Thesis (M. Sc.)--College of William and Mary. / Vita. Includes bibliographical references.

Thesis (M. Sc.)--College of William and Mary. / Vita. Includes bibliographical references (leaves 85-89).

Thesis (Ph.D.)--University of Rhode Island, 2007. / Includes bibliographical references (leaves 98-129).

Nearshore processes on barred beaches are studied with a process-based numerical model. The two major goals of the study are to expand the body of knowledge about nearshore processes on barred beaches gaining a better understanding of the physical mechanisms affecting bar migration events and to enhance the numerical model in order to accomplish realistic simulations of bar migration events on storm time scales. The numerical model is used to study the effect of physical processes on the hydrodynamics and morphodynamics in the nearshore environment. The numerical model system consists of a linear spectral refraction-diffraction model, REF/DIF S, a quasi-3D nearshore circulation module, SHORECIRC, energetics-based sediment transport models, and a morphological evolution model. A laboratory experiment with an offshore bar migration case followed by an onshore bar migration case is used for modeling purposes and verifications. A number of enhancements are made to the wave and circulation modules of the numerical model system specifically for simulations on barred beaches. The model modifications and enhancements are: a combined breaking wave parameter with a spatial variation in the wave model, a method accounting for breaking wave persistence in the wave model, a method accounting for the new breaker roller lag in the wave model, the dynamic pressure component in the radiation stress forcing, a roller contribution with different depth variation options for the short wave forcing in the circulation model, wave height instead of water depth as the turbulent length scale in the eddy viscosity calculations in the circulation model, and a slope term for the default sediment transport formula. The effect of surface shape parameter and the roller face angle on radiation stress and mean water level predictions are investigated. In reality, the organized wave energy is transferred to roller development over a transition distance and the roller does not immediately contribute to the radiation stresses; therefore, showing the importance of the roller lag mechanism for mean water level predictions. The cross-shore variation of the vertical momentum balance is studied to observe the variation of forcing agents of the undertow current. The cross-shore pressure gradient is the most dominant forcing term affecting the depth structure of the undertow current. The effect of different depth variations of the roller contribution to the short wave forcing on the undertow current is investigated. The mechanism accounting for breaking wave persistence and the mechanism accounting for the roller lag are shown to be important for predictions of the undertow currents on barred beaches. The skewed wave orbital velocities are introduced to the linear wave model by an empirical parametrization method and are found to contribute strongly to the onshore bar migration. The enhancements made to the wave dissipation and roller are found to significantly affect the predicted migration of the bar as well as the maintainance of the trough.

Heading on microfiche: Fitzgerald, Timothy Patrick. Thesis (M.S.)--University of Hawaii at Manoa, 2002. Includes bibliographical references (leaves 45-50). Also available on microfiche.

Multiple scales of beach morphodynamic processes ranging from those of wave-breaking induced turbulence, individual wave, storm, seasonal, to inter-annual are examined in this dissertation based on both laboratory and field data. These processes were simulated using process-based numerical models and data-driven models. At a microscale, separating turbulence from orbital motion under breaking waves in the surf zone is essential to understanding wave-energy dissipation. Velocity data under monochromatic and random waves in the large-scale sediment transport facility (LSTF) were analyzed. Moving averaging provides a simple method for extracting turbulence from velocity measurements under random breaking waves collected at a reasonably high frequency. Various moving averaging time intervals were examined. An optimum moving averaging interval of approximately 30° to 42° phase angle (relative to peak wave period) allows a reasonable extraction of turbulence. An adaptive moving averaging with variable averaging time at wave crest and trough are proposed to improve the effect of turbulence extraction. At a mesoscale, hydrodynamic conditions associated with onshore migration of a sandbar and the subsequent equilibrium state of a stable bar were examined in the LSTF. Wave and near bottom velocity across the surf zone were measured during the onshore sandbar migration. The near-bottom velocity skewness indicates that before the sandbar reached equilibrium, the velocity was skewed offshore in the nearshore region, and skewed onshore seaward of the bar. The velocity skewness pattern reversed when the beach profile reached equilibrium and the sandbar became stable. The peak onshore directed acceleration was greater than the peak offshore directed acceleration throughout the surf zone during the periods of both onshore migrating and stable sandbar. The macroscale portion of the study examines the beach processes, particularly the morphodynamics of nearshore bar, at storm and seasonal scales. The bar height and bar position were extracted from bimonthly surveyed beach-profiles spaced at 300 m along the 22-km long Sand Key barrier island, West-Central Florida from October 2010 to August 2015. Seasonal beach cycle in the study area is illustrated by onshore sandbar migration during the summer and offshore sandbar migration during the winter, while subaerial beach remains rather stable. Alongshore variations of onshore and offshore sandbar migration were observed over storm events. The water depth over the pre-storm sandbar crest, or the bar crest elevation, is a major factor controlling the onshore or offshore sandbar movement. The offshore moving sandbar tends to have a shallower pre-storm bar crest, while the onshore moving sandbar tends to have a deeper pre-storm bar crest. A dynamic equilibrium bar height of 0.5 m for the study area was identified. The sandbar tends to evolve toward this equilibrium height during the seasonal cycle. The energetic conditions associated with Tropical Storm Debby caused a deviation from the above dynamic equilibrium conditions. The sandbar at most of the profile locations became higher than the pre-storm bar height regardless of the initial height of being greater or less than 0.5 m. After the storm, the higher and shallower bar experienced substantial erosion, the eroded sand was deposited in the trough landward. This resulted in a lower sandbar height, returning to the dynamic equilibrium height of 0.5 m. The Unibest-TC model (Walstra et al., 2012) is able to capture the measured trend of bar migration. The Modelling results suggest that offshore bar migration is dominated by suspended sediment transport. While onshore bar migration is driven mainly by bedload transport. At megascale, a data-driven model was developed to predict beach-profile evolution at multiple-annual scale. Empirical Orthogonal Function analysis was conducted on a time-series beach profile (R61) to identify temporal and spatial trends. Trends in the temporal EOF are modeled using a simple curve fitting. In this case, logarithmic and linear trends were identified. After the trend in temporal EOF values are identified, the curve fitting can be calibrated with 14-month data. The calibrated temporal EOF curve yielded accurate reproduction of profiles. The close examination of multiple scales of beach processes provides a comprehensive understanding of nearshore morphodynamics.

Recent U.S. legislation applies a precautionary approach to setting catch regulations in federal fisheries management. A transparent approach to complying with federal guidelines involves calculating the catch recommendation that corresponds to a specified probability, P*, of exceeding the "true" overfishing limit (OFL) located within an estimated distribution. The P* methodology aims to manage the risk of overfishing explicitly, but choice of P* alone does not provide sufficient information on all of the risks associated with a control rule—both the probability of overfishing and the severity of overfishing. Rather, the ramifications of P* choices depend on the amount of uncertainty in the stock assessment and on the life history of the species in question. To evaluate these effects on the risks associated with P* rules, my study simulated fishing three example species under three levels of uncertainty. Trends identified among example species were consistent with predictions from life history. Periodic strategists, which have highly variable recruitment, experienced probabilities of overfishing which exceeded P* and which increased in time. Equilibrium strategists showed more predictable risks of overfishing but may have less capacity to recover from depleted biomass levels. Differences in the size of the OFL distribution—representing differences in levels of uncertainty—led to mixed results depending on whether the distribution was biased or whether uncertainty was fully characterized. Lastly, because OFL distributions are themselves estimates and subject to uncertainty in their shape and size, lower P* values closer to the tails of the estimated distribution produced more variable resulting risks. / Master of Science

Submitted by Fabricia Fialho Reginato (fabriciar) on 2015-06-16T23:24:33Z No. of bitstreams: 1 Crippa.pdf: 92752 bytes, checksum: 705c764746213cbbe4b6d38f8af8384e (MD5) / Made available in DSpace on 2015-06-16T23:24:33Z (GMT). No. of bitstreams: 1 Crippa.pdf: 92752 bytes, checksum: 705c764746213cbbe4b6d38f8af8384e (MD5) Previous issue date: 2011 / Nenhuma / A Lagoa do Peixe situada no Parque Nacional da Lagoa do Peixe – sul do Brasil - tem sua conexão com o mar aberta artificialmente todos os anos no final do inverno. Entretanto, esse manejo vem sendo realizado sem avaliar os impactos da abertura da barra na biodiversidade aquática das áreas úmidas da região. As seguintes questões foram testadas nesse estudo: 1) A riqueza, a abundância e a composição de macroinvertebrados da planície de inundação da Lagoa do Peixe variam temporalmente com a abertura e fechamento da barra? 2) O padrão de variação da comunidade de macroinvertebrados varia com a abertura e fechamento da barra? Um total de quatro coletas foi realizado entre março e outubro de 2008 em três áreas úmidas localizadas na planície de inundação da Lagoa do Peixe que recebiam influência da abertura artificial da barra e em duas áreas úmidas sem a influência da abertura da barra (áreas controle). Um total de 19.333 indivíduos distribuídos em 45 famílias de macroinvertebrados aquáticos foi amostrado nas áreas úmidas estudadas. A riqueza de macroinvertebrados (F1,3= 41, 645, p = 0, 008) e abundancia (F1,3= 1499,37; p < 0, 001) foram maiores nas áreas úmidas que não receberam influência da abertura artificial da barra (áreas controle) do que naquelas sujeitas à abertura da barra. A composição de macroinvertebrados variou significativamente entre as áreas úmidas sujeitas e não sujeitas à abertura da barra (F1,16= 6, 2422, p < 0, 001). Os resultados obtidos nesse estudo sugerem que a abertura artificial da barra da Lagoa do Peixe afeta a dinâmica da comunidade de macroinvertebrados aquáticos em áreas úmidas costeiras no Sul do Brasil. / The Lagoa do Peixe located in the Parque Nacional da Lagoa do Peixe – South of Brazil - has its connection with the sea artificially opened every year in the end of winter. However, this management is being accomplished without assessing the impacts of the sandbar opening in the aquatic biodiversity of the region’s humid areas. The following questions were tested in this study: 1) The richness, the abundance and the composition of macroinvertebrates in the wetlands of the Lagoa do Peixe vary temporally with the opening and closing of the sandbar? 2) The macroinvertebrates community range’s pattern varies with the opening and closing of the sandbar? A total of four collections was accomplished between March and October 2008 in three humid areas located in the Lagoa do Peixe flooding plain that were influenced by the artificial opening of the sandbar in two humid areas without being influenced by the opening of the sandbar (control areas). A total of 19,333 individuals distributed in 45 families of aquatic macroinvertebrates was sampled in the humid areas studied. The macroinvertebrates richness (F1,3= 41, 645, p = 0, 008) and abundance (F1,3= 1499,37; p < 0, 001) were superior in the humid areas that weren’t influenced by the artificial opening of the sandbar (control areas) than in those ones subjected to the opening of the sandbar. The macroinvertebrates composition significantly ranged between the humid areas subjected and the ones not subjected to opening of the sandbar (F1,16= 6, 2422, p < 0, 001). The obtained results in this study indicate that the artificial opening of the Lagoa do Peixe sandbar affects the dynamics of the associations of aquatic macroinvertebrates in humid coastal areas in the South of Brazil.

La plupart des côtes de la Terre reculent et 80% sont rocheuses. La prévision du recul des falaises littorales est primordiale afin d’anticiper les risques futurs pour les aménagements littoraux. Cependant, la compréhension de ce recul est difficile car de nombreux paramètres le contrôlent. Des expériences en canal à houle de petite échelle ont été effectuées où nous avons mis en place un massif de sable humide soumis à l’attaque des vagues par sapement. Le but est de comprendre comment l’effet des vagues contrôle l’érosion des falaises. La technique de mesure par ombroscopie a été employée et nous a permis de détecter la surface du sable et la surface libre en fonction du temps. Nous avons ainsi analysé l’influence du forçage des vagues (F, ξ) (où F est le flux d’énergie des vagues incidentes au large et ξ est le paramètre de similitude de “surf”) sur la vitesse de recul de la falaise et sur la profondeur des évènements d’effondrement. La vitesse de recul de la falaise augmente linéairement avec le flux d’énergie F. Les débris de falaise érodés changent la morphologie du fond, les types de morphologie du fond dépendent fortement du paramètre de similitude de “surf” au déferlement, ou encore du paramètre de Dean Ω. Des profils du fond instationnaires présentant une oscillation auto-entretenue de la barre sédimentaire ont été observés. Nous avons de plus étudié l’effet de la granulométrie du sable utilisé : pour un sable plus fin, la falaise est plus cohésive et s’effondre au cours d’évènements de plus grande ampleur. Etonnamment, le recul de la falaise est plus important pour du sable fin. Ceci est probablement dû à une modification de la morphologie du fond conduisant à une dissipation de l’énergie des vagues moins importante. Le volume de sable injecté dans le système a finalement été quantifié, la barre sédimentaire a d’abord été prélevée périodiquement et il a été observé que la vitesse de recul de la falaise vr est constante. Puis, la hauteur de falaise a été modifiée, le recul des falaises est plus important pour des petites falaises. Il semblerait que l’instationnarité d’un profil du fond se déclenche à partir d’un volume seuil de sable érodé. / Most of the Earth coasts recedes and 80 % are rocky. Prediction of sea-cliff recession is essential to anticipate future risks for coastal development. However, it is difficult to understand this recession because many parameters control it. In addition, both the space and time scales are too big for the different mechanisms of cliff erosion to be fully analysed. Experiments in a small-scale wave flume were conducted in which a massif made of wet sand is submitted to wave attack. The aim is to understand how cliff erosion is wave-controlled. The technique of shadow graph measurements was used to detect the time evolution of sand and water surfaces. We have analyzed the influence of wave forcing (F, ξ) (where F is the incident offshore wave energy flux and ξ is the surf similarity parameter) on the cliff recession rate and on collapse event size. The cliff recession rate increases linearly with the wave energy flux F. The eroded cliff materials change the bottom morphology ; the types of bottom morphology strongly depend on the surf similarity parameter at the breaker point, or the Dean parameter Ω. Bottom profiles characterized by unsteady self-sustained sandbar oscillation were observed. In addition, we studied how sand granulometry change the system evolution. Finer the sand is, more cohesive is the cliff and bigger are cliff collapses. Contrary to what was expected, cliff recession is more important for a finer sand : this could be due to a more dissipative bottom morphology built by fine sands. The sand volume within the system changes following cliff collapses and a sandbar removal during particular experiments. The cliff recession rate is constant when the sandbar is removed and decreases with cliff height. It seems that the unsteadiness of the bottom profile is activated when the volume of eroded sand exceeds a threshold value.

Le long des littoraux sableux tels que la côte Aquitaine, les vagues et principalement les courants moyens induits par celles-ci jouent un rôle majeur dans l’évolution morphologique des plages. Que ce soit d’un point de vue socio-économique (aménagement des plages, protection de l’environnement) ou sécuritaire (noyade), comprendre la dynamique de tels environnements est devenu un réel enjeu scienti?que ces dernières années. Le développement d’une plateforme de modélisation morphodynamique opérationnelle a été menée au cours de cette thèse. Ce modèle est basé sur le couplage du modèle spectral de houle SWAN (Delft University of Technology) avec le modèle MARS 2DH (Ifremer), initialement conçu pour calculer les courants induits par la marée et les vents. Après avoir ajouté les phénomènes liés à la houle, un modèle sédimentaire a été développé pour estimer les évolutions morphodynamiques. La campagne de mesures Biscarrosse-PréECORS menée en juin 2007 sur la plage de Biscarrosse a permis de valider le modèle pour une large gamme d’état de mer. Le modèle a montré son e?cacité et sa robustesse pour décrire les courants et des circulations induites par les vagues au dessus de fortes hétérogénéités bathymétriques. Nous avons mis en évidence la forte modulation tidale des courants sagittaux qui sont intenses même pour de faibles conditions de vagues. La plateforme de modélisation morphodynamique a permis d’analyser la formation et le développement de morphologies tridimensionnelles rythmiques pour des systèmes simple et double barre. Pour les environnements à double barre comme la côte Aquitaine, l’intense couplage morphologique entre la barre externe et la barre interne a été étudié en réponse aux conditions de forçages. Nous avons mis en évidence l’in?uence de la marée sur la croissance des barres et révélé la corrélation existant entre croissance des barres et dissipation d’énergie des vagues sur les barres. Cette thèse a abouti au développement d’un modèle complet permettant d’appréhender la dynamique des environnements littoraux sableux. / Along many sandy environments as the Aquitanian Coast, waves and wave-induced currents play a key role on the beach morphodynamics. Within a socio-economic (human interventions, natural environment protection) and touristic (human safety) framework, understand the complex dynamics of these systems is a real scienti?c challenge these last decades. The development of an operational morphodynamical modeling platform was performed during this PhD thesis. The modeling strategy consists in coupling the spectral wave model SWAN (Delft Univer- sity of Technology) with the non-linear shallow water model MARS 2DH (Ifremer). The MARS model was initially designed to compute tide- and wind-induced currents. Thus, the wave processes and a sed- imentary unit were implemented inside MARS to compute morphological evolutions of wave-dominated sandy beached. The Biscarrosse-PréECORS ?eld experiment carried out in June 2007 at Biscarrosse Beach was used to validate our modeling platform for a large range of o?shore wave conditions. Results have proved the e?ciency and the robustness of our model to calculate wave-induced currents and circulations over alongshore non-uniformities. The strong tidal modulation of currents and the intense rip currents for low-energy conditions were highlighted. The morphodynamical modeling platform was also used to analyze the generation and the development of rhythmic three-dimensional morphologies for one- and double-barred systems. For double-barred en- vironments, the intense morphological coupling between the inner and outer bar was studied in the response of wave and tide forcing. We have highlighted the in?uence of the tide on the bar growth and showed the correlation between the growth and the wave dissipation over the bar. This thesis has succeeded in the development of a complete model for understanding the dynamics of sandy coastal environments.