The Dalles Watershed
The Dalles Watershed area is 82,219 acres and covers all lands draining to the Columbia River between River Mile 180 to RM 191. These drainages include Threemile, Dry Hollow, Mill, Chenoweth, Browns and Hidden Valley Creeks, as well as lands draining to the Columbia River as far was as Rowena Overlook. The principal stream in this watershed is Mill Creek. The headwaters of Mill Creek are located in the Mt. Hood National Forest on the east slopes of the Cascade Mountains, near 4,000 feet. Mill Creek flows to the Columbia River through the City of The Dalles. The other streams in the watershed, principally Threemile, Chenoweth, and Brown's Creeks, are smaller streams that also flow to the Columbia River through the City of The Dalles. Coniferous forests at elevations above approximately 2,000 feet cover The Dalles Watershed area, giving way gradually to oak forests and then to grasslands at lower elevations. Land cover at any given location is determined principally by precipitation, which varies from 60+ inches per year at the headwaters, to as little as 12 inches per year in lower Threemile Creek. Forestry is the dominant land use near the headwaters. At lower elevations, principal land uses include urban development, rural residential development, and fruit orchards. The City of The Dalles covers 4,550 acres along the Columbia River. Orchards and vineyards within the watershed cover more than 6,000 acres. Minor land uses include irrigated crops, pasture, and dryland crop production. Stream flows are influenced by spring snowmelt, winter precipitation, and human regulation. Persistent winter snowpack is limited to areas above about 3,500 feet. Below that, precipitation is a mixture of snow and rain, falling mostly in the winter. South Fork Mill Creek serves as the main water source for the City of The Dalles. Crow Creek Reservoir is located at RM 10 on South Fork, while the City's water treatment plant is located at RM 2. In addition, the City has a water right on the Dog River, a tributary to Hood River. Flow from Dog River is transferred into the headwaters of South Fork Mill Creek and allowed to flow down the creek to the Crow Creek Reservoir, where it is stored until needed. Water from the dam is released and allowed to flow down South Fork Mill Creek to the water treatment plant, where the City takes what it needs. As a results, flows in South Fork Mill Creek, both upstream and downstream of the City water intake, are more related to municipal needs than to natural hydrologic patterns. In contrast to South Fork Mill Creek, North Fork Mill Creek flows are almost entirely unregulated and unaffected by diversions until RM 2, where an irrigation diversion serves a small orchard. Several irrigation diversions exist on the mainstem of Mill Creek. Threemile Creek originates at a lower elevation where winter snow does not typically last long. High flows therefore occur earlier in the year than in Mill Creek, and summer flows are very low. Brown's Creek and Chenoweth Creek are similar in this regard. In fact, Brown's Creek typically runs dry eight months of the year, while Chenoweth Creek has perennial flow for only a few miles near its mouth. Irrigation diversions exist on Threemile Creek, but not on Chenoweth or Brown's Creeks.