Red Rock Hydro
Project Location: Pella, Iowa
Synopsis of work:
For the first 18 months of the project, Ames crews performed the majority of civil and underground work at the Red Rock Hydro Project where Ames Construction is retrofitting an existing dam for hydroelectric power. This initial construction, which started in August 2014, included earthwork, rock excavation and concrete pours for ground improvements. In February 2016, the project’s focus shifted to construction of the powerhouse.
The powerhouse encases the generators, rotor shafts and turbine blades as well as the powerhouse controls. The turbine blades are attached to the generators by the vertical shafts and are rotated by water flowing from the intake structure, through the penstocks (21’ diameter pipelines), into the spiral case and finally through the wicket gates. The wicket gates act as a throttle to control the speed of the turbine by regulating the optimum water flow feeding the turbine rotors.
Crews are currently working on some of the most challenging sections of the powerhouse construction, the spiral case walls, floor and roof that direct water flow into the wicket gates. As the spiral case winds around in a snail shell configuration, it reduces in both height and width demanding strict attention to minimum and maximum tolerances.
Installation of the owner-furnished turbine assemblies has also begun. A high degree of precision is required for components to align with the installation of the turbines, starting with custom wood draft tube forms that are unique to the vertical Kaplan turbine powerhouse being built. The Ames team had to position the centerline of the units vertically and horizontally to align within thousandths of an inch. With the draft tube portion of the concrete complete, crews have begun to assemble the turbines by placing the large embedded components that hold and support the non-embedded, rotating parts.
The intake structure work began in fall 2016. The intake structure is being constructed within a cofferdam on the reservoir side of the existing dam. Both the intake structure and gate assemblies must be watertight before cutting through the existing dam. Two 21-foot-diameter penstocks will connect the intake to the powerhouse with installation slated for first quarter 2017. The steel penstock liner will be embedded in concrete and feed the powerhouse with 14,000 cubic feet of water—equivalent to 2,456 standard bathtubs full—per second.