Overview
The Hydrologic Study of the Skagit Estuary was a follow-up to the Skagit Basin Water Supply and Demand Analysis. The research integrated work conducted by the University of Washington Salish Sea Modeling Center (UW), the Northwest Fisheries Science Center (NWFSC), and the Skagit River System Cooperative (SRSC). The State of Washington Water Research Center (SWWRC) served as the lead on the project. The project aimed to:
- Collect data about topographical and seasonal inundation dynamics
- Improve understanding of temporal variation in aquatic habitat characteristics
- Conduct a synthesis of habitat suitability index development of targeted fish species
- Conduct hydrodynamic modeling
Key Findings from the Comprehensive Hydrologic Study of the Skagit Estuary
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The modeled efforts provided here improved resolution and accuracy over previous models (i.e., the Duke Study), especially in small tidal channels.
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Overall, juvenile Chinook salmon and other estuarine species were most abundant in low-salinity, low-velocity, and moderate-depth waters.
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The South Fork of the Skagit delta was most affected by increased salinity under high water use scenarios, especially in low-flow years.
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Flows reduced habitat suitability for juvenile Chinook salmon, although this effect was nonlinear, and was dependent on location in the delta and time of the year.
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Under high water use and low-flow conditions, shrub cover declined by up to 27%, replaced by herbaceous species. These changes could reduce habitat quality for species like beavers, which create important rearing habitats for juvenile salmon.
Report Summary, Submitted to the Washington State Joint Legislative Task Force on Water Supply 30 June 2025
Presentation of Results: Skagit Watershed Studies: An Estuary, a Tributary, and the Groundwater
On December 9, 2025, the State of Washington Water Research Center hosted the Skagit Watershed Studies: An Estuary, a Tributary, and the Groundwater (recorded) with opening and closing remarks by Washington State Legislators, Former Co-chairs of the Joint Legislative Task Force on Water Supply:
- Representative Debra Lekanoff, 40th Legislative District of Washington State
- Senator Keith Wagoner, 39th Legislative District of Washington State.
Presenting research teams:
- Chad Wiseman, Groundwater Study Lead, Skagit Groundwater Study
- Thomas Gast, Tributary Study Lead, Skagit River Tributary Instream Flow Habitat Assessment Study
- Correigh M. Greene, Ph.D. Estuary Study Lead, Preliminary Evaluation of the Effects of Water Withdrawals on Estuary Habitats Study
- Ria Berns, Washington State Department of Ecology
- Michael F. Goodchild, Ph.D. Washington State Academy of Sciences
- Jonathan Yoder, Ph.D. State of Washington Water Research Center
- Julie Padowski, Ph.D. Washington State University
- Cindy Fabbri, Ph.D. State of Washington Water Research Center
Related Research