Overview of the Monsoon-influenced Ayeyarwady River delta, and delta shoreline mobility in response to changing fluvial sediment supply

International audience ; A morpho-sedimentary analysis of the Ayeyarwady delta shoreline was conducted based on a field mission in Myanmar in November 2016 and interpretation of satellite images spanning the period 1974-2019. These analyses were complemented by data on land-to-water conversion and vice versa within a 2 km-wide coastal fringe, and on MERIS-derived seasonal and decadal-scale evolution of suspended particulate matter (SPM) off the delta. The objectives were to: (1) characterize the 450 km-long delta shoreline and coastal sediment transport pathways, (2) define the shoreline status (stability, erosion, accretion), and (3) identify potential causes of shoreline change and the future outcome of this status in terms of delta vulnerability. The delta shoreline was characterized on the basis of qualitative alongshore tidal, wave-energy, and sediment grain-size patterns (muddy, sandy or a mixture of both), and morphology (sandy beaches and mudflats). The deltaic coast exhibits a mixed wave-and-tide-dominated morphology and comprises a western sector characterized by four of the five main distributary mouths separating inter-distributary plains bounded by low overwash-influenced beaches devoid of aeolian dunes. The eastern sector, in the Gulf of Martaban, is embayed, much less prograded and bounded by dominantly muddy shores. This simple shoreline dichotomy reflects the overarching alongshore sediment redistribution and storage patterns that have accompanied the growth of the delta, resulting in the two facies: sand dominantly retained in the western sector where the multiple distributary mouths have constrained potential alongshore sand transport by low- to moderate-energy monsoon-generated southwesterly waves, and mud transported by the regional monsoon-influenced coastal shelf circulation towards the eastern sector. The recent multi-decadal shoreline mobility in the Ayeyarwady delta points to the influence of fluvial sediment supply on these two fades. Between 1974 and 2019, 49% of the delta's shoreline ...