Vortex energy dissipator for San Diego ocean outfall – laboratory investigations

Abstract

The sewage effluent from the new sewage treatment plant for the City of San Diego, located on a bluff 95 feet above sea level on Point Lorna, is discharged to the ocean through a long submarine outfall pipe. Under almost all conditions of flow, the hydraulic head at the treatment plant exceeds that required for flow through the outfall. Therefore, the excess energy must be dissipated in a special hydraulic drop structure located on the shoreline between the treatment plant and the ocean outfall. The laboratory model investigation described herein basically sought to find a method for dissipating this excess energy safely without heavy entrainment of air into the flow in the ocean outfall. Such air entrainment could cause unsteady conditions of the pipe flow, and possibly bubbling at the point of discharge in the ocean, both of which must be avoided. The responsibility of this laboratory was to develop the hydraulic principles and a recommended hydraulic configuration which would provide assurance that the prototype to be designed by the sponsors (Holmes and Narver-Montgomery) would give satisfactory hydraulic performance.