Sediment dynamics during low flow conditions in the Mekong river estuary, Vietnam

Field studies of fine sediment dynamics carried out in the Mekong River estuary, Vietnam, during the low flow season in April 1996 show semidiurnal macro-tides and shallow water effects result in a tidal asymmetry with peak flood tidal currents 10% stronger than peak ebb tidal currents. The salinity intrusion extended 50 km up-river with vertical stratification in salinity occurring around slack tidal currents. The suspended sediment was mainly fine silt, with flocculation occurring in the saline region. The asymmetry of tidal currents, along with the baroclinic circulation, pump sediment upstream. The saline water region of the estuary was more turbid than the freshwater region and the location of the turbidity maximum varied spatially with the tides. Our study suggests that the proposed construction of about 100 hydroelectric dams and water diversion schemes on the Mekong River and tributaries will impact negatively on the Mekong delta.