Red Rock Hydroelectric Project powerhouse components start to take shape

The landscape at the Red Rock Hydroelectric Project (RRHP) near Pella, Iowa is changing quickly now that powerhouse construction is under way.

Crews spent the first year and a half of work at RRHP installing pilings and other underground support structures to prepare for the construction of the powerhouse, and then excavating the site to reveal those support structures. Now, action is taking place above ground and progress can be seen.

The first pieces of equipment, the steel draft tube liners for Turbine Units 1 and 2, were installed in early December. Since then, stay rings have been placed over the steel draft tube liners and pit liners were mounted on top of the stay rings.

The first sections of steel penstock liners were installed in late 2016. Penstocks are conduits or pipes that deliver water from the intake structure on the upstream side of the dam, through the existing dam, to hydro turbines in the powerhouse on the downstream side of the dam.

Once the plant is in operation, water entering the powerhouse from the penstocks will go through the formed-concrete spiral case, which is built in a snail shell shape to evenly deliver water around the stay ring. The stay rings contain fixed vanes that are designed to efficiently direct water into the turbines in an effort to capture the most energy possible. After the water passes through the turbines, it will continue through the cone-shaped steel draft tube liners that will diffuse and slow the flow before the water enters the tailrace and returns to the Des Moines River.

To prepare for continued installation of Penstock #1, crews are excavating down to a level where they can start installing additional sections of steel penstock liners that will eventually be encased within reinforced concrete.

Also, workers have made cuts to square up a section of the existing face of the concrete dam, or monolith. The cuts were made by drilling core holes both horizontally and vertically into the monolith and inserting a wire saw. The wire saw operates by making a continuous loop over a series of pulleys that hold the shape of the loop as the wire runs repeatedly through the concrete. The cuts allowed workers to remove a wedge-shape block of concrete, which squared up the face of the dam so the penstock can be attached.

It took about three weeks to make the 19½-foot triangular cut into the core of the monolith. The dam remained completely sealed on both the upstream and downstream sides throughout this cut and it also will remain sealed during all future cuts.

Missouri River Energy Services (MRES), which is building the project, serves 60 member municipally owned utilities in the states of Iowa, Minnesota, North Dakota, and South Dakota. The Red Rock Hydroelectric Project, when operational, will produce enough electricity to serve about 18,000 homes and it will be the second largest hydroelectric facility in the State of Iowa.