A numerical simulation method is proposed

which can correctly reflect the breach mechanism of earth-rock dams due to seepage failure and can rationally depict the full process of the development of seepage passages

the collapse of dams and the failure due to overtopping for earth-rock dams.In this method

the critical incipient velocity for the occurrence of seepage failure is derived by analyzing the forces acting on soil particles in the seepage passage;and the formulas respectively put forward for calculating the erosion of dam materials during the development of seepage passages and the development of the breaches after dam failure due to overtopping.The calculated results of the breach development rules

flood hydrographs and peak values are close to the observed ones.Accordingly

the rationality of the proposed numerical method is validated.Moreover

the impact of different elevations of initial seepage passages on the breach development rules

flood hydrographs and peak values are discussed

some significant conclusions are made.Therefore it may be used to accurately evaluate disastrous consequences and draw flood control emergency plans for earth-rock dams due to seepage failure.