Search

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. [ABSTRACT FROM AUTHOR]

A circulation-water quality model, coupled with an outfall plume model, has been developed, to predict three-dimensional circulation and effluent dispersion as functions of circulation forcing, ocean turbulent mixing, discharge rate and diffuser parameters. The coupled model was applied to the Lions Gate outfall discharging sewage into Burrard Inlet, British Columbia; in this case, the circulation was driven by the tides and density variations. The model results have good agreement with dye survey data and acoustic Doppler current profiler (ADCP) measurements from the inlet. Under typical oceanographic conditions for the area, the model predicts submerged plumes below 8 m depth at most times. Short-lived surfacing occurs for a few minutes at slack tide. The near-field trapping level and initial dilution are controlled by tidal flows through First Narrows and the effluent discharge rate. [ABSTRACT FROM AUTHOR]