Mathematical Model and Application of Overtopping Breach of Cascade earth-rock dams Considering Flood peak Enhancement Effect

The flood caused by the overtopping breach of cascade earth-rock dams significantly exceeds that of a single dam breach. Rapid and precise predictions of dam-break flood in cascade earth-rock dams are essential for risk prevention, control, and early safety warnings in water conservancy projects. Through the analysis of typical dam breach cases and model testing, this study confirmed the flood peak enhancement effect in the breach of cascade earth-rock dams. By focusing on the soil erosion rates, the inflow discharge and velocity were identified as the fundamental causes of this enhancement effect from a physical and mechanical perspective. The lognormal distribution function was employed to equivalently quantify the inflow discharge and velocity processes, with each parameter bearing clear physical significance. Based on this, a mathematical model for overtopping breach in cascade earth-rock dams incorporating the flood peak enhancement effect was proposed. Along with the widely used DBC-IWHR model, this model was applied to the Dawei-Busigou-Shuangjiangkou cascade reservoirs, and the calculation results were subsequently compared and analyzed. The results indicated that the proposed model effectively reflect the flood peak enhancement effect in cascade earth-rock dams breach. Furthermore, the impact of this enhancement effect was determined by the curvature of the river and storage capacity of the downstream reservoirs. The greater storage capacity in the downstream regulation reservoir or increased river curvature, led to higher energy dissipation of the dam-break flood during routing process, thereby significantly reducing the flood peak enhancement effect.