Flood simulation using the hydrological model and the hydrological–hydrodynamic coupling model in a small watershed in semi-arid and sub-humid region, North China

Flood disasters occur frequently in semi-arid and sub-humid mountain watersheds, and their formation mechanism is affected by many factors, resulting in low simulation accuracy. The main purpose of this study is to evaluate the impact of adding actual river channel data on the accuracy of flood simulation. In order to obtain higher-resolution terrain data, an unmanned aerial vehicle (UAV) was used to survey the study area. Taking the Liulin Watershed in Xingtai City, Hebei Province as the research area, the HEC-HMS hydrological model and the HEC-HMS and HEC-RAS coupling model were constructed, respectively, to simulate 26 flood events during the period from 1982 to 2016. The results indicate that the coupled model can reflect the evolution process of river floods. When simulating certain major flood events, the percentage of flood peak error and Nash–Sutcliffe efficiency coefficient (NSE) have improved, such as the NSE of No. 160812 floods increasing from 0.9 to 0.95. However, the simulation accuracy of these two models for small floods in the watershed is relatively low. Future research should focus on how to accurately evaluate the parameter curve number (CN) of the watershed before rainfall and obtain more accurate runoff yield.