Social, Economic and
Sustainable Design Considerations
Project: Hansen Creek Alluvial Fan and Wetland Restoration
Herrera Environmental Consultants was able to transform Hansen Creek in Skagit County from a constrained channel with dredge spoil levees to a beautifully restored and productive alluvial fan and wetland floodplain with walking trails for the public.
Removing levees to open a floodplain of 140 acres in an area surrounded by homes, farms, bridges and roads required the collaboration of engineering, geomorphology, hydraulic modeling, fishery, wetland and revegetation experts.
The Hansen Creek project has been cited by the National Park Service and the U.S. Environmental Protection Agency as a model for how large-scale habitat restoration projects can be done in a manner that enhances fish and wildlife habitat while protecting infrastructure. The project includes:
• Two levee setbacks aimed at restoring and reconnecting the natural floodplain.
• Constructed floodplain restoration, including 65 acres of wetlands, 66 acres of alluvial fan and three miles of meandering distributary channels throughout these habitats, which increased salmon habitat 10-fold.
• Strategic placement of over 300 in-stream and floodplain engineered-log structures, which provided habitat complexity and floodplain roughness to help restore alluvial fan functions.
• Excavation of over 200,000 cubic yards of fill materials to restore alluvial fan and floodplain wetlands.
• Planting of over 105,000 plants, including trees, shrubs, live stakes and emergent vegetation plugs.
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