As part of a beach erosion field experiment conducted at Cape Hatteras, NC in February 2010, this study focuses on quantifying longshore currents, which are the basic mechanism that drives longshore sediment transport. Using video imagery, the longshore currents in view of a video camera are estimated with the Optical Current Meter technique and the nearshore morphology is estimated by analyzing breaking wave patterns in standard deviation images. During a Nor‟easter storm event on February 12 and 13, 2010, the video longshore currents are compared to in situ data and it is found that the currents are most affected by the angle of incidence of incoming waves, increasing in magnitude as the angle becomes more oblique due to a larger component of radiation stress forcing in the longshore direction. The magnitude of the radiation stress forcing, which is at least an order of magnitude larger than the surface wind stress, increases as wave height increases or tide level decreases, which causes more wave breaking to occur. The normalized standard deviation images show wave breaking occurring at an inshore and offshore location, corresponding closely to the locations of an inner and outer bar indicated in survey data. Using two profiles from the survey data, one profile that intersects a trough and one that intersects a terrace, the video currents are also compared to currents simulated in one-dimension using the circulation module, SHORECIRC, and the wave module, REF/DIF-S, as part of the NearCoM system. Although the simulated currents greatly underpredict the video currents when the flow is only driven by radiation stresses, a mean water level difference between the two profiles creates a longshore pressure gradient. Superimposing a pressure gradient forcing term into the longshore momentum balance that assumes an equilibrium state of the flow, the magnitude of the simulated currents are much larger than the magnitude of the video estimated currents. Using analytical solutions of simplified forms of the mass and momentum equations to determine the effects of accelerations on the flow, it is seen that the acceleration term greatly affects the flow due to the relatively large mean water level difference that acts over a relatively short distance. Therefore, the pressure gradient forcing term is modified to include the effects of accelerations. By including the two-dimensional effects of the acceleration in the one-dimensional model through the modified pressure gradient, the quasi two-dimensional model simulated currents are very similar to the video estimated currents, indicating that the currents observed in the video may be pressure gradient driven.

The Florida Reef Tract (FRT) extends from the tropical Caribbean northward along the Florida coast into a warm temperate environment where tropical reef communities diminish with increasing latitude. This study was designed to map the nearshore benthic habitats including coral reefs and evaluate how the benthic communities differ between habitats and along the coast. Benthic communities across the northern FRT from Key Biscayne to Hillsboro Inlet (25.5°-26.3° N) were digitized from aerial photography taken in 2013 at a 1:1,000 scale. Three main hard-bottom habitat types were identified that ran parallel to shore and consecutively further away from shore: Colonized Pavement, Ridge, and Inner Reef. Five 1-km wide cross-shelf corridors (numbered 1-5, south to north) were designated and spaced as evenly as possible throughout the region. Five sites per habitat per corridor (70 total) were randomly selected and quantitative data collected within 4,200 m2. Significant differences in percent benthic cover among habitats were found in all corridors and within habitat types between corridors, indicating cross-shelf and latitudinal variation. Mean stony coral density increased with depth, with the Inner Reef habitat being significantly higher than both the Colonized Pavement and Ridge. Mean stony coral species richness also increased with depth, with all habitats significantly different from one another. A total of 22 stony coral species were identified within the mapped region, the three most abundant being Porites astreoides, Siderastrea siderea, and Acropora cervicornis. Results from this study support the ecosystem regions denoted in the Walker (2012) study. Corridor 1, located in the Biscayne Region, was the only corridor to contain any seagrass. In addition, Corridor 1 Inner Reef had significantly higher values for mean stony coral density, mean stony coral species richness, mean gorgonian density of the plume morphotype, and mean density of stony corals infected with Cliona spp. Corridors 2-4, located in the Broward-Miami Region, had some variability associated with them, but were generally similar in benthic composition. Corridor 5, likewise located in the Broward-Miami Region but in close proximity to the Deerfield Region, also had differences associated with it. Both the Colonized Pavement and Ridge habitats in Corridor 5 had the lowest mean coral species richness, as well as total absence of both sponge species noted in this study. Corridor 5 Inner Reef also had significantly lower mean stony coral densities compared to Corridors 1, 2, and 4. As such, these results support the idea of different biogeographic regions occurring off the southeastern Florida coast. This study produced two key findings. It discovered over 110 large (>2 m) resilient coral colonies, of which 50 were alive in various conditions. This study also found 38 acres of dense Acropora cervicornis patches, tripling the previously known area within the study region. These are the largest dense patches in the continental United States.

Coastal cliff erosion is a widespread problem that threatens property and infrastructure along many of the world’s coastlines. The management of this risk calls for robust quantification of cliff erosion rates, which are often difficult to obtain along rocky coasts. Quantification of sea-cliff rates of retreat on annual to decadal time scales has typically been limited to rapidly eroding soft rock coastlines. Rates of erosion used for shoreline management in the UK are generally based on analysis of historic maps and aerial photographs which, in rocky coast environments, does not wholly capture the detail and timing at which the processes operate and the failures occur across the cliff face. The first stage of this study uses airborne LiDAR (Light Detection and Ranging) data at nine sites around a rocky coastline (Cornwall, UK) to gain a quantitative understanding of cliff erosion where average recession rates are relatively low (c. 0.1 m yr-1). It was found that three-dimensional volumetric changes on the cliff face and linear rates of retreat can be reliably calculated from consecutive digital elevation models (DEMs) several years apart. Rates of erosion ranged between 0.03–0.3 m yr-1. The spatial variability in recession rates was considered in terms of the relationship with the varying boundary conditions (rock mass characteristics, cliff geometries, beach morphology) and forcing parameters (wave climate and wave exposure). Recession rates were statistically correlated with significant wave height (Hs), rock mass characteristics (GSI) and the ratio between the two (GSI/Hs). Although the rates derived using airborne LiDAR are comparable to the longer term rates of retreat, the detail of erosion to the cliff-face provides additional insight into the processes occurring in slowly eroding environments, which are vital for understanding the failure of harder rock coastlines. In addition to this, the importance of the wave climate and rainfall needs further attention on a more localised scale. Monthly cliff face volume changes, at two particularly vulnerable sites (Porthleven and Godrevy, Cornwall, UK), were detected using a Terrestrial Laser Scanner (TLS). Using these volumes alongside information on beach profile, beach- cliff junction elevation changes and nearshore hydrodynamics have allowed an insight into how the cliffs respond to seasonal fluctuations in wave climate and beach morphology. Monthly variability in beach morphology between the two sites over a one-year survey period i  indicated the influence that beach slope and the elevation of the beach-cliff junction have on the frequency of inundation and the power of wave-cliff impacts. Failure mechanisms between the two sites ranged from rotational sliding of superficial material to quarrying and block removal over the entire cliff elevation, according to the extent of wave-cliff interaction. This particular survey period highlighted the sensitivity of cliff erosion to the variability in wave climate and beach morphology at two different locations in the south-west of the UK, where the vast majority (over 85% of the annual value) of cliff face erosion occurs during the winter when extreme storm waves prevail. Coastal cliff erosion from storm waves is observed worldwide but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs, limiting our understanding of cliff processes. Over January-March 2014, during the largest Atlantic storms in at least 60 years with deep water significant wave heights of 6 – 8 m, cliff-top ground motions of a rocky cliff in the south-west of the UK (Porthleven, Cornwall) showed vertical ground displacements in excess of 50–100 μm; an order of magnitude larger than observations made previously. Repeat terrestrial laser scanner surveys, over a 2-week period encompassing the extreme storms, gave a cliff face volume loss 2 orders of magnitude larger than the long-term erosion rate. Cliff-top ground motions and erosion volumes were compared at two different locations, one a reflective beach with steeply shelving bathymetry (Porthleven, Cornwall) and the other an intermediate, low tide bar-rip beach with a wide coastal slope (Godrevy, Cornwall). Under similar wave conditions (6–8 m Hs and 15–20 s. Tp) the vertical ground motions were an order of magnitude greater at the cliffs fronted by steeply shelving bathymetry, where the breaking waves plunge right at the shoreline, with little prior dissipation, leading to large energetic runup impacting the cliff. These storm results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long-term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts as well as the wave dissipation that occurs as a function of the nearshore bathymetry. Having recorded microseismic cliff-top motion on this scale for the first time and determined an effective method of monitoring the energetic wave impacts, this study emphasises how investigations of cliff behaviour during storms is not only obtainable, but paramount to understanding coastal evolution under extreme conditions.

Rip currents are the most dangerous hazard at surf beaches. Rip currents in South Florida have previously not been studied. Beach profiles for three Florida beaches (Miami Beach, Lido Beach, Sarasota, and Pensacola Beach) and one Georgia beach (South Cumberland Island) were chosen for surveying because of their variable sand bar heights. Rip current hazard at each beach was assessed by lifeguard rip rescue and drowning statistics. A relationship was found between sand bar height, beach slope and rip current hazard. Rip current measurements in South Florida, which involved utilizing GPS drifters, laser rangefinder and drone-imaged fluorescent tracer dye, showed that the speed ranged from 0.1-0.5 m/s, which is fairly slow compared to such measurements undertaken in California and Australia. The effect of rip currents on swimmers was analyzed based on the drag force acting on swimmers and the power they generate to overcome the currents when swimming against them. The drag force and power increase quadratically and cubically, respectively, with the increase of rip current and swimming speeds. Hence, even rip currents of low velocity can be dangerous and swimming against the current should be avoided if possible. Strong rips in California have been shown to exhibit a circulatory pattern, which could bring a floater back to the safety of a shallow sand bar. Field measurements of rip currents in South Florida clearly defined the flow characteristics of a nearly straight-line current, sometimes deflected to the east-southeast. Therefore, the traditional approach of swimming left or right, parallel to the shore is the best escape strategy, but not against the longshore current if present. A logistic regression analysis was conducted to predict the occurrence of rip currents based on beach conditions. The logistic model showed that wave height, wave period and wind speed were statistically significant factors in rip generation. Rips were found to be most commonly generated by relatively small, non-threatening waves (e.g., 0.6 to 0.9m in height). These physical factors, along with social and safety considerations, pose a significant problem for coastal management.

Les non-linéarités des ondes de surface, qui se caractérisent par leur aspect dissymétrique, sont reconnues comme l'un des principaux moteurs du transport de sédiments en zone littorale. Cependant, l'estimation du transport reste imparfaite, en partie du fait d’une description inexacte des non-linéarités de la vitesse de l'écoulement orbital. Les ondes infra-gravitaires, qui coexistent avec les ondes courtes en zone littorale, sont des ondes de longue période (20-200 s) associés aux groupes d'ondes courtes. Les mécanismes de génération, propagation et dissipation de ces ondes sont maintenant relativement bien compris, mais leur effet sur le transport sédimentaire est encore mal connu. Afin (i) d’améliorer les paramétrisations existantes des non-linéarités de vitesse et (ii) d’étudier le rôle des ondes infra-gravitaires dans le transport sédimentaire, de nouvelles expériences ont été réalisées dans deux canaux à houle, l’un avec un fond fixe et l'autre avec un fond mobile constitué de sédiments de faible densité. Les données obtenues avec ces modèles physiques ont été utilisés conjointement à des données de terrain et des simulations numériques pour étudier les deux sujets.}TEXT{}{Les paramétrisations classiques pour les non-linéarités de vitesse prennent seulement en compte l'influence de paramètres locaux (la hauteur de vague, la longueur d'onde et la profondeur d’eau), ce qui entraîne des erreurs importantes dans les estimations, en particulier les valeurs maximales de non-linéarité. Ce travail montre que les non-linéarités de vitesse ont aussi une dépendance avec des paramètres qui ne sont pas locaux: (i) la cambrure de vague et (ii) la largeur de la bande spectrale au large, ainsi que (iii) la pente de la plage. Une nouvelle paramétrisation est proposée, qui réduit d’environ 50% l'erreur sur les résultats obtenus avec les paramétrisations existantes. Les résultats expérimentaux obtenus dans le canal à houle avec un fond mobile montrent que des conditions de vagues avec la même énergie d'ondes courtes, mais avec une modulation basse fréquence différente, modèlent des profils de plage différents. L'influence des ondes infra-gravitaires sur le transport sédimentaire est mis en évidence par deux mécanismes distincts: (i) l’advection par les ondes infra-gravitaires de sédiment mis en suspension par l'action des ondes courtes, qui dépend de la hauteur des ondes infra-gravitaires et de leur phase par rapport aux groupes d'ondes courtes et (ii) les ondes infra-gravitaires modifient les non-linéarités des ondes courtes, que ce soit directement ou indirectement, par modulation de la hauteur de la colonne d'eau. Les variations morphologiques du haut de plage induites par les ondes infra-gravitaires sont associées à des changements du profil de la plage dans les zones de déferlement et de levée, en mettant en évidence le lien entre les différentes régions du profil transversal de la plage. / Wave nonlinearities have long been recognised as being among the main drivers of sediment transport in the coastal zone. However, there are still significant errors in the prediction of this transport associated, partially due to inaccurate predictions of the velocity nonlinearities. The infragravity waves, which coexist with the short waves in the coastal zone, are long-period waves (with 20-200 s) associated to the short-wave groups. Their generation, propagation and dissipation mechanisms are already reasonably well understood, but their influence on sediment transport is still very poorly characterised. In order to (i) improve current predictions of velocity nonlinearities and (ii) investigate the role of infragravity waves in sediment transport, new experiments were carried out both in a fixed-bed wave flume and in a light-weight-sediment wave flume. The physical-modelling data set is used in combination with field data and numerical simulations for studying both subjects. Existing parameterizations of velocity nonlinearities account only for the influence of local wave parameters (e.g. wave height, wave length and water depth), which leads to considerable estimation errors, especially of the maximal values of nonlinearity. This work shows that the velocity nonlinearities depend also on non-local wave parameters: (i) offshore wave steepness, (ii) offshore spectral bandwidth and (iii) beach slope. A new parameterization is proposed, which reduces by about 50% the root-mean-square error relatively to former parameterizations. The experimental results in the light-weight-sediment wave flume demonstrate that wave conditions with the same short-wave energy, but different low-frequency modulation, shape different equilibrium beach profiles. The influence of the infragravity waves on the sediment transport is confirmed and depends on two different mechanisms: (i) advection of the short-wave suspended sediment by the infragravity-waves, which is dependent on the infragravity-wave height and phasing with the short-wave groups and (ii) modulation of short-wave nonlinearities by infragravity-wave motion, both directly and indirectly, through water-depth modulation. Changes in the beachface morphology induced by infragravity waves are connected to beach-profile changes in the surf and inner-shoaling zones, highlighting the existent link between the different zones of the cross-shore beach profile.

Climate change and increasing anthropogenic activities are causing rapid changes to environmental and ecological processes in the Arctic Ocean. To better understand these changes, scientists have increased research efforts in these regions, but to date the number of studies on Arctic nearshore habitats are lacking. My dissertation responds to the paucity of information and investigates patterns in Arctic nearshore fish communities and food webs to gain insight to how these ecosystems may shift as these changes continue. I used multivariate statistical analysis to examine patterns in community structure and composition to determine that Arctic nearshore fish communities are largely driven by prey availability, salinity and temperature; and that species that are more abundant in warmer conditions are likely to increase in abundance as climatic conditions in the Arctic continue to warm. I improved the ability to apply stable isotope methods to Arctic food web studies by determining more appropriate model parameters using a laboratory-based isotope study on a common Arctic nearshore fish, and discuss its potential as a biological monitor species. These new parameters are used to confirm that a shift in prey resource dependence occurs across the seasonal shift from ice-covered winter to open-water summer conditions. Changes in basal resource dependence also occur later in the season across a latitudinal gradient where a shift to dependence on allochtonous inputs from nearby rivers increased trophic diversity. Using isotopic niche space theory, it was determined that the Arctic nearshore has a diverse prey base but that niche spaces of Arctic warm-water and cold-water species do overlap, and if numbers of warm-water fish continue to increase it will likely increase competition for resources for potentially less-adaptable, well-established, cold-water forage fish. On the other hand, if pelagic productivity is expected to increase and support larger fish biomasses, then there will be more than enough resources for warm-water and cold-water species to coexist, thus creating a more diverse prey base for piscivores in the Arctic.

In this study, a two-dimensional depth-averaged beach evolution numerical model is developed to study the medium and long term nearshore sea bottom evolution due to non-cohesive sediment transport under the action of wind waves only over the arbitrary land and sea topographies around existing coastal structures and formations. The developed beach evolution numerical model is composed of four sub-models: a nearshore spectral wave transformation model based on energy balance equation including random wave breaking and diffraction terms to compute the nearshore wave characteristics, a nearshore wave-induced circulation model based on the non-linear shallow water equations to compute the nearshore depth averaged wave-induced current velocities and mean water level changes, a sediment transport model to compute the local total sediment transport rates occurring under the action of wind waves and a bottom evolution model to compute the bed level changes in time due to gradients of sediment transport rates in cross-shore and longshore directions. The governing partial differential equations are solved utilizing finite difference schemes. The developed models are applied successfully to several theoretical and conceptual benchmark cases and an extensive data set of laboratory and field measurements. As an alternative approach to be used in beach evolution problems, a distributed total sediment load formula is proposed based on the assumption that the local total sediment transport rates across the surf zone are proportional to the product of the rate of dissipation of wave energies due to wave breaking and wave-induced current velocities. The proposed distribute load approach is validated with the available laboratory and field measurements.

Models of the fate and transport of river plumes and the bacteria they carry into lakes are developed. They are needed to enable informed decisions about beach closures to avoid economic losses, and to help design water intakes and operate combined sewer overflow schemes to obviate exposure of the public to potential pathogens. This study advances our understanding of river plumes dynamics in coastal waters by means of field studies and numerical techniques. Extensive field measurements were carried out in the swimming seasons of 2006 and 2007 on the Grand River plume as it enters Lake Michigan. They included simultaneous aerial photography, measurements of lake physical properties, the addition of artificial tracers to track the plume, and bacterial sampling. Our observed results show more flow classes than included in previous studies (e.g. CORMIX). Onshore wind can have a significant effect on the plume and whether it impacts the shoreline. A new classification scheme based on the relative magnitude of plume-crossflow length scale and Richardson number based on the wind speed is devised. Previous studies on lateral spreading are complemented with a new relationship in the near field. The plume thickness decreased rapidly with distance from the river mouth and a new non-dimensional relationship to predict thickness is developed. Empirical near field models for surface buoyant plumes are reviewed and a near field trajectory and dilution model for large aspect ratio surface discharge channels is devised. Bacterial reductions due to dilution were generally small (less than 10:1) up to 4.5 km from the river mouth. E. coli decay rates were significantly affected by solar radiation and ranged from 0.2 to 2.2 day-1 which were within the range of previous studies in Lake Michigan. Total coliform survived longer than E. coli suggesting different die-off mechanisms. Mathematical models of the bacterial transport are developed that employ a nested modeling scheme to represent the 3D hydrodynamic processes of surface river discharges in the Great Lakes. A particle tracking model is used that provides the capability to track a decaying tracer and better quantify mixing due to turbulent diffusion. Particle tracking models have considerable advantages over gradient diffusion models in simulating bacterial behavior nearshore that results in an improved representation of bacteria diffusion, decay and transport. Due to the complexity and wide variation of the time and length scale of the hydrodynamic and turbulent processes in the near field (where plume mixing is dominated by initial momentum and buoyancy) and far field (where plume mixing is dominated by ambient turbulence), a coupling technique is adapted. The far field random walk particle tracking model incorporates the empirical near field model. It simulates the transport, diffusion and decay of bacteria as discrete particles and employs the near field output as the source and transports the particles based on ambient currents predicted by the 3D hydrodynamic model. The coupled model improves dilution predictions in the near field. The new techniques advance our knowledge of the nearshore fate and transport of bacteria in the Great Lakes and can be ultimately applied to the NOAA Great Lakes Coastal Forecasting System to provide a reliable prediction tool for bacterial transport in recreational waters.

Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Well-planned monitoring of the 2004 Upham Beach nourishment project in west-central Florida collected high-spatial and -temporal resolution field data. Three hurricanes passed by the project soon after nourishment was complete.Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual as pred icted by the typical diffusion models. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges.Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only due to hurricane passage, but also during a winter season. The duration between nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration.The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. The direction of cross-shore transport was governed by wave steepness. Onshore sediment transport occurred during a storm event, in contrast with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as cited in the literature.By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects.

River mouths are very active coastal regions. Continuous sediment supply by the river and the movement by wave action cause the shoreline to change in time and space. Modeling of shoreline changes is an essential step before the design of any coastal engineering project. This research aimed to develop a system of numerical models to present the shoreline changes around a river mouth. The system of numerical models has three components: 1) modeling of nearshore wave characteristics, 2) modeling of longshore sand transport rates using the results of the first component, 3) modeling of shoreline changes using the estimated sand transport rates. Thus, firstly, deep water wave characteristics including the annual wave rose affecting Manavgat River mouth have been obtained from the database of NATO TU-WAVES Project. Then REF/DIF1 and SWAN nearshore wave models have been used to find out nearshore wave conditions. Since the results obtained from REF/DIF1 wave model have been found to be more reasonable compared to SWAN&rsquo / s output, REF/DIF1 wave model has been used in preparing a time series nearshore reference wave file with three hours time interval. This reference file has been used to run GENESIS. Last step of the numerical shoreline change modelling of Manavgat River mouth was the calibration procedure in which the &ldquo / transport parameters&rdquo / k1 and k2 have been determined. As there is lack of measurements of shoreline positions that can be used in calibrating shoreline change model, k1 and k2 has been approximately found to be k1=0.516 and k2=0.9 by using an empirical sediment transport formula. As a future study, it is recommended that when the protection structure controlling the river mouth is finished, the measurements of shoreline position behind the structure should be used in verification of shoreline change model in order to get more accurate results.