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Focused Studies - Oakland Bay

In 2004, we developed the Hammersley Oakland Bay Oceanographic (HOBO) model for the Washington State Department of Health.  The city of Shelton was considering the possibility of increasing their wastewater discharge via an outfall that straddles two sanitary lines, which define a shellfish closure zone in Oakland Bay and Hammersley Inlet.  The Washington State Department of Health needed to evaluate these sanitary lines.

The HOBO model was based on the Environmental Fluid Dynamics Code (EFDC), a three-dimensional hydrodynamic computer primitive equation model (Hamrick, 1992, 1996). HOBO is driven by real data acquired at its boundaries.  The air-sea boundary conditions were generally provided from the nearby airport, Sanderson Field.  The open sea boundary conditions were recorded near Libby Point as a part of the overall study.  We used the HOBO model to stimulate various discharge scenarios and to determine consequences at the two sanitary lines during periods specified by the Washington State Department of Health.

We also participated in a dye study to determine the far-field dilution factor at the sanitary lines at a specific time, April 2003, and to validate the model. Model results show that extending the diffuser horizontally across Hammersley Inlet can be very effective in controlling the far-field dilution at the sanitary line, although releasing effluent further north toward Munson and away from Eagle Point can cause problems on the east end of the Oakland Bay sanitary line. 

Holding back effluent at slack tide is another effective method of controlling initial dilution at the sanitary lines.  Controlling the vertical plume trapping depth is not very effective as a control method since there is a substantial amount of vertical mixing in this estuary, and the plume gets mixed anyway by the time it gets to either sanitary line.