302 research outputs found
Sources and impacts of inorganic and organic fine sediment in salmonid spawning gravels in chalk rivers
No full textPoor salmonid spawning habitat due to excessive fine sediment inputs has been identified as a major factor limiting survival in chalk rivers. A lack of knowledge about the complex processes and factors affecting survival was the driver for this study and gaps in the research were identified concerning the sources of fine sediment and the impact organic material had on salmonid survival in chalk streams. Consequently the main objectives of this study were to characterise spawning habitat quality of a chalk catchment, assess the sources of sediments accumulating within artificial redds, describe the composition of organic sediments using emerging technology and to create a novel method to assess the sediment oxygen consumption of those sediments. Methods were based around a catchment wide field based monitoring programme, consisting of artificially constructed spawning gravels which allowed hyporheic measurements to be taken, and sediment analysis and sediment oxygen consumption methods were carried out using different laboratory methods. Spawning habitat characteristics of the chalk catchment were found to exhibit; low sediment accumulation rates although original levels of fine sediment were high, high organic matter content, variable intra-gravel flow and intra-gravel oxygen concentrations and groundwater influences. Primary sources of fine sediment accumulating in spawning gravels and suspended sediments were found to be attributed to catchment surface sources, namely pasture (50-68%) and arable (32-50%) using inorganic and organic parameters. Organic composition of redd gravels was found to be dominated by protein material rather than humic substances, the more commonly found fluorescent compound in freshwater systems and the sediment oxygen consumption of sediments varied throughout the catchment and was found to consume the greatest oxygen in <63?m size fraction. Application of sediment oxygen consumption rates to existing parameter based models that predict salmonid survival, highlighted the need to address the sensitivity of current models to rivers experiencing low sediment accumulation rates. Outcomes of this study further the knowledge of the sources, organic composition and sediment oxygen consumption capacity of fine sediments accumulating in spawning gravels which can lead to appropriate mitigation on chalk rivers to improve salmonid spawning habitat
Engineering properties of chalk with regards to cliff slope stability: Mechanical properties of chalk and the impact of weathering on the UCS and tensile strength
No full textCoastal chalk cliff instability is a major issue in the UK’s southern region. In order to further the understanding into what drives and influences chalk cliff collapse, a series of laboratory tests have been done on samples taken from West Melbury Marly Chalk, Seaford Chalk, Newhaven Chalk and Lewes Nodular Chalk. Tests have been done to find out if there is anisotropy in permeability, what the influence of weathering is on the tensile strength and what the influence of sea water cycles on the UCS strength is. No anisotropy permeability has been found. Significant weakening has been found due to progressive mass-loss from dissolution in vinegar. No weakening from salt water cycles has been found. Between the grey chalk and white chalk subgroups, big differences exist in the behaviour when exposed to weathering
Chalk putty: specimen preparation and aging properties
No full textChalk putty is a soil-like material that is formed when intact chalk is disturbed. Recently, it has become of special interest due to the development of offshore wind farms in the North and Baltic Seas, where in a number of sites piles are driven into chalk strata. Several pile tests reported in the literature show increased shaft capacity up to 4 months after driving. Although it is a widespread remark in the scientific publications that chalk properties improve over time, laboratory replications of this phenomenon are scarce and the results are inconclusive. The aim of this thesis is to develop a specimen preparation technique yielding representative specimens as well as feasible for commercial purposes. Thereafter, the evolution of the characteristics of chalk putty over time is assessed through laboratory tests. Triaxial with Bender Elements, Direct Simple Shear, Constant Rate of Strain and Thixotropy have been conducted on specimens aged up to 3 months. Finding that the behavior of chalk putty cannot be classified among the classic types of soils. On one hand, Constant Rate of Strain tests have shown that the response is comparable to silty soil, with a gradual transition between re-loading and virgin compression lines, leading to difficulty in the determination of the yield point. On the other hand, in shear, the critical state friction angle is in the range of dense sand. Regarding the volumetric response, there is an initial compressive response, succeeded by a constant volume phase during destructuration and eventual dilation or contraction at larger strains. Furthermore, it was determined that the material possesses thixotropic properties when mixed with de-ionized water. Finally, no increase in the shear strength or was recorded while the initial shear stiffness decreases with aging time -due to unconfined preservation of the samples. However, the ultimate dilatancy of the specimens increases over time, this may be a result of dissolved calcium carbonate during crushing and saturation which re-precipitates or re-cements around the grains.Applied Earth Science
Portraits of Leonardo da Vinci
No full textUsing an iterative method, applied to image processing, a portrait of a young man, probably a self-portrait of Leonardo da Vinci, is restored. Merging this portrait with the self-portrait in red chalk, we can have the features of a middle-aged Leonardo. This digital portrait can be compared with the image of Plato, depicted by Raphael in the Scuola di Atene, generally considered as a portrait of Leonardo. The iterative method used for the image processing had been developed by the author on previous iterative calculations used to solve the Boltzmann equatio
A multi-media approach to teaching basic life support – the development of a cd-rom
No full textThe Interactive Teaching and Learning (INTaL) project aimed to encourage the use of new technologies in nurse education, including the development of a basic life support (BLS)CD-ROM, from an existing teaching pack. Funded by the National Health Service Executive Teacher Development Group in the South West, it involved representatives from all five Higher Education Institutions (HEIs) in the region. Using 'The Hyperlearning Model' as the basis for the structure of the CD-ROM, the production team author ed, storyboarded, recorded on video and edited materials for inclusion. The CD-ROM comprises the 'What How Why' of resuscitation, four problem-based Critical Thinking scenarios, a diagnostic pre-test and a summative post-test. The CD-ROM offers a highly interactive, flexible and student-centred resource, which has which has received positive feedback on initial use. It supports a paradigm shift in the delivery of knowledge for an essential nursing skill. © 2001 Harcourt Publishers Ltd
Deformation, diagenesis and the mechanical behaviour of chalk.
No full textThe chalk of England is a highly variable material resulting from numerous deformation processes of which the most important are diagenetic or tectonic in nature. The engineering behaviour of the chalk is influenced greatly by these processes thus giving rise to the necessity of carrying out studies of physical properties to aid the prediction of engineering performance. -from Author
Biological surveillance of chalk-streams
No full textAn article reviewing the methods of biological surveillance of chalk-streams developed and commonly used at that time, with a focus on their application to the River Frome catchment in Dorset. In evaluating the surveillance methods, the author looks at sampling methods (including cores and kick-sampling), the level of identification of macroinvertebrates, and temporal and spatial variations. Responses of indices to organic pollution are also discussed. A number of accompanying figures are also included
Acidic flow experiments to seal highly permeable thief zones in chalk formations
No full textThis work is based on the idea that an acid mixture of hydrochloride and sulpheric acid react with the calcite in a chalk oilfield to create anhydrite which has a larger molecular size. This will clog the present fractures to prohibit that these fractures sometimes shortcut the injected water from the injector well to the producing oil well which otherwise would result in artificial thieve zones. In this work mass balance calculations and experimental lab work has been done to see how the acidic reaction works. It is concluded that during the conversion of calcite to anhydrite 60% of the resulting CO2 is dissolved in the present liquid; the rest is in the gaseous phase. The samples of fractured chalk are approximately 30 cm long and have a diameter of 10 cm. The fracture is situated in the flow direction. The samples are tested under reservoir conditions, and the flow rate of the acids is 2 ml/min. The resulting permeability change indicates that the fracture is sealed after half an hour of acid injection, but this seal in the fracture is only a pasty substance clogging the flow. After approximately six hours of injection the first wormholes appear and the fracture is totally sealed. Mass change is calculated based on the amount of anhydrite created during acid injection. The mass changes are equivalent to the mass change measured during the experiment. CT-scans are made before, during and after many experiments and each scan series of approximately 300 images. These images are used in a specially written program to divide all present volume components in the chalk: fracture, calcite, anhydrite, wormholes and fossils. They are also used to calculate volume percentages, and coincide with the calculated weight percentages. Fracture experiments under reservoir temperature and pressure conditions and Brazilian tests under atmospheric are done on the sealed samples to see if the fractures can be reopened. The samples were tested with an annular pressure of 310 bar, 80oC and injection pressure of 270 bar. The production pressure was released, even with a pressure difference over the core of 160 bar and did not fracture. The tensile strength of the sealed samples proved to be as strong as original chalk samples without fractures.Petroleum EngineeringGeotechnologyCivil Engineering and Geoscience
The Chironomidae and their ecology in chalk streams
No full textThe taxonomy of the family Chironomidae is first discussed in this article, since there is considerable confusion over nomenclature. The author goes on to consider various aspects of the ecology of the family in chalk streams; preliminary studies on a reach of the Tadnoll Brook supplying most of the information
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