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Tropical Cyclone-Induced Waves and Storm Surge at four locations along the Southern African East Coast

dc.contributor.advisorSchoonees, J. S.en_ZA
dc.contributor.authorVan Niekerk, David Jamesen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.en_ZA
dc.date.accessioned2016-12-22T13:06:05Z
dc.date.available2016-12-22T13:06:05Z
dc.date.issued2016-12
dc.identifier.urihttp://hdl.handle.net/10019.1/100020
dc.descriptionThesis (MEng)--Stellenbosch University, 2016.en_ZA
dc.description.abstractENGLISH ABSTRACT: Tropical cyclones are synoptic scale rotating storms that form over oceans with warm water, producing powerful winds and rainfall. The characteristic low pressure of the system and the extreme winds generate high levels of storm surge, ocean waves and currents, which pose a threat to a coast and its infrastructure. The social and economic consequences of these storms can be devastating, often resulting in human fatalities. Quantification of the risk exposure to these storms is therefore crucial for human safety and the design of infrastructure along the coast of a tropical cyclone-prone region, such as the Southern African East Coast. Considerable research into the risk presented by tropical cyclones, has been conducted using numerical models, although very little has been done for the South-West Indian Ocean. The present research focusses on the tropical cyclone-induced waves and storm surge, along the Southern African East Coast. The primary results of this thesis are estimates of the 50-, 100-, 200- and 500-year significant wave height and storm surge levels, expected to be produced by tropical cyclones, at four locations along the Southern African East Coast. Third-generation numerical models were used to generate the wave and storm surge estimates at the four locations, namely; Durban, Maputo, Beira and Pemba. Historical tropical cyclone data from the Best Track data, as well as the results of other studies, were used to develop input parameters for the numerical models. Sensitivity tests of these parameters were conducted in order to see how each parameter influences the model results. The results of the sensitivity tests were used to determine the design storm parameters for the proposed numerical model tests. The model tests comprised of simulating a tropical cyclone varying in time and space, resulting in estimates of the significant wave height and storm surge levels at the location of interest. A total of four return periods were simulated for each of the four locations, resulting in a total of 16 simulations. The output of the simulations were specified at points along the 20 m contour for the waves and the 10 m contour for storm surge. These depths were chosen in order to determine estimates before certain coastal processes such as refraction and diffraction, have a major influence on the results. The numerical model was calibrated by simulating Hurricane Ike, which occurred over the Gulf of Mexico in September 2008. The model produced reasonably good results when compared to the measured data, although the model did under-estimate the storm surge. It is advisable to take this into account when using the estimates of the expected storm surge levels. The results of the model tests indicate that the expected waves produced by tropical cyclones along the Southern African East Coast, do pose a major threat and need to be taken into consideration in the planning and design of coastal infrastructure. The largest waves are expected to occur at Beira and the smallest at Durban. At the 100-year return period, Durban, Maputo, Beira and Pemba are expected to produce significant wave heights of 2.1 m, 4.6 m, 6.3 m and 4.4 m respectively. Estimates of the expected tropical cyclone-induced storm surge indicate that Durban and Pemba are not at risk of flooding, with maximum expected storm surge levels of roughly 0.3 m at the 500-year return period. Beira and Maputo on the other hand, are potentially at risk with maximum storm surge levels of 2.1 m and 1.1 m respectively, at the 500-year return period.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Tropiese siklone is sinoptiese skaal roterende storms wat oor oseane met warm water vorm, wat lei tot kragtige winde en reënval. Die kenmerkende lae druk van die stelsel en die uiterste winde, wek hoë vlakke van stormvloed, see golwe en strome, wat 'n bedreiging vir die kus en sy infrastruktuur inhou. Die sosiale en ekonomiese gevolge van hierdie storms kan verwoestend wees, dikwels lei dit tot menslike sterftes. Kwantifisering van die risiko blootstelling aan hierdie storms is dus noodsaaklik vir menslike veiligheid en die ontwerp van infrastruktuur langs die kus waar tropiese siklone voorkom, soos die Suider-Afrikaanse Ooskus. Aansienlike navorsing oor tropiese sikloon risiko modellering is gedoen hoewel baie min al gedoen is vir die Suid-Wes Indiese Oseaan. Die huidige navorsing fokus op golwe wat veroorsaak word deur tropiese siklone en die stormvloede langs die Suider-Afrikaanse Ooskus. Die primêre resultate van hierdie tesis is skattings van golfhoogte en stormvloed vlakke vir die 50-, 100-, 200- en 500-jaar herhaal periodes wat na verwagting deur tropiese siklone geskep sal word. Die skattings is vir vier plekke langs die Suider-Afrikaanse Ooskus gedoen. Derde generasie numeriese modelle is gebruik om die golf en stormvloed skattings op die vier plekke te genereer, naamlik; Durban, Maputo, Beira en Pemba. Historiese tropiese sikloon data van die Best Track data, sowel as die resultate van ander studies, is gebruik om die inset-parameters te ontwikkel vir die numeriese modelle. Sensitiwiteit toetse van hierdie parameters is uitgevoer ten einde te sien hoe elke parameter die model resultate beïnvloed. Die resultate van die sensitiwiteit toetse is gebruik om die invoer parameters te bepaal van die voorgestelde numeriese model toetse. Die model toetse bestaan uit die simuleering van 'n tropiese sikloon wat varieer in tyd en ruimte, wat lei tot skattings van die golfhoogte en stormvloed vlakke by die plek van belang. 'n Totaal van vier herhaal periodes was gesimuleer vir elk een van die vier plekke, wat lei tot 'n totaal van 16 simulasies. Die uitset van die simulasies is gespesifiseer op punte langs die 20 m kontoer vir die golwe en die 10 m kontoer vir die stormvloed. Hierdie water dieptes was gekies om skattings te bepaal voordat sekere kus prosesse soos breking en diffraksie, ‘n groot invloed op die resultate het. Die numeriese model is gekalibreer deur die simuleering van Orkaan Ike, wat plaasgevind het oor die Golf van Mexico in September 2008. Die model het redelike goeie resultate gelewer in vergelyking met die gemeet data, alhoewel die model die stormvloed onder-skat het. Dit word aanbeveel om dit in aanmerking te neem wanneer die skattings van die verwagte stormvloed vlakke gebruik word. Die resultate van die model toetse dui daarop dat die verwagte golwe wat deur tropiese siklone geskep word langs die Suider-Afrikaanse Ooskus, 'n groot bedreiging is en moet in ag geneem moet word in die beplanning en ontwerp van die kus infrastruktuur. Die grootste branders word verwag om plaas te vind naby Beira en die kleinste naby Durban. By die 100-jaar herhaal periode, kan Durban, Maputo, Beira en Pemba na verwagting beduidende golf hoogtes onderskeidelik verwag van 2.1 m, 4.6 m, 6.3 m en 4.4 m. Die beramings van die verwagte tropiese sikloon wat stormvloede veroorsaak, dui daarop dat Durban en Pemba nie in gevaar van oorstromings is nie, met 'n maksimum verwagte stormvloed vlak van sowat 0.3 m by die 500-jaar herhaal periode. Beira en Maputo aan die ander kant, is moontlik in gevaar met 'n maksimum stormvloed vlak van 2.1 m en 1.1 m onderskeidelik, by die 500-jaar herhaal periode.af_ZA
dc.format.extentxviii, 59 pages : illustrations, mapsen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.subjectCyclones --Tropicsen_ZA
dc.subjectWavesen_ZA
dc.subjectStorm surgesen_ZA
dc.subjectHydrodynamics -- Mathematical modelsen_ZA
dc.subjectUCTDen_ZA
dc.titleTropical Cyclone-Induced Waves and Storm Surge at four locations along the Southern African East Coasten_ZA
dc.typeThesisen_ZA
dc.description.versionMastersen-ZA
dc.rights.holderStellenbosch Universityen_ZA


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