Publication Summary

The Upper Chehalis River Basin TMDL, developed by the Washington State Department of Ecology , is being established for heat caused by solar radiation. Heat is considered a pollutant under Section 502(6) of the Clean Water Act. Heat generated by the amount of solar radiation from sunlight reaching the stream provides energy to raise water temperatures. This TMDL is designed to address impairments due to surface water temperature increases on nine water quality-limited streams (representing 19 segments) located in the watershed and provide goals for protection of all remaining streams. Streamside shade is used as a surrogate for water temperature increases, as allowed per federal regulations. A decrease in shade increases incoming solar radiation and the resultant heat transfer to the stream. A more complete description of the factors influencing stream system temperatures appears in Appendix E.