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Fifteenmile Watershed

The Fifteenmile Watershed area encompasses 235,341 acres and includes all land drained by Fifteenmile Creek, which discharge into the Columbia River just downstream of The Dalles dam. Major tributaries to Fifteenmile Creek include Fivemile, Eightmile, Ramsey, Pine and Dry Creeks. Most of the headwaters are located near 4,500 feet elevation on the east slopes of the Cascade Mountains within the Mt. Hood National Forest, which covers the westernmost one third of the watershed. Fifteenmile Watershed is mostly covered by coniferous forests at elevations above 2,000 feet 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 10 inches per year near the mouth and along the eastern edge of the watershed. Land use follows closely with the precipitation gradient. Forestry is the dominant land use near the headwaters and dryland crop production is the dominant land use in the east. Most upland areas with soils unsuitable for crop or forest production are utilized for grazing or are enrolled in the Conservation Reserve Program. Many of the floodplains are irrigated from the Creek to grow hay. Minor land uses include urban development and fruit orchards. The City of Dufur covers some 800 acres on Fifteenmile Creek near river mile 22. Orchards, irrigated from groundwater currently cover about 1,000 acres.  Stream hydrology is influenced by spring snowmelt and winter precipitation. Persistent winter snowpack is limited to areas above 3,000 feet. Below that, precipitation is a mixture of snow and rain, falling mostly in the winter. Summer streamflows from Fifteenmile, Ramsey and Eightmile Creeks typically benefit from snowmelt, while tributaries originating at lower elevations disappear or fall to very low levels in the summer.

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