River discharge - tide interactions and tide propagation in the mesotidal tropical estuary of the Van Uc river, Red River delta, Vietnam

Abstract

This study documents the hydrodynamics of the Van Uc estuary, one of the main distributaries of the Red River in Vietnam, examining the roles of river discharge and tides on the hydrodynamics of this mesotidal estuary. Hourly discharge and water level data from two stations located respectively in the estuary and near shore are used to study the tidal propagation within the estuary. The results show that the estuary is flood dominated, i.e. with a shorter flood (11 h) than ebb period (14 h), more pronounced for high river discharge and for spring tide (10 h vs 15 h). A tidal range damping is found in the upstream estuary, also increasing with the river discharge and the tidal amplitude (r > 0.50, p < 0.01). Spring tides strongly increase the difference between the maximum inflowing and outflowing velocities and the duration of the flood currents (r = 0.25, p < 0.01). A high river discharge reduces the maximum inflow velocity, decreases the duration of the flood currents and increases the outflow duration (from 9 h to no flood current). It shifts the time of in- to out-flow reversal closer to high tide, and the out- to in-flow reversal from mid-flood to late flood. The characterization of tidal propagation contributes to improve the understanding of the behavior of this estuary, providing insights for further studies focusing on hydrodynamics and sediment transport.