General characteristics of long waves around the South African Coast

Abstract

Long-period waves are almost invisible waves due to the long wave-lengths of several hundreds of metres and heights of only decimetres. The effect of these long waves can, however, be devastating in the form of harbour basin oscillations and their effect on moored ships. Measurements indicate that the South African coast and ports are exposed to relatively high levels of long wave energy. This exposure can lead to significant mooring problems in some of the ports. Data on long waves have been collected in a number of ports where moored ships experienced excessive motions. This information formed the basis of an assessment of the long wave conditions around the South African coast. Since the long waves could be correlated with offshore swell conditions, it was also possible to derive a predictive algorithm to forecast the long waves a number of days in advance.