A mathematical model to simulate the natural dam break process and to forecast the flood hydrograph in the breach is developed in this paper. The breach is assumed trapezoidal, coupling with the bottom width and side slope angle keeping constants during the overall process of dam breach. Simulation of dam breach evolution is based on the conservation of mass of reservoir capacity and sediment transport capacity. Particularly, broad-crest weir relation is utilized to simulate the outflow in the breach, and an empirical equation is used to compute the rate of erosion in the breached section. Because of the implicit form of these equations, an iterative solution is proposed with convergence achieved in a few iterations. The model can be used by engineers or decision makers for a wide range of applications including risk assessment of natural dams, flood routing forecasting in the downstream reach as well as floodplain inundation mapping .