Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation     

Megan L. Baker  Jaco H. Baas 《Sedimentology》2020,67(5):2645-2671

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Near‐surface hydraulic conductivity of northern hemisphere glaciers          下载免费PDF全文

Ian T. Stevens  Tristram D.L. Irvine‐Fynn  Philip R. Porter  Joseph M. Cook  Arwyn Edwards  Martin Smart  Brian J. Moorman  Andy J. Hodson  Andrew C. Mitchell 《水文研究》2018,32(7):850-865

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day^?1, with a mean of 0.185 ± 0.019 m day^?1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.  相似文献   

Prediction of open stope hangingwall stability using random forests     

Qi  Chongchong  Fourie  Andy  Du  Xuhao  Tang  Xiaolin 《Natural Hazards》2018,92(2):1179-1197

Natural Hazards - The prediction of open stope hangingwall (HW) stability is a crucial task for underground mines. In this paper, a relatively novel technique, the random forest (RF) algorithm, is...  相似文献   

Mechanical Study of Shear Failure of Vertical Goaf Drainage Hole     

Khanal  Manoj  Adhikary  Deepak  Balusu  Rao  Wilkins  Andy  Belle  Bharath 《Geotechnical and Geological Engineering》2022,40(4):1899-1920

Geotechnical and Geological Engineering - Most of the published research on goaf-hole failures are performed using 2D numerical analyses. However, 2D analyses of the goaf-hole failure mechanism,...  相似文献   

Supraglacial weathering crust dynamics inferred from cryoconite hole hydrology          下载免费PDF全文

Joseph Mitchell Cook  Andy J. Hodson  Tristram D. L. Irvine‐Fynn 《水文研究》2016,30(3):433-446

Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Using FTIR spectroscopy to characterise the soil mineralogy and geochemistry of cryoconite from Aldegondabreen glacier,Svalbard     

Harry Langford  Andy Hodson  Steve Banwart 《Applied Geochemistry》2011

Mineralogical and geochemical diversity in cryoconite granules from Aldegondabreen glacier was investigated using FTIR spectroscopy. Results suggest that the technique is an effective tool for investigating mineralogy and identifying spatial differences in geochemistry, based upon characteristic spectral signatures.  相似文献   

Development of Specimen Curing Procedures that Account for the Influence of Effective Stress During Curing on the Strength of Cemented Mine Backfill   总被引：2，自引：1，他引：1  

Martin Fahey  Matthew Helinski  Andy Fourie 《Geotechnical and Geological Engineering》2011,29(5):709-723

Paste backfill used to provide ground support in underground mining is generated from full-stream tailings and is almost always placed underground with cement. For the backfill, both the rate of strength development and the final strength are important considerations for design, particularly when the backfill is subsequently exposed in the stope-mining sequence. There is strong evidence that strengths measured on specimens obtained from coring the in situ cemented backfill are much greater than laboratory-cured specimens with the same cement content. The paper reviews some of the experimental evidence showing that one of the major reasons for the different strength is the difference in effective stress acting on the backfill during curing. Laboratory specimens are (almost) always cured under zero total stress, so no effective stress develops. In contrast, backfill in a stope may cure under high effective stress, which develops due to either “conventional” consolidation in free-draining backfills, or to the so-called “self-desiccation” mechanism in fine-grained fills. Evidence is presented showing how the final strength is affected by applying stress to specimens at different stages of curing and at different rates. It is shown that a fully-coupled analysis of the filling behaviour is required to determine the appropriate effective stress regime to apply in curing laboratory specimens, where “fully-coupled” in this context means taking account of the interaction of consolidation/drainage rate, filling rate and cement hydration rate. Curing protocols for laboratory specimens are proposed, which would ensure that the strengths obtained are representative of in situ conditions.  相似文献   

A geomorphological mapping approach for the assessment of seabed geohazards and risk     

Gayle Hough  Jennifer Green  Paul Fish  Andy Mills  Roger Moore 《Marine Geophysical Researches》2011,32(1-2):151-162

Exploration and development of offshore hydrocarbon resources has advanced into remote deepwater regions over the last decade and poses significant technical challenges for the design and installation of wells and facilities at extreme water depths. Seafloor and shallow subsurface processes and conditions in these areas are complex and generally poorly understood, and the geohazards to development are larger scale and fundamentally different to those encountered onshore; consequently the geohazard risk to deepwater development projects is potentially significant and requires careful evaluation and mitigation during the front-end planning and engineering design stages of projects. There are no established industry standards or methods for the assessment of geohazards and engineering-quality geophysical data at the scale of development. The paper describes an integrated and systematic map-based approach for the assessment and mitigation of seabed geohazards and risk to proposed deepwater development. The approach employs a multi-disciplinary team working with engineering-quality field calibrated data to accurately map and assess seafloor ground conditions and ensure that development proposals are not exposed to intolerable geohazard risk. The approach taken is very similar to the practice of establishing geological models for land-based engineering projects, in which the complete geological history of the site is used to characterise and predict the performance of the ground. Such an approach is routine for major projects on land but so far does not seem to be common practice in the offshore industry. The paper illustrates the seafloor geomophological mapping approach developed. The products are being used to optimise development layouts to avoid geohazards where possible and to support site-specific engineering design of facilities based on a detailed understanding of the potential geohazard loadings and associated risk.  相似文献   

Characterizing the effects of policy instruments on the future costs of carbon capture for coal power plants     

Gregory F. Nemet  Erin Baker  Bob Barron  Samuel Harms 《Climatic change》2015,133(2):155-168

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Stream nitrate uptake and transient storage over a gradient of geomorphic complexity,north‐central Colorado,USA     

Daniel W. Baker  Brian P. Bledsoe  Jennifer Mueller Price 《水文研究》2012,26(21):3241-3252

The understanding of nutrient uptake in streams is impeded by a limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigated these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180‐m long geomorphically distinct reaches on each of two streams in north‐central Colorado. The agricultural stream has been subject to historically variable cattle‐grazing practices, and the urban stream exhibits various levels of stabilisation and planform alteration. Reach‐scale geomorphic complexity was characterised using highly detailed surveys of channel morphology, substrate, hydraulics and habitat units. Breakthrough‐curve modelling of conservative bromide (Br^?) and nonconservative nitrate (NO₃^?) tracer injections characterised transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. In addition, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献