Development of ST:REAM: a reach‐based stream power balance approach for predicting alluvial river channel adjustment          下载免费PDF全文

Chris Parker  Colin R Thorne  Nicholas J Clifford 《地球表面变化过程与地形》2015,40(3):403-413

River channel sediment dynamics are important in integrated catchment management because changes in channel morphology resulting from sediment transfer have important implications for many river functions. However, application of existing approaches that account for catchment‐scale sediment dynamics has been limited, largely due to the difficulty in obtaining data necessary to support them. It is within this context that this study develops a new, reach‐based, stream power balance approach for predicting river channel adjustment. The new approach, named ST:REAM (sediment transport: reach equilibrium assessment method), is based upon calculations of unit bed area stream power (ω) derived from remotely sensed slope, width and discharge datasets. ST:REAM applies a zonation algorithm to values of ω that are spaced every 50 m along the catchment network in order to divide the branches of the network up into relatively homogenous reaches. ST:REAM then compares each reach's ω value with the ω of its upstream neighbour in order to predict whether or not the reach is likely to be either erosion dominated or deposition dominated. The paper describes the application of ST:REAM to the River Taff in South Wales, UK. This test study demonstrated that ST:REAM can be rapidly applied using remotely sensed data that are available across many river catchments and that ST:REAM correctly predicted the status of 87.5% of sites within the Taff catchment that field observations had defined as being either erosion or deposition dominated. However, there are currently a number of factors that limit the usefulness of ST:REAM, including inconsistent performance and the need for additional, resource intensive, data to be collected to both calibrate the model and aid interpretation of its results. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Geophysical constraints on deep weathering and water storage potential in the Southern Sierra Critical Zone Observatory   总被引：1，自引：0，他引：1       下载免费PDF全文

W. Steven Holbrook  Clifford S. Riebe  Mehrez Elwaseif  Jorden L. Hayes  Kyle Basler‐Reeder  Dennis L. Harry  Armen Malazian  Anthony Dosseto  Peter C. Hartsough  Jan W. Hopmans 《地球表面变化过程与地形》2014,39(3):366-380

The conversion of bedrock to regolith marks the inception of critical zone processes, but the factors that regulate it remain poorly understood. Although the thickness and degree of weathering of regolith are widely thought to be important regulators of the development of regolith and its water‐storage potential, the functional relationships between regolith properties and the processes that generate it remain poorly documented. This is due in part to the fact that regolith is difficult to characterize by direct observations over the broad scales needed for process‐based understanding of the critical zone. Here we use seismic refraction and resistivity imaging techniques to estimate variations in regolith thickness and porosity across a forested slope and swampy meadow in the Southern Sierra Critical Zone Observatory (SSCZO). Inferred seismic velocities and electrical resistivities image a weathering zone ranging in thickness from 10 to 35 m (average = 23 m) along one intensively studied transect. The inferred weathering zone consists of roughly equal thicknesses of saprolite (P‐velocity < 2 km s^?1) and moderately weathered bedrock (P‐velocity = 2–4 km s^?1). A minimum‐porosity model assuming dry pore space shows porosities as high as 50% near the surface, decreasing to near zero at the base of weathered rock. Physical properties of saprolite samples from hand augering and push cores are consistent with our rock physics model when variations in pore saturation are taken into account. Our results indicate that saprolite is a crucial reservoir of water, potentially storing an average of 3 m³ m^?2 of water along a forested slope in the headwaters of the SSCZO. When coupled with published erosion rates from cosmogenic nuclides, our geophysical estimates of weathering zone thickness imply regolith residence times on the order of 10⁵ years. Thus, soils at the surface today may integrate weathering over glacial–interglacial fluctuations in climate. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

3-D seismic tomography of the Adelaide fold belt     

Peter Clifford  Stewart Greenhalgh  Greg Houseman  Frank Graeber 《Geophysical Journal International》2008,172(1):167-186

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Experimental field assessment of suspended sediment pathways for characterizing hydraulic habitat     

Gemma L. Harvey  Nicholas J. Clifford 《地球表面变化过程与地形》2010,35(5):600-610

The distribution of particulate matter within river channels, including sediments, nutrients and pollutants, is fundamental to the survival of aquatic organisms. However, the interactions between flow and sediment transport at the patch scale of river systems represents an under‐researched component of physical habitat studies, particularly those concerning the characterization of ‘physical biotopes’ (riffles, runs, pools, glides). This paper describes a field methodology for exploring the transfer of particulate matter at small scales within river channels, which may be used to aid hydraulic habitat characterization. The field protocol combines field measurement of high frequency flow properties, to characterize hydraulic habitat units, and deployment of spatial arrays of turbidity probes, to detect the passage of artificially‐induced sediment plumes through different biotope units. Sediment plumes recorded by the probes are analysed quantitatively in the manner of the flood hydrograph, and qualitative inferences are made on the dominant mixing processes operating within different parts of the channel. Relationships between the nature of spatio‐temporal hydraulic variations within glide, riffle and pool biotopes, and the character and mixing behaviour of sediment plumes within these habitat units are identified. Results from these preliminary experiments suggest that investigating and characterizing the transfer and storage of sediments, nutrients and pollutants within and between different biotopes is a viable avenue for further research, with potential to contribute to improved physical habitat characterization for river management and habitat restoration. The experiments are also an illustration of the value of neglected synergies between process geomorphology, ecology and river hydraulics. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Landscape response to tipping points in granite weathering: The case of stepped topography in the Southern Sierra Critical Zone Observatory     

Barbara S. Jessup  W. Jesse Hahm  Scott N. Miller  James W. Kirchner  Clifford S. Riebe 《Applied Geochemistry》2011

The dynamics of granitic landscapes are modulated by bimodal weathering, which produces patchy granular soils and expanses of bare rock ranging from meter-scale boulders to mountain-scale domes. We used terrain analysis and with cosmogenic nuclide measurements of erosion rates to quantitatively explore Wahrhaftig’s decades-old hypothesis for the development of “stepped topography” by differential weathering of bare and soil-mantled granite. According to Wahrhaftig’s hypothesis, bare granite weathers slower than soil-mantled granite; thus random erosional exposure of bare rock leads to an alternating sequence of steep, slowly weathering bedrock “steps” and gently sloped, but rapidly weathering, soil-mantled “treads.” Our investigation focused on the terrain surrounding the Southern Sierra Critical Zone Observatory (CZO), which is underlain by granitic bedrock and lies outside the limits of recent glaciation, in the heart of the stepped topography described by Wahrhaftig. Our digital terrain analysis confirms that steep steps often grade into gentle treads, consistent with Wahrhaftig’s hypothesis. However, we observe a mix-and-match of soil and bare rock on treads and steps, contrary to one of the hypothesis’ major underpinnings – that bare rock should be much more common on steps than on treads. Moreover, the data show that bare rock is not as common as expected at step tops; Wahrhaftig’s hypothesis dictates that step tops should act as slowly eroding base levels for the treads above them. The data indicate that, within each landscape class (i.e., the steps and treads), bare rock erodes more slowly than surrounding soil. This suggests that the coupling between soil production and denudation in granitic landscapes harbors a tipping point wherein erosion rates decrease when soils are stripped to bedrock. Although broadly consistent with the differential weathering invoked by Wahrhaftig, the data also show that steps are eroding faster than treads, undermining Wahrhaftig’s explanation for the origins of the steps. The revised interpretation proposed here is that the landscape evolves by back-wearing of steps in addition to differential erosion due to differences in weathering of bare and soil-mantled granite.  相似文献   

Permafrost thaw in a nested groundwater-flow system   总被引：3，自引：2，他引：1  

Jeffrey M. McKenzie  Clifford I. Voss 《Hydrogeology Journal》2013,21(1):299-316

Groundwater flow in cold regions containing permafrost accelerates climate-warming-driven thaw and changes thaw patterns. Simulation analyses of groundwater flow and heat transport with freeze/thaw in typical cold-regions terrain with nested flow indicate that early thaw rate is particularly enhanced by flow, the time when adverse environmental impacts of climate-warming-induced permafrost loss may be severest. For the slowest climate-warming rate predicted by the Intergovernmental Panel on Climate Change (IPCC), once significant groundwater flow begins, thick permafrost layers can vanish in several hundred years, but survive over 1,000 years where flow is minimal. Large-scale thaw depends mostly on the balance of heat advection and conduction in the supra-permafrost zone. Surface-water bodies underlain by open taliks allow slow sub-permafrost flow, with lesser influence on regional thaw. Advection dominance over conduction depends on permeability and topography. Groundwater flow around permafrost and flow through permafrost impact thaw differently; the latter enhances early thaw rate. Air-temperature seasonality also increases early thaw. Hydrogeologic heterogeneity and topography strongly affect thaw rates/patterns. Permafrost controls the groundwater/surface-water-geomorphology system; hence, prediction and mitigation of impacts of thaw on ecology, chemical exports and infrastructure require improved hydrogeology/permafrost characterization and understanding.  相似文献   

Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA)   总被引：3，自引：2，他引：1  

Tristan P. Wellman  Clifford I. Voss  Michelle A. Walvoord 《Hydrogeology Journal》2013,21(1):281-298

In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze–thaw physics is used to examine the effect of climate, lake size, and lake–groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost range from ～200 to >?1,000  years (vertical thaw rates <?0.1–0.5  m?yr^?1). Seasonal temperature cycles along lake margins impact supra-permafrost flow and late-stage cryologic processes. Warmer climate accelerates complete permafrost thaw and enhances seasonal flow within the supra-permafrost layer. Prior to open talik formation, sub-lake permafrost thaw is dominated by heat conduction. When hydraulic conditions induce upward or downward flow between the lake and sub-permafrost aquifer, thaw rates are greatly increased. The complexity of ground-ice and water-flow interplay, together with anticipated warming in the arctic, underscores the utility of coupled groundwater-energy transport models in evaluating hydrologic systems impacted by permafrost.  相似文献   

An evaluation of the engineering properties of some Nigerian limestones as construction materials for highway pavements     

S. Clifford Teme 《Engineering Geology》1991,31(3-4):315-326

Several hundred limestone samples representing eight different deposits within Nigeria have been evaluated and results indicate that some of the deposi highway pavement construction materials. The evaluation included tests on index properties, strength, chemical, petrographic and resistance-to-attritio

The suitability or adverse features of the eight limestone deposits have been evaluated and the various engineering characteristics are discussed. base recommendations are made for the use of selected limestones as pavement materials in Nigeria.  相似文献   

Geotechnical characteristics of some clays from south—western Nigeria: implications for industrial utilization     

S. Clifford Teme 《Engineering Geology》1991,30(3-4):305-324

Clays in adequate quantity and of quality for industrial use occur in the Ifon area of Ondo State, Nigeria, in the form of alluvial deposits at Sobe, as sedimentary deposits at Non and Arimogija and as residual clays at Omialafara.

The alluvial clays from Sobe and the sedimentary clays from Ifon are highly plastic while the sedimentary clays from Arimogija are moderately plastic and the Omialafara residual clays only slightly plastic. The clays in general are kaolinitic in composition with minor amounts of illite.

The unconfined compressive strength characteristics of fired pellets of these various clays indicate that the reddish to greyish-brown alluvial clays at Sobe tend to have higher strength values than the dark grey clays of Arimogija. Porosity, firing shrinkage, clay mineralogy and colour after firing all indicate that the clays are very suitable for the manufacture of ceramic wares.  相似文献   

Descriptive statistics forN-dimensional closed arrays: A spherical coordinate approach     

Clifford R. Stanley 《Mathematical Geosciences》1990,22(8):933-956

Recent publications have demonstrated that the composition of a system can be described by the angles which define the vector resulting from the projection of the composition onto the unit hypersphere. Although published trigonometric relationships allow determination of the angles in any number of dimensions, no general hyperdimensional recursive formulae exist for the calculation of these quantities and their variances and covariances. A general methodology for calculating the angles which describe the compositions of systems in any number of dimensions is presented. These angles can be used to calculate statistics (central moments and resultant vectors) describing the central tendency and dispersion among rock compositions, as well as to quantify the angular differences between compositions. Equations that relate the variances and covariances of these angular variables to the variances and covariances of the actual component proportion variables are presented, allowing projection of these measurements from one reference frame to another (cartesian to spherical and vice versa).  相似文献