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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

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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

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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-

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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).

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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~.

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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

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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.

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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.

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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

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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

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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

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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

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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

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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.

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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 DamsFinal 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.