Flood risk zonation and reduction strategies in the Deduru Oya River Basin in Sri Lanka

Abstract

Floods are one of the most frequent and destructive natural hazards in river basins, causing serious consequences for the community and regional development. The intensity of seasonal monsoon rainfall and the dynamics of land use practices have accelerated the flood events in the Deduru Oya basin. The intensity and frequency of flood occurrences expand the exposure and vulnerability of the community. Therefore, this study aims to assess the flood risk zonation in Deduru Oya basin and propose Flood Risk Reduction (FRR) strategies by integrating the holistic approach. This study used the Multi Criteria Decision Analysis (MCDA) approach with Analytical Hierarchical Process (AHP) combination of physical and socioeconomical parameters. Structured questionnaire survey conducted to identify the FRR strategies from the communities in the high risk zone in Deduru Oya basin. AHP technique, descriptive statistics and thematic analysis methods were used as data analysis techniques. Flood risk map indicated that 290 km2 is very high risk,1226.56 km2 high risk, 820.40 km2 moderate risk, 255.51 km2 low risk and 83.30 km2 risk free, respectively. The thematic analysis proposes to manage the reservations of the river, develop proper land use practices, identify and map out the flood inundation areas, enhancing technology for real-time flood monitoring and early alerts, develop community preparedness, and upgrade the drainage systems and flood defences can reduce vulnerability. In addition, legal power should be vested in local governments with legal frameworks that define responsibilities and protocols for flood risk management, and the weaknesses of the current legislation should be removed