Investigation of Long-Term Transport in Tanshui River Estuary, Taiwan

Abstract

The net, long-term transport of materials in estuaries is governed primarily by the residual (or tidally averaged) circulation in the system. Knowledge of the residual circulation is essential for predicting the transport of algal patches, debris, and pollutants of concern in an estuary. A real-time, two-dimensional, laterally averaged hydrodynamic model is used to analyze residual current and salinity distributions in the Tanshui River estuary. The model results were filtered to arrive at the subtidal, or residual quantities. The characteristic two- layered estuarine circulation prevails for most of the time at Kuan-Du station near the river mouth. Though the circulation strengthens with increasing river discharge at low flow, its strength decreases at moderate river discharge and the two-layered circulation ceases at moderately high flow. This implies a weak trapping capacity in the estuary. At the upriver stations where salinity is lower, strength of circulation generally decreases with increasing river discharge. The response of residual velocity to the spring-neap cycle indicates stronger residual circulation during neap tide than spring tide.