Quantifying how hillslopes respond to river incision and climate change is fundamental to understanding the geomorphic evolution of tectonically uplifting landscapes during glacial-interglacial cycles. Hillslope adjustment in the form of deep-seated bedrock landslides can account for a large proportion of the regional sediment yield and denudation rates for rapidly uplifting landscapes. However, the timing and magnitude of the response of hillslopes to climatic and tectonic forcing in moderate uplift temperate maritime catchments characteristic of many active margins worldwide is not well quantified. This study seeks to investigate how hillslopes respond to climate-modulated river incision and to quantify the magnitude of the sediment flux from this response in a typical active margin setting. The non-glacialWaipaoa Sedimentary System (WSS) on the East Coast of the North Island of New Zealand consists of river catchments, coastal foothills to uplifting mountain ranges, and terrestrial and marine sediment depocentres collectively underlain by relatively young (Cretaceous and younger) sedimentary rocks within a tectonically active setting and temperate maritime climate. These attributes make theWSS similar to many coastal catchments on oceanic-continental convergent margins worldwide. However, because of widespread destruction of primary forests for conversion to pasture lands by the mid 20th Century, theWSS is currently a globally significant source of sediment to the world’s oceans. Because of these factors, theWSS was selected as one of two global study sites for the international, NSF supported, MARGINS Source-to-Sink initiative designed to investigate the transfer of sediment from terrestrial source to marine sink. Previous studies on theWSS have shown a strong link between climate change and geomorphic response in the system. River incision since the last glacial coldest period has generated a significant amount of topography, leaving small remnants of the ca.18,000 cal. yr BP last glacial aggradation terrace scattered up to 120 m above modern rivers. In this study, the hillslope response to river incision is quantitatively examined using new high resolution topographic data sets (lidar and photogrammetry) in combination with 3 field mapping and tephrochronology. Hillslopes are found to be coupled to river incision and adjusted to rapid incision through the initiation and reactivation of deep-seated landslides. In the erodible marine sedimentary rocks of the terrestrialWSS, post-incision deep-seated landslides can occupy over 30% of the surface area. Many of these slides show evidence of multiple “nested” failures and landslide reactivation. The ages of tephra cover beds identified by electron microprobe analysis show that following an initial 4,000 to 5,000 year time lag after the initiation of river incision, widespread hillslope adjustment started between the deposition of the ca. 13,600 cal. yr BPWaiohau tephra and the ca. 9,500 cal. yr BP Rotoma tephra. Tephrochronology and geomorphic mapping analysis indicates that river incision and deep-seated landslide slope adjustment is synchronous between mainstem rivers and headwater tributaries. Tephrochronology further shows that many slopes have continued to adjust to channel incision into the late Holocene. Hillslope response in the catchment can involve the entire hillslope from river to ridgeline, with some interfluves between incising sub-catchments being dramatically modified through ridgeline retreat and/or lowering. Using the results of the landform tephrochronology and geomorphic mapping, a conceptual time series of hillslope response to uplift and climate change-induced river incision is derived for a timeframe encompassing the last glacial-interglacial cycle. Using the same high resolution topography datasets, in-depth field analysis, and tephrochronology, the 18,000 year sediment yield from terrestrial deep-seated landslides in theWSS is estimated in order to investigate the magnitude of hillslope response to climate-modulated, uplift driven river incision. This completes one of the first processbased millennial time-scale sediment budgets for this class of temperate maritime, active margin catchments. Fluvial and geomorphic modelling is applied to reconstruct pre 18,000 cal. yr BP topography in 141 km2 of detailed study area and the resulting volumetric estimates from 207 landslides are used to estimate deep-seated landslide sediment flux for the broader system. An estimated 10.2 km3 of deep-seated landslidederived sediment with a multiplicative uncertainty of 1.9 km3 (+9.2 km3, -4.8 km3) was delivered to terrestrial and marine sinks. This accounts for between 10 and 74% of the total mass of the terrestrialWSS budget of ca. 91,000 Mt (+37,000 Mt, -26,000 Mt). Combining the deep-seated landslide results with other studies of terrestrial sediment sources and terrestrial and shelf sinks, the estimated terrestrial source load ranges from 4 Abstract 1.2 to 3.7 times larger than the mass of sediment sequestered in terrestrial and shelf depocentres. This implies that off-shelf transport of sediment is important in this system over the last 18,000 cal. yr BP, as it is today for anthropogenic reasons. Based on the derived sediment budget, the denudation rate for the terrestrialWSS of 0.8 mm yr-1 (+0.3 mm yr-1, -0.2 mm yr-1) is indistinguishable from the average terrestrialWaipaoa late Quaternary uplift rate, indicating an approximate steady-state balance between denudation and uplift. This thesis provides a quantitative analysis of the role of deepseated landslides in an active margin catchment that is used to improve the understanding of landscape and terrestrial source-to-marine-sink sediment transfer dynamics.

O objetivo principal deste estudo é a análise do balanço de sedimentos arenosos na enseada de Balneário Camboriú, localizada no litoral centro-norte do Estado de Santa Catarina. Para alcançar os objetivos deste trabalho a enseada foi compartimentada em células e utilizadas diferentes metodologias que envolveram a análise de diversos parâmetros, tais como: sedimentologia e morfologia da praia e antepraia; estabilidade da praia em planta e perfil; perfil de equilíbrio da enseada; transporte de sedimentos por ondas e correntes e perda de sedimentos para fora da praia através dos banhistas. A praia de Balneário Camboriú é composta de areia fina a muito fina, de composição quartzosa, bem a moderadamente classificados. A distribuição das fácies sedimentares da enseada de Balneário Camboriú demonstra a inexistência de trocas de sedimentos arenosos da praia com a região da antepraia, sendo esta dominada principalmente por sedimentos finos (silte e argila). A estabilidade da praia em planta encontra-se em equilíbrio dinâmico na porção norte e sul da enseada. A morfologia praial em valores de variação de volume e largura demonstrou que os perfis localizados na porção norte, que corresponde a região mais exposta da praia, apresentam maiores variações do que os demais perfis localizados nas porções mais protegidas. Verificou-se um processo de rotação praial entre os perfis, havendo acresção em alguns enquanto ocorre erosão em outros, mostrando uma troca de sedimentos entre eles. O volume de sedimentos ganho pela praia entre 1994 e 2005 foi de aproximadamente 49.000 m3 que foram adicionados artificialmente por uma obra de alimentação executada pela prefeitura municipal. A profundidade de fechamento apresenta um comportamento gradacional, com diminuição dos valores de norte para o sul da enseada, em acordo com os padrões de distribuição do fluxo de energia das ondas e correntes. Os valores definidos para a profundidade de fechamento variam entre 4 m e 1,7 m. Este limite de profundidade é também demonstrado na variação faciológica entre a praia e antepraia. Os cenários de refração, difração de ondas e transporte de sedimentos associado demonstrou que a praia se comporta como uma célula fechada, não havendo troca significativa de sedimentos entre esta e a região de antepraia. Portanto, gerando um balanço arenoso nulo entre estes dois ambientes. Verificou-se, que o volume sedimentar removido da praia pelos banhistas não causou grande impacto no balanço de sedimentos durante o período amostral. Por outro lado, sugere-se que em longo prazo, esta retirada de areia possa representar um déficit mais significativo, da ordem de 970m³. O cálculo do balanço de sedimentos arenosos para a praia e enseada de Balneário Camboriú apresentou um valor negativo de 152 m3/ano. Este valor pode ser considerado mínimo quando comparado ao volume total de sedimentos da praia, e corresponde a metade do valor calculado para a perda anual de sedimentos causadas pelos banhistas Com isso pode-se concluir que a enseada de Balneário Camboriú está em equilíbrio quanto ao balanço sedimentar, sem perdas e ganhos de sedimentos consideráveis. / The overall goal of this study is the sandy sediment budget analysis in the Balneário Camboriú bay, located in central-northern coast of Santa Catarina State. To achieve the objectives of this work the bay was compartments in cells and used different methodologies that involved the analysis of various parameters such as: the beach and bay sedimentology and morphology; planform and profile beach stability; equilibrium beach profile; sediment transport by waves and currents and loss of sediment through the beach users. The Balneário Camboriú beach is composed of the fine and very fine sand, quartz and to moderately classified. The sedimentary facies distribution shows there are no exchanges of sediment from the sandy beach with the bay, dominated mainly by fine-grained sediments (silt and clay). The planform beach stability is in dynamic equilibrium in the north and south beach portion. The beach morphology change in volume and width values showed that the profiles located in the northern portion, more exposed to the beach, have more variations than the other profiles located in portions more protected. There was a process of beach rotation between the profiles, there was accretion in some profiles and erosion in others, showing an exchange of sediment between them. The sediment volume gain the beach between 1994 and 2005 was approximately 49,000 m3 which were artificially added to the beach for nourishment implemented by Municipality. The depth of closure presents a gradational behavior, with declining values of north to the south of the bay, in accordance with the waves and currents flow of energy distribution patterns. The values defined for the depth of closure ranging from 4 m to 1.7 m. This limit of depth is also shown in facies variation between the beach and shoreface. The waves refraction and diffraction scenarios and sediment transport showed that the beach is behaving like a closed cell, with no exchange between beach and shoreface. Therefore, generating a null balance between these two sandy environments. It was found that the sediment volume removed by users beach causes no major impact on the coastal sediment sampling during the period (summer 2003/2004). Moreover, it is suggested that a long-term Balneário Camboriú, the sand removal could present a more significant deficit in the coastal sediment, as this beach is mostly populated flow in twenty years where the sediment volume would be withdrawn from 970m³ . The beach and shoreface Balneário Camboriú sandy sediment balance calculation presented a negative value of 152 m3/year. This quantities can be considered minimal when compared to the total sediment volume from the beach. The estimated value is half the value calculated for the loss of sediment removed by users. This can be concluded that the inlet of Balneário Camboriú bay is totally balanced on the sediment, with no considerable sediment losses and gains.

O objetivo principal deste estudo é a análise do balanço de sedimentos arenosos na enseada de Balneário Camboriú, localizada no litoral centro-norte do Estado de Santa Catarina. Para alcançar os objetivos deste trabalho a enseada foi compartimentada em células e utilizadas diferentes metodologias que envolveram a análise de diversos parâmetros, tais como: sedimentologia e morfologia da praia e antepraia; estabilidade da praia em planta e perfil; perfil de equilíbrio da enseada; transporte de sedimentos por ondas e correntes e perda de sedimentos para fora da praia através dos banhistas. A praia de Balneário Camboriú é composta de areia fina a muito fina, de composição quartzosa, bem a moderadamente classificados. A distribuição das fácies sedimentares da enseada de Balneário Camboriú demonstra a inexistência de trocas de sedimentos arenosos da praia com a região da antepraia, sendo esta dominada principalmente por sedimentos finos (silte e argila). A estabilidade da praia em planta encontra-se em equilíbrio dinâmico na porção norte e sul da enseada. A morfologia praial em valores de variação de volume e largura demonstrou que os perfis localizados na porção norte, que corresponde a região mais exposta da praia, apresentam maiores variações do que os demais perfis localizados nas porções mais protegidas. Verificou-se um processo de rotação praial entre os perfis, havendo acresção em alguns enquanto ocorre erosão em outros, mostrando uma troca de sedimentos entre eles. O volume de sedimentos ganho pela praia entre 1994 e 2005 foi de aproximadamente 49.000 m3 que foram adicionados artificialmente por uma obra de alimentação executada pela prefeitura municipal. A profundidade de fechamento apresenta um comportamento gradacional, com diminuição dos valores de norte para o sul da enseada, em acordo com os padrões de distribuição do fluxo de energia das ondas e correntes. Os valores definidos para a profundidade de fechamento variam entre 4 m e 1,7 m. Este limite de profundidade é também demonstrado na variação faciológica entre a praia e antepraia. Os cenários de refração, difração de ondas e transporte de sedimentos associado demonstrou que a praia se comporta como uma célula fechada, não havendo troca significativa de sedimentos entre esta e a região de antepraia. Portanto, gerando um balanço arenoso nulo entre estes dois ambientes. Verificou-se, que o volume sedimentar removido da praia pelos banhistas não causou grande impacto no balanço de sedimentos durante o período amostral. Por outro lado, sugere-se que em longo prazo, esta retirada de areia possa representar um déficit mais significativo, da ordem de 970m³. O cálculo do balanço de sedimentos arenosos para a praia e enseada de Balneário Camboriú apresentou um valor negativo de 152 m3/ano. Este valor pode ser considerado mínimo quando comparado ao volume total de sedimentos da praia, e corresponde a metade do valor calculado para a perda anual de sedimentos causadas pelos banhistas Com isso pode-se concluir que a enseada de Balneário Camboriú está em equilíbrio quanto ao balanço sedimentar, sem perdas e ganhos de sedimentos consideráveis. / The overall goal of this study is the sandy sediment budget analysis in the Balneário Camboriú bay, located in central-northern coast of Santa Catarina State. To achieve the objectives of this work the bay was compartments in cells and used different methodologies that involved the analysis of various parameters such as: the beach and bay sedimentology and morphology; planform and profile beach stability; equilibrium beach profile; sediment transport by waves and currents and loss of sediment through the beach users. The Balneário Camboriú beach is composed of the fine and very fine sand, quartz and to moderately classified. The sedimentary facies distribution shows there are no exchanges of sediment from the sandy beach with the bay, dominated mainly by fine-grained sediments (silt and clay). The planform beach stability is in dynamic equilibrium in the north and south beach portion. The beach morphology change in volume and width values showed that the profiles located in the northern portion, more exposed to the beach, have more variations than the other profiles located in portions more protected. There was a process of beach rotation between the profiles, there was accretion in some profiles and erosion in others, showing an exchange of sediment between them. The sediment volume gain the beach between 1994 and 2005 was approximately 49,000 m3 which were artificially added to the beach for nourishment implemented by Municipality. The depth of closure presents a gradational behavior, with declining values of north to the south of the bay, in accordance with the waves and currents flow of energy distribution patterns. The values defined for the depth of closure ranging from 4 m to 1.7 m. This limit of depth is also shown in facies variation between the beach and shoreface. The waves refraction and diffraction scenarios and sediment transport showed that the beach is behaving like a closed cell, with no exchange between beach and shoreface. Therefore, generating a null balance between these two sandy environments. It was found that the sediment volume removed by users beach causes no major impact on the coastal sediment sampling during the period (summer 2003/2004). Moreover, it is suggested that a long-term Balneário Camboriú, the sand removal could present a more significant deficit in the coastal sediment, as this beach is mostly populated flow in twenty years where the sediment volume would be withdrawn from 970m³ . The beach and shoreface Balneário Camboriú sandy sediment balance calculation presented a negative value of 152 m3/year. This quantities can be considered minimal when compared to the total sediment volume from the beach. The estimated value is half the value calculated for the loss of sediment removed by users. This can be concluded that the inlet of Balneário Camboriú bay is totally balanced on the sediment, with no considerable sediment losses and gains.

This study focuses on quantifying explicitly the sediment budget of deeply incised ravines in the lower Le Sueur River watershed, in southern Minnesota. High-rate-gully-erosion equations along with the Universal Soil Loss Equation (USLE) were implemented in a numerical modeling approach that is based on a time-integration of the sediment balance equations. The model estimates the rates of ravine width and depth change and the amount of sediment periodically flushing from the ravines. Components of the sediment budget of the ravines were simulated with the model and results suggest that the ravine walls are the major sediment source in the ravines. A sensitivity analysis revealed that the erodibility coefficients of the gully bed and wall, the local slope angle and the Manning’s coefficient are the key parameters controlling the rate of sediment production. Recommendations to guide further monitoring efforts in the watershed and increased detail modeling approaches are highlighted as a result of this modeling effort.

L’érosion et la redistribution des particules détachées représentent un enjeu environnemental, sociétal et économique majeur. Afin de mettre en place des mesures de protection, il est nécessaire d’identifier et quantifier les sources et puits de sédiments ainsi que leur dynamique spatiale et temporelle. L’objectif de cette thèse est donc de dresser le bilan sédimentaire d’un large bassin versant (Loire Bretagne, 155 000 km2) aux paysages contrastés. Sur les versants, les particules détachées issues des différentes sources (érosion diffuse, concentrée, mouvements de masse) représentent un apport de 1.5 * 107 t.an−1 (contribution respective au stock : 82.4%, 12.9%, 4.7%). La prise en compte de la distribution spatiale des processus mis en jeu dans le transfert particulaire et des caractéristiques du site d’étude (ruissellement par saturation en zone de plaine et présence de haies) dans un indice qualitatif permet d’évaluer la connectivité des versants. L’érosion de berge contribue également au stock sédimentaire à hauteur de 6.9 * 105 t.an−1. Au final, seuls 5% des particules détachées, toutes sources confondues, sont transportées jusqu’à l’exutoire du bassin versant et témoignent du fort taux de dépôt au sein du bassin. En parallèle, une valorisation de la base de données des éléments dissous permet de montrer l’importance des flux sédimentaires exportés sous forme dissoute (~ 90% des exports totaux). La représentation de l’ensemble de ces résultats à différentes résolutions spatiales permet de développer une approche qualitative du transfert particulaire et d'identifier les zones à risque. / Erosion and particles redistribution represent major environmental, societal and economic issues. To adopt protection measures, it is essential to identify and quantify sources and sinks of sediment and their spatial and temporal dynamic. The aim of this work is thus to establish a sediment budget for a large river basin (Loire and Brittany river basin 155,000 km2) with contrasted landscapes. On hillslopes, detached particles from the miscellaneous form of erosion (sheet and rill erosion, gullies and mass movements) represent a supply of 1.5 * 107 t.yr−1 (contribution to the stock of 82.4%, 12.9%, and 4.7% respectively). The consideration of the spatial distribution of processes involved in sediment transport and the characteristics of the study site (soil saturation and presence of hedgerows) in a qualitative landscape-based index allows us to assess the hillslope connectivity. Bank erosion also participates in the sediment budget with 6.9 * 105 t.yr−1 of material provided to the river network. In the end, only 5% of detached particles, from all sources of sediment, reach the basin outlet indicating a substantial deposition on the way from source to outlet. In parallel, the use of the database of dissolved elements allows us to highlight the importance of the dissolved sediment fluxes ( 90% of the total exports of the Loire river). The presentation of all results at different spatial scales permits to provide a qualitative approach of sediment source-to-sink transfers and to identify hotspots of erosion and transfers.

Dans les bassins versants abrupts de montagne, de larges quantités de sédiments provenant des pentes escarpées viennent se déposer dans la partie supérieure des torrents et sont remobilisées par les laves torrentielles ou par charriage. Le but de ce travail était d'étudier le transport des sédiments grossiers dans les petits bassins versants torrentiels et d’analyser l’influence du stockage de ces sédiments dans le chenal sur les laves torrentielles. Cela a requis sur le terrain une intense surveillance géomorphologique des événements d'écoulement dans les bassins versants des torrents du Manival et du Réal, susceptibles de produire des laves torrentielles et du transport solide par charriage chaque année.Le bilan sédimentaire du Manival a été réalisé grâce à des mesures topographiques répétées entre les événements importants d’écoulements (sections transversales et relevés au scan laser terrestre). Deux évènements de laves torrentielles et plusieurs évènements de charriage ont été observés. La reconstitution de leur budget sédimentaire a révélé que la majeure partie de leurs volumes a été apportée par l'érosion du chenal. Les évènements de charriage de l’automne ont contribué à la recharge sédimentaire du chenal principal par le dépôt de grands bancs de gravier. Ce processus est fondamental au déclenchement de laves torrentielles lors des printemps et été suivants. Un décalage dans le temps des séquences érosion /dépôt a été observé entre les parties supérieure et inférieure du chenal, révélant un transfert discontinu de sédiments dans le bassin versant. Un modèle conceptuel de transfert des sédiments est proposé pour les différentes magnitudes d’écoulement.Dans le Réal, le volume de sédiment transporté est similaire à celui du Manival avec une augmentation importante du volume dans le chenal. La plus importante lave torrentielle observée a révélé une diminution en aval des hauteurs d'écoulement maximales, des contraintes de cisaillement, de la vitesse et de la résistance à l'écoulement. Cela suggère que le front de la lave torrentielle érode et déstabilise le chenal, mais qu’il ne peut pas transporter les matériaux en raison de sa concentration élevée en sédiments. La vague hyperconcentrée qui suit se charge des matériaux restants, croît en volume et fusionne avec la lave torrentielle en décélération. Le front et les vagues suivantes jouent un rôle essentiel pour l'érosion lors d'un événement de lave torrentielle.Les laves torrentielles ont créé une érosion significative à la variabilité spatiale importante alors que les déformations du lit induites par le charriage sont en équilibre. L’érosion du chenal par les laves torrentielles est contrôlée étroitement par la pente en amont et les conditions de stockage des sédiments et peut être prédite par une relation logarithmique. Les matériaux les plus sensibles à l'érosion dans le Manival sont les bancs de gravier non consolidés formés par le charriage. Ils constituent une surface lisse au sein du chenal rugueux qui peut être automatiquement cartographiée à partir de données de laser scan terrestre ou aérien. Ceci fournit une évaluation des zones sensibles à l'érosion dans un chenal au moment du relevé au scan laser.Cette étude a permis d’alimenter le domaine des laves torrentielles en observations quantitatives sur le terrain. Des bases de données détaillées ont été obtenues par l'intégration de multiples relevés des différentes sections transversales, des nombreux balayages laser et des données des stations de mesure à haute fréquence. Les mesures de transfert de sédiments, des interactions/contrôles dans le chenal, de la dynamique des laves torrentielles. La caractérisation des stockages dans ces bassins différents fournit une base solide pour le développement de modèles conceptuels et statistiques. Ces observations ont également mis en évidence les paramètres importants à mesurer sur le terrain qui ont une influence sur les laves torrentielles. / Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. The purpose of this research was to investigate the coarse sediment transport through steep catchments and how channel storage can influence debris-flows. This required intensive field-based geomorphic monitoring of flow events in the Manival and Réal torrent catchments which can experience debris-flows and bedload transport every year.In the Manival Torrent, the sediment transfers were characterized at a seasonal time scale by a complete sediment budget of the catchment derived from multi-date topographic measurements between important flow events (cross-section surveying and terrestrial laser scanning). Sediment budget reconstitution of two debris-flows revealed that most of their volumes were supplied by channel scouring (more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitudes is proposed.In the Réal Torrent, post-event surveying and high-frequency monitoring stations were used to compare and compile measurements of flow events. Three debris-flow events and three periods of bedload transport with small headwater debris-flows were observed. Sediment transport volumes for debris-flows were very similar to the Manival with important volume growth in the channel. The largest observed debris-flow revealed a downstream decrease of maximum flow heights, shear stress, velocity, and flow resistance. We hypothesize that the debris-flow front scours and destabilizes the channel, but it cannot transport the material because of its high sediment concentration. Therefore, the trailing hyperconcentrated surge picks up the remaining material, grows in volume, and coalesces with the decelerating debris-flow. Both the front and following surges play an integral role for net erosion during a debris-flow event.Multi-date cross-sections in the Manival and Réal have shown that debris-flows have significant scouring with large spatial variability. Bedload transport was observed to be at equilibrium with little variability. Field observations of channel deformations show that debris-flow scouring is strongly controlled by upstream slope and storage conditions. A logarithmic relationship is proposed as an empirical fit for the prediction of channel erosion. The most susceptible materials for erosion in the Manival are the unconsolidated gravel wedges developed from bedload transport. This material has a smooth surface within the rugged channel which can be automatically mapped with a 20 cm digital elevation model from either terrestrial or airborne laser scans by calculating roughness with a one meter window. This provides an automatic assessment of erodible areas in a channel at the time of the laser scan survey.This study has contributed to the need of quantitative field observations in the realm of debris-flow research. Complete and thorough databases were obtained by integrating multi-date cross-section surveys, multi-date laser scans, and high-frequency monitoring stations. Quantified evidence revealing sediment transfers, channel interactions/controls, debris-flow dynamics, and storage characterizations in two different catchments provides a strong basis in the development of conceptual and statistical models. These observations also highlighted the significant field parameters that have an influence on debris-flows and steep catchment systems.

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

The morphodynamics of an inlet channel draining an estuary or bay are governed by a complex system of temporally and spatially varying physical processes, including wind, waves, tides, sediment transport, and both tide and wave driven currents. In addition, sediment availability and characteristics in conjunction with underlying geologic framework bear on the morphology and morphologic behavior of an inlet system. This study examines the morphodynamics, sediment transport patterns and time-series morphologic change of John’s Pass and Blind Pass, two structured tidal inlets that collectively make up a dual-inlet system sharing the tidal prism of northern Boca Ciega Bay, in Pinellas County, Florida. To quantify wave and tidal forcing and response mechanisms an array of hydrodynamic sensors were deployed over a 12 month period at both inshore and offshore locations. In order to capture morphologic changes and quantify volumetric changes within the inlets, bathymetric surveys of the inlets were conducted in 2010, 2011, 2012, and 2014. Similarly, bi-monthly beach survey data for the same range of time was acquired in order to quantify volumetric changes along adjacent stretches of beach. In addition to gaining insights into sediment pathways based on morphologic and volumetric variability, those data were also used to develop a regional sediment budget along the studied stretch of coast. To gain insights into the morphodynamics of the dual-inlet system, bathymetric and hydrodynamic data was used to develop a numerical model of the dual inlet system. Numerical model simulations based on existing or baseline conditions were compared with numerical simulations employing synthetic bathymetric and hydrodynamic conditions in order to examine inlet behavior under a range of different morphological and hydrodynamic conditions. John’s Pass is the dominant of the two inlets. It exhibits mixed-energy straight morphology and captures ca 81% of the available tidal prism. The inlet has a well-developed mature ebb shoal, and actively bypasses sediment from one side of the inlet to the other supplying sediment to the downdrift littoral system. Blind Pass captures less than 20% of the available tidal prism, and while also exhibiting mixed-energy morphologic characteristics has a less well developed ebb shoal that currently has not fully established a sediment bypassing system. Both inlets channels and ebb shoals have been dredged on multiple occasions to provide sediment for the nourishment of nearby chronically eroding stretches of beach. Dredge pits excavated along the distal margins of the ebb shoals are infilling at rates substantially slower than expected due to limited sediment transport along those regions of the ebb shoal, while inlet channel dredge pits infill at rapid and expected rates. The objective of this study was to characterize the morphodynamics of the dual-inlet system with the aim of identifying sediment pathways and bypassing mechanisms, and quantify a balanced regional sediment budget in order to design more sustainable approaches to inlet management.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22052号 / 工博第4633号 / 新制||工||1722(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 角 哲也, 准教授 Sameh Kantoush, 准教授 竹門 康弘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Les plages sableuses et les dunes côtuères occupent encore de nos jours une place importante dans la zone côtière du Nord-Pas-de-Calais. Ces accumulations sableuses, qui sont parfois le seul rempart protégeant les zones basses de la plaine côtière des submersions marines, sont des milieux particulièrement vulnérables dans le contexte actuel de l'élévation du niveau de la mer associée au changement climatique. Les objectifs principaux de la thèse étaient d'analyser les variations du trait de côte et du bilan sédimentaire à l'échelle régionale, d'apprécier le rôle des variations du volume sédimentaire sur la stabilité de la ligne de rivage, et d'évaluer les zones les plus menacées par les risques littoraux dans un avenir proche, de travail reposant en grande partie sur l'utilisation de données topographiques acquises par LiDAR aéroporté entre 2008 et 2014 ainsi que de photographies aériennes de 1963 à 2009. L'analyse de l'évolution du trait de côte a montré des évolutions contrastées, que ce soit spatialement ou temporellement. En effet, plusieurs portions de littoral ont connu une propagation du trait de côte à long terme, comme à court terme, tandis que d'autres sites ont subi un très fort recul à l'échelle de plusieurs décennies, mais aussi ces dernières années. La comparaison entre l'évolution du trait de côte et le volume initial du haut de plage en 2008, a montré que les reculs les plus importants se sont essentiellement produits dans les secteurs où l'on pouvait observer une absence de haut de plage à marée haute. Sur plusieurs sites, nos résultats suggèrent également qu'à partir d'un volume seuil de sédiments sur le haut de plage, le trait de côte est stable ou montre une tendance à la propagation vers le large. La cartographie de l'aléa de submersion marine à l'horizon 2050, prenant en compte la hausse du niveau marin liée au changement climatique, a montré clairement des franchissements du cordon dunaire sur plusieurs sites. Cette cartographie étant établie sur les données topographiques les plus récentes, à savoir décembre 2013 et janvier 2014, ces submersions potentiells ont une forte probabilité de se produire bien plus tôt que l'année 2050 en raison des forts taux d'érosion constatés sur certains massifs dunaires. Le calcul des bilans sédimentaires de l'ensemble du littoral régional, a montré, dans l'ensemble, une tendance à l'accrétion. Cette accrétion est d'autant plus significative pour le haut de plage et les dunes côtières, hormis pour quelques sites qui connaissent un grave déficit sédimentaire (particulièrement dans la baie de Wissant et sur la rive nord de la baie de l'Authie). Ces résultats suggèrent que la côte du Nord-Pas-de-Calais ne se trouve pas dans une situation de pénurie sédimentaire mais connaitrait plutôt une accumulation sur la majeure partie de son linéaire côtier. / Sandy beaches and coastal dunes still represent a significant portion of the coastal of Nord-Pas-de-Calais, northern France. These sandy accumulation landforms, which sometimes constitute the only defense protecting low-lying coastal areas from coastal flooding, are particularly vulnerable to sea level rise associated with climate change. The main objectives of the thesis were to analyze shoreline change and coastal sediment budget at the regional scale, to assess the role of changes in sediment volume on shoreline stability,and to evaluate areas at risk from coastal hazards in the near future, using airborne topographic LiDAR data collected between 2008 and 2014 and aerial photographs from 1963 to 2009. Analyses of shoreline change revealed spatially as well as temporally variables evolutions.Seaward shoreline progradation occured along several stretches of coastline at multidecadal and short times-scales, while significant coastal retreat took place at other sites during the same time periods. The comparison between coastline evolution and the initial volume of the upper beach in 2008 showed that the higher retreat rates were mainly observed in areas where the upper beach was lacking at high tide. Our results also suggest that there is a sediment volume threshold on the upper beach at each site above which the coastline is stable or progrades seaward. Mapping of areas at risk of marine flooding in 2050, taking into account a projection of sea level rise due to climate change, clearly shows that the submersion of coastal dunes would take place at several sites during storm-induced high water level events. The mapping of these areas at risk being based on topographic data collected in December 2013 and January 2014, coastal flooding is very likely to occur much earlier than 2050 at several sites, however, where very high rates of coastal retreat result in severe erosion of the coastal dunes. The calculation of sediment budget based on the repetitive LiDAR surveys shows that, overall, sediment accretion predominates over the entire regional coastal zone. This accretion is particularly significant for the upper beach and coastal dunes, except for a few sites that are characterized by a strong sediment deficit (particularly Wissant bay and the Northern shore of the Authie estuary). These results suggest that the coastal zone of Northern France does not experience sediment shortage, but is rather dominated by sediment storage in the backshore of the sand beaches