Streams and Floodplains
Floodplain function in large and small river systems
Floodplain function is assessed using connectivity, land cover and land use for the 17 major rivers of Puget Sound. Areas that have natural land cover and unrestricted river flow are expected to be the most functional and provide the most ecosystem services. Floodplain areas with non-natural land cover and restricted river flow due to constraints (e.g. roads, railroads, levees) will have impaired or loss of floodplain function.
Floodplain function in large and small river systems
By: Category
2011 baseline floodplain condition assessment for the 17 major rivers of Puget Sound. Total area is shown in acres for each category of floodplain condition.

Key Vital Sign Indicator Results

  • Floodplain function in Puget Sound's major rivers has been quantified for the year 2011 (2013 in the Puyallup River). A comparison with one or more additional years will determine if we are making progress toward no net loss of floodplain function.
  • 36% (161,104 acres) of the 17 major river floodplains are highly functional (categorized as connected natural land cover), while 64% (283,301 acres) have reduced function.
  • Over half of the region’s floodplain areas are found in three of the 17 major rivers: Nooksack, Skagit, and Snohomish Rivers.
  • Since 2011 at least 39 activities managed by Washington State Recreation and Conservation Office's (RCO) online system, PRISM, have conserved 731 high-quality floodplain acres and 188 activities have improved or restored 8,162 floodplain acres.

Contributing Partners


No targets are currently set for this indicator.

Data Source
  • Floodplain Extent: Delineated by NOAA Status and Trends Habitat Program, Northwest Science Center, and where NOAA data were lacking, FEMA 500 year (0.2%) and USGS Low Floodplain (Konrad 2015) were used.
  • Connectivity: USGS refined methods from Konrad (2015) using roads, railroads, and regional and local levee data
  • Land Use: Washington State Department of Agriculture (2011) and local agriculture in pilot watersheds, if available
  • Land Cover: NOAA CCAP Land Cover (2011), WDFW High Resolution Land Cover (2011)

Reports and source data are available at the Floodplains Indicator Source Materials.

Vital Sign Indicator Reporter
Indicator Details
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