Tidal characteristics of South Africa

Abstract

The tidal characteristics of South Africa are explored in the present study by means of a calibrated and validated regional numerical model. The coastal tidal characteristics and semi-diurnal resonance of the South African coastline have yet to be accurately quantified. Model development was conducted in the numerical code Delft 3D for a two year simulation period. A horizontal model resolution of 1/16th geographical degree was employed. The results were calibrated against long-term measured water levels provided by the South African Navy Hydrographic Office. Model validation was performed for each major constituent's amplitude and phase lag at nine coastal locations around the South African coastline. Regional, two-dimensional comparisons were also made between this study's model results and those of the data assimilative TPXO 8 African regional model. The tide was characterized in terms of constituent amplitude and phase lag, Form Factor and tidal ellipse eccentricity regional by means of map plots. The model was particularly sensitive to bathymetry-related friction and model resolution. Accurate model results were obtained, providing the first identification and quantification of the semi-diurnal coastal resonance around South Africa. The phase lag associated with the shallower shelf areas is also clearly observed with Form Factor calculations confirming the semi-diurnal dominance of the South African coastline. The intermediate and shallow water friction-induced phase lag of the mixed progressive and standing tidal wave is also mapped, together with the tidal current phase lags.