Modelling wastewater effluent mixing and dispersion in a tidal channel

Abstract

The dilution and dispersion behaviour of wastewater effluent discharged from the Lions Gate Wastewater Treatment Plant into Burrard Inlet in British Columbia is investigated. This investigation focuses on the initial dilution zone, where low dilutions or high concentrations of contaminants contained in the effluent potentially pose a water-quality problem. We took the numerical approach and used field measurements of effluent dilutions, ambient stratification, and currents made in the vicinity of the discharge point for model input and verification. Predictions of effluent dilution and trapping compare well with the field results. We successfully determined the zone of exposure, effluent dilutions, trapping depths, and dispersion pathways as a function of discharge flow rate, ambient currents, and ambient stratification. It is shown that effluent trapping and dilutions in the initial dilution zone are governed mainly by the ambient currents, discharge rate, and, to a small extent, ambient stratification.