OVERVIEW OF THE 2005 TAUM SAUK UPPER RESERVOIR BREACH, REYNOLDS COUNTY, MO

The Taum Sauk Pumped Storage Project was constructed during the early 1960's in order to generate up to 450 Mw of off-peak hydroelectric power. The plant consisted of a lower reservoir sited along the East Fork of the Black River and an upper reservoir atop Proffit Mountain. The upper reservoir had a capacity of 5.67 million cubic meters (~4,600 acre-ft), with a vertical drop of 232 to 259 m, depending on the pool level. This offstream storage unit was a kidney-shaped rockfill dike approximately 25 m high and capped by a 3 m concrete parapet wall.

The upper reservoir failed catastrophically on the morning of Dec 14, 2005 due to malfunctions of the reservoir's instrumentation system, which allowed the pool to overtop the parapet wall, which behaved as a thin-crested weir (the upper reservoir did not have a spillway). This overflow scoured the rockfill embankment, causing the wall to collapse by overturning. The wall failure unleashed a much larger outflow, which rapidly eroded a 680 ft wide breach of the rockfill embankment, stripping the mountainside of vegetation and residuum, exposing the underlying bedrock. Residuum, rockfill, concrete wall fragments, HDPE liner remnants, and steel rebar was deposited in Johnson's Shut-ins State Park, located about 1.6 km away and 215 m below. Post failure measurements suggest that the peak outflow was around 8,200 m3/s. The reservoir drained in approximately 12 minutes.

The outbreak flood left a path of destruction and debris, obliterating the state's most popular summertime campground, with only five injuries and no deaths, because the facility was shut down for the winter. The flood waters and their associated debris were largely contained by the lower reservoir, which had been pumped down to fill the upper reservoir the previous night.

Consequences could have been far worse had this occurred during a busy summer weekend at Johnson's Shut-ins State Park, when upwards of 800 campers and park employees might have been sleeping in the path of the flow, most of whom would have been killed.