Design Procedures for Effluent Discharge to Estuaries during Ebb Tide

Abstract

A design method is presented for a wastewater disposal scheme suitable for coastal communities in both developed and developing countries. The disposal technique exploits the natural flushing mechanisms of estuaries to pump effluent out of the estuary and away from the coast. By placing the outfall within an estuary near the mouth and timing the waste discharge to coincide with the ebbing tide, two advantages ensue: (1) Upstream transport is avoided; and (2) the chance of effluent being re‐entrained at the entrance is minimized. Where there are sensitive environmental targets between the outfall and entrance, Monte Carlo simulation of the transport dispersion processes within the channel is used to predict the distribution of pollutant concentration and, hence, the standard of treatment required. Timing of the discharge cycle is determined by consideration of the dynamics of the ebb and flood flow patterns at the channel entrance. The method is applied to a case study being considered for New South Wales, Australia.