Flood hazard and vulnerability assessment in a riverine flood prone area a case study

Abstract

Khoksabari Union of Sirajganj Town is surrounded by a network of rivers namely the Jamuna, the Bangali and the Karatoa which makes the Union vulnerable to flooding. The present study assesses the hazard and vulnerability of riverine flood in a flood prone area using Remote Sensing (RS) and Geographic Information System (GIS). In the context of flood hazard and vulnerability assessment, flood frequency analysis is carried out to assess flooding for different flood magnitudes. Flood inundation maps are prepared based on DEM and satellite image for different risk elements using ILWIS software. LANDSAT satellite images have been downloaded and used to develop land use map in the study area. The land use map is used for mapping of settlement and fishery by using ILWIS software. The vulnerability function is developed for preparing vulnerability maps for settlements and fisheries. For the development of vulnerability function, depth-damage relation has been developed. Present monetary values of settlement and fishery damage are collected through field survey from actual flood of the study area. Vulnerability functions of settlements and fisheries are used to produce raster-based vulnerability maps. The flood frequency analysis shows that the Pearson Type III distribution is the best fitted distribution for flood frequency analysis in the study area. In 100-year return period flood, inundation percentage of the total agriculture, settlement, fishery and road areas are 48, 35, 53 and 38, respectively. High land (F0) of the study area is 55% which is not much inundated in normal monsoon flood. Vulnerability scaled as low, very low, moderate, high and very high vulnerable settlement areas are found to be 17, 12, 3.43, 1.03 and 1.35 percent, respectively for 100-year flood. These correspond to a maximum of 20%, 40%, 60%, 80% and more than 80% damage of the respective settlement areas. In 100-year flood magnitude, low, very low, moderate, high and very high vulnerable fishery areas are found to be 18, 19, 9, 3 and 4 percent. These correspond to a maximum of 20%, 40%, 60%, 80% and more than 80% damage of the respective fishery areas. The results of this study may be useful for future flood damage mitigation plan in the study area.