Estuarine Circulation Patterns in a Complex Geometry Estuary: Dinh An Estuary, Mekong River

摘要

Estuarine circulation (EC) is a natural phenomenon that contributes to the evolution of estuaries worldwide. This paper uses the Dinh An estuary, Mekong River as a case study to investigate patterns of EC in a complex cross-section estuary. An Acoustic Doppler Current Profiler (ADCP) measured a series of river discharge and current profiles at a transect near the mouth of the estuary between 15 and 30 September 2009. Tidal elevation was also recorded concurrently with the river discharge by using a leveling rod. The observed data reveal that the river-discharge phase lagged 6 h behind the tidal phase in the high-flow season (May to October). Four main types of EC were observed during the reversal time in the ebb tide with river discharges in a range of −5000 m_(3)/s to 13,600 m_(3)/s. There were two main flood tide patterns, which corresponded to the discharges from −6000 m_(3)/s to 5000 m_(3)/s. The classical EC type (seawater flows landward near the bed and river water flows seaward near the surface) appeared only in the deepest channel in the ebb tide as saline intrusion induced a density imbalance. The results suggest that tidal phase and bed geometry play important roles in forming EC patterns in estuaries. This paper provides essential information related to flow structure in complex bathymetry estuaries for further studies on saline intrusion, environmental processes, sediment dynamic and estuarine morphology.