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Bagnell Dam

Bagnell Dam History  

In 1912, Ralph W. Street of Kansas City first proposed damming the Osage River to generate electricity. However, it wasn’t until 1924 that Street and Walter Cravens, also of Kansas City, arranged financing and formed the Missouri Hydro-Electric Power Company.
The company began building roads, housing, an administration building, mess hall and other facilities needed to support construction of a dam near the tiny town of Bagnell. However, financial difficulties brought the project to a halt in 1926.
On July 27, 1929, Union Electric Company of St. Louis (now known as Ameren Missouri) purchased the facilities, and construction resumed on August 6. The New York Stock Exchange “crashed” two months later, bringing on the Great Depression, but work on the project continued. It became the only major construction project in the nation at the time, attracting thousands of workers from all over the country.
Records show more than 20,000 people worked on the project at one time or another. Although there were some steam shovels and other powered equipment, most labor was done by hand. Pay rates for construction workers were as low as $0.35 an hour. But during the Depression era, when a person could be hired for farm work for $0.50 a day, workers were glad to make the hourly wage.
The project was truly massive. Nearly 60,000 acres of land had to be acquired, and about 30,000 acres cleared of trees and brush. One million cubic yards of earth and rock had to be moved. Enough concrete was poured to build an 18-foot-wide highway from St. Louis to Topeka, Kansas. Enough carloads of material were used in the dam to fill a freight train stretching from St. Louis to Tulsa, Oklahoma.
Construction was completed two years after work began. Commercial operation of the Osage Power Plant began October 16, 1931.
At the time, Bagnell Dam was truly an engineering marvel, and dignitaries from all over the country and the world came to see it. Engineers proudly predicted the amount of electricity the Osage Power Plant would generate in future years, but no one dreamed of the millions of hours of recreation, the Lake of the Ozarks would provide for tourists, local residents and second homeowners.

The lake extends approximately 93 river miles from Bagnell Dam to Harry S. Truman Dam near Warsaw, MO.  The lake contains 1,150 miles of shoreline, and has about 90 square miles of surface area, passing through the counties of Miller, Camden, Benton and Morgan. 

How the Osage Power Plant Works  

Bagnell Dam holds back water from the Osage River to create the Lake of the Ozarks. This stored water serves as “fuel” for the Osage Power Plant, located inside the dam.

When the plant is operating, water flows from the lake through a large pipe called a penstock, which carries the water to large water wheels called turbines. Each turbine is connected to a generator by a 30-inch diameter steel shaft. A generator is a device in which a type of magnet spins inside a stationary coil of wire. As the pressure of water flowing through the plant turns the turbine, the turbine turns the magnet inside the generator, producing electricity. In a typical year, the Osage Plant produces more than 500 million kilowatts of electricity - enough to supply the needs of nearly 42,000 average households.

When excess water flows into the Lake of the Ozarks, such as during times of very heavy rainfall, the floodgates are used to pass this excess water downstream.  In years past, you could get an idea of the size of a flood by the number of floodgates open.  However, this was changed during the process of obtaining a new FERC license for Osage.  Beginning about 2007, Ameren agreed to partially open 11 of its 12 gates in any flood.  This was done to spread the flood flows across a wider area thus minimizing the number of fish that would be pulled through the gates during a spill event.

Bagnell Dam Failure  

Ameren Missouri has an emergency action plan in place in the very unlikely event of a dam failure.  In the event of a dam failure, the areas that would be inundated with this excess water would include the Special Flood Hazard Area (floodplain) along the Osage River from Bagnell Dam to the Missouri River. This includes Miller, Cole, Osage and Callaway Counties. 

Downstream areas of the Bagnell Dam would only have several hours before the floodwater would reach them.  The flood arrival time for the Highway 50/63 Bridge is approximately 11 hours with a peak time of approximately 31 hours.  The flood arrival time for the Bonnots Mill area is approximately 16.5 hours with a peak time of approximately 35 hours.  The flood arrival time for the Chamois area is approximately 19.5 hours with a peak time of approximately 43 hours.  Peak time is the amount of hours it would take for the water level to rise to within two feet of the peak elevation.


The Harry S. Truman Dam impounds the Harry S. Truman Reservoir, containing approximately 11,500 square miles of drainage area.  Water from this drainage area flows into the Lake of the Ozarks as it is discharged through Truman Dam.  If Truman Dam failed, a Bagnell Dam overtopping event would be possible, especially if Truman Lake was higher than elevation 720 at the time of failure. Downriver would have a little more time to evacuate. 

In any dam failure (called a “Condition A”) or potential failure (called a “Condition B”), Bagnell Dam will send out an emergency notification message to affected emergency response agencies and residents along the Osage River advising them to take action.  Ameren Missouri is updating their list of phone numbers for residents that live and own property along the Osage River.  Residents that request to be added to the list would be notified in the event of an emergency at Bagnell Dam, to include a failure in the dam itself. In an effort to obtain current contact information for our list, we ask that you contact your local Floodplain Administrator and provide your contact information to him/her.  He/she will compile the information and provide it to us for our database.

Did you know that if the Bagnell Dam had a failure, the Osage River, at its peak flood elevation, might cross the Osage River Bridge (WBL) at Highway 50/63? 


Osage County MO

Emergency Management Agency

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