An enhanced inundation method for urban flood hazard mapping at the large catchment scale

Urban flooding occurs frequently in the world and urban hydrological models are widely applied in urban flood management and disaster mitigation. In this study, an enhanced inundation method (EIM) for urban flood hazard mapping at the large catchment scale is proposed. EIM can be easily coupled with urban hydrological models and the coupled framework can consider both source flooding and non-source flooding in floodwater generation. In EIM, the floodwater spreading order in the positive process is based on the topological relationship between depression outlets; the floodwater from lower depression elements is considered as a feedback process. These improvements make this proposed method suitable for inundation estimation in large urban catchments. Dahongmen (DHM) catchment in Beijing, China was selected as the case study area to illustrate the applicability of the proposed method. Historical inundation records during one heavy storm were applied to test the performance of the method. EIM is compared with USISM (urban storm-inundation simulation method) on the flood hazard map in the DHM catchment, which reveals the effectiveness of the improvements. The results show that all inundation locations are successfully identified by EIM and are distributed in flooding areas (water depth greater than 0.15 m) in the catchment. The average relative error of simulated inundation depths is 15%, which indicates that EIM can successfully simulate flooding scopes and depths in the study area. The results revealed that EIM can be a valuable tool for mapping urban flood hazards at the large catchment scale based on GIS techniques.