Flood Hazard Assessment in Paspaage Korala Divisional Secretariat Division Using Geospatial Technology

Flooding is a frequent and catastrophic disaster in Sri Lanka, exacerbated by intense monsoon rainfall, rapid urbanization, and poor land-use planning and management. The prime aim of this study is to assess the flood hazard and risk in the Paspaage Divisional Secretariat Division. The specific objectives are to study past flood events and its severity using Standedized Precipitation Index and generate flood hazard and flood risk maps using Analytical Hierarchy Process. Both primary and secondary data were used in this study. The primary data were collected through observations, interviews, and discussions. Monthly rainfall data were collected from the Department of Meteorology, Colombo, Sri Lanka, for the period from 1991 to 2025. Satellite images were obtained from various web sources. The research employed a mixed-methods approach, combining quantitative and qualitative methods. Parameters such as Land Use/Land Cover, digital elevation model, slope, rainfall, drainage density, and population density map were generated to assess the flood hazard and risk. The research uses a Multi-Criteria Decision Analysis approach, integrating the Analytical Hierarchy Process with GIS to systematically evaluate and weight flood-conditioning factors. The weighted-sum overlay technique was applied to integrate vector and raster data. To analyse flood occurrences, the Standardized Precipitation Index was applied. The results reveal that 2021 experienced extreme flooding, while severe floods occurred in 2022, 2020, and 2018. The flood frequency indicates the increasing trends in recent decades compared to earlier periods. Frequent flooding was observed in Navalapitiya, Karahandukala, Weligampola, and the surrounding areas. The results indicate that about 11.14 % of the study area is at severe risk, around 23.9 % at moderate risk, 33.71 % at low risk, and the remaining areas are rarely endangered. This flood risk information could contribute to reducing flood vulnerability and enhancing mitigation efforts.