Apparent dynamic stability of the southeast African coast despite sea level rise

Alan Smith, Simon Bundy, Andrew Cooper

Research output: Contribution to journalArticle

2 Citations (Scopus)
12 Downloads (Pure)

Abstract

The coast of southeast Africa is dominated by sandy beaches that tend to be confined within log-spiral or headland-bound embayments. Investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast. We show that conclusions drawn from this data, with respect to the high water mark (HWM) positionare fraught with errors, which include tidal state, pressure regime, beach slope, high-swell erosion, seasonal and multi-annual changes. We highlight and discuss these sources of error, together with their magnitudes. The most significant of these are the high-swell, seasonal and multi-annual variations. From case studies we show that the seasonal beach rotation and long-term beachwidth variation are responsible for tens of metres of unaccounted HWM variation, 30 to 50 m is common, with maximums reaching 60 to 100 m. Overall the southeast African coastline appears to be in a state of long-term dynamic equilibrium. There is no evidenceof any sea-level rise-forced transgression in the coastal sediment budget, despite sea-level rise (SLR). If such a signal is, in fact present,it is lost within the beach width variation. Some southeast African coastal reaches are suffering chronic erosion, but these are related to anthropogenic impacts. The extreme difficulty of placing a HWM, with any temporal validity on this coast precludes the routine use of the Bruun Rule. Although no transgressive signature is found, there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change, or both. This decrease in the coastal sand volume is likely to result in increased future erosion.
Original languageEnglish
Pages (from-to)1494-1503
JournalEarth Surface Processes and Landforms
Volume41
Issue number11
Early online date2 Feb 2016
DOIs
Publication statusPublished - 15 Sep 2016

Keywords

  • coastal erosion
  • headland-bound bay
  • climate change
  • dynamic coastline stability
  • sea-level rise (SLR)
  • high water mark (HWM)

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