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1.
坡面径流挟沙力是土壤侵蚀过程模型的核心输入参数。在系统界定坡面径流挟沙力概念的基础上,深入分析了坡面径流水动力学特性和泥沙特性对坡面径流挟沙力的影响及其机制,受降雨、地形、土壤、植被、土地利用、结皮形成、细沟发育和砾石出露等多种因素时空变异的综合影响,坡面径流挟沙力具有强烈的时空变化特征,导致坡面径流挟沙力的测定较为困难。将确定挟沙力常用的方法划分为河流挟沙力方程修正法、推理法、模型模拟法和测量法,比较分析了不同方法的优缺点。未来的研究应该重点关注挟沙力测定方法与技术、坡面径流输沙过程的动力机制、典型土壤的挟沙力、挟沙力方程构建与验证及变化条件下坡面径流挟沙力等方面。 相似文献
2.
地下环境中可移动的胶体能够促进强烈吸附的污染物质的运移,而胶体自身在运移过程中也会伴随发生沉淀、释放。根据高岭石胶体的土柱出流实验,对不同离子强度条件下胶体在饱和多孔介质中的沉淀和释放行为进行分析,并采用不同模型对其过程进行数值模拟。结果表明,离子强度是影响胶体沉淀和释放过程的重要因素,随着离子强度的增加,胶体的出流峰值逐渐降低,即胶体在多孔介质中的沉淀量逐渐增大,且沉淀速率系数K d 与离子强度成正相关;模型拟合的释放系数与NaCl 浓度显著相关,Grolimund 模型可以很好地模拟胶体的沉淀过程（R 2 >0.95）,但不能准确地模拟释放过程;而胶体运移方程耦合溶质运移方程能够模拟不同离子强度影响下胶体的释放过程（R 2 >0.9） 相似文献
3.
Understanding particle transport in porous media is critical in the sustainability of many geotechnical and geoenvironmental infrastructure. To date, the determination of the first-order rate coefficients in the advection–dispersion equation for simulating attachment and detachment of particles in saturated porous media typically has been relied on the result of laboratory-scale experiments. However, to determine attachment and detachment coefficients under varied hydraulic and geochemical variables, this method requires a large experimental matrix because each test provides only one set of attachment and detachment coefficients. The work performed in this study developed a framework to upscale the results obtained in pore-scale modeling to the continuum scale through the use of a pore network model. The developed pore network model incorporated variables of mean particle size, the standard deviation of particle size distribution, and interparticle forces between particles and sand grains. The obtained retention profiles using the pore network model were converted into attachment coefficients in the advection–dispersion equation for long-term and large-scale simulation. Additionally, by tracking individual particles during and after the simulation, the pore network model introduced in this study can also be employed for modeling the clogging phenomenon, as well as fundamental investigation of the impact of particle size distribution on particle retention in the sand medium.
相似文献4.
径流分离上壤是侵蚀泥沙的主要来源,也是建立土壤侵蚀物理模型的控制参数之一。对国内外坡面径流分离土壤过程的研究方法、流速测定、控制方程、分离能力、挟沙力及存在的问题进行了系统深入的论述,旨在综合已有研究经验和成果,促进相关研究的发展。 相似文献
5.
Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Matlab, south-eastern Bangladesh: Insight from experimental studies 总被引：1，自引：0，他引：1
Clare Robinson Mattias von Brömssen Prosun BhattacharyaSara Häller Annelie BivénMohammed Hossain Gunnar JacksKazi Matin Ahmed M. Aziz HasanRoger Thunvik 《Applied Geochemistry》2011,26(4):624-635
Targeting shallow low-As aquifers based on sediment colour may be a viable solution for supplying As-safe drinking water to rural communities in some regions of Bangladesh and West Bengal in India. The sustainability of this solution with regard to the long-term risk of As-safe oxidized aquifers becoming enriched with As needs to be assessed. This study focuses on the adsorption behaviour of shallow oxidized sediments from Matlab Region, Bangladesh, and their capacity to attenuate As if cross-contamination of the oxidized aquifers occurs. Water quality analyses of samples collected from 20 tube-wells in the region indicate that while there may be some seasonal variability, the groundwater chemistry in the reduced and oxidized aquifers was relatively stable from 2004 to 2009. Although sediment extractions indicate a relatively low amount of As in the oxidized sediments, below 2.5 mg kg−1, batch isotherm experiments show that the sediments have a high capacity to adsorb As. Simulations using a surface complexation model that considers adsorption to amorphous Fe(III) oxide minerals only, under-predict the experimental isotherms. This suggests that a large proportion of the adsorption sites in the oxidized sediments may be associated with crystalline Fe(III) oxides, Mn(IV) and Al(III) oxides, and clay minerals. Replicate breakthrough column experiments conducted with lactose added to the influent solution demonstrate that the high adsorption capacity of the oxidized sediments may be reduced if water drawn down into the oxidized aquifers contains high levels of electron donors such as reactive dissolved organic C. 相似文献
6.
《Earth》2007,85(3-4):87-102
Predicting rill erosion rates for a given discharge and slope minimally requires a model for rill hydraulics that allows the prediction of hydraulic parameters and a model for sediment detachment. Several relationships that describe rill hydraulics and/or sediment detachment within an eroding rill have been proposed and are incorporated into state of the art soil erosion models.In this paper a critical review of the theoretical concepts that are underpinning current rill flow and sediment detachment models is made in the light of recent experimental results. Approaches to define detachment–hydraulics relationship are generally based on developments in alluvial river hydraulics. However, experimental evidence to support the use of these concepts in models of rill erosion is scarce and recent experimental findings suggest that the basic assumptions used to model rill erosion are to some extent flawed. An analysis of empirically collected data on rill hydraulics conclusively shows that the empirical Manning equation does not hold for rill flow and should therefore not be used in rill erosion models. An empirical power law relationship relating velocity to discharges is much better in agreement with available experimental data, both for soils with and without rock fragments. In the absence of vegetation residue and/or other macroscopic, immobile elements such as rock fragments, total shear stress and unit length shear force can be used to predict soil detachment. The use of unit length shear force has the advantage that no information about rill geometry is necessary.The evidence for sediment load and rill flow detachment interaction is somewhat conflicting: the presence of a heavy sediment load appears to restrict rill flow detachment, but the exact form of the relationship between detachment rate and sediment load remains unclear. The effect of the presence of a sediment load on flow detachments under natural conditions is also limited by the nature of the detachment and transporting capacity relationships: on a rectilinear hillslope, transporting capacity increases much more rapidly with discharge than detachment capacity.We propose modifications to the theoretical formulations used in rill erosion models so that they are in better agreement with experimental evidence. Finally, we illustrate the potential of simplified models and conclude that the combination of empirical equations for flow detachment and rill hydraulics leads to results that are consistent with empirical data relating rill erosion rates to topography. 相似文献
7.
在坡面土壤侵蚀输沙计算中,可选用的输沙能力模式较多,但这些模式多运用于恒定输沙,在非恒定输沙中运用不多。建立了坡面土壤侵蚀非恒定输沙数学模型,模型中的输沙能力运用水流切应力、水流功率、单位水流功率3种模式,对模型过程采用有限差分格式离散求解。根据实测水沙资料进行模型参数率定,运用3种输沙能力模式于不同降雨强度、不同坡度的非恒定坡面输沙过程中。结果表明:在坡面非恒定输沙计算中,不同输沙能力模式对计算结果有明显影响,在降雨强度较小时,单位水流功率模式结果较其他两个模式为好,而在雨强较大时,切应力模式计算结果较好。 相似文献
8.
沙洲是塑造分汊型河道最重要的形态因子,其发育与蚀退由于上游来水来沙变化呈现冲淤交替,从而影响分汊河道输水输沙平衡.通过单个卵石沙洲的淤积和冲刷试验,揭示不同加沙速率、粒径和来流量条件下,沙洲淤积和冲刷规律,并建立简化理论模型分析沙洲淤积速率.结果表明,4组加沙试验中,分流点后出现明显淤积下延至洲头,左汊和右汊成为输沙通道,洲尾中心线两侧的左右汊道有泥沙淤积,洲尾未出现淤积.7组清水冲刷试验中,洲头最先承受冲刷和蚀退,并沿洲体冲刷延伸,洲头冲刷的泥沙沿左右汊水流带到下游,洲尾未出现明显冲刷.卵石沙洲以洲头淤积为主导发育模式,泥沙粒径、洲头坡角和分流角是决定淤积速率的关键因子. 相似文献
9.
In the classical view of fine sediment transport and deposition in streams, particles are expected to be removed from flowing water simply by direct sedimentation onto the streambed. However, recent research has demonstrated that fine sediments can propagate into pore spaces in the streambed due to hyporheic exchange and be removed by a combination of physical and chemical processes. This behaviour can significantly alter fine sediment size distributions during in-stream sediment transport because the physical transport of fine particles and their attachment to bed sediment grains are both a function of the particle size. Herein, we present model simulations for deposition of suspended sediments with a bimodal size distribution. We also applied this approach to analyse the results of laboratory flume observations of suspended sediment deposition. Results from model simulations and flume experiments clearly show that the rate of particle deposition increases with increasing particle size. Thus, the larger particles are preferentially removed from mixtures and there is a fining of the mixed suspensions over time. Both particle deposition mechanisms, i.e. particle sedimentation and filtration, contribute to the fining of the mixed fine particle suspensions over time, and their effects are clearly demonstrated using the fundamental process-based model. These results clearly demonstrate the effects of stream-subsurface exchange on the temporal evolution of the suspended fine sediment size distribution in downstream transport. 相似文献
10.
Modeling microbial processes in porous media 总被引：8，自引：1，他引：7
The incorporation of microbial processes into reactive transport models has generally proceeded along two separate lines
of investigation: (1) transport of bacteria as inert colloids in porous media, and (2) the biodegradation of dissolved contaminants
by a stationary phase of bacteria. Research over the last decade has indicated that these processes are closely linked. This
linkage may occur when a change in metabolic activity alters the attachment/detachment rates of bacteria to surfaces, either
promoting or retarding bacterial transport in a groundwater-contaminant plume. Changes in metabolic activity, in turn, are
controlled by the time of exposure of the microbes to electron acceptors/donor and other components affecting activity. Similarly,
metabolic activity can affect the reversibility of attachment, depending on the residence time of active microbes. Thus, improvements in quantitative analysis of active
subsurface biota necessitate direct linkages between substrate availability, metabolic activity, growth, and attachment/detachment
rates. This linkage requires both a detailed understanding of the biological processes and robust quantitative representations
of these processes that can be tested experimentally. This paper presents an overview of current approaches used to represent
physicochemical and biological processes in porous media, along with new conceptual approaches that link metabolic activity
with partitioning of the microorganism between the aqueous and solid phases.
Received, January 1999 · Revised, June 1999, July 1999 · Accepted, October 1999 相似文献
11.
Transport and retention of microparticles in packed sand columns at low and intermediate ionic strengths: experiments and mathematical modeling 总被引：1，自引：1，他引：0
Functional relationships correlating particle filtration coefficients and porewater ionic strength are herein proposed and
validated, based on deposition experiments of micrometer-sized particles onto siliceous sand. Experiments were conducted using
one-dimensional laboratory columns and stable monodisperse aqueous suspensions of negatively charged latex particles with
a mean size of 1.90 μm. The role of ionic strength was systematically investigated and six different monovalent salt concentrations
(1, 3, 10, 30, 100, 300 mM) were employed by addition of sodium chloride to the aqueous solution. A mathematical advection–dispersion-deposition
transport model was adopted assuming that attachment and detachment of particles in the porous medium are concurrent mechanisms
of particle filtration, and including a Langmuir-type blocking function to account for availability in deposition sites. The
system of equations modeling colloid transport was solved numerically. Attachment rate and detachment rate coefficients were
thereby determined for each employed ionic strength, as well as a blocking coefficient in the form of a maximum particle concentration
in the solid phase. Therefore, functional relationships expressing the dependence of these coefficients on ionic strength
were proposed, based on literature findings and present experimental observations. The existence of a critical salt deposition
concentration (and release concentration) separating a favorable attachment (and detachment) regime from an unfavorable condition
is assumed. In respect to the blocking coefficient, a power–law dependence on ionic strength is hypothesized. The proposed
functional relationships proved adequate to reproduce the coefficient trends extrapolated from data fitting by the transport
model. They may represent a powerful tool to describe and predict microparticle mobility in saturated porous media if embedded
a priori in the related mathematical transport models. 相似文献
12.
从导致土壤侵蚀的降雨和径流能量出发,提出了基于物理学原理的降雨能和径流能的概念,并采用人工模拟降雨实验,分析了泥沙输移与降雨和径流能的关系,结果显示:坡面薄层径流泥沙剥蚀量随着地表坡度、降雨能和径流能的增加而增加,雨滴击溅作用下泥沙剥蚀量远远大于无雨滴击溅作用时泥沙剥蚀量;薄层水流泥沙浓度随着坡度和降雨能的增加而增加,当坡度和降雨能一定时,泥沙浓度随着径流能的增加而减小;降雨扰动系数与降雨和径流能的比值按照对数关系增长,在相同坡度下,当降雨能一定时,降雨扰动系数随着径流能的增加而减小,当径流能一定时,降雨扰动系数随着降雨能的增加而增加。降雨能是导致泥沙剥离的本质,径流能是泥沙搬运的动力。 相似文献
13.
14.
The effect of distribution of iron-oxyhydroxide grain coatings on the transport of bacterial cells in porous media 总被引：3，自引：0，他引：3
E. P. Knapp Janet S. Herman George M. Hornberger Aaron L. Mills 《Environmental Geology》1998,33(4):243-248
Among the demonstrated processes influencing the transport of bacteria through aquifers, the deposition of cells on mineral
surfaces is one of the most important. For example, understanding the transport of introduced bacteria through aquifers is
essential to designing some in situ bioremediation schemes. The impact of the presence and distribution of Fe(III)-oxyhydroxide-coated
sand grains on bacterial transport through porous media was evaluated in column experiments in which bacteria (short rods;
1.2 μm length) were eluted through columns of quartz sand (0.5–0.6 mm in diameter) for several conditions of chemical heterogeneity
of mineral substrate. Fe(III)-oxyhydroxide-coated sand was present as 10% of the mass, and it was arranged in three treatments:
(1) homogeneously distributed, and present as a discrete layer (2) at the top and (3) at the bottom of 14-cm-long sand columns.
A pulse input of 108 cells ml–1 was introduced in an artificial groundwater solution flowing at 14 cm h–1 through the column, and eluted cells were counted. Peak breakthrough occurred at 1.0 pore volume. A large proportion of cells
were retained; 14.7–15.8% of the cells were recovered after three pore volumes of solution had eluted through clean quartz
sand, and only 2.1–4.0% were recovered from the Fe(III)-oxyhydroxide-coated sand mixtures. The three physical arrangements
of the chemical heterogeneity resulted in essentially the same breakthrough of cells, indicating that the spatial distribution
of iron coating does not affect the transport of bacteria. The results of the column transport experiments, which mimic hydrogeological
conditions encountered in field problems, are consistent with our mechanistic understanding of bacterial sorption.
Received: 10 April 1996 · Accepted: 17 February 1997 相似文献
15.
16.
《Sedimentology》2018,65(3):931-951
Submarine leveed channels are sculpted by turbidity currents that are commonly highly stratified. Both the concentration and the grain size decrease upward in the flow, and this is a fundamental factor that affects the location and grain size of deposits around a channel. This study presents laboratory experiments that link the morphological evolution of a progressively developing leveed channel to the suspended sediment structure of the turbidity currents. Previously, it was difficult to link turbidity current structure to channel–levee development because observations from natural systems were limited to the depositional products while experiments did not show realistic morphodynamics due to scaling issues related to the sediment transport. This study uses a novel experimental approach to overcome scaling issues, which results in channel inception and evolution on an initially featureless slope. Depth of the channel increased continuously as a result of levee aggradation combined with varying rates of channel floor aggradation and degradation. The resulting levees are fining upward and the grain‐size trend in the levee matches the upward decrease in grain size in the flow. It is shown that such deposit trends can result from internal channel dynamics and do not have to reflect upstream forcing. The suspended sediment structure can also be linked to the lateral transition from sediment bypass in the channel thalweg to sediment deposition on the levees. The transition occurs because the sediment concentration is below the flow capacity in the channel thalweg, while higher up on the channel walls the concentration exceeds capacity resulting in deposition of the inner levee. Thus, a framework is provided to predict the growth pattern and facies of a levee from the suspended sediment structure in a turbidity current. 相似文献
17.
Characterization on arsenic sorption and mobility of the sediments of Chia-Nan Plain, where Blackfoot disease occurred 总被引：1，自引：1，他引：0
Zhaohui Li Hanlie Hong Jiin-Shuh Jean Andria J. Koski Chia-Chuan Liu Selim Reza Jeffrey J. Randolph Stephan R. Kurdas Jonathan H. Friend Sarah J. Antinucci 《Environmental Earth Sciences》2011,64(3):823-831
Higher levels of arsenic in the aquifers of Chia-Nan Plain in southwestern Taiwan were attributed to the cause of Blackfoot
disease in the area half a century ago. Although extensive studies were conducted on the occurrence, speciation, mobility,
and transport of arsenic in the region, the relationship between arsenic adsorption by different aquifer materials and the
concentration and speciation of arsenic in these aquifers was poorly delineated. This study focused on characterization of
sediments in the region, as well as determination of relations between arsenic adsorption and other geochemical and clay mineralogical
properties of the sediments. The arsenic adsorption capacity was positively related to the clay minerals, Fe, and Mn contents
in the sediments. The higher arsenic adsorption capacity of the sediments served as a sink for the arsenic during its transport
from the central mountains to the coast and as a source for its release under reduced environment and in the presence of humic
substances. 相似文献
18.
Because South Africa is situated in a semi-dry region, the limited water resources are placed under increasing pressure by
consumers from different sectors. Irrigation consumes more than half of the available water resources in South Africa. In
the Northwest Province large volumes of water are found in dolomitic aquifers. Since 1970 irrigation from these aquifers has
resulted in an exponential growth in the withdrawal of groundwater. The purpose of this study is to evaluate the effectiveness
of groundwater utilization with centre-pivot irrigation in the Northwest Province, as well as to identify the most important
variables that influence this effectiveness. Factor Analysis and Multiple Regression Analysis were used to establish a model
with which the probable effectiveness of groundwater utilization on a specific farm can be predicted. The results show that
four variables have a significant effect on the net profit margin from centre-pivot irrigation in the study area, namely:
• Knowledge regarding the water capacity of the soil • Adjusting irrigation according to precipitation • The use of a yield
target for fertiliser application, and • Soil characteristics The above parameters were used to develop a model with which
farmers in the study area can be ranked according to the effectiveness of their water usage for centre-pivot irrigation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
土壤侵蚀包括土壤分离、泥沙输移和泥沙沉积3个子过程,研究这些过程发生、发展的水力、地形、土壤及地表特性等临界条件及各过程间相互影响、相互制约的机制,是建立土壤侵蚀过程模型继而准确预报土壤侵蚀的基础。为加强对径流驱动土壤分离过程的认识,推动土壤侵蚀过程与机理的研究,从径流水动力学特性、土壤特性、近地表特性、土壤分离过程的时空变异特性等方面对径流驱动的土壤分离过程影响因素及机制进行了总结和梳理,在此基础上,从土壤分离过程研究的时空尺度、土壤分离过程的动力学机制、细沟发育及其形态特征、网络结构对土壤分离过程的影响机制、土壤分离与泥沙输移的耦合机制、土壤分离测定方法与标准、土壤侵蚀阻力参数获取与预报等方面,展望了该领域有待深化的问题及今后的发展方向。 相似文献
20.
为探究砾石对工程堆积体土壤侵蚀的影响与其作用机制,通过室内模拟降雨研究了连续降雨下不同砾石含量的重壤质堆积体水蚀过程。结果表明:①堆积体砾石含量增加,坡面产流历时延长,产流率线性减小,土壤剥蚀率降低;②连续降雨下,堆积体所含砾石主要通过对坡面产流历时、坡面产流率、砾石覆盖率的多重影响发挥减沙作用,主成分回归方程可表达多个变量与平均土壤剥蚀率的关系;③一定砾石含量下,堆积体坡面砾石覆盖率随表土的剥离而增大,导致土壤剥蚀率呈指数函数递减趋势,并与累积土壤侵蚀总量存在较好的函数关系。工程堆积体所含砾石对土壤侵蚀程度的削减可为生产建设项目下垫面水土保持治理提供重要参考。 相似文献