Flood Inundation Modeling Using Coupled 1D–2D HEC-RAS Model in Lower Kosi River Basin, India with Limited Data

Abstract

In the present work coupled 1D–2D hydraulic modeling has been done with the limited available data in the lower Kosi river basin, India, which is prone to flood inundation. The research was carried out using data from the Shuttle Radar Topography Mission-Digital Elevation Model (SRTM-DEM), land use/land cover (LULC), daily water level (WL), and precipitation. The river cross-sections were extracted using the SRTM-DEM 30 m, Google Earth, and measured at Baltara (upstream) and Kursela (downstream) during the field visit. The Manning’s roughness coefficients (n) for the channel and 2D flow area were assigned according to land use/land cover. The analysis has been performed during the monsoon season (July–October) for the years 2011–2015. The water level was defined as a boundary condition at upstream (u/s) and downstream (d/s). The HEC-RAS model was capable of estimating inundated areas in the main channel and low-lying surrounding areas. SRTM-DEM with 30 m spatial resolution was used to extract the river channel, riverbanks, flow paths, and river cross-sections. The flood inundation maps were developed from 2005 to 2016 using water level data. The maximum inundation depth and inundated area found in the year 2011 were 7.33 m and 177.79 km2, respectively. The inundated areas were compared with the observed inundated area, which showed a good R2 = 0.811. The inundated area was compared with the observed inundated area obtained from the Flood Management Information System (FMIS) and National Remote Sensing Agency (NRSA). Further, the daily precipitation was used as a boundary condition for the two-dimensional flow area and the flood inundated area in the floodplain was estimated. The coupled hydraulic model was applied successfully in the main river and the surrounding areas. Integration of easily available data, i.e., DEM, land use/land cover, water level, and precipitation may be helpful to simulate inundation in the floodplain, in case of limited data.KeywordsKosi riverHydraulicFlood inundationLand useSRTM-DEMWater level