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Abstract
The present study is concerning with failure of cohesive earth dams due to overtopping flow through the flood season. Where earthfill dams are the commonest and oldest types of dams more often of small rather than medium height. Earth dam basically is a trapezoidal embankment or fill built in a valley or river to control floods. Modes of earth dam failure can be grouped into three general categories: overtopping failure, which represents 40% of earth dam failure, seepage failure, which represents 35% of earth dam failure, and structural failure, which represents 25% of earth darn failure
Overtopping failures, as a present study, result from the erosive action of water on the embankment. Erosion is due to uncontrolled flow of water over, around, and adjacent to the dam, where the earth embankments are not designed to be overtopped and therefore are particularly susceptible to erosion. Once erosion has begun during overtopping, it is almost impossible to stop. The breach cross section may be triangle, rectangle, parabolic, or trapezoidal but from all collected data, the breach shape for all practical purposes can be approximated as trapezoidal. Depending on the conditions and configurations of embankment and whether or not tailwater exist, the initial erosion may begin at any point on the downstream slope, thus the toe is the most common location for initiation of erosion.