Calculation Model of Soil Dam Wash-Away Due to Overflow

Water flow over soil dam crest causes its fast failure. Break-through wave being formed in dam ebb side leads to drastic economic and social consequences. Accuracy in calculation of the break-through wave parameters depends on the accuracy of discharge hydrograph construction in the dam erosion site. A calculation scheme for soil dam wash-away due to overflow has been devised on the basis of the experimental data. Wash-away process is divided in two stages in accordance with the devised scheme. Wash-away of the downstream toe occurs at the first stage. The crest level from the side of upstream edge remains constant. Intensive crest lowering is observed at the second stage. The eroding body is considered to have a shape of a round-crested weir. In such a case the washed-away massif has a form of nappe-shaped crest profile. A mathematical model has been developed on the basis of this scheme and according to this model equations of deformation and flow motion are considered simultaneously. The model is consistent in a good way with physical erosion pattern during fast flood rise and when the erosion width is known; the model is recommended for calculation of breaching sections in reserve water outlets. In general case and when the width is unlimited (three-dimensional problem) calculation formulae have one more unknown variable that is flow width within the erosion site. The paper describes peculiar features in physiccal erosion pattern for such case and a number of the known formulae for determination of the erosion have been given and analyzed in the paper. The equation which fits in a good way in the proposed mathematical model has been chosen, and it provides the possibility to adapt the model for three-dimensional erosion conditions. Calculations made in accordance with the proposed methodology make it possible to construct discharge hydrograph in the dam erosion site.

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