From the Mckenzie River Reflections

A white spray towered over observers standing on top of the Cougar Dam powerhouse, left, on Saturday after a concrete plug was removed. That action caused a surge of muddy water to rush downstream, right.

BLUE RIVER: A huge white spray was followed by muddy waters when dynamiters blew out a concrete plug at the base of Cougar Dam on Saturday.  Spectators had to wait longer than expected after a last minute decision was made to remove more equipment from the dam's diversion tunnel. Around 12:45, their patience was rewarded as sirens blared and an explosion a quarter mile under ground was let loose.

   More than two-thirds of the plug had already been taken out in previous blasts. The final explosion was the most critical since it would reopen the old tunnel.
   When Cougar Dam was being built in the 1960s, the tunnel was used to divert river water away from the construction area, providing a dry zone for workers. With the dam's completion in 1963, the tunnel was plugged with about 550 cubic yards of concrete and hasn't been used since.
   With the plug out, water rushed through the tunnel for about an hour, flushing sediment from the tunnel. Levels in the South Fork rose more than three feet as a standing wave of brown water rushed downstream. By Saturday evening, dam operators gradually reduced flows back to the normal 1,120 cubic feet per second.  They had been as high as 2,950 cfs during the test. 

   Turbidity on the South Fork increased as well but dropped off as the stream joined the main McKenzie River. Observers kept a close watch on how the level of turbidity affected water quality, especially as it relates to fish.
   In early March, the US Army Corps of Engineers plans to continuously divert water through the tunnel until reservoir levels are about 157 feet below normal winter operating levels. At that point, crews will begin construction on the water intake tower, which will include attaching a new weir system to the face of the existing tower. As a result of the draw down, all boat ramps on Cougar Reservoir will be closed during the three years of construction.
   The new weir system will allow water to be drawn from differing depths in the reservoir, mixing it to the optimum water temperature for release below the dam.  The changes are designed to improve water temperatures for salmon and resident fish in the McKenzie River, keeping them closer to natural conditions needed by the fish.

   During construction, the Corps is working with the U.S. Fish and Wildlife Service and the Oregon Department of Fish and Wildlife (ODFW) to maintain a residual pool above the dam. Biologists will also be involved in a program to collect adult bull trout below the dam and transport them to release sites above the reservoir.
   The overall project is under contract to ASI RCC, Inc., of Buena Vista, Colorado.  The $9.8 million contract involved installation of regulating gates inside the diversion tunnel, lining it to maintain its structural integrity and removing the plug. The work began in the summer of 2001
   The Corps also plans to add similar water temperature control structures at Blue River Dam on the Blue River. That work is tentatively scheduled to follow after completion of the Cougar Dam modifications.

© 2002 Mckenzie River Reflections