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Puget Sound Georgia Basin Model

Freshwater Inflows to the Salish Sea Model

Freshwater discharged to the Salish Sea Model (SSM) consists of flows from 19 major rivers (with permanent U.S. Geological Survey [USGS] gages), streamflow runoff from 45 additional watersheds, and wastewater discharges from 99 municipal and industrial outfalls. Permanent USGS gaging stations capture approximately 69% of the watershed tributary to the main study area. Hydrologic analyses were conducted using past records to estimate streamflow runoff from the remaining watersheds. This included scaling of normalized continuous records from nearby stations by watershed areas and average annual rainfalls. The flow estimates used in the Salish Sea Model were developed by the Washington State Department of Ecology and are described by Mohamedali et al. (2011).

Freshwater inflows (64)

Municipal wastewater treatment plants and industrial discharges (99)

Source: Mohamedali T, M Roberts, B Sackmann, and A Kolosseus. 2011. Puget Sound Dissolved Oxygen Model Nutrient Load Summary for 1999-2008. Publication No. 11-03-057, Washington State Department of Ecology, Olympia, Washington.

In general, river flows in Puget Sound peak during the high-precipitation winter months of November, December, January, and February. In contrast, the Fraser River inflow on the Canadian side of the domain, which is significantly larger than the rest of the inflows into Puget Sound and the Straits combined, shows a very different seasonal distribution pattern—high flow in the late spring and summer dominated by snowmelt and low flow in the fall and winter. The figure below shows a plot of basin-wide freshwater discharges grouped by their discharge basins. The Whidbey Basin consists of the three largest rivers in Puget Sound (Skagit River, Snohomish River, and Stillaguamish River) and accounts for almost 70% of the total freshwater flow into Puget Sound. Fraser River discharges to the Georgia Basin.

Time histories of freshwater inflows to Puget Sound in 2006 grouped by their individual basins are plotted. Fraser River inflow time history to Georgia Basin is also plotted for comparison

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