Flood Hazard Assessment Using Gis-based Multicriteria Analysis: a Case Study From Downstream of Kelani River Basin, Sri Lanka

Abstract

Increasing the occurrence of extreme rainfalls due to climate change has become a common feature of the climate in Sri Lanka during the past decades. According to the study on national climate change adaptation strategy for Sri Lanka - 2011 to 2016 undertaken by the Environmental Ministry of Sri Lanka, increase in the intensity of rainfall in the wet-zone is expected to increase the propensity for flooding of the flood-prone rivers. Accordingly, the Kelani and Kalu rivers are recorded the highest flood frequencies and the accompanying flood damages among the river basins in the wet zone. In this respect, it is important to assess flood hazard in Sri Lanka. Therefore, the aim of the study is to assess and map the spatial distribution of flood hazard in downstream of the Kelani River basin. Both primary and secondary data have been used fo A ’ ’ As secondary data, rainfall data, GIS data layers such as land use, drainage network, contour data and soil type were used. GIS-based spatial multi-criteria analysis method was used for the study. Accordingly, the study mainly revealed that land use of the study area is the main flood hazard contributing factor among considered factors. The flood hazard assessment map illustrates that high and very high hazard zones are concentrated in the western side and low and very low flood hazard zones in the eastern and southern parts of the study area. The study identified that the spatial distribution of flood-affected areas in the inundation map of the 2016 flood and flood hazard zones of the study area are quite similar. This study, suggests that the GIS-based MCDA method can be very effective for mapping flood hazards and may be beneficial for decision-making in flood management.