Application Study of Coupling Rainfall-runoff Modeling and Floodplain Inundation Mapping

Flood researches include model simulation of runoff and inundation. In order to investigate the rainfall, runoff-producing, flow concentration, and inundation in a basin and to improve the accuracy of flood forecasting, this study established a hydrological hydrodynamic coupling flood forecasting model. Two HEC software modules, HMS and RAS, were used to integrate the two- dimensional hydrodynamic model with the traditional hydrological model. Taking Wende River Basin in Jilin Province as an example, the flooding process of 2017 "7• 13" flood in Wende river sub-basin is simulated. Firstly, input data was preprocessed. A HEC-HMS hydrological model was established and optimized by multi-parameter calibration. Then, the hydrographic model output were assigned as the boundary conditions of a new RAS two-dimensional hydrodynamic model, which was used to simulate the inundation of key sub- basins. The hydrological simulation provided an optimal NSE coefficient of 0.988 for the hydrograph while the two-dimensional hydrodynamic analysis provided a maximum inundation depth of 9.3 m with a relative error of -5.2%. The simulated inundation map showed that plenty of cultivated fields in the upstream area were flooded with a water depth ranging from 0.5 to 2 m, and an average flow velocity smaller than 1 m/s. In the downstream area of Kouqian Town, the maximum inundation depth was close to 1 m, and the flow velocity was from 0.2 to 1.5 m/s, which was consistent with the field measurement. The simulated results from our hydrological hydrodynamic coupling model have high accuracy. It provides a meaningful technical method for flood forecasting in basins with complex hydrological and hydraulic conditions. © 2021, Science Press. All right reserved.