Streamline topography in periodic surf zone waves from LDA measurements

Ensemble-averaged, repetitive, kinematic structures in nominally periodic surf zone waves have been obtained in a 2D vertical plane using laser Doppler anemometry. Temporal velocity variation at a point is transformed to spatial by assuming that the waves are slowly varying to enable velocity and stream function fields to be obtained. The bulk velocity in the roller above trough level is shown to be close to the wave speed with superimposed circulations in the initial breaker zone. A 'divergent' stagnation point is formed on the surface at all positions in the surf zone, close to the toe of the roller in the initial breaker zone and landward of the roller thereafter. On the bed a 'convergent' stagnation point is formed in the initial breaker zone and in the inner surf zone, but a divergent stagnation point is formed over a small zone after the initial breaker zone, with a vortex structure on the streamline connecting the two stagnation points. © 2005 IOP Publishing Ltd.