Gruner 1964 Dam Disasters

Paper No. 6648

DAM DISASTERS by

Edward Gruner, A.M.I.C.E. Partner, Gruner Brothers, Consulting Engineers, Basle

For discussion at an Ordinary Meeting on Tuesday, 19 February, 1963, at 5.30p.m. and for subsequent written discussion

SYNOPSIS The Paper mentions several recent failures of dams and the resultant damage by

flooding. The causes of different types of failure are reviewed and brief histories given of the examples chosen. The effects of reservoirs on the balance of nature are mentioned, the design of dams is considered and suggestions advanced for the protection of persons and property. The question of insurance against damage is raised. The author concludes that every dam which impounds water presents a potential danger and the risk of sudden disaster is for ever inescapable.

INTRODUC~ON DURING 1961 the following were added to the list of recorded dam disasters:

The failure of a dam in the Babii Yar gorge of the Ukraine as the result of overtopping due to high winds. The flood released inundated the lower- lying parts of the city of Kiev.

The failure of the Panshet dam near Poona in India during the monsoon rains, and the consequential destruction of the Khadekvasla dam a few miles downstream.

The failure of the Hyokiri dam 125 miles south of Se01 in South Korea as the result of torrential rains.

F ~ D S DUE TO NATURAL DAMS

2. Out of 265 floods recorded in the Rhone Valley in Switzerlandno fewer than a tenth were caused by the breaching of glacial barriers. Lake Maeryelen which lies adjacent to the Aletsch glacier has been the cause of periodic disasters, the most recent occurring in 1913 when 7800 acre-ft of water were suddenly released. The unusual phenomena associated with such disasters had been observed by Alpine herdsmen from very early times and they had noticed that on occasion the ice barrier would lift and suddenly release the water stored in the lake.

3. A more recent example of such natural disasters occurred in 1934 when the Trans-Andean Railway was breached near Mendoza in the Argentine. In- vestigations showed that the Nevado glacier had blocked the valley of the Rio Plonio and had created a temporary lake of 46 800 acre-ft. At its peak the flood

47

48 GRUNER ON DAM DISASTERS

released by the Nevado glacier was between five and six times greater than the flow which could be accounted for by the passage beneath the glacier-clearly indicating that the barrier had floated, allowing the lake to empty and that it had afterwards subsided again.

4. It sometimes happens that river valleys become blocked by landslides. The barriers thus created subsequently erode so rapidly as to release a destructive flood. In 1960 a severe earthquake in south Chile caused a landslide which blocked the outlet of lake Rinihue. The lake level rose 86 ft representing three million acre-ft of stored water. A critical situation was thus created which menaced the port of Valdivia on the Pacific coast. This perilous situation was mitigated by cutting a 5-ft wide ditch across the barrier which allowed the impounded water to escape. The escaping water rapidly eroded the pilot channel which very soon attained a width of 270 ft. These measures had the effect of restricting the peak of the flood to 250 OOO cusecs and although the lower quarters of the town were inundated to a depth of 4 ft an even worse disaster was undoubtedly prevented.

DAMS OF ANTIQUITY

5. The building of dams is as old as the recorded history of mankind. Traces of these ancient dams are found today in both the old and the new worlds and bear witness to the achievements of civilisations which have long passed away. 6. One such dam built of earth is to be found in the valley of the Orontes near

Horn in Syria. It was old in the days of Strabo the Greek geographer who visited it 2000 years ago. The reservoir formed by this ancient dam is fed by clear springs and in consequence has enjoyed an exceptionally long life. In time, however, piping gradually developed beneath its foundations and prior to the reconditioning of the embankment in 1934, its ability to hold water had virtually disappeared. In spite of its long record the new dam, which retains 172 080 acre-ft of water, nearly met with disaster in March 1961 when high winds combined with an exceptionally high reservoir level, caused overtopping of the embankment.

REIXIRDED DAM FALLURES

7. The earliest record of a dam failure relates to an earth embankment near Grenoble which failed in 1219 after 28 years’ service. A list of 1764 dams has been published in America, giving all those built up to 1959. Of these 33 had failed between 1918 and 1958. Five of these failures were classed as major disasters involving the loss of 1680 lives. Two thirds of the failures were attributed to geological and technical causes. The number of failures was greatest among multiple arch darns (10%), while among those classed as concrete gravity dam failure occurred in less than 1%. Up to this time there had been no recorded failure of an arch dam. 8. In 1961 the Spanish publication “Revista de Obras Publicas” mentioned

a list of 1620 dams. Over the 145 years between 1799 and 1944, 308 of these had been the subject of serious accidents. In the case of over half of them actual breaching had not occurred, while in 77 cases the cause of failure was not described. Of the failures listed 163 were classed as earth embankments, 14 were described as dykes, 70 were concrete gravity dams, two were arch dams, seven were multiple arch dams, while 52 were of other types.

GRUNER ON DAM DISASTERS 49

9. The causes of failure of the dams listed were attributed as follows:- Foundation failure . . . . . . . . . . . . . 4% Inadequate spillway. . . . . . . . . . . . . 23 % Poor construction . . . . . . . . . . . . . 12% Uneven settlement . . . . . . . . . . . . . 10% High pore pressure in the case of pumped fill embankments . 5% Acts of war . . . . . . . . . . . . . . 3% Embankment slips . . . . . . . . . . . . . 2% Defective materials . . . . . . . . . . . . . 2% Incorrect operation . . . . . . . . . . . . . 2% Earthquakes . . . . . . . . . . . . . . 1%

Total . . 1 0 0 % 10. The determination of the cause of a dam failure is often difficult and the

reason assigned must inevitably depend to some extent on the judgement of the engineer. For example, where a dam possesses no well defined cut-off, failure might be attributed to engineering design, to insufficient grouting, or to percolation. Sometimes an attempt has been made to distinguish between failures arising from human errors and failures due to force majeure. The distinction is quite arbitrary and is clearly dependent upon the state of the science of dam building at the time.

EXAMPLES OF FAILURES

11 . The construction of the Mohammed Ali barrage north of Cairo was commenced in 1835. In 1867, however, the works had to be abandoned following a blow-out beneath the foundations as the result of piping. At the time of its construction the theory of the flow of water through sands was not understood and it was only in 1857 that Darcy published his theory governing flow through sand strata. Since that time a proper understanding of the flow of water under such conditions has made it possible to build permanent water- retaining structures on sand foundations.

12. On 1 December, 1923, the Gleno dam in the Bergamese Alps in north Italy suddenly failed. The extent of the ensuing disaster was fortunately mitigated by the partial absorbtion of the flood in lake Iseo lying 17 miles downstream. Subsequent analysis of the design of the Gleno dam revealed the exis- tence of shear stresses along a curved surface varying from 28 to 41 lb/sq. in. It was the high intensity of these shearing stresses combined with poor workman- ship which led to the failure of the dam. The Gleno disaster occurred at a time when dam design was in a state of evolution and engineers were anxious to allay public disquiet and to satisfy themselves that existing dams built in accordance with accepted theory and under proper supervision were safe. While much attention was paid at this time to the theoretical aspects of design no attempt was made to study the flood wave which followed the sudden destruction of the dam.

13. On 26 November, 1927, the El Habra dam in Algeria failed when, as the result of an unusual flood, the reservoir rose 13 ft above its normal maximum level. A Government Commission which enquired into the disaster attributed the failure partly to the high specific gravity of the muddy water in the reservoir and partly to the effect of uplift pressure acting on horizontal joints in which the mortar had deteriorated. As a result of this accident French engineers

5


devoted much attention to the general question of uplift and the method of allowing for it in stability calculations. The French Ministry of Agriculture proposed that the problem of uplift should be dealt with by reducing the value assigned to the specific gravity of the masonry and suggested that the assumed weight of the masonry should be reduced by 0.2 tons/cu. m. Maurice Levy went so far as to suggest that the specilic gravity should be reduced by 1.0 ton/ cu. m. and that over and above this a further allowance should be made for uplift pressure.

14. In November 1925 disaster overtook the small town of Dolgarrog in North Wales as the result of a blow-out beneath the base of the Eigiau dam, a concrete structure which had been built some Mteen years previously. The water released by the blow-out caused the overtopping and destruction of the Coedty dam-a small embankment which lay about two miles downstream. This event subsequently led to the introduction of legislation to protect the public.

15. On 12 March, 1928, the St Francis dam belonging to the Los Angeles water undertaking, failed and released a flood which swept through the St Francis valley into the Santa Clara river and thence into the Pacific ocean. The disaster was investigated by no less than five separate commissions, representing different interests. Their reports were published within one month of the event and all were unanimous in attributing the cause of the failure to defective foundations. No blame was laid on the structural design of the dam. Following the disaster the State of California enacted legislation which required that the design and construction of dams should in future be supervised by a competent authority. 16. On 9 January, 1959, the sudden failure occurred of the de Tere Vega

dam-a buttress structure built on a tributary of the Douro river in Spain. Failure occurred during the first 6lling of the reservoir and was said to have started near the left abutment initiating the successive collapse of 17 buttresses. The contents of the reservoir, amounting to 6300 acreft, was discharged within twenty minutes. The disaster occurred in the depth of winter and owing to the severity of the weather no official inspection of the site was made until the following April. It has to be recorded that in spite of the heavy loss of life, the report of the Commission which investigated the causes of the disaster has never been made public. 17. On 25 March, 1960, the earthfill dam at Oros in the State of Ceara in

Brazil, which was still under construction, was overtopped by a flood and in 15 hours the major part of the embankment was washed away. The construction programme had not been achieved and the dam was in a vulnerable state when the rainy season arrived. Between 21 and 25 March, heavy rains caused the flow of the Jaguaribe river to rise to 80 OOO c u s e c s of which only one fifth could be dealt with by the diversion tunnel. In consequence the remainder was stored behind the embankment. A critical situation arose and it proved impossible to raise the dam with the necessary speed. Events soon became out of control with the result that the water flowed over the top of the embankment. Over l miIIion a. yd of fill were washed away in a few hours leaving a gap 660 ft wide. At its peak the flow through the breach reached 340 ooOcusecs. The flood waters were discharged down the Jaguaribe valley and in three days reached the Atlantic 210 miles away. In view of its importance in developing the economy of the country the Oros dam was reconstructed and has been in service since February 1961 to the benefit of the arid region which it serves.

ORUNER ON DAM DISASTERS 51

18. The history of the 180-ft high dam on the Banabuiu river, a tributary of the Jaguaribe, was more fortunate. At the time of the storm which destroyed the Oros dam it too was under construction but it proved possible in this case to confine the flood waters to a temporary spillway and thus save the main embankment,

CAUSES OF DAM FAILURES

19. A study of past dam failures has revealed that such causes as neglect of maintenance, defects in construction or faulty operation of the outlet works can account for only the minority of the recorded disasters. In the majority of cases failure occurred because the knowledge available at the time of the event proved to be incomplete.

20. Among the major causes of destruction ranks the percolation of water through a dam or its foundations. Since the time of Levy many experiments have been made to determine uplift pressures, but to date no universally accepted method of determining such pressures has been put forward. Observations of pore water pressures in American dams have shown the value of installing a drainage system behind the upstream face. A feature of the design of recent dams in Siberia is the adoption of drainage systems extending deep into the foundation rock. Professor Terzaghi has expressed the opinion that the evaporation of seepage water from the downstream face of a dam may cause surface stresses of the order of tenths of a pound per square inch. However, no method of measuring such pressure has yet been devised.

21. Recent experiments carried out by the Hungarian Hydrographic Service show that the level of a water table is sensitive to changes in barometric pressu~, These changes in level are the result of evaporation or condensation and as a consequence the ground above the water table is subject alternately to the up- ward diffusion of water vapour and to downward percolation of condensate. This phenomenon causes internal changes of stress in an embankment and tends to enhance its natural stratification. The presence of this water vapour is sometimes disclosed by differences in the growth of vegetation on the downstream slope.

DELIBERATE DESTRUCnON OF DAMS

22. The number of dams which have failed greatly exceeds the number of those which have been deliberately destroyed by enemy action. History, however, records instances in which military commanders have resorted to the destruction of a dam as a means of either eliminating enemy forces or of denying them the passage of a river. Coming to more modern times an unsuccessful attempt was made during the Spanish Civil War by the troops of General Franco to blow up the Ordunte dam near Bilbao, a concrete gravity structure 130 ft high. Fifteen tons of explosives were placed in an inspection gallery and detonated but without achieving the intended result.

23. In December 1938 a party of German army officers visited the Aswan dam for the purpose of studying the best method of encompassing its destruction. Had this taken place 3-9 million acre-ft of water would have been suddenly released down the valley of the Nile with consequences which can readily be imagined.

24. In September 1941 the Soviet army withdrawing before the German advance took the drastic step of destroying the Dnjeprogues dam. The road


over the dam was packed with Russian fugitives when 90 tons of explosives were set off in the inspection tunnel. The explosion destroyed the upper part of the dam over a length of 660 ft. The flood which was released through the breach attained a peak of 1 260 OOO cusecs, or 75% more than the estimated extreme natural flood of 720 OOO cusecs, a factor which may serve to indicate the scale of the catastrophe.

25. On the night of 16 March, 1943, the Mohne dam in the Ruhr was success- fully bombed by the Royal Air Force. It was the devastating consequences of this event which brought home to those acquainted with the facts the realization of the vulnerability of great centres of population and industry occupying a valley dominated by a great volume of stored water. On the same night similar attacks were made on the Eder dam, a masonry gravity structure, and the Sorpe dam, an earth embankment. These attacks were less effective than that on the Mohne dam and it was held in certain quarters that solid masonry dams could not be breached by bombing provided the crest thickness exceeded about 50 ft, and that embankments were less vulnerable than dams of concrete or masonry.

26. In this nuclear age the destruction of dams by hostile action has lost much of its significance for it is now possible by means of a nuclear bomb to spread the contents of a lake or reservoir far and wide over a countryside in the form of radioactive rain.

INADEQUACY OF SPILLWAYS

27. It has been pointed out that something like one quarter of recorded dam failures has been attributed to insufficient spillway capacity. Estimates of future floods have in the past usually been based on an extrapolation of available records in accordance with the Gaussian theory. More recently attempts have been made to determine a value for the maximum possible theoretical flood which could arise by considerations of the purely physical factors involved. However, values determined in this way may appear unrealistic when compared with past records and may lead to the adoption of extravagant spillway capacities. Probably a sounder and more logical method of estimating design floods is that based on the unit hydrograph which provides a means of relating the physical characteristics of a river basin to actual observed discharges.

28. Recent advances in methods of estimating design floods have been accom- panied by changes in the method of providing for their safe passage. Where conditions are suitable the total design flood can be divided into two parts. A normal type of spillway can be used to deal with floods of the order of those recorded in the past, while a destructible section of the dam can be provided to act as a ‘fuse plug’ to provide additional relief in the event of a catastrophic flood. An extension of this conception has been studied in the Soviet Union with the object of protecting long embankment darns. The suggestion is to armour such an embankment by laying concrete slabs, like tiles on a roof, to permit the safe discharge of water in the event of overtopping.

EXTREME FLOODS

29. Recent experience in connexion with the Rio Negro in Uruguay demon- strates the difficulty of making a reliable forecast of extreme floods. When the Rincon de Bonete Hydroelectric Scheme was designed in 1935 flood records were available for a period of 27 years. The greatest flood recorded at that time

GRUNER ON DAM DISASTERS 53 was 135 OOO cusecs, although there was a tradition that an exceptional flood of even greater magnitude had occurred during the days of the early settlers. From extrapolation of the years on record, a design flood of 325 OOOcusec~ was adopted. This flood was intended to be dealt with to the extent of 200 OOO cusecs by a permanent spillway, the balance being temporarily stored in the reservoir which had a surface area of 282 OOO acres.

30. In April 1959 the catchment area of the Rio Negro was subjected on three occasions during a period of four weeks to a climatic condition known locally as the Sudestada Prolongada. Under this condition cold air coming up from the Antarctic meets the warm moist air of the sub-tropical zone of the Atlantic seaboard. The sudden cooling effect arising from the temperature differences between the two air masses (estimated on this occasion as 23°F) causes intense precipitation. On the occasion in question 14-2 million acre-ft of water were precipitated over an area of 9.4 million acres during a period of ten days. AS the ground surface had previously been saturated a very high runoff occurred (80% of the rainfall). The inflow into the Bonete reservoir attained a peak of 605 OOO cusecs. Of this total, 340 000 cusecs were discharged over and around the dam, flooding the power station, while the balance was temporarily stored in the reservoir which rose 15 ft above its designed maximum level.

31. Had the dam failed it would have suddenly released 1 1 million acre-ft of water, equivalent to one third of the volume of lake Constance. The consequences would have been catastrophic. The possibility that such a failure was imminent had been broadcast to the public and the knowledge undoubtedly adversely affected the efforts of the rescue teams. The design flood adopted for the Rincon de Bonete dam was thought at the time to have a probability of occurrence of once in a thousand years, and yet the flood which actually occurred within 14 years of its completion would, on the same basis of calculation, have a theoretical probability of once in half a million years. Meteorologists have since expressed the opinion that the peculiar conditions set up by the Sudestada Prolongada might conceivably give rise to a temperature differential of as much as 35°F. If this were to happen the precipitation released over the catchment of the Rio Negro might reach the astronomical figure of 21 million acre-ft.

32. To release safely such enormous floods the spillway would have to be so large as to render the scheme quite uneconomic. This is a situation with which the engineer is sometimes faced; the choice of either providing at great cost for the passage of floods which may never occur-and in so doing perhaps render the scheme uneconomic-or taking a caIculated risk of disaster by adopting more modest assumptions.

EFFECT OF RESERVOIRS ON NATURAL REGIME

33. Those who are responsible for the operation and maintenance of dams should appreciate that such works interfere with the equilibrium of nature. It is not only the fish which have to adapt themselves to the new conditions, but changes may be introduced in the environmental factors governing plant and animal life. The exploitation of a catchment area not only reduces the incidence of floods but where water is diverted often leads to a marked reduction in the total flow carried by the stream bed. In consequence vegetation tends to encroach upon the natural water course adversely affecting its ability to carry away flood water. Thus people may be misled into settling in valley bottoms which as the


result of control works appear to be safe, only to suffer in the event of exceptional floods.

PLANNING RIVER BASIN DEVELOPMENT

34. As the need grew for making an ever more efficient use of water resources the idea of complete river basin development arose. In recent times such proposals have often been political in their concept and have involved the pre- paration of schemes for the unified control of international rivers affecting the rights of two or more independent sovereign states. Where international politics control the activities of the engineer, purely technical considerations are likely to be subordinated to the necessity of achieving a solution which is acceptable to the governments concerned. Thus a solution which is based solely on technical considerations often has to be rejected or amended to meet the need of reaching a practical compromise, and in the process the responsibility of the individual engineer is often lost. It is naturally disappointing to the engineer who is anxious to make the best possible use of natural resources, to see his plans whittled down or changed by his political masters.

DAM DESIGN

35. In the 1920s there was a marked rise in the number of dams built through- out the world. At that time the choice of type and the details of design were generally the sole responsibility of the engineer concerned. There were virtually no regulations in force to provide guidance and each engineer carried on his own shoulders the full responsibility for the outcome of his work. Up to that time the design and construction of dams had lain in the exclusive domain of the civil engineer. It soon became recognized however that the design of a dam should be considered in close association with the properties of the ground on which it was to stand; as a consequence a closer collaboration grew up between the engineer and the geologist. Many engineers at the time were conscious that the basis of dam design was largely empirical and because of this attempts were frequently made to check the validity of their assumptions by making measure ments of the behaviour of the works after completion and by exchanging in- formation with other members of their profession. At a meeting of the World Power Conference in Berlin in 1929 this awareness of the deficiencies in the science of dam design and construction led to the foundation of the International Commission on Large Dams. Since 1948 meetings of the Commission have been held at intervals of three years.

36. Safety and economy were among the subjects discussed at the Inter- national Congress on Large Dams held in Paris in 1955. It was then said by one of the contributors that the evolution of dam design should be directed towards making more effective use of the materials of construction. This philosophy had led in France to an increasing preference for arch dams as opposed to those relying mainly on deadweight for stability. This is shown by the fact that between 1924 and 1934 only two arch dams were constructed as compared with fifteen of the gravity type. However, during the ten years 1944 to 1954 only four gravity dams were built as compared with no less than twenty-six arch dams.

37. The same contributor to the 1955 Congress pointed out that the profile of a gravity dam can only be reduced by encroaching on its factor of safety and that such dams might become unsafe should the uplift exceed the design assumptions, or should the level of the reservoir rise to a higher value than had been

ORIJNER ON DAM DISASTERS 55

assumed. He pointed out that arch dams not only make a better use of the materials employed but offer a greater inherent factor of safety. Extreme examples of the employment of the arch principle are the Gage dam in France, with a height of 115 ft and the Tolla dam in Corsica with a height of 235 ft.

38. During the discussion at the Paris conference it was claimed by other speakers that gravity dams were more suitable for sites which presented hetero- geneous foundations, since they were better able to adapt themselves to changes in the physical characteristics of the rocks. Because of this it was generally accepted that arch dams were not suitable if irregular settlement or deformation of the foundations was anticipated. An Italian speaker suggested that further study of these problems would assist in reducing the areas of ignorance which surrounded them and so lead to further economies of design. He added, however, that it was always prudent to maintain an adequate factor of safety. These divergent views represent two schools of engineering thought; the one trusting to theory, the other preferring to be guided by experience. Discussion on these lines was continued at the Congress held in Rome in 1961 and the views expressed were summarized by the General Reporter dealing with under- ground works associated with dams. In presenting the views expressed at the Congress he suggested that for any given site the type of design adopted should represent the best which could be chosen in the light of the engineering and scientific knowledge available. He also drew attention to the fact that all dams are subject to gradual deterioration, and that because of lack of homogeneity in the foundations the factor of safety might in fact be lower than the value assumed in design.

BOUNDARY BETWEEN SAFETY AND DISASTER

39. It has to be recorded that disasters have overtaken dams which were built by those who were in their day acknowledged masters of their profession. In spite of the inherent soundness of the original design it is not always possible to recognize potential weaknesses and once such a weakness has been discovered it may be too late to remedy. 40. Recently a small earthdam in Bavaria was endangered by piping but in

this case it was possible to prevent a failure by emptying the reservoir through the bottom outlet. An unexpected situation confronted the Albinasca dam in Switzerland when test grouting operations caused artesian water under a head of seven atm to break out. It was subsequently noted that a crack had developed across a corner of one of the monoliths. Fortunately the gravity type of design localized the effect and it was possible to carry out remedial measures.

DURABILITY OF DAMS

41. Suggestions that a definite life can be attributed to an individual dam must be considered in the light of experience. In Scandinavia for instance it has been found that soft water attacks concrete and serious deterioration can take place in a few years, while extreme temperature variations can also produce rapid disintegration. There are few dams of any significance over a hundred years old, although there are several important ones which are approaching their centenary. In the main ageing of dams can be attributed to two fac torwne physical and the other chemical. The physical effects are brought about by changes in the forces acting on the dam, including those due to temperature


variations, while chemical attacks arise from the penetration of the dam by aggressive waters leading to the leaching out of some of the constituents of the concrete and resulting eventually in its complete disintegration. Studies in this field have been carried out by the Tbilisi Research Institute in the Soviet Union. It should not be overlooked that many of the great irrigation works of antiquity were eventually destroyed because the knowledge of those who built them was not passed on to later generations who inherited the responsibility for their care. Such experience brings home the obvious truth that all dams are subject to natural decay and that their preservation requires continual maintenance.

PROTECTION OF THE PUBLIC

42. In 1877 the Swiss Federal Parliament introduced legislation which brought the control of water courses under federal supervision. The Act was revised as the result of the destruction of the Mohne dam and it was again amended in 1953 to provide compensation for those who might suffer from the destruction of a dam, whether as the result of natural causes or enemy action. A further amendment in 1957 brought within the scope of federal control all dams more than 33 ft in height, and all reservoirs with a volume in excess of 39 acreft. The Act in its present form provides that both design and construction shall be properly supervised and stipulates the precautions which shall be taken in the event of a dangerous situation arising. To date, however, the Swiss regulations make no provision for the periodic inspection of the works once they have been completed.

43. In 1930 as a result of the Dolgarrog disaster, the British Parliament passed the Reservoirs (Safety Provisions) Act. The Act provides that the owner of a reservoir containing more than 5 million gallons shall obtain at intervals of not more than ten years a certificate from a duly authorized engineer as evidence of the safety of the reservoir. 44. In 1933 the German authorities prepared a set of draft regulations cover-

ing the design, construction and operation of dams. In 1953 these draft regulations were superseded by DIN 19700. While this code possesses no mandatory authority, it has nevertheless proved of value as a means of reminding the owners of dams of their duty to the public. The code was drafted by a team of 69 specialists and as might be anticipated is too elaborate and detailed for ease of application. As an example, regulation 3.322 requires that the hydro- static conditions set up in the floor of the reservoir shall be investigated, while regulation 3.7 lays down how deformation of both the dam and reservoir shall be determined. Regulation 5.2 requires that in the event of danger the custodian of the dam shall not only inform the owners immediately but shall issue a warning to the inhabitants of the area which might be affected.

45. The Federal Government of the U.S.A. exercises no authority over the design and construction of dams. Instead the responsibility is delegated, as may be appropriate, to the U.S. Bureau of Reclamation, The Tennessee Valley Authority and the U.S. Corps of Engineers, or if the dam serves a farming community the responsibility lies with the Department of Agriculture. This division of responsibility is rather surprising in a country which has been the scene of so many dam disasters. Moreover, on comparing the various sets of regulations it is found that considerable diversity exists between the different authorities. For example, those issued by the Corps of Engineers specify a


higher factor of safety than those of the Bureau of Reclamation, possibly imply- ing the recognition of greater latitude in the quality of maintenance to be ex- pected. If a company or a public authority in the United States wishes to build a dam the designs have to be submitted for approval to one of the authorities mentioned above. In recent years several states including California, Oregon and South Carolina, have issued their own regulations covering the design and construction of dams. 46. The Water Code on the Supervision of Dams issued in 1960 by the

Department of Water Resources of the State of California states that “if it is found that an unsafe condition exists the Department shall take such action as is necessary to render or cause the condition to be rendered safe” (paragraph 6392). Paragraph 6371 of the same Code states that “evidence shall show that a sufficient portion of the dam has been removed to permit the safe passage of floods down the water-course across which the dam was located.”

47. In France the state electricity authority, Electricit6 de France, issued instructions covering the supervision of their own dams: these instructions provide for regular inspection. However no provision is made for any independent inspection since the inspector concerned is himself an employee of the authority.

48. Usually the deterioration of a dam is a slow process, the effect of which is not always apparent to the eye of the observer. The conclusion that the safety of a dam can no longer be confidently assumed is one which must be reached by the engineer on the basis of his general experience. Such a conclusion clearly carries important financial implications for the owner who may find himself compelled to undertake heavy expenditure as an alternative to abandoning the works completely.

FLOOD ROUTING

49. In the belief that war was imminent the effect of a flood arising from the breaching of the Cancan0 I dam in the Italian Alps was studied by De Marchi in 1940. The results of this theoretical study have since been checked by model tests. The method developed by De Marchi has been used to prepare flood maps relating to a series of reservoirs which might inundate Swiss territory. For instance the Sihl reservoir near Einsiedeln lies in a flat basin holding 72 OOO acre-ft of water. The water is impounded by a concrete dam and an earth dyke and should it ever be destroyed the water released would inundate parts of Zurich including its railway marshalling yards. The water discharged by a breach in the Sihl dam could be retained by building a subsidiary dam further down the valley. Although such a precautionary measure may appear fantastic its cost would in fact compare favourably with that which would arise in the event of a failure of the dams in service.

50. The necessity for such measures may arise suddenly. However, it is probable that in peace time the public would remain indifferent to the risks and might even view the taking of such precautions with a certain amount of SUS- picion. To be effective at times of international tension any warning system must be capable of being put into immediate effect, since with modem weapons it is now possible to destroy a series of dams by means of rockets virtually without warning and to a sequence designed to insure maximum flooding. During the last war flood-warning systems were organized to cover all major Swiss reservoirs. The experience gained from the Oros and Malpasset disasters make

58 GRUNER ON DAM DISASrBRS

it clear that such warning systems should be maintained in peace time. As the passage of the head of a flood wave is a function of time, those living at some distance below the dam may be given a chance to escape provided they are warned in good time and are told what action to take. Levels likely to be reached by the peak of a flood can be marked on the sides of the valley and appropriate safe areas can be selected. The progress of a flood wave down a valley can be passed on to the inhabitants by radio signals. In the case of the Malpasset disaster both the electric power lines and the telephone system were swept away before any warning could be issued to the people of Fdjus.

51. Special difficulties over the control of water conservation works are likely to arise where catchment areas affect more than one country. This is especially so in Central Europe where a flood arising from the bursting of a reservoir, for instance in the Black Forest or the Silvretta region, would inundate Swiss territory, while a flood arising from a reservoir in the Engadine would affect Austria. Similarly a flood from a reservoir in the Jura region would extend into France. Because of this interdependence between the ownership of reservoirs and their possible effects the countries concerned should endeavour to agree upon safety precautions.

RESPONSIFIIUIY FOR DAMAGE

52. In most countries the courts will hold, in a case of action for damages, that compensation for the damage suffered shall be the responsibility of the party which has caused the damage.

53. In Great Britain responsibility for injury under Common Law appears to be covered by a court ruling in 1868 in the case of Rylands U. Fletcher when it was decided “that the person who for his own purpose brings on his own land and collects and keeps there anything likely to be mischieveous if it escapes must keep it in at his peril, and if he does not do so he is prima facie answerable for all the damage which is the natural consequence of its escape. And upon authority this we think is established to be the law whether the thing so brought be beasts or water or filfth or stenches.”

54. In Switzerland the “Code of Obligations’’ states in paragraph 58 that “the owner of a building or a work is under an obligation to cover any damage arising out of defective construction or fabrication, except in cases where responsibility has been delegated to a third party.”

SCALE OF DAMAGE

55. The following are some examples of the material losses arising from recent

Netherlands, 1953-The damage resulting from a storm surge in the North

France, 1959-The damage caused by the collapse of the Malpasset Dam was

Chile, 1960-The damage due to an earthquake was estimated at E20 million. Morocco, 1960-The damage caused by the Agadir earthquake has never

56. Where the cost of making good the loss suffered by a catastrophe is beyond the capacity of the country concerned it becomes necessary to seek international assistance. Such assistance may be rendered on a voluntary basis

disasters:

Sea was estimated at L42 million.

estimated at E22 million.

been computed.


or the help to be rendered may be fixed by previous international agreement. Pleas for voluntary assistance, although fairly frequent, usually meet with a relatively poor response. In the case of the Netherlands, for instance. the money received from sources outside the country represented only one tenth of the damagc+-while that received in respect of the Chile and Agadir catastrophies was on an even smaller scale. In the case of Malpasset, offers of foreign help were at first refused-possibly to avoid the legal implications of such aid or Simply out of national pride. Moreover. there is in France a body called the “Organisations des Secours” (ORSEC) which exists for the purpose of alleviating hardship as the result of such disasters.

INSURANCE 57. It is worth recording that an attempt to set up an international fund was

made in 1927 under the title of Union lnternationale des Secours. Of the original 43 countries which subscribed only 23 are now left. Contributions to the fund represented one tenth of the scale applying to subscriptions to the old League of Nations. Changes in international exchange rates led to difficulties in the administration of the fund, contributions were reduced and the fund was left with an available balance of only E50 OOO, the governments concerned undertaking to make further contributions should the need arise. Although the agency set up under the League of Nations is no longer effective, the need for organized international assistance is today no less urgent than it was in 1927.

58. Dr E. R. Froelich of Zurich has suggested that the assistance to be received by a member country from such an international body might be proportional to the amount which it would be prepared to provide in the case of a disaster to another member. The extent of a disaster might be defined in terms of national income. Thus in the case of Switzerland a figure of 0.2 per cent would represent a s u m of E5 million. All losses are relative. In the United States the recent series of hurricanes caused losses estimated to range between €44 and E137 million. Although these are large sums they do not in terms of the wealth of such a country as the United States represent a calamity on a national scale. Each country would subscribe to the fund in proportion to its national income, and in giving assistance to another member the contribution which it would itself make to the relief fund would be proportional to its own wealth. Thus the rich countries would bear a larger share of the cost of relief than the poorer ones. The proposal differs from the accepted principles of insurance in that the commit- ments of the contributors would be proportional to their means.

59. The development of nuclear power carries with it the risk that a serious accident to a reactor might result in heavy claims for compensation. In the United Kingdom the owner of a reactor is required to take out an insurance policy under which claims to a maximum of E5 million are covered. In the event of the claims exceeding this s u m it is understood that the State would come to the aid of the claimants.

CONCLUSIONS

60. Our present knowledge of the forces which lead to the deterioration of dams is incomplete and much help can be obtained in filling the gaps in our knowledge by making a close study of disasters when they occur. The breaching of an ice barrier offers an example of how a natural obstruction, causing a temporary interference with the equilibrium of nature, reaches a sudden climax in


the slow process of restoring that equilibrium. Natural barriers and man-made darns are both governed by the same law of decay. Every dam which impounds water presents a potential danger which should neither be under- nor over- estimated. The risk of sudden disaster is for ever inescapable, and while knowledge and vigilance may reduce such a risk it can never be entirely banished. All man-made works carry within them the seeds of their own decay and eventual destruction.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13. 14.

15.

16.

BIBLIOGRAPHY A. STUCKY. Der Talsperrenbruch im Val Gleno. Schweizerische Bauzeitung vol. 83,

no. 617, 1924 H. E. GRUNER. Neuere Untersuchungen an Grossen Talsperren des Auslandes.

Schweizerische Bauzeitung vol. 127, no. 8, 1946 D6partement Federal de l'hterieur. Publication de YInspecteur F6d6ral des

Travaux Publics. Commission Suisse des Grands Barrages. Mesures, observations et essais sur les Grandr Barrages Suisses, 1919-1945, Berne 1956

West German Regulations. Fachnormenausschuss Wasserwesen im Deutschen Normanausschuss (DNA) Stauanlagen, Richtlinien fur den Entwurf, Bau und Betrieb, Teil I, Talsperren DIN 19700, February 1953

A. COYNE. Economy and safety of different types of concrete dams. 5th Congr. Int. Comm. Large Darns, Paris 1955

Swiss ReguIations. Bundesgesetz uber die Eranzung des Bundesgesetzes betreffend Wasserbaupolizei. Vollziehungsverordnung zu Artikel 3bis des Bundesgesetzes betreffend Wasserpolizei (Talsperrenverordnung) 9th July 1957

A. Corn. New dam techniques. Proc. Instn-civ. Engrs, vol. 14 (Nov. 1959), PP. 275-290

B%sh Regulations. Reservoirs (Safety Provisions) Act 1930. 20 & 21 Geo 5 , Ch. 51. Nuclear Installation (L.icensing and Insurance) Act 1959. 7 & 8 Elk. 2, Ch. 46

U.S.A. Regulations. California, Division 3 of the Water Code, Supervision of Darns 1960: Rules and regulations pertaining to supervision of dams in California Oregon,OregonRevisedStatues; 540.350 Water Law; 540.380Rules andregulations

G. WUSTE~~ANN. Betrachtungen uber die Ursache des Bruches der Talsperre von Malpasset bei Fr6jus. Neue Ziircher Zeitung No. 1068, 30 March, 1960 G. W~STEMANN. Der Bruch des Erddammes Ora. Neue Zurcher Zeitung No. 2544,

27 July, 1960 Talsperrenprobleme. Oesterreichische Wasserwirtschaft, 1960, No. 8/9 Springer

Verlag, Vienna E. R. FROELICH. Die Kalamiat. Neue Ziircher Zeitung No. 1280, 8 April, 1961 A. U. HUGGENBERGER. Das Verhalten und die Sicherheit von Talsperren. Neue

A. CASAGRANDE. Control and seepage through foundations and abutments of

SIR CLAUDB INGLIS. The Poona Flood Disaster of 12 July, 1961. Proc. Instn civ.

Ziircher Zeitung No. 1335, 12 April, 1961

dams. Gdotechnique, vol. 11,1961, pp. 161-181

Engrs, vol. 22 (May 1962), pp. NlO-Nll.

The Paper was received on 5 October, 1962.

Written discussion on this Paper should be forwarded to reach the Institution before 15 March, 1963, and will be published in or after July 1963. Contribu- tions should not exceed 1,200 words.-SEC.

Documents

Gruner 1964 Dam Disasters