Puget Sound Watershed Characterization Project

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Watershed characterization.jpg

Washington State Department of Ecology has worked primarily with Environmental Protection Agency resources to delineate and describe the relative condition of Puget Sound watersheds. This major effort supports local Watershed Planning and implementation of GMA. Polygons were developed using SSHIAP stream segements, and grouped to generate watershed segments of a similar size. Headwater watersheds were differentiated from lowland watersheds. Watersheds were grouped into Watershed Management Units, each of which is a tributary to a major river. A series of models were created to describe the relative condition of each watershed unit, including hydrologic processes and a variety of water quality models. WDFW contributed a terrestrial, freshwater and saltwater habitat model.

A phase of work began in 2017 to create a more robust hydrologic model that is sensitive to land use and development change, but doesn't require a full hydrologic model.

Current landing page: https://fortress.wa.gov/ecy/coastalatlas/wc/landingpage.html

Hydrologic Model Improvements (2017-18)

  • This new phase of work builds on Lucchetta et al 2014 which explores the ability of a Hydrologic Condition Index to predict High Pulse Count (the number of times that discharge exceeds twice the mean annual flow for more than 24 hours.)
  • The work is intended to allow for quantification of development effects on watershed health from remote sensing data, by extrapolating from watersheds with stream flow data and an IBI record.
  • File:Stanley et al 2018 memo watershed characterization hydrologic condition index.pdf describes initial work to describe catchment condition with a single index that describes relative impairment of hydrologic functions.
  • The effort concludes with Stanley et al 2019 mid-scale hydrologic characterization, which describes efforts to describe watershed impairment using landcover change.
  • This effort continues with the practical applicaiton of a Hydrologic Condition Index to evaluate alternative policies for effects of stream dynamics (particularly flashiness).

Watershed Characterization Notes

  • The watershed characterization remains the most comprehensive sound-wide assessment of watershed condition.
  • Volume 1 - The Water Resource Assessments
  • On-line Mapper
  • There are unresolved overlaps between this watershed focused project and the PSNERP coastal analyses. Integrating coastal process, and watershed process analyses is likely to strengthen work that crosses these boundaries, like in smaller coastal watersheds or deltas.
    • This effort and PSNERP efforts each use a different watershed boundary polygons
    • PSNERP more finely defines coastal units based on c. 2006 LIDAR.
  • There is no analytical differentiation between large river floodplain dominated units and tributaries. Many metrics used to characterize unit condition are linked to floodplain structure (wetlands, salmonid diversity) and so these analyses when taken superficially at a landscape scale, may in some cases differentiate between floodplain and tributary rather than providing a finer view of either. The Floodplains by design effort by TNC may provide a supporting line of analysis.
  • Metric work is synthesized to provide a develop, restore, or protect recommendation, under the assumption that a prupose of the study is to place inevitable new development in the location where it does the least damage.
  • Leonetti 2015 provides an initial effort to compare assumptions of water flow models to field conditions, and found weak relationships between recharge importance and variation in stream temperatures.