共查询到6条相似文献，搜索用时 15 毫秒
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Estuarine and coastal sediment transport is characterised by the transport of both sand-sized particles (of diameter greater than 63?μm) and muddy fine-grained sediments (silt, diameter less than 63?μm; clay, diameter less than 2?μm). These fractions are traditionally considered as non-cohesive and cohesive, respectively, because of the negligible physico-chemical attraction that occurs between sand grains. However, the flocculation of sediment particles is not only caused by physico-chemical attraction. Cohesivity of sediment is also caused by biology, in particular the sticky extra-cellular polymeric substances secreted by diatoms, and the effect of biology in binding sediment particles can be much larger than that of physico-chemical attraction. As demonstrated by Manning (2008) and further expanded in part 1 of this paper (Manning et al., submitted), the greater binding effect of biology allows sand particles to flocculate with mud. In many estuaries, both the sand and fine sediment fractions are transported in significant quantities. Many of the more common sediment transport modelling suites now have the capability to combine mud and sand transport. However, in all of these modelling approaches, the modelling of mixed sediment transport has still essentially separated the modelling of sand and mud fractions assuming that these different fractions do not interact except at the bed. However, the use of in situ video techniques has greatly enhanced the accuracy and reliability of settling velocity measurements and has led to a re-appraisal of this widely held assumption. Measurements of settling velocity in mixed sands presented by Manning et al. (2009) have shown strong evidence for the flocculation of mixed sediments, whilst the greater understanding of the role of biology in flocculation has identified mechanisms by which this mud-sand flocculation can occur. In the first part of this paper (Manning et al., submitted), the development of an empirical flocculation model is described which represents the interaction between sand and mud particles in the flocculation process. Measurements of the settling velocity of varying mud-sand mixtures are described, and empirical algorithms governing the variation of settling velocity with turbulence, suspended sediment concentration and mud-sand content are derived. The second part of this paper continues the theme of examination of the effects of mud-sand interaction on flocculation. A 1DV mixed transport model is developed and used to reproduce the vertical transport of mixed sediment fractions. The 1DV model is used to reproduce the measured settling velocities in the laboratory experiments described in the part 1 paper and also to reproduce measurements of concentration of mixed sediments in the Outer Thames. In both modelling exercises, the model is run using the algorithms developed in part 1 and repeated using an assumption of no interaction between mud and sand in the flocculation process. The results of the modelling show a significant improvement in the ability of the 1DV to reproduce the observed sediment behaviour when the empirical equations are used. This represents further strong evidence of the interaction between sand and mud in the flocculation process. 相似文献
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Jin Li Andrew D. HeapAnna Potter Zhi HuangJames J. Daniell 《Continental Shelf Research》2011,31(13):1365-1376
Spatially continuous data of environmental variables is often required for marine conservation and management. However, information for environmental variables is usually collected by point sampling, particularly for the marine region. Thus, methods generating such spatially continuous data by using point samples to estimate values for unknown locations become essential tools. Such methods are, however, often data- or even variable-specific and it is difficult to select an appropriate method for any given dataset. In this study, 14 methods (37 sub-methods) are compared using samples of mud content with five levels of sample density across the southwest Australian margin. Bathymetry, distance-to-coast, slope and geomorphic province were used as secondary variables. Ten-fold cross validation with relative mean absolute error (RMAE) and visual examination were used to assess the performance of these methods. A total of 1850 prediction datasets are produced and used to assess the performance of the methods and the effects of other factors considered. Considering both the accuracy and the visual examination, we found that a combined method (i.e., random forest and ordinary kriging: RKrf) is the most robust method. This method is novel, with a RMAE up to 17% less than that of the control. No threshold in sample density was detected in relation to prediction accuracy. No consistent patterns are observed between the performance of the methods and data variation. The RMAE of three most accurate methods is about 30% lower than that of the best methods in previous publications, highlighting the robustness of the methods selected in this study. The implications and limitations of this study are discussed and a number of suggestions are provided for further studies. 相似文献
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O. A. Mel’nikov 《Journal of Volcanology and Seismology》2011,5(6):409-420
Visual observations of the activities of three gas-water-lithoclast (“mud”) volcanoes in the Pugachevo group in the Makarov
District of Sakhalin Island were used to analyze the dynamics of these volcanoes. Our analysis confirmed the previous inference
that a multirank periodicity is present in the eruptions of the volcanoes, with the periodicity being comparatively frequent
and low in magnitude for the eruptions (every 1–2 years) at the Glavnyi or Central volcano and a very long but violent (every
65–70 years) at all the three volcanoes. Comparison of this periodicity with a similar periodicity observed in natural seismicity
in the adjacent, highly seismic Uglegorsk District shows that the two phenomena are relatively independent. The natural seismicity
in the form of large earthquakes is superimposed upon the gas-water-lithoclast volcanism mostly to serve as a trigger. The
high-rank periodicity of 65–70 years noted above may be related to 11–22-year cycles of solar activity. Analysis of the orohydrographic
setting in the area shows that the location of the present low-lying basin with volcanoes inside was formerly occupied by
a dome uplift with a major gas field that controlled the generation of these volcanoes; it continues to drive their activity,
causing a continued gradual subsidence or collapse of the deep basin with volcanoes, thus providing evidence of the high gas
potential in the area of study. 相似文献
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Yoshiki Saito 《中国科学D辑(英文版)》2006,49(6):604-614
The last 2000 years are an important time span both for IGBP-PAGES and CLIVAR of WCRP. One of the main aims of these projects is to obtain high-resolution records of global change, such as that stored in ice cores, tree rings, speleothems, corals, lakes, marine records, etc., and then use these data to make sound estimates for future global change. To accomplish these projects, we first need to obtain high-resolution geological records and proxies for climatic/environ- mental changes. … 相似文献