Abstract: Research into and apply of the overland flow model have been one of the major themes in hydrology due to the basic unit on which physically based distributed parameter hydrological model development is based. Runoff coefficient calculation of the overland, however, is the critical step in doing so. On the other hand, it is necessary to determine the coefficient for evaluating the forest plantation impacts on the surface runoff. Dynamical overland flow model under artificial rainfall simulations was developed for forested infiltrating slope based on the surface runoff generation and hydrological traits. Soil water movement was simplified as one dimensional vertical flow while overland flow kinematic wave model. Single step Lax Wendroff difference scheme and iterative calculation method were adopted to simulate the overland flow and estimate the surface coefficient. Parameter optimisation results have shown that the overland flow resistance(effective surface roughness)of Black locust(Robinia pseudoacacia L.)plantation plots are between 0.1931～0.2131, Mongolian oak(Quercus monogolica) plot 0.1701, and Chinese pine(Pinus tabulaeformis Carr.)plantation 0.1423. Optimised m values in the overland flow kinematic approximation q=αh^m are between 2.76～3.090 with are near m=3 representing sheet flow. The model and parameter verification results have shown that computed and measured rising limb and partial equilibrium hydrographs fitted very well.

Key words: Infiltrating slope, Overland flow, Numerical simulation, Effective surface roughness, Parameter optimisation