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Shallow lakes in semi-arid environments are very sensitive to hydrological alterations associated with climate change. Their shorelines and geometry can change according to water level fluctuations. Gallocanta Lake (NE Spain) is a typical example of such lacustrine conditions because it is exposed to strong winds parallel to its elongation axis and is located in a semi-arid Mediterranean environment. In this work, a high-resolution digital elevation model (DEM) of the area is used to compare the distribution of coastal forms (beaches, barrier islands, deltas, lagoons, etc.) with the frequency at which different water levels are attained. As a result, a clear relationship is obtained between presently active forms and the water levels most frequently reached in the lake. It is deduced that, once formed, the surrounding coastal plains related to these coastal forms control the permanence of water around a given height interval, favouring the development of these morphologies, in a positive feedback mechanism only broken by subsequent climate warming and lake water lowering. The hydrodynamic conditions responsible for activating the coastal forms have been analysed by applying a mathematical model of wind-driven currents in the lake that predicts the present erosional/progradational trends associated with them. The combination of the different results obtained was used to generate a synthetic map of active coastal processes and trends along the lake shore during high water episodes, with two versions according to the two dominant wind scenarios in the region. The distribution of erosion/sedimentation trends along the lake shores has helped to propose the existence of longitudinal littoral cells, each one recording different shoreline trend (retreat, progradation, and stability), depending on the prevailing wind scenario. This synthetic scheme can be useful for predicting the eco-morphological trends of the lake shore and adapting the present management practices in thi, Postprint (author's final draft)

Modelling the response of sandy beaches to sea level rise is a major scientific challenge and several types of models can be applied. Given the long-time scales involved, different sources for model forcing must be combined (wave and sea-level, e.g., from buoys or hindcast models). We here apply the XBeach process-based morphodynamic model and the Q2Dmorfo reducedcomplexity model to El Castell, a Mediterranean embayed beach. The models are first calibrated with data measured during 161 days with an AWAC at 14 m depth in front of the beach. XBeach predicts reasonably well the bathymetric dynamics while Q2Dmorfo can only reproduce the shoreline evolution. The calibrated versions of the models are then applied using other potential forcing sources. The source for sea level does not affect the results but both models are sensitive to the wave forcing source., Peer Reviewed, Postprint (published version)

A variety of morphodynamic patterns are typically present in the nearshore zone of sandy beaches that develop due to the interactions between waves, currents and the morphology. The most common are one or several nearshore sandbars that vary in configuration from shore-parallel to crescentic, the latter consisting of alongshore-rhythmic (i.e., undulating) bars (also called rip-channel systems). Crescentic bars are often coupled to similar undulations in the shoreline called megacusps. Understanding the evolution of nearshore sandbars and their coupling to the shoreline is important as they significantly affect the nearshore morphology and hydrodynamics. Alongshore sandbar variability has been studied extensively, but mostly at beaches with substantial tidal range and medium-high energetic waves. Furthermore, the dynamics of megacusps and their coupling with crescentic bars are much less understood. This thesis uses nearly 8 years of hourly time-exposure video images to study the development and interactions of crescentic bars and megacusps at the open, low-energetic, tideless beach of Castelldefels (northwestern Mediterranean Sea, Spain). This requires accurate directional wave conditions at shallow water which can be obtained in various ways. Here, the accuracy of two available large-scale wave models and propagating measured wave conditions (integrated wave parameters and 2D frequency-direction spectra) using wave ray theory or the SWAN wave model was assessed. Comparing the results of the different methods to a short-term dataset of in-situ measurements showed that propagating measured 2D frequency-direction spectra using SWAN yielded the most accurate predictions for all wave parameters. The other methods resulted in increased errors in wave direction, particularly for shore-oblique and bimodal wave climates due to underestimation of refraction. The video images together with the hourly wave conditions at shallow water in front of Castelldefels beach (obtained w, En la zona sumergida de las playas arenosas aparecen típicamente patrones morfológicos resultantes de las interacciones entre el oleaje, las corrientes y el fondo marino. Los más frecuentes son barras de arena, paralelas a la costa o crescénticas (con ondulaciones longitudinales). Las barras crescénticas a menudo se acoplan a patrones similares en la orilla conocidos como megacúspides. La evolución de estos patrones afecta significativamente la morfología y la hidrodinámica próxima de la orilla. Las barras crescénticas se han estudiado ampliamente, principalmente en playas con mareas importantes y oleaje de energía media-alta. Sin embargo, existe un gran desconocimiento sobre la dinámica de las megacúspides y su acoplamiento con las barras crescénticas. Esta tesis utiliza casi 8 años de imágenes horarias de video para estudiar el desarrollo y las interacciones de barras crescénticas y megacúspides en Castelldefels (noroeste del mar Mediterráneo, España), una playa abierta de baja energía y sin mareas. El estudio requiere de datos precisos de oleaje direccional en aguas someras que se pueden obtener con varias metodológías. Aquí se evaluó la precisión de dos modelos de oleaje a gran escala y la propagación de oleaje medido (parámetros de oleaje y espectros 2D en dirección y frecuencia) utilizando la teoría de rayos o el modelo SWAN. La comparación de los diferentes métodos con un conjunto de datos a corto plazo de medidas in situ mostró que la propagación de espectros 2D con SWAN produce las predicciones más precisas. Los otros métodos dieron como resultado errores mayores en la dirección, debido a la subestimación de la refracción durante climas de oleaje bimodal y oblicuo a la costa. Las imágenes de vídeo junto con los datos de oleaje en aguas someras frente a la playa de Castelldefels (obtenidos con el método óptimo) se utilizaron para investigar la dinámica de barras crescénticas y megacúspides, así como el acoplamiento correspondiente. Las barras crescénticas es, A la zona submergida de les platges de sorra apareixen típicament una varietat de patrons morfològics que resulten de les interaccions entre les onades, els corrents i el fons marí. Els més comuns són barres de sorra que poden ser paral·leles a la costa o crescèntiques (amb ondulacions longitudinals). Les barres crescèntiques sovint s’acoblen a patrons similars a la riba (megacúspides). L’evolució d’aquests patrons afecta significativament la morfologia i la hidrodinàmica a prop de la costa. Les barres crescèntiques s’han estudiat àmpliament, però principalment a platges amb marees importants i onatge d’energia mitjana-alta. La dinàmica de les megacúspides i el seu acoblament amb les barres crescèntiques es coneixen molt menys. Aquesta tesi utilitza gairebé 8 anys d’imatges horàries de vídeo per estudiar el desenvolupament i les interaccions de barres crescèntiques i megacúspides a Castelldefels (nord-oest del mar Mediterrani, Espanya), una platja oberta de baixa energia i sense marees. Això requereix dades precises d’onatge direccional en aigües poc profundes que es poden obtenir de diverses maneres. Aquí es va avaluar la precisió de dos models d’onatge a gran escala i la propagació d’onatge mesurat (paràmetres d’onatge i espectres 2D en direcció i freqüència) utilitzant la teoria de rajos o el model SWAN. La comparació dels diferents mètodes amb un conjunt de dades a curt termini de mesures in situ va mostrar que la propagació d’espectres 2D amb SWAN produeix les prediccions més precises. Els altres mètodes van donar com a resultat errors més grans en la direcció, a causa de la subestimació de la refracció durant climes d’onatge bimodal i oblic a la costa. Les imatges de vídeo juntament amb les dades d’onatge en aigües poc profundes davant de la platja de Castelldefels (obtingudes amb el mètode òptim) es van utilitzar per investigar la dinàmica de barres crescèntiques i megacúspides, així com l’acoblament corresponent. Les barres crescèntiques van estar presents u, (Neerlandès) De ondiepe (< 10 m) wateren van zandige kusten worden meestal gekenmerkt door een grote verscheidenheid aan morfologische patronen, welke ontstaan als gevolg van de interacties tussen golven, stromingen en de morfologie. Veelvoorkomende patronen zijn een of meerdere kustnabije zandbanken die qua configuratie variëren van parallel langs de kust tot crescentisch, waarbij de laatste gekenmerkt worden door een kustlangse ritmische (golvende) periodiciteit. Crescentische zandbanken zijn vaak morfologisch gekoppeld aan soortgelijke ritmische patronen in de kustlijn die megacusps worden genoemd. Het begrijpen van de evolutie van kustnabije zandbanken en hun koppeling met de kustlijn is belangrijk aangezien ze de morfologie en hydrodynamica in ondiep water aanzienlijk beïnvloeden. De kustlangse variabiliteit van zandbanken is in het verleden al uitgebreid bestudeerd, maar vooral op stranden met aanzienlijke getijden en gemiddeld tot hoog-energetische golven. Daarnaast zijn er nog veel open vragen omtrent de dynamica van megacusps en hun koppeling met crescentische zandbanken. Dit proefschrift maakt gebruik van bijna 8 jaar aan uurlijkse videobeelden om de ontwikkeling en interacties van crescentische zandbanken en megacusps te bestuderen op het open, laag-energetische strand met verwaarloosbaar getij van Castelldefels (noordwestelijke Middellandse Zee, Spanje). Om dit te doen zijn nauwkeurige golfcondities op ondiep water noodzakelijk die op verschillende manieren kunnen worden verkregen. Voor Castelldefels werd de nauwkeurigheid bepaald van twee beschikbare grootschalige golfmodellen en het propageren van gemeten golfcondities (geïntegreerde golfparameters en 2D spectra in frequentie en richting) met behulp van golfstraaltheorie of het SWAN-golfmodel. Door de resultaten van de verschillende methoden te vergelijken met een korte-termijn dataset van metingen ter plaatse bleek dat het propageren van gemeten 2D spectra in richting en frequentie met behulp van SWAN, Postprint (published version)

Se realizaron 14 campañas topo-batimétricas desde la playa emergida hasta los 15 m de profundidad, a lo largo de 1 km en la playa de Castelldefels (Delta del Llobregat, Barcelona) durante el periodo 2011-2020. Se analizan las variaciones morfológicas que tienen lugar, los cambios volumétricos y sus posibles implicaciones en los intercambios sedimentarios en el perfil litoral. Los principales cambios morfológicos están causados por los desplazamientos transversales de las barras de arena, generalmente hacia tierra durante condiciones de buen tiempo y hacia mayor profundidad durante las tormentas más fuertes. Los cambios volumétricos sugieren que el retroceso de la línea de costa durante la última década aporta sedimento a la parte superior de la playa sumergida, mientras que los eventos más extremos producen una transferencia de sedimento hacia la plataforma continental, que podrían ser parcialmente irrecuperables para la dinámica litoral. El balance sedimentario resultante es negativo, Postprint (updated version)

UBathy is an open source software developed for bathymetry estimation from video images. The proposed scheme is based on extracting the wave modes from videos of the nearshore surface wave propagation. These videos can be formed either from raw camera images, which must have been previously calibrated, or from georeferenced planviews. For each wave mode extracted from the videos, the wave frequency and the spatially dependent wavenumbers are obtained. The frequencies and wavenumbers from different videos are used to estimate the bathymetry by adjusting the dispersion relationship for linear surface water waves. The bathymetry at different times can further be weighted and aggregated using the Kalman filter. The new software is suitable for Argus-type video monitoring stations and for moving cameras mounted on drones or satellites, and it is meant for users familiar with coastal image processing and suitable for non-experienced users. The software and an application example are available on the GitHub platform., Postprint (author's final draft)

Alongshore changes in shorelines along sandy beaches are a result of variations in wave conditions and nearshore morphology, which can cause straight shorelines to develop large-scale (100–1000¿m wavelength) undulations, called megacusps, which cause local shoreline accretion and erosion. Megacusps are often morphologically coupled to alongshore variability in the nearshore sandbar (crescentic bars). Sandbar rhythmicity has been studied extensively, whilst megacusp dynamics and their coupling with crescentic bars have received less attention. This study uses a long-term dataset of hourly time-exposure video images and detailed propagated wave conditions to investigate megacusp dynamics and the corresponding sandbar–shoreline coupling at the low-energetic, tideless beach of Castelldefels (northwestern Mediterranean Sea, Spain). Megacusps were observed during 24% of the study period. Crescentic bars were present during 91% of the days with megacusps, whilst megacusps were not observed during 50% of the days with crescentic bars. Megacusp wavelengths (100–700¿m) were comparable to those of crescentic bars, whilst cross-shore amplitudes (3–8¿m) and alongshore migration speeds (0–15¿m/day) were smaller than those of crescentic bars. No clear relation was observed between wave conditions and megacusp formation, migration and disappearance. However, megacusp presence was strongly linked to crescentic bar presence, as megacusps mostly developed some days after the formation of a crescentic bar. Coupling between shoreline and inner sandbar was significant during 74% of the time with simultaneous presence of megacusps and crescentic bars. No dominance of one particular coupling pattern was observed, although the pattern depended on the wave height and the wave angle. It is hypothesised that the wave height and angle determine the type of flow pattern over the inner crescentic bar (single or double rip cell circulations versus meandering currents) and thus control the type of, Postprint (published version)

Coastal landforms can sometimes result in unique and visually mesmerizing spatially-organized patterns. Different spatial patterns develop over scales ranging from centimeters to tens of kilometers, and are observed at the shoreline (e.g., ripples, beach cusps, shoreline undulations), in the surf zone (e.g., crescentic or multiple sandbars) and even in the continental shelf (e.g., sand ridges, sand waves) where wind waves may play a minor role. Here, we provide a review of the characteristics of rhythmic patterns that develop in the nearshore and of some of their formative processes, a topic of ongoing debate within the research community., Postprint (author's final draft)

This work aims to explore the potential of UAV-captured videos for the characterization of shoreline dynamics at time scales of seconds to minutes. A 2 min video recorded by a UAV at Playa de la Victoria in Cádiz, on a day when there were beach cusps, was used. To begin, the images corresponding to the frames of the video to be analyzed were extracted and calibrated. For this, two software from GitHub were used. The first of them is called UClick and it allows to manually calibrate a subset of frames. The second is called Udrone and allows you to calibrate all the other frames from the previous subset and make planviews (images with a zenith view) of the different areas to be studied: an area around the coastline and an area at open sea. The second step was to develop a Python code for the automatic detection of the coastline from the planviews of this area. Currently, there is no standard methodology to automatically detect the coastline. In this work, image processing tools have been used, such as filters, and two different methodologies have been applied to be able to compare the results. The first is based on the calculation of the gradient of different channels that characterize the colours of the image and that change rapidly around the coastline. The second is based on classifying the pixels between sea and land according to a combination of two colour channels. The best method for coastline detection has turned out to be the gradient of the Red/Green channel, a channel widely used for these applications. The RMSE (Root Mean Square Error) obtained in four frames, which have been taken as an example, have been from 0.4 to 9.7 meters. Next, the dynamics of the line have been characterized using an EOF (Empirical Orthogonal Functions) decomposition through an already existing code. In both shoreline extraction methodologies, the first EOF has been seen to describe a significant percentage of variance and can therefore be considered to represent a significant por

Nearshore sandbars are important features in the surf zone of many beaches because they strongly influence the mean circulation and evolving morphology. Due to variations in wave conditions, sandbars can experience cross-shore migration and vary in shape from alongshore uniform (shore-parallel) to alongshore rhythmic (crescentic). Sandbar dynamics have been studied extensively, but existing observational studies usually do not quantify the processes leading to crescentic bar formation and straightening. This study analyses the dynamics of crescentic bar events at the fetch-limited beach of Castelldefels (northwestern Mediterranean Sea, Spain) using 7.5 years of hourly time-exposure video images and detailed wave conditions. The results show that, despite the generally calm wave conditions, the sandbars were very dynamic in the cross-shore and longshore directions. They often migrated rapidly offshore during storms (up to 70¿m in one day) and more slowly onshore during post-storm conditions. Crescentic bars were often present at the study site (48% of the time), but only when the sandbar was at least 10¿m from the shoreline. They displayed a large variability in wavelengths (100–700 m), alongshore migration speeds (0–50 m/day) and cross-shore amplitudes (5–20 m). Wavelengths increased for larger bar–shoreline distances and the alongshore migration speeds were strongly correlated with the alongshore component of the radiation stresses. Crescentic patterns typically developed during low–medium energetic waves with limited obliquity (¿¿20° at 10¿m depth), while bar straightening occurred during medium–high energetic waves with strong oblique angles of incidence (¿¿15°). Overall, this study provides further proof for the important role of wave direction in crescentic bar dynamics and highlights the strong dependence of crescentic bar development on the initial bathymetric configuration., Peer Reviewed, Postprint (published version)

Sand ridges, with length scales of several km, are prominent features of the seafloor landscape of many sandy continental shelves. Knowledge about the extent to which these ridges influence the large-scale (i.e., decadal and kilometer scales) morphodynamic evolution of the adjacent shoreline and vice versa (shelf-shoreline morphodynamic coupling) is limited. The present work aims at quantifying this coupling by using a coupled nonlinear shelf-shoreline model forced by tides and different wave conditions. Model results show that the presence of sand ridges on the shelf creates longshore non-uniform wave patterns, which act as a forcing template for the morphodynamic development of the shoreline. The shelf-shoreline coupling primarily works one way, meaning that the morphodynamic evolution of the shelf affects the evolution of the shoreline. When wave propagation is predominantly aligned with the long axis of the shelf ridges, the forced shoreline undulations are so prominent, that they affect the shelf morphology (significant two-way coupling). Moreover, for those waves, the longshore spacing of the ridges is strongly imprinted on the shoreline morphology. Weaker shoreline undulations develop for waves that propagate more across the ridges and the weakest for time-varying wave conditions with large variability in their angles of propagation. Model results compare fairly well with observations. Physical mechanisms underlying the different morphodynamic responses of the coupled shelf-shoreline system to different wave conditions are also given., Postprint (author's final draft)

andbars often display an alongshore variable morphology (crescentic bars), which is often mimicked at the shoreline (megacusps). The processes resulting in these patterns are not yet clear and particularly the coupling between sandbar and shoreline deserves more attention. This contribution presents 8 years of video observations on the dynamics of crescentic bars and megacusps, including coupling, at the open, fetch-limited beach of Castelldefels (Spanish Mediterranean coast). Wave conditions were propagated from the nearest wave buoy to the study site (10 m depth). Crescentic bars and megacusps were detected visually from video images, after which the barlines and shoreline were extracted to compute characteristics like wavelengths, amplitudes and alongshore migration rates. Finally, the bar-shoreline coupling was evaluated using cross-correlation. Crescentic bars were only observed when the sandbar- shoreline distance was at least 10 m. They developed during lower energetic waves with both oblique and shore-normal angles, whereas straightening occurred primarily during high-energetic obliquely-incident waves. Megacusps only developed in the presence of a crescentic bar and were less pronounced and dynamic compared to crescentic bars. During megacusps presence, a highly-significant coupling was present during 73% of the time but the relative phase varied, partly due to different alongshore migration rates of the two patterns., Peer Reviewed, Postprint (published version)

Following the path set out by the “Argus” project, video monitoring stations have become a very popular low cost tool to continuously monitor beaches around the world. For these stations to be able to offer quantitative results, the cameras must be calibrated. Cameras are typically calibrated when installed, and, at best, extrinsic calibrations are performed from time to time. However, intra-day variations of camera calibration parameters due to thermal factors, or other kinds of uncontrolled movements, have been shown to introduce significant errors when transforming the pixels to real world coordinates. Departing from well-known feature detection and matching algorithms from computer vision, this paper presents a methodology to automatically calibrate cameras, in the intra-day time scale, from a small number of manually calibrated images. For the three cameras analyzed here, the proposed methodology allows for automatic calibration of >90% of the images in favorable conditions (images with many fixed features) and ~40% in the worst conditioned camera (almost featureless images). The results can be improved by increasing the number of manually calibrated images. Further, the procedure provides the user with two values that allow for the assessment of the expected quality of each automatic calibration. The proposed methodology, here applied to Argus-like stations, is applicable e.g., in CoastSnap sites, where each image corresponds to a different camera., Postprint (author's final draft)

Measuring the nearshore bathymetry is critical in coastal management and morphodynamic studies. The recent advent of Unmanned Aerial Vehicles (UAVs), in combination with coastal video monitoring techniques, allows for an alternative and low cost evaluation of the nearshore bathymetry. Camera calibration and stabilization is a critical issue in bathymetry estimation from video systems. This work introduces a new methodology in order to obtain such bathymetries, and it compares the results to echo-sounder ground truth data. The goal is to gain a better understanding on the influence of the camera calibration and stabilization on the inferred bathymetry. The results show how the proposed methodology allows for accurate evaluations of the bathymetry, with overall root mean square errors in the order of 40 cm. It is shown that the intrinsic calibration of the camera, related to the lens distortion, is the most critical aspect. Here, the intrinsic calibration that was obtained directly during the flight yields the best results., Postprint (author's final draft)

Joint intrinsic and extrinsic calibration from a single snapshot is a common requirement in coastal monitoring practice. This work analyzes the influence of different aspects, such as the distribution of Ground Control Points (GCPs) or the image obliquity, on the quality of the calibration for two different mathematical models (one being a simplification of the other). The performance of the two models is assessed using extensive laboratory data (i.e., snapshots of a grid). While both models are able to properly adjust the GCPs, the simpler model gives a better overall performance when the GCPs are not well distributed over the image. Furthermore, the simpler model allows for better recovery of the camera position and orientation., Postprint (author's final draft)

Accurate directional wave conditions at shallow water are crucial for nearshore field studies and necessary as boundary conditions for morphodynamic models. However, obtaining reliable results for all wave parameters can be challenging, particularly regarding wave direction. Here, the accuracy of two global hindcast models and propagation of measured wave conditions using linear wave theory or the SWAN wave model (forced by integrated wave parameters or 2D spectra) is assessed to obtain directional wave conditions at shallow water for Castelldefels beach, northwestern Mediterranean Sea. Results are analyzed using different statistical error parameters and for different wave climates (shore-normal, shore-oblique and bimodal). The analysis shows that global hindcast models correctly predict the trends in wave height and mean wave period but predictions for mean wave direction are only accurate for shore-normal waves. Linear wave theory provides good results for wave height but underestimates refraction, resulting in significant errors in mean wave direction for shore-oblique waves. Finally, SWAN forced with 2D spectra results in the most accurate predictions for all wave parameters. When using integrated wave parameters as boundary conditions, the results for wave height and mean period stay the same whilst the errors in peak period and mean direction worsen for shore-oblique and bimodal wave climates. The reason is that for these wave conditions the directional spectrum constructed out of integrated wave parameters does not resemble the actual directional spectrum., Peer Reviewed, Postprint (published version)

Double sandbar systems often characterize the surf zone of wave-dominated beaches and display a variety of poorly explained spatial configurations. Here, we explore the morphodynamic stability of double-barred beaches using a model based on linear stability analysis. Surf zone hydrodynamics are described by coupling depth and wave-averaged conservation of mass and momentum with the wave energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence, an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars can be unstable, thereby resulting in the development of crescentic and/or rip channel patterns. Our study demonstrates that sandbar coupling can be either in phase (highs and lows of both sandbars are at the same alongshore position) or out of phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). In line with observations, results of simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that modes of which the amplitude of the inner sandbar perturbation is larger than that of the outer sandbar are dominant for large height–depth differences between the two sandbar crests and small offshore wave heights. Patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. For intermediate differences between the two sandbar depths, patterns on both longshore bars appear to be fully coupled (similar growth rates and strongly correlated pattern shapes). For relatively large waves and large depth over the outer sandbar, patterns can also develop close to the shoreline and/or inner surf zone together with patterns in the inner or outer sandbar., Postprint (author's final draft)

A new approach to infer the bathymetry from coastal video monitoring systems is presented. The methodology uses principal component analysis of the Hilbert transform of video images to obtain the components of the wave propagation field and their corresponding frequency and wavenumber. Incident and reflected constituents and subharmonics components are also found. Local water depth is then successfully estimated through wave dispersion relationship. The method is first applied to monochromatic and polychromatic synthetic wave trains propagated using linear wave theory over an alongshore uniform bathymetry in order to analyze the influence of different parameters on the results. To assess the ability of the approach to infer the bathymetry under more realistic conditions and to explore the influence of other parameters, nonlinear wave propagation is also performed using a fully nonlinear Boussinesq-type model over a complex bathymetry. In the synthetic cases, the relative root mean square error obtained in bathymetry recovery (for water depths 0.75m¿h¿8.0m) ranges from ~1% to ~3% for infinitesimal-amplitude wave cases (monochromatic or polychromatic) to ~15% in the most complex case (nonlinear polychromatic waves). Finally, the new methodology is satisfactorily validated through a real field site video., Postprint (published version)

Peer Reviewed, Postprint (published version)

Peer Reviewed, Postprint (published version)

Peer Reviewed, Postprint (published version)

Bathymetric inversion using video images is a new and promising technique in order to monitor beach morphology. In this TFG, a Boussinesq model called FunWave and a linear wave propagation routine will be used to create synthetic wave propagation over different bathymetries. Two bathymetric inversion methodologies will be subsequently applied to retrieve the bathymetry, comparing their results and analysing their sensitivity to different aspects, in order to understand and improve their performance.

INTRODUCTION Shoreface-connected sand ridges (SCSR) are accumulations of sand that occur in the inner shelfs of the world at spatial scales of a few kilometers and temporal scales of centuries. Sometimes, several ridges appear attached to the coast and extending seaward with an oblique orientation, the alongshore distance between the different bars being remarkably constant (see examples in figures 2 and 18 of the attached article). These features are relevant for engineering applications, biology and geology. The formation of such alongshore-rhythmic ridges can be due to, The large amount of sand provided by coastal erosion in the river mouth and the combination between high-speed currents induced by Mistral wind and severe wave-storm events might have been the favourable conditions in the Ebro delta for the formation of structures that can be considered the initial stages of shoreface-connected sand ridges development. This type of dynamic submerged structures are elongated sand bed forms that evolve during storms when high waves and intense storm-driven currents erode and transport sediment by exerting shear stresses at the sandy seabed. The morphological characteristics of these sand ridges are investigated for the case of the Ebro delta with two adapted codes called Morfo25 and Morfo62, based on linear stability analysis, and designed to describe inner shelf and surf zone morphodynamics, respectively. The hydrodynamic and geomorphological conditions of the Delta are applied on both models and the modelled results are analyzed and compared with the obtained data in the Ebro delta. Model results presents shoreface-connected sand ridges with morphological characteristics similar to those of the Ebro Delta, thereby confirming the hypothesis. It is proved that these ridges requires of strong NW wind and E-SE storm events at the same time. Furthermore, an improved description of wave processes does not have any effect on their characteristics because waves are shore-normal., La gran cantidad de arena proporcionada por la erosión costera en la desembocadura del río y la combinación de fuertes corrientes inducidas por viento Mistral y olas generadas por las tormentas podrían haber sido las condiciones favorables en el delta del Ebro para la formación de estructuras que pueden considerarse las etapas iniciales del desarrollo de crestas de arena en la placa continental (shoreface-connected sand ridges). Este tipo de estructuras sumergidas dinámicas son crestas de arena alargadas que evolucionan durante las tormentas cuando las altas olas y las intensas corrientes erosionan y transportan los sedimentos ejerciendo tensiones de corte en el lecho marino. Las características de estas crestas se investigan para el caso del delta del Ebro con dos códigos adaptados, Morfo25 y Morfo62, basados en el análisis de estabilidad lineal, y diseñado para describir los procesos morfodinámicos de la plataforma continental y de la zona de oleaje, respectivamente. Las condiciones hidrodinámicas y geomorfológicas del Delta se aplican en ambos modelos y los resultados modelados se analizan y comparan con los datos obtenidos en el delta del Ebro. Los resultados de los modelos presentan shoreface-connected sand ridges con características similares a éstas del delta del Ebro, confirmando así la hipótesis. Es demostrado que estas crestas requieren de fuerte viento NO y tormentas del E-SE al mismo tiempo. Además, una mejor descripción de los procesos del oleaje no tienen ningún efecto en sus características porque las olas son perpendicular a la orilla., La gran quantitat de sorra proporcionada per l'erosió costanera a la desembocadura del riu i la combinació entre els forts corrents induïts pel vent de Mistral i les onades generades per tempestes podrien haver estat les condicions favorables del delta de l'Ebre per a la formació d'estructures que es poden considerar les etapes inicials del desenvolupament de les crestes de sorra a la placa continental (shoreface-connected sand ridges). Aquest tipus d'estructures submergides dinàmiques són crestes allargades que evolucionen durant les tempestes, quan les ones altes i els corrents intensos de la tempesta erosionen i transporten sediments exercint tensions al fons de fons de sorra. Les característiques s'investiguen pel cas del delta de l'Ebre amb dos codis adaptats, Morfo25 i Morfo62, basat en l'anàlisi d'estabilitat lineal, i dissenyat per a descriure els processos morfodinàmics de la plataforma continental i de la zona de surf, respectivament. Les condicions hidrodinàmiques i geomorfològiques del Delta s'apliquen en ambdós models i s'analitzen els resultats modelats i es comparen amb les dades obtingudes en el delta de l'Ebre. Els resultats dels models presenten shoreface-connected sand ridges amb característiques similars a aquestes del delta de l'Ebre, confirmant així la hipòtesi. És demostrat que aquestes crestes requereixen de fort vent NO i tempestes de l'E-SE al mateix temps. A més, una millor descripció dels processos de l'onatge no tenen cap efecte en les seves característiques perquè les onades són perpendicular a la riba.

Este vídeo forma parte del MOOC "El lenguaje de la Ingeniería". Módulo de Física. (https://www.upc.edu/es/otra-oferta-formativa/mooc/el-lenguaje-de-la-ingenieria)

Este vídeo forma parte del MOOC "El lenguaje de la Ingeniería" (https://mooc.upc.edu/)

Este vídeo forma parte del MOOC "El lenguaje de la Ingeniería". Módulo de Física., Este vídeo forma parte del MOOC "El lenguaje de la Ingeniería". Módulo de Física.

Este vídeo forma parte del MOOC "El lenguaje de la Ingeniería" (https://mooc.upc.edu/)

Waves with a large incidence angle in deep water can drive a morphodynamic instability on a sandy coast whereby shoreline sand waves, cuspate forelands, and spits can emerge. This instability is related to bathymetric perturbations extending offshore in the shoaling zone. Here, we explore a different mechanism where the large incidence angle is supposed to occur at breaking and the bathymetric perturbations occur only in the surf zone. For wave incidence angles at breaking above ˜¿45°, the one-line approximation of coastal dynamics predicts an unstable shoreline. This instability (EHAWI) is scale-free and the growth rate increases without bound for decreasing wavelength. Here we use a 2DH morphodynamic model resolving surf zone instabilities to investigate whether EHAWI could approximate a real instability in nature with a characteristic length scale. Assuming very idealized conditions on the bathymetric profile and sediment transport, we find a 2DH instability mode consisting of shore-oblique up-current bars coupled to a meandering of the longshore current. This mode grows for high-angle waves, above about 30° (offshore) and the maximum growth rate occurs for the angle maximizing the angle at breaking, about 70° (offshore). The dominant wavelength is of the order of the surf zone width. Interestingly, for long sand waves, the growth rate never becomes negative and it matches very well the anti-diffusive behavior of EHAWI. This distinguishes the present instability mode from other modes found in previous studies for other bathymetric and sediment transport conditions. Thus, we conclude that EHAWI approximates a real morphodynamic instability only for quite particular conditions. In such case, a characteristic length scale of the instability emerges thanks to surf zone processes that damp short wavelengths., Postprint (author's final draft)

© 2017 Elsevier Ltd. An idealised study that identifies the mechanisms in the long term evolution of crescentic bar systems in nature is presented. Growth to finite amplitude (i.e., equilibration, sometimes referred to as saturation) and higher harmonic interaction are hypothesised to be the leading nonlinear effects in long-term evolution of these systems. These nonlinear effects are added to a linear stability model and used to predict crescentic bar development along a beach in Duck, North Carolina (USA) over a 2-month period. The equilibration prolongs the development of bed patterns, thus allowing the long term evolution. Higher harmonic interaction enables the amplitude to be transferred from longer to shorter lengthscales, which leads to the dominance of shorter lengthscales in latter post-storm stages, as observed at Duck. The comparison with observations indicates the importance of higher harmonic interaction in the development of nearshore crescentic bar systems in nature. Additionally, it is concluded that these nonlinear effects should be included in models simulating the development of different bed patterns, and that this points a way forward for long-term morphodynamical modelling in general., Preprint

The alongshore wave driven sediment transport can render a rectilinear coastline unstable in case of very oblique wave incidence., Peer Reviewed, Postprint (published version)

A number of morphodynamic models have been developed to simulate the dynamics of large-scale bedform patterns on the continental shelf. Most of the models are based on linear stability analysis and, therefore, only describe the characteristics of the bedforms at their formation. Apart from studying the principal formation mechanism, the models have take into account various processes (three dimensional flows, sediment sorting, wave stirring, different tidal constituents, etc) to describe the characteristics of the bedforms at specific locations. Exploration of the finite amplitude regime have also been made with simplified models. Future model developments are needed to explore long-term dynamics., Postprint (author's final draft)

Peer Reviewed, Postprint (published version)

We present a novel process-based morphodynamic model, which includes transport processes due to both velocity and acceleration skewness and a new formulation for intrawave motions, that successfully simulates observations of onshore sandbar migration. Results confirm findings of previous studies, in which each process was considered separately and in which sediment transport was computed from the observed water motion. However, our results indicate that accounting for the joint action of both velocity and acceleration skewnesses causes major improvement of the modeled onshore bar migration and is essential to accurately model the evolution of the entire cross-shore bottom profile, when compared with observations. We also demonstrate that the morphodynamics in the shoaling zone are dominated by velocity skewness (bed shear stresses), while sediment transport induced by acceleration skewness (pressure gradients) controls the morphodynamics in the inner surf zone., Postprint (author’s final draft)

The nearshore zone is plenty of 3D morphodynamic patterns resulting from the interaction of waves, currents and sediments. The dynamics of formation and evolution of these patterns is at present a controversial point in coastal research. However, frequently nearshore zone shows a strongly persistent uniformity. In this situation, morphodynamic changes are dominated just by crossshore processes. Remarkably, although this situation displays much less morphological complexity, cross-shore beach profile morphodynamics is still a research challenge, as sediment transport, in this case, is the result of a very subtle balance between onshore and offshore directed forces that still remain unsolved. The aim of this thesis is to get more insight on the physical processes involving cross-shore beach profile evolution and how relevant are them in the nearshore zone morphodynamics. To this end, a 1D non-linear morphodynamical model for the evolution of the profile is developed to analyze some relevant aspects of cross-shore beach profile morphodynamics. The AMORFO70 model couples hydrodynamics, sediment transport and bottom changes to account for the morphodynamics feedback. The model considers the depth-integrated and wave-averaged momentum and mass conservation equations coupled with wave- and roller-energy conservation, Snell's law and the dispersion relation under the assumption of alongshore uniformity. It is well-known that the intra-wave processes, particularly the near-bottom orbital velocity and acceleration, can lead to net onshore sediment transport. The model accounts for the most novel parameterization of the near-bed intra-wave velocity, to analyze the effects of the temporal distribution of the intra-wave near-bottom velocities and accelerations on cross-shore morphodynamics. It is found that accounting for both velocity and acceleration skewness in the sediment transport is essential to properly simulate onshore sandbar migration and the entire profile evolution., La zona costanera és plena de patrons morfodinàmics 3D que són el resultat de la interacció de l’onatge, els corrents i els sediments. La dinàmica de formació i evolució d’aquests patrons és un punt polèmic en la recerca de la dinàmica costanera. Tot sovint la zona costanera mostra una forta i persistent uniformitat longitudinal. En aquest cas, els canvis morfodinàmics són dominats pels processos transversals. Tot i que aquesta situació suposi una complexitat morfològica menor, la morfodinàmica del perfil transversal de platges és encara un repte científic, ja que, en aquest cas, el transport de sediment és el resultat d’un balanç molt subtil entre les forces onshore i offshore. L’objectiu d’aquesta tesis és obtindre una visió més clara dels processos físics involucrats en l’evolució del perfil transversal i com de importants són en la morfodinàmica costanera. Amb aquesta finalitat, s’ha desenvolupat un model morfodinàmic 1D no lineal per a l’evolució del perfil transversal per tal d’analitzar alguns aspectes importants de la morfodinàmica del perfil. El model AMORFO70 acobla la hidrodinàmica, el transport de sediments i els canvis de fons per tal de tenir en compte el feedback morfodinàmic. El model compta amb les equacions de conservació de massa i de moment integrades en el temps i en la vertical, acoblades amb les equacions de conservació d’energia de l’onatge i dels rollers, la llei d’Snell i la relació de dispersió tot suposant uniformitat longitudinal. Els processos entre-ona, i en particular la velocitat i l’acceleració orbitals a prop del fons, poden conduir al transport de sediments cap a terra. El model compta amb una nova parametrització de la velocitat a prop del fons per tal d’analitzar l’efecte de la distribució temporal de les velocitats i acceleracions a prop del fons en la morfodinàmica del perfil. S’ha provat que comptar amb l’skewness de la velocitat i de l’acceleració en el càlcul del transport és essencial per simular correctament la migració c, Postprint (published version)

This review highlights the important role of the depth-averaged sediment concentration (DASC) to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and shoreface-connected sand ridges. We present a formulation and methodology, based on the knowledge of the DASC (which equals the sediment load divided by the water depth), that has been successfully used to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and other disciplines, are located in different parts of the coastal zone and are characterized by different spatial and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur in the presence of depth-averaged currents, the sediment transport approximately equals a sediment load times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and the current increases this mobilization and advects the sediment. In such conditions, knowing the spatial distribution of the DASC and the depth-averaged currents induced by the forcing (waves, wind, and pressure gradients) over the patterns allows inferring the convergence/divergence of sediment transport. Deposition (erosion) occurs where the current flows from areas of high to low (low to high) values of DASC. The formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features, but the physical mechanisms for their migration, their finite-amplitude behavior and their decay can also be explored., Peer Reviewed, Postprint (author's final draft)

Many inner continental shelves are characterized by the presence of large rhythmic bedforms, such as shoreface-connected ridges and the more offshore located sand ridges, which have heights of several meters and are spaced several kilometers apart. This study focuses on explaining the observed orientation difference between shoreface-connected sand ridges and the more offshore located ridges. For this, an existing idealized morphodynamic model is used, but modified such that sea level rise simultaneously induces a steepening of the inner shelf and a retreating shoreface. Different settings (rate of sea level rise; landward depth of the inner shelf) are systematically explored. For each setting, the gross characteristics of ridges (growth rate, height, migration, orientation) during their initial formation and long-term evolution are quantified. Model results show that a rising sea level and associated shoreface retreat and shelf steepening lead to new ridges in the shallow area of the inner shelf, which remain active in time (i.e. ongoing growth and downstream migration in time). Old ridges that were already formed in the antecedent area of the shelf and which in the course of time experience deeper water become less active with the rising sea level. In the case that migration of the offshore parts of the ridges vanishes, these parts change orientation to become more shore-parallel compared with the active onshore parts of these ridges. In the case of small landward depths of the inner shelf and a decreasing rate of sea level rise, the active onshore parts migrate too fast, thereby causing the drowned offshore parts to detach and to become inactive. The characteristics of modeled shore-oblique shoreface-connected and more parallel offshore located ridges agree with those of observed sand ridges., Postprint (author’s final draft)