Powering Red Rock Dam – HydroWorld

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Located about 3 miles southwest of Pella, Iowa, a project to retrofit an existing dam for hydroelectric power has completed significant milestones. Ames Construction — a heavy civil and industrial general contractor headquartered in Minnesota with regional offices throughout the U.S. — is the general contractor for the Red Rock Hydro Project. While Red Rock Dam will retain most of its original structure, Ames is adding the components necessary for the dam to aid in the operation of the new hydroelectric plant.

Rising up

Arriving at the site in August 2014, crews spent the first 18 months below ground installing pilings and other underground support structures to prepare for powerhouse construction. The site was then excavated to expose those support structures.

By 2016, the project’s focus had shifted to constructing the powerhouse, located downstream of Red Rock Dam, and the upstream intake structure. The spiral case walls, floor and roof were built, along with concrete draft tubes, including the necessary embedded components for turbine-generator installation.

Draft tube liners for the powerhouse were the first large embedded components set for the turbine-generator units. Stacked vertically with other components, this assembly directs water through the turbine to produce electricity. The spiral cases within the powerhouse swirl the water around into the turbine runner, creating the forces to turn it.  Crews also substantially completed the first of two penstocks downstream of the dam to carry water from the upstream intake structure through the dam and into the powerhouse.

Throughout 2017, crews completed the center of the powerhouse, which required stacking multiple embedded parts and constructing other concrete features to support the generator. Project progress had also advanced to above-ground visibility. Crews installed other mechanical support systems within the powerhouse, along with the electrical cable tray system that carries, literally, miles of wires within the powerhouse. Specialized concrete of the new intake structure had taken shape by year-end, with crews from both Ames Construction’s western and midwest regions working together to build a 96-foot-tall structure of unique, thick concrete lifts within a special cofferdam.

During 2018, the second of two penstocks was substantially constructed downstream of the dam, with all concrete for both the powerhouse and intake structure completed. The downstream exterior structure of the powerhouse was enclosed and crews installed heavy draft tube gates between the powerhouse and the tailrace to stop the flow of water during water-up activities. Water was introduced into the tailrace, tested for leaks, and certified as watertight.

Another major milestone was erecting the turbine-generators. With the turbine runners positioned, numerous other parts surrounding them formed the water seal. Assembled separately, the generator rotor included stacked steel plates made up of hundreds of pieces. The generator rotor — weighing nearly 160,000 pounds — was lifted by crane and bolted to the top of the runner, resulting in the turbine, blades, and its rotor becoming one piece, ready to test its rotational properties.

Final steps

Capping off the progression of successes throughout the project, the powerhouse equipment has been set and is in final stages of testing, and construction of the new switchyard is finished. However, excessive rains in 2019 have intensified the impacts of an already unusually wet flood season. Crews had to wait for flood waters to recede so that final construction of the penstocks can resume. As the flood control reservoir reaches acceptable water levels, the intake structure’s hydraulic gates will be installed, aligned, tested and sealed.  The penstocks between the intake structure and the dam will also be completed and sealed, which then allows Ames to cut the holes through the existing dam, enabling the water to reach the powerhouse.

When operational, water entering the powerhouse from the penstocks will go through the spiral case that delivers water evenly around the stay ring. Fixed guide vanes and wicket gates in the stay rings will efficiently direct water into the turbines, capturing the most energy possible. Water will pass through the turbines and into the draft tubes, which will diffuse the flow before the water enters the tailrace and returns to the Des Moines River.

Unique partnership

Red Rock Dam is owned by the U.S. government and operated by the U.S. Army Corps of Engineers. The Red Rock Hydroelectric Project is being constructed and will be operated by Missouri River Energy and is owner-financed by Western Minnesota Municipal Power Agency. Considered a unique partnership, the Red Rock Hydro Project is one of the only hydroelectric projects where a non-federal owner has built a powerhouse at a dam owned by the federal government.

In business for more than five decades, Ames began performing hydropower work as far back as the 1980s, with expertise in constructing complex water-related projects throughout the nation.

Red Rock Hydro at a Glance

Upstream

  • Install a 240-foot by up to 133-foot deep diaphragm wall with 26 elements of varying sizes
  • Install a 100-foot by 85-foot-deep concrete diaphragm cut-off wall along the axis of the earthen dam to ensure dam stability during project construction
  • Construct secant pile cofferdam to facilitate construction of the intake structure
  • Construct intake structure to draw water into the penstocks

Downstream

  • Install cellular cofferdam and earthen dike to facilitate powerhouse construction
  • Install secant pile retaining wall to hold back the earth embankment of the dam during powerhouse construction
  • Powerhouse construction (185 feet long, 112 feet wide, 143.5 feet tall)
  • Construct two penstocks
  • Install equipment, including turbines, generators, controls and transformers
  • Construct 69-kV substation and transmission line
  • Construct 12.47-kV backup distribution line and utilities

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