The Sandy River is heavily influenced by past volcanic activity on Mt Hood which filled the drainage basin with fine sediments. The river is still adapting to the influx of these lahars as it erodes and deposits bed and bank material shifting position across the valley. Needing to improve habitat and protect recreational infrastructure along the Sandy River, the Portland Water Bureau hired Wolf Water Resources (W2r) to help increase side channel and floodplain connectivity for several projects sites located at Dabney State Recreational Area and Oxbow Regional Park.
A landslide in Dabney Park blocked and rerouted a tributary stream to the Sandy River floodplain, cutting off over 3,000 feet of habitat. The restoration design for this site reconnects the stream to its previous alignment and enhances floodplain, channel, and wetland habitats. Careful consideration of what existing site features could be preserved was key to W2r’s engineering approach and to the project’s success. For example, by preserving the floodplain forest and wetlands, the project reconnected complex floodplain habitats providing both cold water and stream velocity refuges.
Rather than rely on LiDAR or conduct extensive topographic and tree surveys, W2r designed the project on the ground and used this information for modeling and permitting. This approach not only minimized impacts to the floodplain forest and wetlands, it reduced costs by ensuring the design addressed specific site constraints. W2r surveyed and staked a reconnection channel around the landslide to maintain connections to wetlands and greatly reduce the number of trees to be impacted/removed. Fill was strategically located to guide overtopping flows along the stream, rather than short cutting to the river and causing avulsion. A large, lush wetland that had formed as a result of the landslide was preserved as a backwater habitat for fish, turtles and frogs.
During construction of this project, large wood was installed by helicopter and channel work implemented by a low ground pressure wide-tracked excavator to minimize impacts to riparian vegetation and park activities. Construction was completed in 2017 with observed salmonid use that following winter.
Along with restoration efforts at Dabney Park, W2r assisted Metro Parks and Greenspaces in restoring four sites at Oxbow Regional Park. Click here for a description of restoration projects at Oxbow Park.