An assessment of flood risk and vulnerability in coastal areas of KwaZulu-Natal

Abstract

Flooding is one of the most significant natural hazards affecting coastal regions worldwide, with increasing frequency and intensity driven by climate change, urbanisation, and environmental degradation. Coastal KwaZulu-Natal (KZN), South Africa, is particularly vulnerable due to its exposure to extreme rainfall events, storm surges, and densely populated river catchments. Despite recurring flood events, there remains limited spatially explicit information on flood-prone areas, vulnerability patterns, and associated risks. This study aimed to assess flood risk and vulnerability in the coastal regions of KwaZulu-Natal by integrating hydrological and hydraulic modelling with spatial and socio-economic analysis. The research focuses on key river systems, including the uMgeni, uMvoti, uMdloti, uMlazi, Mbokodweni, and uMkomazi catchments. Hydrological modelling was conducted using HEC-HMS to simulate rainfall-runoff processes, while hydraulic modelling using HEC-RAS was applied to determine flood depth, extent, and inundation patterns, consistent with integrated flood inundation modelling approaches described by Saksena et al. (2019).These outputs were integrated into a GIS environment (QGIS) to generate flood hazard maps. A vulnerability assessment was conducted using a Multi-Criteria Decision Analysis (MCDA) approach, incorporating socio-economic and environmental indicators such as population density, land use, settlement type, and proximity to rivers. The Analytic Hierarchy Process (AHP) was used to assign weights and develop a flood vulnerability index. The results indicate clear spatial variations in flood hazard and vulnerability across the study area. Larger river systems exhibited delayed but high-magnitude flood responses, while smaller, urbanised catchments showed rapid runoff and increased localised flood risk. Areas with high population density, informal settlements, and inadequate infrastructure were identified as the most vulnerable. The study highlights the importance of integrating hydrological modelling with socio-economic analysis to improve flood risk assessments. The findings provide valuable insights for disaster risk reduction, spatial planning, and climate adaptation strategies in KwaZulu-Natal. It is recommended that future efforts focus on improving data availability, strengthening early warning systems, and incorporating vulnerability assessments into policy and planning frameworks.