Thesis (Masters Diploma (Engineering))--Cape Technikon, 1997 / The idea for this study occurred when movement of the caisson extension to the breakwater was observed. The major concern was, what would happen if the caisson breakwater extension failed? What would the financial implications be to the port? The CSIR have carried out a number of studies with regards to the safety of the structure. The consequences of caisson failure and the possible effects on the port were however not investigated. When it was determined that settlement was taking place, information concerning the condition of the caisson structure and factors influencing the structure were gathered. Investigations on the following were done: (a) Extent of caisson settlement. (b) Sediment movement around the structure. (c) Foundation condition. (d) Wave impacts of long and short period waves on the Ben Schoeman Dock in the event of caisson failure. (Refraction and diffraction). (e) Financial implications due to possible container operation downtime at Ben Schoeman Dock in the event of caisson failure. (f) The tourist potential of the structure. The conclusion reached in this study was that the Ben Schoeman Dock would not be adversely effected if partial or complete failure of the main breakwater should take place. One could even question the length of the extension and whether it was actually required. The recommendations of this study would be as follows follows: Maintain the caisson extension in good condition as it will be important for possible future extensions to the port. Develop the breakwater as it is an asset which has potential for tourism to Cape Town.

ENGLISH ABSTRACT: Current understanding of the hydraulic stability of a stacked geotextile tube structure under wave attack is limited. Failure mechanisms that lead to instability are complicated and there is, as yet, no generic approved design method. 2D physical modelling in the large wave/current flume of the Stellenbosch University was done to test various set-up and hydraulic conditions to determine the hydraulic stability of a stacked geotextile tube structure against wave attack. Sixty-five test runs of approximately 1,000 waves each were run. Modelling was done on two different scales that had good similitude, despite the fact that the same geotextile and fill material were used in both. The results provided by the physical modelling gave wave conditions larger than anticipated for hydraulic stability. It was found that the term ―failure‖ was too loosely defined in most cases and that, depending on the definition of structure failure the severity of the wave conditions at failure increased substantially. Sliding was found to be the key failure mechanism for a structure constructed from stacked, 80% sand filled, geotextile tubes. The crest tube receives the most severe loading and is the critical tube in the structure. Structures with double tube crests were found to be negligibly more stable than structures with single tube crests, but reduce energy transmission to the leeside of the structure. Impact loading of the structure combined with wave transmission over the structure explained the wave force on the crest tube of the structure. A modified Goda (1974) method incorporating a wave reduction factor for wave transmission and an angle descriptive of the crest tube position were used. The descriptive angle was derived from results obtained from the physical modelling. The use of this method provides results that correlate well with those found in the physical modelling and with results obtained in previous research. The method has the additional advantage that it is less constrained by limitations for application than those of previous studies / AFRIKAANSE OPSOMMING: Die begrip van die hidroliese stabiliteit van ‘n struktuur gebou uit gepakte geotekstielsandbuise teen golf aanval, is tans beperk. Faal meganismes wat lei tot die onstabiliteit van ‘n struktuur is ingewikkeld en daar is geen generiese aanvaarde ontwerp metode tans in gebruik nie. 2D fisiesemodellering is in die groot golfkanaal van die Universiteit Stellenbosch uitgevoer. ‘n Verskeidenheid van struktuur-uitlegte en hidroliese toestande is getoets om die hidroliese stabiliteit van die struktuur teen golf aanval te bepaal. ‘n Totaal van 65 toetse van ongeveer 1,000 golwe elk is voltooi. Modellering is op twee verskillende skale gedoen, wat goed vergelyk het ten spyte van die feit dat dieselfde geotekstiel en vul materiaal in albei gebruik is. Resultate verkry vanaf die fisiese modellering het groter as verwagte golftoestande vir hidroliese stabiliteit gegee. Dit is gevind dat die definisie van faal (mislukking) in die meeste gevalle swak beskryf is en dat, afhangende van wat as faal van die struktuur beskou word, die golftoestande aansienlik beïnvloed word. Die skuif van die buise is die hoof faal meganisme vir ‘n gepakte geotekstielbuis-struktuur met ‘n vulpersentasie van 80%. Die buis op die kruin van die struktuur word die swaarste belas en is die kritiese buis in die struktuur. Strukture met dubbel buis kruine is onbeduidend meer stabiel as dié met slegs ‘n enkele buis as kruin. Die energie wat na die lysy van die struktuur oorgedra word, is egter beduidend minder. Impak belasting van die struktuur gekombineer met golf-transmissie oor die struktuur, verduidelik die stabiliteit van die buis op die kruin van die struktuur. ‘n Gemodifiseerde Goda (1974) metode met ‘n golfverminderigs faktor word gebruik om golf-transmissie oor die struktuur te akkommodeer, saam met ‘n hoek wat beskrywend is van die posisie van die kruin buis. Die beskrywende hoek is afgelei uit resultate verkry uit die fisiesemodellering. Hierdie metode gee resultate wat goed korreleer met dié verskaf deur die fisiese modellering en die resultate van vorige navorsing oor geotekstielbuis stabiliteit. Die metode het ‗n bykomende voordeel deurdat dit minder begrens is deur beperkings m.b.t. toepassing as die van vorige studies.

The planning and management of coastal and river structures such as breakwaters, groynes, jetties, bridges and tidal inlets require accurate predictions of equilibrium morphologies. Generally these types of situations are modelled numerically using process - based models, where wave, current and sediment transport modules are applied over a number of time - steps until a steady - state morphology is obtained. Two alternative methods have been developed and applied in this thesis, based on self - organisation and entropy approaches. The self - organisation - based method utilises a cellular automata model, where local rules produce a global stable pattern through positive and negative feedback. The entropy - based method is able to predict equilibrium morphologies directly. It compares different randomly generated morphologies using an objective function and optimisation, instead of moving to an equilibrium morphology through intermediate states. This avoids some potential problems associated with traditional models such as error propagation and reliance on accurate initial conditions. The models developed in this thesis have been applied to a number of case studies. It was found that the cellular automata model obtained a higher Brier Skill Score than a comparable process - based model when predicting the equilibrium morphology associated with a channel obstruction. The entropy - based method was able to predict a realistic erosional channel in a coastal lagoon, similar to field observations at the Murray River Mouth in South Australia. It had difficulties predicting the deposition pattern due to the bias of the objective function towards erosional environments. The entropy - based method outperformed a conventional model prediction of the equilibrium erosional channel associated with a laboratory - sized lagoon, but similar problems were observed with its deposition predictive ability. The modelling methods developed in this thesis are a first step into the use of non - traditional, entropy - and self - organisation - based models for the prediction of complex equilibrium morphologies. They have made use of non - conventional models in order to explore different objective function formulations or self - organisation rules and the sensitivity of these, and have compared the models to laboratory results. The work documented in this dissertation shows that it is possible to use self - organisation - and entropy - based modelling methods to predict stable, equilibrium morphologies in coastal and river environments. / Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2006.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Sea-level rise due to climate change results in deeper water next to existing coastal structures, which in turn enables higher waves to reach these structures. Wave overtopping occurs when wave action discharges water over the crest of a coastal structure. Therefore, the higher waves reaching existing structures will cause higher wave overtopping rates. One possible solution to address increasing overtopping, is to raise the crest level of existing coastal structures. However, raising the crest level of a seawall at the back of a beach, will possibly obstruct the view to the ocean from inland. Alternatively, recurves can be incorporated into the design of both existing and new seawalls. The recurve wall reduces overtopping by deflecting uprushing water seawards as waves impact with the wall. The main advantage of seawalls with recurves is that their crest height can be lower, but still allow for the same wave overtopping rate as vertical seawalls without recurves. This project investigates the use of recurve seawalls at the back of a beach to reduce overtopping and thereby reducing the required wall height. The objectives of the project are twofold, namely: (1) to compare overtopping rates of a vertical seawall without a recurve and seawalls with recurves; and (2) to determine the influence that the length of the recurve overhang has on the overtopping rates. To achieve these objectives, physical model tests were performed in a glass flume equipped with a piston type wave paddle that is capable of active wave absorption. These tests were performed on three different seawall profiles: the vertical wall and a recurve section with a short and a long seaward overhang, denoted as Recurve 1 and Recurve 2 respectively. Tests were performed with 5 different water-levels, while the wall height, wave height and period, and seabed slope remained constant. Both breaking and non-breaking waves were simulated. A comparison of test results proves that the two recurve seawalls are more effective in reducing overtopping than the vertical seawall. The reduction of overtopping can be as high as 100%, depending on the freeboard and wave conditions. Recurve 2 proves to be the most efficient in reducing overtopping. However, in the case of a high freeboard (low water-level at the toe of the structure), the reduction in overtopping for Recurve 1 and Recurve 2 was almost equally effective. This is because all water from the breaking waves is reflected. Even for the simulated lower relative freeboard cases, the recurve walls offer a significant reduction in overtopping compared with the vertical wall. A graph is presented which shows that the length of the seaward overhang influences the overtopping performance of the seawall. As the seaward overhang length increases, the wave overtopping rate decreases. However, for high freeboard cases the length of the seaward overhang becomes less important. The graph gives designers an indication of how recurves can be designed to reduce seawall height while retaining low overtopping. It is recommended that further model tests be performed for additional overhang lengths. Incorporation of recurves into seawall design represents an adaptation to problems of sea-level rise due to global warming / AFRIKAANSE OPSOMMING: Stygende seevlak as gevolg van klimaatverandering, veroorsaak dat dieper water langs bestaande kusstrukture voorkom. Gevolglik kan hoër golwe hierdie strukture bereik. Golfoorslag vind plaas wanneer water oor die kruin van ‘n kusstruktuur, hoofsaaklik deur golfaksie, spat of vloei. Dus sal hoër golfhoogtes tot verhoogde golfoorslag lei. Een moontlike oplossing vir hierdie verhoogde golfoorslag is om die kruinhoogte van bestaande kusstrukture te verhoog. In die geval van ‘n seemuur aan die agterkant van ‘n strand, kan hoër strukture egter die see-uitsig na die see vanaf die land belemmer. Om hierdie probleem te vermy, kan terugkaatsmure in die ontwerp van bestaande en nuwe seemure ingesluit word. Terugkaatsmure verminder golfoorslag deurdat opspattende water, afkomstig van invallende golwe terug, na die see gekaats word. Die grootste voordeel van ‘n terugkaatsmuur is dat hierdie tipe muur ‘n laer kruinhoogte as die vertikale seemuur sonder ‘n terugkaatsbalk, vir dieselfde golfoorslagtempo kan hê. Hierdie projek ondersoek dus die gebruik van terugkaatsmure aan die agterkant van ‘n strand met die doel om golfoorslag te verminder en sodoende die vereiste muurhoogte te verminder. Die doelwit vir die projek is tweeledig: (1) om die golfoorslagtempo van terugkaatsmure te vergelyk met dié van ‘n vertikale muur sonder ‘n terugkaatsbalk; en (2) om die invloed van die terugkaatsmuur se oorhanglengte op die golfoorslagtempo te bepaal. Om bogenoemde doelwitte te bereik, is fisiese modeltoetse in ‘n golfkanaal, wat met ‘n suiertipe golfopwekker toegerus is en wat aktiewe golfabsorbering toepas, uitgevoer. Hierdie toetse is op drie verskillende seemuurprofiele, naamlik ‘n vertikale muur en ‘n terugkaatsmuur met ‘n kort en lang oorhang, genaamd “Recurve 1” en “Recurve 2” onderskeidelik, uitgevoer. Die muurhoogte, die seebodemhelling asook die golfhoogte en –periode is tydens al die toetse konstant gehou. Vir elke profiel is toetse by 5 verskillende watervlakke vir beide brekende en ongebreekte golwe uitgevoer. Uit die toetsresultate is dit duidelik dat terugkaatsmure meer effektief as vertikale mure is om golfoorslag te beperk. Die vermindering van golfoorslag kan tot 100% wees, afhangende van die vryboord en golftoestande. Daar is bevind dat “Recurve 2” golfoorslag die effektiefste verminder. In die geval van hoë vryboord (lae watervlak by die toon van die struktuur) is daar egter gevind dat “Recurve 1” en “Recurve 2” die golfoorslag feitlik ewe goed beperk. Dit is die geval aangesien alle water van die brekende golwe weerkaats word. In die geval van ‘n lae vryboord, word die voordeel van die terugkaatsmuur teengewerk deurdat daar ‘n kleiner verskil in golfoorslagtempo’s tussen die drie profiele is. ‘n Grafiek is voorgelê wat wys dat die lengte van die terugkaatsmuur se oorhang golfoorslag beperk. ‘n Groter oorhanglengte van die terugslagmuur veroorsaak ‘n groter vermindering in golfoorslag. Vir gevalle met ‘n hoë vryboord, is daar egter gevind dat die oorhanglengte van die terugslagmuur minder belangrik is. Hierdie grafiek gee ontwerpers ‘n aanduiding van hoe terugslagmure ontwerp kan word met ‘n lae hoogte terwyl ‘n lae oorslagtempo behou word. Die gebruik van terugslagmure bied ‘n aanpassing vir die probleme van seevlakstyging, as gevolg van klimaatverandering.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: For the safekeeping or harbouring of small craft, whether for leisure or commercial use, a tranquil basin is the principle requirement in designing a functional harbour facility. Waves transmitted through the perimeter structures of a marina result in agitation of the basin and thereby a reduction in tranquillity. Similarly, waves reflected off the perimeter structures that line entrance channels could result in difficulty when manoeuvring through the entrance channel water areas. An alternative to the conventional breakwater becomes a necessity when the conventional mass-filled or caisson breakwaters are not feasible in technical or financial terms. One of the alternative options could be to consider a piled row breakwater. In broad terms, this consists of closely spaced piles that attenuate wave energy whilst not forming an impermeable barrier, allowing for currents and sediment to pass through. When comparing the different options for creating a piled row breakwater the quantity of material used to achieve a desired level of wave dissipation could be the most important aspect in considering possible alternatives, as this would relate directly to construction costs and time when considering implementation. A literature review revealed multiple references to theories that predicted the transmitted and reflected waves for various breakwater porosities and wave conditions. However, there is limited coverage in literature enabling prospective designers. For example, literature describing the applicable ranges of shape configurations that one should start off with when developing concepts is not readily available. This thesis study used physical modelling to compare the wave transmission properties of breakwaters comprised of three different piled element shapes, namely round, square and diagonal square piles. The pile element shapes are compared for varying porosity values over a range of input wave parameters. A comparison of the transmission incurred by these configurations with previous work is presented and it was found that the physical model experiment closely simulated the predicted values. The tests were scaled from actual conditions in possible marina locations and therefore the performance criteria measured could be applied in reverse to potential site locations. From analysis of the physical model results, it was clear that the highest energy loss was found, in general, to occur with low porosities (below 10%), as could be expected. For a fixed screen configuration in terms of pile element shape and porosity, the performance is heavily dependent on wave steepness, the steeper waves incurring a lower transmission coefficient than the less steep waves. For a given porosity, circular piles performed the best (transmit the least) followed by square piles and then diagonal square. When comparing the material used, diagonal square piles yielded better performing breakwaters due to the expanded cross section gained in elevation. The work has provided useful insight into the performance of piled row breakwaters in restricting transmission of wave energy. Design guidance has been provided when considering the parameters for deriving conceptual layouts for piled row breakwater structures. Recommendations were put forward for further work in this field, including potential study areas, data gathering, and study methods, as well as more applied uses of piles, for example in combination with other elements in a marina. / AFRIKAANSE OPSOMMING: die veilige bewaring van klein vaartuie, hetsy vir ontspanning of kommersiële gebruik, is die hoofvereiste in die ontwerp van 'n funksionele hawe fasiliteit dat die beskermde hawegebied ‘n rustende water oppervlak sal moet handhaaf. Golwe wat oorgedra word deur die omtrek golfbrekers van ‘n hawe deur middel van transmissie veroorsaak oppervlak versteurings in die hawe bak en dus ook ongewensde versteurings in die vasmeer kondisies. Op ‘n soortgelyke wyse, veroorsaak golwe wat gereflekteer word vanaf die toegangs kanaal golfbrekers problematiese kondisies vir die navigeer van bote deur die kanaal. Die behoefte aan 'n golfbreker alternatief vir die konvensionele oplossing word genoodsaak wanneer die konvensionele stortrots of caisson golfbrekers nie haalbaar is nie as gevolg van tegniese of finansiële aspekte (Park et al. 2000). Een van die opsies wat oorweeg kan word as 'n alternatief is ‘n heipaal-ry tipe breekwater. In breë terme, bestaan dit uit naby gespasieërde heipale om golf energie te breek, sonder om ‘n ondeurdringbare versperring te vorm. Wanneer die verskillende opsies vir die skep van 'n heipaal-ry tipe breekwater vergelyk word, kan die hoeveelheid konstruksie materiaal benodig per opsie die belangrikste vergelykende parameter word. Die rede hiervoor is die direkte verwantskap aan konstruksie kostes sowel as tyd aspekte wat gepaardgaan met die konstruksie materiaal hoeveelhede. Vanuit die literatuurstudie is verskeie verwysings geïdentifiseer waarin vorige teorieë oor oordrag en refleksie van golwe evalueer word vir wisselende porositeit waardes en intree golf waardes. Daar is egter 'n beperkte dekking in die literatuur wat ontwerps-riglyne betref. Byvoorbeeld, die toepaslike omvang van die vorm konfigurasies wat oorweeg moet word wanneer konsep ontwerp gedoen word, is nie geredelik beskikbaar nie. Hierdie tesis vergelyk, deur middel van fisiese skaal model toetse, drie heipaal-ry element vorms, naamlik ronde, vierkantige en diagonal geroteerde vierkante vir verskillende porositeit waardes oor 'n verskeidenheid van golf inset parameters. 'n Vergelyking is getref tussen die toetsdata en vorige werk en daar is bevind dat die fisiese model eksperiment die voorspelde waades uit die literatuur redelik akkuraat kon naboots. Die toets kondisies is geskaal vanaf werklike moontlike marina terreine en dus kon die toets resultate toegepas word in die ontwerp van potensiële terreine. Vanuit die data-analise, is waargeneem dat die hoogste energie verliese oor die algemeen plaasvind by laer porosititeit waardes (onder 10%) soos wat verwag kon word. Vir 'n gegewe golfbreker opset, in terme van die heipaal element vorm en porositeit, is die verrigting hoogs afhanklik van die golf steilheid, met hoër verrigting by steiler golwe. Vir 'n gegewe porositeit, sal ronde heipaal elemente die beste verrigting gee, gevolg deur vierkante heipale en laastens diagonal geroteerde vierkante. Vir soortgelyke hoeveelheid heipale, sal diagonal geroteerde vierkante beter verrigting lewer moontlik as gevolg van die verlengde deursnit dimensie in vooraansig. Hierdie navorsing het goeie insig verskaf oor golfdeurlaatbaarheid en weerkaatsing van heipaalry breekwaters. Ontwerp riglyne word ook verskaf wat betref die parameters wat gebruik kan word vir die konsep ontwikkelings fase vir heipaal-ry breekwaters. Aanbevelings word gemaak vir verdere navorsingswerk in hierdie veld, insluitend moontlike studie-areas, data insameling, studie metodes, sowel as vir meer toegepasde situasies, byvoorbeeld waar die heipaal elemente in kombinasie met ander marina komponente ontwerp moet word.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Strand is located within False Bay and frequently encounters large quantities of wave overtopping over the coastal defences. This results in the damage of property and infrastructure and causes streets to be flooded. Physical modelling tests were done by a consultancy firm to determine a solution by making use of a recurve structure at the back of the beach. This study is an expansion of the previous physical modelling that was done and focuses on several factors that were not tested by the consultancy firm that could have an influence on the overtopping rate and provide additional information on the recurve design. These tests were: (i) the effectiveness of the proposed recurve wall design in reducing overtopping was compared to a vertical wall; (ii) the influence that modifications to the beach profile such as the beach slope, beach width and beach level have on the overtopping rate; and (iii) the sensitivity of overtopping to changes in wave period was tested. The information gathered from these tests was used to propose a possible solution for the Strand. Numerical modelling was done with Delft3D-Wave to determine the wave height at the back of the beach using a nested grid. The waves at the Strand are depth limited and therefore very sensitive to changes in water level. By altering the beach level the model showed how the significant wave height at the back of the beach changes. First estimates of overtopping were determined using the relevant empirical calculations from the EuroTop Manual 2007 for a vertical seawall. No estimate could be made for the recurve wall since it did not fall in the valid range of the equations. From the physical modelling it was found that the overtopping reduced significantly from a vertical to a recurve seawall by a factor of about 50% depending on the wall height. All the prediction methods tested proved to be accurate in estimating the overtopping when the ratio of freeboard to significant wave height was ≤1.83. For non-breaking wave conditions the beach profiles that were gently sloped (1:50) and wide produced more overtopping than the beach profiles that were steep (1:10) and narrow. Increasing the beach level only decreased the overtopping if the water depth was shallow enough to cause the waves to break before they reached the back of the beach. Overtopping was found to increase with longer wave periods until the wave period became too long and the waves broke offshore which resulted in the overtopping decreasing. Possible solutions to overtopping were proposed based on two beach levels and the implementation of a recurve seawall. Revised crest levels for the wall were made along the length of the beach for both the 1:20 and 1:100 year water levels. / AFRIKAANSE OPSOMMING: Die Strand is in Valsbaai geleë en ervaar dikwels baie oorspoeling deur golwe bo-oor kusverdedigingswerke. Dit lei tot skade aan eiendom sowel as aan infrastruktuur en veroorsaak dat strate oorstroom. Fisiese modelleringstoetse is deur ’n konsultasiefirma gedoen om ’n oplossing te probeer vind deur van ’n teruggebuigde struktuur aan die agterkant van die strand gebruik te maak. Hierdie studie is ’n uitbreiding van die vorige fisiese modellering wat gedoen is en fokus op verskeie faktore wat nie deur die konsultasiefirma getoets is nie. Dit kan moontlik ’n invloed op die oorspoelingstempo hê en verskaf bykomende inligting oor die ontwerp van die terugbuiging. Hierdie toetse is: (i) die doeltreffendheid van die voorgestelde ontwerp van die teruggebuigde strandmuur in die vermindering van oorspoeling word vergelyk met ’n vertikale muur; (ii) die invloed wat veranderinge aan die strandprofiel soos die helling van die strand, die wydte van die strand asook die strandvlak op die oorspoelingstempo het; en (iii) die sensitiwiteit van oorspoeling op veranderinge in golfperiode is getoets. Die inligting wat uit hierdie toetse verkry is, word gebruik om ’n moontlike oplossing vir die Strand voor te stel. Numeriese modellering is met Delft3D-Wave gedoen om die golfhoogte aan die agterkant van die strand vas te stel deur van ’n genestelde ruitenet gebruik te maak. Die golwe by die Strand word deur diepte beperk en is dus baie sensitief vir veranderinge in die watervlak. Deur die strandvlakke te verander het die model getoon hoe die betekenisvolle golfhoogte aan die agterkant van die strand verander. Die eerste beramings van oorspoeling is bepaal deur van die relevante empiriese berekenings uit die EuroTop-handleiding 2007 vir ’n vertikale strandmuur gebruik te maak. Daar kon geen beraming vir die teruggebuigde muur gemaak word nie aangesien dit nie binne die geldige bereik van die vergelykings val nie. Uit die fisiese modellering is daar vasgestel dat oorspoeling noemenswaardig met ’n gemiddeld van ongeveer 50% verminder is, afhangend van die muurhoogte. Al die voorspellingmetodes wat getoets is was akkuraat in die beraming van die oorspoeling wanneer die verhouding van vryboord tot betekenisvolle golfhoogte ≤1.83 was. Vir nie-brekende golftoestande het strandprofiele met ’n lae helling (1:50) en wat wyd was meer oorspoeling tot gevolg gehad as strandprofiele wat steil (1:10) en nou was. ’n Verhoging in die strand se vlakke het die oorspoeling slegs verminder indien die diepte van die water vlak genoeg was om die golwe te laat breek voordat hulle die agterkant van die strand bereik het. Oorspoeling is gevind om te vermeeder met verlengde golflengte tot dat die golflengte só lank geword het dat die golwe in dieper water begin breek wat aanlieding tot verminderde oorspoeling gegee het. Daar word moontlike oplossings vir oorspoeling voorgestel gebaseer op twee strandvlakke en die implementering van ’n teruggebuigde strandmuur. Voorgestelde golfkruinvlakke vir die muur is al langs die lengte van die strand gemaak vir beide die 1:20- en 1:100-jaar watervlakke.

Thesis (MEng)–Stellenbosch University, 2014. / ENGLISH ABSTRACT: The Port of Durban is forecasted to reach its capacity in terms of container handling soon, which necessitates the investigation of an alternative port in the vicinity. The old Durban Airport site has been identified as a potential location to develop a new deep water container harbour. This is driven by a demand for deep water berth capacity as a result of shipping liners preferring the benefits of scale in their operations, leading to the use of larger ships with deeper drafts. To protect the new port from wave energy penetrating inside the basin as well as from sedimentation from the adjacent beaches, the design and construction of breakwaters are required. The proposed main breakwater for this dig-out port is expected to extend 1 200m into the sea, up to depths of 30m at the seaward roundhead. The deeper parts of the breakwater face wave onslaught in a different manner than a conventional breakwater in shallower waters. At these larger depths, the breakwater has to dissipate the energy of non-breaking waves. In this thesis, the wave climate nearshore, adjacent to the proposed breakwater is studied and extreme wave events are simulated with a SWAN numerical model. The results for a range of wave conditions, corresponding to selected events up to a return period of one in 100 years, are presented. A study of deep water breakwaters was undertaken to investigate other examples of similar structures. This indicated a clear distinction between vertical wall type breakwaters and the more traditional rubble-mound type breakwaters. For this thesis, a rubble-mound breakwater was chosen as the breakwater type for testing under conditions of the Durban Dig-Out Port (DDOP). Focussing on a deep water trunk section of the proposed main breakwater, a concept cross-section was designed using deterministic design methods. The formulae incorporated in this method did however not take into account the packing density of the armour layer and only assumed the recommended values. The hypothesis is thus put forward that the breakwater will still be hydraulically stable for packing densities below the recommended values. This would decrease material consumption and save on cost over the entire breakwater. A physical model was designed to experiment with different armour layer configurations of single- and double layer Cubipod arrangements. The unit was chosen for its massive shape and structural integrity even during impact. A physical model study was performed at the facilities of the CSIR in Stellenbosch. It entailed setting up a fixed-bed two-dimensional physical model in a glass wave flume. Measuring wave heights, wave reflection, overtopping, wave transmission and armour damage, the hydraulic stability and operational performance were analysed for several tests. Based on the results of the first few test series, alterations were made to the breakwater geometry and armouring. The results confirmed the hypothesis that lower packing densities were still hydraulically stable under 1 in 100 year return period wave conditions without inhibiting operational performance. A final cross-section is presented as concept design for the deep section of the proposed DDOP main breakwater. / AFRIKAANSE OPSOMMING: Volgens vooruitsigte gaan Durban hawe binnekort sy kapasiteit bereik wat die hantering van skeepshouers betref. Hierdie verwikkeling noodsaak die ondersoek na ‘n alternatiewe hawe in die nabye omgewing. Die voormalige Durban lughawe is intussen geïdentifiseer as ‘n potensiële perseel waar ‘n diep water houervrag hawe ontwikkel kan word. Dit word gedryf deur die aanvraag na diep water kaai kapasiteit as gevolg van skip operateurs wat skaalvoordele verkies, sodat groter skepe met diep rompe meer populêr word. Die ontwerp en konstruksie van breekwaters word dus benodig, om te verhoed dat beide golwe, sowel as sediment van aangrensende strande, die hawe binnedring. Die voorgestelde hoof breekwater vir hierdie hawe sal na verwagting tot 1200m in die see in strek, waar dit tot 30m diep is naby die seewaartse hoof van dié breekwater. Die dieper gedeeltes van só ‘n breekwater sal blootgestel word aan ‘n ander soort golf aanslag as ‘n soortgelyke konvensionele breekwater in vlakker water. In hierdie waterdiepte is die breekwater verantwoordelik vir die energie verbreking van ongebreekte golwe. In hierdie tesis word die golfklimaat langs die kus, naby aan die voorgestelde breekwater bestudeer. Die uiterste golf gebeurtenisse word gesimuleer met ‘n SWAN numeriese model. Die resultate van ‘n reeks golf kondisies, ooreenstemmend met bepaalde gebeurtenissemet herhaal periodes van tot 100 jaar, word aangebied. ‘n Studie van diep water breekwaters is onderneem om voorbeelde van soortgelyke strukture te ondersoek. Die studie toon ‘n definitiewe onderskeid tussen vertikale muur breekwaters en die meer tradisionele “rubble-mound” breekwater tipes. Vir hierdie tesis is die “rubble-mound” breekwater tipe gekies vir toetsing, onderhewig aan die kondisies van die “Durban Dig-Out Port” (DDOP). ‘n Konsep deursnit is ontwerp vir ‘n diep water romp gedeelte van die voorgestelde hoof breekwater, deur van deterministiese metodes gebruik te maak. Die formules soos vervat in hierdie proses maak egter nie voorsiening vir die pakdigtheid van die bewapeningslaag nie, maar aanvaar slegs die voorgestelde waardes. Die hipotese word dus aangevoer dat die breekwater steeds hidrolies stabiel sal wees vir pakdigthede wat laer as die voorgestelde waardes is. Dit sal die verbruik van materiale verlaag en lei tot koste besparings vir die breekwater. ‘n Fisiese model is ontwerp om te eksperimenteer met verskillende opstellings van die bewapeningslaag. Dit sluit enkel- en dubbel laag bewapening met Cubipod eenhede in. Hierdie eenheid is gekies vir sy massiewe vorm en strukturele integriteit, selfs tydens impak. ‘n Fisiese model studie is uitgevoer by die fasiliteite van die WNNR in Stellenbosch. Dit het die opstel van ‘n vaste-bodem, twee-dimensionele fisiese model in ‘n glas golftenk (“wave flume”) behels. Hidroliese stabiliteit en operasionele werksverrigting is geanaliseer deur golf hoogtes, -weerkaatsing, -oorslag, -deurlating, en skade aan die bewapening te meet vir verskeie toetse. Gebasseer op die resultate van die eerste paar toetsreekse, is veranderinge gemaak aan die breekwater se geometrie en bewapening. Die resultate het die hipotese bevestig dat laer pakdigthede steeds hidrolies stabiel is tydens golf kondisies met ‘n 1 in 100 jaar herhaal periode, sonder om die werksverrigting van die breekwater te belemmer. ‘n Finale deursnit word voorgestel as ‘n konsepontwerp vir die diep water deursnit van die DDOP se hoof breekwater.