| dc.description |
Dairy Creek, located in Washington County, Oregon, has a drainage area of
approximately 230 square miles, and includes West Fork, East Fork, and McKay Creek
drainages. Dairy Creek is a major tributary of the Tualatin River which experiences algal
problems during the late summer when stream flows decrease and water temperatures
increase.
The upper reaches of Dairy Creek are forested land, while the lower reaches are
devoted to intensively irrigated agricultural production. It has been proposed that
excessive algae blooms are associated with elevated nutrient concentrations during
summer low-flow conditions. The objective of this project was to evaluate nutrient
loading to the Tualatin River from the Dairy Creek watershed. Water quality parameters
were selected to examine relationships between precipitation, flow, solids and nutrient
constituents.
The following conclusions were reached:
1. Surface runoff and erosion processes did not appear to occur and
hence had little impact on water quality during the months of July
through October during 1990 and 1991.
2. Groundwater moving to the stream appears to drive flow and have
significant influence on water quality during summer low-flow
conditions.
3. Nutrient concentrations are greatest during the summer. This may be
a consequence of increased solubility and greater contact time between
soils and groundwater moving toward the creek. A second alternative
is the winter time sediment deposition.
4. Most of the nutrient and solids loading occurs during the winter and
early spring at times of highest stream flows. |
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