PEAK DISCHARGE, FLOOD PROFILE, FLOOD INUNDATION, AND DEBRIS MOVEMENT ACCOMPANYING THE FAILURE OF THE UPPER RESERVOIR AT THE TAUM SUAK PUMP STORAGE FACILITY NEAR LESTERVILLE, MISSOURI

At approximately 5:16 am on December 14, 2005, a 680-foot wide section of the upper reservoir embankment at the Taum Sauk Pump Storage Facility failed suddenly, sending water rushing down the western side of Proffit Mountain. The water discharge emptied into the floodplain of East Fork Black River, and into the lower reservoir on the East Fork Black River. On December 15, 2005, Light Detection and Ranging (LiDAR) data were collected and used to support hydraulic analyses, forensic failure analyses, and damage extent. To evaluate the impact of sedimentation in the lower reservoir, a bathymetric survey conducted on December 22 and 23, 2005, was compared to a previous bathymetric survey conducted in April, 2005. Survey results indicated the maximum reservoir capacity difference of 147 acre-feet existed at a pool elevation of 730 feet. Peak discharge estimates of 289,000 cubic feet per second along Proffit Mountain and 95,000 cubic feet per second along the East Fork Black River were determined through indirect measurement techniques. The magnitude of the embankment failure flood along the East Fork Black River was approximately 3 times greater than the 500-year flood frequency estimate of 30,500 cubic feet per second. Dynamic wave unsteady flow models Dam Break (DAMBRK) and Unsteady NETwork (UNET) were used to route the flood wave from the embankment failure breach of the upper reservoir to the spillway of the lower reservoir. Simulated velocities ranged from 20 to 51 feet per second along Proffit Mountain and 12 to 32 feet per second along the East Fork Black River. Simulated shear stress values reached as high as 232 pounds per square foot along the slope of Proffit Mountain and 144 pounds per square foot within Johnson Shut-Ins in the East Fork Black River.