Secondary Flows and Sediment Problems near Coastal Marine Outfalls

The purpose of this study is to define the flow pattern of nearshore bottom currents driven by wave-current interaction and thus to confirm hydrodynamic mechanisms associated with morphological changes at open channel ocean outfalls at the shore. Use is made of an earlier study reported by the authors on the interaction of horizontal momentum jets and opposing shallow water waves at a shore, and of an unpublished later laboratory study. The turbulent jet discharge was shore-normal, directed offshore, and the incident wave direction was shore-normal, travelling toward shore. The waves approaching shore were refracted by the horizontal shear of the jet. Flow visualization was used to determine the flow pattern in the jet and the induced circulation on both sides of the jet, for a range of wave and jet characteristics. The experimental data showed several distinct flow pattern regimes. Theoretical analyses were conducted to yield quantitative design parameters to characterize various flow pattern regimes. The observed flow regimes were found to depend on the ratio of the wave momentum action on the jet to the jet initial momentum. Confirmation of the obtained design parameters was obtained by comparison with field data for the formation of accretion shoals and erosion spots near marine outfalls.