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The Taum Sauk pumped storage plant (which suffered a catastrophic failure December 14, 2005) is located in the St. Francois mountain region of the Missouri Ozarks approximately 90 miles (145 km) south of St. Louis near Lesterville, Missouri. The Pumped-storage hydroelectric plant, operated by the AmerenUE electric company, is designed to help meet peak power demands during the day. Electrical generators are turned by water flowing from a reservoir on top of Proffit Mountain into a lower reservoir on the East Fork of the Black River. The generators and turbines at river level are reversible, and at night the excess electricity available on the power grid is used to pump water back to the mountaintop.
The Taum Sauk plant is notable in that it is a pure pump-back operation – there is no natural primary flow available for generation, unlike most other pumped storage sites. It was among the largest such project when it was built. Construction of the Taum Sauk plant was begun in 1960 and operation began in 1963. The two original reversible pump-turbine units were each capable of generating 175 megawatts of power. They were upgraded in 1999 to units capable of 225 megawatts each.
The upper reservoir has a capacity of 4,350 acre-feet (5,366,000 m³). The upper reservoir is 800 feet (244 m) above the hydroelectric plant, which gives it a greater head than that of Hoover Dam. The two are connected by a 7000 ft (2100 m) tunnel through the mountain.
This powerplant is a net consumer of electricity; the laws of thermodynamics dictate that more power is consumed pumping the water up the mountain than is generated when it comes down. However, the plant can still be economical to operate – the reservoir is filled at night when the electrical generation system is running at baseline capacity, and the power used for pump-back would otherwise be wasted.
That the Taum Sauk reservoir (37d32m10s N, 90d49m05s W) is atop Proffit Mountain and not Taum Sauk Mountain (37d34m13s N, 90d43m40s W) is often a source of confusion to tourists seeking to visit the site. Taum Sauk Mountain, the highest point in Missouri, is about five miles (8 km) east of Proffit Mountain and hosts a state park, not a reservoir. The reservoir is plainly visible from the lookout tower on Taum Sauk Mountain adjacent to the state park. Visitors can usually drive to the top of Proffit Mountain and walk a ramp to an observation deck at the top of the reservoir. At the entrance gate Ameren also operates a museum highlighting the natural history of Missouri. The powerplant is frequently visited by geology students because of a striking example of Precambrian/Cambrian unconformity in the rock layers exposed by the plant's construction.
Leaks and lining
There had been minor leaks in the reservoir since it was constructed. From September 13, 2004 to November 15, 2004 Geo-Synthetics Inc. installed lining material to reduce leaks.[1]
Upper reservoir breached
- For more information see Taum Sauk Dam Failure
On the morning of December 14, 2005, a triangular section on the northwest side of the upper reservoir failed, releasing a billion gallons (4 million m³) of water in twelve minutes and sending a 20 foot (7m) crest of water down the Black River. According to AmerenUE, a computer software problem cause the reservoir to continue filling even though it was already at its normal level. The water overtopped the walls, leading to the failure at 5:12 a.m. In addition, preliminary indications are that minor leakage through the dam walls over a prolonged period, had carried away fine material in the walls, weakening the reservoir's holding walls. Piping ultimately creates voids in reservoir walls and causes reservoir walls to slump and fail. The failure of the reservoir occurred as the reservoir was being filled to capacity or may have possibly been overtopped.
There was no overflow spillway. A maximum fill level was reported to be 6 feet below the top. If the reservoir was filled in 16 hours and is 55 acres across, that would calculate to about 1 ft of water rise in 12 minutes. The reservoir would have overflowed in appoximately 72 minutes, once the maximum level was exceeded. It likely that the reservoir failed once water overflowed the reservoir as earthen levees will erode when overtopped.
The reservoir had been lined with a membrane in 2004 to minimize water leakage. The reservoir had been losing two foot of water for some time prior to the lining. When fine material is washed out of a reservoir structure, the phenomena is known as "piping". When piping occurs, the reservoir structure can settle in or slump, which means water may start flowing over its top – but that is because a weakened area in the reservoir has settled down
Periodic surveys are necessary at a reservoir to identify if leakage and "piping" is occurring.
No fatalities were reported. Jerry Toop, his wife and three children were swept away when the wall of water obliterated their home. Toop is the superintendent of Johnson's Shut-Ins State Park and Taum Sauk State Parks -- which make up Missouri's second largest state park (Lake of the Ozarks is larger). They survived with injuries and suffering from exposure however their problems were compounded by improper treatment by rescue workers for Hypothermia which resulted in severe burns. The children were treated for the problems in St. Louis and later released. An unknown number of homes and vehicles were flooded.
The dam of the lower reservoir held, trapping much of the deluge. If it had given way then towns downstream, including Lesterville and Centerville would have been in grave danger. A voluntary evacuation order was issued for those areas, but there was no damage. The high water was stopped at Clearwater Lake, the dam of which was not damaged by the rising waters.[2]
A memo from Richard Cooper, superintendent of Ameren’s Taum Sauk Hydroelectric Plant, indicated that the reservoir had a "Niagra Falls" style overflow on September 27 at the same spot that was breached. Another Cooper memo had also indicated that Cooper had warned that gauges used to monitor the water height in the reservoir were malfunctioning in October.
Church Mountain reservoir
In June, 2001, Ameren Development Corp, a subsidiary of Ameren Corporation, announced that it had filed for a permit from the Federal Energy Regulatory Commission in order to begin evaluating the construction of a much larger pump-back plant on neighboring Church Mountain. The upper reservoir of this 770 megawatt plant would be 130 acres (0.5 km²), and the lower reservoir would flood 400 acres (1.6 km²) of the scenic and environmentally significant Taum Sauk Creek valley. Resistance from a number of environmental groups, the Missouri governor's office, and the state's attorney general caused the company to conclude it was impossible to build the plant in both an environmentally friendly and cost-effective manner, and the permit application was withdrawn in August of 2001.