One Dimensional Steady Flow Analysis Using HEC-RAS—A Case of Sabarmati River, Gujarat, India

This study aims to examine the probability of over spilling from banks of Sabarmati River in reach between Gandhinagar and Ahmedabad for various return periods. The probable peak discharge for return periods of 20, 25, 30, 50, 60, 75, and 100 years calculated using Gumbel’s frequency distribution and further simulated under steady condition in HEC-RAS 5.0.1 software. In present study, integration of Arc Map 10.0.1, HEC GeoRAS 10.0, and HEC-RAS 5.0.1 has been practiced to produce geometric data at every 200 m interval utilizing Cartoset 1 DEM. The flow hydrograph of the respective year at Chiloda Bridge, Gandhinagar, and normal depth at Vasna Barrage, Ahmedabad, have been selected as the upstream and downstream boundary, respectively. The flow is simulated under steady condition by selecting the computational time step of 1 min in HEC-RAS. The simulated maximum water surface levels have been compared for elevations of both the left (east) and right (west) banks of Sabarmati River for all the 190 numbers of cross sections. The cross sections having elevation lesser than relative water surface elevation on corresponding bank have marked as unsafe and have probability of water spill. The analysis concludes that the percentage of cross section prone to spilling of water during high discharge on left bank is 58% and for right bank is 35.33% for 20 year return period, while for 50 year return periods, it has come out as 67.01% on left bank and 44.16% on right bank. For all the return periods, it has been observed that left bank of Sabarmati River which represents east side of old wall city is more prone to water spill from higher water levels in river than the right bank of city locating on west side of river considered as new Ahmedabad city.