Floodplain Mapping of Pawana River Using HEC-RAS: Fid-Bau Portal

Floodplain Mapping of Pawana River Using HEC-RAS

Bhagwat, Tejas R. / Thube, Aruna D.

A flood is catastrophic natural high stage at which the stream overflows its banks and inundates the surrounding area of river banks. It is a natural hazard and threat to life and property. In this study, flood inundation mapping is done for the downstream of Pawana dam located on Pawana river in Upper Bhima sub-basin of Krishna basin in Pune district. Flood mapping has been done for entire river stretch of 58 km till its confluence with the Mula river. Mapping involves locating blue line, orange line, and red line which are the extent of the inundated area for the discharges of 25-year, 50-year, and 100-year return period flood and identification of the most affected villages as they come under prohibitive and restrictive regions. The study utilizes the Digital Elevation Model (DEM) data for the procurement of cross-section and HEC-RAS software developed by USACE for the steady flow analysis. which provides the water surface profiles and water depths obtained are further utilized to create the floodplain map. For model calibration, Manning’s roughness coefficient is varied between 0.015 to 0.045 for channel and 0.010–0.050 for floodplain. The Coefficient of determination (R²) and Nash Sutcliffe Coefficient (NSE) values is found to be above 0.60 and 0.75 for both calibration and validation. The locations coming under the flood lines are identified by importing the flooding map to Google Earth as a layer. The significant findings found from the study was that under prohibitive zone, up to river station 29,966, i.e., Godumbre village, there is not much urbanization present. But there are urbanized locations downstream of river station 27,965, i.e., Gahunje village. From this river station 27,965, there are residential sectors, buildings, and small slums located on the banks of river which are getting flooded even for 25-year return period flood and fall under prohibitive zone. Such type of construction is strictly prohibited in this zone, but structure exists, so government agencies should monitor existing structures and should be well prepared in advanced with Emergency Action Plan (EPA) and Disaster Management Plan if the flooding situation arises.