Time series analysis of data measured in the nearshore area

Abstract

ENGLISH ABSTRACT : Factors that lead to the generation of currents in the nearshore area within the Natal Bight were investigated. The investigation was carried out on data that spans from the 6th June 2012 to the 16th January 2013. The data comprised current measurements, wave measurements, water level measurements, as well as wind measurements. The measurements were decomposed into different direction components in order to study their impacts on corresponding current measurements. Current measurements were resolved into tidal currents and non-tidal currents through the use of harmonic analysis. Stokes drift was estimated using a monochromatic spectrum to obtain the wave induced current. The effect of the wind on the currents was analysed through the use of wind roses and duration analysis. The study was completed with an exploration of the contribution of the Agulhas current. It was found that the waters are characterized by a semi-diurnal, micro-tidal system and tides have a limited contribution to the generation of currents. The contribution of Stokes drift to the overall currents is less than that of tides. Wind is the most significant generator of the nearshore currents.

AFRIKAANSE OPSOMMING : Faktore wat lei tot die opwekking van strome in die kusgebied binne die Natal Bog (Eng. Natal Bight) was ondersoek. Die ondersoek is uitgevoer op data wat strek vanaf die 6de Junie 2012 tot die 16de Januarie 2013. Die data bestaan uit stroom metings, golf metings, watervlak metings asook wind metings. Die metings word ontbind in verskillende komponente ten einde die impak daarvan op die ooreenstemmende stroom metings te bestudeer. Stroom metings was onderskeidelik in gety strome en nie-gety strome verdeel deur gebruik te maak van harmoniese analise. Stokes dryf was bereken deur van ’n monochromatiese golfspektrum gebruik te maak. Die uitwerking van die wind op die strome is analiseer deur die gebruik van wind rose en ’n analise van die duurte waaroor winde uit spesifieke rigtings gewaai het. Die studie is voltooi met ’n ondersoek na die bydrae van die Agulhas-stroom tot die gemete strome. Daar is gevind dat die waters gekenmerk word deur ’n twaalf-uurlikse, mikro-gety stelsel en dat getye ’n beperkte bydrae tot die opwekkinging van strome het. Die bydrae van Stokes dryf tot die algehele strome is minder as die bydrae van getye. Wind is die belangrikste stroomopwekker van die strome langs die kus.