Erosion along the West Coast over the last few decades has seen a vast portion of South Africa’s longest beach disappear into the Atlantic Ocean.
Also read: 10 things to do in Yzerfontein – a surfer’s paradise on the West Coast
A comparison between aerial photographs taken in 1937 indicates that Sixteen Mile Beach in the West Coast National Park has narrowed by 52m over the last 85 years.
The most eroded area is roughly 6km north of Ysterfontein, where the shore is 100m closer to the dunes than it was a little under a century ago. Scientists predict that the ocean could reach the foot of the dune by 2040.
This is according to the team from Wits and Free State Universities who analysed Sixteen Beach amid concerns that the country’s 3,000km of coastline are under threat of destruction from coastal erosion.
Last week, in an article published in the peer-reviewed journal Remote Sensing, scientists stated that the “severe and rapid erosion” 80km north of Cape Town has accelerated, adding that coastlines change dynamically under the influence of factors such as storms, sediment movements, infrastructure development and sand mining.
“While coastal erosion is exacerbated by climate-driven sea level rise and anthropogenic forces, the extent and severity vary from region to region,” they say.
According to the scientists, these findings “could potentially be attributed to broader changes in the overall coastal and inland dune systems that have occurred over the decades, or changes in regional ocean and climate systems”.
Their research marked the shoreline on 20 aerial photographs from 1937, 1960 and 1977 and on satellite images taken at five-year intervals between 1985 and 2020. Specialised technology was then used to create maps, tables and heatmaps depicting the erosion of the beach.
The findings were that 95% of the beach had experienced erosion, with an average loss of 38m.
A 100m slice of the beach at its southern end lost 99.29m while a similar slice in the north gained 13,8m. “Sixteen Mile Beach experienced the greatest average change of 52,13m,” say the scientists.
“The most drastic changes are those between 2015 and 2020, whereby most of the shoreline shows an increased landward movement. All of Pearl Bay, Yzerfontein main beach and the southern end of Sixteen Mile Beach show the largest amount of change within this period.”
The beach is a “logarithmic spiral”, meaning it has developed its gentle curve in the “shadow zone” created by the rocky headland on which most of Yzerfontein is built.
“A possible reason for these differences in erosion trends could be how the wave energy is dissipated along this extensive log-spiral beach system,” say the scientists.
The team, consisting of Jennifer Murray, Elhadi Adam, Stephan Woodborne and Mary Evans from Wits, as well as Duncan Miller and Sifiso Xulu from UFS, said their model does not show “substantial movement” from the current high-water line.
“The forecasting model is only based on statistical trends in the data and must therefore be used with caution since it cannot take into account other parameters such as underlying geology, beach profile or wave conditions,” they say. “Such forecasts cannot be the main tool for coastal management and planning.”
Also read:
Pictures: Cape{town}Etc Library and Remote Sensing
