Sensitivity of tides and net water transport in an estuarine network to river discharge, network geometry and sea level rise

Quite a number of estuaries are characterised by a complex network of branching channels, in which the water motion is primarily driven by tides and river discharge. Examples are the Berau estuary (Indonesia), the Pearl estuary (China) and the Yangtze estuary (China). Knowledge about tides are required for construction of dikes/harbours, while knowledge about net water transport is important for agriculture, fresh water supply to cities and for quantifying transport of sediment, nutrients and etc.

In this contribution, we present a generic, weakly nonlinear 2DV estuarine network model to study tides and net water transport and to understand the dependence of their along-channel and vertical structure on geometric characteristics and sea level changes. The model will be applied to the Yangtze Estuary for different situations, such as the wet and dry season, with and without a shortcut channel and sea level rise for scenarios for the coming 50 to 100 years.

It will be demonstrated that, for the current conditions, the model results are in good agreement with observations. Both tidal amplitude and current are weaker during the wet season than that during the dry season and the reason for these changes will be explained in terms of river-tide interactions. Effects of local changes in geometry are investigated by creation of a shortcut channel between two main channels. Results show that changes in tides are merely local, but they can be rather strong. Sea level rise (up to 2 meters) causes tides to increase, mainly as a consequence of less friction resulting from larger water depth. Net water transport turns out to be less sensitive to geometry and sea level rise compared to tides.