Geomorphic evolution of a tropical river basin in the Deccan Volcanic Province: a critical water supply source to Mumbai metropolitan region (MMR), India

Reservoir siltation lowers a dam’s effective storage capacity, which is mostly determined by the sediment discharge from soil erosion in the watersheds. The morphometric parameters are significant in determining erosional susceptibility of watersheds. In the present study, morpho-hypsometric aspects of the Surya sub-basin, a major tributary of Vaitarna river, has been considered. This river system and associated dams provide the major source of drinking water supply to the Mumbai Metropolitan Region (MMR). A major part of the river flows through the Deccan Volcanic Province (comprising basalts) and Quaternary alluvial deposits. The seven sub-watersheds (SWs) of Surya sub-basin were analysed using the morphological parameters (linear, areal, and basin shape aspects), along with ratio factors and hypsometric integral (HI) values. The HI values for the SWs range from 0.11 (SW-1) to 0.51 (SW-6) with a HI value of 0.21 for the whole Surya sub-basin. The relatively high HI values of SW-6 (0.51) and SW-7 (0.31) indicate that these SWs are relatively prone to high erosion and sediment discharge resulting in dam siltation, and will be a great threat to livelihood of millions of people in the MMR. Therefore, prioritizing these SWs for proper engineering measures could reduce erosion and improve recharge.