GIS-based methodology for erosion risk assessment of the muddy coast in the Yangtze Delta

Muddy coasts are widely distributed around the world, especially adjacent to large estuaries. These regions are highly susceptible to coastal erosion with its dense population, developed economy and low-lying land. Due to immense natural and human pressures, there is an urgent need for a more comprehensive understanding of coastal erosion risk in such areas. Various models have been established, but most of them focused on sandy coasts and physical factors that influence coastal erosion while socioeconomic factors were usually ignored. Accordingly, this study presents a GIS-based risk assessment of coastal erosion for muddy coasts by combining both the physical and socioeconomic aspects of erosion. The method is used to assess coastal erosion risk in the Yangtze Delta. Based on the DPSIR (Driving forces, Pressure, State, Impact, and Response) framework, 10 vulnerability indicators and 3 impact indicators corresponding to physical and socioeconomic aspects, respectively, are identified to constitute an indicator system. These indicators are weighted using the Analytic Hierarchy Process (AHP) technique, and then are combined into a Vulnerability Index and a Hazard Index, which then are merged into a Risk Index. Then, these indexes are normalized to 0%-100%. Finally, the normalized values are ranked into 5 levels: very low (<20%), low (20%≤Is<40%), moderate (40%≤Is<60%), high (60%≤Is<80%) or very high (≥80%). This study is the first to comprehensively assess coastal erosion risk in the Yangtze Delta by integrating physical and socioeconomic factors at a detailed spatial scale. The results provide a clear picture of the current coastal erosion risk in the study area, despite of some limitations. The study also reveals key gaps in data gathering and coastal management practices that need to be addressed in order to develop more effective long-term coastal management.