Foster Floodplain Natural Area Portland, Oregon
In restoring 5,600 feet of stream bank and retrofitting seven stormwater outfalls, a flood-prone neighborhood was transformed into the Foster Floodplain Natural Area, benefiting both regional wildlife and the surrounding community. The large undertaking was completed in close collaboration with the City of Portland and also spurred the Springwater Wetlands restoration. Otak provided both the restoration and transportation design, including hydraulic modeling and topographic surveying while supporting public involvement, permitting, and construction.
Transforming a Flood-Prone Neighborhood into Habitat and a Public Asset
Centered on a reach of Johnson Creek, the very wide and complex nature of the Foster Floodplain posed unique challenges to managing flooding in for the area. The restoration design required a thorough understanding of the geomorphology and flooding dynamics in the area, developing an unsteady flow hydraulic model that properly evaluated the acre-feet of flood storage capacity available within the project footprint. Based on this modeling, design alternatives accounted for 10-year storm, 25-year flood, and 100-year flood events. That data also supported floodplain permitting as well as both Conditional Letter of Map Revision (CLOMR) and Letter of Map Revision (LOMR) applications. The excavation and grading combined with a hydraulic control structure maximizes flood storage in the area while the removal of existing bank armoring and addition of vegetated stormwater facilities contribute to improved water quality. Three of the stream’s outfalls would also be redirected as part of mitigation efforts and log jams were engineered to protect the stream banks from lateral migration toward major infrastructure while still allowing the channel to naturally adjust in other locations. From various fish to the Red-Legged Frog and Bald Eagle, the area provides improved habitat for a wide range of the region’s native species.
Through a Willing Seller Acquisition Program, the City of Portland purchased land from 60 families and helped them move out of the 100-year floodplain and expand the natural area. With 1,000 feet of new roadway and utilities, access for service and remaining homeowners was maintained despite the removal of three bridges. Another 1,800 feet of multi-use trail, including a pedestrian bridge, as well as a parking lot and sidewalks along Foster Road add to the community accessibility of this public asset.
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