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Two dimensional experimental and numerical modeling of wave transmission and wave-induced current over detached submerged breakwaters has been carried out in this thesis. Two preliminary 3D and a comprehensive series of 2D laboratory experiments have been conducted in the wave basin and 3 m wide wave flume. The preliminary 3D experimental tests qualitatively investigated the flow behavior behind a submerged breakwater and confirmed the validity of the 2D tests. The 2D laboratory tests examined wave breaking, reflection, transmission as well as wave-induced set-up and currents over submerged breakwater/reef structures. Different approaches to experimental data processing are examined in producing reliable application of the 2D laboratory measurements. Sensitivity of wave transmission coefficient, wave-induced set-up and wave-induced discharge over submerged breakwaters to other dimensional and non-dimensional parameters are comprehensively investigated. Previously published analytical/experimental studies for predicting/calculating wave breaking, wave transmission, wave-induced set-up and current are discussed and compared with the present experimental results. Improved equations/models are presented. Numerical modeling of the hydrodynamic effects of wave breaking and flow over a submerged breakwater is investigated using Delft3D. The capability of the Delft3D numerical model to simulate wave height transformation and wave-induced current over submerged breakwaters is provided. Four different approaches using combinations/options within the two main modules of Delft3D (SWAN and FLOW) are tested in the numerical simulations and the results are compared to the laboratory experimental data. Guidance is provided as to the most appropriate application of WAVE/FLOW/ROLLER modules in Delft3D for the reliable prediction of discharge and wave height over different width submerged breakwaters.

Thesis (M. Eng.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 68-69.

In this thesis, a numerical simulation model is applied to investigate the long-term shoreline changes behind detached breakwaters. The model includes three components, namely a wave model, a current model, and a shoreline change model. In the numerical simulations, various combinations of wave conditions and the placement of detached breakwater are chosen to explore the effect of detached breakwaters on the shoreline change. The results of calculation show that with incident wave angles within 0~45, wave height in the range of 0.5~1.5m, or the offshore distance to the detached breakwaters being 60~120m, the larger in any one of these three parameters is, the bigger the erosion distance onshore from the original shoreline and the extent of salient offshore are behind detached breakwaters. When incident angle of the wave increases, shoreline plan form becomes skewed, and the time required to arrive at equilibrium also increases, in addition to the position of the top of salient moves downcoast. Within the wave periods of 7~10 seconds tested, waves with large period are found to show slight decrease of the erosion distance onshore and the extent of salient offshore behind detached breakwaters. The plan form of the salient is not affected by wave period. However, the larger the wave period is, the sooner the long-tern shoreline will result. Moreover, for a detached breakwater constructed in the range of offshore distances within 1.0¡ÕS/B¡Õ2.0, variable offshore distances do not produce much difference in the erosion distance onshore and the extent of salient offshore behind detached breakwaters, and salient only will form. In the case of the S/B =< 0.8, a tombolo will result. Finally, the results of shoreline plan form from the numerical modeling are verified by the empirical parabolic bay shape equation of Hsu and Evans (1989), a small-scale hydraulic model, and two numerical models based on GENESIS and LITPACK. Overall, the result are in good agreement with these four different approaches, and therefore, the present model is suitable for practical engineering applications.

In the present study, the influence of geometric scale, unit orientation (alternatively, flow direction), and the dimensionless Reynolds and Keulegan-Carpenter quantities on the hydrodynamic loading of Core-Loc armour units is explored through a series of physical modelling tests under unsteady and oscillatory flow conditions.

A 2-D fully nonlinear numerical wave tank (NWT) is developed to investigate the Bragg resonance scattered by submerged multi-array breakwaters for random waves. This model is based on a boundary integral equation method with linear element scheme. The fully nonlinear free surface boundary condition is treated using the Mixed Eulerian-Lagrangian method and the 4th-order Runge-Kutta method. The incident random waves are generated by JONSWAP spectrum at one end of the wave tank. Two damping zones are deployed at both ends of the NWT to absorb the energy of the reflected and transmitted waves. In the regular wave cases, the results of Bragg reflection calculated are in good agreement with that of other experiments and numerical models. In addition, the simulated spectrum of random waves is also verified by the original input spectrum. The results of the random waves have the same trend as those of the Regular waves. The reflection coefficient for random waves at the first peak of resonance is about 70 percent of that of the regular wave, but the frequency of band width of Bragg effect has become wider and this advantage may compensate the peak reduction. Finally, we may conclude that the present model is adequate to use as a tool for coastal protection. Systematic studies for random waves propagating over series submerged breakwaters are conducted. The Bragg reflection will be enhanced with the increase of relative height, the length of bars, the number of breakwaters, and the toe angle of submerged breakwaters. In this study, it also reveals that the frequency of peak reflection for higher breakwaters has down shift phenomenon.

M. Tech. Electrical Engineering. / This dissertation presents vision-based systems for monitoring model breakwater armour structures. These model breakwater armour structures are subjected to wave simulations in model halls. The goal of this research was to produce a system that is able to detect changes in the model breakwater armour structure. These changes are detected autonomously or semi-autonomously depending on the method being used. The proposed systems are intended to replace the current flicker technique method, which is subject to human error. This dissertation reviews common image processing methods for monitoring changes in three dimensions. This review refines the search to two techniques, namely the stereopsis and fiducial methods. Each method approaches the problem differently. The stereo method treats the entire structure as a holistic 2.5D volume and shows changes in this volume. In the fiducial method special fiducial targets are attached to key areas on the breakwater armour units. The targets are tracked to compute displacement vectors.

This thesis examines the relationships between rising water levels, vulnerable land, and sedimentation within the Chesapeake Bay watershed. Climate induced sea level rise threatens low lying coastal land, especially in regions of continuing subsidence such as the Chesapeake Bay. Alterations to shorelines over time have impacted the ability of coastal landscapes to capture and build up sediment, exposing them to continual erosion. The low lying neighborhood of Belle View along the Potomac River is the focus of the investigation due to its vulnerability to flooding and its cultural and ecological connections to the adjacent landscapes of Dyke Marsh and the George Washington Memorial Parkway. Through careful placement of breakwater infrastructure, sediment will build over time as the water rises, mitigating the effects of coastal flooding in this region. Alterations to the landscapes of the marsh and parkway allow for their cultural and recreational values to be strengthened over time as the landscape adjusts to the rising sea level. / Master of Landscape Architecture / Climate change, or the belief that human activity is altering the earth's climate, is projected to increase the occurrence of flood events due to water levels rising over time from glaciers melting. Previously, shorelines have been hardened with levee or seawall infrastructure to creates a barrier between the water and developed land. Hardened shorelines may increase water velocity and reflect wave energy in riverine landscapes, consequentially disturbing natural shorelines. This disturbance leads to the gradual loss of sediment over time and therefore a loss of ground elevation. When landscapes lose elevation, they become more vulnerable to rising water levels and flooding. This relationships between shoreline types, sedimentation, rising water, and vulnerability inspired me to discover and design a threatened landscape that would capture sediment within the river's water column to build elevation over time and protect the adjacent development from rising water. The area encompassing the low lying neighborhood of Belle View, Dyke Marsh, and the George Washington Memorial Parkway along the Potomac River is the focus of the investigation due to its vulnerability to flooding. With a careful understanding of sediment capture infrastructure dynamics, the design introduces breakwaters on the site to allow sediment to build over time as the water rises. This research and design thesis demonstrates a strategy to create landscapes that will evolve over time to mitigate future flooding events and create more resilient landscapes.

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.

Le double tombolo de Giens, situé dans la ville de Hyères, dans le sud-est de la France, est une formation géomorphologique unique et rare dans le monde, qui relie l'île de Giens au continent. Il a été principalement formé en raison de la diffraction d'onde et de la réfraction par les îles. Il se compose de deux parties : la branche ouest (plage de l'Almanarre) directement en face du golfe de Giens et la branche orientale située sur la côte ouest de la baie d'Hyères. Ces parties sont séparées par l'étang salé des Pesquiers. La partie orientale du tombolo de Giens s'étend sur plus de dix kilomètres de l'embouchure de la rivière Gapeau au nord jusqu'à la plage de La Badine au sud. Les plages le long du tombolo oriental, en particulier les plages de Ceinturon et de Bona, sont sujettes à l'érosion et au rétrécissement en raison de causes naturelles et d'interférences humaines, mais les interventions anthropiques dominent.Afin d'atténuer ou d'empêcher l'érosion côtière, diverses structures côtières ont été utilisées le long du tombolo oriental de Giens. Elles ne peuvent résoudre l'érosion locale que dans certains cas, mais peuvent aussi engendrer des effets indésirables. Les structures côtières qui interfèrent avec le transport des sédiments le long des côtes, non seulement entraînent un déficit de sédiments et l'érosion dans la dérive en aval, mais aussi effacent le paysage environnant des plages.Les principaux objectifs de cette thèse étaient de mieux comprendre les processus physiques sous-jacents à la morpho-dynamique et d'anticiper l'évolution future du tombolo oriental de Giens en réponse aux différentes actions et interventions le long de la côte. La mesure structurelle la plus appropriée a été proposée non seulement pour protéger les plages de Ceinturon et Bona et pour stabiliser le rivage à long terme, mais aussi pour maintenir l'accessibilité ou l'esthétique des plages. Les modèles numériques MIKE 21 et LITPACK de DHI sont utilisés pour atteindre ces objectifs. L'évolution historique et future à long terme du rivage est également évaluée et prédite en utilisant la combinaison de techniques de télédétection, de système d'information géographique (SIG) et de régression linéaire. Ces modèles numériques ont été testés de manière satisfaisante sur des données historiques disponibles, car ils pouvaient reproduire l'hydrodynamique observée et l'évolution côtière.En particulier, une nouvelle approche suggérée pour simuler la présence de posidonies et divers types de fonds marins est présentée dans ce travail. Les résultats numériques interprètent le rôle ainsi que l'impact du changement de vent, la variation saisonnière, les événements extrêmes, les herbiers de posidonies, l'élévation du niveau de la mer et le ré-ensablement de la plage sur l'évolution morphologique du tombolo oriental de Giens. De plus, les résultats obtenus démontrent que les digues sous-marines jouent un rôle très important dans la protection des plages de Ceinturon et Bona, elles permettent de réduire efficacement la hauteur des vagues, la vitesse du courant et le transport des sédiments ainsi que contrecarrer le retrait du rivage dans toutes les conditions des vagues, à l'exception des tempêtes semi-centenaires et centennales pour lesquelles une certaine érosion persiste. Combinées à des ré-ensablements périodiques mais limités en espace et en temps, elles semblent constituer le meilleur compromis de protection à moyen et long terme. / The double tombolo of Giens, located in the town of Hyères, South East of France, is a unique and rare geomorphological formation in the world, which links Giens Island to the continent. It was mainly formed due to the wave diffraction and refraction by the islands. It consists of two parts: the western branch (Almanarre beach) directly facing the Gulf of Giens and the eastern branch lying on the western coast of Hyères bay. These parts are distinctly separated by the salt pond of Pesquiers. The eastern part of Giens tombolo extends over more than ten kilometers from the mouth of Gapeau river in the north to La Badine beach in the south. The beaches along the eastern tombolo, especially Ceinturon and Bona beaches are subject to beach erosion and beach narrowing due to both natural causes and human interference, but anthropogenic interventions are still dominant. In order to mitigate or prevent coastal erosion, various coastal structures have been used along the eastern Giens tombolo. They can only solve local erosion in some cases, but may also trigger some undesirable effects as well as disadvantages. Even the shore-normal structures that interfere with longshore sediment transport, not only result in the deficit of sediment and erosion in the downstream drift, but also blot out surrounding landscape of the beaches.The main objectives of this study was to better understand the physical processes underlying the morphodynamics, and also anticipate future evolution of the eastern Giens tombolo in response to different actions and interventions taking place along the coast. Thereof, the submerged breakwater (SBW) was proposed to not only protect the Ceinturon and Bona beaches and stabilize the shoreline in the long term, but also maintain beach amenity or aesthetics. DHI’s MIKE 21 and LITPACK numerical models are used in order to achieve these above-mentioned objectives. Additionally, the historical and future medium-term shoreline evolution along the eastern Giens tombolo is also evaluated and predicted by using the combination of remote sensing, geographic information system (GIS) techniques coupled with the Digital Shoreline Analysis System (DSAS) along with linear regression method. These numerical models were satisfactorily tested available historical data, as they could reproduce the observed hydrodynamics and coastal evolution. Especially, a novel approach suggested to simulate the presence of Posidonia seagrass and various types of seabed is presented in this work. The numerical results interpret the role as well as impact of wind change, seasonal variation, extreme events, Posidonia seagrass, sea level rise, and beach nourishment on the morphological evolution of the eastern Giens tombolo. Moreover, the results obtained strongly demonstrate that the SBWs play a very important in protecting Ceinturon and Bona beaches to a certain degree, viz. effectively reducing the nearshore wave heights, current speed and sediment transport as well as counteracting the retreat of the shoreline under the wave conditions apart from the semi-centennial and centennial storms.