavitation-damaged areas.

A total of 26 cubic yards of 3000 psi ready-mixed concrete was placed by

pumping. Maximum aggregate sizes of 3/8-in. and 3/4-in. were used for general

repair and invert entrance backfill, respectively.

The constrictor frames were made from 1/2-in. and 3/4-in. steel plate.They were installed in the LLOs by means of the following: 1) bolting the

constrictor frame to the existing concrete with a double row of 1-in.

diameter adhesive anchors at 12-in. spacing; 2) keying the constrictor infill

concrete into the existing concrete; 3) welding the constrictor frame to the

existing gate metal-work in the walls and soffit; and 4) embedding the

constrictor sill shear bar into the existing concrete invert (Fig. 2.7).

PERFORMANCE

A test with a full reservoir and a peak discharge of 7000 ft.3-/s, with

both gates opened 7 ft, verified that the constrictor frames and concrete

repairs, downstream of the closure gates, performed as designed. Nocavitation erosion of the wall and ceiling surfaces was observed.

DISCUSSION

Piezometer readings confirmed that the constrictor frames in the LLO'shelped maintain pressures above atmospheric, indicating that cavitation

should not be a problem in the future.

REFERENCES

B.C. Hydro, "Terzaghi Dam, Low Level Outlet Repairs -- Memorandum on

Construction," Report No. EP6, Vancouver, B.C., Dec. 1986.

B.C. Hydro, "Terzaghi Dam, Low Level Outlet Tests," Report No. H1902,

Vancouver, B.C., Mar. 1987.

CONTACT/OWNER

British Columbia Hydro

Hydrotechnical Department, HED

6911 Southpoint DriveBurnaby, British Columbia, Canada V3N 4X8

YELLOWTAIL AFTERBAY DAM

Bighorn River, Montana

BACKGROUND

Yellowtail Afterbay Dam, operational in 1966, is a 33-ft-high concrete

gravity diversion type structure, 300 ft long, located about 1 mile

downstream from Yellowtail Dam. In 1967 following a heavy winter/springsnowpack in the upstream drainage basin, flood flows passed through both

Yellowtail Dam and the Afterbay Dam.

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PROBLEM

Divers examined the Afterbay Dam sluiceway and stilling basin after theflood flows had passed. They found cavitation damage on the dentates (baffle

blocks) and adjacent floor and wall areas in the spillway stilling basin.

Although the cavitation damage was moderate, repairs were necessary to lessen

the likelihood that future cavitation damage would occur.

Damage to the dentates and floor in the sluiceway was caused by abrasion.The relatively low sill at the downstream end of the sluiceway was permitting

downstream gravel and sand to be drawn into the stilling area, where a ball

mill-type action ground away the concrete surfaces.

In the stilling basin downstream of the reverse ogee section, cavitationseverely eroded the sides of the dentates and the adjacent floor areas. A

similar condition developed in the sluiceway except that it was caused by

abrasion erosion. Since the damage from the two causes occurred essentially

side by side, the situation graphically illustrated the dissimilar types of

erosion resulting from cavitation and abrasion.

SOLUTION

Following the flood, low flows at the dam could be maintained for only one

month. That situation required that all repairs be completed quickly and

concurrently. In addition to repairing damaged areas, the downstream sill in

the sluiceway was raised about 3 ft to stop river gravels from being drawninto the sluiceway. Repairs were completed using a combination of bonded

concrete, epoxy-bonded concrete and epoxy-bonded epoxy mortar, depending upon

thickness of the repair. Epoxy used in this repair was a polysulfide-type

material. After repaired materials had been placed and cured, they were

ground to provide a smooth, cavitation-resistant surface.

PERFORMANCE

The dam has now been in service about 23 years since the repairs were made.

With the exception of a minor number of spalls, the performance of the

repairs has been excellent.

REFERENCES

Graham, J.R., "Spillway Stilling Basin Repair Using Bonded Concrete and

Epoxy Mortar," Proceedings, Irrigation and Drainage Specialty Conference,Lincoln, NE, Oct. 1971, pp. 185-204.

Graham, J.R., and Rutenbeck, T.E., "Repair of Cavitation Damaged Concrete,

a Discussion of Bureau of Reclamation Techniques and Experiences,"

Proceedings, International Conference on Wear of Materials, St. Louis, MO,

April 1977, pp. 439-445.

CONTACT

Bureau of Reclamation

P.O. Box 25007, Denver Federal CenterDenver, CO 80225

YELLOWTAIL DAM

Bighorn River, Montana

BACKGROUND

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The dam, operational in 1966, is a concrete arch structure 525 ft high with

a crest length of 1480 ft. Normal flow through the dam occurs in two 84-in.

outlet pipes and through the turbines of the powerhouse. Flows exceeding thecapacity of these facilities are routed through a high-head spillway located

in the left abutment. At this spillway, water enters through a radial-gated

intake structure, then passes into an inclined section of tunnel varying in

diameter from 40.5 ft at the upper end to 32 ft at the beginning of the

vertical elbow. Thereafter, flow follows the 32-ft-diameter tunnel throughthe elbow and 1200 ft of near horizontal tunnel, exiting into a combinationstilling basin-flip bucket, then into the river.

During the spring of 1967, heavy rains in the watershed area of the Bighorn

River resulted in high inflows into Bighorn Lake behind Yellowtail Dam. A

total of 650,000 acre-ft of flood waters was released through the spillwayover a period of 30 days. Maximum flow was 18,000 ft.3-/s.

PROBLEM

During the 1967 spill, severe damage occurred to the concrete tunnel lining

and underlying rock in the elbow, as well as upstream and downstream. Afterthe flows into the river had subsided sufficiently for a temporary shut-down

of the tunnel, divers made an examination. Major damage was found in the

near-horizontal section of the tunnel lining and in the elbow. Failure

occurred along the tunnel invert in a leapfrog fashion, typical of cavitation

damage. The largest cavity was about 100 ft long, 20 ft wide and 6 to 8 ft

deep. After the tunnel was dewatered, it was found that a small concretepatch placed during construction had failed, thereby causing the

discontinuity in the flow that triggered the cavitation.

SOLUTION

The tunnel liner was repaired using several systems depending on the size

and depth of the damage. Areas where the damage extended through the lining

into the foundation rock were repaired with high quality replacement con-

crete. Major areas of damage where the erosion did not penetrate through the

concrete lining were repaired with bonded concrete. Shallow-damaged concrete

was repaired with epoxy-bonded concrete and epoxy-bonded epoxy mortar.Surfaces were ground where necessary to bring tolerances into conformance

with specifications requirements. Finally, tunnel surfaces below spring line

were painted with an epoxy-phenolic paint, to help seal the surface and bond

any aggregate particles that may have been loosened.

In order to avoid recurring damage, an aeration device was model tested in

the laboratory and then constructed in the tunnel a few ft upstream of the

point of curvature of the vertical elbow. This aeration slot measured 3 ft

wide and 3 ft deep and extended around the lower three quarters of the tunnel

circumference. It was designed to entrain air in the flow for all discharges

up to 92,000 ft.3-/s, without the slot filling with water. A 27-in.-longramp was constructed upstream of the slot which raised the upstream face of

the slot 3 in. at the tunnel invert. Under most flow conditions the bottom

of the jet was forced away from the tunnel floor surface. The jet remained

free for a considerable distance downstream, all the while drawing air into

the jet from the aeration slot. Aeration has reduced the discharge capacityby approximately 20 percent.

PERFORMANCE

It has now been 23 years since the tunnel was repaired and the aeration

slot installed, but flows in the river have never been sufficient to requireuse of the spillway. However, a controlled prototype test with flows to

16,000 ft.3-/s was conducted in 1969 and 1970. As a result of this test,

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less than one percent of the concrete repairs failed and no cavitation damage

was observed, even in areas down stream from discontinuities. To ensure that

the tunnel will always be ready for the next flow, there is a regular main-tenance program to repair ice damage and remove calcium carbonate buildups.

REFERENCES

Borden, R.C., et al., "Documentation of Operation, Damage, Repair, andTesting of Yellowtail Dam Spillway," Report No. REC-ERC-71-23, Bureau ofReclamation, Denver, CO, May 1971.

Colgate, D., and Legas, J., "Aeration Mitigates Cavitation in Spillway

Tunnel," Meeting Preprint 1635, National Water Resources Engineering Meeting,

Jan. 24-28, 1972, Atlanta, GA, American Society of Civil Engineers, New York,NY, 29 pp.

CONTACT

U.S. Bureau of Reclamation

Denver Office, Code D-3700P.O. Box 25007, Denver Federal Center

Denver, CO 80225

KEENLEYSIDE DAM

Columbia River, near Castlegar, B.C., Canada

BACKGROUND

The dam, operational in 1968, consists of an earthfill embankment 1400 ft

long and about 171 ft high and a concrete gravity section about 1180 ft longand 190 ft high. The concrete section contains four 55 ft wide sluiceways,

eight 20 by 24 ft high low level ports, and a navigation lock.

The sluiceway downstream of the gate slot has an ogee section designed very

conservatively for 65 percent of the design head. Upstream of the gate sill

the profile is a fairly broad three-radius compound curve. Accordingly, nonegative pressures should occur anywhere on the crest under free discharge

operation.

PROBLEM

Cavitation damage has occurred on the sluiceway crest near the gate slots

on all four bays. The damage extended from inside the upstream portion of

the gate slot to a point about 4 ft downstream, extending at an angle of

about 30 degrees to the direction of flow (Fig. 2.8).

All attempts to repair the eroded concrete with epoxy mixtures and steelfiber-reinforced concrete (FRC) in 1973, 1975, and 1977 were unsuccessful.

Continued cavitation soon pitted the repaired areas which later progressed to

development of major voids. By 1980 approximately 80 percent of the previous

repair had eroded. During a high water inspection in 1986, sluiceway No. 2

was flow tested for 4 hr at gate openings of 4, 8, 12 and 16 ft and fullopening. Characteristic noises of cavitation bubble collapse could be heard

intermittently at all gate settings. The highest rate of cavitation activity

was observed to be with gate openings from 4 to 12 ft.

The deepest erosion usually occurred just outside the gate slot with depths

ranging from about 8 to 14 in. Downstream of the badly eroded area, theconcrete at the invert was observed to be roughened for another 2 ft. The

maximum width of the eroded area varied from 18 to 24 in.

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The cavitation erosion at the ft of the gate slot damaged not only the

concrete invert but also the lower part of the steel liner within the gate

slot and an area of the wall immediately downstream of the liner. The 1986study concluded that the severe concrete erosion at and just downstream of

the gate slots was due to 1) cavitation caused by vortices originating in the

upstream corners of the gate slots at small, part-gate operation; and 2) lack

of rounding and lack of offset of downstream edge of gate slot.

SOLUTION

Initially, it was recommended that 1) eroded areas should be filled with

concrete and armored with steel plates, and 2) field tests should be con-

ducted to identify cavitation zones. Later, the recommendation was changed to

back-fill cavitated areas with 3/4-in. aggregate, high strength (6000 psi)concrete. The bond between the back-fill and the original sluiceway concretes

was enhanced by epoxy bonding agent. The top surface of the new patch and

the surrounding original concrete were coated with an acrylic latex selected

through an extensive laboratory screening process. The work was carried out

in the summer of 1990.

PERFORMANCE

In order to test the effectiveness of the repairs, during the following

year it was decided to operate the sluice gates mostly in the worst range. A

year later, the repaired and coated surfaces began to show signs of pitting.

The performance of the repair still did not appear satisfactory. It becameobvious that besides repairing the eroded areas other initiatives were needed

to alleviate recurrence of the problem.

DISCUSSION

Based on the observations of the effect of gate opening on cavitation, it

was decided to limit gate operation to that outside of the destructive range.

Gate operating orders were rewritten to require "passing over" the rough

zones as quickly as possible without any sustained operation in those zones.

REFERENCES

B.C. Hydro, Hydroelectric Engineering Division, "Hugh Keenleyside Dam,

Cavitation Damage on Spillway," Report No. H1922, Vancouver, B.C., Mar. 1987.

B.C. Hydro, Hydroelectric Engineering Division, "Keenleyside Dam,Comprehensive Inspection and Review 1986," Report No. H1894, Vancouver, B.C.,

May 1987.

B.C. Hydro, Hydroelectric Engineering Division, "Hugh Keenleyside Dam,

Cavitation Damage on Spillway, Field Investigation of Cavitation Noise and

Proposed Gate Operating Schedules," Report No. 2305, Vancouver, B.C., June1992.

CONTACT/OWNER

British Columbia Hydro Structural DepartmentHED6911 Southpoint Drive

Burnaby, British Columbia, Canada V3N4X8

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Fig. 2.8-Keenleyside Dam. Cavitation erosion of concrete invert & adjacent damage to steel liner.

Maximum depth approximately 9 in.

CHAPTER 3 - ABRASION-EROSION CASE HISTORIES

ESPINOSA IRRIGATION DIVERSION DAMEspanola, New Mexico, on the Santa Cruz River

BACKGROUND

The diversion dam is a reinforced concrete structure that is capable ofdiverting up to 13 ft.3-/s in the Espinosa Ditch for irrigation purposes. A

50-ft-long reinforced rectangular concrete channel, sediment trap, and sluice

gate structures were constructed between the headgate and the ditch heading.

A sidewall weir notch is provided in the rectangular ditch lining to allow

emergency discharge of flood flows back to the river. A 24-in.-round sluicegate at the right side of the dam was placed at the slab invert elevation, to

sluice sand and cobbles through the dam and to prevent these materials from

entering the irrigation ditch head gate. The dam is tied back into the

riverbanks on either side with small earthen dikes that protect the sur-

rounding land against flood flows of 1000 ft.3-/s or less.

PROBLEM

Debris plugged the sluice gate, preventing the diversion of the bedload

from the irrigation ditch. The structure experienced severe erosion damage

to the apron and floor blocks (Fig. 3.1) due to impact and abrasion by thebedload. The bedload consists of gravels and boulders ranging up to 24 in.

in diameter. The concrete in the apron in the impact area was abraded to a

depth of 6 in. Except for very low flows and flows diverted for irrigation,

the bedload is carried over the weir.

Fig. 3.1-Espinosa Irrigaion Diversion Dam. Erosion damage to the floor blocks

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Fig. 3.2-Espinosa Irrigation Diversion Dam. Steel plate protection added to the floor blocks and

endsill

SOLUTION

Repairs were made by extensive structural modifications. These modifi-

cations included the following (Fig. 3.2): 1) removing and replacing the top

layer of reinforcement in the apron; 2) removing and replacing the top 6 in.

of concrete; 3) protecting the apron with a 1/2-in. steel plate; and 4)

replacing the 24-in.-round sluice gate with a 36-in. square sluice gate.

PERFORMANCE

The structure has been operating satisfactorily since rehabilitation in

1982.

DISCUSSION

Five alternatives were evaluated for the placement of the diversion dam

back into service. The ones not selected as the solution are as follows:

1. Install a reinforced concrete lining inside the walls and apron of theexisting structure.

2. Protect the apron with a 1/2-in. steel plate.

3. Remove the entire apron of the structure and replace it with one that

is adequately reinforced. Add the liner inside the structure.

4. Remove the entire structure and replace it with a new one.

REFERENCES

U.S. Department of Agriculture, "Espinosa Diversion Dam, Report of

Investigation of Structural Failure," Soil Conservation Service, Albuquerque,

NM, Nov. 1980.

U.S. Department of Agriculture, "Espinosa Diversion Dam, Design Engineer's

Report, "USDA, Soil Conservation Service, Albuquerque, NM, Sept. 1982.

CONTACT/OWNER

State Conservation Engineer

U.S. Department of Agriculture Soil Conservation Service

517 Gold Avenue, SW, Room 3301

Albuquerque, NM 87102

KINZUA DAM

Allegheny River, Warren County, Pennsylvania

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BACKGROUND

Kinzua Dam became operational in 1965. The stilling basin consists of ahorizontal apron, 160 ft long and 204 ft wide. It contains nine 7-ft-high by

10-ft-wide baffles, located 56 ft upstream from the end sill. The vertical-

faced end sill is 10 ft high and 6 ft wide. The basin slab was constructed

of concrete with a 28-day compressive strength of 3000 psi.

The outlet works consists of two high-level and six low-level sluices. Amaximum conservation flow of about 3600 ft.3-/s is supplied by the high-level

sluices. The low-level sluices with flared exists containing tetrahedral

deflectors are located 26 ft above the stilling basin slab. Bank-full capa-

city, 25,000 ft.3-/s, can be discharged through these sluices at reservoir

elevation 1325. The maximum 24,800-ft.3-/s record discharge was dischargedthrough the sluices in 1972. The maximum velocity at the sluice exit was 88

ft/s.

PROBLEM

Because of the proximity of a pumped-storage power-plant on the leftabutment and problems from spray, especially during the winter months, the

right side sluices were used most of the time. Use of these sluices caused

eddy currents that carried debris into the stilling basin. The end sill was

below streambed level and contributed to the deposition of debris in the

basin.

Divers reported erosion damage to the basin floor as early as 1969. Also,

piles of rock, gravel, and other debris in the basin were reported. About 50

cubic yards of gravel and rock, ranging up to 8 in. in diameter, were removed

from the basin in 1972. Abrasion-erosion damage reached a depth of 3.5 ft in

some areas before initial repairs were made in 1973 and 1974.

These repairs were made with steel fiber-reinforced concrete. Approximately

1400 cubic yards of fiber concrete was required to overlay the basin floor.

From the toe of the dam to a point near the baffles, the overlay was placed

to an elevation 1 ft higher than the original floor.

In April 1975, divers reported several areas of abrasion-erosion damage in

the fiber concrete. Maximum depths ranged from 5 to 17 in. Approximately 45

cubic yards of debris were removed from the stilling basin. Additional

erosion was reported in May 1975, and another 60 cubic yards of debris were

removed from the basin. At this point, symmetrical operation of the lowersluices was initiated to minimize eddy currents down-stream of the dam.

After this change, the amount of debris removed each year from the basin was

drastically reduced and the rate of abrasion declined. However, nearly 10

years after the repair, the erosion damage had progressed to the same degree

that existed prior to the repair.

SOLUTION

A materials investigation was initiated prior to the second repair, to

evaluate the abrasion-erosion resistance of potential repair materials. Test

results indicated that the erosion resistance of conventional concretecontaining a locally available limestone aggregate was not acceptable (Fig.

3.3). However, concrete containing this same aggregate with the addition of

silica fume and a high-range, water-reducing admixture exhibited high

compressive strengths (approximately 14,000 psi at 28 days' age) and very

good resistance to abrasion erosion. Therefore, approximately 2000 cubic

yards of silica-fume concrete were used in a 12-in. minimum thickness overlaywhen the stilling basin was repaired in 1983 (Fig. 3.4).

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Construction of a debris trap immediately downstream of the stilling basin

end sill was also included in the repair contract. Hydraulic model studiesshowed that such a trap would be beneficial in preventing downstream debris

from entering the stilling basin. The trap was 25 ft long with a 10-ft-high

end sill that spanned the entire width of the basin.

PERFORMANCE

In August 1984, after periods of discharge through the upper and lower

sluices, abrasion-erosion along some cracks and joints was reported by

divers. The maximum depth of erosion was about 1/2 in. The divers also

discovered two pieces of steel plating that had been embedded in the concrete

around the intake of one of the lower sluices. Because of concern aboutfurther damage to the intake, the use of this sluice in discharging flows was

discontinued. This nonsymmetrical operation of the structure resulted in the

development of eddy currents.

The next inspection, in late August 1984, found approximately 100 cubic

yards of debris in the basin. In September 1984, a total of about 500 cubicyards of debris was removed from the basin, the debris trap, and the area

immediately downstream of the trap. The rock debris in the basin ranged from

sand sized particles to over 12 in. in diameter. Despite these adverse

conditions, the silica-fume concrete continued to exhibit excellent resist-

ance to abrasion. Erosion along some joints appeared to be wider but

remained approximately 1/2-in. deep.

Sluice repairs were completed in late 1984, and symmetrical operation of

the structure was resumed. A diver inspection in May 1985 indicated that the

condition of the stilling basin was essentially unchanged from the preceding

inspection. A diver inspection approximately 3-1/2 yr after the repairindicated that the maximum depth of erosion, located along joints and cracks,

was about 1 in.

Fig 3.4-Kinzua Dam. Typical silica-fume concrete placement operation for a stilling basin slab

REFERENCES

Fenwick, W.B., "Kinzua Dam, Allegheny River, Pennsylvania and New York;

Hydraulic Model Investigation," Technical Report HL-89-17, U.S. Army EngineerWater ways Experiment Station, Vicksburg, MS, Aug. 1989.

Holland, T.C., "Abrasion-Erosion Evaluation of Concrete Mixtures for

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Stilling Basin Repairs, Kinzua Dam, Pennsylvania," Miscellaneous Paper

SL-83-16, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS,

Sept. 1983.

Holland, T.C., "Abrasion-Erosion Evaluation of Concrete Mixtures for

Stilling Basin Repairs, Kinzua Dam, Pennsylvania," Miscellaneous Paper

SL-86-14, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS,

Sept. 1986.

Holland, T.C.; Krysa, A.; Luther, M.D.; and Liu, T.C., "Use of Silica-Fume

Concrete to Repair Abrasion-Erosion Damage in the Kinzua Dam Stilling Basin,"

Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SP-91, V. 2,

American Concrete Institute, Detroit, MI, 1986, pp. 841-863.

McDonald, J.E., "Maintenance and Preservation of Concrete Structures,

Report 2, Repair of Erosion-Damaged Structures," Technical Report No. C-78-4,

U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April 1980.

CONTACT/OWNER

U.S. Army Engineer District

Pittsburgh William S. Moorhead Federal Building

1000 Liberty Avenue

Pittsburgh, PA 15222

LOS ANGELES RIVER CHANNEL

Los Angeles River, California

BACKGROUND

The Los Angeles River Channel is an improved structural channel that drains

a watershed of 753 square miles. The majority of the channel was constructed

in the 1940s. In the invert of the concrete-lined main channel is a rein-

forced concrete low-flow channel. This low-flow channel is approximately 12

miles long and was originally constructed with an invert thickness of 12 in.Water velocities in that channel range from 20 to 30 ft/s.

PROBLEM

Over the years abrasion erosion has occurred to varying degrees along thelow-flow channel. In some reaches, erosion had progressed completely through

the concrete by the early 1980s. This erosion was the result of a combina-

tion of abrasion by waterborne sediment and debris passing over the concrete,

and chemical attack.

SOLUTION

Prior to repair, laboratory studies were conducted to evaluate the

abrasion-erosion resistance of concretes containing locally available

aggregates. Typically, these aggregates exhibit a relatively high abrasion

loss tested according to ASTM C 131, using the Los Angeles machine. Resultsof the laboratory tests indicated that concrete with a high cement content, a

silica fume content of 15 percent by mass of portland cement, and a low

water-cement ratio would provide excellent abrasion-erosion resistance, even

when produced with aggregates that might be marginal in durability.

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Fig 3.5-Los Angeles River Channel. Concrete for a full depth replacemnet was placed with a

conveyor & finished with a specially shaped vibratory screed

Beginning in 1983, the existing concrete in the approximately 1/2-mile

reach of most severe damage was removed and replaced with reinforced,

silica-fume concrete (Fig. 3.5). The thickness of the replacement concrete

was 12 in. Subsequent rehabilitation of the remaining channel during 1984and 1985 was accomplished by either full-depth slab replacement or an overlay

on the existing concrete. Full-depth repairs consisted of a new, reinforced

base slab of conventional concrete and 6-in. overlay of silica-fume concrete.

Overlays on the existing concrete were 4- to 6-in.-thick sections of silica-

fume concrete. Various mixture proportions were used with compressivestrengths ranging from 8000 to 10,500 psi. Approximately 27,500 cubic yardsof silica-fume concrete were required to complete the rehabilitation. The

unit costs for the silica-fume concrete decreased with time as bidders became

more familiar with the material. The unit cost for the 1985 project was

$154/cubic yard, which was slightly less than twice the unit cost of

conventional concrete.

PERFORMANCE

Scour gauges were installed to monitor long-term wear of the silica-fume

concrete. Because of the nature of the mechanism causing abrasion-erosion,

an evaluation of performance will require an extended period of time.However, the abrasion resistance of the silica-fume concrete, according to

the laboratory tests, should be two to four times better than the

conventional concrete previously used. Visual inspections of the channel

surfaces indicate little or no erosion of the concrete has occurred in the 8

years following repair.

REFERENCES

Holland, T.C., "Abrasion-Erosion Evaluation of Concrete Mixtures for Repair

of Low-Flow Channel, Los Angeles River," Miscellaneous Paper SL-86-12, U.S.

Army Engineer Waterways Experiment Station, Vicksburg, MS, Sept. 1986.

Holland, T.C., and Gutschow, R.A., "Erosion Resistance with Silica-Fume

Concrete," Concrete International, V. 9, No. 3, Detroit, MI, March 1987, pp.

32-40.

CONTACT/OWNER

U.S. Army Engineer District, Los Angeles

300 North Los Angeles Street

Los Angeles, CA 90012

NOLIN LAKE DAM

Nolin River, Edmonson County, Kentucky

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BACKGROUND

Nolin Lake Dam became operational in 1963. The stilling basin is 40 ftwide, 174 ft long with a 7-ft-high end sill and 35-ft-high sidewalls. The

basin contains a parabolic section with an 8.4-ft drop in elevation from the

outlet tunnel invert to the horizontal floor slab. The design discharge is

12,000 ft.3-/s with an average velocity of 61 ft/s entering the basin. The

structure was built of reinforced concrete with a design compressive strengthof 3000 psi.

PROBLEM

The conduit and stilling basin at Nolin were dewatered for inspection in

1974, following approximately 11 years of operation. Erosion was reported inthe lower portion of the parabolic section, the stilling basin floor, the

lower part of the baffles, and along the top of the end sill. The most

severe erosion was in the area between the wall baffles and the end sill,

where holes 2 to 3 ft deep had been eroded into the stilling basin floor

along the sidewalls.

SOLUTION

The stilling basin was dewatered and repaired in 1975. Conventional

concrete designed for 5000 psi compressive strength was used to restore the

basin slab to an elevation 9 in. above the original grade. A hydraulic model

study of the existing basin was not conducted, but the structure was modifiedin an attempt to reduce the amount of debris entering the basin. New work

included raising the end sill 12 in., adding end walls at the end of the

stilling basin, and paving a 50-ft-long channel section.

PERFORMANCE

A diver inspection in 1976 indicated approximately 4 tons of rock was in

the stilling basin. The rock, piled up to 15 in. deep, ranged up to 12 in.

in diameter. Also, 18-in.-deep rock piles were found on the slab down-stream

from the stilling basin. Erosion, up to 8 in. deep, was reported for

concrete surfaces that were sufficiently clear of debris to be inspected.

In August 1977, approximately 1 to 1-1/2 tons of large, limestone rock, all

with angular edges, was reported in the stilling basin. No small or rounded

rock was found. Since the basin had been cleaned during the previous

inspection, this rock was thought to have been thrown into the basin byvisitors. When the stilling basin was dewatered for inspection in October

1977, no rock or debris was found inside the basin. Apparently, the large

amount of rock discovered in the August inspection had been flushed from the

basin during the lake drawdown, when the discharge reached a maximum of 7340

ft.3-/s.

Significant erosion damage was reported when the stilling basin was

dewatered for inspection in 1984. The most severe erosion was located behind

the wall baffles, similar to that prior to repair in 1975. Each scour hole

contained well-rounded debris ranging from marble size to approximately

12-in. diameter. Temporary repairs included removal of debris from the scourholes and filling them with conventional concrete. Also, the half baffles

attached to each wall of the stilling basin were removed.

A hydraulic model of the stilling basin was constructed to investigate

potential modifications to the basin to minimize chances of debris entering

the basin and causing subsequent erosion damage to the concrete. Results ofthis study were incorporated into a permanent repair in 1987. Modifications

included rebuilding the parabolic section in the shape of a whale's back,

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overlaying the basin floor, adding a sloping face to the end sill, raising

the basin walls 2 ft, paving an additional 100 ft of the retreat channel,

slush-grouting all derrick stone in the retreat channel, and adding newslushgrouted riprap beside the basin.

The condition of the concrete was described as good with no significant

defects when the basin was dewatered for inspection in August 1988. The

maximum discharge to that point had been 5050 ft.3-/s for a period of 13days.

REFERENCES


Report 2, Repair of Erosion-Damaged Structures," Technical Report No. C-78-4,U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April 1980.

McDonald, J.E., and Liu, T.C., "Repair of Abrasion-Erosion Damage to

Stilling Basins," Concrete International, V. 9, No. 3, American Concrete

Institute, Detroit, MI, March 1987, pp. 55-61.

CONTACT/OWNER

U.S. Army Engineer District, Louisville

P.O. Box 59

Louisville, KY 40201-0059

PINE RIVER WATERSHED, STRUCTURE NO. 41

La Plata and Archuleta Counties, Colorado

BACKGROUND

Structure No. 41 is a high velocity reinforced concrete chute spillway with

a St. Anthony Falls (SAF) stilling basin. The SAF stilling basin is a design

developed by the Agricultural Research Service at the St. Anthony Falls

Hydraulic Laboratory of the University of Minnesota. The design includes

chute and floor blocks with an end sill sized by hydraulic modeling formaximum energy dissipation. The floor of the basin in Structure No. 41 is

depressed about 4.6 ft below the downstream channel grade. The design wall

thickness is 8 in. and the design floor thickness is 9 in. The reinforcement

is a single mat of steel centered in the floor and walls.

PROBLEM

From 1974 to 1984 the structure had displayed significant erosion of the

concrete. The most severe erosion had occurred at the lower end of the SAF

stilling basin. The stilling blocks, end sill, and reinforcement was

completely deteriorated. The reinforcing steel was exposed in the floor,sidewalls (Fig. 3.6), and wingwalls from immediately upstream of the end sill

downstream through the structure. The exposed reinforcement showed

considerable wear.

Erosion in the floor of the chute was limited to about 1/4 in. Thiserosion appeared constant throughout the length of the chute.

During a 1984 investigation, it was concluded that the damage exhibited the

characteristics of erosion and abrasion damage by the ball mill effect, as

described on pages 14 and 15 of Chapter 1 of the Bureau of Reclamation

Concrete Manual. The major damage to the structure is attributed to graveland larger sized material being introduced into the stilling basin from the

outlet channel slope protection rock.

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fIG. 3.6-Pine River Watershed, Structure No.41. Erosion of sidewall, exposing reinforcing steel

The SAF outlet channel was designed and constructed with a 3 to 1 adversegrade from the top of the end sill to the canal invert elevation, approxi-

mately 4 ft above the end sill. It has a bottom width of 10 ft with 2 to 1

side slopes. The entire section is lined with loose rock riprap. The rock

is rounded to subrounded and is easily dislodged. Much of the rock on theadverse slope appears to have been displaced and the slope eroded, so that it

is considerably steeper than originally constructed. Hydraulic transport ofthe smaller rock into the basin appears to be the method of debris

introduction.

SOLUTION

The investigating team made the following recommendations:

1. Study the hydraulics of the outlet and design an outlet basin to fit

most favorably with those predicted by model studies. Minimize use of

rock riprap but, if needed, grout to prevent movement.

2. Replace concrete end sill, floor blocks, and chute blocks using high-strength concrete. The effect on hydraulic performance will need to be

studied.

A model study was conducted in 1984 to determine the design for apreshaped, riprapped energy dissipation pool. The design was recommended for

the repair and rehabilitation of the structure and was also considered

appropriate information for use in the design of similar pools.

PERFORMANCE

No permanent work has been completed on the repair of the structure to

date. Options for repair are being considered at this time.

REFERENCES

Bureau of Reclamation, Concrete Manual, 8th Edition, U.S. Department of the

Interior, 1981.

Rice, C.E., and Blaisdell, F.W., "Energy Dissipation Pool for a SAF

Stilling Basin," Applied Engineering in Agriculture, V. 3, No. 1, USDA-ARS,

Stillwater, Oklahoma, 1987, pp. 52-56.

CONTACT/OWNER

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State Conservation Engineer

U.S. Department of Agriculture, Soil Conservation Service

Sixth Avenue Central, 655 Parfet Street, Room E200CLakewood, CO 80215-5517

POMONA DAM

Hundred Ten Mile Creek, Vassar, KS

BACKGROUND

The stilling basin at Pomona Dam, operational in 1963, is 35 ft wide and 80

ft long. The reinforced concrete transition and horizontal basin floor have

a design discharge velocity of 58 ft/s. Two staggered rows of baffles, 3 ftwide and 5 ft high, are spaced at 7 ft on centers. A two-step, vertical-faced

end sill is 4 ft high. Fill concrete was placed the width of the basin for a

distance of 20 ft downstream from the end sill.

PROBLEM

The initial dewatering of the basin in February 1968 revealed erosion

damage at the downstream end of the transition slab and on the upstream one-

third of the basin slab. This erosion, caused by the abrasive action of rocks

and other debris, had exposed reinforcing steel along the left wall of the

basin. An inspection in October 1970 revealed significant additional erosion

and extensive exposure of reinforcing steel. The major damage was attributedto flow conditions at relatively low discharges, since approximately 97

percent of the releases had been 500 ft.3-/s or less.

Fig. 3.7-Providence-Millville Diversion Structure. Erosion of the surface of the concrete apron

and sidewalls

SOLUTION

Hydraulic model tests confirmed that severe separation of flow from one

sidewall, together with eddy action strong enough to circulate stone in themodel, occurred within the basin for discharges and tailwaters common to the

project. Various modifications including raising the apron, installing chute

blocks, constructing interior side-walls with reduced flare, and providing a

hump down-stream of the outlet portal were model tested to evaluate their

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effectiveness in eliminating the undesirable separation of flow and eddy

action within the basin.

Based on the model study, it was recommended that the most practical

solution was to provide a 3-ft-thick overlay of the basin slab upstream of

the first row of baffles, a 1-1/2-ft overlay between the two rows of baffles,

and 1 to 1 sloped face to the existing end sill. This solution provided a

wearing surface for the area of greatest erosion and provided a depression atthe down-stream end of the basin for trapping debris. However, flowseparation and eddy action were not eliminated by this modification. There-

fore, it was recommended that a fairly large discharge, sufficient to create

a good hydraulic jump without eddy action, be released periodically to flush

debris from the basin.

The final design for the repair included 1) a minimum 1/2-in.-thick epoxy

mortar topping applied to approximately one-half of the transition slab; 2)

an epoxy mortar applied to the upstream face of the right three upstream

baffles; 3) a 2-ft-thick concrete overlay slab placed on the upstream 70

percent of the basin slab; and 4) a sloped concrete end sill. The reinforced

concrete overlay was recessed into the original transition slab and anchoredto the original basin slab. The coarse aggregate used in the repair concrete

was Iron Mountain trap rock, an abrasion-resistant aggregate. The average

compressive strength of the repair concrete was 6790 psi at 28 days.

PERFORMANCE

The stilling basin was dewatered for inspection five years after repair

(Fig. 3.7). The depression at the down-stream end of the overlay slab

appeared to have functioned as desired. Most of the debris, approximately 1

cubic yard of rocks, was found in the trap adjacent to the overlay slab. The

concrete overlay had suffered only minor damage, with general erosion ofabout 1/8-in. and maximum depths of 1/2-in. The location of the erosion

coincided with that occurring prior to the repair. Apparently, debris is

still being circulated at some discharge rate. Based on a comparison of

discharge rates and slab erosion, before and after the repair, it was

concluded that the repair had definitely reduced the rate of erosion. The

debris trap and the abrasion-resistant concrete were considered significantfactors in this reduction.

The next inspection, in April 1982, indicated the stilling basin floor slab

remained in good condition with essentially no damage since the previous

inspection. Approximately 5 cubic yards of debris, mostly rocks, wereremoved from the debris trap at the downstream end of the basin.

REFERENCES


Report 2, Repair of Erosion-Damaged Structures," Technical Report No. C-78-4,U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April 1980.

Oswalt, N.R., "Pomona Dam Outlet Stilling Basin Modifications," Memorandum

Report, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, 1971.

CONTACT

U.S. Army Engineer District, Kansas City

601 E. 12th Street

Kansas City, MO 64106

PROVIDENCE-MILLVILLE DIVERSION STRUCTURE

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Near Logan, Utah

BACKGROUND

The Providence-Millville Diversion Structure is a reinforced 60-ft-wide

concrete drop structure, with a drop of 4 ft, a weir height of 4 ft, an apron

length of 10 ft, and a sill height of 15 in. Two 4-by 4-ft slide gates in the

right abutment headwall direct flow from Blacksmith Fork into the irrigationcanal.

A considerable number of reinforced concrete diversion structures have been

constructed in mountain streams in the Western United States. These streams

are usually on a steep gradient and generally transport a heavy bedload of

sands, gravels, and cobbles. Frequently permanent drops are incorporated inthe diversion to provide the necessary head for diverting the irrigation

flow, sluicing the bedload, and stabilizing the stream gradient.

PROBLEM

In spite of engineering practices such as providing sluiceways, usinggrated inlet devices, and special entrance configuration, the transported

sediment causes abrasion to the exposed concrete in the diversions. At times

of flood flows or above normal high water, excessive bedload (quantity and

size of particles) also imparts severe impact to the surfaces of stilling

basins or aprons of drop structures. This impact as well as the grinding

action of highly abrasive aggregate causes loss of concrete, exposure ofsteel reinforcement, and, if unchecked, loss of the structure.

The bedload of sand, gravel, and boulder materials in Blacksmith Fork has

caused erosion of the concrete in the apron and walls of the Providence-

Millville diversion structure and consequent exposure of the reinforcingsteel (Fig. 3.8).

SOLUTION

Following the extreme flooding years of 1983 and 1984, the SCS (Soil

Conservation Service) in Utah was faced with repairing or replacing amultitude of irrigation structures that had been damaged or lost. The

decision was made to make the repairs or replacements, using some of the

proprietary concrete products available to enhance durability under high

bedload conditions.

The new Providence-Millville structure was one of five in which field

trials were conducted for the evaluation of defensive measures available.

The product selected for this site was a metallic aggregate topping. This

product consists of premixed metallic floor topping composed of iron

aggregate, high-early portland cement, and water-reducing admixtures. A

surface treatment was applied to the hardened surface.

1-in.-thick metallic aggregate topping was placed over a new concrete

structure substrata following application of an epoxy or latex bonding aid.

A proprietary sealer, recommended by the topping supplier, was applied to the

overlay surface to reduce permeability.

The cost for 604 square ft of surface treated was $11.00/square ft (1986

price level.)

PERFORMANCE

High water prevents close inspection of the treated areas. Inspections

since the installation indicate the overlay is still intact. High water

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conditions and the accompanying abrasive bedload have been only moderate

since the repairs in September 1986.

Fig. 3.8-Providence-Millville Diversion Structue. Erosion of the surface of the concrete apron

and sidewalls

DISCUSSION

This metallic floor topping hardener is supplied in pre-packaged 55-lb

bags, which is enough to apply a 1-in. layer to a 18- to 20-square ft area.

Installation must be in accordance with the manufacturer's directions.

The floor topping develops approximately 13,000 psi compressive strength in

3 days and is especially suited for building floor slabs subjected to impact

loads. While not specifically marketed for use on hydraulic structures, its

abrasion-resistant properties are attractive. Performance in drop structures

with heavy sediment bedloads has been positive to date.

REFERENCES

U.S. Department of Agriculture, "Memorandum, Dated April 17, 1990, to

Francis T. Holt, State Conservationist, SCS, Salt Lake City, UT, from Robert

A. Middlecamp, Construction Engineer, SCS, West National Technical Center,Portland, OR."

CONTACT/OWNER

State Conservation EngineerSoil Conservation Service, U.S. Department of Agriculture

P.0. Box 11350

Salt Lake City, UT 84147-0350

RED ROCK DAMDes Moines River, Iowa

BACKGROUND

Red Rock Dam, operational in 1969, is 6200 ft long and 95 ft high. The tworolled earth embankment sections of the dam are separated by a concrete

section that serves as the outlet works and spillway. The spillway has an

ogee crest with five 41-ft

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