Flood Inundation Mapping Using 2D Hydrodynamic Model and GIS Technique for Lower Tapi Basin, India

A two-dimensional (2D) hydrodynamic (HD) model is developed for densely populated Surat city, India, located on the bank of the lower Tapi River. Surat city has experienced flooding in the past during the monsoon period due to heavy releases from the Ukai Dam situated 100 km upstream of the city. In the current study, the 2D HD model is developed for the lower Tapi basin (LTB), focusing on Surat city for the past flood that occurred in August 2006. The hourly discharge from the Ukai Dam and tidal levels at the Arabian Sea was used as upstream and downstream boundary conditions, respectively. The distributed floodplain roughness coefficient based on the existing land use land cover (LULC) of the study area is considered across the flood plain. The performance of the model is evaluated against observed water levels along the channel, including maximum flood depth across the flood plain of Surat city and found satisfactory. The developed model will be useful for the local administration in predicting maximum water depth, velocity, and flood duration for various return periods floods of high magnitude and help prioritize the mitigation strategies.