Cette thèse présente une plateforme d'assimilation de données issues de l'imagerie vidéo et intégrée au modèle numérique d'évolution de profil de plage 1DBEACH. Le manque de jeux de données bathymétriques haute-fréquence est un des problèmes récurrents pour la modélisation morphodynamique littorale. Pourtant, des relevés topographiques réguliers sont nécessaires non seulement pour la validation de nos modèles hydro-sédimentaires mais aussi dans une perspective de prévision d'évolution morphologique de nos plages sableuses et d'évolution de la dynamique des courants de baïnes en temps réel. Les récents progrès dans le domaine de l'imagerie vidéo littorale ont permis d'envisager un moyen de suivi morphologique quasi-quotidien et bien moins coûteux que les traditionnelles campagnes de mesure. En effet, les images dérivées de la vidéo de type timex ou timestack rendent possible l'extraction de proxys bathymétriques qui permettent de caractériser et de reconstruire la morphologie de plage sous-jacente. Cependant, ces méthodes d'inversion bathymétrique directes sont limitées au cas linéaire et nécessitent, selon les conditions hydrodynamiques ambiantes, l'acquisition de données vidéo sur plusieurs heures voire plusieurs jours pour caractériser un état de plage. En réponse à ces différents points bloquants, ces travaux de thèse proposaient l'implémentation puis la validation de méthodes d'inversion bathymétrique basées sur l'assimilation dans notre modèle de différentes sources d'observations vidéo disponibles et complémentaires. A partir d'informations hétérogènes et non redondantes, ces méthodes permettent la reconstruction rapide et précise d'une morphologie de plage dans son intégralité pour ainsi bénéficier de relevés bathymétriques haute fréquence réguliers. / This thesis presents data-model assimilation techniques using video-derived beach information to improve the modelling of beach profile evolution.The acquisition of accurate and recurrent nearshore bathymetric data is a difficult and challenging task which limits our understanding of nearshore morphological changes. This is particularly true in the surf zone which exhibits the largest degree of morphological variability. In addition, surfzone bathymetric data are crucial from many perspectives such as numerical model validation, operational rip current prediction or real-time nearshore evolution modelling. In parallel, video imagery recently arose as a low-cost alternative to direct measurement in order to daily monitor beach morphological changes. Indeed, bathymetry proxies can be extracted from video-derived images such as timex or timestacks. These data can be then used to estimate underlying beach morphologies. However, simple linear depth inversion techniques still suffer from some restrictions and require up to a 3-day dataset to completely characterize a given beach morphology. As an alternative, this thesis presents and validates data-assimilation methods that combine multiple sources of available video-derived bathymetry proxies to provide a rapid, complete and accurate estimation of the underlying bathymetry and prevent from excessive information.

The state of Georgia has two large ports that are accessed by way of navigable entrance channels. One of these ports is located in Brunswick, Georgia, and is maintained by the United States Army Corps of Engineers via periodic dredging. Sediments removed from the channel are typically pumped several miles offshore of Brunswick and placed in dredged material mounds, thus removing the sediment from the littoral cycle. This offshore placement, while being the most economically viable method, often negatively impacts the sediment budget of the coastal region and causes erosion downdrift of the channel, specifically along Jekyll Island. Onshore placement of the dredged material is not feasible due to increased associated costs and the high fraction of fines present in the material; thus, nearshore placement is a potentially viable alternative. Nearshore placement could possibly reduce erosion rates and provide protection to property from waves and storms. The USACE initiated a thorough field data collection campaign in 2002 to study the possibility of beneficial placement of dredged material. The author analyzed the existing data to predict the rate and direction of sediment movement away from an existing dredge mound. These predictions are then compared to bathymetric survey data in an effort to validate the results and methodologies used for sediment transport predictions. The ultimate goal is to use the results of this study along with numerical models currently being developed by the Corps to assess the possibility of sediments being transported toward the shore thus re-entering the littoral cycle and providing a benefit to the coast of Georgia.

Η παρούσα εργασία μελετά τις περιβαλλοντικές και γεωλογικές παραμέτρους στη θέση κατασκευής του νέου λιμένα της πόλης του Αιγίου. Για την μελέτη αυτή, σημαντικό ρόλο έπαιξε η χρήση των Γεωγραφικών Συστημάτων Πληροφοριών (GIS) και ειδικότερα του προγράμματος ArcGIS έκδοση 9, με το οποίο αναλύθηκαν και εκτιμήθηκαν οι διάφορες παράμετροι που επιλέχθησαν, αυξάνοντας έτσι την αποτελεσματικότητα των μεθοδολογιών και συγκροτώντας ταυτόχρονα μία πολύτιμη τράπεζα δεδομένων για τη θαλάσσια περιοχή κατασκευής του λιμένα. Παρουσιάζονται δηλαδή τα αποτελέσματα μιας θαλάσσιας γεωφυσικής έρευνας που έλαβε χώρα στην παράκτια ζώνη του Αιγίου. Ο σκοπός της είναι διττός καθώς επιχειρείται να δοθούν λύσεις και απαντήσεις σε δύο σημαντικά ερωτήματα: α) στον εντοπισμό των επικινδυνοτήτων της περιοχής και β) στην ποσοτική ανάλυση των γεωφυσικών μεθόδων. Το μέγεθος της εργασίας εκτείνεται σε τέσσερα κεφάλαια στα οποία περιγράφονται αναλυτικά η όλη διαδικασία που ακολουθήθηκε καθώς και τα αποτελέσματα και συμπεράσματα που προέκυψαν για τον πυθμένα του λιμένα, από τις μετρήσεις και αναλύσεις που έγιναν μέσω των τομογραφιών. Πρέπει να τονιστεί ότι αφετηρία για τις οποιεσδήποτε μελέτες έγιναν, αποτέλεσαν οι αρχικοί χάρτες του προγράμματος Autocad καθώς και οι τομογραφίες που είχαν ληφθεί από τον τομογράφο υποδομής πυθμένα 3.5KHz. Έτσι στο πρώτο κεφάλαιο, γίνεται μία περιγραφή των γεωφυσικών μεθόδων που χρησιμοποιούνται για την κατασκευή θαλάσσιων τεχνικών έργων. Επίσης γίνεται αναφορά στις γεωλογικές και ανθρωπογενείς επικινδυνότητες από τις οποίες επηρεάζεται ο πυθμένας και οι οποίες μπορεί να προκαλέσουν βλάβες στα τεχνικά έργα μέσω των φορτίων που εξασκούν σε αυτά. Στο κεφάλαιο αυτό αναφέρονται και τα όργανα που χρησιμοποιούνται για την εφαρμογή των μεθόδων αυτών, όπως είναι οι τομογράφοι, οι ηχοβολιστές πλευρικής σάρωσης και τα κατευθυνόμενα βαθυσκάφη. Το δεύτερο κεφάλαιο της διπλωματικής εργασίας αναφέρεται στη θέση που βρίσκεται η περιοχή που μελετάται και στα γεωλογικά φαινόμενα που χαρακτηρίζουν αυτή. Το τρίτο κεφάλαιο αφορά στις μεθοδολογικές προσεγγίσεις που εφαρμόστηκαν για α) την αποτύπωση της βυθομετρίας και της μορφολογίας του πυθμένα, β) τον προσδιορισμό της υποδομής και του πάχους των σύγχρονων επιφανειακών ιζημάτων, γ) τον υπολογισμό της κλίσης των υποεπιφανειακών στρωμάτων και δ) τον εντοπισμό πιθανών γεωλογικών επικινδυνοτήτων, όπως ρηγμάτων, κατολισθητικών φαινόμενων και αέριων υδρογονανθράκων στου πόρους των ιζημάτων. Επίσης αναφέρεται το μεθοδολογικό σχήμα ανάλυσης και επεξεργασίας των αναλογικών καταγραφών με βάση την ποσοτικοποίηση των αναλογικών καταγραφών του τομογράφου υποδομής πυθμένα και την εφαρμογή της πολυδιάστατης στατιστικής ανάλυση όπως της Παραγοντικής Ανάλυσης (Factor Anlysis) και της ανάλυσης Επιφανειών Τάσης (Trend Surface Analysis). Τέλος, το τέταρτο και τελευταίο κεφάλαιο της εργασίας αυτής, αφορά τα αποτελέσματα και τα συμπεράσματα που προέκυψαν από τις παραπάνω αναλύσεις. Λαμβάνοντας υπόψη τις επιφανειακές κατανομές της βυθομετρίας τόσο του πυθμένα και των υποεπιφανειακών οριζόντων όσο και των άλλων παραμέτρων που μετρήθηκαν, αλλά και τα αποτελέσματα της παραγοντικής ανάλυσης, επιχειρείται η εξαγωγή συμπερασμάτων για την κατανόηση των όσων αναφέρθηκαν και μετρήθηκαν στην εργασία αυτή. / The present master thesis examines the environmental and geologic parameters of the new harbour site in the city of Aegio. In this research the Geographic Information Systems (GIS) played a major role and more specifically the software ArcGIS version 9, which was used to analyze and evaluate the various parameters, increasing thus the methodology effectiveness and at the same time creating a valuable data bank concerning the sea area of the harbour site. In the research below are presented the results of a marine geophysical survey that took place in the coastal region of Aegio. The object of this survey is double, as it attempts to provide answers and solutions to two substantial questions: a) the localization of the areas risks and b) the quantitative analysis of the geophysical techniques. The research is extended in four chapters, in which it is detailed the whole process followed as well as the results and the conclusions arising from the seafloor of the harbour, from the measurements and the analysis done through the tomographies. We should point out that the starting point of our research were the original maps of the Autocad as well as the tomographies taken from the subbottom profiler 3.5 KHz In the first chapter, we describe the geophysical techniques used for the construction of the sea technical works. It is also mentioned the geologic and anthropogenic risk which affects the seafloor and could damage the works due to the pressure put on them. There are also mentioned the instruments used for the implementation of these techniques, such as the subbottom profilers, side scan sonars and the bathyscaphes. The second chapter is dedicated to the location of the region and its typical geologic phenomena. The third chapter is about the methods we implemented for: a) the plotting of the seafloor bathymetry and morphology, b) the definition of the substructure and the thickness of the contemporary superficial sediments, c) the estimation of the gradient of the sub-superficial beds and d) the detection of possible geological risks, such as faultings, landslides and hydrocarbon gases in the sediments pores. It is also mentioned the methodological plan used for the analysis and the processing of the analogue recordings on the basis of the quantification of the subbottom profilers analogue recordings and the application of the multidimensional statistical analysis, such as the Factor Analysis and the Trend Surface Analysis . Finally in the fourth chapter of this master thesis are included the results and the conclusions that arose from the aforementioned analysis. Taking into account the superficial distribution of the bathymetry of the seafloor and of the sub-superficial horizons as well as of the other parameters counted, but also the results of the factor analysis, we attempted to arrive at a conclusion in order to make more intelligible what has been mentioned in this master thesis.

L’imagerie hyperspectrale aéroportée constitue un candidat potentiel pour la cartographie et le suivi des récifs coralliens à large échelle et à forte résolution spatiale. Dans cette thèse, nous présentons tout d’abord les traitements à appliquer au signal hyperspectral afin d’en extraire des informations sur la nature du fond marin, la bathymétrie et les propriétés optiques de l’eau, et nous les mettons en perspectives devant deux principaux verrous : (i) le faible rapport signal sur bruit du signal mesuré, (ii) le nombre et la variabilité des interactions onde-matière ayant lieu entre l’entrée des rayons lumineux dans l’atmosphère et leur mesure par le capteur hyperspectral. En considérant ces limitations, nous examinons les performances d’une des méthodes existantes de traitement de la colonne d’eau : l’inversion de modèle semi-analytique par optimisation. Nous évaluons d’abord la robustesse des estimations des types de fond et de la bathymétrie pour six paramétrisations du schéma d’inversion. Les résultats sur des images hyperspectrales acquises à l’île de La Réunion en 2009 montrent que la paramétrisation de l’inversion joue un rôle crucial sur la qualité des estimations et que la paramétrisation la plus communément utilisée ne présente pas toujours les meilleures performances. Nous évaluons par la suite l’importance de la précision de la paramétrisation du modèle semi-analytique direct à travers une analyse de sensibilité réalisée sur des données hyperspectrales synthétiques puis sur des données réelles que nous avons acquises en 2015 à La Réunion. L’analyse est en outre effectuée pour toutes les paramétrisations de l’inversion précédemment étudiées. Cette étude montre qu’en milieu récifal l’importance de la précision de la paramétrisation du modèle direct est faible devant le choix de la paramétrisation de l’inversion. Nous montrons en outre qu’il n’est pas possible d’identifier le(s) paramètre(s) du modèle direct le(s) plus influent(s) car cela dépend des concentrations relatives de chacun des éléments optiquement actifs de l’eau. / Airborne hyperspectral imaging is a potential candidate for mapping and monitoring coral reefs at large scale and with high spatial resolution. In this thesis, we first present the processing steps to be applied to hyperspectral signals for extracting information about seabed types, bathymetry and water optical properties, and we discuss their efficiency with respect to two main confounding factors: (i) low signal to noise ratio of the measured signals, and (ii) large number and variability of physical interactions occurring between the entrance of sunlight into the atmosphere and its measurement by the hyperspectral sensor. Considering these limitations, we examine the performance of an already existing water column processing method: semi-analytical model inversion by optimization. We first evaluate the robustness of seabed type and bathymetry estimation for six different inversion setups. The results on hyperspectral images acquired over Réunion Island reefs in 2009 show that the choice of the inversion setup plays an important role on the quality of the estimations and that the most widely used inversion setup does not always produce the best results. We then evaluate the importance of the accuracy of the parameterization of the direct semi-analytical model. This is done through a sensitivity analysis performed on both simulated and real hyperspectral data acquired in Réunion Island in 2015. The analysis is performed for each inversion setup previously studied. This study shows that in coral reef context the accuracy of the parameterization of the direct model is less important than the choice of the inversion setup. We also demonstrate that it is not possible to identify the most influent parameters of the direct model because it depends on the relative concentration of each optically active constituent.

La rade de Brest constitue un cadre idéal pour étudier et restituer les transferts sédimentaires terre-mer dans un contexte de bassin côtier semi-fermé macrotidal. Dans cette perspective, deux axes majeurs, d’échelle temporelle différente, ont été développés avec pour objectifs (a) de caractériser le modèle sédimentaire et sa dynamique par charriage à l’actuelle, (b) de déterminer la mise en place des dépôts sédimentaires au cours de la dernière transgression marine.(a) L’analyse combinant une approche sédimentaire et analogique a permis de montrer le contrôle majeur des courants de marée sur la dynamique sédimentaire actuelle. La morphologie du littoral et des fonds marins renforcent l’intensité des courants tidaux qui facilite les échanges en sables coquilliers entre la rade interne et la mer d’Iroise. Le système est néanmoins en érosion et enregistre un déséquilibre en apports sédimentaires. Les sédiments fins sont remobilisés par les courants de flot et les actions anthropiques colmatant les secteurs peu profonds.(b) L’étude litho- et chronostratigraphique de la séquence sédimentaire, a mis en évidence le recul successif des processus estuariens lors de la dernière remontée du niveau marin (holocène). La morphologie héritée du substratum, combinée à la transgression marine, a fortement influencé l’architecture des dépôts, leur préservation et leurs variations lithologiques latérales et longitudinales. Après la stabilisation du niveau marin (3 000 BP), les variations climatiques (optimum climatique médiéval, et petit âge glaciaire) et les activités anthropiques impactent d’avantage la dynamique des particules en suspension.La rade a donc eu un impact différent sur le transfert des sédiments au cours de la remontée du niveau marin. Actuellement, elle acte comme un « piège à sédiment fin » et enregistre dans le même temps un déficit de stock sédimentaire grossier potentiellement remobilisable. Cette configuration favorise une érosion des parties les plus profondes du système. / The bay of Brest is a tide-dominated, semi-enclosed coastal basin, which is connected with two rivers (Aulne and Elorn). Its jagged shoreline and seabed morphology constitute an ideal setting to understand sedimentary transfer at the land-sea interface. In this aim, this study is divided in two different time scale. The first (a) focuses on the present-day sedimentary bedload dynamic and the second (b) on the reconstruction of the Holocene infilling, during the last marine transgression. (a) A analyse combining a sedimentology approach and numerical has highlighted the major control of the tidal currents. Swells and rivers have a minor impact, because the inherited morphology accentuates and promotes tidal currents. There are responsible of a shelly sandy exchange between the oceanic domain (Iroise Sea) and confined (bay of Brest). At present, the bay of Brest suffers from an imbalance of shelly sand. Fine sediments are eroded and redistributed in the shallow parts of the bay. In ideal conditions (strong tidal current) they can be exported.(b) From the stratigraphic and chronostratigraphic analyses, the successive landward retreat of estuarine processes, during the last marine transgression, has been observed. The sea level acts as the major factor control of the sedimentary geometry deposits. However, the morphological particularity of the bay of Brest influenced their preservation and it is possible to determinate the longitudinal and transversal asymmetry. After the sea level stabilisation (3 000 BP), the Holocene climatic variations and anthropic activities have disturbed the suspension dynamic.The bay of Brest had a different impact on the sedimentary transfer during the last marine transgression. At present, it acts as a « sediment trap » for the fine particles and has not enough sandy sediment. This configuration tends to an erosion of the system.

La marge Ligure est une marge passive soumise à une déformation tectonique compressive associée à la tectonique salifère messinienne. La reprise en compression de la marge s’accompagne d’une sismicité modérée récurrente ponctuée d’évènements plus forts. La marge Ligure est le siège d’une sédimentation importante au Plio-Quaternaire. Elle constitue un environnement propice à l’étude des déstabilisations gravitaires. L’objectif principal de ce travail était de décrire et caractériser les principaux mouvements en masse ayant affecté la marge continentale Ligure au cours du Plio-Quaternaire, de localiser les principales zones sujettes aux déstabilisations et d’identifier les facteurs pré-conditionnant et déclenchant les ruptures dans le but de mieux évaluer l’aléa gravitaire. Une large couverture de données bathymétriques, géophysiques et des carottages acquis sur l’ensemble de la marge a permis de réaliser une étude multi-échelles des processus de ruptures gravitaires et des facteurs déclenchant associés. Près de 1500 glissements ont été identifiés. L’étude de leur répartition spatio-temporelle illustre que l’ensemble de la marge a toujours été affectée par des déstabilisations de pente mais que les principales zones de ruptures auraient migré vers l’ouest au cours du Plio-Quaternaire. Les grandes ruptures sous-marines sont préférentiellement associées aux zones de déformation maximale, cette dernière étant contrôlée par la tectonique crustale et/ou la tectonique salifère. Il apparaît que les ruptures résultent plus généralement d’une association de facteurs distincts qui ont participé à fragiliser la stabilité des dépôts de la pente et qui ont pu provoquer leur rupture. / The Ligurian margin is a passive margin characterized by high sedimentation rates during the Plio-Quaternary. It is affected by a compressive tectonic deformation leading to the inversion of the margin, together with a salt tectonic. The present-day moderate seismic activity is punctuated by stronger seismic events. Thus, this margin offers a good natural laboratory to study submarine landslides and their triggering factors. Although the Var Turbidite System has been well investigated over the last 20 years, the morphology and tectonics/sedimentary processes affecting the whole margin remained poorly known. This study aims to describe and to characterize the main types of mass movements, their preferential locations along the Ligurian margin during the Plio-Quaternary and their triggering factors to improve geohazards assessment related to landslides. A dataset including bathymetric and geophysical data and cores allowed to realize a multi-scale study of submarine failures and their associated triggering factors. About 1500 landslides were identified on the margin and in the basin. The study of their spatio-temporal distribution revealed that the margin has always been affected by mass-wasting processes and that the main zones of landsliding migrated westward during the Plio-Quaternary. The largest submarine landslides are preferentially associated with the highest deformation rates and their location is controlled by crustal tectonics and/or salt tectonics. The initiation of failures results from the combination of several factors including the margin deformation, earthquakes, salt tectonics and sediment under-consolidation.

This study explores shallow lake numerical hydrodynamic processes that support model development and validation, extreme events and effects of water circulation in Lake Victoria. Lake Victoria is the second largest freshwater lake in the world, and the largest in East Africa. It is the major freshwater reservoir and source for domestic, agriculture, industrial, fishery, and transport. The resources support livelihoods and ecosystem services for over 40 million people. The lake is severely affected by water quality degradation by pollution. This thesis aims at improving the understanding by following recommendation of the Lake Victoria Environment Management Project, Lake Victoria Basin Commission climate change adaptation strategy and action plan 2018-2023, Lake Victoria Basin Commission operational plan 2015-2020, and Lake Victoria Basin Commission report. These reports suggested detailed lake bathymetry survey, modelling of lake flow, study of lake hydrometeorological processes by modelling and simulation, to identify extreme weather events, assess water circulation effect, and study lake pollution near the shore. A numerical hydrodynamic model was built in the COMSOL Multiphysics (CM) software for assessing lake flows and water turn-over from river inflows which carry pollution. The work included the development of systematic methods for lake bathymetry that are relevant for lake numerical and hydrodynamic modelling. The hydrometeorological driven simulation model was employed to assess lake water balance, water circulation and soluble transport. Paper 1 creates a bathymetry from several methods and from several data sources, and a vertically integrated free surface flow model was implemented in CM. The model was used to investigate outflow conditions, mean velocities driven by river inflow, outflow, precipitation and evaporation. It is shown to be exactly conservative and give water level variation in reasonable agreement with measurements. The results indicate that the shallow water model is close to linear. An outflow model, linear in water level, predicts water level reasonable agreement with measurements. The findings suggest that the model should consider wind stress driven flow to provide more accurate lake flow behavior. Paper 2 performed an assessment of the hydro-meteorological processes and extreme weather events that are responsible for changing the characteristics of lake water balance, and changing streamflow variations, and lake transportation. We compare historical data over a long time with data from the model including water balance, sources of data uncertainty, correlations, extreme rain and inflow years, and seasonal variations. Solute loading and transportation was illustrated by tracing the water from the river inflows. The results indicate that the lake rainfall has a strong seasonal variation with strong correlations between tributary inflows and precipitation, and between lake outflow and water level. The tracer transport by mean flow is very slow. Flow increases somewhat in wet periods and is faster in the shallow Kenya lake zone than in the deeper Uganda and Tanzanian lake zones, where the major inflow, from the Kagera River, appears to strongly influence transportation. / Denna studie undersöker med numerisk metodik hydrodynamiska processer i den mycket grundaVictoriasjön och hur de påverkas av extrem väderlek, inflöden, och nederbörd. Victoriasjön är denandra största sötvattensjön i världen, och den största i Afrika. Den är färskvattenförråd och källa förhushåll, jordbruk, industri, fiske och transporter. Resurserna ger livsuppehåll och ekosystemtjänsterför mer än 40 miljoner människor. Sjön är utsatt för allvarliga föroreningar som försämrarvattenkvaliteten. Detta arbete avser att förbättra förståelsen genom att följa rekommendationer somgivits ut av Lake Victoria Environment Management Project (LVEMP), och Lake Victoria BasinCommissions (LVBC) rapporter om strategi för anpassning till klimatförändringar, åtgärdsplan2018-2023 och översiktsplan 2015-2020. Rapporterna föreslår detaljerad genomgång avdjupkartor, modellering av strömning i sjön i syfte att identifiera extrema väderhändelser,undersöka vattencirkulationen, och studera föroreningarna nära stränder. En hydrodynamisknumerisk modell har byggts i simuleringspaketet COMSOL Multiphysics (CM) för uppskattning avströmning och vattenutbyte från förorenade inflöden. Arbetet innefattade utveckling av metoder förvattendjups-modeller för hydrodynamiska studier. Simuleringsmodellen drivs avhydrometeorologiska data och används för vattenmängds-balans, cirkulation ochföroreningstransport.Artikel 1 skapar vattendjupskartan från flera data-mängder med olika metoder. En vertikaltintegrerad modell med fri yta implementerades i CM. Modellen ger vertikalt medelvärdesbildadehastigheter drivna av flodinflöden, utflöde, nederbörd och avdunstning. Modellen representerarvattenbalansen exakt och ger variationer i vattennivå i rimlig överensstämmelse med mätningar.Resultaten antyder att modellen är nära linjär och tids-invariant. En utflödesmodell ansatt somlinjär i vatten-nivån kan anpassas noggrant till historiska data. Bättre realism kan uppnås omvindens pådrivande verkan inkluderas.Artikel 2 går igenom de hydro-meteorologiska processer och extrema väder-händelser som ändrarvattenbalans, strömningsmönster och transport. Vi har jämfört data över femtio år med modellens,inkluderande vattennivå, källor för osäkerhet i data, korrelationer, år med extrema regn ochinflöden, och årstidsvariationer. Resultaten tyder på att nederbörden varierar kraftigt medårstiderna, och signifikanta korrelationer ses mellan nederbörd och inflöden, och mellan utflöde ochvattennivå.Transport av lösliga föroreningar illustrerades genom spårning av vatten från de olika inflödena.Spårämnestransport med vertikalt medelvärdesbildade hastigheter är mycket långsam.Strömningen ökar något i våta årstider och är snabbare i den grunda zonen i Kenya än i de djuparedelarna i Uganda och Tanzania. Det största inflödet som kommer från Kagera tycks ha stor inverkanpå transporten. / <p>QC 20191106</p>

No description available.

The tidal prism, or the volume of water exchanged from the sea to an estuary from mean low to mean high tide, influences system hydrodynamics and ecological functioning. Since 1884, the tidal prism in Morro Bay, California has been estimated to be decreasing over time due to sedimentation from upstream practices. What is the current tidal prism in Morro Bay and how will that change with sea level rise? How will eelgrass respond to rising sea levels? For this study, inexpensive tidal gauges were deployed at four locations in Morro Bay from March to August 2023 to measure spatially varying tidal elevations and datums within the bay. I utilized a Digital Elevation Model (DEM) and tidal information to determine volumes of water in Morro Bay. Estimated sea level rise scenarios were utilized to project the 2022 tidal prism into the years 2050 and 2100. Additionally, I estimated the 2019 and 2022 viable eelgrass habitat area using the vertical growth range. I estimated the future potential viable habitat area in the years 2050 and 2100 using estimated sea level rise scenarios. Future projections were made assuming no change in bathymetry over time. Different instruments used to obtain water levels yielded up to ~4 percent differences in the tidal prism estimate. Measurement uncertainty in the monthly tidal datums produced ~3 percent uncertainty within the tidal prism estimate. Compared to the tidal prism in August 2019, the August 2022 tidal prism was lower by ~2 percent. Compared to the tidal prism in August 2019, the August 2023 tidal prism estimated from two nearly co-located tidal instruments at the mouth of Morro Bay were higher by ~5 and ~7 percent, respectively. Spatially varying tidal datums in Morro Bay were found to affect the tidal prism by up to ~3 percent, compared to tidal prism estimates using only a tidal datum near the estuary mouth. However, the effect of spatially varying tidal datums on the tidal prism is the same order of magnitude as measurement uncertainty and is thus not statistically significant. As sea levels rise, the tidal prism is projected to increase by ~40 percent by 2100 from 2022 under the most extreme scenario, H++. Initially, as sea levels rise, the potential viable eelgrass habitat area will increase from the area in 2022 (1108 acres (4.47E+06 m2)). After sea levels rise to 1.5 m above 2000 levels, the potential viable eelgrass area will have reached a maximum area of 1938 acres (7.82E+06 m2). However, under SLR scenario H++, potential viable habitat area is predicted to decrease by up to 59% by 2100 from 2022. The tidal prism, or the volume of water exchanged from a bay to the seathe sea to an estuary from mean lowhigh to mean highlow tide, influences system hydrodynamics and ecological functioning. Since 1884, the tidal prism in Morro Bay, California has been estimated to be decreasing over time due to sedimentation from upstream practices. What is the current tidal prism in Morro Bay and how will that change with sea level rise? How will eelgrass respond to rising sea levels? For this study, inexpensive tidal gauges were deployed at four locations in Morro Bay from March to August 2023 to obtain measure spatially varying tidal elevations and datums within the bay. I utilized a Digital Elevation Model (DEM) and tidal information from NOAA to determine volumes of water in Morro Bay at the estimated monthly mean tidal datums. Estimated sea level rise scenarios were utilized to project the 2022 tidal prism into the years 2050 and 2100. Additionally, I estimated the 2019 and 2022 viable eelgrass habitat area using the vertical growth range. I estimated the future potential viable habitat area in the years 2050 and 2100 using estimated sea level rise scenariosfor various sea level rise scenarios.Future projections were made assuming no change in bathymetry over time. Different instruments used to obtainwater levels yielded up to ~4 percent differences in the tidal prism estimate. Measurement uncertainty in the monthly tidal datums produced~3 percent uncertainty within the tidal prism estimate. Compared to the tidal prism in August 2019, the August 2022 tidal prism from Stilltek decreasedwas lower by ~2.05 percent. Compared to the tidal prism in August 2019, the August 2023 tidal prism estimated from the Stilltek gauge and the Cal Poly Coast Guard gaugetwo nearly co-located tidal instruments at the mouth of Morro Bay increased were higher by ~5.06 and ~6.777 percent, respectively. Spatially varying tidal datums in Morro Bay were found to affect the tidal prism by up to ~2.883 percent, compared to tidal prism estimates using only a tidal datum near the estuary mouth. However, the effect of spatially varying tidal datums on the tidal prism is the same order of magnitude as measurement uncertainty and is thus not statistically significant. As sea levels rise, the tidal prism is projected to increase by ~to a maximum of 40 percent by 2100 from 2022 under the most extreme scenario, H++. InitiallyInitially, as sea levels rise, the potential viable eelgrass habitat area will increase from the area in 2022 (1108 acres (4.47E+06 m2)). ABut after sea levels rise to 1.5 m above 2000 levels, the potential viable eelgrass areas will have reached the thresholda maximum area of 1938 acres (7.82E+06 m2). However, under SLR scenario H++, potential viable habitat area is predicted to decrease by up to 59% by 2100 from 2022.

The steep forearc slope along the northern sector of the obliquely convergent Hikurangi subduction zone is characteristic of non-accretionary and tectonically eroding continental margins, with reduced sediment supply in the trench relative to further south, and the presence of seamount relief on the Hikurangi Plateau. These seamounts influence the subduction process and the structurally-driven geomorphic development of the over-riding margin of the Australian Plate frontal wedge. The Poverty Indentation represents an unusual, especially challenging and therefore exciting location to investigate the tectonic and eustatic effects on this sedimentary system because of: (i) the geometry and obliquity of the subducting seamounts; (ii) the influence of multiple repeated seamount impacts; (iii) the effects of structurally-driven over-steeping and associated widespread occurrence of gravitational collapse and mass movements; and (iv) the development of a large canyon system down the axis of the indentation. High quality bathymetric and backscatter images of the Poverty Indentation submarine re-entrant across the northern part of the Hikurangi margin were obtained by scientists from the National Institute of Water and Atmospheric Research (NIWA) (Lewis, 2001) using a SIMRAD EM300 multibeam swath-mapping system, hull-mounted on NIWA’s research vessel Tangaroa. The entire accretionary slope of the re-entrant was mapped, at depths ranging from 100 to 3500 metres. The level of seafloor morphologic resolution is comparable with some of the most detailed Digital Elevation Maps (DEM) onshore. The detailed digital swath images are complemented by the availability of excellent high-quality processed multi-channel seismic reflection data, single channel high-resolution 3.5 kHz seismic reflection data, as well as core samples. Combined, these data support this study of the complex interactions of tectonic deformation with slope sedimentary processes and slope submarine geomorphic evolution at a convergent margin. The origin of the Poverty Indentation, on the inboard trench-slope at the transition from the northern to central sectors of the Hikurangi margin, is attributed to multiple seamount impacts over the last c. 2 Myr period. This has been accompanied by canyon incision, thrust fault propagation into the trench fill, and numerous large-scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in down-slope length from a few hundred metres to more than 40 km. The indentation is directly offshore of the Waipaoa River which is currently estimated to have a high sediment yield into the marine system. The indentation is recognised as the “Sink” for sediments derived from the Waipaoa River catchment, one of two target river systems chosen for the US National Science Foundation (NSF)-funded MARGINS “Source-to-Sink” initiative. The Poverty Canyon stretches 70 km from the continental shelf edge directly offshore from the Waipaoa to the trench floor, incising into the axis of the indentation. The sediment delivered to the margin from the Waipaoa catchment and elsewhere during sea-level high-stands, including the Holocene, has remained largely trapped in a large depocentre on the Poverty shelf, while during low-stand cycles, sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope. The formation of the indentation and the development of the upper branches of the Poverty Canyon system have led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision. Sediment has also accumulated in the head of the Poverty Canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes. Prograding clinoforms lying seaward of active faults beneath the shelf, and overlying a buried inactive thrust system beneath the upper slope, reveal a history of deformation accompanied by the creation of accommodation space. There is some more recent activity on shelf faults (i.e. Lachlan Fault) and at the transition into the lower margin, but reduced (~2 %) or no evidence of recent deformation for the majority of the upper to mid-slope. This is in contrast to current activity (approximately 24 to 47% shortening) across the lower slope and frontal wedge regions of the indentation. The middle to lower Poverty Canyon represents a structural transition zone within the indentation coincident with the indentation axis. The lower to mid-slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east-facing thrust-propagated asymmetric anticlines separated by early-stage slope basins. North of the canyon system, sediment starvation and seamount impact has resulted in frontal tectonic erosion associated with the development of an over-steepened lower to mid-slope margin, fault reactivation and structural inversion and over-printing. Evidence points to at least three main seamount subduction events within the Poverty Indentation, each with different margin responses: i) older substantial seamount impact that drove the first-order perturbation in the margin, since approximately ~1-2 Ma ii) subducted seamount(s) now beneath Pantin and Paritu Ridge complexes, initially impacting on the margin approximately ~0.5 Ma, and iii) incipient seamount subduction of the Puke Seamount at the current deformation front. The overall geometry and geomorphology of the wider indentation appears to conform to the geometry accompanying the structure observed in sandbox models after the seamount has passed completely through the deformation front. The main morphological features correlating with sandbox models include: i) the axial re-entrant down which the Poverty Canyon now incises; ii) the re-establishment of an accretionary wedge to the south of the indentation axis, accompanied by out-stepping, deformation front propagation into the trench fill sequence, particularly towards the mouth of the canyon; iii) the linear north margin of the indentation with respect to the more arcuate shape of the southern accretionary wedge; and, iv) the set of faults cutting obliquely across the deformation front near the mouth of the canyon. Many of the observed structural and geomorphic features of the Poverty Indentation also correlate well both with other sediment-rich convergent margins where seamount subduction is prevalent particularly the Nankai and Sumatra margins, and the sediment-starved Costa Rican margin. While submarine canyon systems are certainly present on other convergent margins undergoing seamount subduction there appears to be no other documented shelf to trench extending canyon system developing in the axis of such a re-entrant, as is dominating the Poverty Indentation. Ongoing modification of the Indentation appears to be driven by: i) continued smaller seamount impacts at the deformation front, and currently subducting beneath the mid-lower slope, ii) low and high sea-level stands accompanied by variations on sediment flux from the continental shelf, iii) over-steepening of the deformation front and mass movement, particularly from the shelf edge and upper slope.