- Before: The steep, riprap-lined, leveed banks limited stream-side vegetation and floodplain access.
- After: Hardened levee removed and floodplain access restored. LWD and side channel increased juvenile rearing by 600%.
- GeoEngineers removed a levee along the Walla Walla River and reestablished the historic landscape of the site by reconnecting approximately 10 acres of riparian floodplain, dramatically increasing habitat and passability for Chinook and steelhead.
- Walla Walla River after the levee was removed and habitat structures were installed. Habitat complexity increased dramatically.
- Before: The inactive floodplain and one continuous riffle lacked desirable habitat diversity.
- Natural river and floodplain habitat restored. Chinook salmon successfully spawned at this location one year after construction.
Walla Walla River Habitat Restoration
Rehabilitating a diverse river habitat increased fish population and restored floodplain function.
GeoEngineers developed a natural habitat restoration design for a 3,000-foot reach of the Walla Walla River near Milton-Freewater, Oregon for the Confederated Tribes of the Umatilla Indian Reservation.
The Tribes were concerned about the lack of juvenile fish-rearing habitat through a reach of the river where spring Chinook and steelhead spawn each year. The Walla Walla River, through the project site and sur-
rounding reaches, has been unnaturally confined, resulting in river conditions poorly suited for juvenile rearing. The Tribes were looking for a solution that would increase fish-rearing habitat in a more natural river and floodplain setting.
To address these challenges, GeoEngineers first assessed the existing conditions at the project site and watershed. Analytic techniques included habitat assessments, geomorphic assessment, hydraulic modeling, hydrologic modeling and sediment transport analysis.
Next, GeoEngineers worked with the Tribes to develop three conceptual restoration alternatives that the project team presented to local stakeholders and regulatory agencies for comment. From that point, the team applied all the available information into a final design package, consisting of plans, specifications, contractor bid documents and a basis-of-design report. We also prepared a no-rise analysis, which documented that the design would yield a net decrease in base flood elevations throughout the project reach. The local Water Control Board reviewed the no-rise analysis favorably and the County subsequently approved it.
GeoEngineers assisted the Tribes at the pre-bid tour by describing the details of the project and answering the prospective contractors’ technical questions. Project construction occurred in summer 2011, and GeoEngineers provided construction observation and guidance to the contractor throughout the construction period.
Completing this highly technical project required a collaborative, interdisciplinary team of scientists and engineers. GeoEngineers’ interdisciplinary River Team is unique to the industry because we treat individual sites as part of the larger watershed and its processes.
- Our team looked beyond the project area and applied site-specific treatments that function within the natural watershed processes, physical landscape and infrastructure constraints.
- GeoEngineers’ experts in hydrology, hydraulics, fluvial geomorphology, geology and ecology collaborated to create a project that will work harmoniously with the surrounding environment and will maintain itself.
- By removing approximately 2,500 linear feet of levee that had confined the Walla Walla River, we restored the river’s access to its historic floodplain and increased vegetation area adjacent to the channel, habitat diversity for fish populations and juvenile rearing habitat and spawning habitat.
- Increased juvenile fish-rearing habitat by more than 600 percent by constructing 1,100 linear feet of perennial floodplain side channel. Juvenile population increased significantly once construction was completed, and the next spring, steelhead redds began to occupy the restored side channel.
- Provided channel stability and secure cover for both fish and wildlife by placing more than 650 trees and root wads for engineered log structures throughout the river, side channel and floodplain.
- Created channel stability and habitat benefits by placing more than fifty 2,000+ pound boulders.
- Developed a natural-appearing, roughened riffle. This riffle functions as fish and aquatic wildlife habitat while providing bed-elevation grade control.
- Reestablished the historic landscape of the site by reconnecting approximately 10 acres of riparian floodplain, dramatically increasing habitat for terrestrial and avian wildlife communities, while increasing ecological productivity that will result in conditions more conducive to rearing Chinook and steelhead.