Keokuk Energy Center: Harnessing the Power of the Mississippi

As the largest hydroelectric station on the Mississippi River and the site of a number of firsts for the industry, the Keokuk Energy Center in Iowa has been making history since it began operating in 1913. Keokuk is the latest inductee to the Hydro Hall of Fame.

By Kent Martin

Standing 10 stories above the top water level and running almost a mile long, Keokuk Energy Center and Dam near Keokuk, Iowa, is the largest privately owned and operated dam and hydroelectric generating plant on the Mississippi River.

More than 1 million cubic yards of earth and rock were excavated when the run-of-river Keokuk Energy Center was built in 1913. Today, it’s one of three hydroelectric plants in the Ameren Missouri system, with the others located at Bagnell Dam Osage Energy Center in Lake of the Ozarks, Mo., and at Taum Sauk Energy Center near Lesterville, Mo.

Over the decades, Ameren Missouri has invested millions of dollars in the modernization and maintenance of the Keokuk plant and dam. Keokuk Energy Center has 15 main turbine-generator units with a net capacity of 142 MW. All of the Keokuk units originally produced 25 Hertz power. However, now all the units have been converted to produce 60 Hz power for local area distribution and transmission to other locations throughout the Ameren Missouri service territory.

Hydropower is important to the reliability of Ameren Missouri’s electric supply because unlike the company’s nuclear and fossil fuel plants, hydro plants can be started in minutes, providing needed power in case of a system emergency. Hydro plants also play a key role in helping meet electrical demand during “peak” periods.

For its long service life and great number of “firsts” for the hydropower industry, Keokuk Energy Center and Dam has been inducted into the Hydro Hall of Fame for 2013.

Keokuk Energy Center
At the time of construction in 1913, the Keokuk Energy Center was the largest monolithic concrete dam in the world. It represents many other “firsts” in the industry as well.

100 years in the making

Keokuk Energy Center first began generating electricity for Union Electric customers in 1913, when energy drawn from the power of the raging river waters in Keokuk was a novel idea. The largest power plant and dam in the world at the time, Keokuk was considered an engineering marvel. As is typical with many great accomplishments, however, construction of the Keokuk plant encountered disappointments and seemingly insurmountable obstacles.

The idea for the Keokuk site came from a young lieutenant named Robert E. Lee, who surveyed the land for the U.S. War Department in 1836. He suggested that the great power he witnessed in this turbulent section of the Mississippi River, known as the Des Moines Rapids, could be harnessed in some fashion. This part of the river included such notable characteristics as a 23-foot fall in a 12-mile stretch. The Des Moines Rapids blocked virtually all upstream navigation.

By 1848, leaders in the community of Keokuk established a company to build a structure that would take advantage of the river’s power. A dam would help place the rapids under water and provide an opportunity to harness the navigational potential of the river with a set of locks. This would also position Keokuk as a town that could provide power to textile and grain mills.

Lack of financing, largely the result of the struggling national economy in the 1850s and 1860s, stalled this effort until 1868, when the U.S government moved ahead to build a 9-mile canal around the rapids to help with river navigation. The idea of building a dam to generate power remained just that: An idea.

Once Thomas Edison developed a system for electricity distribution in 1880, interest in the Keokuk site was revived, and it began to be viewed as a “natural” location for a hydroelectric plant. But it wasn’t until the end of the 19th century that a group of businessmen from the region organized the Keokuk and Hamilton Water Power Company to harness the rapid flow of the river.

The company began with limited funds – $2,500 (almost $68,000 today) – and the city councils of Keokuk and nearby Hamilton, Ill., added ,500. It sought to raise additional funds to develop the project by approaching the Secretary of War, requesting a study that confirmed it was possible to build a dam from bluff to bluff (7/8 of a mile in length). Congress passed and President Theodore Roosevelt signed a bill in February 1905, giving the Keokuk and Hamilton Water Power exclusive rights to build a dam at this location, so long as they began construction within five years. The company sent its proposal to engineers and financial interests throughout the U.S., Canada, Europe and even Australia, but no one stepped up to help further finance the project.

Then, in September 1905, Hugh L. Cooper – who had engineered the construction of a hydroelectric plant at Niagara Falls, N.Y., the Toronto Power Generating Station (which ceased operating in 1974), and was rapidly gaining a reputation as a renowned engineer and enthusiastic problem-solver – wrote the company to express his interest in the Keokuk dam. He invited a committee of Keokuk and Hamilton representatives to visit Niagara to see his work up close and quickly convinced the Keokuk and Hamilton Water Power executives of his ability to manage development of the Keokuk project.

Even under Cooper’s direction, however, financing remained a problem. In September 1905, members of Keokuk and Hamilton Water Power agreed to a contract with Cooper, in which in return for $20,000 (more than $500,000 today), the amount they had spent on the plan so far, they would give to a Toronto syndicate represented by Cooper a two-year option to take over their franchise. During those two years, the Toronto syndicate would take surveys and make preliminary engineering plans and cost estimates to decide if they still wanted to proceed. But just one year later, in 1906, the San Francisco earthquake sent shock waves throughout the insurance industry, and the Toronto interests that initially backed the Keokuk and Hamilton plan withdrew their support.

Cooper had to scramble quickly because an option in his contract gave him and his supporters the right to buy out Keokuk and Hamilton Water Power’s stock franchise within two years. It took Cooper almost two years and most of his own wealth before he was able to secure backing from a group of financiers from the eastern U.S., Canada, England, France, Germany and Belgium.

Cooper and Keokuk and Hamilton Water Power also landed contracts in 1910 to deliver 44.7 MW of electricity to three customers located more than 100 miles south in St. Louis, Mo., at a time when no electric power had been transmitted more than a few miles: The Union Electric Light and Power Company, Laclede Gas Company and United Railways Company, which operated the St. Louis Street Railway Company. The plan was to attract additional investors who would back construction of the project.

Cooper and Keokuk and Hamilton Water Power determined the electricity transmitted to St. Louis would be 110,000 volts, which meant developing high-voltage transformers, transmission towers and insulators. Today’s high-voltage transmission technology is based on principles and equipment designed for the Keokuk project. Some of the same towers and insulators installed at Keokuk are still in use today. In fact, much of the original equipment in the entire system remains unchanged to this day.

Keokuk Energy Center
Work on the first seven units of the powerhouse was progressing in February of 1912. At the time this photo was taken, instake and pit linings were being placed.

Construction begins

Construction of the Keokuk Dam and Power Plant began Jan. 10, 1910. The entire project was being financed with private funds. However, the lock and dry dock were turned over to the U.S. Army Corps of Engineers as a condition of the original construction permit. Both the power plant and dam were completed in 1913.

Raising the level of the Mississippi River to create a 60-mile-long lake posed problems along the Iowa shoreline. The company wound up buying out almost half of three towns and moving the residents higher up on the bluff. Another challenge was raising the elevation of nearly 14 miles of track that belonged to the Chicago, Burlington and Quincy Railroad and ran along the Iowa river bank.

The complexity of the Keokuk plant construction required considerable creativity by Cooper and his team. First, they had to build the largest concrete dam ever made. The powerhouse, dam, lock, dry dock and ice fender had to be one concrete monolith that measured 2.5 miles in length, to span the river. The ice fender is a barrier that extends from the west end of the dam toward the Iowa shore and diverts the annual ice flow of the river toward the dam to protect the powerhouse. The dam is 7/8 of a mile in length, 29 feet wide at the top, 42 feet wide at the bottom and 53 feet high. Total length of the dam, powerhouse, lock, dry lock and sea wall is about 9,000 feet.

A massive traveling crane was customized for the Keokuk project; at 250 feet in length, the crane could deposit cofferdam cribs as much as 125 feet beyond the end of the section just finished.

Workers positioned the concrete piers upon which the forms were mounted by “shooting” a line back toward the piers they had just poured using a standard surveyor’s transit, a process repeated for each of the 119 piers. Any error in measurement was additive on to any previous errors. In the end, they met the end point of the wall of the powerhouse within less than 1/8 inch of the intended target – an achievement that would be considered very good today even with the most modern lasers.

Sections of the dam by the archways had to be built first to mitigate excessive pressure from the Mississippi River on the completed section. As one section was completed, the cofferdam was removed and the river was allowed to flow through the arches. Cooper built a bridge across the Mississippi while a second team followed to fill in the spillways. By constructing the dam without spillways, Cooper was able to span the river with minimal resistance from the river flow, since the piers comprised about 16% of the total length of the dam.

After completion of the arches and bridgeway, spillway bays were built one by one. Builders worked on one archway at a time and constructed a 5-foot-tall block of spillway bays all the way across the Mississippi. Then another 5 feet was added, opening by opening, which helped equalize water pressure all along the length of the dam during construction. So the spillways were raised sequentially, as all arches in a specific section of the dam were raised to an intermittent level and workers then started over and raised them again until they reached the final elevation.

Nature presented its own challenges to construction. The winter of 1911 to 1912 was very harsh, causing 2.5 feet of ice build-up above the dam. Cooper had the upstream cofferdam heightened and reinforced, stockpiled thousands of sand bags and brought three steam shovels to be prepared when the ice broke up. In March 1912, the ice began breaking up, jamming large chunks of ice in the gap between the cofferdam and powerhouse, but the dam withstood the assault.

Those large ice chunks, however, began backing up the Mississippi River when they formed a jam about 5 miles downstream. Crews worked around the clock for four days plugging leaks and strengthening the lower cofferdam. Finally, the ice jam broke and the river began flowing again. But in a few days, a storm drove waves over the top of the sand bags, and water poured down into the excavation. More workers were called to shore up the dam before winds finally subsided and the waters dropped.

By the end of July 1912, the final section of cofferdam was built, and both upper and lower legs of the cofferdam were finished by September. In May 1913, the final spillway was topped off and the lock was opened as two excursion steamers passed through side by side. The government assumed formal control of the new lock at that time. Navigation also benefited from construction of the new lock: Ships could move through the new lock in about 20 minutes, compared with several hours with the old locks.

On June 23, 1913, the 110-kV transmission line to St. Louis was energized.

100 years of firsts

The Keokuk Energy Center has provided several notable “firsts” for hydroelectricity in the U.S.:

– Longest monolithic concrete dam;
– Largest privately-funded hydropower construction project;
– Largest turbines ever constructed;
– Heaviest rotating weight suspended on a single bearing;
– Largest penstocks;
– Largest inland dry dock;
– Only pneumatically-raised lock gate;
– Only commercial hydroelectric facility on the Mississippi River;
– First long-distance transmission line;
– First high-voltage transformers; and
– First high-voltage insulators.

Union Electric Co. purchased the facilities in 1925. Today, Keokuk Energy Center remains the largest privately owned and operated dam on the Mississippi River.

Another notable feature of the plant – the generator rotor, turbine and shaft assemblies – may be the largest ever built. A single bearing that was four times larger than anything built previously supports each assembly. Engineers were uncertain a scale-up of the roller bearing would be adequate to provide the desired service life for the system. Only half of the turbines were installed with roller bearings. The others were installed using a new type of bearing that had just been invented by Kingsbury Thrust Bearings. These new bearings were so effective that they replaced all of the roller bearings at the plant within the following decade. After a century of virtually continuous operation, none has needed more than minimal repair.

In the years since it began operating, Keokuk Energy Center has seen a variety of changes and improvements. The 25-cycle generators were converted to 60-cycle generators in the 1940s and 1950s. The final units were converted in 2002. In 2001, Ameren Missouri began converting and replacing the original turbines, first installed when the plant opened in 1913, with more efficient stainless steel turbines. Automation came to Keokuk Energy Center in the 1980s and 1990s.

Lasting impact

Besides the environmental advantages of hydropower itself, Keokuk Energy Center benefits the environment in other ways. Ameren Missouri owns about 2,000 acres of flowage land (land subject to flooding), some covered by water at the Keokuk site. The dam provides sufficient water levels to support an important transportation corridor for barge traffic that moves everything from coal and fertilizer to a large volume of grain up and down the river.

As a major driver in the regional economic engine, Keokuk Energy Center has served as a stable source of employment for generations of residents from Iowa, Illinois and Missouri for the past century. Today, Keokuk Energy Center continues to provide customers with safe and reliable electricity throughout the Ameren Missouri system.


Kent Martin is communications executive at Ameren Missouri.

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