Floodplains

Floodplain

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

Salish Sea References

• Watershed Characterization Mapper
• The Encyclopedia of Puget Sound
• PRISM Project Search
• Washington Coastal Atlas
• WDFW's Salmonscape Map

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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

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

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

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

The following Topic Pages are categorized with Floodplain.

Beaver  •  Channel Migration Zone  •  Engineered Log Jams  •  Flood fencing  •  Floodplain Restoration  •  Integrated Floodplain Management  •  Letter of Map Revision  •  No Rise and The Letter of Map Revision  •  Riparian Buffers  •  Rivers and Harbors Act

Floodplain Places By Region

The following Floodplain Pages are organized by region.

Fraser Lowlands

North Fork Nooksack Floodplain  •  South Fork Nooksack Floodplain

Hood Canal

Skokomish Confluence

Whidbey Basin

French Slough Floodplain and Watershed  •  Lower Skykomish Floodplain  •  Lower Stillaguamish Floodplain  •  North Fork Stillaguamish Floodplain  •  Snohomish Lord Hill Reach  •  South Fork Stillaguamish Floodplain

Floodplain Workgroups and Efforts

The following Workgroups and Efforts are associated with Floodplain.

Workgroups

Floodplains Local and Regional Exchange  •  Floodplains for the Future  •  Northwest Regional Floodplain Management Association  •  Skagit Climate Science Consortium  •  Sno-Valley Tilth  •  Snohomish Sustainable Lands Strategy  •  Watershed Science and Engineering  •  Western Washington Agricultural Association

Effort

Barnaby Reach Restoration  •  Black River Farm  •  Channel Migration Zone Mapping  •  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  •  Riparian Data Engine  •  Scatter Creek Farm and Conservancy  •  Skagit Farmland Legacy Program  •  Skykomish Braided Reach Project  •  Skykomish Habitat Mitigation Bank  •  Snohomish Agricultural Resilience  •  Snohomish Agriculture Resilience Plan  •  Snoqualmie Fish, Farm and Flood Initiative  •  The Ecosystem Guild/Bio-Cultural Restoration Field Stations  •  Whatcom Drainage Maintenance Guidance  •  Working Buffer Pilot Project

particles of clay, silt, sand, gravel, or cobble, transported by water, are called sediment.