Sediment dynamics in Rangoon River, Myanmar

The behavior of fine-grained sediment in Rangoon River depends on seasonal variations in freshwater discharge and tidal amplitudes that range from 2 to 5 m. During the monsoon, freshwater with sediment concentrations of 1 grl, or less, causes unidirectional, seaward flow. In the dry season, salinities reach 20‰ and sediment concentrations rise to 6 grl. The saline intrusion advects large quantities of sediment landward from seaward sources. Near-surface sediment concentrations are very low during neap tides, while a layer of ‘fluid mud’ rests on the bottom. Current speeds greater than 0.2 mrs are needed to entrain sediment into the upper layer. Layered suspensions occur most commonly during decelerating phases of tidal flow and are dispersed by rapidly accelerating flow. When current speeds exceed 0.6 mrs, no ‘fluid mud’ forms, and sediment concentrations as great as 6]8 grl extend through the water column.