Floodplains are dynamic and diverse landscapes that provide invaluable ecosystem services including critical habitat for the health, growth, and survival of Pacific salmon and steelhead, flood damage mitigation, improved water quality, vital habitat for a suite of flora and fauna, recreational opportunities, and economically valuable lands such as agriculture.

There is an estimated 438,933 acres of floodplain along the 17 major Puget Sound rivers. As population growth and associated development needs continue to modify floodplains, the ability of floodplains to provide ecosystem services becomes increasingly impaired, with potentially adverse consequences to people, property, habitats, and the species that depend on floodplains.

The Floodplains Vital Sign monitors the protection, loss, and restoration of functional floodplain areas in the 17 major rivers of Puget Sound in support of recovery planning, land use protection, and recovery investments.


Key Messages

In Puget Sound, intact, healthy floodplains provide:  Puget Sound floodplain

  • Rearing and refuge habitat for Endangered Species Act (ESA)-listed salmon, especially Chinook salmon, an important species to generations of Tribes and resident killer whales.
  • Flood storage and flood flow mitigation to protect an estimated $18 million dollars of residential, commercial, and industrial development and infrastructure (Floodplains by Design 2016)
  • Productive agricultural lands
  • Public recreational opportunities
  • A variety of ecosystem services and resiliency functions such as stormwater filtration, wildlife habitat, etc.

Puget Sound floodplains are impaired:

  • Over 60% of the floodplain areas in the 17 major rivers have either lost some degree or all of their functions relative to historic conditions.

What is the floodplain community doing?

  • To date, over 4,000 acres of floodplain habitat have been restored!

What are the effects of climate change? The effects are complex:

  • Some floodplain communities are experiencing more frequent and severe floods and the pattern is expected to continue (Floodplains by Design, UW Climate Impacts Group 2016).
  • Salmon use of floodplains will be impeded:
    • Summer flows are expected to diminish, further reducing floodplain habitat due to lack of connectivity to portions of the system
    • Water temperatures are expected to increase
  • Well-functioning floodplain systems with low levels of development are likely to be more resilient to climate change than compromised floodplains in urban watersheds

Strategies, Actions, and Effectiveness

The Puget Sound Partnership convened partners in the floodplain community to develop a floodplain implementation strategy for the region. The Floodplain Implementation Strategy is currently managed and implemented by the Washington Department of Wildlife and Department of Natural Resources with financial support from Environmental Protection Agency's National Estuary Program.

Floodplain recovery is a priority focus topic for the Partnership's 2018 Action Agenda.

What is working to improve Puget Sound floodplains?

  • View effectiveness factsheets for floodplain restoration projects.

Other Resources

Grant programs investing in improving floodplain function:

Washington State Department of Ecology Floodplain Management

State of our Watersheds report by the Northwest Indian Fisheries Commission

Articles related to floodplains in the Encyclopedia of Puget Sound

Climate Change Impacts on Puget Sound Floodplains (UW Climate Impacts Group, February 2016)

General floodplain information through the National Geographic Resource Library

Contributing Partners


Jennifer Burke, Nathalie Hamel and Leah Kintner, Puget Sound Partnership
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