Unsteady Flow Model of Gaurang River at Kokrajhar Using HEC-RAS 6.0

The present study uses flow simulation capability of Hydrologic Engineering Center’s River Analysis System (HEC-RAS), an open-source software developed by U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center (HEC) for developing a 2D unsteady flow model of Gaurang River from Chandamari Bridge (26°25'27.29"N, 90°15'53.78"E) upto the right bank of Brahmaputra basin (26°11'17.67"N, 90°16'22.58"E) where it acts as a tributary to the Brahmaputra river. For analysis, rivers that reach the length of 38.7 km from Chandamari Bridge up to the right bank of Brahmaputra basin are taken into consideration. Detailed underlying terrain information available from Google Earth was exercised to generate the geometry of the river. The cross-section of the river was extracted from Google Earth Pro at 25 stations with 76 m interval along the reach and was imported in HEC-RAS as geometry data of the river. Stream flow data for 20 years (January 1999–December 2019) from government surveyed data were taken as upstream boundary condition for the complete unsteady flow hydraulic modeling along the reach and the normal depth as downstream boundary condition.