Resource assessment and strategic planning for improvement of water supply to Shimla city in India using geo-spatial techniques

This study focuses on suggesting short term corrective measures for improving water supply to Shimla city which is the state capital of Himachal Pradesh in India. The city is getting water supply from seven sources located in three watersheds, namely, Nauti, Ashwani and Giri watershed. Nauti and Ashwani watersheds have fully been tapped but Giri watershed is partly tapped. Presently, only 20 MLD (million litres per day) of water is being drawn from Giri River which is about 37% of the present water demand.Resource assessment in Giri watershed was accomplished using Remote Sensing Techniques and GIS based Arc-SWAT Hydrological Model. Study has established that average annual precipitation in the Giri watershed for 26 years (1984–2010) is about 1011.44 mm, out of which about 32% flows as runoff, 12% as groundwater and about 56% as evapotranspiration. The monthly inflow varies from 0.37 to 18.93 m3/s and 75% annual dependable discharge is 2.80 m3/s at the existing Headworks.Being ungauged watershed there are no statistical data for validation of results. However considering Water Balance Equation as the validation criteria, coefficient of correlation “R” between observed Rainfall and simulated Runoff was found to be 0.94 which validates the output. Results were further validated through actual measurement of inflow in lean period, which surprisingly has shown very good correlation (R = 0.95) between simulated and observed stream flow. Model output further reveals that the excess inflow can be utilized to fulfill additional water demand of 42.61 MLD (2031) for Shimla city by creating storage of about 1.12 MCM (million cubic metres).