Thresholds in the storm response of a lake chain system and the occurrence and magnitude of lake overflows: Implications for flood frequency     

Dyah I. Kusumastuti  Murugesu Sivapalan  Iain Struthers  David A. Reynolds 《Advances in water resources》2008,31(12):1651-1661

The aim of this paper is to illustrate the effects of spatial organization of lake chains and associated storage thresholds upon lake-overflow behaviour, and specifically their impact upon large scale flow connectivity and the flood frequency of lake overflows. The analysis was carried out with the use of a multiple bucket model of the lake chain system, consisting of a network of both lakes and associated catchment areas, which explicitly incorporated within it three storage thresholds: a catchment field capacity threshold that governs catchment subsurface stormflow, a total storage capacity threshold that governs catchment surface runoff, and a lake storage capacity threshold that determines lake overflow. The model is driven by rainfall inputs generated by a stochastic rainfall model that is able to capture rainfall variability at a wide range of time scales. The study is used to gain insights into the process controls of lake-overflow generation, and in particular, to explore the crucial role of factors relating to lake organization, such as the average catchment area to lake area (A_C/A_L) ratio and the distribution of A_C/A_L with distance in the downstream direction (increasing or decreasing). The study showed that the average A_C/A_L value was the most important factor determining the frequency of occurrence and magnitude of floods from a landscape consisting of lake chains. The larger the average A_C/A_L value the more runoff is generated from catchments thus increasing both the occurrence and magnitude of lake overflows. In this case the flood frequency curve reflects that of the catchment area, and lake organization does not play an important role. When A_C/A_L is small the landscape is lake dominated, the spatial organization of lakes has a significant impact on lake connectivity, and consequently on flood frequency. One of the aspects of lake organization that may have a significant influence on lake connectivity is the spatial distribution of A_C/A_L from upstream to downstream (increasing or decreasing). In a landscape in which A_C/A_L increases downstream, lake overflow will occur more frequently relative to a similar landscape (i.e. identical A_C/A_L) with a constant value of A_C/A_L. When A_C/A_L decreases downstream, however, runoff inputs from the upstream parts will trigger lake overflow in the downstream parts, and consequently, full connectivity may be achieved leading to increased flood frequencies.  相似文献   

Paris Basin VSPs: case history establishing combinations of fine-layer (or lithologic) anisotropy and crack anisotropy from modelling shear wavefields near point singularities     

Iain Bush  Stuart Crampin 《Geophysical Journal International》1991,107(3):433-447

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Glacier thermal regime linked to processes of annual moraine formation at Midtdalsbreen,southern Norway     

Benedict T. I. Reinardy  Iain Leighton  Peter J. Marx 《Boreas: An International Journal of Quaternary Research》2013,42(4):896-911

Glacier thermal regime is shown to have a significant influence on the formation of ice‐marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up‐glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast‐form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin (<10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge‐shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ～40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the Little Ice Age and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze‐on, which requires stable glacier geometry. While the annual moraines on the eastern side of Midtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice‐stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold‐based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought.  相似文献   

Recognition of micro‐scale deformation structures in glacial sediments – pattern perception,observer bias and the influence of experience     

Iain D. Leighton  John F. Hiemstra  Christoph T. Weidemann 《Boreas: An International Journal of Quaternary Research》2013,42(2):463-469

It is a scientist's mission to try to remain unbiased. However, certain factors play a role in scientific analyses that are not controlled by conscious thought. These factors are potentially very important in areas of science where interpretations are based on a scientist's ability to identify patterns or structures. One such area is the micromorphology of glacial sediments. In this paper we investigate the role of an analyst's experience in relation to pattern perception with specific reference to turbate microstructures in glacial diamictons. An experiment was conducted on 52 participants, which demonstrated that, as may be expected, more experienced (glacial) micromorphologists tend to exhibit a higher sensitivity‐to‐signal, but that complete novices, if given clear instructions, can reach levels of sensitivity similar to those of experts. It also showed, perhaps more surprisingly, that response bias does not decrease with experience. We discuss psychological factors, such as the drive for success and consistency, that may have contributed to these results and investigate their possible implications in the micromorphological analysis and interpretation of glacial sediments.  相似文献   

Environmental geochemistry: 40 years research at Imperial College,London, UK     

Iain Thornton 《Applied Geochemistry》2012

This paper reviews the development of multi-purpose geochemical mapping and the progress of research in applied environmental geochemistry and health at Imperial College over the past 40 years. With funding from the research councils, UK government, EU, industry and NGOs, research has provided the basis for postgraduate training in areas ranging from the applications of geochemistry to plant, agricultural livestock and wildlife nutrition, to evaluating contamination from metalliferous mining and smelting, understanding the chemical nature of the urban environment and relationships between geochemistry and human health and disease. Examples include (1) the influence of Mo in marine black shales on the Cu nutrition of grazing cattle and sheep, (2) the importance of soil ingestion on trace element intake and metabolism and metal exposure in farm livestock, (3) the impacts of soil contamination from historical metalliferous mining and smelting on agriculture and human exposure to metals, including potential health problems from Cd at Shipham and from As in SW England, (4) the growth of urban geochemistry and the importance of Pb in the urban environment, (5) the health impacts due to Hg losses from the informal sector Au mining in Brazil, and (6) health issues relating to F^- excess and Se deficiency in China.  相似文献   

Small-Scale Flux Emergence Observed Using <Emphasis Type="Italic">Hinode</Emphasis>/SOT     

L. M. Thornton  C. E. Parnell 《Solar physics》2011,269(1):13-40

The aim of this paper is to determine the flux emergence rate due to small-scale magnetic features in the quiet Sun using high-resolution Hinode SOT NFI data. Small-scale magnetic features are identified in the data using two different feature identification methods (clumping and downhill); then three methods are applied to detect flux emergence events. The distribution of the intranetwork peak emerged fluxes is determined. When combined with previous emergence results, from ephemeral regions to sunspots, the distribution of all fluxes are found to follow a power-law distribution which spans nearly seven orders of magnitude in flux (10¹⁶ – 10²³ Mx) and 18 orders of magnitude in frequency. The power-law fit to all these data is of the form

\fracdNdY = \fracn0Y0\fracYY0-2.7,\frac{\mathrm{d}N}{\mathrm{d}\Psi} = \frac{n_0}{\Psi_0}\frac{\Psi}{\Psi _0}^{-2.7},  相似文献    107. Bosumtwi impact structure,Ghana: Geochemistry of impactites and target rocks,and search for a meteoritic component      Xiongxin Dai  Daniel Boamah  Christian Koeberl  Wolf Uwe Reimold  Gordon Irvine  Iain McDonald 《Meteoritics & planetary science》2005,40(9-10):1493-1511 Abstract— Major and trace element data, including platinum group element abundances, of representative impactites and target rocks from the crater rim and environs of the Bosumtwi impact structure, Ghana, have been investigated for the possible presence of a meteoritic component in impact‐related rocks. A comparison of chemical data for Bosumtwi target rocks and impactites with those for Ivory Coast tektites and microtektites supports the interpretation that the Bosumtwi structure and Ivory Coast tektites formed during the same impact event. High siderophile element contents (compared to average upper crustal abundances) were determined for target rocks as well as for impactites. Chondrite‐normalized (and iron meteorite‐normalized) abundances for target rocks and impactites are similar. They do not, however, allow the unambiguous detection of the presence, or identification of the type, of a meteoritic component in the impactites. The indigenous siderophile element contents are high and possibly related to regional gold mineralization, although mineralized samples from the general region show somewhat different platinum‐group element abundance patterns compared to the rocks at Bosumtwi. The present data underline the necessity of extensive target rock analyses at Bosumtwi, and at impact structures in general, before making any conclusions regarding the presence of a meteoritic component in impactites.  相似文献    108. Geochemical studies of impact breccias and country rocks from the El'gygytgyn impact structure,Russia          下载免费PDF全文 Ulli Raschke  Ralf Thomas Schmitt  Iain McDonald  Wolf Uwe Reimold  Dieter Mader  Christian Koeberl 《Meteoritics & planetary science》2015,50(6):1071-1088 The complex impact structure El'gygytgyn (age 3.6 Ma, diameter 18 km) in northeastern Russia was formed in ~88 Ma old volcanic target rocks of the Ochotsk‐Chukotsky Volcanic Belt (OCVB). In 2009, El'gygytgyn was the target of a drilling project of the International Continental Scientific Drilling Program (ICDP), and in summer 2011 it was investigated further by a Russian–German expedition. Drill core material and surface samples, including volcanic target rocks and impactites, have been investigated by various geochemical techniques in order to improve the record of trace element characteristics for these lithologies and to attempt to detect and constrain a possible meteoritic component. The bedrock units of the ICDP drill core reflect the felsic volcanics that are predominant in the crater vicinity. The overlying suevites comprise a mixture of all currently known target lithologies, dominated by felsic rocks but lacking a discernable meteoritic component based on platinum group element abundances. The reworked suevite, directly overlain by lake sediments, is not only comparatively enriched in shocked minerals and impact glass spherules, but also contains the highest concentrations of Os, Ir, Ru, and Rh compared to other El'gygytgyn impactites. This is—to a lesser extent—the result of admixture of a mafic component, but more likely the signature of a chondritic meteoritic component. However, the highly siderophile element contribution from target material akin to the mafic blocks of the ICDP drill core to the impactites remains poorly constrained.  相似文献    109. The effect of surface flooding on the physical-biogeochemical dynamics of a warm-core eddy off southeast Australia   总被引：1，自引：0，他引：1   Mark E. Baird  Iain M. Suthers  David A. GriffinBen Hollings  Charitha PattiaratchiJason D. Everett  Moninya Roughan  Kadija OubelkheirMartina Doblin 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):592-605   相似文献    110. Chemical partitioning of trace and major elements in soils contaminated by mining and smelting activities   总被引：4，自引：0，他引：4   Xiangdong Li  Iain Thornton 《Applied Geochemistry》2001,16(15) Soils from historical Pb mining and smelting areas in Derbyshire, England have been analysed by a 5-step sequential extraction procedure, with multielement determination on extraction solutions at each step by ICP-AES. Each of the chemical fractions is operationally defined as: (i) exchangeable; (ii) bound to carbonates or specifically adsorbed; (iii) bound to Fe–Mn oxides; (iv) bound to organic matter and sulphides; (v) residual. The precision was estimated to be about 5%, and the overall recovery rates were between 85 and 110%. The carbonate/specifically adsorbed and Fe–Mn oxide phases are the largest fractions for Pb in soils contaminated by both mining and smelting. Most of the Zn is associated with Fe–Mn oxide and the residual fractions. Cadmium is concentrated in the first 3 extraction steps, particularly in the exchangeable phase. The most marked difference found between soils from the mining and smelting sites is the much higher concentrations and proportions of metals in the exchangeable fraction at the latter sites. This indicates greater mobility and potential bioavailability of Pb, Zn and Cd in soils at the smelting sites than in those in the mining area. The most important fraction for Fe and Al is the residual phase, followed by the Fe–Mn oxide forms. In contrast, the Fe–Mn oxide fraction is the dominant phase for Mn in these soils. In the mining area, most of the Ca is in the carbonate fraction (CaCO3), while the exchangeable and residual phases are the main fractions for Ca at the smelting sites. Phosphorus is mainly in the residual and organic fractions in both areas. The exchangeable fractions of Pb, Zn and Cd in soils were found to be significantly related to the concentrations of these metals in pasture herbage.  相似文献    [首页] « 上一页 [6] [7] [8] [9] [10] 11 [12] [13] [14] [15] [16] 下一页 » 末  页»