Prototype-Scale Investigation of Spillway Cavitation Damage and Numerical Modeling of Mitigation Options

This paper documents a prototype-scale investigation of cavitation damage to a newly resurfaced spillway being used operationally during phased construction work to replace all piers and radial gates. Initial concrete damage on the right abutment spillway steps occurred in December 2015 as a result of over 300 h of continuous spilling from a new spillway gate. No cavitation damage had been observed on the original spillway constructed in the 1930s. Factors that contributed to the cavitation damage for this spillway are reviewed, including the duration of continuous spill and the increased cavitation potential of both a smooth concrete surface compared to one that is uniformly rough and sharp-edged steps compared to steps with rounded edges. Continued spilling through 2016 exacerbated concrete damage to the spillway steps leading to an experimental interim measure of constructing a tetrahedron concrete wedge to reduce the magnitude of flow separation and mitigate material loss in the location of greatest damage. Although damage to the steps continued to progress with ongoing spilling, the concrete wedge was successful in reducing the extent of damage at that location. A numerical model was calibrated by comparing simulated pressures to observed concrete damage allowing a long-term cavitation mitigation option to be designed with increased minimum pressures of approximately 50% and greater at the spillway steps compared to the 2015 as-built geometry.