Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The various consequences of climate change pose a significant threat to developments near the coast. These threats include saltwater intrusion, coastal erosion and flooding. In the coastal context, the climate change effect often raising the most concern is that of sea-level rise. Much work has therefore been done on the linear setback caused by a rise in sea-level. In order to get the full picture of possible changes caused by sea-level rise, the secondary effects of a rising sea-level also need to be considered. Sea-level rise could cause changes to the nearshore wave climate and could have impacts such as coastal erosion and changes to the coastline shape. The primary objective of this study was therefore to investigate the effects of sea-level rise on the nearshore wave climate and, consequently, the coastline stability. Other consequences of climate change considered in this study include increasing average wave heights and a rotation of offshore wave directions. The many headland-bay beaches on the South African coastline are generally in a state of dynamic equilibrium and find their planforms based on the local wave climate. Changes to the wave climate may therefore disrupt the equilibrium shapes of these bays. This study was therefore also aimed at investigating the effects of the changes to the wave climate on the stability of headland-bay beaches. The three consequences of climate change expected to affect the nearshore wave climate were identified as (1) sea-level rise; (2) an increased wave height; and (3) changing offshore wave angles. Although changes to storm frequency and intensity are also possible, the impacts of these changes were not studied. In order to assess the impacts of the three considered changes on a typical headland-bay beach, two numerical models were set up for Mossel Bay – a headland-bay beach on the southern coast of South Africa. The modelling approach included a wave transformation model to calculate nearshore wave climates from offshore data and a coastline model to assess the stability of the bay under the changed nearshore wave climates. The model results indicated that the rising sea-level alone would cause changes in the nearshore wave direction. These changes were shown to alter the longshore sediment transport regime such that rotations are expected in the south-western corner and eastern end of Mossel Bay. These rotations do not include the cross-shore effects of inundation and erosion, as suggested by models such as the Bruun Model. The results for an increased offshore wave height were inconclusive. The southerly rotation in offshore wave angles was shown to affect the nearshore wave angles. These changes affected the longshore transport regime such that the outward sediment transports were reduced. A minor accretion resulted in the centre of the bay for a 1° southerly rotation in offshore wave angles. For a 2° rotation, the extent of accretion increased and shifted towards the eastern end of the bay, primarily due to the dominance of south-westerly waves in the local wave climate. A valuable observation was made regarding the current stability of Mossel Bay. Inter-tidal reefs are present along three sections of the bay. These reefs protect the coastline such that the current bay shape contains sharp bends between the reefs. Under a rising sea-level, however, the effect of the reefs will become less pronounced. If a water level should be reached where these reefs become less significant, the planform of the bay is expected to smooth out through a significant redistribution of sediment. This smoothing effect was shown to cause erosion of the coastline in the order of 80m near the town of Klein Brak River. / AFRIKAANSE OPSOMMING: Die verskeie gevolge van klimaatsverandering bied ‘n merkwaardige bedreiging vir ontwikkelings naby die kus. Hierdie bedreigings sluit die versouting van varswaterbronne, kuserosie en oorstromings in. Vir kusgebiede is seevlakstyging gereeld die effek van klimaatsverandering wat die meeste kommer wek. Dus is heelwat navorsing rakende die direkte erosie as gevolg van seevlakstyging reeds gedoen. Om die volle beeld van die gevolge van ‘n stygende seevlak te verkry, is dit egter nodig om ook die sekondêre effekte hiervan in ag te neem. Seevlakstyging kan veranderinge in die golfklimaat naby die kus veroorsaak, en kan impakte soos kuserosie en veranderende baaivorms tot gevolg hê. Die primêre doel van hierdie studie is dus om die effek van seevlakstyging op die golfklimaat by die kus en gevolglik die stabiliteit van die kuslyn, te ondersoek. Benewens die styging van die seevlak word die effekte van groter gemiddelde golfhoogtes en die rotasie van diepsee golfrigtings ook in hierdie studie ondersoek. Die vele landpunt-baaie (headlandbay beaches) op die Suid-Afrikaanse kus is meestal in ‘n dinamiese ekwilibriumtoestand, waarvan die vorm deur die lokale golfklimaat bepaal word. Veranderinge aan dié golfklimaat mag dus die ekwilibrium vorms van sulke baaie versteur. Hierdie studie het dus ook die stabilititeit van landpuntbaaie onder ‘n veranderende golfklimaat ondersoek. Die drie gevolge van klimaatsverandering wat verwag word om die golfklimaat naby die kus te beïnvloed is geïdentifiseer as (1) seevlakstyging; (2) vergrote golfhoogtes; en (3) veranderende diepsee golfhoeke. Veranderinge aan die frekwensie en intensiteit van storms is ook moontlike gevolge van klimaatsverandering, maar die impakte hiervan is nie in die studie ondersoek nie. Twee numeriese modelle is toegepas om die impak van die drie bogenoemde gevolge op Mosselbaai – ‘n tipiese landpunt-baai aan die suidkus van Suid-Afrika – te ondersoek. ‘n Golfmodel is ingespan om die golfklimaat naby die kus te bepaal waarna ‘n kuslynmodel gebruik is om die stabiliteit van die baai onder die veranderde golfklimaat te ondersoek. Die resultate van die studie dui daarop dat die golfhoeke naby die kus beïnvloed word deur seevlakstyging. Daar is aangetoon dat dié veranderinge die langsstroomvervoer sodanig sal verander dat kuslynrotasies in die suid-westelike hoek asook die oostelike rand van Mosselbaai verwag word. Hierdie rotasies sluit nie die lineêre landwaartse verplasing van die kuslyn as gevolg van erosie en oorstroming in nie. Die effek van vergrote golfhoogtes kon nie met akkuraatheid ondersoek word nie. Daar is wel gevind dat die suidwaartse rotasie van diepsee golfhoeke rotasies in die golfklimaat naby die kus veroorsaak. Hierdie rotasies verander die langsstroom sedimentvervoer sodanig dat die uitwaartse sedimentvervoer verminder word en ‘n klein opbou van sediment in die middel van die baai vir ‘n 1° diepsee rotasie verwag word. Vir ‘n 2° suidwaartse rotasie is daar ‘n groter opbou van sediment wat verder ooswaarts veplaas is. Die ooswaartse veplasing is primêr ‘n gevolg van die oorheersing van suid-westelike golftoestande in die golfklimaat. ‘n Waardevolle gevolgtrekking rakende die huidige stabiliteit van Mosselbaai is ook gemaak. Langs drie gedeeltes van die Mosselbaaise kus word riwwe in die gebied tussen hoog- en laagwater aangetref. Hierdie riwwe beskerm die kus sodanig dat skerp kinkels in die vorm van die baai tussen die riwwe gesien kan word. Wanneer die seevlak styg, word die beskermende effek van die riwwe egter minder doeltreffend. Indien ‘n watervlak bereik word waar dié effek genoegsaam verminder is, word daar verwag dat die baai deur ‘n merkwaardige verplasing van sediment die kinkels sal uitstryk. Deur hierdie proses word erosie in die orde van 80m naby die dorp van Klein Brakrivier verwag.

Les littoraux sableux dominés par l'action des vagues sont des zones très dynamiques où l'aléa érosion menace les activités humaines et la sécurité des personnes. Comprendre et prévoir les évolutions du trait de côte est crucial pour informer et guider les gestionnaires du littoral. Actuellement, aucun modèle numérique ne permet de reproduire les évolutions du trait de côte sur l'ensemble des échelles spatio-temporelles et des configurations de côte requises du fait de limitations numériques et physiques. Cette thèse se concentre sur le développement de nouveaux outils de modélisation à complexité réduite pour simuler les évolutions du trait de côte le long des littoraux sableux dominés par l'action des vagues sur des échelles de temps allant de l'heure à plusieurs décennies avec des temps de calcul réduits. D'abord, un modèle statistique de trait de côte s'appuyant uniquement sur les occurrences saisonnières de régimes de temps est développé. Ce modèle permet de simuler la variabilité du trait de côte à l'échelle pluriannuelle, sans avoir besoin de connaitre les conditions de vagues ou de modéliser le transport sédimentaire. Puis, un nouveau modèle numérique de trait de côte basé sur les vagues (LX-Shore) est développé en intégrant entre autres les forces de certains modèles existants. Il inclut les processus cross-shore et longshore, et couple la dynamique du trait de côte à la propagation des vagues via le modèle spectral de vagues SWAN. Ce modèle permet de simuler l'évolution de formes complexes comme par exemple les flèches sableuses. Ces outils ouvrent aussi la voie vers une meilleure évaluation des évolutions futures du trait de côte, ainsi que de la contribution respective des processus impliqués. / Wave-dominated sandy coasts are highly dynamic and populated systems increasingly threatened by erosion hazard. Understanding and predicting shoreline change is critical to inform and guide stakeholders. However, there is currently no numerical model able to reproduce and predict shoreline evolution over the full range of temporal scales and coastal geometries owing to numerical and physical limitations. This thesis focuses on the development of new reduced-complexity models to simulate shoreline change along wave-dominated sandy coasts on the timescales from hours to decades with low computation time. First, a statistical shoreline change model based on the seasonal occurrences of some oceanic basin weather regimes is developed. This model allows simulating shoreline variability at the seasonal and interannual scales, without resorting to wave data or sediment transport modeling. Second, a new so-called LX-Shore numerical wave-driven shoreline change model is developed, which takes the best from some existing models and includes additional numerical and physical developments. LX-Shore couples the primary longshore and cross-shore processes and includes the feedback of shoreline and bathymetric evolution on the wave field using a spectral wave model. LX-Shore successfully simulates the dynamics of coastal embayments or the formation of subsequent nonlinear evolution of complex shoreline features such as flying sandspits. It is anticipated that LX-Shore will provide new and quantitative insight into the respective contributions of the processes controlling shoreline change on real coasts for a wide range of wave climates and geological settings.

This paper examines the regional longshore sediment transport pattern of the seaward coast of the United States and Gulf of Mexico from northern Maine to Tampa Bay, Florida. From previous studies it is known that along the coast there are variations in direction of sediment transport known as nodal zones as well as variations in sediment transport rate. Wave Information Study (WIS) hindcast data for the interval 1976 through 1995 (United States Army Corps of Engineers, 2003) provide a spatially continuous model of the regional longshore current directions in the study area. In chapter one, all available published field studies of longshore current direction and sediment transport directions and rates are compiled to create a description of the direction and, whenever possible, magnitude of longshore transport. A detailed compilation of regional and local published studies are provided in tables. An interpretation of sediment transport rates and directions is provided in eight regional maps of the study area. In chapter two the results of the literature compilations are compared with gross and net potential sediment transport directions and rates modeled using WIS hindcast data. The WIS deep-water wave characteristics are used to predict the directions and rate of longshore sediment transport at local outer coast positions using the method of Ashton et al. (2003a). The WIS-derived transport directions, including nodal zones, generally agree with the published field studies, although there are a few local inconsistencies particularly near inlets, shoals and irregular bathymetry. Trends in longshore transport rates, such as increases and decreases in gross transport rates are well represented by the WIS-derived potential transport rates. The discrepencies between the published field studies and WIS results are apparently primarily due to assumptions in the WIS model, such as assuming shore-parallel bathymetric contours.

Actuellement, la prévision de l'évolution d'un système littoral représente un enjeu social important. De nombreuses études sont réalisées afin de mieux connaitre la dynamique côtière et donc de comprendre les facteurs qui influencent son évolution. Cette dynamique est contrôlée par la morphologie, les apports sédimentaires, l'hydrodynamique, l'eustatisme... qui agissent à des échelles de temps différentes et avec de fortes interactions. A l'échelle géologique, l'architecture des dépôts, contrôlée par l'eustatisme et la subsidence, est parfaitement décrite dans les zones à forts apports sédimentaires. Par contre, dans les zones à faibles apports sédimentaires, l'enregistrement des cortèges côtiers est réduit et est difficile à interpréter. L'analyse de 250 kilomètres de profils sismiques THR sur le littoral languedocien (Nord du Golfe du Lion, France), de carottages et de données de terrain a permis de déterminer la géométrie en trois dimensions des cortèges sédimentaires côtiers depuis le Quaternaire jusqu'à l'actuel. Ces observations montrent l'importance de la dynamique longshore sur les littoraux pauvres en apports sédimentaires directs. De plus, l'étude d'un système lagunaire sur ce littoral met en évidence les concepts de lagunes protégées et lagunes isolées ainsi que l'importance des vallées incisées dans la génèse de ces environnements. Enfin, la modélisation en laboratoire des processus d'incision de chenaux sous contrôle eustatique et climatique permet de discuter le rôle des vallées incisées en milieu côtier.

A numerical model based on one-line theory is developed to evaluate the wind wave driven longshore sediment transport rate and shoreline change. Model performs wave transformation from deep water through the surf zone and computes the breaking parameters. The formula of longshore sediment transport rate used in the numerical model is selected as a result of comparative studies with the similar expressions and the field measurements. Offshore breakwater module of the numerical model is developed to compute the change of shoreline behind single or multiple offshore breakwaters. The validity of the numerical model was confirmed by comparing model results with the shoreline change given within the sheltered zone behind the offshore breakwaters. A series of offshore breakwaters are hypothetically proposed for a case study where a series of groins were constructed whose numerical model results qualitatively matched well with the field measurements. The results of the influences of offshore breakwaters on the shoreline predicted by the model are discussed comparatively with the case study.

In this study, a numerical model is developed to determine shoreline changes due to wind wave induced longshore sediment transport, by solving sediment continuity equation and taking one line theory as a base, in existence of seawalls, groins, T-groins, offshore breakwaters and beach nourishment projects, whose dimensions and locations may be given arbitrarily. The model computes the transformation of deep water wave characteristics up to the surf zone and eventually gives the result of shoreline changes with user-friendly visual outputs. A method of representative wave input as annual average wave characteristics is presented. Compatibility of the currently developed tool is tested by a case study and it is shown that the results, obtained from the model, are in good agreement qualitatively with field measurements. In the scope of this study, input manner of long term annual wave data into model in miscellaneous ways is also discussed.

Longshore sediment transport rate was measured during energetic sea breeze activity, on intermediate-to-reflective sandy beaches in Southwestern Australia. Estimates of suspended load were obtained using backscatter sensors, current meters and streamer traps. Total load was determined using fluorescent tracer sand and an impoundment study. The measurementsw ere cross-compareda nd usedt o evaluates everalw idely-used longshore transport equations. The streamer trap measurement revealed an exponential distribution of the suspended sediment flux with vertical mixing decreasing in the onshore direction. A continuous time series of the longshore suspended sediment flux across the surf zone was obtained by combining the streamer trap measurements with data collected using surf zone instruments. Comparison of the suspended longshore flux with the total longshore flux derived from the dispersal of the sand tracer indicated that the relative contribution of the suspendedlo ad to the total load was at least 59 %. The movement of sandt racer on four different beaches demonstrated that nearshore sediments were transported obliquely across the surf zone, challenging our conventional view of dividing nearshore sediment transport into cross-shore and longshore components. Furthermore, tracer was found to move from the outer surf zone to the swash zone and vice versa, indicating a cross-shore sediment exchange. The contribution of the swash zone to the total longshore flux was estimated around 30-40 %. Despite large differences in the temporal and spatial scales of the measurement techniques, the littoral drift rates are comparable, suggesting a northward transport rate of 138,000-200,000 m3 year-1. Longshore sediment transport during sea breezes is mainly the result of a high longshore energy flux exerted by wind waves. This is accurately predicted by the equations of Inman and Bagnold (1963) and CERC (1984). The bimodal wave field, characteristic of Southwestern Australia, renders the Kamphuis (1991b) formula unsuitable in this instance.

As ondas geradas por tempestades causam as alterações mais significativas na costa arenosa. Este trabalho avaliou a influência da variabilidade interanual do clima de ondas nos processos costeiros do litoral Sudeste e Sul do Brasil. O clima de ondas foi determinado a partir de resultados entre 1997 e 2010 do modelo numérico NOAA WAVEWATCH III (NWW3) com seis pontos de água profunda. O modelo numérico MIKE 21 SW foi utilizado para verificar o efeito destas ondas na Enseada de Massaguaçu (SP) e no trecho Sul de Imbituba (SC). Foram simuladas as direções de ondas mais frequentes e foi calculado o transporte longitudinal de sedimentos gerado por elas. As ondas do quadrante Sul foram mais energéticas e não foi identificado um padrão na variação interanual do clima de ondas. Em São Paulo, as direções de onda mais frequentes (Sul e Sul-Sudoeste) não geraram quantidade efetiva de transporte de sedimentos, e foram as ondas de Leste-Sudeste a Sudeste-Sul que geraram a maior quantidade de transporte longitudinal de sedimentos. Em Santa Catarina foram as ondas de Leste a Sul que geraram maior transporte longitudinal de sedimentos. / The coastal dynamics is mainly controlled by waves, being the energetic storm waves the most influential. This study aims to assess the wave climate influence on coastal processes in the South and Southeastern coast of Brazil. The wave climate was defined through NOAA WAVEWATCH III (NWW3) numerical model results for six offshore points, from 1997 to 2010. In order to propagate the waves onshore the Spectral Wave FM from MIKE 21 numerical model has been applied on Massaguaçu bay (SP) and Imbituba (SC). Most frequent storm waves have been simulated for each year and sector and sediment longshore transport along each sector was calculated. Waves from the South are the most energetic. There is no clear interanual pattern in the time-series. For SP, the most frequent directions (South and South-Southwest) do not generate considerable longshore sediment transport, with East-Southeast to Southeast-South waves generating most sediment transport, which was northwards for all beaches. In SC the sediment transport was northwards in Vila and Vila Nova beaches and southwards on Itapirubá beach, with waves from Eastern and Southern quadrants generating more longshore sediment transport.

A deriva litorânea é estudada no litoral sul do Espírito Santo através de diferentes técnicas: distribuição de Minerais Pesados (MP); modelo conceitual Análise de Transport de Sedimento (Sediment Trend Analysis - STA), através da variação de parâmetros texturais do sedimento; dados de clima de onda entre 1997 e 2010 do modelo global WaveWatch III propagados para a zona costeira através do modelo Delft-3D, fornecendo parâmetros necessários para as equações de deriva; e imagens de satélite e fotografias aéreas para avaliar a variação espaço-temporal da morfologia costeira. O modelo STA mostrou-se confiável apenas nos dois setores ao norte, enquanto nos demais os resultados foram mascarados por altos teores de MP e/ou carbonato e a entrada de outras fácies no sistema; as equações representaram bem a variação da morfologia costeira na área de estudos. De maneira geral, os setores ao sul apresentaram transporte longitudinal para sul, e os setores ao norte, para norte, fato relacionado à batimetria local. A orientação da linha de costa auxiliou na compreensão dos fenômenos erosivos, pois em sua maioria estão orientados no sentido NEN, formando 45º com as ondas dos setores de ESE e SE. / Longshore drift is studied in the southern portion of Espírito Santo through different techniques: Heavy Minerals (HM) distribution; the conceptual model Sediment Trend Analysis (STA) by sediment textural parameters fluctuation; wave climate data between 1997 and 2010 from WaveWatch III propagated to the coastal zone through Delft-3D model, providing the required data for longshore drift equations; and satellite images and aerial photograph to survey time-space coastline variations. The STA model appears to be trustworthy only within the northern sectors, as high HM and/or carbonate content and different facies input into the system may mask the results. Broadly speaking, the southern sectors showed longshore transport southward, while northern sectors showed northward longshore transport, which is related to local bathymetry. Shoreline azimuth helped understanding the location of erosive zones, since most of them are turned NEN, 45o with ESE and SE wave sectors.

Os ambientes costeiros podem ser caracterizados por sua grade dinâmica, onde existe o embate entre o continente e o mar. A dinâmica sedimentar da linha de costa constitui conhecimento básico em obras de engenharia e na compreensão do ambiente costeiro. Buscou-se compreender os mecanismos do funcionamento dinâmico da região em torno do Porto de Tubarão, Vitória-ES, através de análises de marés, de clima de ondas, agitação marítima, de correntes induzidas por ondas e transporte sedimentar. Os resultados permitiram algumas interpretações tanto de curtíssimo prazo como de longo prazo. As correntes de marés são particularmente importantes, sobretudo próximo as bocas dos canais de Vitória e da Passagem atingindo valores de até 0,.7m/s. As ondas atingem a área com alturas significativas variadas, dependendo do grau de exposição. Na praia de Camburi as ondas dificilmente ultrapassam 1 metro de altura significativa, enquanto na praia Mole ondas de 2.5m de altura significativa ocorrem com certa freqüência. A direção da corrente na praia Mole está diretamente relacionadas com as direções de incidência das ondas variando de NE até SW, enquanto sua intensidade está relacionada com as alturas e períodos, variando de 0 até 0.44 m/s. A praia de Camburi, por sua vez apresenta correntes rumo ENE independente da direção de propagação das ondas ao largo da Baia do Espírito Santo. As velocidades médias variam entre 0 e 0,3 m/s. O porto de tubarão serve de abrigo às ondas, influenciando na direção média do fluxo de energia nas praias adjacentes. A longo prazo a tendência da praia de Camburi é de sofrer uma rotação acentuando os processos erosivos na porção ocidental. / The coastal zones can be characterized by the huge dynamic battle, continent forces against the ocean forces. The sedimentary dynamic of the coast line is a basic knowledge necessary to carry out engineering features and to understand the natural coastal environment. This work tried to understand the mechanisms that control those dynamics in the region near to the Tubarão Harbour, Vitória- ES. The effects of the tides, wind generated wave clima, wave induced currents and sedimentary transport was analyzed in short and long terms. In short terms, tide currents are specially important near the estuaries mouth (Vitória and Passagem channels), with velocities reaching 0.7m/s. The waves reach the coast line with different significant wave heights, depending on the each site expositions to in coming waves. At Cambury beach the waves hardly gets significant wave height over 1meter, in other hand, at Mole beach, waves with 2,5m significant wave height are quite often. At Mole beach, wave induced currents directions are directly correlated with the wave direction in outside zones, oscillating between NE and SW directions. The current velocities, which depends on wave height and wave period, presents values between 0 and 0,44 m/s. At Cambury beach the currents always goes to ENE, independent of outside wave directions. The velocities varies between 0 and 0,3 m/s. The Tubarão harbour acts like a wall creating shadows for the incident waves in the beaches behind. In long terms, the Mole beach seems to be stable and Cambury Beach seems to rotate some degrees of it mean direction, with the intensifications of the erosional process in the oriental portion of the beach.