Coos Watershed Association (CoosWA)
The East Fork (EF) Millicoma River is the largest tributary to the Millicoma River in the Coos River basin and has the potential to provide habitat to important aquatic species such as fall chinook, chum, Coho, steelhead, and cutthroat. Originally, 2 trestle bridges spanned the EF Millicoma River at Mile 7 on the Weyerhaeuser Allegany Mainline, where a tight meander bend crossed under the mainline twice within 500 feet due to a resistant ridgeline. When the road was rebuilt in 1958, the ridgeline was blasted to create the "Bypass Chute" that channelized the entire flow of the EF Millicoma River, and the 2 trestle bridges were buried with fill from the blasted ridge. The channelization reduced the effective stream reach from the 0.6 mile "Oxbow" to under 0.1 miles, over which the river dropped roughly 20 feet in elevation. Increased streamflow velocities over the stepped bedrock chutes substantially impeded adult salmonid passage and cut off all juvenile passage through the chute to the 16 miles of habitat upstream of the Oxbow.
Collaborations among CoosWA, Weyerhaeuser, and Oregon Department of Fish & Wildlife (ODFW) began in 2006. CoosWA was awarded 2 OWEB technical assistance grants (#209-2011 and #213-2014) to analyze project alternatives to improve passage through this reach. From these, the Oxbow Reconnection project was developed to replace the 2 historic bridges, fill in the Bypass Chute, and divert the EF Millicoma River back through the 0.6 mile historic channel to reconnect 0.6 miles of original habitat. The channel grade was reduced from 6% over nearly 200 feet to less than 1% over 3,168 feet. McGee Engineering developed the bridge and channel plug designs.
West Coast Contractors constructed both bridges by July 2016. LBA Contract Cutting then moved 60,000 cubic yards of earth from under the newly constructed bridges and placed it in the Bypass Chute to construct the engineered channel plug. On August 23, 2016, the entire flow of the EF Millicoma River was diverted into the Oxbow. Water pumps ran 24 hours prior to the diversion to pre-wet the Oxbow and establish a baseflow downstream of the project site to assist with fish salvage during the reconnection. Nearly 30 volunteers from CoosWA, ODFW, Weyerhaeuser, Bureau of Land Management (BLM), US Fish & Wildlife Service (USFWS), and Coos Soil & Water Conservation District (Coos SWCD) were on site to help with fish salvage in the Bypass Chute and downstream of the project site. The entire EF Millicoma River was reconnected and freely flowing through the Oxbow after 38 hours. All construction was completed by September 14, 2016.
CoosWA and ODFW developed a monitoring program for a minimum of 6 years that will evaluate the effectiveness of the oxbow reconnection. There is a long history of spawning data throughout the basin with 2 standard OASIS survey reaches above and below the project site. Crews will conduct spawning and snorkel surveys above and below the Oxbow site to determine if there has been a shift in adult salmonid distribution basin wide. CoosWA is also working on basin-wide restoration for the EF Millicoma with instream habitat, road sediment reduction, and fish passage improvement projects.
Photos courtesy of CoosWA. Each row shows before and after the project from a different photo point.
: looking downstream at the Bridge 4 inlet
: looking upstream from Bridge 4 into the bottom of historic Oxbow Channel
Bottom row: looking downstream into the bypass chute (now the top end of the channel plug)
For complete reports on this and other OWEB projects, please search OWEB's Grant Management System (OGMS).