Abstract:Two dimentional simplified (including kinematic wave and diffusion wave) and full hydrodynamic models have been widely applied to the study of flash floods. However, there are still few guidelines to help modelers to select an apropriate model for flash flood simulation on field scale. This paper, firstly, presented a comparative study of simplified and full hydrodynamic models in terms of physical basis. Then, the models were applied to unsteady flow with lateral inflow, experimental rainfall-runoff and a field study case in Sanjia village respectively to explore their stability and applicability. The results showed that differences in theoretical basis results in differences of limitations in applicability and accuracy in simulation: even under the calibration of Manning roughness, the simplified hydrodynamic models were invalid for simulating the rainfall-runoff on experimental scale and were unsuitable for modeling on field scale like Sanjia village study case. The full hydrodynamic model was needed for the accurate simulation of flash floods.