No description available.

This project utilises study sites in slowly permeable soils with artificial tile drainage typical of the lowland study region in the North East of England. The three selected sites investigate sediment loss processes at a range of scales, from the field, to catchment. Sediment monitoring and in a 0.6 km2 farm ditch catchment indicated that the majority of sediment losses occur during a small number of large runoff events. Source fingerprinting suggested that over 50% of the sediment is derived from arable tile drains, and approximately 10% from the farm track. A small outlet sediment trap was partially effective, with 37% sediment removal on average. It is estimated that a trap of 100-200 m3 volume may be effective for a catchment of this size. Detailed plot study of tile drain sediment losses under winter cereals showed conventionally tilled land generated mean sediment losses of 333 kg.ha-1 over a single winter. Over 80% of total sediment loss was via tile drain rather than surface flow. The use of a shallow cultivation minimum tillage system significantly reduced mean sediment losses to 183 kg.ha-1. Buffer strip treatments were not effective, particularly as they were unable to mitigate the majority of sediment loss occurring through the subsurface pathway. At the catchment scale the importance of topographically controlled concentrated runoff pathways was recognised as a key sediment loss issue. Channel erosion sediment losses of up to 750 kg.ha-1 were estimated for one field in the catchment during a single runoff event. The retention of c. 1 t of sediment was recorded during the same event in a field with an engineered flood retention barrier. A novel field method of event sediment loss estimation is presented. An investigation of a wider catchment area demonstrated that tile drainage exceedance during flood events is a major source of field erosion and sediment loss. While surface runoff events are infrequent in this landscape, they are of high magnitude and the relatively small capacity of the drainage network results in concentrated flows of high erosive potential. The effectiveness of buffer strips is likely to be limited in these landscapes due to the role of concentrated runoff and subsurface sediment pathways. Grassed waterways and in-field soil conservation techniques are likely to be more effective against these two pathways respectively. Engineered structures also appear to be effective, and appear to be most justified where runoff control is also desirable.

This thesis examines patterns of pyroclastic dispersal and sedimentation from active volcanoes located in the Andean Central and Southern volcanic zones. Numerical approaches are utilized, including single-particle trajectories, advection-diffusion and particle-tracking models, in order to gain insights into the impact of future volcanic eruptions in the region. Numerical models and wind data have been tested considering recent eruptions that have occurred in the Andes, and both tephra dispersal and recorded fallout have been successfully rebuilt. As volcanic zones are separated by several degrees of latitude, different environmental conditions are observed. For the Central Volcanic Zone interseasonal variability is present, and even opposite transport directions are observed between austral summer and winter months. Interannual variability is also detected, being mostly related to the El Nifio Southern Oscillation in the troposphere, and to the Quasi-Biennal Oscillation in the stratosphere. Outcomes from the modeling indicate that distal regions from the volcanic sources are likely to be impacted for tephra fallout, in particular when westward transport occurs during the summer (northern segment) or when eastward transport is intensified during winter (southern segment) . In contrast is the southernmost Southern Volcanic Zone where eastward transport is dominant throughout the year. Pyroclast dispersal is more widespread during the autumn-winter period, in connection with the arrival of frontal systems. Differences in atmospheric circulation between the upper troposphere and lower stratosphere are less evident at these latitudes. Probabilistic maps of tephra accumulation on the surface, derived for different eruptive scenarios, have been outlined for areas close to active volcanoes. Additionally, exceedance probability curves were estimated for places of interest. Volcanoes analyzed include El Misti in southern Peru, Parinacota in the Chile-Bolivia border and Lascar in northern Chile, which are located in the Central Volcanic Zone. Hudson volcano was selected from the Southern Volcanic Zone. Volcanic hazard implications are discussed for all case studies. In addition, pyroclastic transport and dispersal have also been addressed in some cases. Lahar flows were numerically simulated for Hudson volcano, and an estimation of the probability of occurrence of a moderate to high magnitude eruption was calculated. Some topics of the methodology are briefly discussed, including the importance of shape factor of particles on settling velocity. A sensitivity analysis of the estimated probability of tephra accumlation on the surface to the total number of simulations was investigated.

No description available.

No description available.

The Dee Estuary, located on the southern side of Liverpool Bay, in the Eastern Irish Sea, is macrotidal with a peak spring tidal range in excess of 10m. The large tidal range and associated strong currents make the estuary a very dynamic system with large fluxes of sediment. River canalisation and land reclamation between 1700 and early 1900 has significantly altered the hydrodynamic and sedimentological conditions. This caused the main navigation channel to migrate from the eastern side to the western shore of the estuary. Large bed forms are visible in the intertidal zones of the mouth of the estuary in aerial photographs. These features can be seen to be migrating into the estuary from X-band radar images. Dune migration can lead to residual sand transport rates, depending of the direction and magnitude of the dune characteristics. It is therefore important to monitor the movement of these large scale bed forms to determine the stability of the complex area of sand banks and channels in the Dee Estuary. Understanding the patterns of dune migration and associated sediment transport is fundamental for effective sediment management of an estuary, as well as an important consideration for offshore construction. Monitoring the migration patterns of large scale bed forms in the mouth of the Dee Estuary will show if they correlate with the transport of sediment into the estuary and how much they contribute to the sediment budget of the estuary. The driving forces behind large scale bed form migration are investigated to determine whether it is the action of waves, tidal currents or a combination of the two which are important. ADCP deployments on West Kirby Sands show a strong flood dominant tide which could be indicative of a flood dominant residual sediment transport. A 'three pronged' approach is taken to understand the migration of large scale bed forms in the mouth of the Dee Estuary. This includes remote sensing with X-band radar data, field measurements using DGPS surveying and numerical modelling techniques. Modelling of the estuary using TELEMAC, validated with ADCP measurements at West Kirby Sands, shows flood dominant sediment transport over a tidal cycle. A 'model chaining' approach is taken to simulate tides, waves, wave generated currents and sediment transport. Developments are made to include a variable bed roughness feedback method into TELEMAC.

The oversupply of fine sediment to lowland streams has been associated with the general degradation of their habitats with symptoms including increased turbidity, decreases in groundwater to surface water exchange and a decline in biodiversity and Salmonid fecundity. Aquatic macrophytes have been implicated as a factor in fine sediment problems, due to their high capacity for localised fine sediment retention caused by macrophyte patches decreasing channel flow velocities. However, there are still gaps in current knowledge relating to seasonal macrophyte growth and the cycling of fine sediment within lowland streams. The objectives of this interdisciplinary study were to: (1) investigate the influence of changing seasonal macrophyte cover on fine sediment deposition and storage at the reach scale; (2) analyse the impact of changing seasonal macrophyte cover on fine sediment transport at the reach scale, and (3) examine the temporal and spatial changes of fine sediment deposits, including particle characteristics within Ranunculus patches. Two chalk stream reaches within the Frome-Piddle catchment were chosen for a two year comparison of two similar streams. The distribution and particle characteristics of deposited fine sediment were analysed at the reach scale using monthly site surveys and fine sediment samples taken within Ranunculus patches at both sites. Seasonal reach scale releases of corn pollen as fine sediment analogues were used to investigate fine sediment particle transport through both reaches in relation to concurrent changes of macrophyte cover and channel porosity. Lastly, three Ranunculus patches were investigated at the patch-scale at both sites over an annual cycle. Investigations were conducted to analyse variations in the volume of deposited and retained fine sediment and particle characteristics within and between patches and within patches in relation to seasonal patch growth. Fine sediment deposits were found within in-channel macrophytes and marginal vegetation, with considerable deposits found within the margins at both sites but particularly within Nasturtium and Apium patches on the Bere Stream. Statistical differences were found in the depth of fine sediment within emergent and submergent Ranunculus patches at both sites. Fine sediment samples from Ranunculus patches were dominated by sand-sized (63-1000 μm) particles in both effective and absolute 3 fractions, with smaller volumes (<10 %) of silt and clay-sized particles. No correlation was found between the seasonal cover of aquatic macrophytes and corresponding values for the transport (FX) and loss (KP) of corn pollen particles. However, corn pollen particles in transport were found to decrease dramatically in number when a combination of factors occurred together. The main influencing factors were the seasonal peak in macrophyte cover, seasonally low channel discharge and high values of channel roughness represented by Manning’s N values. Estimated values of channel porosity were not associated with corn pollen transport and retention. Values of corn pollen transport distance (SP) and depositional velocity (Vdep) were not associated with macrophyte cover or channel porosity. Fine sediment was found to be generally distributed within the rooted area of Ranunculus patches, with fine sediment deposited in the tail section in the summer months. The head zone of the Ranunculus patches were found to possess lower D50 values for fine sediment particle size at both sites, other than this there was little differentiation between all of sections within patches. The results from this study suggest that further development of a holistic approach to aquatic macrophyte management is required within some lowland streams to promote a sustainable balance for fine sediment transport. Future management involving localised weed-cuts should address problems with fine sediment and flow conveyance while also being considerate to habitat ecology and biodiversity.

La « Formation Cangalli » (Cordillère Orientale, Bolivie) est une formation détritique, glaciofluviatile au potentiel aurifère (paléo-placer) avéré dans la région de Tipuani-Mapiri. Cette thèse a pour objectif de déterminer l’origine, la source, les modalités d’apport ainsi que les conditions de dépôts de la « Formation Cangalli » sur un secteur en cours d’évaluation par la société Rexma SAS (secteur de la mine « La Esperanza », sud de Caranavi). L’analyse de la structure de la formation et de la répartition de l’or doit permettre d’évaluer le potentiel aurifère de ce secteur et de proposer des guides de prospection de l’or. Le travail a consisté à développer en parallèle des approches terrain (topographie, cartographie, exploration de ruisseaux, étude de faciès sédimentologiques, études granulométriques sur gros volume, échantillonnage) et laboratoire (caractérisation des clastes et de la matrice par pétrographie optique, MEB, DRX, microsonde, CHONS). L’analyse sédimentologique a permis de proposer un modèle de remplissage en adéquation avec l’évolution tectonique de la Cordillère Orientale des Andes. Le remplissage présente 4 séquences dont 3 d’entre elles possèdent une alternance entre des dépôts fluviatiles et des dépôts de cônes alluviaux.La comparaison des deux faciès de Cangalli aisément identifiables sur le terrain par deux couleurs différentes (bleu et rouge) a montré que la distinction n’était pas stratigraphique mais liée à une altération affectant la formation initiale bleue.L’étude de la distribution des particules d’or (125-1000 μm) a montré que l’or est d’origine hydrothermale. De plus, les résultats montrent clairement que la distribution de l’or est hétérogène dans la « Formation Cangalli » les niveaux les plus enrichis se trouvant en base de séquence. Ces résultats permettent de poser les bases d’une exploitation industrielle de la concession minière. / The “Cangalli Formation” (Eastern Cordillera, Bolivia) is a detrital, glacofluvial formation with an established gold potential (paleo-placer) in the Tipuani-Mapiri region. This thesis aims to determine the origin, source, contribution and deposition conditions of the "Cangalli Formation" on an area being assessed by the Rexma SAS Company (area of the mine “La Esperanza”, south of Caranavi). The analysis of the formation structure and gold distribution should allow to evaluate the gold potential of this sector and to provide guidelines for gold prospecting. Two parallel approaches have been developed: fieldwork (topography, mapping, stream exploration, sedimentological study of facies, granulometry, sampling) and laboratory experiments (clasts and matrix characterization using optical petrography, SEM, XRD, microprobe, CHONS). Sedimentological analysis allowed to propose a filling model in line with the tectonic evolution of the Andean Cordillera Real. The filling shows 4 sequences, 3 of them consist of an alternation between fluvial and alluvial deposits. Comparison of the two Cangalli facies easily recognizable on the field by two different colors (blue and red) showed that the distinction was not stratigraphic but associated with an alteration affecting the initial blue formation. The study of the distribution of gold particles (125-1000 microns) showed that gold is of hydrothermal origin. In addition, the results clearly show that the gold distribution is heterogeneous in the "Cangalli Formation" the riches levels being in the basal sequences. These results lay the groundwork for industrial exploitation of the mining concession.

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Η χαρτογράφηση των περιβαλλόντων ιζηματογένεσης της λεκάνης προχώρας της Πίνδου στην Δυτική Πελοπόννησο στις περιοχές της Τριταίας στα βόρεια, του Χρυσοβιτσίου στα κεντρικά και της Φοινικούντας στα νότια, η οποία βασίστηκε στα υποπεριβάλλοντα των τουρβιδιτικών αποθέσεων έδειξε την ύπαρξη των αποθέσεων εσωτερικού, εξωτερικού ριπιδίου, και αποθέσεις πεδίου λεκάνης. Η ανάπτυξη των τουρβιδιτικών αυτών υποπεριβαλλόντων έλαβε χώρα από το Ανώτερο Ηώκαινο έως το Κατώτερο Ολιγόκαινο (NP18-NP21), ηλικίες οι οποίες προσδιορίστηκαν από ασβεστιτικά ναννοαπολιθώματα. Το συνολικό στρωματογραφικό πάχος των υπό μελέτη τουρβιδιτών της λεκάνης προχώρας στην Δυτική Πελοπόννησο είναι 418m στην περιοχή της Φοινικούντας, 1096m στην περιοχή της Τριταίας και 327m στην περιοχή του Χρυσοβιτσίου, και φαίνεται να αποτέθηκαν κατά την διάρκεια ενός κύριου τεκτονικού γεγονότος όπου η Γάβροβος και η Ιόνιος ζώνη συμπεριφέρθηκαν ως μια ενιαία λεκάνη προχώρας. Κατά την διάρκεια του Ανώτερου Ηώκαινου η προχώρα στην Δυτική Πελοπόννησο αποκτά μεγάλο πλάτος με αποθέσεις εσωτερικού και εξωτερικού ριπιδίου. Οι αποθέσεις λοβών εξωτερικού ριπιδίου αναπτύσσονται στο ανατολικό τμήμα της (περιοχή Τριταίας, περιοχή Φοινικούντας) ενώ οι αποθέσεις πεδίου λεκάνης το διάστημα αυτό εντοπίζονται μόνο στην περιοχή της Φοινικούντας στο δυτικό τμήμα της λεκάνης. Η παρουσία των αποθέσεων του πεδίου λεκάνης αυτής της ηλικίας των ιζημάτων στο δυτικό τμήμα της περιοχής της Φοινικούντας, δείχνει μια πιθανή βύθιση, η οποία σχηματίστηκε εξαιτίας πιθανά της δράσης της εσωτερικής επώθησης που βρέθηκε κατά την διάρκεια της διατριβής στην λεκάνη της Φοινικούντας. Το γεγονός ότι η ροή των ιζημάτων, όπως προέκυψε από τα παλαιορευματικά δεδομένα, έχει στις τρεις υπό μελέτη περιοχές φορά προς τα δυτικά, υποδεικνύει ότι ακόμα δεν έχει ενεργοποιηθεί η επώθηση της εσωτερικής Ιονίου, οπότε τα ιζήματα προελαύνουν προς τα δυτικότερα τμήματα της λεκάνης. Στην περιοχή του Χρυσοβιτσίου στο διάστημα αυτό η ιζηματογένεση χαρακτηρίζεται από την απόθεση καναλιών μεσαίου ριπιδίου, γεγονός που υποδεικνύει ένα καθεστώς μεγαλύτερης ευστάθειας του δυτικού περιθωρίου της λεκάνης σε αυτό το τμήμα της. Πρέπει να σημειωθεί ότι στο στάδιο αυτό οι αποθέσεις λοβών στην περιοχή της Φοινικούντας και τμήμα των αποθέσεων του εσωτερικού ριπιδίου στην περιοχή της Τριταίας παρουσιάζουν τεκτονική παραμόρφωση που εκφράζεται με πτύχωση, γεγονός που σημαίνει ότι οι αποθέσεις αυτές αφού αποτέθηκαν και διαγενέθηκαν, υπέστησαν παραμόρφωση πιθανά από την δράση της επώθησης της εσωτερικής Ιονίου. Θα πρέπει ωστόσο να ειπωθεί ότι η παραμόρφωση των αποθέσεων αυτών πιθανά να οφείλεται εν μέρει και σε ολισθήσεις (slump). / The study area lies on the W Peloponnesus, and contains three areas, Tritea on the North, Xrysovitsi on the central and Finikounda on the south. The aim of this thesis is the detailed study of the sedimentary rocks deposited on West Peloponnesus during late Eocene to early Oligocene. Sediments consist of submarine fan and shelf deposits respectively. Study was realized by combining both field and laboratory data that included: detailed sedimentological and tectonic analysis, organic and inorganic geochemical research, porosity and permeability assessment, age determination, petrographical research and grain-size statistic and hydraulic parameters determination. The object of the thesis is the certain classification of the submarine fan system, the palaiogeographic reconstruction of the Pindos foreland turbidite deposits in west Peloponnesus region and the exploration of possible generation, existence and preservation of hydrocarbons. Outcrops of both deep-water and shelf sediments were selected for study on the three study areas. Due to the scarcity of the outcrops, the studied outcrops were restricted to road cuts and beaches. The lithological units were described in terms of colour, texture, thickness, grain size and sedimentary structures. During this time interval (NP18-NP21) the study area was characterized by the deposition of submarine fans that overly shelf deposits with this swallowing upward trend to be owed to tectonic activity. The flow types that controlled the depositional processes of the submarine fans were grain flows, debris flows and low-, medium- and high-density turbidity currents while the deposition of shelf can be attributed to both turbidity and shelf storm currents. The turbidity system is structured by a “basin floor” fan that is presented overlying a “slope” fan and was constructed under the simultaneous interaction of both progradation and aggradation processes. “Basin floor” fan is the more distal and lower positioned, unchannelized fan and is composed of lobe, lobe-fringe and fan-fringe deposits. The “slope fan” consists of channel-overbank deposits where channel-fill facies without base conglomerate underlying the equivalent with base conglomerate demonstrating greater proximity to the source area. Both “basin floor” and “slope” fans constitute the lower parts of the stratigraphic column in the study area and have been interpreted as parts of a sand-rich submarine fan on the base of slope to basin floor environment in Finikounda area, and as a mixed sand-mud submarine fan system in Tritea area.