Dungeness River Watershed | Olympic National Forest
The Dungeness basin drains 215 square miles in the northeast corner of the Olympic Peninsula from the Olympic Mountains to the Strait of Juan De Fuca. It has a maritime climate, mild and wet. About 75 percent of the precipitation falls between October and March (Kruckeberg 1991). On the ridge tops in the upper portion of the basin the average precipitation is over 180 inches per year, while Sequim near the mouth of the Dungeness River receives less than 17 inches annually (Phillips 1965). This rapid decrease in precipitation from the headwaters to the mouth is due to the Dungeness basin being in the rain shadow of the Olympic Mountains (Kruckeberg 1991).
The headwaters are in the steep mountainous terrain of the Olympic Mountains. The upper portions of the basin have characteristic U-shaped valleys, alpine ridges, and cirque basins characteristic of alpine glaciation (Kruckeberg, 1991).Peaks on the upper watershed include Mounts Buckhorn, Constance, Fricaba, Deception, Cameron, and McCartney. All of these peaks are over 2,000 meters in elevation. The bedrock geology in this portion of the basin is mostly lower Tertiary marine sandstones and argillatte (Schuster 1992). The Olympic National Park and U.S. Forest Service administer most of this part of the basin.
In contrast to the upper basin, the middle reaches of the Dungeness basin are characterized by moderate sloping terrain largely the result of continental glaciation and a complex deglaciation history (Dungeness Watershed Analysis-DWA). The bedrock is lower Tertiary marine sandstones and basalts (marine volcanic) (DWA and Schuster 1992). After the glaciers receded, there were high erosions rates which moderated over time as the vegetation developed (Kruckeberg 1991). The resulting soils and slopes in the mid-portion of the basin still have high natural sediment yields (DWA). This portion of the basin is largely administered by the U.S. Forest Service.
The lower portion of the basin is low-relief Quaternary sediments. It is naturally primarily lowland forest. This portion of the basin is largely settled with small rural holdings and suburban development.
The most significant natural processes that move sediment in the Dungeness basin are debris flows, debris avalanches, and snow avalanches/debris flows. These account for about 85 percent of the sediment delivered to the stream in the middle portion of the basin (DWA). The basin generates a very high amount of sediment, mostly from glacial erosion and glacial depositional areas (DWA).
The Dungeness Basin is predominantly in the Western hemlock forest zone. Only small portions of the upper basin are in the alpine zone (Kruckeberg 1991). The dominant forest tree species include Douglas fir, Western hemlock, and Western red cedar.
Seven species of salmonids are found in the Dungeness River. These are fall chinook, coho, pink, summer chum, summer and winter steelhead, cutthroat trout, and bull trout. Two stocks of pink salmon are considered to be in the Dungeness River by the Washington Department of Fish and Wildlife (WDFW) . One is found primarily in the upper river (above mile ten) and spawns a month earlier than the other lower river stock (SASSI 1992). The WDFW’s Salmon and Steelhead Stock Inventory (SASSI) described the status of the following stocks as depressed: coho, upper river pink, steelhead or critical: lower Dungeness pink (SASSI 1992). According to SASSI, a depressed stock is a stock of fish whose production is below expected levels based on available habitat and natural variations in survival rates but above the level where permanent damage to the stock is likely to occur. A stock of fish is considered critical when the stock is experiencing production levels that are so low that permanent damage to the stock is likely to occur or has already occurred.
Kruckeberg, A.R. 1991. The natural history of Puget Sound country. University of Washington Press.
Phillips, E.L. 1965. Climate of Washington. Weather Bureau, U.S. Department of Commerce.
SASSI 1992. Washington State Salmon and Steelhead Stock Inventory.
Schuster, J.E. 1992. Geologic Map of Washington. Washington Department of Natural Resources.