Hydraulic Modelling and Flood Impact Assessment in the Periyar River Basin: An Integrated Approach of HEC-RAS, HEC-GeoRAS and Salt Concentration Method

The state of Kerala has been constantly facing the situations of disastrous flooding events for the past few years from 2018. The need for developing an efficient flood model has become inevitable in understanding and analysing the impact of flood phenomenon on different regions of a river basin. In this study, a steady hydraulic flood model is developed for the Periyar river basin in order to assess the flood parameters corresponding to various flood return periods with the help of the HEC-RAS modelling software. The inflow discharge values for the Muthika Thodu (canal), a water body in the Periyar river basin, are calculated using the salt concentration method. In addition, the post-processing procedure of the simulated HEC-RAS results is conducted with the combined application of HEC-GeoRAS tool and ArcGIS. Through post-processing of the results, the limit of the flood plain zones and proper flood zoning are carried out in the Periyar river basin. The extraction of limit of flood plain boundaries in the basin helps in the process of differentiating the regions under specified categories of flood risk zones such as low risk, moderate risk and high risk. The flood zoning aids in the accurate identification of the most vulnerable flood-affected regions in the basin corresponding to various return periods.