Upstream construction moves to higher elevation

Jun 19, 2015

Upstream construction moves to higher elevation

Crews at the Red Rock Hydroelectric Project (RRHP) have completed work on one portion of a 240-foot diaphragm wall. The diaphragm wall is designed to hold back the existing Red Rock earthen dam and provide a channel for water to enter an intake structure that will send water to the hydroelectric turbine/generator. That work was conducted from a work platform at the 760-foot elevation on the upstream side of the Red Rock Dam. Crews are now working from a temporary platform that they constructed at the 781-foot elevation and will install five additional diaphragm wall concrete piers.

Reservoir water levels have been an ongoing concern for the project while work was under way at the 760-foot work platform. Water levels, as monitored daily by the U.S. Army Corps of Engineers, have fluctuated with recent rainfall in the Des Moines River watershed area and hit a high level of 751.75-feet on June 16. The forecast is for the water level to reach 759-feet by June 21 or 22. Now that crews are working from the 781-foot platform, work can continue until the water level approaches that elevation.

On the downstream side of the dam, rip-rap is being placed on the banks of the closure dike to prevent erosion. The closure dike and a cofferdam will help keep water out of the site during the excavation and construction of the powerhouse. The cofferdam protects the site against high velocity water coming out of the tailrace. The closure dike protects against the smaller wave action in the cove just past the cofferdam. Dewatering efforts and pumping will continue throughout the duration of the construction as needed to keep this area dry. Excavation and reinforcement work is continuing in the area where the powerhouse will be located.

Missouri River Energy Services, which is constructing RRHP and will operate the plant once it is completed, reminds the public that the construction areas will remain closed for the duration of the hydro project. Closed areas include the North Tailwater Recreation Area, the North Overlook Picnic Area, and the Volksweg Bike Trail from Howell Station Campground to the North Overlook Picnic Area.