Abstract
Abstract. Sandy shorelines are dynamic with constant changes that can cause hazards in developed areas. The causes of change may be either natural or anthropogenic. This paper evaluates evidence for shoreline changes and their causative factors using a case study on the east coast of South Africa. Beach morphology trends were found to be location-specific, but overall the beaches show a receding trend. It was hypothesized that wave, tide, sea level and wind trends as well as anthropogenic influences are causative factors, and their contributions to shoreline changes were evaluated. Maximum significant wave heights, average wave direction, peak period and storm event frequencies all show weak increasing trends, but only the increases in peak period and wave direction are statistically significant. The chronic beach erosion cannot be attributed to wave climate changes since they are still too small to explain the observations. Instead, the impacts of sea level rise and reductions in the supply of beach sediments are suggested as the main causative factors. The analysis also identifies a trend in the frequency of severe erosion events due to storms that coincide with a 4.5-yr extreme tide cycle, which demonstrates the potential impact of future sea level rise.
Highlights
Shoreline erosion has long been a concern to engineers (Kinmont, 1954)
2 DeMcaedthalodtrsends in beach morphology need to be considered in formulating coastal management plans to mitigate f2u.t1ure Criaskses.sTtuhdroyusgithea case study of the east coast of South Africa, this paper aims to evaluate evidence for (1) trends in sThhoerelciintye/boefaDchurebvaonluitsioan;p(o2p)uclhaarntgoeusriisnt wdeasvteincaltiimonateonsutchhe aesatsrtecnodassitnowf aSvoeuptharAamfreictear(sFaingd. /1o)r. thLeikferemquaennyccyooafsteaxltrceitmiees eDveunrbtsa;n(3is) clionnkcserbneetwd eaebnousthtohreelriinsek/sbepaocshedchbaynwgeasveanadndwsaevdecilmimenattetrtreennddss. oTrhoetheeTrhceakuwsaintiiveMfuanctiocirps.ality (Durban’s local authority) has adopted a pro-active approach to addressing climate change issues and has recently begun to quantify the 2potMenetitahloidmspacts
37 yr of beach profile data on the east coast of South Africa have been analyzed for evidence of trends
Summary
Shoreline erosion has long been a concern to engineers (Kinmont, 1954). Long-term erosion of a coastline has three main causes: sea level rise (e.g. Mather, 2008; Han et al, 2010), meteorological changes (Rouault et al, 2009, 2010) that may result in wave climate changes, and a reduction in sediment supply. Woodroffe (2003) identified waves as the principal energy source for erosion in the coastal zone, while erosion due to an increase in water level is a well-developed concept (Bruun, 1962). Zhang et al (2004) analyzed the recovery of the US east coast barrier beaches and found that the beaches recovered to their long-term trend positions after storms regardless of storm severity. Zhang et al (2004) stated that, since no evidence has been given to show significant increases in storminess and since human interference is neither worldwide in extent nor uniform regionally, sea level rise is the most plausible contributor. It is worth noting that this statement may not consider dams and sediment mining on rivers that are arguably a worldwide human interference and contribute to long-term coastal erosion. Wave data were not considered, and Singh (1997) identified significant erosion. Since anthropogenic impacts such as sediment mining are not an issue in Trinidad, it was speculated that the erosion was from sea level rise
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