Experimental insights into consolidation rates during one-dimensional loading with special reference to excess pore water pressure     

Olek  Bartłomiej Szczepan 《Acta Geotechnica》2020,15(12):3571-3591

Acta Geotechnica - Consolidation rate has significant influence on the settlement of structures founded on soft fine-grained soil. This paper presents the results of a series of small-scale and...  相似文献   

Post‐wildfire changes in suspended sediment rating curves: Sabino Canyon,Arizona     

Sharon L. E. Desilets  Bart Nijssen  Brenda Ekwurzel  Ty P. A. Ferré 《水文研究》2007,21(11):1413-1423

Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short‐term variations in post‐fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post‐fire sediment dynamics in a semi‐arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km². Surface water samples were collected in an affected watershed using an event‐based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time‐invariant set of sediment rating parameters. A sediment mass‐balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm‐based sampling in areas with intense monsoon activity to characterize post‐fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high‐intensity rainstorms. These findings can be used to constrain rapid assessment fire‐response models for planning mitigation activities. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Circulation statistics and climate change in Central Europe: PRUDENCE simulations and observations     

Aad van Ulden  Geert Lenderink  Bart van den Hurk  Erik van Meijgaard 《Climatic change》2007,81(1):179-192

PRUDENCE simulations of the climate in Central Europe are analysed with respect to mean temperature, mean precipitation and three monthly mean geostrophic circulation indices. The three global models show important circulation biases in the control climate, in particular in the strength of the west-circulations in winter and summer. The nine regional models inherit much of the circulation biases from their host model, especially in winter. In summer, the regional models show a larger spread in circulation statistics, depending on nesting procedures and other model characteristics. Simulated circulation biases appear to have a significant inluence on simulated temperature and precipitation. The PRUDENCE ensemble appears to be biased towards warmer and wetter than observed circulations in winter, and towards warmer and dryer circulations in summer. A2-scenario simulations show important circulation changes, which have a significant impact on changes in the distributions of monthly mean temperature and precipitation. It is likely that interactions between land–surface processes and atmospheric circulation play an important role in the simulated changes in the summer climate in Central Europe.  相似文献   

Recent Developments Concerning High-Velocity Clouds     

Bart P. Wakker 《Astrophysics and Space Science》2004,289(3-4):381-390

I summarize the new developments in HVC research that have occurred in the pastfew years. These include a) the determination of approximate distances to someIVCs and HVC complex A; b) the measurement of the metallicity of the MagellanicStream and the conclusion that tidal forces are dominant in creating the Stream;c) the derivation that the metallicity of complex C is 0.1 solar, with someevidence for metallicity variations; d) the result that N/O in complex C is 0.2times the solar ratio, a value otherwise only seen in dwarf galaxies and DampedLyα systems; e) the discovery of high-velocity OVI absorption, bothassociated with previously known HI HVCs and in directions without a HI HVC;f) the proposal that HVCs form a population of objects permeating the LocalGroup.  相似文献   

The impact of wildfire on baseflow recession rates in California          下载免费PDF全文

Ryan R. Bart  Christina L. Tague 《水文研究》2017,31(8):1662-1673

The effect of wildfire on peak streamflow and annual water yield has been investigated empirically in numerous studies. The effect of wildfire on baseflow recession rates, in contrast, is not well documented. The objective of this paper was to quantify the effect of wildfire on baseflow recession rates in California for both individual watersheds and for all the study watersheds collectively. Two additional variables, antecedent groundwater storage and potential evapotranspiration, were also investigated for their effect on baseflow recession rates and postfire baseflow recession rate response. Differences between prefire and postfire baseflow recession rates were modeled statistically in 8 watersheds using a mixed statistical model that accounted for fixed and random effects. For the all‐watershed model, antecedent groundwater storage, potential evapotranspiration, and wildfire were each found to be significant controls on baseflow recession rates. Wildfire decreased baseflow recession rates 52.5% (37.6% to 66.0%), implying that postfire reductions in above‐ground vegetation (e.g., decreased interception, decreased evapotranspiration) were a stronger control on baseflow recession rate change than hydrophobicity. At an individual watershed scale, baseflow recession rate response to wildfire was found to be sensitive to intraannual differences in antecedent groundwater storage in 2 watersheds, with the effect of wildfire on baseflow recession rates being greater with lower levels of antecedent groundwater storage. Examination of burn severity for a subset of the study watersheds pointed to riparian zone burn severity as a potential primary control on postfire recession rate change. This study demonstrates that wildfire may have a substantial impact on fluxes to and from groundwater storages, altering the rate at which baseflow recedes.  相似文献   

How do species and data characteristics affect species distribution models and when to use environmental filtering?     

Lukáš Gábor  Vojtěch Barták  Vincent Lecours 《International journal of geographical information science》2020,34(8):1567-1584

ABSTRACT

Species distribution models (SDMs) are widely used in ecology and conservation. However, their performance is known to be affected by a variety of factors related to species occurrence characteristics. In this study, we used a virtual species approach to overcome the difficulties associated with testing of combined effects of those factors on performance of presence-only SDMs when using real data. We focused on the individual and combined roles of factors related to response variable (i.e. sample size, sampling bias, environmental filtering, species prevalence, and species response to environmental gradients). Results suggest that environmental filtering is not necessarily helpful and should not be performed blindly, without evidence of bias in species occurrences. The more gradual the species response to environmental gradients is, the greater is the model sensitivity to an inappropriate use of environmental filtering, although this sensitivity decreases with higher species prevalence. Results show that SDMs are affected to the greatest degree by the species response to environmental gradients, species prevalence, and sample size. Models’ accuracy decreased with sample size below 300 presences. Furthermore, a high level of interactions among individual factors was observed. Ignoring the combined effects of factors may lead to misleading outcomes and conclusions.  相似文献   

Numerical Analysis of the Effects of Wind and Sprayer Type on Spray Distribution in Different Orchard Training Systems     

Ashenafi T. Duga  Donald Dekeyser  Kris Ruysen  Dany Bylemans  David Nuyttens  Bart M. Nicolai  Pieter Verboven 《Boundary-Layer Meteorology》2015,157(3):517-535

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Truncated multiGaussian fields and effective conductance of binary media     

Sean A. McKenna  Jaideep RayYoussef Marzouk  Bart van Bloemen Waanders 《Advances in water resources》2011,34(5):617-626

Truncated Gaussian fields provide a flexible model for defining binary media with dispersed (as opposed to layered) inclusions. General properties of excursion sets on these truncated fields are coupled with a distance-based upscaling algorithm and approximations of point process theory to develop an estimation approach for effective conductivity in two-dimensions. Estimation of effective conductivity is derived directly from knowledge of the kernel size used to create the multiGaussian field, defined as the full-width at half maximum (FWHM), the truncation threshold and conductance values of the two modes. Therefore, instantiation of the multiGaussian field is not necessary for estimation of the effective conductance. The critical component of the effective medium approximation developed here is the mean distance between high conductivity inclusions. This mean distance is characterized as a function of the FWHM, the truncation threshold and the ratio of the two modal conductivities. Sensitivity of the resulting effective conductivity to this mean distance is examined for two levels of contrast in the modal conductances and different FWHM sizes. Results demonstrate that the FWHM is a robust measure of mean travel distance in the background medium. The resulting effective conductivities are accurate when compared to numerical results and results obtained from effective media theory, distance-based upscaling and numerical simulation.  相似文献   

Tidal impact on the division of river discharge over distributary channels in the Mahakam Delta     

Maximiliano G. Sassi  A. J. F. Hoitink  Benjamin de Brye  Bart Vermeulen  Eric Deleersnijder 《Ocean Dynamics》2011,61(12):2211-2228

Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides.  相似文献   

Investigation of the different binding edge sites for Zn on montmorillonite using P-EXAFS - The strong/weak site concept in the 2SPNE SC/CE sorption model     

Rainer Dähn  Bart Baeyens  Michael H. Bradbury 《Geochimica et cosmochimica acta》2011,75(18):5154-5168

The 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) sorption model has been used over the past decade or so to quantitatively describe the uptake of metals with oxidation states from II to VI on 2:1 clay minerals; montmorillonite and illite. One of the main features in this model is that there are two broad categories of amphoteric edge sorption sites; the so called strong (S^SOH) and weak (S^W1OH) sites. Because of their different sorption characteristics, it was expected that the coordination environments of the surface complexes on the two site types would be different. Zn isotherm data on two montmorillonites, Milos and STx-1, were measured and modelled using the 2SPNE SC/CE sorption model. The results were used to define the most favourable experimental conditions under which Zn sorption was either dominated by the strong (S^SOH, ∼2 mmol kg⁻¹) or by the weak sites (S^W1OH, ∼40 mmol kg⁻¹). Highly oriented self-supporting films were prepared for polarised extended X-ray absorption fine structure (P-EXAFS) investigations.Montmorillonites often contain Zn incorporated in the clay matrix. The Zn bound in this form was quantified and the results from the analysis of the P-EXAFS spectra were taken into account in the interpretation of the spectra measured at low Zn loadings (∼2 mmol kg⁻¹) and medium Zn loadings (∼30 mmol kg⁻¹). The Zn spectra on the “strong sites” exhibited a pronounced angular dependency and formed surface complexes in the continuity of the Al-octahedral sheets at the montmorillonite edges. In contrast, the Zn “weak site” spectra showed only a weak angular dependency. The spectroscopic evidence indicates the existence of two distinct groups of edge surface binding sites which is consistent with a multi-site sorption model and in particular with the strong/weak site concept intrinsic to the 2SPNE S/CE sorption model.  相似文献