Dickerson Creek Culvert Replacement

Fish are a critical natural resource in Washington State. Salmonid species are the backbone of the state’s fishing industry and an important cultural icon for Washington Tribes, but over the last century fish populations have been decimated—in part due to human infrastructure. Culverts and bridges often create obstacles that prevent salmonid fish from accessing their historical upstream spawning and rearing habitat. To correct this ecological and economic issue, departments of transportation and local municipalities are working to remove these fish barriers by renovating or replacing stream crossings.

Kitsap County wanted to replace two existing fish barrier culverts conveying Dickerson Creek under David Road and Taylor Road and decided to take the opportunity to also restore and enhance riparian and floodplain habitat along the entire reach between these two road crossings, as well as downstream to the confluence with Chico Creek. GeoEngineers completed habitat characterization, environmental permitting, and geotechnical engineering design for the project. The team also provided biologic monitoring to ensure that sensitive fish species would not be harmed during construction.

Our scientists identified a nearby section of another creek with limited human impacts to use as a “reference reach.” The team performed habitat characterization along both the reference reach and project reach to identify specific design objectives and criteria for improvements that could be incorporated. Habitat recommendations included identifying floodplain expansion areas, specifying the quantity and type of large woody material added to the in-stream habitat, and a comprehensive riparian planting plan.

GeoEngineers’ team worked closely with project-lead Northwest Hydraulic Consultants on an in-water work plan that would satisfy the requirements of the many regulatory agencies involved. Our biologists secured permits for and then monitored the complex dewatering and fish-removal plan necessary to complete construction. Dickerson Creek was diverted after GeoEngineers staff worked with others to safely remove and relocate fish from the channel.

In addition to environmental and biologic services, GeoEngineers delivered geotechnical recommendations for the two culverts. The team investigated the site and found the soil competent enough for shallow spread footings but advised that to construct them Dickerson Creek would need to be temporarily dewatered or redirected around work areas.

Approach

• Habitat Characterization: Biologists researched information on streams, wetlands, and priority plant, fish and wildlife species documented within the vicinity before performing on-site assessments. Habitat characterization included a wetland delineation, Ordinary High-Water Mark (OHWM) determination and in-stream habitat assessment. The team found a nearby “reference reach” with few human impacts and used it as a guide for habitat baselines.
• Environmental Permitting: As environmental consultant, GeoEngineers secured a Nationwide Permit (NWP) from the U.S. Army Corps of Engineers for compliance with the Clean Water Act, Endangered Species Act consultation with the National Marine Fisheries Service using a programmatic Biological Opinion process, and a Fish Habitat Enhancement Hydraulic Project Approval (FHE-HPA) from the Washington Department of Fish and Wildlife.
• Habitat Enhancement: The client asked GeoEngineers to provide a detailed riparian planting plan to restore and enhance habitat in this reach of Dickerson Creek.
• Biological Monitoring Services: During the in-water work window, GeoEngineers scientists monitored and supervised work area isolation and fish removal activities as areas of Dickerson Creek were dewatered and diverted to allow construction.
• Geotechnical Recommendations: GeoEngineers investigated and characterized soil conditions at the two culvert sites and recommended shallow spread footings to support the new designs. The team also delivered recommendations for temporary cut slopes, fill, groundwater handling and shoring. The team’s previous experience with culverts also led them to suggest design features that would reduce the risk of scour.

Results

The project successfully constructed new, fish-friendly culverts for Dickerson Creek under David Road and Taylor Road, along with approximately 800 feet of enhanced floodplain and riparian habitat that will support fish and the overall health of the stream system. Without barriers at these two crossings, salmonid fish can once again access upstream spawning and rearing habitat.