Operation, maintenance, and inspection procedures for earthfill dams [1995]

OPERATION, MAINTENANCE, AND INSPECTION PROCEDURES
FOR EARTHFILL DAMS
GEORGIA DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION

OPERATION, MAINTENANCE, AND INSPECTION PROCEDURES FOR EARTHFILL DAMS
INDEX
PAGE
Acknowledgements ................................................................ ii
1. Introduction ..................................................................... .
2. 1978 Georgia Safe Dams Act ........................................................ .
3. Parts of a Dam ................................................................... . A. Embankment and Foundation .................................................... . B. Principal Spillway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 C. Emergency Spillway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 D. Drawdown Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Performing Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 A. Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 B. Principal Spillway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 C. Emergency Spillway ....................................................... , . . . . 6 D. Gates, Valves, Internal Drainage Systems, and Miscellaneous Mechanical Features . . . . . . . . . . . . . . 6
5. Owner Inspection ................................................................. 13 A. Seepage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 B. Erosion ..................................................................... 13 C. Cracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 D. Slides and Slumps ............................................................. 13 E. Subsidence .................................................................. 14 F. Vegetation ................................................................... 14 G. Boils ....................................................................... 14 H. Animal Burrows ............................................................... 14 I. Debris ...................................................................... 14
6. Information and Assistance ........................................................... 18
LIST OF FIGURES
Figure 1 - Parts of a Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Plates 1 through 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Plates 8 through 11 ................................................................ 16

ACKNOWLEDGEMENTS
The Georgia Department of Natural Resources wishes to express its gratitude to the following: The Federal Emergency Management Agency, for
furnishing the financial support for this publication. The Kentucky Department for Natural Resources and Environmental Protection, for their information from developing a similar booklet. The Staff of the Dam Safety Program, for invaluable lessons gained from experience with dams.
ii

1. INTRODUCTION
Prepared as a public service for owners and operators of dams in Georgia, the principal objective of this manual is to outline the proper maintenance and operation practices for dams and provide simple guidelines for visual safety inspections. The manual is not intended as a design guide.
A regular program of dam maintenance will help prevent major problems and avert potential failure. Even with the best maintenance, visual inspections are necessary because problems may develop as a dam ages. When a potential problem arises, the owner should obtain the professional advice of an engineer experienced in the design and construction of dams. If the dam is regulated by the State, the owner is required to report any suspected problems immediately. "Home remedies" can lead to serious difficulties, including collapse of the structure.
Most dam failures are a direct result of a lack of maintenance and regular visual inspection. A dam owner can be held liable for any damage or injuries resulting from a failure of his dam. Therefore, following the guidelines of this manual and consulting an engineer about suspected problems is a worthwhile investment.
2. 1978 GEORGIA SAFE DAMS ACT
Georgia's Dam Safety Program began after the collapse of the Kelly Barnes dam in Toccoa on November 6, 1977. The failure of the dam resulted in 39 deaths and enormous property damage. In 1978, the Georgia General Assembly passed the Safe Dams Act. This Act provided for an inventory and classification system of all the dams in the state, and an inspection and permit system. The word "dam" is defined as "any artificial barrier, including appurtenant works which impounds or diverts water, and which (1) is twenty-five feet or more in height from the natural bed of the stream or watercourse measured at the downstream toe of the barrier, or from the lowest elevation of the outside Iimit of the barriers, if it is not across a stream channel or watercourse, or (2) has an impounding capacity at maximum water storage elevation of 100 acre-feet or more."
Dams are classified as either Category I (where failure would cause probable loss of human life) or Category II (where failure would not be expected to cause probable loss of human life). At least once every five years dams are re-inventoried to determine if any downstream development has occurred which would cause a reclassification.
Both existing and proposed dams classified as Category I must have permits to continue operation or be constructed. The permitting process starts with a detailed visual inspection by State engineers or by a private engineering consultant under contract with the State. If this inspection reveals deficiencies not related to routine

maintenance, the owner of the dam is required to retain a qualified engineer (registered in Georgia) to design the repairs necessary to correct the deficiencies. A permit is issued when the repair or construction plans are approved by the Safe Dams Program. State engineers make periodic inspections during the repair process and at least annually thereafter, to ensure the dam is properly maintained and no serious problems have developed.
The owner is legally responsible for his dam. Negligence in fulfilling his responsibilities can lead to extremely hazardous conditions if the dam fails. In the event of failure, the owner may be liable for losses of property and human life. Criminal charges have been filed on numerous occasions as the result of dam failures.
The purpose of the Georgia Safe Dams Act is to protect the health, safety, and welfare of all the citizens of the State by reducing the risk of dam failure, thus preventing death and injury. However, it is up to the owner to operate and maintain a dam safely.
3. PARTS OF A DAM
This section is intended to acquaint owners with the common terms used when discussing inspection and maintenance of earthfill dams. The vast majority of the dams in Georgia are of the earthfill type. Figure I shows a typical earthfill dam and illustrates the terms used in this booklet. The parts of a dam are grouped into four categories: (A) Embankment and Foundation; (B) Principal Spillway; (C) Emergency Spillway; and (D) Drawdown Facilities.
(A) EMBANKMENT AND FOUNDATION The earth embankment is the barrier which impounds a lake. The materials in the embankment must be impermeable enough to hold back water and strong enough to stand on a slope. Earthfill dams may be homogeneous (composed of essentially the same material throughout) or zoned. Many of the smaller dams in Georgia are homogenous. Several materials are used in a zoned embankment. The most impermeable material is used in the core to cut off water flow. More pervious materials make up the remainder of the slopes. In most dams a cutoff trench prevents water from flowing under the dam through its foundation. A compacted clay core forms this impermeable zone. Even with clay cores and cutoffs most dams seep through the embankment. The amount of seepage is proportional to the type of construction material used and the type of soil in the foundation. Seepage through the dam should be collected and controlled by an internal drainage system such as a toe drain, foundation drain, blanket or chimney drain. The seepage control system is not designed to stop the flow of water, but to provide

OPERATION, MAINTENANCE, AND INSPECTION PROCEDURES FOR EARTHFILL DAMS
INDEX
PAC E
Ack now ledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
1. Introduction ............................... . ... . ......... .. . . . .. . ... .......... . .. .
2. 1978 Georgia Safe Dams Act . . . ... . . ... . .... .. . ..... . .... ... .. . . . ... . ... . . . ......... .
3. Parts of a Dam .... .. ... . . . . . . . . . . .. . . . . .... . . . .. .. . . . . ...................... . .... . A. Emba nkment and Found ati on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 B. Princi pa l Spill way .... . .. .. ... . ........ . . . .. . ..... ... . ... .. ... . ...... . . .. .... .. 3 C. Emergency Spillway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 D . Drawdown Fac iliti es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Performing Maintenance ............. . ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 A. Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 B. Pri nci pal Spillway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 C. Emergency Spil lway ... ..... . ... . .... .... .... .. .. . ........ . .. . .. .. . . . . ... .. , . . . . 6 D . Gates, Va lves, Intern al Drai nage Systems, and Miscell aneous Mechanica l Features . . . . . . . . . . . . . . 6
5. O w ner Inspection .. . .. ........ . . ... . .. . . ... . .. . .. . .... . . . .. . .......... . .. . ... . . . . . 13 A . Seepage ... .... . ...... . .... ... .. ... . .... . . ... ..... ... ... .. .. .. ........ . ..... 13 B. Eros ion ... . . . . . . .. . ............ .. . . ...... . . .. ... . . . .. . . . . ... . .. . . . .. . . ..... . 13 C. Crac ks ..... . .. .. . .... . ... . ... . . . .. .. . . . . . . . . ..... ... . ... ............ . ...... . 13 D . Sl ides and Slumps .. . .... . ..... . . . . . ..... . .... ... . . . ... . . . ... . . ... . ... .. . . . .. .. 13 E. Subsi dence . . . .... . .. . ..... .. ... . ...... . ... .. ... . .. . ......................... 14 F. Vegetation . . ..... . ......... .. . ... ....... .. ... . ....... . . ...... ... . .... ... .. . .. 14 G. Boils ...... ..... .. .. . . .... . .. ... ... . ..... . .... .. ... .... ... . .. .. . ..... ... .. . . 14 H . Ani mal Burrows ....... . . .. . . . . . ... .. ... . . . .. . . .. .............. . . ...... .. .. . ... 14 I. Debri s . .. .. .. . ..... . . . .... . ... .... . . .. ... ... . .. .. ......... . ... .. .. . . .. .. . ... 14
6. Information and Ass istance .. . . . . .. . ... ........... . ... . . . ..... .. . . ..... .. . . .... . ..... . 18
LIST OF FIGURES
Figure 1 - Parts of a Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Plates 1 through 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Plates 8 through 11 . ... .. .. . ... . .. .. . . ... . .... .. ... . ...... . . . ... . . .. . .... ... .... ... 16

a method of discharging the water safely. It seep-

dam to the stilling basin . Because the conduit

age is collected and controlled , the slopes will be

penetrates the entire dam it forms a normal path

less likely to slough and easier to maintain . A

for seepage flows. To prevent seepage along th e

seepage collection system may also be necessary

conduit, the material around the pipe must be

to prevent water pressure from building up under

properly compacted during installation . Some-

the dam .

times concrete bedding is the only way to insure

The foundation material must be strong enough

the required compaction under the conduit. Anti-

to safely support the embankment and reservoir.

seep collars also reduce seepage along the con-

The foundation material determines the size and

duit. The collars are most effective when placed

depth of the cutoff trench.

inside of the core of the dam.

The dimensions of a dam depend on its pur-

(C) EMERGENCY SPILLWAY

pose, foundation conditions, and hazard classifi-

In extreme conditions, the emergency spillway pre-

cation . Top width or crest is determined by the

vents the dam from overtopping. Most emergency

height of the dam but is sometimes enlarged to

spillways are grassed earth channels at one end

accommodate a roadway . Steepness of the slopes

of the dam . The spillway has a level control sec-

varies with the type of material used; whether or

tion which sets the elevation of the spillway. The

not an internal drainage system is installed and such

emergency spillway's exit slope should not be

considerations as maintenance and access . The

steep enough to cause erosion problems when it

slopes must be protected from the erosion effects

operates. The channel should exit well away from

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of rain , with the front slope protected at the

the toe of the dam to prevent flows from encroach-

waterline from wave action by riprap or by a

ing on the toe of the dam. The emergency spill-

berm. The elevation differences between the

way must not be located on easily erodible soil ,

principal spillway, emergency spillway, and the

because spillway failure can be as catastrophic as

crest of the dam are dictated by the design storm

the failure of the dam embankment.

which the dam must be able to withstand . The

A few dams in Georgia incorporate both the

Safe Dams Act sets guidelines for the minimum

principal and emergency spillway into a single

design storm on which the spillway design must

structure . This is usually accomplished by a rein-

be based . The guideline varies with the size of

forced concrete chute spillway or by very large

the dam and its hazard classification. The top of

risers and conduits. These single spillways are most

the dam must be at an elevation sufficient to pass

common when property constraints or erodible

the design storm and prevent overtopping due to

soil preclude an earth emergency spillway.

wave action. Overtopping of an earthfill dam can

(D) DRAWDOWN FACILITIES

lead to a rapid failure of the structure.

The drawdown facility provides a means of drain-

(B) PRINCIPAL SPILLWAY

ing the reservoir safely. All dams should have

The principal spillway is designed to control the

some means of lowering the lake when structural

normal level of the reservoir. The most common

repair is necessary, or when failure of the dam

type of principal spillway consists of a metal or

may be imminent. Most drawdown facilities con-

concrete pipe through the base of the dam con-

sist of a pipe through the dam with a valve oper-

nected to a riser or standpipe in the lake. The top

ated by a wheel at the lake surface. Many times

of the riser is equipped with a trash guard to pre-

the principal spillway conduit and the drawdown

vent debris from obstructing flows through the

conduit are combined into the same component.

pipe . The normal flows carried by the spillway

The gate valve is on the upstream side of the riser

must be safely discharged to the stream channel

structure or in the structure itself. The valve must

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in a non-erosive manner. Because flows in the

be on the reservoir end of the pipe so there will

principal spillway pipe can reach high velocities,

be no water pressure in the conduit. A dam could

a stilling basin or plunge pool should be used to

fail suddenly if pressure caused a pipe to rupture

prevent erosion . This basin is protected by con-

inside the dam .

crete or riprap and reduces the velocity of the

It is good engineering practice to combine the

water so it will not erode the downstream channel .

principal spi II way conduit and the drawdown con-

Any conduit or pipe through the dam is a major

duit because this limits the number of penetra-

source of problems in an earthfill structure . The

tions through the dam to one. If conditions are

conduit must be strong enough to support the

such that the two conduits must be separate, the

weight of the embankment, have watertight

same precautions must be taken to insure com-

joints, and extend past the downstream toe of the

paction and prevent seepage along both pipes.

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4. PERFORMING MAINTENANCE
Maintenance includes applying measures to prevent

problems are observed . Severe erosion of the front slope can be repaired only by lowering the lake and regrading the entire slope .

deterioration, restoring, rebuilding, replacing, and put-

4- Animals: The dam should be kept free of animal

ting together parts that are torn, broken, or deteriorated.

traffic and habitation. Domestic animals can dam-

Routine maintenance can be, and usually is, important

age the vegetative cover, especially if the cover is

in reducing or avoiding future costly repairs.

thin or the dam is wet from rainfall. Grazing

A. EMBANKMENT:

should be controlled to ensure proper vegetative

1- Vegetation : A good cover of grass should be estab-

cover. Burrowing animals such as muskrats ,

lished and maintained by performing the follow-

beavers, and badgers should be kept away fror.n

ing tasks on a regular schedule:

smaller dams. Dens should be filled in with com-

a. Reseed, resod, and fertilize areas where there

pacted soil. Dams have failed because animals

is a poor stand or areas destroyed by erosion.

burrowed through the embankment.

Fertilize at regular intervals.

5- Sloughs and Slides: The many reasons for sloughs

b. The vegetation on a dam should be mowed at

and slides include seepage, improper compaction,

least twice a year to allow the grass to estab-

and overly steep slopes . Before an unstable area

lish a thick, erosion-resistant sod, and to make

is repaired , the cause of the slough should be

it easier to detect potentially dangerous condi-

determined. Corrective action may include con-

tions such as seepage, erosion gu II ies and .

structing a berm, flattening the slope, or installing

cracks.

an internal drainage system to dry the slope and

c. Undesirable vegetation such as trees, bushes,

control the seepage.

vines and briars should be removed. Local ordi-

B. PRINCIPAL SPILLWAY :

nances should be observed regarding use of

The primary purpose of this spillway is to pass

herbicides or burning. Trees and brush develop

normal flows safely. Maintenance to ensure the

extensive root systems which provide conduits

spillway safety includes:

for seepage. Large trees on a smaller dam can

1- Riser and Conduit Pipe: The conduit used for a

topple, leaving large holes which could lead

spillway riser or pipe must be watertight and con-

to breaching of the dam . Brush, vines, kudzu,

structed of sound material. The conduit must be

and briars obscure the surface of the embank-

strong enough to support the weight of the dam

ment, limiting thorough inspections. Bushes

and lake. Joints between pipe sections must be

and tall grasses along the waterline must be

designed to remain watertight. If a section of pipe

kept cut to discourage burrowing animals from

collapses or a joint becomes separated, the soil

digging dens.

surrounding the pipe can be eroded away by the

2- Erosion: Erosion problems develop from not hav-

flowing water and the dam will eventually col-

ing a good stand of grass, allowing vehicles to

lapse. If a problem with the conduit is suspected

travel on the dam, or by improper drainage which

it should be investigated and repaired immedi-

allows surface runoff to concentrate. Erosion gul-

ately.

lies should be refilled and compacted and drain-

2- Concrete Spillways: All concrete spillway struc-

age improved to prevent concentrated flows. Ero-

tures should be on a firm foundation, have an

sion along the abutments is a common problem

underdrain system and have a turndown at the

,,

because of concentrated flows. Wheel ruts from

end to prevent undermining of the end of the

vehicular traffic on a dam's crest should be filled

spillway. Joints and cracks in a spillway should

to prevent ponding water. Erosion control is essen-

be free of vegetation and tightly sealed with a

tial in avoiding future problems.

mastic joint filler. Hollow spots under the spill-

3- Wave Protection: If a dam impounds a large reser-

way should be backfilled. Many spillways have

voir and does not have surrounding trees to serve

weep holes or drains which allow any water under

as windbreaks, the front slope of the dam may

the spillway to exit safely. These outlets should

erode from wave action . Unchecked wave action

always be open and functional. Failure to keep

will reduce the width of the dam crest. A com-

drains open or to repair separated joints or cracks

mon type of protection is riprap placed on either

can lead to complete failure of the spillway and

a drainage stone or a filter fabric. Wave protec-

to major repair costs.

tion devices are susceptible to weathering, move-

3- Erosion Control: Since the principal spillway will

ment and settlement from waves, rain and ice.

always be passing flows from the lake, and dur-

They should be repaired or replaced as soon as

ing storms some very high flows , it must do so in

5

------
CONTROL
SECTION--~ EM~RGENCY
SPILLWAY

CORE TRENCH
FIGURE 1

ANTI- SEEP COLLARS
BASIN/ PLliNGE POOL
OUTLET CHANNEL

Photo A : An example of a well maintained dam.
Photo 8: A poorl y maintained dam which fai led at the principal spillway pipe. Plate 1 7

a manner which does not cause erosion at the outlet end. The plunge pool or stilling basin is designed to prevent erosion from spillway flows . The most common means of erosion prevention is the use of riprap . During hi gh flows, riprap may be displaced or lost altogether. Replacement is an important maintenance task. The riprap should be of various sizes with the larger big enough to stay in place during peak flows . 4- Obstructions : If the principal spillway is the riser type it should have a trash guard . Otherwise, the spillway will attract floating debris which will clog it and become very difficult to remove. This w ill result in increased use of the emergency spillway which can cause erosion problems. An obstructed spillway increases the possibility of the dam' s failing due to overtopping during a severe storm . Any trash collected on the trash guards or in front of concrete spillways should be removed as a part of regular maintenance. C. EMERGENCY SPILLWAY: The emergency spillway is designed to pass flood flows safely, keeping the dam from overtopping. If propertly designed the emergency spillway will handle flows only a few times a year. 1- Vegetation : Most emergency spillways are earthen , and require a vegetative cover to prevent erosion . Grasses should be thick, well-bedded sod which is mowed and fertilized regularly . Barren areas should be reseeded as they develop. The spillway should be kept free of trees, fences, or shrubs which may trap floating debris and restrict flows . 2- Erosion Control : If an emergency spillway is used too frequently or must pass flows during a major storm, erosion problems may develop. It is important to correct erosion problems immediately; otherwise they can become so serious that a new spillway must be constructed and the old one filled in and abandoned . Elevations across the

spillway channel should be the same to prevent concentrated flows in one location . 3- Concrete Structures: A concrete emergency spillway must be maintained the same as a concrete principal spillway, although it is used infrequentl y. 4- Obstructions : Both the in let to the emergency spi 11way and the spillway channel must be kept clear of trash , debri s, trees, brush, buildings, fences, boat docks and other obstacles which can reduce the spillway capacity. D . GATES, VALVES, INTERNAL DRAINAGE SYSTEMS AND MISCELLANEOUS MECHANICAL FEATURES : 1- Drawdown facilities must be tested periodicall y to insure they function properly. All threads and gears should be lubricated to prevent seizing. Badly rusted parts should be replaced immediately . 2- Gates and Flashboards : Spillway gates and flashboards should be inspected periodically for deterioration . Moving parts on metal gates should be kept lubricated, and all metal parts painted to prevent rust. Flashboards should be replaced as necessary to prevent premature collapse. 3- Alarm Systems : If the dam is equipped with a water level alarm system it should be tested at least twice a year. Vegetation and debris should be kept from around the installation . 4- Seepage Control System s: Dams which have a system for collecting and discharging seepage w ill have one or more outlet pipes which should be kept above the ground line and free of vegetation . Sediments may build up in the pipes making it necessary to clean the pipes periodically. If the outlets are near the ground surface a bar screen should be placed over the ends to prevent animals from living in the pipe . Photographs of so.me dams on the following pages indicate both poorly and properly maintained dams .

6

Photo E: An example of erosion in the emergency spillway channel which now is controlling normal pool.
Photo F: A maintained emergency spillway with a dense cover of grass. Plate 3 9

Photo C: An example of erosion of the front slope due to wave action.
Photo 0 : A maintained front slope with riprap for wave protection . Plate 2
8

Photo 1: An internal drain outlet which is obstructed by vegetation and is not equipped
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with a small animal guard.
Photo j : An internal drain outlet that is visible and free from any obstructions .
Plate 5 11

Photo C: An example of erosion in the plunge pool at the princ ipal spillway outlet.
Photo H: A protected pluge pool using riprap. Plate 4
10

5. OWNER INSPECTION

refilling, regrading, and revegetation. Left unat-

Regular inspection of dams is vital to proper care and

tended, erosion can reach proportions which dam-

maintenance. Only by regular inspections can problems

age the integrity of the dam.

be detected early. Early detection and remedy is essential in preserving the integrity of the structure and avoiding costly repairs.
Inspections should include areas other than the dam and spillway. The scope of the inspection should include areas downstream, on the abutments, and a general overview of the pool area. The dam and lake area must be viewed in proper perspective with the surrounding terrain. Failure to do so is to ignore the possibility of unseen problems in the valley and abutments which can be influenced by the dam and lake.

Erosion along the waterline due to wave action is another easily detected danger sign . Remedies usually involve revegetation and refilling the eroded area with rock or earth .
Erosion from seepage through the dam , foundation , and abutments is a danger signal. This is difficult to repair due to seepage water. Repair generally involves refilling the areas as well as measures to collect and filter the seepage water. Repairs require the services of a qualified engineer.

During an inspection the owner should be aware of various signs of danger. Such signs are often overlooked

C. Cracks

unless the inspection is thorough and the dam has been

The entire embankment should be closely in-

properly maintained. An inspection cannot be adequately

spected for cracks. Short, isolated cracks are not

,.

performed by just driving by the dam . Signs of danger

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which should be searched for are:

A. Seepage

The appearance of seepage on the downstream slope, abutments or downstream areas is a cause for concern. The type and quantity of seepage should be studied. If the water is muddy or murky and is issuing from a well-defined hole, material is probably being eroded from inside the embankment and a potentially dangerous situation can develop. This type of problem requires immedi-

usually significant, but larger, well-defined cracks indicate a problem is developing. Cracks are of two types : transverse and longitudinal. Transverse cracks appear across the dam and indicate settlement. Such cracks are an avenue for seepage water and piping could develop very quickly. Longitudinal cracks run parallel to the dam and may be the signal for a slide or slump on either face of the dam . Cracks usually call for lowering of the lake and reconstruction measures. They require the consultation of an engineer for remedy .

ate attention to stop the removal of material and

If cracks develop in concrete spillway structures,

control the seepage. If the water is clear, it may

water may start flowing under the spillway, erod-

be coming from an older hole and should be

ing away the foundation material. Danger signals

monitored closely for any changes in color and

consist of muddy water flowing from foundation

quantity.

drainage outlets, or a hollow sound when the

Seepage can also occur on abutments, under

structure is struck. Cracks may be evident in other

spillways, and through the foundation and may at

areas, such as spillway cuts and landslides around

times occur some distance from the dam. Gener-

the pool area. Cracks can only be detected if

'.

ally, the further away seepage exits from the dam

vegetation on the dam is kept mowed.

the less the probability of danger. However, it is

D . Slides and Slumps

important that all areas of seepage be watched for changes .

Slides and slumps are usually the most detectable danger signals. A massive slide can mean cata-

Ponding water or saturated soil caused by poor

strophic failure of the dam . Slides occur for many

surface drainage may be mistaken for seepage. The

and varied reasons, and their occurence can mean

dam and the area below it should be graded to allow

a major reconstruction effort. Slides and slumps

proper drainage.

are normally preceded by cracks, and regular

B. Erosion

inspection can avoid sudden failure .

Erosion on the dam and spillway is one of the most evident signs of danger. Even a slight amount of rainfall can greatly increase the size of erosion

Lowering a reservoir should be done cautiously . A sudden drawdown of the lake can cause slides on the front slope of the dam .

channels and gullies. Early detection of erosion

Minor slides caused by heavy rainfalls or spring

channels can greatly facilitate necessary repairs:

thaws can be repaired with minimal effort. Repair

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Photo K: A principal spillway inlet which has an inadequate trash guard. Trash severely restricts the capacity of this spillway.
Photo L: A trash guard on a repaired principal spillway riser.
Plate 6 12

Photo M: Seepage at the downstream toe of the dam near the principal spillway outlet.
PhotoN : Gates should not be located on the downstream end of pipes which pass through a dam . Plate 7
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of major slides and slumps should not be undertaken without knowledge of their cause; such problems require the services of an engineer.
Slides in spillway areas should be removed immediately since their presence reduces hydraulic capacity. Slides into the lake area can cause sudden displacement of lake water and subsequent overtopping of the embankment.
E. Subsidence
Subsidence is vertical movement of the foundation materials due to failure of consolidation . Subsidence may occur so slowly that its detection may go unnoticed without proper inspection procedures .
Foundation settlement can result if the dam and reservoir are placed on an area not having suitable geologic strength, or over collapsed caves or mines . Subsidence is movement over and beyond that anticipated . Subsidence may not cause any well defined cracks or seepage at its onset. Danger signals of subsidence include conduit displacements or separations at joints, conduit ruptures or collapses , and structure movements .
Conduit separations or ruptures can cause the leakage of water into the embankment and the subsequent weakening of the dam . Pipe collapse can result in hydraulic failures due to diminished capacity. It should be noted that rigid pipes (such as concrete) are most likely to separate and crack, while flexible pipes (such as metal) are most subject to collapse . Murky water exiting the conduit when the inflow from the lake is clear is an indication of conduit problems.
Structure movements can be signs of subsidence. Listing or tilting of structures set in foundation material is a sign of distress. Movement of intake or discharge structures can result in loss of conduit function and diminished hydraulic capacities . The introduction of water at conduit rupture points can cause instability of the dam .

Subsidence is measured on embankments by referencing some permanent markers on the dam and associated structures to points off the dam. Elevations should be regularly checked for readings which can give indications of subsidence .
F. Vegetation
The appearance of vegetation such as cattails, reeds, mosses, and other " wet environment" types of vegetation can be a sign of seepage or poor surface drainage.
Prominent areas for undesirable vegetation are the toe of the dam, the area downstream and the abutments . These areas should be examined closely for signs of seepage and appropriate measures should be taken promptly. (See paragraph on seepage.) Maintenance on these areas should involve the mowing and clearing necessary to maintain the regular inspection of changes in seepage.
G. Boils
Boils are a serious danger signal and indicate seepage water exiting under some pressure. Boils typically occur in areas downstream of the dam, and indicate that material is being removed . Measures must be taken to filter and discharge the seepage in a controlled manner. Determination of the cause and a permanent remedy requires the consultation of an engineer.
H. Animal Burrows
Animal burrows are a potential danger area . Inspection should include a careful search for dens on the dam and abutments. Remedies should include removing the animals and refilling the dens.
I. Debris
Debris on the dam and spillways is a potential danger. Debris should be removed as soon as possible so it cannot reduce the function of spillways, damage structures and valves, and destroy vegetative cover.

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Photo Q: Sloughing on the backs/ope of a dam .
Photo R: Severe erosion in the spillway outlet channel.
Plate 10 17

Photo 0: An entrance to a muskrat den located in the front slope below normal pool.
Photo P: Water is flowing from under the concrete spillway through a crack. Note the vegetation in the cracks. Plate 8
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6. INFORMATION AND ASSISTANCE
Additional information about a specific problem with a dam is available from the Dam Safety Program. Owners of Category I dams having Operation Permits are reminded to notify the Dam Safety Program before taking corrective action if a deficiency which threatens the safety of the dam is found during an owner' s inspection . However, if failure is imminent, the owner should take whatever actions are required to reduce the potential threats of the failure and then immediately notify the Dam Safety Program :
Georgia Department of Natural Resources Environmental Protection Division

Safe Dams Program 4244 International Parkway Suite 110 Atlanta, GA 30354 (404) 362-2678
24 hour number: 1-800-341-4113 (Law Enforcement)
24 hour number: 404/656-4300 (Emergency Response)
In addition , local authorities and the local Emergency Management Agency should be contacted. If danger signals are noticed in time, actions can be taken which will minimize catastrophic damages which could result from failure of the dam .

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I

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