Durban - Scientists are predicting that several Durban beaches and other parts of the KwaZulu-Natal coastline could be in for severe coastal erosion in the winter of 2015 because of the influence of the moon.
Writing in the latest South African Journal of Science, the researchers suggest that a phase of the moon known as the lunar perigee subharmonic cycle will create far stronger gravity effects on the ocean, in so doing worsening normal winter coastal erosion at Umdloti, uMhlanga, Westbrook, eManzimtoti, Submarine Bay (near Scottburgh), Umkomaas and Trafalgar beaches.
Three South African researchers – Alan Smith, Lisa Guastella and Andrew Mather – and British oceanographer Ivan Haigh, said one of the most severe coastal erosion events was in March 2007 when an 18.6-year lunar nodal cycle coincided with a powerful cold front and equinox tides.
However, recent analysis of coastal-erosion records dating back to 1937 as well as more recent photographic images also suggest a pattern of increased erosion every 4.4 years.
The researchers note that the exact relationship between lunar cycles and coastal erosion in KZN still needed more study.
“Whether the moon is influencing coastal erosion directionally through increased tidal current action, or indirectly by influencing the weather (and hence the swell climate) has yet to be established.”
They also said there are several known erosion hot spots. These are areas where beaches were underlain by shallow bedrock (uMhlanga, Umdloti and Westbrook) or places with wide, sandy and deep beaches (eManzimtoti, Submarine Bay, Umkomaas and Trafalgar).
During June 2011, for example, the swell height off Durban was only about 3m offshore and about 4.5m inshore, but the swells came from an unusual direction and also had a longer duration.
The researchers predict that coastal erosion similar to the winter of 2011 is likely to become more severe over time because of rising sea levels, a predicted increase in wave heights and continuing destruction of the coastal dune cordon by developers.
They recommend that coastal planners should consider diarising 2015 for planning purposes.
However, there is no indication in their article that the 2015 erosion will be as severe as the March 2007 storm damage, which devastated several parts of the KZN coastline, at a time when wave heights rose to more than 8.5m and also coincided with the equinox, a severe storm at sea and the 18.6 year lunar nodal cycle. - The Mercury