4 minute read
Horsetail and Oneonta Creek
Corbet, Oregon, United States
Restoring stream and floodplain habitat for migrating salmon. Between 1900 and 1960, land use transformed the Horsetail and Oneonta Creek floodplain, near the confluence with the Columbia River—conversion of a forested wetland to cattle pasture, construction of major transportation routes, the straightening and rerouting of creek channels through borrow ponds remaining from gravel mining activity. All of these changes were problematic for salmon. The cold water from the upstream watershed became too warm in the summer from a stagnant borrow pond; and stretches of the streams lacked shade, limiting its use as a cold-water refuge. Further, salmon could only reliably access the culvert running under the interstate during high water, typically spring. Finally, the straightened streams lacked suitable habitat, like fallen trees, where salmon could hide or rest. Therefore, in 2010, the Lower Columbia Estuary Partnership undertook restoring the streams and former floodplain, aiming to reduce thermal loading and to enhance the habitat quality. With construction complete in 2013, replanting and maintenance of established plants occurred over the next several years. The project is a model for implementing complex floodplain and stream restoration in a heavily impacted area.
Article cover: A new alcove is an example of the created floodplain rearing habitat that was built with in-stream large wood and riparian habitat elements. (Photo by Inter-Fluve)
Producing Efficiencies
An assessment and feasibility study led to detailed designs. The project team routed flows through the historical channels, avoiding the warm water of the gravel pit. The team also partially filled in the gravel pit to reduce water depths and surface area, which enhanced the floodplain and emergent wetland habitat. To offset the lack of large woody debris for fish habitat and beaver dams, the team installed approximately 700 pieces across the site, using a helicopter due to site access and sensitivity issues. Finally, the team modified the interstate’s culvert to provide year-round access by migrating fish, including Pacific lamprey (Entosphenus tridentatus).
Using Natural Processes
Placing large woody debris in the restored streams, as well as planting trees in the area, created immediate areas of habitat cover for fish while also providing future sources of woody debris. The channels mimic predisturbance conditions and foster natural system responses on the floodplain and in the stream. The restoration mimics the natural processes of erosion, sediment transport and deposition, channel migration, and large wood recruitment. In this way, the project corrected anthropogenic disruptions, which allows the system to recover with minimal intervention.
Broadening Benefits
The project team took a process-based, interdisciplinary approach that combined engineering, hydrology, geology, geomorphology, botany, fisheries biology, and wetlands science, restoring the balance between human and fish needs. It reduces summer thermal loading in both Horsetail and Oneonta Creeks and improves floodplain habitat quality and access for adult and juvenile threatened and endangered salmonids, such as Chinook (Oncorhynchus tshawytscha), coho (O. kisutch), and chum (O. keta). The newly restored streams now provide migrating salmon another option for suitable habitat as they make their way downstream to the Pacific.
Promoting Collaboration
The project represents a collaboration with local governments, other state agencies in Oregon, U.S. Fish and Wildlife, National Marine Fisheries, and nonprofit and private stakeholders. Additionally, in 2013, a complex construction sequence involved coordination with several other stakeholders, including the U.S. Forest Service, the Oregon Department of Transportation, Cascade Locks Electric, the Union Pacific Railroad, and the many regulatory entities with jurisdiction over the area.
