No description available.

No description available.

No description available.

The morphodynamics of a steeply sloping gravel beach in the south western UK (tanβ = 0.15–0.2; d50 = 6 mm; ξb = 1–4) were measured during low energy wind-wave conditions (Hb < 0.5 m). Measurements of water depth, groundwater-level, waves and currents, concurrent with observations of morphological change and swash sediment loads, were successfully obtained over two spring-to-neap tidal cycles and used to investigate the short-term evolution of gravel beach morphology. Incident frequency motions dominated the hydrodynamics since wave transformation was concentrated at the base of the beach. Subharmonic energy was of secondary importance at most, never exceeding 15% of the total energy. Standing edge waves were generally absent since the lack of swell waves limited their forcing, and there was c. 50% reflection of the gravity-band energy.

The majority of terrestrially derived suspended particulate matter (SPM) is transported to the open ocean by rivers, therefore the river estuary transition zone (RETZ) represents a globally significant boundary separating the riverine and coastal regimes. The RETZ is comprised of the Tidally-Influence River (TIR), found above the limit of salt intrusion and the upper part of the estuary including the Estuarine Turbidity Maximum (ETM). The fate of SPM in the RETZ depends on its physical properties which are likely to be extremely variable in the RETZ which is characterised by large temporal and spatial gradients in hydrodynamic properties. Therefore, quantifying SPM properties in relation to physical forcings is key to determining the transfer flux of SPM from the catchment to the coastal ocean. The aim of this study is to interrogate the relationship between floc properties and the turbulence regime in the RETZ of a tidally dominated estuary over tidal, lunar and seasonal temporal scales. Flocs are fragile in nature and their properties fluctuate on short spatial and temporal scales; therefore in situ optical instruments (LISST-IOO and transmissometer) were deployed in the RETZ to obtain volume and mass concentrations of SPM. Turbulence measurements were determined via acoustic methods; ADCP and ADVs were deployed near to the bed to estimate TKE dissipation rates relating to the floc measurements. Data have been collected over five field campaigns, each included; spatial surveys characterising vertical profiles of SPM properties from the mouth of the estuary to the TIR, anchor station surveys measuring the temporal variations in SPM properties, bed-mounted mooring deployments in the RETZ and river surveys of the five main tributaries. Diurnal and semi-diurnal signals in floc properties in the RETZ were observed: resuspension occurred at peak tidal flows, usually on the flood tide; the maximum floc sizes corresponded with minimum effective densities and largely corresponded with high and low waters, as a result of particle flocculation during low turbulence conditions. Turbulence dissipation did not simply scale on tidal current velocities due to the additional contribution of wind stress and direction to the turbulence field. The Kolmogorov turbulence microscale correlated significantly with floc size during periods of marine conditions (i.e. the flood and early ebb tides) but showed a variable relationship during the late ebb when the RETZ was dominated by fluvial conditions and particles. This was most evident in the ETM where marine influence was greater compared to the TIR where it occurred only on larger tides. Thus floc size was related to the turbulence microscale but differences between flood and ebb relationships were probably due to different floc strengths of marine and terrestrial particles. During the lunar cycle, the variations observed on springs were repeated on neaps except that the flocculation signal occurred late in the flood rather than at high water. These tidal and lunar variations of particle properties in the RETZ were observed at all seasons.

A fully distributed coupled hydrological-sediment yield model was developed. An assessment was made of the predictive uncertainty in the individual model predictions, as well as the uncertainty propagated from the primary hydrological model to the secondary sediment yield model, using the Generalised Likelihood Uncertainty Estimation (GLUE) methodology. The value of additional data, in the form of additional periods of flow data, as well as deterministic (based on landuse and soil type) and random spatial parameterisation of hydrological parameters in restricting model uncertainty of the spatially lumped model parameterisation were examined, using Bayesian updating. The results revealed significant model uncertainty in both the hydrological and sediment yield models, with uncertainty bounds widest at peak flow and sediment flux, and predictive failure in recession flows, similar to other applications of GLUE methodology. Uncertainty in the sediment yield model was found to be due to uncertainty inherited from the hydrological model, as well as simplifying assumptions made about sediment removal and transport, and resulted in lower model efficiencies and generally poorer qualitative sedigraph fit. The model validation exercise revealed that the calibrated 'optimum' parameter set was not 'optimum' for all validation periods and resulted in inaccurate spatial and temporal hydrological response predictions for the validation periods. This suggested that traditional split-sample model calibration methods may not be effective in capturing the true spatial and temporal variability of the system. Successive periods of flow data were effective in reducing the calibration period uncertainty bounds. Similarly, the use of sediment yield predictions to update hydrological model uncertainty resulted in a reduction in hydrological model uncertainty. Spatially distributed parameterisation was found to also improve model predictions, resulting in a reduction in uncertainty bounds, particularly for soil-distributed parameterisation. However, stochastic parameterisation of spatially variable hydrological parameters provided equally acceptable predictions for both models, suggesting that a deterministic approach might not be required to capture the spatial variability in hydrological and sedimentological response in the study catchment, and that a stochastic approach may be adequate.

No description available.

Cette thèse a pour objectif la reconstitution des étapes ayant conduit au remplissage sédimentaire de la plaine maritime flamande française au cours de l'Holocène. L'approche utilisée a consisté en l'utilisation conjointe de bases de données de forages, de sondages et d'observations réalisées au cours de cette étude et, pour la première fois de données issues d'une campagne de sismique à très haute résolution dans les voies navigables de la plaine côtière. La relecture des données lithologiques au regard de nos propres observations permet de définir précisément les faciès de remplissage de la plaine. Les données lithologiques, minéralogiques (argiles) et micropaléontologiques (foraminifères et pollens) sont à la base de la reconnaissance de 5 faciès sédimentaires représentatifs du remplissage. Ces faciès ont été interprétés en assemblages de faciès de dépôt. Ceux-ci ont été regroupés en 3 unités caractérisant l'évolution verticale des conditions de dépôt. A la base une plaine alluviale, puis une série estuarienne dominée par la marée et une série d'estran tidal. La première unité correspond à des dépôts tardi-pléistocènes, tandis que les deux autres représentent les dépôts holocènes remplissant la majorité de l'espace d'accommodation disponible. Une série de 10 profils au travers de la plaine maritime permet de comprendre la distribution et la géométrie de ces unités ainsi que l'organisation des faciès sédimentaires. L'arrangement stratigraphique met en évidence les interactions entre le taux de remontée du niveau marin et les conditions hydrodynamiques caractérisées par un régime macrotidal et influencées localement par la houle. Notre étude permet de mieux comprendre le fonctionnement de ce type de zone basse et ouvre des perspectives de modélisation de scénarios futurs d'évolution. / The aim of this study is to reconstruct the evolution of the Holocene deposits along the French Flemish Coastal Plain. This approach is achieved combining available and newly dataset from boreholes, cores descriptions and, for the first time in this plain, the interpretation of VHR seismic profiles on the coastal plain waterways. The study of lithology, micropaleontological assemblages (foraminifera and pollen analyses) and clay mineralogy provides the basis to recognize five sedimentary facies as representative of the Holocene infill. These sedimentary facies were interpreted as depositional facies assemblages in accordance to their depositional features. Depositional facies were grouped in three sedimentary units that better define the depositional environment. From base to top, the units are: alluvial plain, tide-dominated estuary and tidal flats. The alluvial plain consists of late Pleistocene deposits while estuarine and tidal flats units represent the Holocene deposits covering almost the whole available accommodation space. Distribution and geometry of these sedimentary units and their internal architecture of depositional facies were observed from ten cross-sections that cover most of the coastal plain. Stratigraphic arrangement shows the interaction of the Holocene sea-level rise and the coastal hydrodynamic conditions, dominated by the macrotidal regime and influenced by waves action, as the main factors that ruled the sedimentation of the area. This study opens new possibilities to better understand the coastal processes that acted in this lowland, as well as serves as a basis for future studies or modelling possible future scenario.

The Paleocene submarine fans of the Central Graben represent important petroleum reservoir units recording the cyclic input of sand-rich turbidity flows into the post-rift basin. Provision of extensive seismic (a subset of ~l5000 km" of the PGS Central North Sea MegaSurvey), well (n = 549) and core (n = 28, totalling ~2760 feet/84l m) datasets by Shell UI Europe enabled a regional-scale re-evaluation of these deposits. This thesis presents new models illustrating the distribution and quality of the Maureen and Lista Formation sandstones and the syn- and post-depositional controls on these deposits. The Lista Formation sandstones occur within northwest (channelised, proximal, ~300 feet net) to southeast (sheet-like, distal, ~50 feet net) trending (axial) fans with western/eastern fairways and minor sidefan sedimentation (west/east). Four sand-rich to sand-poor facies are defined, with distinct grain size distributions. Mean grain size is the main control on porosity and permeability. Progradation occured between the Ll and L2 units with retrogradation in the L3. This variability, and internal porosity trends, is linked to global sea level change. Characterisation of the Maureen Formation sandstones is complicated by the presence of variable chalk facies derived from turbidite, debris flow and pelagic processes. However, these deposits can still be classified in a similar manner to the Lista Formation and exhibit similar spatial distributions, although the sandstones are thinner ~125 feet in the northwest to 25 feet in the southeast, suggesting that similar depositional controls were active. Sandstone quality is controlled by grain size (with calcitisation also important) although the porosity/permeability values are lower than in the Lista Formation. Progradation occured between the TlO and T20/30 sequences with retrogradation in the T35. The current MlIM2 divisions do not describe the complexity of this formation. The routing of the sandstones was defined by the relict graben structure with offset stacking an additional local control. Routing from the shelf to the basin was controlled by global sea level change. Although these systems are often labelled as basin floor fans they do not resemble classical examples, thanks to their confined nature.

Submarine sediment density flows are a major process for transporting sediment from the continental shelf to the deep-ocean. Understanding submarine flow dynamics relies upon analysis of their deposits (beds) because monitoring them directly is difficult. However, it is rare to be able to correlate individual beds for long distances. This limits our understanding to ‘idealized’ models based on field data with limited lateral extent. Validation of these models requires individual beds to be mapped out. Using > 100 shallow sediment cores this thesis correlates individual beds across their depositional extent (over 2000 km), within the Late Quaternary Moroccan Turbidite System, offshore NW Africa. The vertical and spatial distributions of facies and grain size are examined in each bed to understand the dynamics of the parent flows. The height to which deposits drape up topography is used to infer flow thicknesses. Proximally, synchronous flows passed into the system from multiple disparate entry points. Earthquakes could have triggered these flows. However, it is not possible to determine if these beds were related to earthquakes, highlighting the difficulties faced extending turbidite palaeoseismology beyond the historical earthquake record. Across the central parts of the system flows are interpreted to have been relatively thin and slow moving, yet able to run out for hundreds of kilometers on slopes of < 0.02º. Current, models cannot explain how this is possible. Distally, channels develop and connect two basins. Examination of these channels reveals they are purely constructional features. Flows were able to bypass > 100 km3 of sediment through the channel axes without eroding. Channel relief was built and maintained by deposition along the channel margins and no erosion. The distribution of grain-size breaks is examined within individual beds across the entire system. Grain-size breaks between sand and mud occur almost everywhere. This is attributed to fluid mud layers bypassing intermediate grain sizes down slope. Such a process should (almost) always occur; hence this type of grain-size break should be recognized as a typical feature rather than an exception. The ability to map out individual beds over such distances provides a rare and valuable opportunity to validate models; developed from laterally restricted outcrops, laboratory experiments and theory. Results from this thesis demonstrate current models are limited and that we still have much to learn about the dynamics of submarine flows and how they transport sediment across vast swathes of the seafloor.