Flood Plain Zoning Using HEC-RAS for Subarnarekha River Basin in Odisha

Abstract

Flood management has become a growing concern for city managers and disaster risk prevention agencies worldwide. Hence, large investments are made towards data collection, archiving and analysis, and technologies such as geographic information systems (GIS) and remote sensing which play an important role. GIS technologies offer valuable means for delineation of flood plains, zoning of areas that need protection from floods, and identification of plans for development and scoping of various kinds of flood protection measures. Flood inundation maps (FIMs) are particularly useful in planning flood disaster risk responses. Floodplain zoning is significantly affected by the diverse and concurrent uncertainties that characterize the modeling chain used for producing inundation maps. To quantify the relative impact of the uncertainties linked to a lumped hydrological (rainfall-runoff) model andFLO-2D hydraulic model, an HEC-RAS procedure is used in this work. This flood analysis is carried out in the Subarnarekha river basin in India, by comparing the different frequency, extent, and depth of inundation simulations associated with varying rainfall forcing and/or hydraulic model roughness realizations. The hydrologic model HEC-HMS has also been used to get the runoff at a junction Deulbar on the mainstream of Subarnarekha. Then after getting the junction discharge, both 1D and 2D HEC-RAS modeling has been performed from the junction to the Rajghat outlet. Flood plain zones for six different return period floods have been found out from 10 yr,25 yr,50 yr,100 yr,500 yr& 1000 years respectively, showing increasing order of inundation areas. Thus this reach of the mainstream can be divided into six different zones and regulation of land use can be thereby restricting the damages caused by floods. Thus, this can be one of the non-structural measures to be contemplated.