Dam Breach Incident
The Taum Sauk project is located in Reynolds County in south-eastern Missouri, about 100 miles south of St. Louis. The project was completed in 1963 as a pumped-storage project, with an upper and a lower reservoir. The lower reservoir, operated as a run-of-river reservoir with outflow being maintained at approximately equal to natural inflow, provides storage for water to be pumped to the upper reservoir at night or during periods of low power demand. The water volume used to generate electricity is cycled between the lower and upper reservoir, so the water elevations of the lower and upper reservoirs fluctuate depending on the pumping/generating modes of operation and time of day. The project structures include a concrete faced rockfill dam (dike), that encircles and forms the upper reservoir; a concrete gravity dam impounding the lower reservoir (the lower dam was designed as a spillway with no spillway gates so that flood waters could safety pass over the dam); a reversible turbine powerhouse; a gravel trap dam located upstream of the outlet canal in the lower reservoir, and a small dike that impounds the seepage collection pond at the toe of the upper reservoir.
The Upper Reservoir is impounded by a kidney shaped rim dike at the top of a planed-off mountain. The rockfill ring dike has a reinforced concrete liner to reduce seepage through the rockfill and has a maximum section approximately 94 feet high and is topped by a 10 foot high concrete parapet wall. The reservoir bottom has an asphaltic liner which ties into the concrete liner which is on the inside slope of the rockfill dam. The surface area of the reservoir is 54.5 acres with total storage of 4,350 acre-feet and live storage of 2,560 acre-feet used for production of power.
The turbine/generator sets are designed to operate in reverse to pump water to the upper reservoir at night. During the daylight peak-demand hours, the turbine/generator sets operate in normal gravity-feed mode to generate electricity.
The upper dam underwent maintenance work during the 2004 construction season. The upstream face of the upper dam was lined with a geomembrane. The purpose of this work was to minimize the leakage through the rockfill dam. This work resulted in a significant decrease in the amount of leakage from the upper reservoir.
FERC dam safety inspectors performed site inspections on December 14 and 15, 2005, where they made an immediate safety evaluation of the lower dam. The lower dam was found to be safe following the incident and had very little water flowing over it as of December 14. FERC will conduct a complete investigation of the rim dike breach.