Publication Summary

The Little Klickitat River and its tributaries - East Prong, West Prong, and Butler Creek - are listed on the 1996 and 1998 Washington State 303(d) list for elevated water temperatures. Field work by Ecology, the Central Klickitat Conservation District, and Yakama Nation Fisheries confirmed further temperature problems throughout the watershed.

Effective shade is used as a surrogate measure of heat flux to fulfill the requirements of Section 303(d) for a Total Maximum Daily Load (TMDL) for temperature.

The Little Klickitat River watershed encompasses approximately 285 square miles in south-central Washington State. The Little Klickitat River and its tributaries - East Prong, West Prong, and Butler Creek - are listed on the 1996 and 1998 Washington State 303(d) list for elevated water temperatures. Field work by Ecology, the Central Klickitat Conservation District, and Yakama Nation Fisheries confirmed further temperature problems throughout the watershed.

Effective shade is used as a surrogate measure of heat flux to fulfill the requirements of Section 303(d) for a Total Maximum Daily Load (TMDL) for temperature. Effective shade is defined as the fraction of incoming solar shortwave radiation above the vegetation and topography that is blocked from reaching the surface of the stream. The load allocations for effective shade under this TMDL are as follows:

1. For perennial streams in the entire Little Klickitat watershed, including East Prong, West Prong, and Butler Creek, the load allocation ranges from 95 to 50% which is the effective shade produced by a mature riparian corridor and the existing topography.

2. For portions of the Little Klickitat River and West Prong, additional temperature reduction may be possible through reduction of the wetted width-to-depth ratio. A Level II Rosgen Channel classification indicated that the mainstem Little Klickitat is a Class C and has an average wetted W/D ratio of 28. As mature riparian vegetation is established, reduction of the current wetted W/D ratio may occur on portions of the Little Klickitat.

3. For all perennial streams in the Little Klickitat watershed, including Bowman, Mill, Spring, and Blockhouse creeks, that were not specifically modeled and that exceeded the water quality standard, 73% effective shade produced by mature riparian vegetation is the load allocation. An effective shade of 73% is the average load allocation for all modeled segments on the Little Klickitat River, West Prong, East Prong, and Butler Creek. Additionally, Bloodgood Creek, which does not exceed water quality standards, provides the only source of cooling water to the Little Klickitat River, and efforts should be made to preserve and protect the cooling influence of the waters from Bloodgood Creek.

In addition to the load allocations for effective shade, other management activities are recommended for reduction of water temperature, including measures to reduce sediment loading and promote water-use efficiency.

The Goldendale Wastewater Treatment Plant (WWTP) is the sole point source in the Little Klickitat watershed. Under current load allocations, the upstream temperature complies with the water quality standard of 18oC; consequently, the wasteload allocation for the Goldendale WWTP effluent is established as 18.3oC.

Appendix B is provided online as a Data Supplement (zip file) in Excel.