Pollutant Trapping at a Coastal Headland

Abstract

A study of flow behavior, namely, pollutant dispersion and trapping near a headland recirculation zone adjacent to it was undertaken experimentally in the Manchester Tidal Facility for steady flows. The planar laser-induced fluorescent technique was used to visualize the flow patterns both horizontally and vertically. Dye was released using a preburied dye diffuser in the bed to simulate trapped pollutant released from the rough bed, and also through a tube placed at middepth to simulate the case of ocean outfall discharges. The discharge points chosen were within the recirculation zone, between the recirculation zone and the main current, and at a point near the main current where the flow changes. For middepth discharges the dye tended to stay near the surface, whereas for dye diffuser discharges the dye stayed near the boundary layer, and also exhibited a three-dimensional plume structure. Trapping was significant especially for certain discharge points in the recirculation zone due to the slower velocities.