Downstream work prepares for RRHP powerhouse construction

Published Feb. 26, 2015

Construction continues at the Red Rock Dam where Missouri River Energy Services (MRES) will construct a new hydroelectric power plant. Much of the construction work being done is in preparation for construction of the powerhouse, which is expected to begin in summer 2015.   

On the downstream side of the Red Rock Dam, the construction of the cofferdam, which is located between the Des Moines River and the power plant site, is well underway. The construction of Cells #1 and #2 are largely complete, Cell #3 is being filled with sand, and the walls of Cell #4 are being installed. The cofferdam will help create a dry work environment during the construction of the power plant. The cofferdam will consist of four cells made of steel sheeting and filled with concrete and sand, and between each circular cell will be a “peanut” cell made of the same materials. The shape of the peanut cell will connect and seal the circular cells to produce a watertight structure. 

Along with the cofferdam, observation wells will be drilled on the downstream side of the dam that will help to collect water from below-ground level to ensure that the excavation site remains dry.

Together, the cofferdam and the wells will keep water out of the site during construction of the power plant. 

Also on the downstream side of the dam, workers in mid-February completed construction of a rigid and waterproof retaining wall known as a “secant pile wall.”  This wall will hold back the earth along the downstream side of the dam during construction of the power plant. The wall consists of 86 concrete elements, half of which have steel I-beam reinforcement in the center and the other half are reinforced by a rebar cage.  Construction of the secant piles was completed on February 17, 2015. 

This week, construction crews will begin to install tieback anchors that will anchor the secant pile retaining wall into the bedrock under the earth. Approximately 153 anchors will be used to brace the secant pile retaining wall.

For more information about the Red Rock Hydroelectric Project, visit the project website at

Release no. 15-016