Simulation of floods under the influence of effective factors in hydraulic and hydrological models using HEC-RAS and MIKE 21

Simulating floods and creating vulnerability maps are essential in urban watershed management systems. The present research aimed to simulate floods and assess floodplain risk in the Khalkai watershed located in Gilan Province, Iran. This river is characterized by extensive agricultural areas and urban areas that become flooded during most rainy seasons. Hence, an accurate assessment of flood extent and behavior is necessary. This study employs HEC-HMS, HEC-RAS, and MIKE 21 for advanced hydrodynamic modeling, focusing on two-dimensional (2D) capabilities essential for urban areas and flood is simulated with probability return periods of 50, 100, and 500 years. The research objectives include comparing HEC-RAS and MIKE 21 to identify the most effective flood simulation model, evaluating the impact of hydrological and hydraulic factors, the influence of GPS topographic mapping compared with DEMs extracted from satellite images and assessing land-use changes on flood behavior. Model accuracy is validated against historical flood data, revealing that MIKE 21 effectively addresses challenges related to grid resolution and flood delineation. Results indicate that while HEC-RAS provides a broader extent of flooding, both models offer critical insights into flood depth and flow characteristics. This research contributes to enhanced flood risk management by illustrating the implications of land-use changes on flood events, offering valuable insights for policymakers in mitigating future flood impacts and developing sustainable urban strategies.