Discharges up to 60,000 cfs that lasted 21 days caused extensive erosion of the unlined spillway chute excavated in alternating layers of limestone and shale. An empirical model allowed to evaluate the extent of erosion anticipated for future events. Parametric calculations showed that relatively low discharges a long period of time are critical for the induced damage. It was determined that the spillway can safely pass the design discharge if weathering of rock exposed by erosion is prevented. Accordingly, the interim repair was designed to protect the rock units, especially the critical limestone layers, from weathering. Although it is expected much of the repair to be eroded during future spillway flows, it will ensure the spillway can safely pass the next discharge event
