South Africa’s beaches lack sufficient monitoring, hindering the holistic understanding of shoreline dynamics under increasing environmental and anthropogenic pressures. This study addresses this critical knowledge gap by using an enhanced, semi-automated CoastSat algorithm to create the first comprehensive shoreline database for South Africa, spanning nearly all sandy coastal areas from 1984 to 2023 (an average of 750 data points per transect, every 100 m alongshore). The satellite-derived data demonstrated good accuracy (R = 0.95) against surveyed data, with an overall root-mean-square-error (RMSE) of 8.5 m to 13.7 m, and bias reduced by up to 79% when wave runup was additionally accounted for. Despite relatively inaccurate beach-face slope estimations at some sites (R = 0.45), the satellite-derived shoreline positions proved to be accurate. This study reveals the spatial and temporal complexity of shoreline dynamics along South Africa’s coast. While shoreline change rates across coastal municipalities were generally moderate (~ 1 m/year), notable local variations were observed. Adjacent municipalities often exhibited contrasting trends, highlighting the influence of localised drivers on shoreline dynamics. Persistent accretion was most notable in northern KwaZulu-Natal. The total envelope of average yearly shoreline change for many beaches of South Africa ranged from 5 m to 20 m, with some areas reaching up to 30 m. Seasonal shoreline variability was strongly modulated by local geomorphology and wave exposure, with deeply indented bays showing clear gradients in seasonal shoreline positions and response, and river mouths and rocky features respectively amplifying or dampening variability. However, regional differences were evident: the West and South Coasts exhibited similar erosion-accretion cycles, while the East Coast—particularly north of Port St Johns—experienced dominant erosion in spring and accretion during winter in its far northern reaches. Year-on-year shoreline changes (m/year) were similar in magnitude across all three regions, with both accretion and erosion having a similar occurrence at mild and extreme rates. Additionally, major storm events—such as the March 2007 storm in KwaZulu-Natal—demonstrated the potential for region-wide erosion. This first-of-its-kind resource for South Africa will guide informed, effective and sustainable coastal management strategies and engineering design.

Monitoring and Analysis of South African Shoreline Dynamics Using Satellite Imagery

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发表日期：

2025年12月13日

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Danie Theron,
Andre Karl Theron

摘要

South Africa’s beaches lack sufficient monitoring, hindering the holistic understanding of shoreline dynamics under increasing environmental and anthropogenic pressures. This study addresses this critical knowledge gap by using an enhanced, semi-automated CoastSat algorithm to create the first comprehensive shoreline database for South Africa, spanning nearly all sandy coastal areas from 1984 to 2023 (an average of 750 data points per transect, every 100 m alongshore). The satellite-derived data demonstrated good accuracy (R = 0.95) against surveyed data, with an overall root-mean-square-error (RMSE) of 8.5 m to 13.7 m, and bias reduced by up to 79% when wave runup was additionally accounted for. Despite relatively inaccurate beach-face slope estimations at some sites (R = 0.45), the satellite-derived shoreline positions proved to be accurate. This study reveals the spatial and temporal complexity of shoreline dynamics along South Africa’s coast. While shoreline change rates across coastal municipalities were generally moderate (~ 1 m/year), notable local variations were observed. Adjacent municipalities often exhibited contrasting trends, highlighting the influence of localised drivers on shoreline dynamics. Persistent accretion was most notable in northern KwaZulu-Natal. The total envelope of average yearly shoreline change for many beaches of South Africa ranged from 5 m to 20 m, with some areas reaching up to 30 m. Seasonal shoreline variability was strongly modulated by local geomorphology and wave exposure, with deeply indented bays showing clear gradients in seasonal shoreline positions and response, and river mouths and rocky features respectively amplifying or dampening variability. However, regional differences were evident: the West and South Coasts exhibited similar erosion-accretion cycles, while the East Coast—particularly north of Port St Johns—experienced dominant erosion in spring and accretion during winter in its far northern reaches. Year-on-year shoreline changes (m/year) were similar in magnitude across all three regions, with both accretion and erosion having a similar occurrence at mild and extreme rates. Additionally, major storm events—such as the March 2007 storm in KwaZulu-Natal—demonstrated the potential for region-wide erosion. This first-of-its-kind resource for South Africa will guide informed, effective and sustainable coastal management strategies and engineering design.