Water Temperature Mapping in the Snoqualmie and Skykomish River Basins

Science Center Objects

Over the past two decades water temperatures in the Snoqualmie and Skykomish River basins has frequently exceeded temperature criteria established to protect Endangered Species Act-listed Chinook salmon, steelhead trout, and bull trout. These rivers combine in Monroe, WA to form the Snohomish River, the second largest producer of Chinook salmon in Puget Sound. The effects of high water temperatures on Chinook salmon populations are considered to have negatively affected the health of ESA-listed Southern Resident Orcas, which rely on Chinook salmon as their primary food source.

The USGS in partnership with the Tulalip Tribes will study the spatial and temporal distribution of water temperature in the mainstem Snoqualmie River, the Middle Fork Snoqualmie River, and the lower Skykomish River by using high-resolution thermal infrared imagery and longitudinal drag-probe temperature surveys. This information will be used by stakeholders to guide the design, siting, and prioritization of habitat restoration and protection options for mitigating high water temperatures, and in doing so support efforts to restore endangered populations of both Chinook salmon and Southern Resident Orcas.

Problem: The waters of the Snoqualmie and Skykomish River Basins have historically provided critical spawning, rearing, and core habitat for several salmonid species. These species include natural populations Chinook salmon and steelhead trout, listed as threatened under the Endangered Species Act (ESA), as well as coho salmon, which are listed as a species of concern, and bull trout, pink salmon, and chum salmon (Storh et al., 2011; Svrjcek et al., 2013; SWM, 2017). The Snoqualmie and Skykomish Rivers combine in Monroe, WA to form the Snohomish River, the second largest producer of Chinook salmon in Puget Sound (Svrjcek et al., 2013; Kaje, 2009).  Washington Executive Order 18-02 recognizes that the “health of ESA-listed Southern Resident Orcas and Chinook salmon are “tightly linked,” and that “reduced Chinook salmon runs undermine the potential for the Southern Resident population to successfully reproduce and recover” (WA, 2018).

Water temperature is one of the most dominant factors limiting the distribution and health of fish and other aquatic life, affecting their physiology and behavior (Fry, 1947; Brett, 1956; Hynes, 1970; Fagerlund et al., 1995). As such, Washington State through the Department of Ecology (henceforth, Ecology) maintains temperature criteria for waters designated for aquatic life uses. These standards vary between 12°C and 20°C, depending on the habitat classification and time of year. However, over the past two decades, water temperatures within these basins has frequently exceeded temperature criteria, as well as the 23°C threshold above which temperatures can be lethal to salmonids (Storh et al., 2011; Svrjcek et al., 2013; Kubo et al., 2016).

Objectives: The objective of this project is to quantify the spatial and temporal distribution of water temperatures in the mainstem Snoqualmie River, the Middle Fork Snoqualmie River, and the lower Skykomish River by using high-resolution thermal infrared (TIR) imagery combined with longitudinal drag-probe temperature surveys. 

Relevance and Benefits: This project will provide critical information for planning effective projects aimed at meeting the water temperature Total Maximum Daily Load (TMDL) requirements in the Snoqualmie River basin as well as the water temperature criterion for core summer, spawning, and rearing habitat in the Snoqualmie, Skykomish and Snohomish River basins. Water temperature data collected in the Skykomish River would inform the planned water temperature TMDL for the Skykomish, to be developed by Ecology. Interpretation of water-surface thermographs and longitudinal water temperature profiles produced from thermal infrared imagery and drag-probe surveys will identify potential areas of groundwater discharge, salmonid habitat and thermal refugia, as well as characterize the relative thermal influence of point sources, tributaries, surface springs, and riparian shading.

Approach: Four methods will be used to collect spatially and temporally distributed water temperature data in the mainstem Snoqualmie River between River Mile (RM) 22 and 75 and the Skykomish River from RM 0 to RM 21: 
- A helicopter-based thermal infrared (TIR) survey
- A longitudinal “Lagrangian” drag-probe water temperature survey
- Unmanned aircraft system (UAS)-based TIR surveys. 
- Continuous water temperature monitoring using in-stream thermistors.