Clean Water Program

Public Works


Cedar Grove Fish Passage Project Description The Cedar Grove Fish Passage Project is primarily focused on improving fish passage upstream of the Ovenell Slough, which is currently constricted by an existing culvert. The preexisting culvert was 2 feet wide and 80 feet long, and buried under almost 18 feet of fill. The project is located south of Concrete, downriver of the Baker River confluence on Ovenell Slough. The slough is primarily fed by springs, and functions as backwater except when the Skagit floods and flows through the channel. Aerial image showing the Ovenell Slough and the Cedar Grove Culvert. Various fish species use this off-channel habitat, including stickleback, cutthroat, Coho, Chinook, and long-nose dace. The existing culvert is undersized and blocks fish access to over 2.4 acres of upstream habitat, which is excellent rearing habitat created by numerous beaver dams. Improving fish passage is typically the most cost-effective way to benefit salmon. This project restores access to fish habitats that are particularly important for fish rearing. Feasibility Skagit Fisheries completed analysis of five preliminary design alternatives, which included no action, full removal, a pedestrian bridge, a vehicular bridge, and an improved culvert. These alternatives were examined and ranked by cost, feasibility, fish access, and other metrics. For various reasons, no action was not advanced, primarily because the preexisting culvert is a barrier to fish passage. Complete removal of the culvert was also not feasible, because it does not meet requirements of the Lands and Water Conservation Fund. A larger culvert did not meet the goal of restoring natural processes and was considered too small for ideal fish passage. Lastly, no vehicular access was needed to the property, and therefore the pedestrian bridge was preferred. The pedestrian bridge was selected as the most feasible option with the highest benefit-to-cost ratio. This design ranked highly in many metrics compared to the other options including cost, fundability, feasibility, and fish passage. Preexisting Cedar Grove culvert before construction. Design Initially, the preferred alternative was a 125-foot bridge with a 40-foot opening. To reduce cost, Skagit County worked with Natural Systems Design to determine the appropriate bridge length and size of the opening. Using geomorphic reach assessments, Natural Systems Design recommended a 24-foot opening. The final design of the project was drafted by KPFF Consulting Engineers, which transitioned the preliminary design to the final design. The pedestrian bridge design is 77 feet long with a 24-foot opening and has a 6.6% slope. Construction Structural work began June 2022 and was completed October 2022. Replanting occurred in November 2022 with maintenance extending through the end of 2023. Project Funding The Cedar Grove Fish Passage Project is supported by funding from the Salmon Recovery Funding Board, National Fish and Wildlife Foundation, Department of Ecology, Puget and Sound Energy. The total project cost $1,088,428.82 through December 2022. This includes design, construction, and riparian restoration. Cedar Grove Fish Passage Funding (project is in progress and funding totals may change as the project is completed). Contact Information Emily Derenne - Project Manager, Habitat Restoration Specialist 360-416-1449 emilyjd@co.skagit.wa.us

Cedar Grove Fish Passage

Project Description

The Cedar Grove Fish Passage Project is primarily focused on improving fish passage upstream of the Ovenell Slough, which is currently constricted by an existing culvert. The preexisting culvert was 2 feet wide and 80 feet long, and buried under almost 18 feet of fill.

The project is located south of Concrete, downriver of the Baker River confluence on Ovenell Slough. The slough is primarily fed by springs, and functions as backwater except when the Skagit floods and flows through the channel.

Aerial image showing the Ovenell Slough and the Cedar Grove Culvert.

Various fish species use this off-channel habitat, including stickleback, cutthroat, Coho, Chinook, and long-nose dace. The existing culvert is undersized and blocks fish access to over 2.4 acres of upstream habitat, which is excellent rearing habitat created by numerous beaver dams. Improving fish passage is typically the most cost-effective way to benefit salmon. This project restores access to fish habitats that are particularly important for fish rearing.

Feasibility

Skagit Fisheries completed analysis of five preliminary design alternatives, which included no action, full removal, a pedestrian bridge, a vehicular bridge, and an improved culvert. These alternatives were examined and ranked by cost, feasibility, fish access, and other metrics.

For various reasons, no action was not advanced, primarily because the preexisting culvert is a barrier to fish passage. Complete removal of the culvert was also not feasible, because it does not meet requirements of the Lands and Water Conservation Fund. A larger culvert did not meet the goal of restoring natural processes and was considered too small for ideal fish passage. Lastly, no vehicular access was needed to the property, and therefore the pedestrian bridge was preferred.

The pedestrian bridge was selected as the most feasible option with the highest benefit-to-cost ratio. This design ranked highly in many metrics compared to the other options including cost, fundability, feasibility, and fish passage.

Preexisting Cedar Grove culvert before construction.

Design

Initially, the preferred alternative was a 125-foot bridge with a 40-foot opening. To reduce cost, Skagit County worked with Natural Systems Design to determine the appropriate bridge length and size of the opening. Using geomorphic reach assessments, Natural Systems Design recommended a 24-foot opening.

The final design of the project was drafted by KPFF Consulting Engineers, which transitioned the preliminary design to the final design. The pedestrian bridge design is 77 feet long with a 24-foot opening and has a 6.6% slope.

Construction

Structural work began June 2022 and was completed October 2022. Replanting occurred in November 2022 with maintenance extending through the end of 2023.

Project Funding

The Cedar Grove Fish Passage Project is supported by funding from the Salmon Recovery Funding Board, National Fish and Wildlife Foundation, Department of Ecology, Puget and Sound Energy. The total project cost $1,088,428.82 through December 2022. This includes design, construction, and riparian restoration.

Cedar Grove Fish Passage Funding (project is in progress and funding totals may change as the project is completed).

Contact Information
Emily Derenne - Project Manager, Habitat Restoration Specialist
360-416-1449
emilyjd@co.skagit.wa.us