Development of a flood hazard zonation map for "Kalu Ganga" basin by GIS modelling

Abstract

"Kalu ganga" (river) is one of the major rivers in Sri Lanka situated in south-western part of the country. Kalu ganga basin area is a highly populated area comprising urban centres and agricultural fields. River floods frequently occur in this area resulting severe damage and destructions. Local planers, decision makers and disaster relief organizations lacks accurate information on the spatial distribution of flooding and the land-use types. Only minimal efforts and resources have been allocated to deal with this problem. The objective of this research is to develop flood hazard zone maps for the Kalu ganga basin area in a Geographic Information Systems (GIS) environment. The applied methodology is comprised of 5 phases. They are preparation phase, fieldwork and data acquisition phase, modelling and flood hazard map generation phase, validation phase and reporting phase. According to the generated flood hazard map, Kuruvita, Elapitiya and Rathnapura divisional secretariats have the highest risk of flooding. Most divisional secretariats in the western province exhibit low or moderate risks of flooding. According to the analysis of flood hazard map with land-use classes, 2307 hectares of residential areas and 5568 hectares of agricultural fields were found to be at high risk of flooding.