Bagnell Dam impounds the Osage River in the U.S. state of Missouri, creating the Lake of the Ozarks. The 148-foot (45 m) tall concrete gravity dam was built by the Union Electric Company (now AmerenUE) for the purpose of hydroelectric power generation as its Osage Powerplant. It is 2,543 feet (775 m) long, including a 520-foot (160 m) long spillway and a 511-foot (156 m) long power station. The facility with eight generators has a maximum capacity of 215 megawatts.
The dam derives its name from Bagnell, Missouri at the dam site which preceded the dam. It in turn derives its name from William Bagnell who platted the town in 1883.
The dam is located at 38°12′09″N 92°37′35″W / 38.2025°N 92.62639°W / 38.2025; -92.62639, on the border between Camden County and Miller County. According to the United States Geological Survey, a variant name is Osage Dam.
Construction started on the dam in 1929 and was completed in 1931. The resulting reservoir, the Lake of the Ozarks, has a surface area of 55,000 acres (223 km²), over 1,150 miles (1,850 km) of shoreline (1850 km), and stretches 92 miles (148 km) from end to end (148 km). At the time of construction it was one of the largest man-made lakes in the world and the largest in the United States.
The concept of a hydro electric power plant on the Osage River was first introduced by a Kansas City developer as long ago as 1912. Ralph Street managed to put together the funding to construct a dam across the Osage River and began building roads, railroads and support structures necessary to begin construction of a dam that would impound a much smaller lake than what is presently known as Lake of the Ozarks. Sometime in the mid 1920’s, Street’s funding dried up and he had to abandon the idea of the first hydro electric power plant on the Osage River.
Upon Street’s failure to deliver the power plant, Union Electric Power and Light stepped in with an engineering firm from Boston, Massachusetts, and designed and constructed Bagnell Dam in one of the most unlikely spots along the Osage River. Many thought the $30 million project would be a disaster with the stock market crash of 1929, but it proved to be a boost to many families in the area as well as the hundreds who traveled across the country seeking work. By today’s standards, all construction was done by hand, and the equipment used in the construction was quite primitive. The construction of Bagnell Dam was completed and Lake of the Ozarks was a full reservoir in fewer than two years.
The stock market crash of 1929, which precipitated the Great Depression occurred just months after construction began on Bagnell Dam. The project employed thousands of laborers, providing a large economic boost to the rural area around the dam and to the state as a whole at a time when jobs were scarce.
Construction of the dam allowed for thirteen floodgates, as the original design called for. However, only twelve floodgates were installed, and the thirteenth spillway opening is walled shut with concrete. The engineers calculated that twelve floodgates provided a large enough margin of safety. It may be apocryphal that Union Electric officials did not want to jinx the dam with the unlucky number 13.
AmerenUE remotely operates the Taum Sauk pumped storage plant from its control room at Bagnell Dam.