Impacts of urbanization on flooding of a coastal urban catchment: a case study of Mumbai City, India

Land use–land cover (LULC) change in space and time is the main cause behind the changing hydrological processes, ecosystem and environment in urban catchments. In the present study, the main focus was on evaluation of spatial and temporal variation of land use and land cover change in a major coastal urban catchment of Mumbai City, India, called Mithi River catchment. The LULC is derived from the topographic map surveyed in the year 1966 and satellite image for the year 2009. The analysis from toposheet and remote sensing data showed that there is a rise in the built-up area of Mithi River catchment, Mumbai by 59.66 % between 1966 and 2009. It also showed adverse human-induced influences on the Mithi River course and its catchment. Flood hydrographs for different land use conditions were derived by using Soil Conservation Service-Curve Number hydrological model and kinematic wave model, for routing available within the HEC-HMS software. Flood plain maps as well as flood hazard maps for the different land use scenarios have been developed by integrating the models HEC-HMS and HEC-RAS with HEC-GeoHMS and HEC-GeoRAS as well as with GIS and remote sensing. Results obtained from the present study revealed marginal increases in the runoff peak discharges and volumes within the catchment. Even though the runoff change is marginal, combined with tidal influence, it may cause major flooding problem. The integrated modeling approach has been found to be very effective for flood estimation, flood plain and flood hazard mapping. The flood plain and flood hazard maps derived can be used as effective tool to minimize the damages within the flood-prone areas of the river basin for the Mumbai City.