Floods from dam failures

Abstract

Floods resulting from dam failures usually are much larger than those originating from snowmelt or rainfall.Dams can be classified as constructed dams and natural dams.Constructed dams are usually concrete arch, buttress, or gravity dams, and earth-or rock-fill dams.Natural dams include ice dams, morainal dams, volcanic dams, and landslide dams.Other unusual kinds of dam failures include drainage of lakes by underground mining, bursts of large water-diversion pipes, bursts of water stored in peatlands (bog-bursts), and failures of large-volume industrial containers.During the last 100 years, there have been about 200 significant failures of constructed dams, resulting in the death of more than 11,100 people.More than 60 percent of this loss of life occurred in three failures alone:Vaiont, Italy, 1963 (2,600), South Fork (Johnstown) Pennsylvania, U.S.A., 1889 (2,200), and Machhu II, India, 1974 (2,000 +).Major causes of constructed-dam failures are overtopping due to an inadequate spillway (34 percent), foundation defects (30 percent), and piping and seepage ( 28 percent).An order-of-magnitude estimate of risk of dam failure is approximately 10" per dam-year.In the United States for the last 2 decades, the annual loss of life from dam failures has been about 14.The average number of fatalities per dam failure is 19 times greater when there is inadequate or no warning.dam height and reservoir volume.For reconstructing past flood peaks from dam failures for paleohydrological or sedimentological investigations, regression equations with dam height and volume as independent variables produce equations with standard errors of 75 to 147 percent.For all types of dams, the dam factor (height times volume of water), a rough measure of potential energy, produced the lowest average standard error.After large floods from dam failures, one or more of the following characteristics can be expected: (1) Aggradation of the valley upstream by trapped sediment, (2) triggering of landslides by the rapid draw-down of reservoir water levels, (3) large amounts of local scour and deposition downstream, (4) erosion of bedrock along valley walls, and (5) the formation of wide, shallow, braided channels downstream.