The Bureau of Reclamation will begin emptying Upper Stillwater Reservoir on Saturday.
The action is being taken so that two sand piles that have been discoloring the water can be stabilized, according to Clifford I. Barrett, Upper Colorado Region director.The reservoir draining will begin with water flowing over the spillway at an uncontrolled rate of approximately 130 cubic feet per second.
Barrett said that after the holiday weekend, reservoir releases through the outlet will vary between 500 and 700 cfs, depending on the river inflow. "This will allow for safe drawdown limits for the dam and reservoir and to minimize any damage to diversion structures along Rock Creek. It will take until late August to drain the reservoir. During this drawdown process, the water may be turbid and red colored," he said.
To stabilize the sand piles, two options are being considered by Bureau of Reclamation officials. One calls for the sand piles to be covered in place by soil cement. The other option requires that the red sand material be returned to and stabilized in the original quarry site.
A decision will be made within the next few weeks, and work will be conducted from about Oct. 1 through Dec. 31.
Concurrent with that, a grouting program will be initiated. Shrinkage cracks in the dam will be grouted to prevent seepage and degradation of the concrete. Shrinkage is a natural phenomenon that takes place as concrete dams cure and does not affect the soundness of the structure.