Rainfall Runoff and Flood Plain Inundation Modeling of the Kharkai River, India using HEC-HMS and HEC-RAS

A rainfall-runoff model using Hydrologic Engineering Center–Hydrologic Modeling System (HEC-HMS) was carried out for the Kharkai River of Subarnarekha Basin, India to determine the magnitude of runoff from a known quantity of rainfall and the terrain inundation. In the present study, for the calibration and validation, the rainfall events of October 1–20, 2017 and July 12–31, 2019 were used. In the process of calibration, the computed discharge was found to be 1,674 cumecs against the observed discharge of 1,820 cumecs, with a Nash-Sutcliffe efficiency of 91.78%. Whereas in the process of validation, the computed discharge was found to be 3,266 cumecs against the observed discharge of 3,589 cumecs, and a Nash-Sutcliffe efficiency of 91.02%. Furthermore, to generate various inundation maps of the Kharkai River, an SRTM-DEM of 30 m x 30 m resolution, and a 30 m resolution DEM was used in the simulation process. The results of the inundation study showed that the 5, 20, 50, 100, and 500-year return period floods determined using Gumbel’s method are 3,647.791 m3/s, 5,797.717 m3/s, 7,160.188 m3/s, 8,181.168 m3/s, and 10,540.5 m3/s, respectively, and the corresponding inundation areas were 20.98 km2, 33.65 km2, 39.89 km2, 44.07 km2, and 56.65 km2, respectively.