The Taum Sauk Pumped Storage Powerplant was constructed between 1960-63 to store water for generation during peak daytime power demands. The plant consists of a lower reservoir, which is sited along the East Fork of the Black River, and an upper reservoir, formed by a kidney-shaped rockfill dike approximately 70 to 90 ft high, capped by a 10 ft concrete parapet wall. The upper reservoir held 1.5 billion gallons (~4,600 acre-feet) when filled. A variety of design/construction flaws, instrumentation error, and human errors contributed to a catastrophic failure of the upper reservoir on Dec 14, 2005. Malfunctioning and improperly programmed/placed sensors failed to indicate that the reservoir was full and didn't shut down the facility's pumps until water had been overflowing for 5-6 minutes. This overflow undermined the parapet wall and scoured the underlying embankment, leading to a complete failure within ~5-6 minutes. The peak flow from this event is estimated at 289,000 cfs.