Beach and dune erosion along the coast of Richards Bay, South Africa and implications for the management of shoreline change

Abstract

Sandy beaches are dynamic in nature and are subject to natural and anthropogenic processes that influence its evolution. One of the key drivers of coastal evolution is the erosion of the coastline. Sandy beaches are more susceptible to erosion because its fine sand is easily erodible. Since approximately 80% of South Africa’s coastline consists of sandy beaches, including environmentally sensitive dune systems, the impetus is to improve our knowledge and understanding of processes taking place at the coastal zone to aid in coastal zone management and planning for future hazards. This research integrated the use of geographical information systems (GIS), remote sensing, and modelling techniques to contribute knowledge on the interrelationships between the spatial and temporal dynamics of shoreline changes along the coast of Richards Bay, South Africa. Shoreline change rates were quantified over a 45 year period between 1977 and 2022 using the United States Geological Survey’s Digital Shoreline Analysis System. The historical data was then used to estimate future shoreline positions 10 and 20 years into the future. The results of the shoreline analysis revealed consistent erosion north of the Richards Bay harbour with a net shoreline movement of 167.80 m in some areas. The beaches south of the harbour recorded an accretional trend with a net shoreline movement of 98.90 m in some areas. The study verified that the development of the port breakwaters has caused an interruption the longshore sediment transport pattern, resulting in accretion on the updrift side (South), and erosion on the downdrift (North). The shoreline change rate statistics were used to predict future shoreline positions using the Extrapolated Linear Regression method 10 and 20 years into the future. In the context of climate change and associated sea level rise, model based approaches in ArcGIS Pro were used to assess the vulnerability of the study area to inundations caused by storm surges. The inundation screening was initated for four different surge levels using a high resolution DEM as input. The results indicated that during a 9 and 10 m storm surge, 60 and 68% of the study area respectively was inundated which serves as important baseline information for disaster risk assessments. This dissertation also explored possible pathways to coastal resilience and proposed strategies to mitigate coastal erosion and flooding in a changing environment.

Strande is dinamies en onderhewig aan natuurlike en antropogeniese prosesse wat die evolusie daarvan beïnvloed. Een van die belangrikste dryfkragte van kusevolusie is erosie van die kuslyn. Strande is meer vatbaar vir erosie omdat fyn sand maklik erodeerbaar is. Ongeveer 80% van Suid-Afrika se kuslyn bestaan uit hoofsaaklik sand dominante strande wat omgewings belangrikke duinstelsels behels. Dus is die doel van hierdie projek om ons kennis en begrip van kussoonprosesse te verbeter asook om te help met kussonebestuur en beplanning vir toekomstige gevare. Hierdie navorsing maak gebruik van ‘n metode wat geografiese inligtingstelsels (GIS), afstandswaarneming en modelleringstegnieke behels. Met die doel om die onderliggende verband tussen die ruimtelike en temporale dinamika van kuslynveranderinge langs die kus van Richardsbaai, Suid-Afrika, beter te verstaan. Die kuslynveranderingstempo's is oor 'n tydperk van 45 jaar, tussen 1977 en 2022, gekwantifiseer met behulp van die Verenigde State se Geologiese Opname se Digitale Kuslynanalisestelsel (DSAS). Hierdie historiese data was gebruik om die toekomstige kuslynposisies te skat oor 10 en 20 jaar. In sommige gebiede het die studie erosie noord van die Richardsbaai-hawe uitgewys met 'n totale kuslynbeweging van 167.80 m. Strande suid van die hawe het 'n akkresionele tendens vertoon met 'n netto kuslynbeweging van 98.90 m in sommige gebiede. Met klimaatverandering en stygende seevlaktes ingedagte, was ArcGIS Pro gebruik om die kwesbaarheid van die studiegebied vir stormvloede te modeleer en assesseer. Vier verskillende stormvloed scenarios was getoets met behulp van hoë resolusie DEMs. Die resultate wys dat 60 of 68 persent van die studiegebied sal vloed met ‘n 9 of 10 m stormvloed scenario en dien as ‘n belangrikke basislyn for toekomstige ramp en risikoassesering. Verder, ondersoek hierdie navorsing opsies om kusveerkragtigheid te verbeter en stel strategië voor om die impak van kuserosie en vloede te versag in ‘n area wat klimaatverandering ondervind.