South Fork Skagit River Estuarine Off-Channel Habitat Design (Diking District #3)

Skagit County Public Works

Skagit River, Washington

South Fork River Design

Hart Crowser designed off-channel habitats to optimize juvenile salmon rearing within tidal freshwater reaches adjacent to the South Fork Skagit River. We conducted detailed hydrologic modeling and geotechnical analyses of the selected alternative to optimize channel design stability, determine the benefits of shaving the existing dike along the river to increase channel inundation, determine the risks to the existing setback levee protecting adjacent agricultural lands, and ensure that the created juvenile salmon off-channel habitats will not adversely impact adjacent agricultural areas in case of tidal inundation and flooding.

Our design included channel buffers at lower elevations to encourage a robust wetland community while avoiding mature riparian trees. Channel excavation volumes will be used along the existing levee setback and vegetated with a native riparian community to augment ecological functions while minimizing disposal costs. We also served as technical participants in public meetings during the design process.