Analytical Hierarchy Process based on Flood Susceptibility Assessment; A Study from Attanagalu Oya River Basin

Abstract

Flood is one of the natural or manmade hydrological events in a river basin hydrological cycle. This is the one of the major disasters in Sri Lanka. Flood susceptibility mapping and assessment is essential for identifying flood risk zones and flood prevention and mitigation strategies because it identifies the most vulnerable areas based on the physical factors that determine susceptibility to flooding. This study aims to define the flood susceptibility zones in Attanagalu Oya River Basin using a multi-criteria approach, especially the Analytical Hierarchy Process (AHP). The secondary data used in this study was obtained from global open-source databases and institutions. Seven flood conditioning factors were chosen in this study such as Elevation, Distance from the river, Drainage density, Rainfall, Slope, Soil type and Normalized Difference Vegetation Index (NDVI). The AHP technique was used to calculate the factor weights using the pairwise comparison method. Finally, the weighted overlay method in ArcGIS was used to create the final flood susceptibility map for the study area. It was classified into five classes based on the risk of flooding such as Very high risk, High risk, Moderate risk, Low risk and Very low risk. The total area of these classes is equal to 21.71 km2 (very high risk), 172.99 km2 (high risk), 440.73 km2 (moderate risk), 194.40 km2 (low risk) and 2.38 km2 (very low risk). It has been found that the southwest area of the river basin is vulnerable to very high-risk flooding. This kind of studies will open new pathways for flood risk management in Sri Lanka.