Water Temperature Mapping of the Skykomish, Snoqualmie, and Middle Fork Snoqualmie Rivers—Longitudinal Stream Temperature Profiles and Airborne Thermal Infrared and RGB Imagery Mosaics

The Skykomish and Snoqualmie River basins in western Washington provide spawning, rearing, and migration habitat for several salmonid species, including Endangered Species Act-listed Chinook salmon, steelhead trout, and bull trout. The production, abundance, distribution, and the health of fish and other aquatic life is strongly influenced by water temperature, which affects their physiology and behavior. The Washington State Department of Ecology establishes water temperature criteria and Total Maximum Daily Load standards for designated aquatic life uses, varying between 12 and 17.5 degrees Celsius, depending on the habitat classification and time of year. However, over the past two decades, water temperatures within the Skykomish, Snoqualmie, and Middle Fork Snoqualmie rivers frequently exceeded water temperature criteria, and the 23 degrees Celsius threshold above which water temperatures can be lethal to salmonids. To inform salmonid restoration efforts within these basins, this study used high-resolution airborne thermal infrared (TIR) imagery to quantify the longitudinal stream temperature profiles (LTPs) of the Skykomish, Snoqualmie, and Middle Fork Snoqualmie rivers. This Data Release presents those results with the following items: Georeferenced, orthorectified TIR and RGB imagery mosaics (.tiff and .sid, respectively) of the Skykomish, Snoqualmie and Middle Fork Snoqualmie rivers, produced by NV5 Geospatial (formerly Quantum Spatial, Inc.), a company specializing in geospatial surveys. The mosaics were made using TIR and RGB images acquired from helicopter-based surveys conducted by NV5 Geospatial during two distinct surveying efforts—August 16-17, 2020, and August 3-5, 2021. The surveys covered a total river length of approximately 133 km, from Goldmyer Hot Springs on the Middle Fork Snoqualmie River to Chinook Bend Natural Area on the Snoqualmie River and from Gold Bar to Monroe, WA on the Skykomish River. LTPs (.shp) produced by NV5 Geospatial and the U.S. Geological Survey (USGS) using the TIR and RGB mosaics. In addition to the helicopter-based TIR surveys, longitudinal "Lagrangian" drag-probe surveys (hereafter, "float surveys") were conducted by the USGS and Tulalip Tribes on the Skykomish and Middle Fork Snoqualmie rivers. The surveys covered a total river length of approximately 68 km, from the Taylor River confluence to Three Forks Natural Area on the Middle Fork Snoqualmie River and from Gold Bar to Monroe, WA on the Skykomish River. For these float surveys, near-streambed and near-surface water temperature and GPS position were measured at three-second intervals from a non-motorized watercraft drifting downstream at ambient stream velocity. The Skykomish River float survey was conducted over several days between August 24 and September 11, 2020. The Middle Fork Snoqualmie River float survey was conducted over several days between August 17 and September 11, 2020, with a follow-up survey on a reach of interest on August 3, 2021. The resulting LTPs from these float surveys are provided as shapefiles (.shp). Prior to the TIR and float surveys USGS staff deployed 37 in-stream water temperature data loggers along the study area to record water temperature during the data acquisition time frame. Water temperature records were shared with NV5 Geospatial staff to radiometrically calibrate the TIR imagery and analyze the float survey data. These records also assist in interpreting the results of the float surveys. Data from the in-stream water temperature loggers is available for download through the Washington Department of Ecology's Environmental Information Management System (https://apps.ecology.wa.gov/eim/search/default.aspx; Study ID WQC-2020-00164).- Georeferenced, orthorectified aerial thermal infrared (TIR) and RGB imagery mosaics (.tiff and .sid, respectively) of the Skykomish, Snoqualmie and Middle Fork Snoqualmie rivers, produced by NV5 Geospatial from TIR and RGB images acquired with helicopter-based surveys they conducted during two distinct surveying efforts--August 16-17, 2020, and August 3-5, 2021--covering a total river length of approximately 133 km.
- LTPs (.shp) produced by NV5 Geospatial and the U.S. Geological Survey (USGS) using the TIR and RGB mosaics.
- Significant Feature Sites (.shp) produced by USGS using the TIR and RGB mosaics.

In addition to the helicopter-based TIR surveys, float surveys (also referred to as, “Lagrangian drag-probe surveys”) were conducted by the USGS and Tulalip Tribes on the Skykomish and Middle Fork Snoqualmie rivers, covering a total river length of approximately 68 km. For these float surveys, near-streambed and near-surface water temperature and GPS position were measured at three-second intervals from a non-motorized watercraft drifting downstream at ambient stream velocity. The Skykomish River float survey was conducted over several days between August 24 and September 11, 2020. The Middle Fork Snoqualmie River float survey was conducted over several days between August 17 and September 11, 2020, with a follow-up survey on a reach of interest conducted August 3, 2021. The resulting LTPs from these float surveys, provided in this Data Release as shapefiles, were processed to allow for comparison with the LTPs obtained from helicopter-based thermal infrared surveys to evaluate the similarity and consistency of the LTPs over time and assess the ability of these two surveying methods to reveal thermal anomalies.

Prior to the TIR and float survey data collection USGS staff deployed 37 instream water temperature data loggers along the study area to record water temperature during the data acquisition time frame. Water temperature records were shared with NV5 Geospatial staff to radiometrically calibrate the TIR imagery and were also used by USGS to adjust the float survey LTPs to remove the diurnal heating signal so that the float survey profiles may be viewed as a 'snap-shot in time' similar to how the LTPs from the helicopter-based TIR surveys may be viewed. Data from the instream water temperature loggers is available for download through the Washington Department of Ecology's Environmental Information Management System (https://apps.ecology.wa.gov/eim/search/default.aspx).

A forthcoming USGS Scientific Investigations Report (SIR) provides further interpretation of the datasets included in this Data Release. The SIR will compare results between the various water temperature surveys conducted in 2020 and 2021, discuss the strengths and limitations of the surveying methods employed, and infer the geomorphic conditions that may be driving the increases or decreases in water temperature observed in the LTPs.