Formulas for the Peak Discharge from Breached Earthfill Dams

Although advanced physically based models have been presented in the last years, there is still much interest in equations for predicting the peak discharge. Indeed, simple relations are very useful for technical purposes, especially when rough calculations are acceptable. This paper presents new equations for assessing the peak discharge of the flood hydrograph caused by the gradual erosion of earth dams. The equations are obtained by a regression analysis carried out on the peak discharges provided by a physically based numerical model. The approach proposed in this paper has the advantage of taking into account some parameters usually neglected by common best-fit equations that have strong influence on the peak discharge. In particular, the equations discussed in this paper take into account the susceptibility to erosion of the dam, the shape of the reservoir, and the ratio of filling of the reservoir for failures caused by piping. The usefulness of the equations is shown through a comparison with the numerical model and with other regression relations by applying them to some real dam-breaching events. Finally, a sensitivity analysis is made in order to assess the influence of parameters that have been fixed in the present analysis, like dam crest width or abutment slopes.