Hydraulic Model Studies for the Gury Hydroelectric Project Report on Spillway Cavitation Damage

The Guri Hydroelectric Project of the Corporation Venezolana de Guayana (CVG) is located on the Caroni River in northeastern Venezuela. The project includes a water impoundment created by a concrete gravity type dam. The dam contains a three-chute concrete spillway, each chute consisting of an overflow gated crest, a steep chute, and a terminal flip bucket. The spillway flow is projected from the bucket in a high arching jet which plunges into the tailwater pool for final dissipation of its energy. Spillway flows were first released from the new structure early in 1969. Inspection of the spillway late in 1969 disclosed significant scouring or erosion of portions of the lips of the buckets and the ends of the side training walls. The Harza Engineering Company, which designed the structure and provided engineering assistance during the construction and initial operations, recommended to CVG that the damaged areas be restored with epoxy concrete and epoxy protective coatings. These repairs were made early in 1970 before the new seasonal water release. Subsequent inspections late in 1970 established that scouring had been renewed and even greater damage had been sustained than in the previous year. Field inspection suggested that the damage was due to the action of cavitation and that the damage might not be self-arresting and was thus potentially hazardous. Early in 1971 staff members of the Harza Engineering Company reviewed the available evidence with staff members of the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota. As a consequence of these discussions the Laboratory was authorized in February 1971 to proceed with an experimental study. The objective of this study was to establish the mechanism of the damage and the modifications of the existing design or operations which would prevent and alleviate future damage. This report describes and summarizes the findings of the study.