The impact of Cyclone Nargis on the Ayeyarwady (Irrawaddy) River delta shoreline and nearshore zone (Myanmar): Towards degraded delta resilience?

The Ayeyarwady River delta (Myanmar) is exposed to tropical cyclones, of which the most devastating has been cyclone Nargis (2-4 May 2008). We analysed waves, flooded area, nearshore suspended sediments, and shoreline change from satellite images. Suspended sediment concentrations up to 40% above average during the cyclone may reflect fluvial mud supply following heavy rainfall and wave reworking of shoreface mud. Massive recession of the high-water line resulted from backshore flooding by cyclone surge. The shoreline showed a mean retreat of 47 m following Nargis. Erosion was stronger afterwards (−148 m between August 2008 and April 2010), largely exceeding rates prior to Nargis (2000-2005: −2.14 m/year) and over 41 years (1974-2015: −0.62 m/year). This implies that resilience was weak following cyclone impact. Consequently, the increasingly more populous Ayeyarwady delta, rendered more and more vulnerable by decreasing fluvial sediment supply, could, potentially, become more severely impacted by future high-energy events.