FLOODPLAIN ANALYSIS AND RISK ASSESSMENT OF LOTHAR KHOLA (STREAM)

4 Associate Professor, Institute of Forestry, Pokhara Abstract: This study aims to find out the extent of floodplain for flood discharge of different return periods using one dimensional hydraulic model HEC-RAS, ArcView GIS and Hec-GeoRAS to inference between HEC-RAS and ArcView GIS in Lothar Khola with catchment area of 170 km 2 , lying between Chitwan and Makawanpur Districts, Nepal. Triangulated Irregular Network (TIN) was prepared from contour and spot elevations in ArcView GIS; required data sets were prepared in HEC-GeoRAS and import file was created and imported in HEC-RAS. In HEC- RAS, boundary conditions, flood discharges for different return periods were inputted. Steady flow analysis and flood risk assessment were carried out. Area inundated by 2, 10, 50, 100 and 200 years return period flood was 230, 239, 246, 249 and 252 ha., respectively. The classification of flood depth area shows most of the flooding area has water depth greater than 3m. The large percentage (> 40 %) of vulnerable area lies on sand area followed by forest, cultivation area, etc. Also, flood area increases with flood intensity. Higher flood depth increases and lower flood depth decreases with increase of flood intensity. Flooding of cultivation land indicates potential damage in food production and negative effects on the livelihoods of local people. Thus, the study may help in planning and management of watershed area for mitigating future probable disaster through technical approach.