SOUTH BACHELOR ISLAND
This year’s RRNW Symposium field trip will be to South Bachelor Island. This restoration project was completed in 2019 in partnership with the Washington Department of Natural Resources, Bonneville Power Administration, US Fish & Wildlife Service, and the Columbia River Estuary Study Taskforce. This is a case study of the potential to create and restore shallow water habitats in human-placed dredge spoils. The South Bachelor Island Restoration Project was completed in 2019 in partnership with Washington Department of Natural Resources, Bonneville Power Administration, US Fish & Wildlife Service, and the Columbia River Estuary Study Taskforce. This multispecies restoration project is a case study of the potential to create and restore shallow water habitats in human placed dredge spoils. For more than 100 years, the USACE has deepened the Navigation Channel of the lower Columbia River to accommodate commercial shipping, with dredged materials placed along the margins of the river. In many cases, this has transformed productive shallow water wetland habitats into uplands, which are inaccessible to fish and other aquatic species.
At RM 90, just upstream of the confluence with the Lewis River in Washington, over 1.5 million cubic yards of dredged spoils were placed within the mainstem along Bachelor Island by the USACE. This effectively covered nearly all existing shallow water habitat, leaving a groundwater connected floodplain lake in the center. The South Bachelor Island Restoration Project excavated approximately 120,000 cubic yards of historically placed dredge material to create a 2,300 ft channel that reconnected the remnant 40 acre open-water wetland to the Columbia River mainstem. Key for waterfowl and turtles was an ability to retain water in the wetland year-round, despite significant seasonal changes in the mainstem. Additionally, it was important to design a self-maintaining channel, despite being carved through sand with a slow revegetation rate.Unique to this project was the placement of excavated material downstream of the channel along the riverbank to be slowly released back into the channel over time. Another unique component was the modification of the remnant pile-dike structure that crossed the wetland, in an effort to improve tidal exchange through the channel. As we continue to manage rivers to provide multiple benefits, determining innovative ways to restore habitat within an altered system will be critical to salmon recovery.