A dynamically coupled outfall plume-circulation model for effluent dispersion in Burrard Inlet, British Columbia

Abstract

A circulation-water quality model, coupled with an outfall plume model, has been developed, to predict threedimensional 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.

Evaluation of Offshore Wastewater Outfall and Diffuser for Onondaga Lake, NY

“…76˚14'34") in metropolitan Syracuse, NY (Figure 1). It has a volume of 0.13 km 3 , surface area of 12 km 2 , and a maximum depth of 20 m. Onondaga Lake is dimictic, strongly stratifying during summer months [14]. The lake flushes about four times per year on average, and thus responds rapidly to changes in material loading [15].…”

“…Various approaches to linkage of near and far field models have been described [2,8,10,11]. The approach taken here follows that used by Owens and Effler [27] and Choi and Lee [11] and utilizes a two-way linkage of the submodels.…”

“…In these cases, a fraction of the effluent is "trapped" in the stratified layers [1], which reduces the transport of nutrients and other pollutants to the productive upper waters [2] and nearshore contact recreation areas [3]. Trapping is achieved by mixing the effluent, which is often warmer and buoyant relative to the stratified layers, with ambient receiving water, producing a cool diluted effluent that loses its buoyancy while rising through the stratified layers [4].…”

“…Simulation of far field water quality requires realistic linkage of the submodels. In large water bodies such as the coastal ocean or the Laurentian Great Lakes, a one-way linkage, which neglects the influence of the effluent on ambient (far field) stratification, has been adopted [9,10], while more general strategies for two-way linkage have been used for smaller systems where there is potential for system-wide impacts [2,11]. This paper evaluates the potential benefits and impacts of an offshore outfall and diffuser for municipal waste-water discharges to a small urban lake (Onondaga Lake, NY) where shoreline outfalls continuously release treated effluent, and intermittently release partially treated wastewater during major runoff events (bypass flow).…”

Plume tracking and dilution of effluent from the Boston sewage outfall

“…Examples are Faisst et al (1990), Roberts and Wilson (1990), Davison et al (1993), Wu et al (1994), Petrenko et al (1998), and Carvalho et al (2002), Parnell (2003), Li and Hodgins (2004), and Ramos et al (2007). This is because of the difficulty and expense of mapping a plume in the ocean over a wide spatial area with changing conditions, particularly when the plume is trapped below the ocean surface by density stratification.…”