ABSTRACT

Green, A.; Cooper, J.A.G., and LeVieux, A., 2013. Unusual barrier/inlet behaviour associated with active coastal progradation and river-dominated estuaries.

The mesoscale behaviour of unusual barrier inlets on the east coast of South Africa is described. The inlets are associated with river-dominated estuaries and are consequently subject to periodic closure during low river flow. They are also located on a prograding barrier coast. Deflection of the estuary channel of a small river in the direction of longshore transport by 1230 m resulted in its capture by the estuarine channel of a larger river. The larger catchment river was not deflected by coastal progradation but maintained its position by periodic breaching of a channel through the barrier during floods. Flood breaches reseal by landward reworking of ephemeral deltas and may undergo limited migration. A tidal inlet at the northern end of the barrier is maintained by a small tidal prism and has a flood-tidal delta. It exhibits limited lateral migration and closes occasionally when wave-generated sediment transport filling the channel overcomes the flushing ability produced by tidal currents and freshwater discharge by the river. Large swell waves and the development of a washover channel cause the occasional breaching of the barrier, creating an ephemeral inlet midway along the barrier. The position of this breach is likely controlled by wave refraction patterns.

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