Johnson Creek Confluence & Milwaukie Bay Habitat Enhancement

Critical fish habitat is enhanced in the alluvial fan of a key cold water tributary to the Willamette River.

The confluence of Johnson Creek and the Willamette River in downtown Milwaukie is a dynamic site for both aquatic organisms and the people of the greater Portland region. The creek, a cold water source, meets the river in a cove that is the site of Milwaukie Bay Park, which the public uses heavily for kayaking, boating, and swimming. It is also a site of critical refugia and rearing habitat for salmon and steelhead. The confluence provides a water quality refuge for fish that enter Johnson Creek to spawn, but also for those that will continue to migrate up the Willamette River to hundreds of other tributaries and spawning sites.

Implementing a design prepared by Wolf Water Resources, Biohabitats helped restore and futureproof critical habitat by installing two large deflector log jams, eight small distributed scour/racking log structures, and eight small nearshore habitat cover log structures. Before installing the structures, Biohabitats led mobilization, stream diversion and dewatering, and coordination of fish salvage with the Council and Oregon Department of Fish and Wildlife staff. These were critical stages of the project, as the presence of lamprey ammocoetes within the alluvial fan called for a slow, methodical dewatering strategy.

The project presented unique challenges related to work area isolation. The site sits within the tidal prism of the lower Willamette River and the channel of Johnson Creek, the largest tributary to the Willamette in Portland. High tides would flood the project area twice daily. Biohabitats developed a plan to temporarily divert Johnson Creek flows around the work area using a coffer dam and excavated channel. To handle tidal inundation, Biohabitats developed a work schedule to take advantage of low tides, with work occurring during daylight hour low tides. The isolated area was encapsulated with floating turbidity curtains. Fish and wildlife were identified and salvaged from the area after every high tide.

The project improves retention and hydraulic separation of cold water inputs from Johnson Creek, increases fish cover habitat, and encourages cool hyporheic flow inputs throughout the creek’s alluvial fan.

TAGS

• Construction
• Ecological Restoration