A Multi-Data Geospatial Approach for Understanding Flood Risk in the Coastal Plains of Tamil Nadu, India

Abstract The coastal plains of Tamil Nadu (India) are highly vulnerable zone for coastal floods, the most common disaster, experienced every year. In the study, the coastal plain is delineated through a watershed approach with 5020 micro-administrative units covering an area of about 3,000 sq.km. A comprehensive flood risk assessment was carried out by preparation of hazards, vulnerability, and exposure layers using multiple data sources including from field surveys, satellite data and secondary data sources. The flood prone regions are delineated initially from Sentinel-1 Synthetic Aperture Radar data coupled with SRTM-DEM on a probability scale (0–1) and validated with the District Disaster Management Plans of 13 coastal districts. In addition, National Resources Conservation Service – Curve Number (NRCS-CN) method was adopted to estimate surface runoff potential for flood risks. The vulnerability and exposure of the population to the flood hazards was determined using census and household data based indicators. A focused group interview was conducted at 514 locations targeting deprived communities of all major settlements of the study area. The public perceptions were used to understand the flood risks and to validate the hazard and vulnerability layers. To estimate location-specific flood risks within the micro-administrative units, built-up areas with different categories were delineated and intersected with the flood hazard. The amalgamation of results shows that very high flood risk prevails in the northern parts of coastal Tamil Nadu, especially the stretch between Chennai and Cuddalore. In addition to provide a baseline datasets for the first time at micro-administrative units for entire coastal plains of Tamil Nadu, the study offers a pragmatic methodology for sustainable development measures in general and flood risk management in particular.