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Floods, sedimentation and tidal exchanges in the Keurbooms Estuary, South Africa

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Abstract

The relatively small Keurbooms/Bitou estuarine system on the south coast of South Africa forms a typical bar-built estuary, with a back-barrier lagoon and a barrier dune almost 4-km long. The lagoon is only about 500-m wide, while the barrier dune is not anchored to any substrate and consequently the position of the tidal inlet, or mouth, varies over the whole length of the barrier dune. This study analyses the sedimentary morphology over the years 2006–2019, during which time, three flood events caused substantial changes in the position of the mouth and the structure of the flood-tidal deltas and flow channels. It is found that after each flood the tidal exchanges reached a maximum, decreasing as sand entered the estuary again. The floods caused considerable infrastructural damage, and the sedimentary changes affected the tourism industry which is dependent on stable tourism attractions in the area. With no management changes, it is surmised that future floods will continue the process of dramatic changes in morphology of the estuary, though climate change may exacerbate these effects.

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Acknowledgements

The initial surveys formed a part of the Department of Environment Affairs (DEA) – Nelson Mandela University Memorandum of Understanding, and the support of both the DEA and NMU is gratefully acknowledged.

The Department of Water and Sanitation (DWS) provided the water level recordings taken at the N2 bridge over the Keurbooms Estuary, as well as flow records on the Keurbooms River. Daily rainfall data from the Plettenberg Bay weather station were provided by the South African Weather Services (SAWS), while sea level measurements from Mossel Bay were provided by the South African Naval Hydrographer (SANH). The provision of these data is gratefully acknowledged.

The comments of the reviewers led to substantial improvements in the paper.

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  1. Department of Geoscience, Institute for Coastal and Marine Research, Nelson Mandela University, P O Box 77000, Port Elizabeth, 6031, South Africa

    Eckart H. Schumann

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  1. Eckart H. Schumann
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Correspondence to Eckart H. Schumann.

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This article is part of the Topical Collection on Coastal and marine geology in Southern Africa: alluvial to abyssal and everything in between

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Schumann, E.H. Floods, sedimentation and tidal exchanges in the Keurbooms Estuary, South Africa. Geo-Mar Lett 41, 34 (2021). https://doi.org/10.1007/s00367-021-00709-4

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