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The water environment of Hood Canal is highly complex; understanding the behavior of its physical, chemical, and biological components and determining what processes are controlling the oxygen content of the Canal's water require computer modeling. Two models will be utilized by the UW-PRISM modelers in support of the HCDOP-IAM study.
The University of Washington's PRISM project (http://www.prism.washington.edu/science/marine/modeling.html), with support from National Oceanographic Partnership Program, has been operating a computer model of circulation for the entire Puget Sound (http://tima.ocean.washington.edu). This model is based on the Princeton Ocean Model (http://www.aos.princeton.edu/WWWPUBLIC/htdocs.pom/), and forced by output from the high resolution operational weather prediction system of the Northwest Regional Modeling Consortium (http://www.atmos.washington.edu/mm5rt/); freshwater inputs derived from the river flow gauges maintained by the USGS; and synthetic tidal forcing and climatological hydrographic conditions on an open boundary in the eastern Strait of Juan de Fuca.
The model equations are those of the standard primitive equation (hydrostatic) dynamics. Given initial and boundary conditions, the circulation models calculate over discrete time-steps the sea surface elevation, three components of circulation velocity, temperature, and salinity. These hydrodynamic conditions and sunlight force biogeochemical calculations of nutrients, oxygen, plankton, and organic matter within the water column.
The model has been providing useful insights into the workings of the Canal for hypothesis generation and field work planning. For instance, the model indicates that wind over the Canal is an important driver of surface currents. On average, the surface layer of the Canal is moving northward and outward carrying fresh water from rivers towards the ocean. A northerly wind can cause a temporary reversal the surface current, while a southerly wind accelerates the northward current.
Such anomalous movements cause the surface layer to evacuate certain parts of the canal, and its place is filled by water upwelling from the depth. Because the upwelled water is also low in oxygen, wind-driven upwelling is an important possible mechanism triggering fish kill events. Regions of upwelling (characterized by anomalously salty water) are concentrated along Kitsap Peninsula during northerly winds, and at the Great Bend and northwards along Olympic Peninsula during southerly winds.
Soon, this model will be coupled to the PRISM Aquatic Biogeochemical Cycling (ABC) model. This model is a comprehensive model of aquatic ecosystem capable of predicting biomass concentrations in different trophic classes and oxygen concentration in the water column. The ABC model is currently tested at a coarse resolution for the entire Puget Sound.
We are planning to improve model resolution of Hood Canal by implementing a high resolution model specifically for the canal. This model will be based on the Regional Ocean Modeling System (ROMS; developed at Rutgers University and UCLA), selected for the modeling system's ability to resolve high property gradients in the surface layer. The model will be forced with local meteorological, river flow and water column data collected by HCDOP-IAM field program.
With our modeling approach, we can evaluate the effects of changes in inputs into the Canal, such as different ocean conditions, elimination of septic inputs, changes in the Skokomish River flow, or replacement of riparian alder trees with cedar, on the system. We can evaluate potential corrective actions for the low dissolved oxygen condition.
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