Map of the Gilligan Floodplain Restoration Project.
Map of the Gilligan Floodplain Restoration Project.

 

The objective of this project is to restore side channel and floodplain habitat in the Skagit River downstream of Gilligan Creek by removing approximately 560 feet of flood control dike and associated riprap bank protection, which will restore function to approximately 170 acres of floodplain. Floodplain vegetation will be improved by removing non-native vegetation and planting native trees.

As an initial step, the Skagit River System Cooperative conducted a feasibility study (2009) to evaluate potential project alternatives to restore habitat that has been isolated and degraded by a large dike on the left bank of the Skagit River, just downstream from Gilligan Creek. The majority of the property that would be affected by restoration is owned by the United States Forest Service and managed as part of the Wild and Scenic Rivers Program. The Forest Service supports removing or modifying the dike on their land, but was concerned about the possibility of increasing flood or erosion risks for downstream property owners. For this reason, the feasibility study used a hydraulic model to identify private parcels that might be affected by flooding or erosion, and developed and selected alternatives that address those risks.

Hydraulic modeling and geomorphic evaluation of the project site for existing conditions and the three habitat restoration alternatives was completed. Restoration alternatives included full dike removal, partial dike removal, and modifying the dike with a notch to increase flow into an historic side channel. The habitat benefits of removing or modifying the dike are to restore natural bank conditions, create off-channel habitat in an existing channel, and improve connectivity between the river and floodplain habitats. Discussions with the Forest Service and Skagit County about the study conclusions have resulted in the development of a conceptual alternative that would include removing all or a significant portion of the existing dike and constructing a new dike and log structures along the southern edge of the Forest Service property. Work is currently underway with the Forest Service, Skagit County, and adjacent private property owners to further develop the conceptual alternative and secure support to proceed to final design and construction.

Project Status/Timeline
A feasibility study and the development of a conceptual alternative has been completed (2009). Work is underway with the Forest Service, Skagit County, and adjacent private property owners to further develop the conceptual alternative and secure support to proceed to final design and construction.

Primary Project Contact
Devin Smith, Senior Restoration Ecologist

Funding Sources
Washington State Salmon Recovery Funding Board

Project Partners
United States Forest Service (Mt. Baker-Snoqualmie National Forest)