Publication Summary

The study area for the upper Naches River Temperature Total Maximum Daily Load (TMDL) consists of the mainstem Naches River from the confluence with the Tieton River to the U.S. Forest Service boundary; all major tributaries along this reach; and Cowiche Creek. Ecology conducted field work in 2004.

This report presents an analysis of the spatial and temporal stream temperature patterns and results of a QUAL2Kw stream temperature model used to investigate possible thermal behaviors. Based on the model, this TMDL sets effective shade load allocations. Other management activities are recommended including measures to increase channel stability and channel complexity.

The study area for the upper Naches River Temperature Total Maximum Daily Load (TMDL) consists of the mainstem Naches River from the confluence with the Tieton River (river mile 17.6) to the U.S. Forest Service (USFS) boundary (RM 38.8), all major tributaries along this reach, and Cowiche Creek.

The Naches River watershed is located within Watershed Resource Inventory Area (WRIA) 38. The Federal Clean Water Act Section 303(d) listings for temperature in the study area include 26 listed segments.

The Washington State Department of Ecology conducted field work for this study in 2004. This report presents (1) an analysis of the spatial and temporal stream temperature patterns of streams within the upper Naches River basin and (2) results of a QUAL2Kw stream temperature model used to investigate possible thermal behaviors of the upper Naches River for different meteorological, shade, and flow conditions.

Reductions in water temperatures are predicted for hypothetical conditions with mature riparian vegetation, channel width reductions, and improvements in riparian microclimate. Model simulations show an expected 2.7°C reduction in temperature compared to current conditions for the upper Naches River (RM 38.8 to 17.6). Potential reduced temperatures are predicted to be lower than the threshold for fish lethality of 23°C, but greater than 16°C in all the stream segments evaluated.

This technical assessment uses effective shade as a surrogate measure of heat flux to fulfill the requirements of Section 303(d) for a TMDL for temperature.

This TMDL sets effective shade load allocations for the upper Naches River study area. The TMDL also incorporates the allocations developed for USFS lands in the Wenatchee National Forest Water Temperature TMDL Technical Report. In addition to the load allocations for effective shade, other management activities are recommended for compliance with the Washington State water quality standards for water temperature. These include measures to increase channel stability and complexity.

Link to EIM data for User Study ID STEB0001