Projects: Flood Control: Fisher Slough Design Plan
Fisher Slough Site Assessment and Restoration Design Plan – Skagit County, Washington
The Fisher Slough Site Assessment and Restoration Design Plan is a levee setback project to improve chinook juvenile rearing habitat conditions as well as improve flood storage for upstream tributaries to the S. Fork Skagit River. The Fisher Slough restoration project will maximize the area influenced by natural stream and tidal processes, allow for a broad range of ecosystem variability, restore estuarine rearing habitat for juvenile and improve flood protection and storage capacity for Carpenter Creek and adjacent tributaries.
The project involved development of detailed, interdisciplinary site assessments for several technical disciplines including:
- Geomorphology, landscape and land use
- Habitat and vegetation
- Hydrology and hydraulics
- Civil design and mapping
The geomorphologic, landscape and land use assessment characterized natural landscape processes, hazards, hydrologic runoff and sedimentation characteristics in relation to existing and future land uses. The geomorphology and landscape information was used in conjunction with a HEC-HMS hydrologic runoff and HEC-RAS unsteady flow routing model of the watershed tributaries and channelized ditch system, to evaluate existing conditions and concept design projects and management strategies to reduce flood and sedimentation problems in the upper watershed.
Output from the watershed assessment (routed hydrologic runoff and sediment loads) were then used with a MIKE-11 model in the tidally influenced Fisher Slough project area to evaluate existing conditions and develop concept alternatives, a preferred restoration plan and detailed cost estimates. Predictive estimates of habitat and vegetation composition and tidal channel morphologic characteristics were used to develop concept alternatives and finalized the preferred plan.
The Tetra Tech team provided a variety of services to the client in developing the preferred restoration plan.
- Interdisciplinary site assessment (geomorphology, habitat and vegetation, hydrology and hydraulics)
- Conceptual design plans
- Hydrologic runoff and hydrodynamic modeling
- Agency workshop and public meetings
- Alternatives assessment methods and preferred alternative recommendations
- Civil design and cost estimating of flood control and habitat restoration measures
Specific project elements of the design include:
Watershed Flood and Sedimentation Concept Design Elements and Management Strategies
- Levee removal and setbacks
- Floodgate retrofit
- Tributary and wetland restoration
- Irrigation canal siphon crossing
- Flood and sediment easements
- Culvert replacements
