Marys River In-Stream Restoration

The Upper and Middle Marys sub-basins are lower gradient systems with a legacy of beaver presence. Historically, these sections of the watershed provided downstream benefits like flood and drought mitigation, water filtration, and water cooling. Beaver removal and channelization removed many of the ecosystem benefits for downstream communities and hurt in-stream habitat quality. In order to restore the Upper and Middle Marys, the Watershed Council installed beaver dam analogs, reconnected side channels, addressed fish passage concerns, and conducted riparian planting to restore sections of the Upper and Middle Marys. Barrier removal, beaver restoration, and side channel reconnection in the Upper and Middle Marys complement each other to recreate new high-quality habitat for aquatic and riparian species.

The Watershed Council was supported by the Oregon Watershed Enhancement Board, the Marys Peak Stewardship Group of the Siuslaw National Forest, the Confederated Tribes of Siletz Indians Forest Product Request program, USFS, Benton County Public Works, Aggregated Resources, and private landowners. The restoration project provides benefits to native aquatic species like beaver, cutthroat trout, and Pacific lamprey.

The Upper and Middle Marys was a historically beaver-dominated ecosystem. Beavers created large, low-gradient and ponded complexes that slowed and spread water while providing habitat to other aquatic species like cutthroat trout and Pacific lamprey. Early landowners in the watershed trapped beavers and removed dams to develop the land underneath. Beaver removal created incised and simplified streams that provide fewer benefits for nearby ecosystems and downstream communities. The Watershed Council chose to install a type of beaver dam analog called post-assisted log structures in each creek. Post-assisted log structures are made by weaving tree branches into posts driven into the streambed. The structures mimic some of the effects of beaver dams and encourage beavers to take up residence where they can continue to maintain the log structures and build new dams.

 Watershed Council staff identified Devitt Creek and the West Fork Marys River as restoration priorities in the Upper and Middle Marys basin because of their salmonid habitat potential and conditions suitable for beaver recolonization. These new dams will reestablish some of the historic Upper and Middle Marys beaver dam complex and address concerns about high stream temperatures and downstream drought and flooding.

Beaver removal in the Willamette Valley disconnected streams from their floodplains. Historically, water would have formed meandering and branching channels across the Marys River floodplain. Researchers have found that side channels and alcoves provide thermal refugia to native trout and amphibians by maintaining different temperature water than the mainstem river. This would have provided habitat for diverse species and mitigated the impacts of extreme events like floods and fire. After beaver removal, high-velocity channels formed that dug into soft alluvial sediments and created deeply incised and erodible banks, decreasing habitat quality and increasing environmental risk. 

The Watershed Council reconnected historic side channels and alcoves to the mainstem river. Side channel and alcove reconnection projects remove barriers between the main channel and the floodplain and allow the river to reestablish complexity. Reconnected floodplains allow more water to be absorbed into the ground and mitigate flood damage. Alongside the floodplain reconnection, the Watershed Council installed ten large woody debris structures and planted over 3 acres of riparian trees. These actions help increase the overall complexity and resilience of the floodplain. The changes increase habitat quality in the creek for native aquatic and riparian species like otters, muskrats, and cutthroat trout.

The effectiveness of Marys River restoration work in providing and enhancing habitat for migratory aquatic species could be limited by fish passage barriers in the upper watershed. The upper reaches of most streams in the Marys River watershed contain the highest quality spawning and summer refugia habitat. Removing fish passage barriers allows fish species to move to these high-quality and recently restored habitats. Watershed Council staff identified four fish passage barriers to remove, including undersized and washed-out culverts and a perched railroad trestle.

After the Watershed Council identified fish passage barriers, they were removed or replaced. The Watershed Council reestablished fish access to 5.6 miles of in-stream habitat by addressing the fish passage barriers. This allowed native species like cutthroat trout, steelhead, and Pacific lamprey to access high-quality habitat. The removal of these barriers helped maximize the positive impact of our nearby restoration projects.