Past Projects

River temperature assessment with instream and remotely sensed data; modeling of current conditions and possible climate change effects

Weï¿½analyze spatial and temporal patterns of summer water temperature in the Wenatchee River, a tributary of the Columbia River, located in the Pacific Northwest Region of the United States. A network of instream sensors indicated that during the summer of a hydologically near-normal year the river can reach values as high as 20-22ï¿½C in the lower reaches. A 5-year historic record of instream recorded data daily indicates that maximum river temperatures can vary between summer high and low flow years by as much as 7-9ï¿½C. River temperature modeling scenarios indicate low cooling potential from the streamside vegetation due to the relatively large size of the river and reduced canopy density in the lower reaches. Model simulations assuming a climate change scenario with reduced streamflows and increased air temperatures indicate that river temperature is likely to increase by a stream-length average of about 1.8ï¿½C compared to the current condition. Modeled increases in temperature due to estimated future global warming are determined primarily by the predicted reduced summer streamflows, and to a lesser extent by the increases in air temperature. The benefits obtained by growing a mature riparian vegetation corridor along the river are likely to be offset by climate change effects.

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Wenatchee River temeprature Total Maximum Daily Load study

Water temperature records in the Wenatchee River and some of its tributaries have shown many exceedences of the numeric criteria of the Washington State water quality standards. As part of the Wenatchee River Total Maximum Daily Load (TMDL) study for temperature, the Washington State Department of Ecology conducted field work during 2002-2003 to support the development of stream temperature model scenarios and load allocations. A stream temperature model, QUAL2Kw, was used to investigate possible thermal behaviors of the Wenatchee River, Nason Creek and Icicle Creek for different meteorological, shade, and flow conditions.Reductions in water temperature are predicted for hypothetical conditions with mature riparian vegetation and improvements in riparian microclimate. This technical assessment uses effective shade as a surrogate measure of heat flux to fulfill the requirements of the federal Clean Water Act Section 303(d) for a temperature TMDL load allocations. Effective shade is defined as the fraction of incoming solar shortwave radiation that is blocked by vegetation and topography from reaching the surface of the stream. In addition to load allocations for effective shade, other management activities are recommended for compliance with the water quality standards for water temperature.

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Modeling the effects of riparian buffer width of effective shade and strean temperature

To evaluate the effects of converting riparian hardwood-dominated stands to coniferous-dominated stands on western Washington stream temperatures, we combined a shade model and water quality model to explore the stream heating potentials of three buffer-width scenarios. Changing one variable at a time, we then ran a series of model simulations for various buffer-width (30-75 feet) and harvest-length (500-1500 feet) scenarios. Results of each simulation were expressed as the change in maximum daily temperature relative to the unharvested state (i.e., upstream boundary condition). When a 500-foot harvest unit and 50-foot buffer were then applied to our model channel, the downstream temperature of the 10-foot-wide stream increased 0.13ï¿½C relative to the upstream state. Temperature continued to rise as harvest-unit length increased, with the 1500-feet-long unit showing the most change (+0.36ï¿½C, or approximately +0.12ï¿½C per 500 feet of harvest length). Wider buffers (75 feet), in contrast, continued to dampen temperature increases for the 10-foot stream, even at a harvest-unit length of 1500 feet. Results for the 20-foot-wide stream showed a similar pattern, but temperature increases in response to harvest-unit length were higher: 0.15ï¿½C (500 feet) ï¿½ 0.60ï¿½C (1500 feet), or about 0.18ï¿½C per 500 feet of harvest length. Temperature of the 10-foot-wide stream was more sensitive to buffer width than the 20-foot-wide stream. In contrast, all buffer scenarios cooled the 20-foot-wide stream less effectively, with predicted downstream temperatures converging somewhat when harvest-unit length reached 1000 feet. Inferences vary depending on the shade curve used. Overall, results indicated that, for the stream scenarios analyzed, riparian vegetation and harvest-unit length exerted greatest control on stream temperature at lower flow rates. Conditions favoring high daily maximum stream temperatures include: shallow and wide streams, north-south channel orientation, low groundwater influx or hyporheic exchange with the channel, and low gradient.

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