Geotechnical aspects of rock erosion

Severe erosion in unlined spillway channels at large Corps of Engineer reservoirs in the 1980s and 1990s caused the Corps to initiate research to predict erosion damage in unlined bedrock spillways. The purpose of this research was to specifically study the erosion phenomena with respect to the combined effects of the geologic and hydrodynamic controls. The research revealed that most of the severe erosion in the unlined spillways was caused by knickpoint (overfall) erosion where large blocks of material had been undercut causing mass failures. It was concluded that the potential for severe erosion was controlled by the geology at the overfall and point of impact, the velocity of the eroding water, and the negative pressures underneath the overfall. The factors that influence geologic resistance to hydraulic erosion which were identified in this research effort can be applied at other sites where rock erosion is a problem.