Mitigating debris-flow hazards is a great challenge in a period after Wenchuan Earthquake. Because of the complexity of debris supply and formation, the debris-flow discharge with respect to flood discharge was amplified in runoff, converging and moving stages of debris flows, and previous methods of calculating debris-flow peak discharge were not available for the debris-flow ravines in the earthquake affected region. The investigation of the formation of post-quake debris flows indicated that debris-flow hydrologic process is not linearly equivalent with flood hydrologic one, and debris-flow amplification coefficient is not linearly proportional to flood peak discharge. An empirical relationship of power function between the amplification coefficient and the flood peak discharge was built by analyzing the field data of seven debris-flow ravines in Subaohe, Weijiagou and Dubahe basins of the earthquake region. Combined the classical modified flood discharge method with the empirical formula, a nonlinear flood method was developed for calculating debris-flow peak discharge, which can be applicable to post-earthquake region.
