2-D Unsteady Flow Modelling and Inundation Mapping for Lower Region of Purna Basin Using HEC-RAS

Abstract

Present investigations utilize two-dimensional flow modelling abilities of (HEC-RAS) Hydrologic Engineering Centres River Analysis System for flood inundation mapping in the downstream area of Purna basin, exposed to recurrent flooding. Floods are natural disasters, which cause loss of life and damages to properties and nature. 2-D Hydrodynamic model is utilized to assess geomorphic viability of floods in downstream side of Purna basin. In this research study, downstream region geometry of Purna river basin, the flood plain of the study area and historical observed flood data of unsteady flow have been used to develop the 2-D hydrodynamic model. For analysis of flooding, a reach of 20 km of river situated downstream of Purna River basin has been considered. Point-by-point fundamental terrain data is taken from a Digital Elevation Model (DEM) of 30-meter resolution image and is utilized to produce the (2D) two-dimensional flow area and stream geometries. River flow information like daily discharge during rainy months, slope available along the river reach from Mahuva gauging station close to Navsari city is utilized for the unsteady flow modeling. Depth of water, velocity distribution and water surface height obtained after 2D flow simulation are utilized to decide the degree of flooding. RAS-mapper is an effective tool in HEC-RAS, which can be utilized for inundation of research area. For unsteady flow analysis, each time step was done based on inflow hydrograph using RAS mapper tool in HEC-RAS, which gives the spatial distribution of the river flow. The outcomes from this research examination can be utilized for disaster management, flood management, early warning system by authorities in addition to infrastructure growth decisions.