Mason Flats Wetland Enhancement stormwater and wetland project is located within the Big Four Corners Natural Area (NE 170th and Airport Way). Farmed for many years, the site borders two waterways, cold water springs and historic wetlands. Environmental Services and Portland Parks & Recreation own the site.
New grading reduces stormwater pollutants from more than 600 acres of upland roads and development. Additional water flow and shallow channels connect the site to nearby cold springs and improves water quality. Increased tree canopy in the summer will also help cool the slough. The project also increases off-channel floodplain and flood storage in the former floodplain of the Columbia River where more than 90% of wetlands have been filled or developed.
BES placed numerous standing logs, root wads, and rocks to increase habitat for sensitive wildlife species, especially redlegged frogs, native fishes, birds and turtles. More shrubs will especially benefit willow flycatchers and yellow warblers. Several existing ponds and their unique aquatic vegetation remain untouched. Beavers are active on the site and beaver dam construction has been continuous in recent years. The effects of beaver dam building provide additional benefits in this wetland area.
Mason Flats is also providing new nesting habitat for turtles. Two long south-facing slopes and additional mounds of gravelly soil have been designed for turtle nesting. Western Painted turtles use ponds in the eastern portion of the site and the gravel and sun-warmed sites are preferred and necessary for egg incubation.
Mason Flats has been partially planted with grass, willow cuttings and shrubs. It already looks fabulous. Multiple benefits from projects like these are called for under Portland’s Watershed Management Plan and the City’s Migratory Bird Act responsibilities.