Author(s)

N.R. Shannon, P.A. Mackinnon, G.A. Hamill & B.M. Doyle

Abstract

A substantial proportion of urban wastewater is discharged through submerged marine out falls for biological breakdown. Saline intrusion, the entrainment of seawater within these outfalls as a result of differences in density between wastewater and seawater, can significantly reduce their operating efficiency. This research addresses the problems that occur when wave action exacerbates saline intrusion. The aim of the investigation was the collection of data to validate an improved numerical model which incorporates the effects of waves on the internal hydraulics of a marine outfall. The model had recently been developed in the School of Civil Engineering at Queen’s University Belfast. A description is provided of the facilities and instrumentation used to record the flow patterns in a model outfall discharging into receiving waters with waves. The paper provides details of the equipment and methods used to collect data on velocity, density, pressure and wave climate. Results are presented for tests in which a simplified two-riser model outfall discharges into freshwater and, later, saline water with waves. A comparison with preliminary results from the numerical model reveals that the latter is capable of reproducing the general flow patterns observed, but also highlights the need for further refinement of turbulence modelling procedures

Keywords