Dam failures by erosion: lessons from ERINOH data bases

Transcription

1 Dam failures by erosion: lessons from ERINOH data bases ICSE6-290 Jean-Jacques FRY 1, Alexius VOGEL 2, Paul ROYET 3, Jean-Robert COURIVAUD 1 1 EDF-CIH Le Bourget du Lac Cedex France: - jean-jacques.fry@edf.fr 2 RISK ASSESSMENT INTERNATIONAL Puschmanngasse 1/3 A-1210 Vienna Austria - vogel@risk-assessment.at 2 IRSTEA CS 40061, Aix-en-Provence Cedex 5 France - paul.royet@irstea.fr This report presents some results of the ERINOH research project, with the support of RAI, dealing with internal erosion in dams and dikes and their foundations. Databases have been compiled on erosion incidents and case histories of failures in France, Europe and in the world. These databases are tools for improving the safety of dams. Recent failures show that is the most frequent cause of the last water-retaining failures. However, overtopping is the most frequent cause of large dams failures during period. The 6 failures recorded in France were caused by concentrated leak erosion or by backward erosion. Fortunately no fatalities occurred. Most incidents occurred, where filters are not effective. Key words Incident, failure,, overtopping, dam, dyke, embankment. I EROSION IS THE THREAT OF WATER RETAINING STRUCTURES The last inquiry launched by Risk Assessment International (RAI) on dams, levees or dikes failures since 2010 led to the list of table 1. During 26 months, 47 failures were recorded, whose 8 large dam failures (ICOLD 1973 definition). It means around 20 published cases of water retaining structures failures per year and 3 large dam failures per year. Two mean physical processes are involved in failure of a water retaining structure: either a mechanical failure by sliding, or a hydraulic failure by erosion. According to the data collected from February 2010 to April 2012, it is obvious that erosion is the major cause of failure. More than 97% of failures between 44 known cases were induced by erosion. The causes of failures are (23 cases between 44), or external erosion (20 cases of overtopping) and 1 case of sliding only, caused by the very severe Tohoku earthquake. In consequence, is the most frequent cause for all the water retaining structures. By the way, external erosion, developed by overtopping (overflowing of reservoir water level over the crest) is the most frequent cause of failure of large dams (5 cases between 8), (3) and earthquake causing 1 failure respectively. Name Country Type Height Length Failure date Failure cause Forge Pond USA EMB 2,4 m 79 m overtopping Barrage du Brault France EMB Kyzylagash (V=42Mm3) Kazakhstan TE 11 m overtopping Sadler Pond USA EMB overtopping Geneva Pond USA EMB overtopping 273

2 Blue Pond USA EMB Millbrook Pond USA EMB Lower Sprague USA EMB overtopping overtopping overtopping Glen Rock USA EMB overtopping Snohomish Lagoon USA EMB 4,6 m Long Hollow Pike USA EMB overtopping Bredthauer Dam USA EMB overtopping Ericson USA EMB overtopping Testalinden Canada TE Hope Mills USA PG 10 m 230 m Bom Conselho Brazil TE 15 m overtopping Caudalosa Chica (Tailing) Peru EMB 10 m Tempe Town Lake USA Steel construction Lake Delhi USA TE 18 m 215 m overtopping Rose Hill USA TE 6,5 m overtopping Niedow (Witka) Poland TE 18 m 270 m overtopping Subbareddy Sagar India TE 85 m 450 m overtopping Zijin (Tailing) China EMB overtopping Granö Sweden TE 9 m Kingstowne Park USA TE Kolontar (Tailing) Hungary EMB Hästberga Sweden TE 7 m Laneuveville-devant-Nancy France EMB Chagrin River (=Gates Mills) USA PG overtopping Stamps Lake USA TE Fujinuma Japan TE 17 m 133 m Seismic sliding Jensen Dam USA EMB Barlovento Canaries reserv 25m Sultan Lake 16 USA PG (c) 3,7m 61 m Lewiston Pond USA TE Kütahya (Tailing) Turkey EMB Puyang River (Zhejiang) China EMB overtopping Boobe Hole USA TE 11 m 56 m Xichuan Minjiang (Tailing) China EMB Besines France TE Echo Lake (=Arden) USA PG 3 m overtopping Shadow Lake USA TE Campos dos Goytacezes Brazil EMB 11 m levee Ivanovo Bulgaria TE 19,0m 146 m Internal erosion Timberlake Pond USA EMB Michigan s Windoga Lake USA TE Oak Grove Lake USA TE 9,5 m Table 1: List of dam failures from 2010 to April (large dams are in the yellow lines) 274

3 Failure of Kyzylagash dam (2010) Failure of Bom Conselho dam (2010) Failure of Niedow or Witka dam (2010) 275

4 Failure of Ivanovo dam (2012) Figure 1: Pictures of recent dam failures. II DAM FAILURES CAUSED BY INTERNAL EROSION OVER THE WORLD Risks associated with dam failures based on statistical studies are difficult to assess, because either the information of different data bases were contradictory or no data were available. For instance, a lot of failures are registered in USA (table 1), not because the dam safety is worst in USA than in other countries, but thanks to the greatest transparency and strongest action of media in that country. Another difficulty is linked to the definitions. In this paper failure is not an accident that destroys a dam. ICOLD definition is used here, as a collapse or movement of a part of a dam or its foundations so that the dam cannot retain the stored water [ICOLD, 1995]. In 1974, ICOLD published a first failure list, where 202 dam failures were collected [ICOLD, 1974]. 5 years later, the result of an investigation presented only 129 dam failures [Goubet, 1979]. In 1995, ICOLD updated this list by defining a failure during construction when a large amount of water was released downstream by a river flood which caused the partial or total destruction of the dam, whereby the dam in construction when the overtopping began should have at least a height of 15 m or reservoir filling had commenced before dam completion. Therefore no failure of dams during construction is considered, as long as the reservoir was empty. According to these definitions 179 failure cases were determined, which all concerned large dams. The weakest dams are the tailings dams, impounding tailing or toxic fluids. For instance, in 1972, the failure of the tailing dam of Buffalo Creek caused 125 fatalities. In 1985, 268 people died after a similar catastrophe in the Stava valley in Italy, not to mention the contamination after the failure of the uranium tailings dam Key Lake in Canada in 1984 or the release of m 3 of cyanide contaminated liquid after the failure of a tailings dam in Romania in January 2000 and the following poisoning of drinking water of more than 2 million people in Hungary. ICOLD recognized the necessity of failure data about such constructions and published first time a bulletin concerning failure events of tailing dams [ICOLD, 2001]. Failures causes must be investigated irrespective of the dimensions of a dam or of the height of its hazard caused the failure of the only 6 m high Canyon Lake dam in the USA the death of 300 persons. Data of failures of small dams include valuable contributions for the assessment of failure modes and failure causes, also for those of large dams [Vogel, 2001]. The latest inquiry led to 432 failures of water retaining structures caused by : 111 large dams, 259 small dams and 61 channel dikes, levees or flood embankments and one unknown type. From collected information, an assessment of the main type, location and initiation location of was attempted. It is important to note that in a lot of cases, not enough information is released and judgment and interpretation replace information to select the class of cause or type of. In consequence, the class with the largest number of failure cases has a real sense (overwritten in orange in table 2), the other percentages are less reliable. 276

5 Small and large dam failures Large dam failures Piping location Number % Number % Piping through the embankment % 50 68% Piping through the foundation 44 17% 18 25% dam-foundation contact 5 2% 5 7% known locations % % Unknown data % 38 34% Total % % Initiation area Number % Number % Conduit 87 39% 22 31% Core 8 4% 6 8% Spillway 29 13% 7 10% dam body 45 20% 6 8% Foundation 36 16% 14 20% Abutment 8 4% 6 8% Upstream slope 3 1% 3 4% Membrane 2 1% 2 3% Crest 5 2% 5 7% known initiation areas % % Unknown data % 40 36% Total % % Type of Number % Number % Concentrated leak % 35 57% Contact erosion 29 13% 14 23% Backward Erosion 29 13% 10 16% Suffusion 4 2% 1 2% Erosion into pipe or culvert 1 0% 1 2% Estimated types % % Unknown data % 50 45% Total % % Table 2: Origins of causing small and large dam failures. The process of may be broadly broken into four phases [Fell & Fry, 2007]: initiation of erosion, continuation of erosion, progression to form a pipe or occasionally cause surface instability (sloughing), and Initiation of a breach. Piping is a potential progression phase of which initiates by backward erosion, or erosion in a crack or high permeability zone, and results in the formation of a continuous tunnel called a pipe between the upstream and the downstream sides of the embankment or its foundation. It is actually the 277

6 culmination of a process of erosion in which a number of phases must occur and be sustained in order that a pipe develops through the dam or its foundation and allows the passage of considerable quantities of water which may lead to a breach. From data compiled in table 2, piping through the embankment is three to four times more frequent than piping in foundation. Piping at contact between embankment and foundation is less frequent than the two previous piping locations. However 1/5 to 1/4 of the failures are induced by erosion path through foundations and abutments. Erosion along conduits and culverts is the most frequent initiation location of piping. About half of failures are induced along structures (conduits, spillway, wall). Initiation of erosion occurs in four mechanisms: concentrated leak, where there is an opening (crack or cavity), through which concentrated leakage occurs and detaches particles from the sides of the opening. Backward erosion, where there is a leakage which detaches particles from the leaking downstream surface or from the bottom of very thin pipes below a roof. Contact erosion which occurs where a coarse soil such as a gravel is in contact with a fine soil, and flow parallel to the contact in the coarse soil erodes the fine soil. Suffusion which occurs when water flows erodes fines particles through internally unstable widely graded or gap graded non plastic soils. From data compiled in table 2, concentrated leak, associated to crack or cavity, is the most frequent mechanism initiating failure (2/3 of the failures). Piping in embankment and concentrated leaks are more frequent in small dams than in large dams. The cause of the gap of performance between small and large dams is the worst protection of small dams, built without filters or with deficient filters. III ERINOH DATA BASES OF INCIDENTS III.1 Background and structure of the databases Two partly bilingual (English - French) databases have been developed as part of a national research project called ERINOH ( ). ERINOH brought together thirty partners, universities, owners and engineering offices to examine the mechanisms of in dams, dikes and their foundations. The "database of incidents" lists the incidents, accidents and failures caused by and external erosion (overtopping) of dams or dikes (retaining navigation or hydroelectric canals and flood levees). An ICOLD incident is either a failure or an accident requiring repair. In that data base some incidents are anomalies. An ICOLD accident occurs when a failure is prevented by immediate remedial measures, possibly including drawing down the water. An ICOLD failure is a collapse or movement of part of a dam or its foundation, to the extent that the dam cannot retain water. The objective of the database is to identify all the mechanisms and use data on the frequency of occurrence for risk analysis. The "validation database" was originally developed by EDF and its partner International Risk Assessment International as part of the project "Erosion of Embankment Dams" led by CEATI / DSIG and continued through ERINOH. Its purpose is to provide robust data on dam failures by overtopping or for validation of numerical models of breach hydrographs. These validation tests include the inputs and outputs necessary for numerical models of breach, such as breach hydrographs, the sizes of the breach and the times that characterize the evolution of the breach process. Both databases are accessible on Internet, by secure access with login and password, to members of the research project. The two databases use a similar structure and many of the same principles. The development, hosting and administration of the data base of incidents is provided by IRSTEA (France) and the validation database by Risk Assessment International (Austria). The following principles of structuring validation data were applied to the data base of incidents: Each data, text or number, is provided with references. Where possible, the sources are downloaded as a file. Each user can then check the validity of the source and the correct transcription of the information in the database. For each field of a test case, the data found in all sources of literature are introduced. As details often vary, they are assigned a confidence level represented by a color code (green = good, orange = 278

7 medium, red = bad) possibly supplemented by a commentary. Each case sheet includes attached files with reports, photos, maps, charts. The database is living and changes are logged. Each sheet contains 70 incident fields, grouped into six sections: identification of the type of structure and the type of incident; geometry of the structure where the incident occurred; materials in the embankment body; materials in the foundation; description of the reservoir (dam, canal or river); description of the incident and the breach. The two databases differ in the selection criteria. The database of incidents is intended to contain as many cases as possible. It contained in August 2011, 174 completed, validated and available cases, 30 more are under validation. Most of these incidents are in France, but a number of cases of dams in other countries have been reported. The breakdown by type of works is: Dams: 41 cases Dikes for navigation or hydropower canals: 45 cases Levees (dikes for protection against floods): 120 cases. The validation database selects only sufficiently well documented cases. It contained, in August 2011, 16 test cases, including 13 cases of failure by overtopping and 3 cases of failure by piping. III.2 Data on dykes on navigation and hydropower canals The main features of navigation or hydropower canals dikes are in table 3. Features Navigation canals Hydropower canals Height 1 to 12 m (often 3 to 6 m) 4 to 20 m Crest width 1,5 to 5 m min 5 m Type of fill homogeneous zoned or a few cases of upstream facing Construction date 19th century 1950 to 1987 Table 3: Main difference between features of navigation canals and hydropower canals. No failure of hydropower canals occurred. Of the 45 incidents, 25 did not lead to failure but sinkholes occurred at 9, piping was detected early and stopped at 13, 7 were cases of landslides and slope erosion, and 20 cases of navigation canals involved partial (12) or total breaches (8). The origin of these breaches was (12), overtopping (5) or both mechanisms simultaneously (2), there was one case of wilful breach. The lengths of only 6 breaches were reported: the average width is 22.5 m and varied from 10 to 38 m, a relatively narrow range. The small number of cases does not allow correlation of the size of the breach to the size of the embankments. III.3 Data on dykes on levees or flood embankments There are 120 datasets on levees, the most numerous, and many cases involve old breaches from archives. The main features of the breached levees were as follows: height of 1.5 to 6 m, usually between 3 and 4.5 m; relatively steep slopes: 1 <H/V <2; systematically sandy clay semi-homogeneous fill, without filter or drain; Very old works, built in stages over the centuries, some from as early as the thirteenth century. Of the 120 records, is identified as an initiating mechanism in 19 cases, the proximity of pipes or burrows are explicitly mentioned in 11 cases. Overtopping is identified as the initiating mechanism in 50 cases and strongly suspected in 51 cases where the mechanism has been initially (tentatively) identified as indeterminate. 279

8 The width of breach opening caused by is an average of 21 m (3 to 65 m). That caused by overtopping is an average of 190 m and can reach remarkable values, up to 740 m for the largest opening. The size of the breach opening appears to be weakly related to the distance between the levee and the riverbed; however the most important breach openings appear where levees are near the riverbed. There is no clear correlation between the breach opening width and the height of the levee. The type of material in the levee does not appear to be influential, but the quality of this data is sometimes questionable. Further research is needed to find a relationship between the breach dimensions and the breach hydrograph. Finally, a remarkable point concerns the erosion of the foundation. Information is available from 62 cases and describes pits of several hectares of erosion up to 600 m long and 650 m wide (the pit is rarely filled in afterwards). The pit erosion is often described as having the form of a glove, erosion developing along preferential paths and the presence of paleo-channels are often mentioned. III.4 Data on embankment dams The 30 cases of in France reported in the database of incidents represent a large variety of dams, from well compacted zoned dams to small dams built without mechanical means and therefore poorly compacted. Six failures are reported, 3 were total breaches, 2 partial breaches and in one failure the reservoir could not retain water without breach. None of these failures causes casualties and none concerned a large dam. Of the four types of erosion [Fell, R. and Fry, J.J. (2007)], concentrated leak, backward erosion, contact erosion and suffusion, only concentrated leak (3) and backward erosion (3) led to failures. Apart from one case where relevant information was not given, all the failures occurred in dams without a filter. All the failed embankments were homogeneous. The erosion path is known in 5 cases: along a conduit (2), in the fill (2) and in the foundation (1). In all cases, the design was flawed. Two breaches were only partial because of the low height of the dam or the small reservoir volume. Filter design is critical (3 accidents occurred where filters were poorly designed), but cannot prevent all accidents (2 accidents occurred where there were correctly designed filters). Internal erosion occurred first in foundations (10/28), erosion along contacts with structures occurred in 9 incidents (7 pipes and 2 spillways) and through fill in 9 cases. Three of the 4 rockfill embankment incidents were caused by through the foundation. Surveillance failed to detect and prevent the 6 failures, in spite of the poor design of these dams requiring adequate surveillance. The 24 accidents were detected and actions taken to prevent them from developing into failures by the increase of seepage (11), or piping (8), sinkholes (5), transport of fines (5), sliding (4), settlement (3) and backward erosion (1). Internal erosion incidents are related to ageing: four incidents involved dams older than 100 years, including three very old dams more than 300 years old. IV ACKNOWLEGMENTS AND THANKS The development of data bases was funded by ERINOH project, IRSTEA and EDF. IREX receives our thanks for his permanent support. V REFERENCES Fell, R. and Fry, J.J. (2007). The state of the art of assessing the likelihood of of embankment dams, water retaining structures and their foundations. In Internal Erosion of Dams and their Foundations. Editors R.Fell and J.J Fry. Taylor and Francis, London Goubet, A. (1979). Risques associes aux barrages. La Houille Blanche. Nr. 8, pp ICOLD, (1973). World Register of Dams. Paris. France. ICOLD, (1974). Lessons from Dam Incidents. Paris. France. ICOLD, (1995). Bulletin 99, Dam Failures, Statistical Analysis, Commission Internationale des Grands Barrages, Paris, 73 pp. ICOLD, (2001). Bulletin 121, Tailing Dams-Risk of Dangerous Occurrences, Commission Internationale des Grands Barrages, Paris. France. Vogel, A. (2001). Lessons from Incidents and Failures of Dam Constructions. Proceedings of the International Conference on Safety, Risk, and Reliability-Trends in Engineering. pp St. Julian. Malta. 280