Publication Summary

The Teanaway River basin drains to the upper reaches of the Yakima River on the east slope of the Cascade mountain range. The basin experiences high stream temperatures detrimental to threatened salmonids. This report summarizes an approach for developing a temperature Total Maximum Daily Load (TMDL), applied on a pilot basis to the Teanaway River basin. The project objectives were to (1) determine potential solutions to the high stream temperature problems, and (2) pilot the use of Geographic Information System techniques for more effective collection and analysis of temperature data.

The Teanaway River basin drains to the upper reaches of the Yakima River on the east slope of the Cascade mountain range. The basin experiences high stream temperatures detrimental to threatened salmonids. This report summarizes an approach for developing a temperature Total Maximum Daily Load (TMDL), applied on a pilot basis to the Teanaway River basin. The project objectives were to (1) determine potential solutions to the high stream temperature problems, and (2) pilot the use of Geographic Information System techniques for more effective collection and analysis of temperature data.

Continuous water temperature data gathered from July 1 to October 8, 1998 show that the middle and lower basin exceeds the 18ºC water quality standard in over 75% of the days monitored. Analysis and stream temperature modeling with Stream Segment Temperature Model (SSTEMP) show that improvements in riparian shade, active channel width, and flow can lower these temperatures. Estimates made with the best available data are that a 1.5ºC to 3ºC reduction in mean daily water temperature could be realized with a mature riparian buffer, sediment controls for roads, and streamflow increases. The reduction in maximum daily water temperature would be approximately 3ºC to 6ºC under the most favorable simulated conditions. These estimates are made for a critical condition, which for stream temperature is a time of low flow and high air temperature.