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OCR for page 4
2
The Safety of Dams
For centuries, dams have provided mankind with such essential benefits as
water supply, flood control, recreation, hydropower, and irrigation. They
are an integral part of society's infrastructure. In the last decade, several
major dam failures have increased public awareness of the potential haz-
ards caused by dams.
In today's technical world, dam failures are rated as one of the major
"low-probability, high-loss" events. The large number of dams that are 30
or more years old is a matter of great concern. Many of the older dams are
characterized by increased hazard potential due to downstream develop-
ment and increased risk due to structural deterioration or inadequate spill-
way capacity.
The National Dam Inspection Program (PL 92-367) developed an inven-
tory of about 68,000 dams that were classified according to their potential
for loss of life and property damage (U. S. Army Corps of Engineers 1982b) .
About 8,800 "high hazard" dams (those whose failure would cause loss of
life or substantial economic damage) were inspected and evaluated. Spe-
cific remedial actions have been recommended, ranging from more de-
tailed investigations to immediate repair for correction of emergency con-
ditions. The responsibility for the subsequent inspections, investigations,
and any remedial work rests with the owners of the dams. In most states the
actions or inactions of the dam owners will be monitored by a state agency
responsible for supervision of the safety of dams.
The National Dam Inspection Program provided a beginning to what is
hoped to be a continuing effort to identify and alleviate the potential haz-
4
OCR for page 5
The Safety of Dams
arcs presented by dams. Essential to the success of such an effort are under-
standings of the causes of dam failures and the effects of age; competent
inspection and maintenance programs; thorough knowledge of individual
site conditions as revealed by design, construction, and operating records,
in addition to inspections and investigations; and an emergency action plan
to minimize the consequences of dam failure. The remainder of this chap-
ter presents a discussion of these elements.
s
CAUSES OF DAM FAILURES
Dam Failure Surveys
A number of studies have been made of dam failures and accidents. The
results of one survey, by the International Commission on Large Dams
(ICOLD), were reported in its publication Lessons from Dam Incidents,
USA. N. J. Schnitter (1979 Transactions of ICOLD Congress, New Delhi)
summarized the survey data in the form illustrated by Figures 2-1 through
2-5. These data pertain only to dams more than 15 meters in height and
include only failures resulting in water releases downstream.
Figure 2-1 shows the relative importance of the three main causes of fail-
ures: overtopping, foundation defects, and piping. Overall, these three
causes have about the same rate of incidence.
Figure 2-2 gives the incidence of the causes of failure as a function of the
dames age at the time of failure. It can be seen that foundation failures
occurred relatively early, while the other causes may take much longer to
materialize.
Figure 2-3 compares the heights of the failed dams to those of all dams
built and shows that 50 % of the failed dams are between 15 and 20 meters
high.
Figure 2-4 shows the relation between dams built and failed for the vari-
ous dam types from 1900 to 1969. According to the bottom graph, gravity
dams appear the safest, followed by arch and fill dams. Buttress dams have
the poorest record but are also the ones used least.
Figure 2-5 shows the improvement of the rate of failure over the 1900-
197S period. The upper graph is in semilogarithmic scale and gives the per-
centage of failed dams in relation to all dams in operation or at risk at a
given time. The lower graph gives the proportion of the built dams that
later failed and shows that modern fill and concrete dams are about equally
safe.
The United States Committee on Large Dams (USCOLD) made a survey
of incidents to dams in the United States. Results of the initial study, which
covered failures and accidents to dams through 1972, were published
OCR for page 6
6
SAFETY OF EXISTING DAMS
Dam failures 1900-1975 (over 15 m height)
CONCR ETE
OV ERTOPP I NG
FOUN DATI ON
PIPING AND
SE EPAG E
OTH ERS
Fl LL
OV ERTOPPI NG
fOUNDATION
PIPING AND
SE EPAGE
OTHERS
ALL TYPES
OVERTOPPI NG
FO UN DATI ON
PIPING AND
SE EPAG E
OTH ERS
~~\~ 1
>. '9'5# To' 'id ~ 21
1=
L2;J6
~\~\~34
::::::.:::. ~30
l
0 10 20
30 40 50
PERCENT OF FAI LUR ES
(excl. failures during construction and acts of wart
FIGURE 2-1 Cause of failure. SOURCE: ICOLD (1973~.
jointly by the American Society of Civil Engineers (ASCE) and USCOLD
in 1975 in Lessons from Dam Incidents, USA. These data were updated
through subsequent USCOLD surveys of incidents occurring between 1972
and 1979. Table 2-1 was compiled from the information developed by the
USCOLD surveys and includes accidents as well as failures. The USCOLD
surveys pertained only to dams IS or more meters in height.
Table 2-2 pertains only to concrete dams and lists the number of inci-
dents in the USCOLD surveys for each principal type of such dams. Tables
2-1 and 2-2 list incidents by the earliest, or "triggering," principal cause as
accurately as could be determined from the survey data. For instance,
where failure was due to piping of embankment materials through a cor-
roded outlet, the corrosion or deterioration was accepted as being the pri-
mordial cause of failure. Also, where a sliding failure was due to overtop-
OCR for page 7
The Safety of Dams
7
ping flows that eroded the foundation at the toe of a concrete dam,
overtopping was listed as the cause of failure. Only one cause is listed for
each incident. While only a few of the incidents were attributed to faulty
construction, it is reasonable to expect that many of the other failures were
due, at least in part, to inadequate construction or design investigations.
However, the information on the specific cases is not sufficient to establish
such inadequacies as the primordial causes.
Failure Modes and Causes
Table 2-3 pertains to embankment dams. It is of particular interest because
it correlates failure modes and causes. As indicated, the modes and causes
of failure are varied, multiple, and often complex and interrelated, i.e.,
i Dam failures 1900-1975 (over 15 m height)
100
On
UJ
UJ
Z O
~ 1 00 it. . ^~1~;^n ~
UJ
m
At
LL
UJ
t~ 50
0 L
O
Foundation
,
| / Overtopping
-
-
CONCRETE
1 1 1
rvullva~'v~
Piping and Seepage
it;=
/
Fl LL
1 1 1
10 20 30
AGE IN YEARS
(excl. failures during construction and acts of war)
FIGURE 2-2 Age at failure. SOURCE: ICOLD (1973).
OCR for page 8
8
~ ~ ~ - . ~ ~ ~ ~ ~ ~
SAFETY OF EXISTING DAMS
Dam failures 1900-1975 (over 15 m height)
inn
UJ
I
LU
z
-
I
~ 100
UJ
o
z
LL
at 50
o
. _ _
O ~
Failed
-
/uilt 1900-1969
/ (Western Europe ~ USA )
CONCRETE
Built 1900-1969
(Western Europe + USA)
, l--J I I I
20 40 60 80
Fl LL
MAX. HEIGHT IN M
(excl. failures during construction and acts of war)
FIGURE 2-3 Height of dams. SOURCE: ICOLD (1973~.
Often the triggering cause may not truly have resulted- in failure had the
dam not had a secondary weakness. These causes illustrate the need for
careful, critical review of all facets of a dam. Such a review should be based
on a competent understanding of causes (and weaknesses), individually
and collectively, and should be made periodically by experts in the field of
· ~
c tam engineering.
Many dam failures could be cited to illustrate complex causes and the
difficulty of identifying a simple, single root cause. For example, the 1976
Teton failure may be attributed to seepage failure (piping) (]ansen 1980~.
But several contributing physical (and institutional) causes may be identi-
fied (Independent Panel to Review the Cause of Teton Dam Failure 1976~.
In another example, a dam in Florida was lost due to a slope failure, trig-
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The Safety of Dams
gored by seepage erosion of fine sandy soils at the embankment's toe. The
soils lacked sufficient cohesion to support holes or cavities normally associ-
ated with piping and were removed from the surface of the dam toe by
excessive seepage velocities and quantities. This undermining of the toe by
seepage resulted in a structural failure, but the prime cause was the nature
of the foundation soils.
The complex interrelationship of failure modes and causes makes it ex-
tremely difficult to prepare summary tables such as Table 2-1. It also ex-
plains why different evaluators could arrive at different conclusions re-
garding prime causes. Certainly any such table should be accompanied by
9
Dams Built
tic ( Arch
Buttress
8 ~ Gravity
Fl LL
Failed Dams
FILL
LL
Buttress
G ravity
LL ~
c: ~ Arch
O ; Buttress
C' ~ Gravity
TOTA L
CONCR ETE
Fl LL
;~ ~
6
. .~ _
~ /~//,26
0 20 40 60 80
PERCENT OF DAMS BU I LT
J
0 20 40 60 80
PE RCENT OF FAI LU R ES
o
FAILED DAMS IN PERCENT OF DAMS BUILT
(Excl. Failures During Construction and Acts of War)
FIGURE 2-4 Dam types (Western Europe and USA, 1900-1969~.
SOURCE: ICOLD (1979~.
OCR for page 10
10
SAFETY OF EXISTING DAMS
10.0
3.0
it 0.3
111
0.1
~\N
10.0
_ ~ 30 ~ ~~
0.3 1 1 1 1 — 1
1900 1910 1920 1930 1940 1950 1960 1970
YEAR
FIGURE 2-5 Probability of failure (Western Europe and USA).
SOURCE: ICOLD (1979).
a commentary to provide the reader with a better understanding of the
data. Thus in the following descriptions of each category of cause identified
in Table 2-1, additional information is given about the involved incidents.
Overtopping
Overtopping caused about 26~o of the reported failures and represents
about 13 % of all incidents. The principal reason for overtopping was in-
adequate spillway capacity. However, in 2 failure cases overtopping was
OCR for page 11
The Safety of Dams
attributed to blockage of the spillways and in 2 others to settlement and
erosion of the embankment crest, thus reducing the freeboard. In 1 of the
latter cases the settlement was great enough to lower the elevation of the
top of embankment below that of the spillway crest.
Six concrete dams have failed due to overtopping and 3 others were in-
volved in accidents. Two of the overtopping failures resulted from instabil-
ity due to erosion of the rock foundation at the toe of dam, and 4 were due
to the washout of an abutment or adjacent embankment structure. In 1 of
these events a saddle spillway was first undermined and destroyed, and
then the abutment ridge between the spillway and the dam was lost by
erosion. In one instance of erosion of the rock at the toe of the dam, piping
was suspected as a contributing cause.
The 3 overtopping accidents reported for concrete dams involved erosion
of the downstream foundation in only 1 case. In another instance the pow-
erhouse and equipment were damaged, but the dam sustained no damage.
11
TABLE 2-1 Causes of Dam Incidents
Type of Dam
Embank-
Concrete ment Other*
Totals
Cause F A F A F A 17 A F & A
Overtopping
Flow erosion
Slope protection damage
Embankment leakage,
piping
Foundation leakage, piping
Sliding
Deformation
Deterioration
Earthquake instability
Faulty construction 2
Gate failures 1
TOTAL
6
3
3
5 6
18
14
23
11
2 5
2 3
6 2
7 3
17
13
14
43
28
29 3
3
2 1
19 19 77 163 7
27 10
17 17
13
37
34
13
23 14
17 49
7 28
6 31
2 9
3 3
2 3
2 5 7
103 182 285
37
66
35
37
11
*Steel, masonry-wood, or timber crib.
F= failure.
A = accident = an incident where failure was prevented by remedial work or operating pro-
cedures, such as drawing down the pool.
SOURCE: Compiled from Lessons from Dam Incidents, USA, ASCE/USCOLD 1975, and sup-
plementary survey data supplied by USCOLD.
OCR for page 12
12
TABLE 2-2 Causes of Concrete Dam Incidents
SAFETY OF EXISTING DAMS
Concrete Dam Type
Arch Buttress Gravity Totals
F A F A F A F A F&A
Overtopping
Flow erosion
Foundation leakage, piping
Sliding
Deformation
Deterioration
Faulty construction
Gate failures
TOTAL
2 1 1 3
1 1 2
2
3 2
4 7
2 6 3
3
5
2
1 1
2 5
2
2 1
10 19
6
2
6
9
3
11
2
2
6
2 2 2
1
4 2 11
3
2
19 38
F = failure.
A= accident.
SOURCE: Compiled from Lessons from Dam Incidents, USA, ASCE/USCOLD 1975, and sup-
plementary survey data supplied by USCOLD.
In the third, structural cracking was believed to have been caused by the
overtopping load on the structure, resulting in subsequent reservoir leakage
through the dam.
Flow Erosion
This category includes all incidents caused by erosion except for overtop-
ping, piping, and failure of slope protection. Flow erosion caused 17 % of
the failures and 12 % of all reported incidents. Of the 17 failures, 14 were at
embankment dams where, except in 2 cases, the spillways failed or were
washed out. In 1 instance the gate structure failed due to erosion of its foun-
dation, and in another the embankment adjacent to the spillway weir was
washed out. In the latter case, overtopping and/or poor compaction of the
spillway-embankment interface was suspected but not confirmed. With re-
spect to the 3 concrete dam failures, the spillways were destroyed in 2 in-
stances and in the other, a small buttress dam, the entire dam was
destroyed.
The 17 reported accidents relating to flow erosion all involved embank-
ment dams. In 1 case the downstream embankment slope was eroded, and
in 2 other instances erosion of the outlets was involved. Two of the acci-
dents actually were due to cavitation erosion in the tunnels. The remaining
12 accidents involved the loss or damage to spillway structures.
OCR for page 13
The Safety of Dams
13
Slope Protection Damage
Damage to slope protection was not reported to be involved in any failures;
however, in 1 accident the undermining of riprap by wave action led to
embankment erosion very nearly breaching the dam. The 13 reported acci-
dents represent about 4 % of all incidents. Of the 13 accidents, 6 involved
concrete protection and the others riprap. In some of the latter cases the
wave action pulled fill material through the riprap, and in the others rip-
rap was either too small or not durable.
Embankment Leakage and Piping
Embankment leakage and piping accounted for 22% of the failures and
13 % of all reported incidents. In 5 of the 37 incidents piping is known to
have occurred along an outlet conduit or at the interface with abutment or
concrete gravity structure.
Foundation Leakage and Piping
Foundation leakage and piping accounted for 17 To of all failures and 24 %
of all reported incidents. It is the number one cause of all incidents. Six
concrete dams, 1 steel dam, and 11 embankment dams were involved in the
18 failures. In at least 11 of the 49 accidents, which involved 6 concrete and
43 embankment dams, the leakage occurred in the abutments. Some re-
ports cite inadequate grouting or relief wells and drains as causing the leak-
age and piping. In 1 event piping was caused by artesian pressures and not
reservoir water.
Sliding
This category covers instability as represented by sliding in foundations or
the embankment or abutment slopes. Sliding accounted for 6 % of all fail-
ures and 12 % of all incidents reported. Of the 6 failures, 1 was a concrete
gravity structure where, during first filling, the structure's slide down-
stream of about 18 inches was preceded by a downstream abutment slide,
followed by large quantities of water leaking from the ground just down-
stream of the dam. The reservoir was emptied successfully, but before re-
pairs were accomplished, the reservoir filled again causing large sections of
the dam to "overturn or open like a door." The 5 embankment failures oc-
curred in the downstream slopes, 1 due to excessively steep slopes and the
others probably due to excessive seepage forces.
All of the 28 reported sliding accidents involved embankment dams. In 2
cases the slides occurred in abutment slopes, in 10 cases in the downstream
OCR for page 14
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OCR for page 30
30
SAFETY OF EXISTING DAMS
records. They will also depend on the evaluator's assessments of risks and
consequences of failure. Such investigations may involve theoretical studies
as well as field investigations. Additional studies are sometimes needed to
better define the stress and stability conditions and to evaluate alternative
remedial measures. The investigative program can consist of a wide variety
of tasks, depending on the nature of the known or suspected problem. The
type of supplemental information and numerical data needed will concern
structural, geologic, and performance features unobtainable by direct vis-
ual examination. Some kind of exploration may be required for sample ex-
traction; for providing access for direct observation; and for instrumental
measurements of deformation, hydrostatic pressures, seepage, etc. Data
may also be obtained by nondestructive testing. Laboratory tests may be
required to determine engineering properties of the materials of the dam
and appurtenances and of the foundation for use in analyses and to assess
their general condition. Performance instrumentation may be required.
Applicable techniques of subsurface exploration, geologic mapping, labo-
ratory testing, and instrumentation are described in numerous excellent
references, such as the Handbook of Dam Engineering and various other
references listed in Chapters S through 10 of this volume.
After additional data have been obtained, the engineering analyses and
methods employed are generally similar to those that would have been con-
ducted in the initial evaluation had the data been available. Particular care
should be taken to study suspicious or questionable features and conditions.
The engineering data and information to be used in the analyses are those
specifically obtained for that purpose during the investigations. For exam-
ple, unless available data on spillway design indicate conclusively that the
spillway meets present-day design standards, a new flood estimate should
be made, and the existing spillway should be analytically tested for its abil-
ity to safely handle the updated flood. Or, as another example, if the stabil-
ity of an embankment dam appears marginal for any reason (such as ap-
parently over-steep slopes, unusual saturation patterns, low-strength soils,
or indications of high foundation pore pressures), a stability analysis and
companion seepage analysis should be made using soil strengths and per-
meability rates obtained by sampling and testing for use in those specific
analyses.
As valuable as they are, numerical analyses cannot provide total and ab-
solute answers upon which to base the evaluation. Many physical condi-
tions and reactive mechanisms cannot be mathematically analyzed. There-
fore, after all the objective factors that may influence the evaluation have
been gathered, interpreted, analyzed, and discussed, the investigator must
still exercise judgment as to whether the dam is adequate in its present con-
dition or requires remedial or other measures. There are no clear-cut rules
OCR for page 31
The Safety of Dams
31
by which the decisions can be made. Instead, the investigator may need to
employ empirical reasoning and objective assessments, compare the case
with successfully performing similar dams, and apply criteria in common
use by the profession. When the perceived problems involve areas of spe-
cialized engineering practice and there would be significant losses from
failure of the structure, experts in the pertinent specialties should be
brought in as consultants.
EMERGENCY ACTION PLANNING
Current Policies and Practices
While the intent of dam design, construction, operation, maintenance, and
inspection of dams is to minimize the risk of dam failures, it is recognized
that the possibility of dam failures still exists. Even though the probability
of such failures is usually small, preplanning is required to (1) identify con-
ditions that could lead to failure, in order to initiate emergency measures to
prevent such failures as a first priority, and (2) if this is not possible, to
minimize the extent and effects of such failures. The operating and mobi-
lizing procedures to be followed upon indication of an impending or postu-
late dam failure or a major flood should be carefully predetermined.
Following the failure of Teton Dam in 1976, President Carter directed
the appropriate federal agencies to develop guidelines for dam safety. Sub-
sequently, in June 1979, Federal Guidelines for Dam Safety was published
by the Federal Coordinating Council for Science, Engineering and Tech-
nology. While these guidelines were developed to encourage high safety
standards in organizational and technical management activities and pro-
cedures of federal agencies, they are also considered applicable to state
dam safety agencies and private and nonfederal dam owners.
A basic tenet of these guidelines is that an emergency action plan, com-
mensurate with the dam size and location (i.e., hazard classification),
should be formulated for each dam. The guidelines require an evaluation
of the emergency potential created from a postulated dam failure by use of
flood inundation maps; development of an emergency action plan, coordi-
nated with local civil preparedness officials; and a formal procedure to de-
tect, evaluate, and mitigate any potential safety problem. Owners of pri-
vate dams should evaluate the possible modes of failure of each dam, be
aware of indicators or precursors of failure for each mode, and consider the
possible emergency actions appropriate for each mode and the effects on
downstream areas of failure by each mode. Evaluation should recognize
the possibility of failure during flood events as well as during normal oper-
ating conditions and should provide a basis for emergency planning actions
OCR for page 32
32
SAFETY OF EXISTING DAMS
in terms of notification and evacuation procedures where failure would
pose a significant danger to human life and property. Plans should then be
prepared in a degree of detail commensurate with the hazard, and instruc-
tions should be provided to operators and attendants regarding the actions
to be taken in an emergency. Planning should be coordinated with local
officials, as necessary, to enable those officials to draw up a workable plan
for notifying and evacuating local communities when conditions threaten-
ing dam failure arise.
Some states and several federal agencies have already developed their
own emergency action planning guidelines and have implemented plans at
dams consistent with the major elements contained in the Federal Guide-
lines. Among the federal agencies, the U.S. Army Corps of Engineers
(1980) has published Flood Emergency Plans, Guidelines for Corps Dams.
The Corps publication merits consideration by private dam owners for its
(retailed procedure and case study examples. Additionally, the Corps
(1982a) has recently published a manual, Emergency Planning for Dams,
Bibliography and Abstracts of Selected Publications, for assisting planners
with relevant materials and references to emergency planning for dams
and preparation of flood evacuation plans.
Finally, the user is directed to technical guidelines and recommenda-
tions on emergency action planning for federal agencies that have been
published by a subcommittee of representatives from federal agencies hav-
ing responsibilities for dam safety for the Interagency Committee on Dam
Safety (ICODS) (FEMA 1982~.
Evaluation of Emergency Potential
Prior to development of an emergency action plan, consideration must be
given to the extent of land areas and the types of development within the
areas that would be inundated as a result of dam failure and to the proba-
ble time available for emergency response.
Determination of Mode of Dam Failure
There are many potential causes and modes of dam failure, depending on
the type of structure and its foundation characteristics. Similarly, there are
degrees of failure (partial vs. complete) and, often, progressive stages of
failure (gradual vs. sudden). Many dam failures can be prevented from
reaching a final catastrophic stage by recognition of early indicators or pre-
cursor conditions and by prompt, effective emergency actions. While
emergency planning should emphasize preventive actions, recognition
OCR for page 33
The Safety of Dams 33
must be given to the catastrophic condition, and the hazard potential must
be evaluated in that light. Analyses should be made to determine the most
likely mode of dam failure under the most adverse condition and the result-
ing peak water outflow following the failure. Where there is a series of
dams on a stream, analyses should include consideration of the potential
for progressive "domino effect" failure of the dams. Appendix A of Chapter
4 provides an example of guidelines on estimating modes of dam failure for
formulating emergency action plans by an investigator-owned utility.
Inundation Maps
To evaluate the effects of dam failure, maps should be prepared that delin-
eate the area that would be inundated in the event of failure. Inundation
maps should account for multiple dam failures where such failures are pos-
sible. Land uses and significant development or improvements within the
area of inundation should be indicated. The maps should be equivalent to
or more detailed than the United States Geological Survey (USGS)
1:24,000-scale quadrangle maps, 7.5-minute series, or of sufficient scale
and detail to identify clearly the area that should be evacuated if there is
evident danger of failure of the dam. Copies of the maps should be distrib-
uted to local government officials for use in the development of an evacua-
tion plan. Figure 2-6 is a sample inundation map.
A 1980 dam break flood study of 50 dams located in Gwinnett County,
Georgia (prepared by cooperating state and federal agencies for the
county) reported flood inundation study results on 1: 12,000 (1 inch =
1,000 feet) maps, which were scaled from the USGS maps (Georgia Envi-
ronmental Protection Division 1980~.
Classification of Inundation Areas
To assist in the evaluation of hazard potential, areas delineated on inunda-
tion maps-should be classified in accordance with the degree of occupancy
and hazard potential. The potential for loss of life is affected by many fac-
tors, including but not limited to the capacity and number of exit roads to
higher ground and available transportation.
Hazard potential is greatest in urban areas. Since the extent of inunda-
tion is usually difficult to delineate precisely because of topographic map
limitations, the evaluation of hazard potential should be conservative. The
hazard potential for affected recreation areas varies greatly, depending on
the type of recreation offered, intensity of use, communication facilities,
and available transportation. The potential for loss of life may be increased
OCR for page 34
34
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OCR for page 35
The Safety of Dams
35
where recreationists are widely scattered over the area of potential inunda-
tion, since they would be difficult to locate on short notice.
Many industries and utilities requiring substantial quantities of water for
one or more stages in the manufacture of products or generation of power
are located on or near rivers or streams. Flooding of these areas and indus-
tries can (in addition to causing the potential for loss of life and damage to
machinery, manufactured products, raw materials, and materials in proc-
ess of manufacture) interrupt essential community services.
Rural areas usually have the least hazard potential. However, the poten-
tial for loss of life exists, and damage to large areas of intensely cultivated
agricultural land can cause high economic loss.
Time Available for Response
Analyses should be made to evaluate the structural, foundation, and other
characteristics of the dam and to determine those conditions that could be
expected to result in slow, rapid, or practically instantaneous dam failure.
Wave travel times, as discussed in Chapter 4, should also be established to
help determine the time available for response.
Actions to Be Taken to Prevent Failure or to Minimize Effects of Failure
Development of an Emergency Action Plan
An emergency action plan should be developed for each dam that consti-
tutes a hazard to life and property, incorporating preplanned emergency
measures to be taken prior to and following assumed dam failure. The plan
should be coordinated with local governmental and other authorities in-
volved in public safety and should be approved by the appropriate top-
level agency or owner management. To the extent possible, the emergency
action plan should include notification plans, which are discussed in the
section Notification Plans.
Emergency scenarios should be prepared for possible modes of failure of
each dam. These scenarios should be used periodically to test the readiness
capabilities of project staff and logistics.
A procedure should be established for review and revision, as necessary,
of the emergency action plan, including notification plans and evacuation
plans, at least once every 2 years. Such reviews should be coordinated
among all organizations responsible for preparation and execution of the
plans.
OCR for page 36
36
Notification Plans
SAFETY OF EXISTING DAMS
Plans for notification of key personnel and the public are an integral part of
the emergency action plan and should be prepared for slowly developing,
rapidly developing, and instantaneous dam failure conditions. Notification
plans should include a list of names and position titles, addresses, office and
home telephone numbers, and radio communication frequencies and call
signals, if available, for agency or owner personnel, public officials, and
other personnel and alternates who should be notified as soon as emer-
gency situations develop. A procedure should be developed to keep the list
current.
Each type of notification plan should contain the order in which key
owner supervisory personnel or alternates should be notified. At least one
key supervisory level or job position should be designated to be manned or
the responsible person should be immediately available by telephone or ra-
dio 24 hours a day. A copy of each notification plan should be posted in a
prominent place near a telephone and/or radio transmitter. All selected
personnel should be familiar with the plans and the procedures each is to
follow in the event of an emergency. Copies of the notification plans should
be readily available at the home and the office of each person involved.
Where dams located upstream from the dam for which the plan is being
prepared could be operated to reduce inflow or where the operation of
downstream dams would be affected by failure of the dam, owners and
operators of those dams should be kept informed of the current and ex-
pected conditions of the dam as the information becomes available.
Civil defense officials having jurisdiction over the area subject to inunda-
tion should receive early notification. Local law enforcement officials and,
when possible, local government officials and public safety officials should
receive early notification. (In some areas such notification will be accom-
plished by civil defense authorities.)
The capabilities of the Defense Civil Preparedness Agency's National
Warning System (NAWAS) should be determined for the project and uti-
lized as appropriate. Information can be obtained from state or local civil
defense organizations.
Potentially affected industries downstream should be kept informed so
that actions to reduce risk of life and economic loss can be taken. Coordina-
tion with local government and civil defense officials would determine re-
sponsibility for the notification Normally, this would be a local govern-
ment responsibility.
When it is determined that a dam may be in danger of failing, the public
officials responsible for the decision to implement the evacuation plan
should be kept informed of the developing emergency conditions.
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The Safety of Dams
37
The news media, including radio, television, and newspapers, should be
utilized to the extent available and appropriate. Notification plans should
define emergency situations for which each medium will be utilized and
should include an example of a news release that would be the most effec-
tive for each possible emergency. Use of news media should be preplanned
insofar as is possible by agency and owner personnel and the state and/or
local government. Information shout be written in clear, concise lan-
guage. Releases to news media should not be relied on as the primary
means of notification.
Notification of recreation users is frequently difficult because the indi-
viduals are often alone and away from any means of ready communication.
Consideration should be given to the use of standard emergency warning
devices, such as sirens, at the dam site. Consideration should also be given
to the use of helicopters with bullhorns for areas farther downstream. Ve-
hicles equipped with public address systems and helicopters with bullhorns
are capable of covering large areas effectively.
Telephone communication should not be solely relied on in critical situa-
tions. A backup radio communication system should be provided and
tested at least once every 3 months. Consideration should be given to the
establishment of a radio communication system prior to the beginning of
construction and to the maintenance of the system throughout the life of
the project.
Evacuation Plans
Evacuation plans should be prepared and implemented by the local juris-
diction controlling inundation areas. This would normally not be the dam
agency or owner. Evacuation plans should conform to local needs and vary
in complexity in accordance with the type and degree of occupancy of the
potentially affected area. The plans may include delineation of the area to
be evacuated; routes to be used; traffic control measures; shelter; methods
of providing emergency transportation, special procedures for the evacua-
tion and care of people from such institutions as hospitals, nursing homes,
and prisons; procedures for securing the perimeter and for interior security
of the area, procedures for the lifting of the evacuation order and reentry to
the area; and details indicating which organizations are responsible for
specific functions and for furnishing the materials, equipment, and person-
nel resources required.
The assistance of local civil defense personnel, if available, should be re-
quested in preparation of the evacuation plan. State and local law enforce-
ment agencies usually will be responsible for the execution of much of the
plan and should be represented in the planning effort. State and local laws
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38
SAFETY OF EXISTING DAMS
and ordinances may require that other state, county, and local government
agencies have a role in the preparation, review, approval, or execution of
the plan. Before finalization, a copy of the plan should be furnished to the
dam agency or owner for information and comment.
Stockpiling Repair Materials
Where feasible, suitable construction materials should be stockpiled for
emergency use to prevent failure of a dam. The amounts and types of con-
struction materials needed for emergency repairs should be determined
based on the structural, foundation, and other characteristics of the dam;
design and construction history; and history of prior problems.
Locating Local Repair Forces
Arrangements should be made with, and a current list maintained of, local
entities, including contractors, and federal, state, and local construction
departments for possible emergency use of equipment and labor.
Training Operating Personnel
Owners of large impoundments should have technically qualified project
personnel who are trained in problem detection, evaluation, and appropri-
ate remedial (emergency and nonemergency) measures. These personnel
should be thoroughly familiar with the project's operating manual. This is
essential for proper evaluation of developing situations at all levels of re-
sponsibility that, initially, must be based on at-site observations. A suffi-
cient number of personnel should be trained to assure adequate coverage at
all times. If a dam is operated by remote control, arrangements must be
made for dispatching trained personnel to the project at any indication of
distress.
Increasing Inspection Frequency
Frequency of appropriate surveillance activities should be increased when
the reservoir level exceeds a predetermined elevation. Piezometers, water-
level gauges, and other instruments should be read frequently and on
schedule. The project structures should be inspected as often as necessary to
monitor conditions related to known problems and to detect indications of
change or new problems that could arise. Hourly or continuous surveil-
lance may be mandated in some instances. Any change in conditions should
be reported promptly to the supervisor for further evaluation.
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The Safety of Dams
62O
~7
The owner or his supervisor should issue additional instructions, as nec-
essary, and alert repair crews and contractors for necessary repair work if
developing conditions indicate that emergency repairs or other remedial
measures may be required.
Actions to Be Taken Upon Discovery of a Potentially Unsafe Condition
Notification of Supervisory Personnel
It is essential, if time permits, to notify the proper supervisory personnel
since development of failure could vary in some or many respects from pre-
vious forecasts or assumptions and advice may be needed.
Initiation of Predetermined Remedial Action
At least one technically qualified individual, previously trained in problem
detection, evaluation, and remedial action, should be at the project or on
call at all times. Depending on the nature and seriousness of the problem
and the time available, emergency actions can be initiated, such as lower-
ing the reservoir and holding water in upstream reservoirs. Other actions to
be taken include notifying appropriate highway and traffic control officials
promptly of any rim slides or other reservoir embankment failures that may
endanger public highways.
Determination of Need for Public Notification
To the extent possible, emergency situations that will require immediate
notification of public officials ire time to allow evacuation of the potentially
affected areas should be predefined for the use of management and project
personnel. If sufficient time is available the decision to notify public offi-
cials that the dam can be expected to fail will be made at a predetermined
supervisory level within the agency or owner organization. If failure is im-
minent or has already occurred, project personnel at the dam site would be
responsible for direct notification of the public officials. The urgency of the
situation should be made clear so that public officials will take positive
action immediately.
REFERENCES
ASCE/USCOLD (1975) Lessons from Dam Incidents, USA, American Society of Civil Engi-
neers, New York.
Chief of Engineers (1975) Recommended Guidelines for Safety Inspection of Dams, National
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40
SAFETY OF EXISTING DAMS
Program of Inspection of Dams, Vol. I, Appendix D, Department of the Army, Washing-
ton, D.C.
Federal Coordinating Council for Science, Engineering and Technology (1979) Federal
Guidelines for Dam Safety, Federal Emergency Management Agency, Washington, D.C.
Federal Emergency Management Agency (1982) Interagency Committee on Dam Safety
(ICODS), Subcommittee on Emergency Action Planning, Dam Safety, Emergency Action
Planning.
Forest Service and Soil Conservation Service, U.S. Department of Agriculture (1980) Guide
for Safety Evaluation and Periodic Inspection of Existing Dams.
Georgia Environmental Protection Division (1980) Georgia Soil and Water Conservation
Committee, et al., Dam Breach Flood Maps for Gwinnett Co., Georgia.
Golze, A. R., ed. (1977) Handbook of Dam Engineering, Van Nostrand Reinhold Co., New
York.
ICOLD (1973) Lessons from Dam Incidents, Abridged Edition, USCOLD, Boston,
Massachusetts.
ICOLD (1979) Transactions of New Delhi Congress.
Independent Panel to Review the Cause of Teton Dam Failure (1976) Failure of Teton Dam,
Report to U.S. Department of Interior and State of Idaho.
Jansen, R. B. (1980) Dams and Public Safety, U.S. Bureau of Reclamation, Government
Printing Office, Washington, D.C. (reprinted in 1983~.
Jansen, R. B., Carlson, R. W., and Wilson, E. L. (1973) Diagnosis and Treatment of Dams,
Transactions of 1973 Congress, ICOLD, Madrid, Spain.
Seed, H. B., Lee, K. L., Idriss, I. M., and Makdisi, F. (1973) Analysis of the Slides in the San
Fernando Dams During the Earthquake of February 9, 1971, Earthquake Engineering Re-
search Center, University of California, Berkeley.
Sowers, G. F. (1961) "The Use and Misuse of Earth Dams," Consulting Engineering, July.
U.S. Army Corps of Engineers (1979) Feasibility Studies for Small Scale Hydropower Addi-
tions, Vol. IV, Existing Facility Integrity.
U.S. Army Corps of Engineers (1980) Flood Emergency Plans, Guidelines for Corps Dams,
Hydrologic Engineering Center, Davis, Calif., June, 47 pp.
U.S. Army Corps of Engineers (1982a) Emergency Planning for Dams, Bibliography and Ab-
stracts of Selected Publications, Hydrologic Engineering Center, Davis, Calif.
U.S. Army Corps of Engineers (1982b) National Program for Inspection of Non-Federal
Dams—Final Report to Congress.
U.S. Bureau of Reclamation (1980) Safety Evaluation of Existing Dams, Government Printing
Office, Washington, D.C.
U.S. Department of Interior Teton Dam Failure Review Group (1980) Failure of Teton Dam,
Final Report.
Representative terms from entire chapter:
dam failure
