Dam failures, which can manifest as a complete collapse of the structure or partial scouring, occur for a variety of reasons. An analysis of historical dam failures indicates that one or more of the following factors often contribute to such catastrophic events:
- Prolonged rainfall and floods
- Insufficient spillway capacity
- Internal erosion leading to piping and seepage
- Inadequate maintenance of dam equipment during operation
- Use of unsuitable design or materials
- Landslides causing water to overtop the dam body
- Failure of another dam located upstream in the dam basin
- Terrorist attacks
- Earthquakes causing cracks along the upper section of the dam body
- Excessive inflow into the dam reservoir
- Insufficient or incorrect selection of filter material
- Human, design, and computational errors.
The causes of dam failures can be broadly categorized into three main groups:
a) Water Overtopping the Dam Crest
Water overtopping the dam body can occur for several reasons but is most commonly due to inadequate spillway capacity. It can also happen if the spillway, even if adequately sized, becomes blocked by solid materials. The water flowing over the dam crest can then cause erosion, ultimately leading to the dam’s failure.
b) Foundation Failures
Foundation failures leading to dam collapse can stem from the inherent characteristics of the foundation soil or rock, as well as from improper improvement works carried out during construction. Differential settlement, cracks, and water seepage can be indicators of foundation problems. Furthermore, the incorrect selection and application of foundation materials during the design phase can lead to serious issues.
c) Piping in the Dam Body
In embankment dams, voids can form over time within the impermeable zone (core) designed to prevent seepage. This occurs when seeping water carries away fine material. These voids can act like pipes, and as water flows through them, they can enlarge, eventually causing the dam to fail. This phenomenon is known as piping.
Dam Collapse Events in History
Dam | Year | Country | Deaths | Cause of Collapse | |
1 | Banqiao/Shimantan | 1975 | China | 171 000 | Cadastrophic precipitation |
2 | Machchu 2 | 1979 | India | 5 000 | Water overflow from the top |
3 | Sempor | 1967 | Indonesia | >2 000 | Water overflow from the top |
4 | South Fork | 1889 | USA | 2 209 | Excessive rainfall |
5 | Vajont | 1963 | Italy | 2 000 | Water overflow from the top |
6 | Tigıa | 1917 | India | 1 000 | Water seepage into the foundation |
7 | Panshet | 1961 | India | 1 000 | Collapse of dam body |
8 | Puentes | 1802 | Spain | 608 | Soft ground |
9 | St. Fıasncis | 1928 | USA | 600 | Geological insensitivity |
10 | Malpesset | 1959 | France | 423 | During the construction phase |
11 | Gleno | 1923 | Italy | 356 | Poor design and construction |
12 | Val di Stava | 1985 | Italy | 268 | Poor design and construction |
13 | Koshi | 2008 | Nepal | 250 | Excessive rainfall |
14 | Dale Dike | 1864 | England | 244 | Poor design and construction |
15 | Canyon Lake | 1972 | ABD | 238 | Flood |
16 | Kantale | 1986 | Sri Lanka | 180 | Flawed operation |
17 | Tangiwai | 1953 | New Zealand | 151 | Crater lake overflow |
18 | Bouzey | 1884 | Algeria | 150 | Slippage |
19 | Vega de Tera | 1959 | Spain | 144 | Collapse of dam body |
20 | Mili Nehri | 1874 | USA | 139 | Defective design |
21 | Buffalo Creek | 1972 | USA | 125 | Excessive rainfall |
22 | Sella Zerbino | 1935 | Italy | 111 | Flood |
23 | Vratsa | 1966 | Bulgaria | 107 | Flood |
24 | Situ Gintung | 2009 | Indonesia | 98 | Excessive rainfall |
25 | Certej | 1971 | Romania | 89 | Defective design |
26 | Bilberry | 1852 | England | 81 | Turbine rupture |
27 | Austin | 1911 | USA | 78 | Intentional destruction |
28 | Sayam/Shushenskaya | 2009 | Russia | 75 | Excessive rainfall |
29 | Shajidor | 2005 | Pakistan | 70 | Excessive rainfall |