1969,2021 36.4mw Red Rock Dam on Des Moines River near Pella, IA

(Satellite, 695 photos)

The dam was finished in 1969 for flood control. The hydropower plant started construction in 2014, and it was finished in 2021. The 36.4mw plant can "power over 18,000 homes and businesses in 61 communities in the states of Iowa, Minnesota, North Dakota, and South Dakota." [hydro]

USACE

USACE_lake
''Lake Red Rock is Iowa's largest lake with more than 15,000 acres of water and 35,000 acres of land for visitors to enjoy. Located on the Des Moines River just 45 miles southeast, and downriver, of the city of Des Moines, Iowa, the reservoir collects runoff and and drainage from a 12,320 square-mile area in Iowa and southern Minnesota....The maximum flood control pool is 780 feet above sea level, over 33 miles long, and covers 65,500 acres."

USACE, Rock Island District posted two photos with the comment: "Today's 'Then & Now' takes us over to U.S. Army Corps of Engineers, Rock Island District, Lake Red Rock and dates back to 1966 during construction of the dam. These photos are looking upstream at the structure. In the original photo, the future Lake Red Rock is a busy staging area for construction workers. Today, a hydroelectric plant owned and operated by Missouri River Energy Services resides next to the gates."

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USACE, Rock Island District posted two photos with the comment: "Throwback Thursday:  The first photo shows site preparation for the dam's stilling basin on August 14, 1962.  The second photo shows the concrete control structure and stilling basin later in the construction process (February 1964). The Des Moines River is visible in the background."

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USACE, Rock Island District posted
Throwback Thursday: In this photo dated November 30, 1962, the footprint of the dam's concrete control structure is visible as excavation continues on the project.

USACE, Rock Island District posted
Throwback Thursday: Work is progressing on the tainter gates' installation in this photo taken September 22, 1965.

USACE, Rock Island District posted three photos with the comment: "Throwback Thursday:  If you visit North Tailwater or South Tailwater Recreation Areas below the dam, you’ll see what looks like a massive sheet covering Tainter Gate #5.  Underneath it, contractors are in the process of sandblasting and repainting the gate – a process that will be repeated on the other four Tainter gates as work continues.  The “throwback” photos show the red-colored gates were primed and waiting to be painted for the first time during the dam’s construction in the 1960s.  Thanks to the family of the photographer Walter Roorda for sharing the historical pictures!"

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[So they built the concrete control structure first and then added the earth embankment. And this photo explains why the description of how they built the hydropower plant talked about boring through the concrete.]

The Mar 2015 Google Earth image shows that construction was just beginning. (The 2015 image is the one that Google Maps is displaying in Nov 2023.) This Feb 2017 image shows that construction is well underway. The Aug 2018 image shows that construction was finished.

Google Earth, Mar 2017

PowerMag, Courtesy: Missouri River Energy Services
"The Red Rock project has two vertical-shaft, single-runner, Kaplan-type hydro turbines with adjustable runner blades and wicket gates. Each unit has a rated turbine output of 21.6 MW while operating at the rated speed and design net head of 62.1 ft....Two circular reinforced concrete penstocks with 21-foot interior diameters convey water from the intake structure to the powerhouse. The two penstocks are sized to provide a velocity of 7.7 feet/second at a full flow of 10,235 cubic feet/second."
[2*21.6 = 43.2mw, but hydro specifies 36.4mw, so I'm confused.]

The project cost $400m and is the second-largest hydroelectric power-generating facility in Iowa. There are two units. "Each unit has a rated capacity of 18 MW but can generate up to 27.5 MW, for a total generation of up to 55 MW under high flows. An intake structure 99-ft-high by 112-ft wide by 60-ft deep contains two water passages, two emergency wheel gates, and bulkhead slots and storage. The two penstocks are 280 ft long, with an inside diameter of 21 ft. Both penstocks penetrate the concrete gravity’s dam monoliths and are lined in steel downstream of the dam. The powerhouse measures 150-ft-wide by 98-ft-deep by 144-ft-high." [enr, paycount]

HydroReview, Courtesy: Missouri River Energy Services

HydroReview
"A downstream cellular cofferdam was installed to serve as a water barrier between the river and powerhouse excavation/construction."
[We can see this cofferdam in the above Mar 2017 Google Earth image.]

HydroReview
These wood forms are custom built for the draft tubes. "A high degree of precision is required for components to align with the eventual installation of the turbines, starting with the draft tube forms. The two custom wood draft tube forms being used are unique to the vertical Kaplan turbine powerhouse being built. The Ames team must position the centerline of the units vertically and horizontally to align within thousandths of an inch. The wood forms must also be very precise – to within an eighth of an inch."

Here are some before and almost after images. According to PowerMag, enr and HydroReview, some of the most challenging work was constructing the upstream structures. Frankly, I didn't understand the explanation. I need a sequence of construction photos and/or diagrams.

Google Earth, Sep 2011

Google Earth, Sep 2020