Floodplain Mapping Using HECRAS Model and Geospatial techniques—A Case Study of Varanasi City

Varanasi, an ancient city of India, lies on banks of River Ganga, one of the largest rivers of the world. Varanasi is proposed to be developed into a Smart City in the first phase of Indian Smart City Mission. The resilience of a city is its ability to persevere in the face of an emergency, so it can continue functioning despite serious challenges. Flood is a frequent phenomenon for Varanasi, but in recent years, it was deluged. The flood-risk zones mapping makes the first step of flood control measures. In this chapter, a one-dimensional hydraulic model, i.e. HEC-RAS has been integrated with Remote sensing and GIS techniques to map the floodplain zones of Ganga River located around the city of Varanasi. The pre-processing includes geometry setup such as digitizing the stream centerline, right bank and the left bank of the river. SRTM DEM is used in ArcGIS software extension HEC-GeoRAS 4.3 for pre-processing of GIS data, i.e. derivation of the channel geometry for input to HEC-RAS. Next, HEC-RAS simulations were performed to generate a water surface profile for a given design flood condition. Finally, simulated results have been imported in ArcMap 10.1 and being overlaid with the DEM for obtaining flood risk zones and flood inundation maps. Floodplain map analysis shows that more than 300% area has a probability of inundation as compared to the normal flow of the river. The results of this research will be helpful in developing a smart Varanasi, which will offer a safe habitation to its residents.