Spatial variability of oceanographic energy and sediment dispersal and trapping on the Ayeyarwady continental shelf

Much of the estimated 600 Mt of river sediment annually carried by the Ayeyarwady and Thanlwin River system (Myanmar) is delivered to a wide continental shelf in the northern Andaman Sea. Called here the Ayeyarwady continental shelf, this area is influenced by strong tides, monsoon conditions, and periodic cyclones; however, the processes that dominate dispersal of riverine material in the coastal ocean of this system have remained largely unknown. The shelf exhibits a dramatic asymmetry of the surface morphology and sediment texture in the east–to–west direction, and recent field observations indicate that sediment accumulation rates increase toward the western portion of the Gulf of Martaban. Modeling-based experiments allow us to explore the roles of oceanographic transport processes within the coastal waters using a numerical model to account for the effects of river input, waves, tidal- and wind-driven currents. Model runs are being developed using ROMS (Regional Ocean Modelling System) and SWAN (Simulating WAves Nearshore) to represent oceanographic conditions in the region. Forcing data is taken from global models such as HYCOM (HYbrid Coordinate Ocean Model) and GFS (Global Forecasting System). Sediment is incorporated into the model via the COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) modeling suite, which has native ROMS and SWAN support. Model estimates of sediment dispersal and deposition during summer monsoon conditions will be analyzed, and compared to spatial patterns found in sediment core, seismic, and water column field measurements. Model results indicate that sediment resuspension is strongly wave-dominated along the Ayeyarwady Delta and tidal-dominated within the Gulf of Martaban, with tidal trapping making the Gulf region conducive to high turbidity. These results align with previous data that the Gulf is a macrotidal region with high suspended sediment concentration.