GIS based Approach for Planning the Evacuation Process During Flash Floods: Case Study for Gampaha Divisional Secretariat Division, Sri Lanka

Gampaha district is one of the areas that suffer from frequent flash floods in Sri Lanka. Since flash floods occur unexpectedly, and with minimal warning, preparedness is essential to minimize losses during such a disaster. Planning the evacuation during a flood is a complex process; therefore, it needs focused consideration on several factors. The main objective of this paper is to propose a Geographical Information Systems (GIS) based approach to plan the evacuation process during a situation where there is a flash flood in the Gampaha Divisional Secretariat Division (DSD), with the intent to reduce negative consequences. The study has considered seven criteria: elevation, accessibility, land-use, availability of buildings, presence of water features, rainfall, and population density, in selecting locations for evacuation centers. These data were analyzed with the tools and models available in the GIS software package. As a first step, the flood inundation map was created using elevation and rainfall data. Evacuation centers were then identified outside of the inundated area. Finally, after field verification, 7 potential locations (Bandaranayake Vidyalaya, Bandarawatta Parakrama Vidyalaya, Sri Sumangalaramaya, Madegama Sri Sunandaaramaya, Sri Wajiraghanaramaya, St. Jude Church Idigolla, and Holy Cross College) were selected by considering the capacities such as elevation (above 15m from the Mean Sea Level), accessibility (within 200m from main roads), ownership (public only), and the number of people accommodated. The results of this study will be very helpful for the government, non-government organizations, and the victims to take immediate actions during a flash flood event in the study area.