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Floodplains occur where large rivers and streams meander in their own sediments

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Floodplains form where rivers flow through a valley of alluvial sediment several times the width of the channel. During floods, the river inundates the floodplain depositing sediments. Floodplains and their rivers are fed by both Headwaters and Lowland Watersheds, and flow into River Deltas as they enter the sea. Floodplains are critical for Biodiversity and Salmon and are also vital for Agriculture. Encroachment of residential Land Use on floodplains is a driver for Flood Hazard Management. Floodplains are generally described by FEMA mapping of flood hazard areas. The Floodplains by Design effort by The Nature Conservancy of Washington aims to provide a stronger assessment of these systems. Lakes and Wetlands are all different kinds of floodplains (where shallow Groundwater is found at or near the surface for parts of the year).

Physical Context[edit]

USGS collaborates with NOAA to provide real-time data on river flow and flood stage. Mauger et al 2015 describes the anticipated change in the flow regime under Climate Change. Rivers are flows of both water and sediment and Czuba et al 2011 summarizes existing data on total sediment budget. Collins & Montgomery 2011 describes a diversity of physical systems, based on how much, and how floodplains have filled since glacial excavation.

Biological Context[edit]

Besides us, beaver are key ecosystem architects, and the reduction in beaver populations combined with flood hazard management has radically changed floodplain ecosystems.

Planning Context[edit]

Because of our dry-summer climate, moist rich floodplain soils are vital to agriculture. The Puget Sound Partnership has adopted a floodplain restoration target as part of Puget Sound Vital Signs. Floodplains by Design has promoted multi-benefit restoration strategies, with novel efforts in the Puyallup/White. Snohomish, Stillaguamish, Skagit, Nooksack, Dungeness and Skokomish basins. Floodplain habitats. The Puget Sound Watershed Characterization identified a unique set of floodplain attributes because of wetlands, including those created by beaver, re-affirming the importance of floodplains already described in salmon recovery planning, particularly for endangered Puget Sound Chinook Salmon. A constellation of authorities and agencies in Flood Hazard Management systems are focused on floodplain dynamics.

Floodplain Topic Pages[edit]

The following Topic Pages are categorized with Floodplain.

Floodplain Places By Region[edit]

The following Floodplain Pages are organized by region.

Admiralty Inlet[edit]

East Sound[edit]

Fraser Lowlands[edit]

Hood Canal[edit]

Juan de Fuca[edit]

San Juan Islands[edit]

South Puget Sound[edit]

South Vancouver Island[edit]

Sunshine Coast[edit]

West Sound[edit]

Whidbey Basin[edit]

Floodplain Workgroups and Efforts[edit]

The following Workgroups and Efforts are associated with Floodplain.


Barnaby Reach Restoration  •  Black River Farm  •  Coastal Resilience to Climate Change  •  Elwha Dam Removal  •  Farmhouse Reach Floodplain Restoration  •  Floodplains by Design (FbD)  •  French Slough Drainage Management  •  Haskell Slough Protection and Restoration  •  Jim Creek Channel Enhancement  •  Larson's Reach Floodplain Restoration  •  Lower Canyon Creek Restoration  •  Lower Skykomish Floodplain Design  •  Lower Skykomish Reach Scale Plan  •  Lower Snohomish Reach Scale Plan  •  Nooksack Floodplain Integrated Management Planning  •  Nooksack Floodplain Restoration with Engineered Log Jams  •  Old Soldiers Home Levee Setback  •  Pierce County Levee Setback Planning  •  Predicting Sea Level Rise Impacts on Ag Production  •  Scatter Creek Farm and Conservancy  •  Skagit Farmland Legacy Program  •  Skykomish Braided Reach Project  •  Skykomish Habitat Mitigation Bank  •  Snoqualmie Fish, Farm and Flood Initiative  •  The Ecosystem Guild/Bio-Cultural Restoration Field Stations  •  Whatcom Drainage Maintenance Guidance  •  Working Buffer Pilot Project