Flood Inundation Mapping of Kankai River Basin, Nepal

Abstract

Flood is growing as major water related hazard in the world. The degree of impairment that it causes to each and every component goes on increasing with the time. The main objective of this research is to analyze the flood frequency, prepare inundation map of Kankai river basin corresponding to different return period, and to identify the hazardous region along the Kankai river basin. Kankai river basin of 1284 km² area is selected for the study. Frequency analysis is done with Gumbel calculation method and HEC-HMS. Flood hazard mapping is the one of the procedure to find the inundation level. Flood hazard map was prepared by using the HEC-RAS 5.0.7 with integration of ArcGIS 10.1 and its extension HEC-GeoRAS. ASTER DEM of 20*20 spatial resolution was used for the research. The discharge data we have used is validated with the discharge data we have measured in the study area. The discharge value was seen to be simultaneously increasing with the return period of 2, 10, 50, 100, 200, 500, 1000 years. The magnitude of flood depth increased with the increasing return period. The number of household inundated corresponding to the return period is also calculated. The maximum depth of inundation we obtained was 6.46m, which was of 1000 year return period and along the chure range where the cross-section is shorter and depth is greater and going downward the depth of inundation decreases. The depth is categorized as high risk, medium risk and low risk based on DHM reference for Kankai river. Inundation of area of settelements indicates that in future human lives are more prone to flood disaster. Thus, the study may help in future planning and management for future probable disaster.