Scholz, Jenna. 2001. The variability in stream temperatures in the Wenatchee National Forest and their relationship to physical, geological, and land management factors. M.S.
Both water quality and the enduring health of wild salmon populations are important to the economy and culture of the PNW. Accordingly, natural variations in stream temperature and the effect of human activities that can warm surface waters are significant concerns for natural resource managers. To determine the natural range of thermal conditions in the eastern Cascades region of Washington State, I examined temperature variability at the landscape and watershed scales, and identified streams that are predisposed to temperatures that exceed regulatory standards. Trends and patterns in stream temperatures were investigated at 59 sites in the Wenatchee National Forest (WNF) during the summer of 1998. In addition to site data collection, longitudinal surveys were conducted from the headwaters to the mouth of each stream system and its major tributaries. Site-specific monitoring and mapping information was also collected, including air temperature, streamside shading, average channel aspect, site elevation, drainage area, distance from watershed divide, precipitation, and distance from the crest of the Cascade Mountains. The majority of streams studied exceeded the WDOE water temperature standard including those in unmanaged areas, suggesting that water temperatures above state standards are a natural feature of these streams. Temperatures in the WNF are influenced by several factors including air temperature, stream size, elevation, and stream shading. However, the physical factors that determine stream temperatures at the landscape scale are not necessarily good predictors of smaller scale temperature regimes. Stream temperatures in several watersheds appear to be influenced primarily by their high geologic potential for groundwater upwelling, especially in basins with little managed area.