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The repercussions produced by the use of fossil fuels, e.g. climate change and sea level rise, have increased attention on the development of renewable energies. The European Commission has adopted the replacement of carbon fuels by renewable energy sources as one of the main objectives for the XXI century. Among these, wave energy is poised to become one of the most important due to the extensive worldwide resource and comparatively low environmental impacts. Although this renewable energy is yet in an early stage of its development and further research is required, the global resource, including the Mediterranean Sea, provides a promising future for wave energy which can enhance the presence of renewable energies in the global energy mix. However, for wave energy to become a fully fledge carbon-free energy source, the repercussions for nearshore hydro- and morphodynamics must be fully understood prior to undertaking any wave farm installation. In fact, wave farms (i.e. arrays of wave energy converters) have been recently proposed to fulfil a dual function as renewable energy producers and coastal defence elements countering erosion. Although these impacts have been previously studied on sandy beaches, gravel dominated coasts have not been addressed so far. These coasts are common in high latitudes and steep hinterlands and they are growing due to the use of coarse sediments for nourishment works on sandy beaches. They are common in the UK, the Mediterranean coast, Canada, New Zealand and Denmark among other areas. The research investigates the impacts of wave farms on gravel dominated beaches. To this end, changes produced by the presence of a wave farm on the shoreline evolution of a gravel dominated beach (Playa Granada, southern Spain) have been studied. This beach has suffered erosion problems since the discharge of the Guadalfeo river, the main source of sediments for the beach, was regulated in 2004 by the construction of Rules' Reservoir. With the construction of this river damn, 85% of the discharge was regulated which altered system's dynamics. Approximately 0.3 hm3 of sediments have been lost which have produced a maximum retreat of the shoreline of 87 m since the construction of the reservoir. The impact on the wave field of different wave farm scenarios and designs has been studied by means of a third-generation spectral wave propagation model (SWAN). Different parameters of the wave field at the breaking line have been extracted from the results of the wave propagation model. To this end, the fraction of breaking waves in each cell was obtained, and the breaking line was fixed in those cells with a 5% of waves breaking. These results were used to apply a longshore sediment transport (LST) formulation on the study site. Finally, LST rates computed were implemented in a one-line model to address changes on the shoreline position. This model, which is based on the continuity equation, relates the advance (or retreat) of the shoreline to the volume gradient, calculated as the sediment balance by means of LST rates. The selected WEC to form the modelled wave farms was WaveCat, an overtopping-type device, which has shown promising results in terms of coastal protection in recent research. This WEC is formed by two hulls, similar to those found in a catamaran, with a total diameter of D = 90 m. Wave farm effects on the wave field and shoreline position were assessed by means of several ad hoc indicators, comparing significant wave height, LST rates, shoreline advance and dry beach surface between scenarios with wave farm and the natural (no-wave farm) baseline scenario. These indicators act as a benchmark of the performance of each wave farm scenario with respect the natural situation, allowing to study the impact of the wave farm on each parameter involved in the shoreline evolution. Finally, the dry beach surface difference is obtained as a representation of the overall impact on the whole stretch of beach. More precisely, the effects of the alongshore location, the layout and the inter-device spacing of a wave farm were studied. Regarding the alongshore position of the wave farm, the results indicate that the wave farm location is a key parameter in terms of coastal protection; indeed, it was found that only three of the eight locations studied generated a weighted increase in dry beach surface with respect to the baseline. The rest of wave farm locations generated loss in dry beach area at the studied stretch of beach with respect to the baseline, thus producing negative effects in terms of coastal protection. The most advisable location for the wave farm increased the dry beach area in 25.58 m2 per storm whereas in the worst location 13.17 m2 are lost. These results show that the alongshore position of a wave farm needs to be carefully selected, as this parameter is able to turn the behaviour of a coast from accretionary to erosionary. In addition, different layouts consisting of a variation in the number of rows of wave energy converters composing the wave farm keeping constant their number are investigated. Results indicate that the best layout is that composed of two rows of WECs. In this case, the increase in dry beach surface with respect to the baseline scenario is 25.94 m2, whereas the farms with 3 and 4 rows yield a lower increase in beach surface. This shows that the extent of coast covered by the wave farm prevails over the number of rows as the impact of the shadow produced by the wave farm reaches a longer stretch of coast. Finally, four inter-device spacings were modelled. In this case, a lower spacing between devices increases local accretion in the lee of the wave farm but rises erosion elsewhere, whereas a greater spacing counter this erosion but accretion is also reduced. The best results were obtained for a spacing of 2D, where D = 90 m is the space between the two bows of the WaveCat. As main findings of this thesis, the research carried out in this work shows that the most important parameter in order to achieve the expected results in terms of coastal protection performance of a dual wave farm is the alongshore position. The analysis of the alongshore position effects shows that the location of the wave farm is a key parameter, not only in terms of energy production but also in order to use the wave farm as a coastal management element. Once the alongshore position is fixed, layout and inter-device spacing may help to improve the obtained results. A wave farm with a greater number of rows does not perform better in terms of coastal protection, as the extension of the stretch of coast covered is more relevant. A similar conclusion can be drawn from the inter-device spacing impact study. Wave farms with a lower inter-device spacing produce higher local peaks of accretion in their lee. On the contrary, wave farms with greater spacing reduce this erosion but accretion is also weaker, affecting the dry beach area difference with respect to the baseline. In this case, the wave farms with an intermediate spacing achieve a balance between these two extremes and stand as the best alternatives. The methodology followed in this work constitutes a useful decision-aid tool which can be applied to other gravel-dominated coasts worldwide. It considers the repercussions for nearshore hydrodynamics and shoreline morphology. The results obtained open up the possibility of using wave farms not only to produce carbon-free energy but also to mitigate coastal erosion problems on coasts across the globe.

Generation of electricity from ocean waves has seen increasing research and commercial interest in recent years. The development of projects of several hundred megawatts rated capacity is now being considered. There is a clear need for improved understanding of the environmental impact of large-scale wave energy extraction, particularly in nearshore regions where sediment transport and cliff erosion may be affected. This thesis investigates the change in nearshore wave conditions and sediment transport due to energy extraction by long strings of wave energy devices. The influence of wave energy converter (WEC) arrays has been studied using transmission coefficients implemented within a spectral wave model. It is shown that the breaking wave height nearshore is larger (5%) if transmission is defined as frequency dependent. This is due to the energy dissipation processes associated with different wave frequencies. Linear wave theory is employed to determine frequency dependent transmission and reflection coefficients across a line of wave energy devices based onthe amplitude of scattered and radiated waves. This approach is compared with experimental measurements of the wave field in the vicinity of an array of five heaving floats. The transmitted wave amplitude is predicted with reasonable accuracy but additional numerical damping is required to predict the measured float response amplitude. This comparison indicates that linear analysis is an acceptable approach for predicting float response and wave field in the vicinity of the array for a certain range of conditions. Linear wave analysis is subsequently applied to investigate the variation of transmission coefficients with distance inshore of a long array of heaving WECs undergoing free response and with damping specified to optimise power extraction. A method is presented for identifying representative transmission and reflection coefficients such that change in wave energy is equal to energy extraction by the devices. These coefficients are employed to quantify the change in nearshore conditions due to deployment of a long line of wave devices at a site near the East Anglian coastline. Wave conditions are modelled at 12 points along the shoreline over a 140 year period and significant wave height reductions up to 30% were obtained. Importantly, changes in nearshorewave direction are also observed. Analysis using the sediment transport model SCAPE (Soft Cliff and Platform Erosion model) indicates that the introduction of the array reduces both the sediment transport rate and cliff recession rate by an average of 50%.

Novel instrumentation plays a crucial role in enabling new observations and providing deeper insights into ocean dynamics. In my thesis, I present methodologies for collecting high spatial-temporal resolution observational data, which allows for a better understanding of physical and biogeochemical processes in the coastal ocean. Specifically, I integrate two novel sensors, the acoustic Doppler current profiler (ADCP) and the Submersible Ultraviolet Nitrate Analyzer (SUNA), onto the Wirewalker (WW) wave-powered profiler. I discuss issues related to fine-scale velocity measurements, biological modulation of nitrate during a harmful algal bloom, and nitrate dynamics over the inner continental shelf.The thesis begins by presenting a new methodology to observe oceanic fine-scale velocity using the combination of velocimeters and the Wirewalker profiler. By correcting vehicle-motion-induced velocity contaminations and removing surface wave signals, a background velocity field with a spectrum wavenumber runoff at a scale of ~3 m over a 100 m vertical range was obtained. This vertical resolution is several times finer than that possible from other velocity-measuring platforms with similar measurement ranges. Next, I present in situ evidence demonstrating the vertical migration of the dinoflagellate that facilitates their nitrate uptake during the 2020 red tide in the Southern California Bight. The vertical migration pattern of Lingulodinium polyedra (the dominant species) and their biological modulations to the subsurface nitrate field were quantified. The loss of nitrate in the nitracline was balanced by proportional increases in phytoplankton concentrations, confirming a 50-year-old hypothesis. The swimming ability of the dinoflagellate allows them to outcompete other non-motile phytoplankton during times of high stratification and nutrient limitation. Finally, an undocumented onshore-directed cross-shore nitrate gradient over the inner shelf of the Southern California Bight was revealed. The nitrate gradient was possibly formed by enhanced vertical nitrate flux due to elevated turbulent diffusivity when isopycnals constantly impinged on a sloping sea floor. Furthermore, the study demonstrated that near-inertial internal waves were responsible for transporting the onshore nitrate offshore, providing a new mechanism for fueling the offshore primary productivity. These findings highlight the need for new instrumentation to better understand complex coastal biogeochemical dynamics.

The ability to understand and predict storm erosion along sandy coastlines is important for safely and sustainably managing these coastlines now and in the future. This thesis investigates the use of data-driven Bayesian networks to assist coastal scientists, engineers and managers to better understand and predict sandy coastline storm erosion using large observational datasets acquired by coastal remote sensing technologies. A methodological study was undertaken using a 10-year dataset of coastal storm events extracted from Argus coastal imaging technology. It was found that Bayesian networks have key advantages for modelling storm erosion including the illumination of causality, uncertainty quantification, and low computational cost. However, these advantages can be limited by the data requirements of the approach. It was determined that, based on data availability and the modelling objective, Bayesian networks can be applied to descriptive or predictive applications. Descriptive networks can be useful for exploring the physical relationships between variables within a specific dataset. In contrast, predictive networks identify general relationships in a dataset that can be used to predict unseen data. A descriptive Bayesian network was used to investigate controls of spatial variability in storm erosion of the berm and dune based on detailed storm erosion observations spanning a 400 km region of the southeast Australian coastline. It was found that spatial variability in storm erosion was driven by both the antecedent morphology of the coastline and hydrodynamic forcing conditions of the storm event, and that controls of erosion of the berm and dune were different. A predictive Bayesian network was developed using multiple large storm erosion datasets from three different global locations. Results showed that while Bayesian networks developed at one specific location poorly predicted the storm erosion response at differing locations, a Bayesian network developed on all three datasets generalised storm erosion response well, predicting changes to the shoreline, dune toe and dune crest with accuracies between 61 – 76% when tested on unseen data. Importantly, similar variables were important in the Bayesian network for predicting storm erosion at the different study regions and included descriptors of the antecedent beach morphology and hydrodynamics forcing of the storm event.

Oceanic uptake of atmospheric heat as well as incorporation of freshwater occurs across a vast range of spatial scales. Subsequently, these buoyant water masses are transported and modified within the ocean interior. Several physical processes relevant to the transport and mixing of heat and freshwater at an array of coastal scales, ranging from 1000s of km at the continental shelf slope to m within estuaries, are the topic of this dissertation. Analysis of a mix of data assimilative and idealized numerical models and field observations has yielded several impactful results that have direct relevance to coastal societies and ecosystems. At the largest scale, a mechanism that delivers warm water within the Antarctic Circumpolar Current to the continental shelf slope where it crosses into the Amundsen Sea outer shelf has been identified. Vorticity input by wind-stress curl results in the poleward motion of heat that has potential to contribute to Antarctic Ice Sheet mass loss and consequently, global sea level rise. At the much smaller scales of the inner-shelf to surf zone, surface gravity wave induced onshore currents and mixing drastically modify low inflow estuarine freshwater outflows by reducing offshore transport and elongating alongshore and vertical extent within the surf zone. Because the freshwater distribution can be thought of as a proxy for tracers such as pollution, nutrients, or other plume constituents, these results have strong implications for beach contamination among other concerns that frequently arise due to the presence of buoyant outflows in the nearshore region. Within the estuary, lateral circulation moves channelized waters to regions of enhanced productivity over bathymetric shoals. In San Diego Bay, a low inflow estuary that lies in a unique parameter space among estuaries, this process is, at least in part, due to differential advection. Field data suggest that this process is sensitive to seasonal variation in buoyancy inputs and that circulation patterns may be altered in future climate change scenarios, thus impacting the wildlife that utilize the bay for breeding, habitat, and foraging. As such, the findings of this dissertation advance the fundamental science necessary to contribute to many societally relevant coastal management issues.

Virtually all mechanistic predictions of landscape evolution are underpinned by predictions of sediment transport rates. Sediment transport via bedload is the primary way by which coarse sediment is transported through landscapes, and thus, accurate prediction of bedload transport represents a fundamental topic in the study of earth surface processes. Specifically, predictions of coarse sediment transport are strongly dependent on the selection of the threshold for motion, or the forcing at which sediment transport begins. However, it is well known that the threshold for motion varies in space and time, and in response to a number of processes. This dissertation aims to identify and quantify the effects of biology and prior flow history on the onset of coarse particle motion through a combination of mathematical modeling, novel physical experiments, and continuous bedload transport measurements in the field. Chapter 2 develops and tests a mechanistic model for the entrainment of coarse sediment by attached kelp, highlighting the significance of biology in setting coastal sediment transport rates. In Chapter 3, we explore the effects of below-threshold, antecedent flow history on gravel bed structure, grain protrusion, and bedload transport through a series of flume experiments. We find that bedload flux, and by extension, the onset of motion, is extremely sensitive to the duration of prior below-threshold flow. This reduction in bedload transport rates is related to the reduction in the population of high protruding grains, related to the pivoting of precariously placed, highly mobile particles into nearby pockets. In Chapter 4, we carry out a systematic analysis of the temporal evolution of the threshold for motion in a natural channel though the analysis of a unique record of continuous bedload transport measurements. We observe that variations in the threshold for motion are significantly linked to previous flow magnitude, highlighting that the onset of motion is a history-dependent quantity. Collectively, these studies provide new observations and approaches towards predicting the temporal and spatial evolution of the threshold for motion, providing a basis for improved bedload transport models.

In coastal rivers, tides can propagate for tens to hundreds of kilometers inland beyond the saltwater line. Yet the influence of tides on river-aquifer connectivity and solute transport in tidal freshwater zones (TFZs) is largely unknown. We estimate that along the TFZ of White Clay Creek (Delaware, USA), more than 17% of river water exchanges through hyporheic and riparian storage zones due to tidal pumping alone. Additional hyporheic processes such as flow through bedforms likely contribute even more exchange. The turnover length associated with the tidal pumping process is 39 km, similar to turnover lengths for all hyporheic exchange processes in non-tidal rivers of similar size. Based on measurements at a transect of piezometers located 17 km from the coast, tidal pumping exchanges 0.44 m3 of water across the bank and 0.49 m3 across the bed per unit river length. Exchange fluxes range from -0.81 to 1.68 m d-1 across the bank and -0.84 to 1.88 m d-1 across the bed. During rising tide, river water infiltrates into the riparian aquifer, and the downstream transport rate in the channel is low (1.45 m3 s-1). During falling tide, stored groundwater is released to the river, and the downstream transport rate in the channel increases by 380%. Tidal bank storage zones may remove nutrients or other contaminants from river water and attenuate nutrient loads to coasts. Alternating expansion and contraction of aerobic zones in the riparian aquifer likely influence contaminant removal along flow paths. A clear need exists to understand contaminant removal and other ecosystem services in TFZs and adopt best management practices to promote these ecosystem services.

There is evidence that a subset of fluvial deposits at Aeolis Dorsa, a basin on Mars, preserve incised valleys carved and filled during changes in base level, which was likely controlled by water surface elevation of a large lake or sea. Three low-albedo, channelized corridors, each several tens of kilometers long, contain relict point bars and scooped boundaries at their bases, indicating that the base and lateral extent of each corridor was defined by a migrating, net-erosional river. Above the basal deposits are stacks several tens of meters thick of “inverted sinuous ridges”, which are channel-filling deposits that have been exhumed and topographically inverted. Indicators of avulsions, channel re-occupations, an overall flattening of basal topography, and confinement of inverted sinuous ridges to the dark corridors are evidence of the gradual filling of a valley cut by the basal migrating river. Valley incision and fill are common responses to sea level change on Earth. Aeolis Dorsa is currently open to the northern lowlands of Mars, where an ocean has been hypothesized to have once existed, although a large lake could have also controlled base level. Cross-cutting valleys require at least two episodes of base level fall and rise. The magnitudes of the base level changes are estimated at about 80 meters, based on the thickness of the valley-filling stratigraphy. Meander asymmetry is consistent with a southeastern flow direction, and is supported by a set of branching fluvial deposits 40 km to the southeast which, qualitatively, appear to be deltaic in origin.

Embayed beaches differ from open coast beaches due to the control exerted by headlands, leading to alongshore gradients in wave height, surfzone width and beach state. Circulation and morphodynamic behaviour of embayed beaches are poorly understood. This study involves observations at three embayed beaches around Sydney, Australia. Methods involve Lagrangian observations of currents and bathymetric surveys. At Whale Beach (600 m long), Lagrangian observations of an entire embayment, including headland rip currents, are presented. Headland geometry and wave direction were found to influence rip current trajectories, and degree of bathymetric non-uniformity correlated with current velocities. Surfzone exit rates increased along the beach from the protected headland to the exposed end. At Bondi Beach (850 m long), observations of morphodynamic response to storm-groups over a three week period are presented. Offshore significant wave heights reached 5.6 m, with a 10-day average >3 m. A mega-rip developed at the exposed headland, while the protected end maintained a low-tide-terrace. Alongshore non-uniformity was found to decrease near the shoreline, and increase in the outer-surfzone and nearshore. At Shelly Beach (2.3 km long), the rip current hazard was investigated, testing the efficacy of 'float' and 'swim parallel' strategies. Human subjects entered three rip channels with Lagrangian measurements of background flow. Swimming parallel was found to be a shorter duration strategy, with lower failure rate. However both strategies failed in some instances and neither can be recommended as a sole preference. Finally, all data are analysed to investigate the degree of bathymetric control on very low frequency (~10 min) current variability due to surfzone eddies. A classification scheme is introduced ranging from: (i) strong bathymetric control where currents exhibit high mean velocities, with velocity pulsation or rip cell oscillations, to (ii) no bathymetric control where randomly directed surfzone eddies occur on planar bars. This study broadens understanding of several aspects of embayed beach dynamics. In particular, it demonstrates that alongshore wave-height and beach state gradients on embayed beaches will force alongshore changes in: (i) current velocities, trajectories and variability; (ii) cross-shore exchange; (iii) morphodynamic response to storms; and (iv) the level of hazard to bathers.

Using ArcGIS, a sea-level rise inundation comparison was conducted using four different techniques under five sea-level rise conditions for the Kauai, Hawaii, towns of Hanalei Bay, Kapa'a, and Waimea. Sea-level rise was mapped in 0.5 m increments from 0.0 m of rise to 2.0 m of rise. Datasets used in the analysis include a digital elevation model (DEM) layer, wave height data, tidal elevation data, and land cover data. The four techniques illustrating projected inundation serve as a comparison of passive versus dynamic models. The primary goals of this study were to not only compare passive and dynamic sea-level rise inundation models, but also to provide a realistic representation of what future sea-level rise will look like on Kauai, and which areas would be inundated at specific future water surface levels. The results of this analysis can be used to aid Kauai government officials in planning for the future and to aid in prioritizing where and what infrastructure and development will need to be considered before actual sea-level rise impacts occur.

Beaches are preserved above sea level along ice-free portions of the Antarctic coastline due to post-glacial rebound associated with glacial isostatic adjustment since the Last Glacial Maximum. The ages and elevations of these beaches provide relative sea-level constraints for glacial isostatic adjustment models and ice-sheet histories. Due to harsh field conditions and difficulty dating Antarctic materials, a lack of geochronological constraints on raised beaches limits our understanding of relative sea level around Antarctica. The focus of the studies discussed here is on Antarctic raised beaches with goals to improve the methods of dating cobble surfaces from raised beaches using optically stimulated luminescence and use the dated beaches to reconstruct relative sea level and better understand Antarctic coastal processes throughout the Holocene. Through a series of cleaning methods applied to sample carriers used for optically stimulated luminescence measurements of sediment, the contamination of dose-dependent, variable signals from sample carriers previously assumed to have neutral signals is eliminated through a series of cleaning methods (Chapter 2). An analysis of optically stimulated luminescence characteristics of quartz from cobble surfaces with sample petrology and cathodoluminescence provides insight on the suitability of Antarctic materials for optically stimulated luminescence dating (Chapter 3). The limited amount of quartz (

Coastal dunes of Lake Michigan and corresponding down-wind lakes are studied for links between dune activity and climatic forcing; to date, little is certain about climate control on dune activity. By unveiling relationships between climate variables and dune activity, it becomes possible to associate the activity of dunes with certain climatic conditions. In this study wind, temperature, precipitation, drought, evaporation, and lake level are correlated individually with 210Pb/137Cs/7Be dated sand deposits from core samples taken in a small lake in the lee side of a dune ridge near Saugatuck, Michigan. Linear regressions were run to evaluate the strength of their relationship year-by-year, and offsets of one to two years. Visual correlations were also attempted by evaluating the trends in the annular data sets. While year-by-year R2 values were not strong, or mixed results made them inconclusive, visually examined trends showed more promising correlations. The strongest correlations existed between sand percent by weight, drought, and lake level. Discrepancies between trends were acceptable within the limits of associated error with isotopic dating methods, and showed a relationship between rising or high lake levels, wet conditions, and strong eolian activity (based on increased presence of sand in lake sediment). The implications of this research are that dune activity is linked to periods of wet conditions and storminess, and results can be used as a modern analogue for coastal dune activity during times of high lake level.

Trinity, East, and Wine Islands make up the eastern half of the Isles Dernieres barrier arc in south-central Louisiana. Formed following the abandonment of the Lafourche delta complex, subsidence and storm erosion have led to rapid deterioration of the system. Since 1887, the land area of the islands has decreased seventy-seven percent, and the gulf shoreline has retreated landward more than a kilometer. Wave ravinement on the shoreface of the islands is responsible for the most sediment loss; liberated sediment travels longshore to tidal inlets. The dominant ebb tidal currents then transport the sediment to where it is deposited in ebb tidal deltas or carried to the west, out of the system. A large lobe of sediment bypassing Cat Island Pass is entering the system from the eastern lower shoreface, which helps replace some of the sediment lost through wave ravinement to the upper shoreface.