Field Investigations on River Bed Changes and Salinity Intrusion along Tien and Hau Rivers in Vietnamese Mekong Delta Considering Upstream Dams' Impacts

Abstract

In the Vietnamese Mekong Delta (VMD), river beds have been degraded and salinity intrusion has been increased. Hydro-, sediment and salinity dynamics modelling of a complex river network in the VMD requires detailed bathymetric, turbidity, and salinity data. Therefore, we conducted two field surveys in the flood and dry seasons of 2017-2018 to measure river bed elevations, turbidity and salinity concentrations along Tien and Hau Rivers due to lacking of homogeneous data available in the delta. The results show that thse rivers can be divided into upper and lower reaches according to the variations of river bed elevation, turbidity, and velocity. These parameters are high in the upper reach, decreased seaward while low in the lower reach, increased seaward. The beds of Tien and Hau Rivers have been significantly degraded due to upstream dam developments with a rapid rate recently. Salinity intrusion varies seasonally. Horizontally, high salinity concentrations appear in the middle of the river. Vertically, salinity concentrations are almost the same near the banks but markedly increase downward in the middle of the river.