Projects

Nason Creek River Mile 2.3 Side Channel & Floodplain Reconnection Project

A major spawning area for spring Chinook salmon, steelhead, and bull trout and providing foraging, migration, and over-wintering habitat, Nason Creek in the Wenatchee watershed has been identified as the top-priority stream for habitat restoration. Given the good potential for increasing the abundance and productivity of Endangered Species Act-listed salmonids, it is a high priority to restore ecosystem function in Nason Creek by reconnecting off-channel habitats and floodplain.

Chelan County Natural Resources Department selected Rio ASE to design a project that would provide high flow and temperature refugia as well as year-round rearing habitat for juvenile spring Chinook and steelhead in Lower Nason Creek near river mile 2.3. The preferred alternative included reconnecting the mainstem Nason Creek to a historical oxbow. The project also included installation of two mainstem engineered log jams to increase flow activation through the oxbow, promote increased lateral channel migration, and provide hydraulic diversity and habitat. Under existing conditions, Nason Creek only activated the oxbow and adjacent wetland with a surface water connection at approximately the 25-year flow event. Once constructed, this project provided  fish perennial access to the side channel habitat, creating over 2 acres of juvenile off-channel rearing and refugia habitat.

Rio ASE provided geomorphic and engineering design (hydrology, hydraulics, stream design, riparian planting zones, and engineered log jam designs) from concept through final design. Major features of the design included excavation of 2,325 feet of new side channel, two engineered log jams, placement of small log habitat structures, and revegetation of native species with the riparian zone.

Side channel inlet (right) and engineered log jam (left) with racked large wood, photographed 3 years post-construction.