The spatial and temporal patterns of aggradation in a temperate,upland, gravel‐bed river     

Emma K. Raven  Stuart N. Lane  Rob I. Ferguson  Louise J. Bracken 《地球表面变化过程与地形》2009,34(9):1181-1197

Intensive field monitoring of a reach of upland gravel‐bed river illustrates the temporal and spatial variability of in‐channel sedimentation. Over the six‐year monitoring period, the mean bed level in the channel has risen by 0·17 m with a maximum bed level rise of 0·5 m noted at one location over a five month winter period. These rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2·6 times and overbank flow time increasing by 12·8 hours. This work raises the profile of coarse sediment transfer in the design and operation of river management, specifically engineering schemes. It emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic. Exploration of the sediment supply and transfer system can explain patterns of channel sedimentation. The complex spatial, seasonal and annual variability in sediment supply and transfer raise uncertainties into the system's response to potential changes in climate and land‐use. Thus, there is a demand for schemes that monitor coarse sediment transfer and channel response. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Interactive Visualization to Advance Earthquake Simulation     

Louise H. Kellogg  Gerald W. Bawden  Tony Bernardin  Magali Billen  Eric Cowgill  Bernd Hamann  Margarete Jadamec  Oliver Kreylos  Oliver Staadt  Dawn Sumner 《Pure and Applied Geophysics》2008,165(3-4):621-633

The geological sciences are challenged to manage and interpret increasing volumes of data as observations and simulations increase in size and complexity. For example, simulations of earthquake-related processes typically generate complex, time-varying data sets in two or more dimensions. To facilitate interpretation and analysis of these data sets, evaluate the underlying models, and to drive future calculations, we have developed methods of interactive visualization with a special focus on using immersive virtual reality (VR) environments to interact with models of Earth’s surface and interior. Virtual mapping tools allow virtual “field studies” in inaccessible regions. Interactive tools allow us to manipulate shapes in order to construct models of geological features for geodynamic models, while feature extraction tools support quantitative measurement of structures that emerge from numerical simulation or field observations, thereby enabling us to improve our interpretation of the dynamical processes that drive earthquakes. VR has traditionally been used primarily as a presentation tool, albeit with active navigation through data. Reaping the full intellectual benefits of immersive VR as a tool for scientific analysis requires building on the method’s strengths, that is, using both 3D perception and interaction with observed or simulated data. This approach also takes advantage of the specialized skills of geological scientists who are trained to interpret, the often limited, geological and geophysical data available from field observations.  相似文献   

Recent Climate Warming: Surface Air Temperature Series and Geothermal Evidence     

Čermák  Vladimír  Šafanda  Jan  Krešl  Milan  Dědeček  Petr  Bodri  Louise 《Studia Geophysica et Geodaetica》2000,44(3):430-441

Long-term (1961 – 1996) meteorological air temperature series together with the reconstructed ground surface temperature histories, obtained by inverting borehole temperature-depth profiles, were used to project regional patterns of the recent (climate) warming rate on the territory of the Czech Republic. The characteristic magnitude of the warming rate of 0.02 –0.03 K/yr was confirmed by the results of several years of monitoring the temperature in two experimental boreholes. The monitoring of shallow temperatures at depths of about 30 –40 m, i.e. below the reach of the seasonal surface temperature variations, can serve as an alternative tool of direct quantitative assessment of the present warming rate. The data also seem to sustain a potential man-made component contributing to the more pronounced recent warming rate observed in the areas of large agglomeration.  相似文献   

Crop modelling: towards locally relevant and climate-informed adaptation     

Louise Beveridge  Stephen Whitfield  Andy Challinor 《Climatic change》2018,147(3-4):475-489

A gap between the potential and practical realisation of adaptation exists: adaptation strategies need to be both climate-informed and locally relevant to be viable. Place-based approaches study local and contemporary dynamics of the agricultural system, whereas climate impact modelling simulates climate-crop interactions across temporal and spatial scales. Crop-climate modelling and place-based research on adaptation were strategically reviewed and analysed to identify areas of commonality, differences, and potential learning opportunities to enhance the relevance of both disciplines through interdisciplinary approaches. Crop-modelling studies have projected a 7–15% mean yield change with adaptation compared to a non-adaptation baseline (Nature Climate Change 4:1–5, 2014). Of the 17 types of adaptation strategy identified in this study as place-based adaptations occurring within Central America, only five were represented in crop-climate modelling literature, and these were as follows: fertiliser, irrigation, change in planting date, change in cultivar and area cultivated. The breath and agency of real-life adaptation compared to its representation in modelling studies is a source of error in climate impact simulations. Conversely, adaptation research that omits assessment of future climate variability and impact does not enable to provide sustainable adaptation strategies to local communities so risk maladaptation. Integrated and participatory methods can identify and reduce these sources of uncertainty, for example, stakeholder’s engagement can identify locally relevant adaptation pathways. We propose a research agenda that uses methodological approaches from both the modelling and place-based approaches to work towards climate-informed locally relevant adaptation.  相似文献   

Surface complexation model for strontium sorption to amorphous silica and goethite     

Susan A Carroll  Sarah K Roberts  Louise J Criscenti  Peggy A O'Day 《Geochemical transactions》2008,9(1):2

Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr²⁺ and SrOH⁺ complexes on the β-plane and a monodentate Sr²⁺complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH⁺ complexes and a tetradentate binuclear Sr²⁺ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr²⁺ and SrOH⁺ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces.  相似文献   

Precise temperature monitoring in boreholes: evidence for oscillatory convection? Part II: theory and interpretation     

Vladimir Cermak  Louise Bodri  Jan Safanda 《International Journal of Earth Sciences》2008,97(2):375-384

In the previous part of this work (Cermak, Safanda and Bodri, this volume p.MMM) we have described experimental data and quantified the heterogeneity features of the microtemperature time series. The spectral analysis and the local growth of the second moment technique revealed scaling structure of all observed time series generally similar and suggested the presence of two temperature forming processes. The longer-scale part can be attributed to the heat conduction in compositional and structural heterogeneous solid rocks, further affected by various local conditions. Short-scale temperature oscillations are produced by the intra-hole fluid convection due to inherent instability of water column filling the hole. Here we present how the observational evidence is supported by the results of the computer simulations. The exact modes of intra-hole convection may be different, ranging from quasi-periodic (“quiescent”) state to close of turbulence. As demonstrated by numerical modeling and referred on laboratory experiments, at higher Rayleigh numbers the periodic character of oscillation characteristic for “quiescent” regime is superseded by stochastic features. This so called “oscillatory” convection occurs due to instability within the horizontal boundary layers between the individual convectional cells. In spite of the fact that the basic convective cell motion is maintained and convection is characterized by slow motion, the oscillatory intra-hole flow and corresponding temperature patterns exhibit typical features of turbulence. The idea of boundary layer instability as a source of stochastic temperature fluctuations could explain many distinct features of borehole temperatures that previously cannot be interpreted.  相似文献   

Hydrogeochemistry of Fe and Mn in small boreal streams: The role of seasonality, landscape type and scale   总被引：1，自引：0，他引：1  

Louise Björkvald  Ishi Buffam  Hjalmar Laudon  Carl-Magnus Mörth 《Geochimica et cosmochimica acta》2008,72(12):2789-2804

Stream water from a stream network of 15 small boreal catchments (0.03-67 km²) in northern Sweden was analyzed for unfiltered (total) and filtered (<0.4 μm) concentrations of iron (Fe_tot and Fe_<0.4) and manganese (Mn_tot and Mn_<0.4). The purpose was to investigate the temporal and spatial dynamics of Fe, Mn and dissolved organic carbon (DOC) as influenced by snow melt driven spring floods and landscape properties, in particular the proportion of wetland area. During spring flood, concentrations of Fe_tot, Fe_<0.4, Mn_tot, Mn_<0.4 and DOC increased in streams with forested catchments (<2% wetland area). In catchments with high coverage of wetlands (>30% wetland area) the opposite behavior was observed. The hydrogeochemistry of Fe was highly dependent on wetlands as shown by the strong positive correlation of the Fe_tot/Al_tot ratio with wetland coverage (r² = 0.89, p < 0.001). Furthermore, PCA analysis showed that at base flow Fe_tot and Fe_<0.4 were positively associated with wetlands and DOC, whereas they were not associated during peak flow at spring flood. The temporal variation of Fe was likely related to varying hydrological pathways. At peak discharge Fe_tot was associated with variables like silt coverage, which highlights the importance of particulates during high discharge events. For Mn there was no significant correlation with wetlands, instead, PCA analysis showed that during spring flood Mn was apparently more dependent on the supply of minerogenic particulates from silt deposits on the stream banks of some of the streams. The influence of minerogenic particulates on the concentration of, in particular, Mn was greatest in the larger, lower gradient streams, characterized by silt deposits in the near-stream zone. In the small forested streams underlain by till, DOC was of greater importance for the observed concentrations, as indicated by the positive correlation of both Fe_tot and Fe_<0.4 with DOC (r² = 0.77 and r² = 0.76, p < 0.001) at the smallest headwater forest site. In conclusion, wetland area and DOC were important for Fe concentrations in this boreal stream network, whereas silt deposits strongly influenced Mn concentrations. This study highlights the importance of studying stream water chemistry from a landscape perspective in order to address future environmental issues concerning mobility of Fe, Mn and associated trace metals.  相似文献   

Flow processes and sediment deformation in the Canary Debris Flow on the NW African Continental Rise     

D. G. Masson  B. Van Niel  P. P. E. Weaver 《Sedimentary Geology》1997,110(3-4):163-179

The Canary Debris Flow formed an extensive deposit on the NW African Continental Margin west of the Canary Islands. Sidescan sonar images and 3.5-kHz profiles show that the middle part of the debris flow deposit consists of complex channel systems separated by banks and ridges of debris. Channels are typically up to 10 km wide and 10 to 20 m deep, and have little or no debris fill. They appear to feed a more laterally continuous debris flow sheet which is seen further downslope. Interchannel banks and ridges are composed of 5 to 20 m thick debris deposits. This morphology is remarkably similar to that seen in subaerial debris flows, and we therefore infer that the observed submarine debris flow morphology is a primary flow fabric, rather than the result of the debris flow interacting with or exploiting pre-existing channels. High-resolution Sidescan sonar images show that the debris flow surface is covered by sediment blocks up to 300 m in diameter. A single core collected from the flow shows that most of the 4.6-m flow thickness at the core site is composed of a single clast. The clast has been folded, with its upper part consisting of an inverted minor image of the lower part. The same sequence occurs again, in situ, beneath the debris flow, suggesting that the clast may have a local source, rather than having been derived from the debris flow source area, some 200 km upslope. This indicates that the debris flow was capable of substantial seabed erosion in the middle part of its course. In these middle reaches, erosion within the channelled areas probably occurred simultaneously with deposition in the interchannel areas. Interchannel deposits may contain both locally derived and original source area material.  相似文献   

Effects of weak layers on particle velocity measurements   总被引：1，自引：0，他引：1  

W. I. Fourney  R. D. Dick  X. J. Wang  T. A. Weaver 《Rock Mechanics and Rock Engineering》1997,30(1):1-18

Summary Results are presented from a testing program to study the effect weak layers embedded in a strong rock strata have on particle velocity when subjected to explosive loading. A similar computational study had been conducted earlier with WONDY — a finite difference Langrangian code developed at Sandia National Laboratory. The experiments were conducted using models fabricated from Hydrocal containing a single dry sand layer or clay layer through which the stress wave traveled. Particle velocity was measured in front of and past the weak layer to determine attenuation, pulse shape changes, and displacement loss. The results from the model testing indicated that particle velocity amplitude decreased significantly when the stress wave passed through the weak layer. The velocity pulse width on the other hand was found to remain relatively constant when passing through the weak layer. The computational results from WONDY predicted similar behavior and hence were in good agreement with the tests. In the experiments, the velocity loss across a sand layer was found to be much larger than the loss across a clay layer. The stress wave velocity in the sand layer was found to be significantly smaller than in the Hydrocal while the experimentally determined wave velocity in the clay was nearly equal to the wave velocity in the Hydrocal.  相似文献   

Geochemical Evolution in the Cambrian-Ordovician Sandstone Aquifer, Eastern Wisconsin: 1. Major Ion and Radionuclide Distribution     

T. R. Weaver  J. Bahr 《Ground water》1991,29(3):350-356

  相似文献