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Green-Duwamish River 2015 Temperature Data Compilation and Analysis

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Record low spring Cascade snowpack and warmer than normal winter, spring, and early summer air temperatures were observed in western Washington in 2015. These conditions generally led to unusually low flows in unregulated streams and rivers and elevated water temperatures. Early in 2015 a statewide drought was declared and some regional scientists suggested that the 2015 water year might become a good proxy for future (mid-21st century) conditions expected as the result of human-influenced climate change.

In order to gain a better understanding of what typical future conditions might look like as the climate becomes warmer, monitoring resources of a number of tribal, federal and local agencies and utilities were directed at a broader collection of temperature data in the Green-Duwamish River in the summer of 2015. This report documents the temperature conditions throughout the Green-Duwamish River in the summer of 2015, including conditions at sites located above Howard Hanson Dam. Comparisons of conditions in summer 2015 are also made to:

• Relevant state water temperature standards

• Water temperatures observed in 2006 below Howard Hanson Dam

• TMDL model water temperature predictions for Existing Shade conditions under “worst case” summer low flow and weather conditions

• Temperatures observed above and below Howard Hanson Dam from 1992 to 2015 to evaluate the influence of the dam and dam operations on outlet temperatures

View the report

    link to report (25.50 MB)

    MSAccess temperature database file (937.00 MB)

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