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1.
To remove chromate from a wastewater, a porous permeable reactive barrier system (PRBS), using pyrite and biotite, was adapted. This study included bench‐scale column experiments to evaluate the efficiency of the PRBS and investigate the reaction process. The total chromium concentration of the effluent from the biotite and pyrite columns reached the influent concentration of 0·10 mM after passing through more than 150 pore volumes (PVs) and 27 PVs respectively, and remained constant thereafter. The CrVI concentration in the effluent from the biotite column became constant at about 0·08 mM , accounting for approximately 80% of the influent concentration, after passing through 200 PVs. Moreover, in the pyrite column, the CrVI concentration remained at about 0·01 mM , 10% of the input level, after passing through 116 PVs. This shows that both columns maintained their levels of chromate reduction once the CrVI breakthrough curves (BTCs) had reached the steady state, though the steady‐state output concentration of total chromium had reached the influent level. The variances of the iron concentration closely followed those of the chromium. The observed data for both columns were fitted to the predicted BTCs calculated by CXTFIT, a program for estimating the solute transport parameters from experimental data. The degradation coefficient µ of the total chromium BTCs for both columns was zero, suggesting the mechanisms for the removal of chromate limit the µ of the CrVI BTCs. The CrVI degradation of the pyrite column (6·60) was much greater than that of the biotite column (0·27). In addition, the CrVI retardation coefficient R of the pyrite column (253) was also larger than that of the biotite column (125). The R values for the total chromium BTCs from both columns were smaller than those of the CrVI BTC. Whereas the total chromium BTC for the pyrite column showed little retardation (1·5), the biotite column showed considerable retardation (80). The results for the 900 °C heat‐treated biotite column were analogous to those of the control column (quartz sand). This suggests that the heat‐treated biotite played no role in the retardation and removal of hexavalent chromium. The parameters of the heat‐treated biotite were calculated to an R of 1·2 and µ of 0·01, and these values confirmed quantitatively that the heated biotite had little effect on the transport of CrVI. These solute transport parameters, calculated by CXTFIT from the data obtained from the column tests, can provide quantitative information for the evaluation of bench‐ or field‐scale columns as a removal technology for CrVI in wastewater or contaminated groundwater. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
Jos C. van Dam 《水文研究》2000,14(6):1101-1117
Single domain models may seriously underestimate leaching of nutrients and pesticides to groundwater in clay soils with shrinkage cracks. Various two‐domain models have been developed, either empirical or physically based, which take into account the effects of cracks on water flow and solute transport. This paper presents a model concept that uses the clay shrinkage characteristics to derive crack volume and crack depth under transient field conditions. The concept has been developed to simulate field average behaviour of a field with cracks, rather than flow and transport at a small plot. Water flow and solute transport are described with basic physics, which allow process and scenario analysis. The model concept is part of the more general agrohydrological model SWAP, and is applied to a field experiment on a cracked clay soil, at which water flow and bromide transport were measured during 572 days. A single domain model was not able to mimic the field‐average water flow and solute transport. Incorporation of the crack concept considerably improved the simulation of water content and bromide leaching to the groundwater. Still deviations existed between the measured and simulated bromide concentration profiles. The model did not reproduce the observed bromide retardation in the top layer and the high bromide dispersion resulting from water infiltration at various soil depths. A sensitivity analysis showed that the amounts of bromide leached were especially sensitive to the saturated hydraulic conductivity of the top layer, the solute transfer from the soil matrix to crack water flow and the mean residence time of rapid drainage. The shrinkage characteristic and the soil hydraulic properties of the clay matrix showed a low sensitivity. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
3.
Uncertainty analysis of radioactive nuclide transport for one-dimensional single fracture has been studied. First order differential analysis is applied to introduce analytical form of output expectation and variance for contaminant transport equation, by regarding uncertainty of dispersion coefficient and retardation factor. Breakthrough curve of dimensionless concentration is demonstrated by taking I-129 as radioactive nuclide in fracture transport. It is possible to pick up critical ranges in spatial and temporal domain from the output variance. From the viewpoint of preliminary performance assessment for nuclear waste disposal the parameter importance in such system can be substantially measured in the site characterization in future. 相似文献
4.
粘土衬垫的防渗性能和吸附阻滞性能对卫生填埋场防渗系统工作性能有着重要影响。通过建立一维对流-弥散模型,分析了渗透系数、扩散系数、入渗强度、吸附能力对渗漏量及衬垫击穿时间的影响。考虑实际工程的复杂性,建立能反映土体分层、土体非均质性、地下水运动及宏观弥散等复杂因素影响的污染物运移二维分析模型,并对各参数的敏感性进行分析。计算结果表明,保持填埋场在低渗滤液水位下运行,对提高衬垫的防渗效果及耐久性有重要意义;受材料本身性质、施工质量等因素的影响,粘土衬垫的渗透系数变异性往往较大,渗透系数提高一个数量级时,衬垫击穿时间显著缩短;渗透系数恒定时,衬垫击穿时间与材料阻滞因子成线性变化关系;地下水分布及运动情况对污染物运移及分布有重要影响,地下水位越低,竖向入渗越明显,入渗区下部土体的吸附性能发挥越充分,到达地下水及下部土体的污染物浓度越低。 相似文献
5.
Within the scope of the interdisciplinary Natural and Artificial Systems for Recharge and Infiltration research project dealing with riverbank filtration processes at the Berlin water works, a semi‐technical column experiment has been ongoing since January 2003. Here, a 30 m long soil column is infiltrated with surface water sampled from Lake Tegel (Berlin, Germany) under saturated flow conditions. Changes in pore water hydrochemistry sampled on 21 non‐equidistant distributed points are verified by coupled transport and reaction modelling. The objective of reactive transport modelling was to identify the main biogeochemical processes within the soil column during the flushing experiment as a conceptual model for riverbank filtration. Modelling was done with a combination of MATLAB and PHREEQC. The main processes identified are: (1) biogeochemical degradation due to interaction of natural surface water with the soil matrix; (2) continuous dissolution of refractory air bubbles from the soil column matrix. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
Hydrocarbon compounds in aquifers are generally known to show a retardation effect due to sorption onto the surfaces of solid particles. In this study, we investigated the effect of sorption on the transport of benzene in sandy aquifer materials by conducting batch and column tests for both sandy aquifer materials and sandy materials to which had been added 0·5% powdered activated carbon. The batch test was conducted by equilibrating dry materials with benzene solutions of various initial concentrations, and by analysing the concentrations of benzene in the initial and equilibrated solutions using high‐performance liquid chromatography (HPLC). The column test was performed to monitor the concentrations of effluent versus time, known as a breakthrough curve (BTC). We injected KCl and benzene solutions as tracers into the inlet boundary as two different types of square pulse and step, and monitored the effluent concentrations at the exit boundary under a steady‐state condition using an electrical conductivity meter and HPLC. Simulation of benzene transport was performed using the convective–dispersive equation model with the distribution coefficients obtained from the batch test and the transport parameters of the conservative solute KCl from the column test. The observed BTCs of KCl and benzene for pulse injection showed that the arrival times of the peaks of both tracers coincided well, but the relative peak concentration of benzene was much lower than that of KCl. Comparison of the simulated and observed BTCs showed a great discrepancy for all cases of injection mode and material texture, indicating the absence of retardation effect. These results reveal that the predominant process affecting the benzene transport in the sandy aquifer materials is an irreversible sorption rather than retardation. This tentative conclusion was verified by simulation of benzene transport using an irreversible sorption parameter that led to a good agreement between the simulated and observed BTCs. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
7.
Cosler DJ 《Ground water》2004,42(2):203-222
Nonequilibrium concentration type curves are numerically developed and sensitivity analyses are performed to examine the relationships between effluent concentrations in partially penetrating monitoring/extraction wells, the vertical plume shape, and the mass transfer characteristics of the aquifer. The governing two-dimensional, axisymmetric nonequilibrium solute transport equation is solved in three stages using an operator-splitting approach. In the first two stages, the advection and dispersion terms are solved with the Eulerian-Lagrangian method, based on the backward method of characteristics for advection and the standard implicit Galerkin finite element method for dispersion. In the third step, the first-order, immobile-mobile domain mass transfer term is computed analytically for both two-site and lognormally distributed, multirate models. Effluent concentration variations with time and contour plots of the pore water concentration distribution in the aquifer are compared for a wide range of field- and laboratory-measured mass transfer rates, various plume shapes, and relevant physical/chemical parameter values, including pumping rate, vertical anisotropy ratio, retardation factor, and porosity. The simulation results show that rate-limited mass transfer can have a significant impact on sample and aquifer pore water concentrations during three-dimensional transport to a partially penetrating well. An alternative dimensionless form of the nonequilibrium solute transport equation is derived to illustrate the key parameter groupings that quantify rate-limited sorption effects and show the relative importance of individual parameters. A hypothetical field application example demonstrates the fitting of dimensional type curves to discrete-interval sampling data in order to evaluate the mass transfer characteristics of an aquifer and shows how type curve superposition can be used to model complex plume shapes. 相似文献
8.
大型浅水湖泊藻类模型参数敏感性分析 总被引：2，自引：1，他引：1
选取太湖作为典型湖泊在之前研究基础上建立藻类模型,对模型中与藻类有关的40个参数进行拉丁超立方抽样,并使用区域敏感性分析方法和普适似然不确定性分析方法进行敏感性分析.结果表明:在所选的40个参数中,有7个参数是敏感的参数,对模拟的结果影响较大.在藻类生长、基础代谢、牧食和沉降4个藻类变化过程中藻类生长的敏感参数最多,影响最大;在藻类生长项中,叶绿素的消光系数是藻类生长光照限制中的最敏感参数,而最低适宜生长温度及其对藻类生长的影响系数则是温度限制中的敏感参数;并且不同湖区的不确定性在不同时间差异明显,对于藻类低浓度湖区和藻类暴发期的模拟需要加以关注. 相似文献
9.
AbstractA parametric uncertainty and sensitivity analysis of hydrodynamic processes was conducted for a large shallow freshwater lake, Lake Taihu, China. Ten commonly used parameters in five groups were considered including: air–water interface factor, water–sediment interface factor, surrounding terrain factor, turbulent diffusion parameters and turbulent intensity parameters. Latin hypercube sampling (LHS) was used for sampling the parametric combinations, which gave predictive uncertainty results directly without using surrogate models, and the impacts of different parametric distribution functions on the results were investigated. The results showed that the different parametric distribution functions (e.g. uniform, normal, lognormal and triangular) for sampling had very little impact on the uncertainty and sensitivity analysis of the lake hydrodynamic model. The air–water interface factor (wind drag coefficient) and surrounding terrain factor (wind shelter coefficient) had the greatest influence on the spatial distribution of lake hydrodynamic processes, especially in semi-closed bays and lake regions with complex topography, accounting for about 60–70% and 20%, respectively, of the uncertainty on the results. Vertically, velocity in the surface layer was also largely influenced by the two factors, followed by velocity in the bottom layer; the middle velocity had minimal impact. Likewise, the water–sediment interface factor (i.e. bottom roughness height) ranked third, contributing about 10% to the uncertainty of the hydrodynamic processes of the lake. In contrast, turbulent diffusion parameters and turbulent intensity parameters in the lake hydrodynamic model had little effect on the uncertainty of simulated results (less than 1% contribution). The findings were sufficiently significant to reduce the parameter uncertainties and calibration workload of the hydrodynamic model in large shallow lakes.
Editor Z. W. Kundzewicz; Associate editor S. Grimaldi 相似文献
10.
Solute leaching in unsaturated soil is influenced by the variability in hydraulic functions (water retention and conductivity) that govern the flow process. Variability in measured soil hydraulic functions of a coarse-, medium- and fine-textured soil group was quantified with the scaling theory of similar media. Solute leaching in these soils was calculated with Monte Carlo simulation assuming, successively, hydraulic conductivity, K, volumetric water content, 0, and pressure head, h, to be constant. In addition to variability in hydraulic functions, variability in the solute retardation factor was also taken into account. To examine this effect five solutes were considered: a conservative solute (chloride), a non-retarded solute subject to decay (nitrate), a retarded solute that does not decay (cadmium) and two organic solutes which are retarded but have different sorption and decay parameters (the pesticide atrazine and a chlorinated hydrocarbon). The numerical results obtained with Monte Carlo simulation were in a number of instances verified with analytical solutions. The three soil groups distinguished showed considerable differences in vulnerability for leaching of the five solutes, emphasizing the importance of the effect of variability in soil hydraulic functions when studying solute leaching. Numerical and analytical results showed good agreement. Therefore, in relatively simple situations analytical solutions are attractive. However, in complicated situations, analytical solutions are cumbersome and numerical solutions are the only realistic alternative. 相似文献
11.
Laboratory Experiments for Describing the Migration of Explosives in Sandy Aquifers Leaching the munition residues from the former explosive production site Elsnig in the Upper Elbe Valley (Saxony, Germany) resulted in an undefined plume of groundwater contaminated by nitroaromatics and nitroamines approaching important drinking water resources. Laboratory experiments were carried out to investigate transport and fate phenomena of such substances in aquifer materials. Specific solute storage and migration parameters for modelling the subsurface migration processes were obtained from steady state experiments in soil cores used as 0-dimensional reactors and from dynamic breakthrough curves in soil columns. Using the 0-dimensional reactor tests we focused on isotherm estimation. Sorption was found to be reflected best by Freundlich isotherms for concentrations of nitroaromatics less than 10 mg L?1 and low organic carbon content in the tested subsurface material. TNT-adsorption was slow and strongly correlated with soil permeability. Preliminary kinetic measurements revealed sorption equilibrium after two days. RDX-adsorption was low. All sorption experiments were conducted under non-sterile and aerobic conditions. Microbial activity was controlled by measuring the enzyme activity and the biomass in water and soil samples. After steady state experiments in the 0-dimensional reactors, products initiated by biodegradation of explosives such as aminonitrotoluenes were found. Based on literature, degradation was estimated and correlated with soil texture. For five components, different retardation was observed depending on soil texture by using native groundwater samples in the columns. Specially designed reactor facilities and soil column installations with temperature and flux control as well as on-line measurements of pH, pE, and conductivity were applied. Concentrations of contaminants were analysed both by high performance liquid chromatography and thin layer chromatography. Photolytic reactions have been prevented. Based on all these laboratory experiments, sorption, degradation, and retardation parameters of trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), dinitrobenzene (DNB), dinitrotoluene (DNT), and mononitrotoluene (MNT) in Elsnig sandy aquifers were estimated. 相似文献
12.
The present study assesses the uncertainty of flow and radionuclide transport in the unsaturated zone at Yucca Mountain using a Monte Carlo method. Matrix permeability, porosity, and sorption coefficient are considered random. Different from previous studies that assume distributions of the parameters, the distributions are determined in this study by applying comprehensive transformations and rigorous statistics to on-site measurements of the parameters. The distribution of permeability is further adjusted based on model calibration results. Correlation between matrix permeability and porosity is incorporated using the Latin Hypercube Sampling method. After conducting 200 Monte Carlo simulations of three-dimensional unsaturated flow and radionuclide transport for conservative and reactive tracers, the mean, variances, and 5th, 50th, and 95th percentiles for quantities of interest (e.g., matrix liquid saturation and water potential) are evaluated. The mean and 50th percentile are used as the mean predictions, and their associated predictive uncertainties are measured by the variances and the 5th and 95th percentiles (also known as uncertainty bounds). The mean predictions of matrix liquid saturation and water potential are in reasonable agreement with corresponding measurements. The uncertainty bounds include a large portion of the measurements, suggesting that the data variability can be partially explained by parameter uncertainty. The study illustrates propagation of predictive uncertainty of percolation flux, increasing downward from repository horizon to water table. Statistics from the breakthrough curves indicate that transport of the reactive tracer is delayed significantly by the sorption process, and prediction on the reactive tracer is of greater uncertainty than on the conservative tracer because randomness in the sorption coefficient increases the prediction uncertainty. Uncertainty in radionuclide transport is related to uncertainty in the percolation flux, suggesting that reducing the former entails reduction in the latter. 相似文献
13.
HUANG Guanhua HUANG Quanzhong ZHAN Hongbin CHEN Jing XIONG Yunwu FENG Shaoyuan 《中国科学D辑(英文版)》2005,48(Z2)
The newly developed Fractional Advection-Dispersion Equation (FADE), which is FADE was extended and used in this paper for modelling adsorbing contaminant transport by adding an adsorbing term. A parameter estimation method and its corresponding FORTRAN based program named FADEMain were developed on the basis of Nonlinear Least Square Algorithm and the analytical solution for one-dimensional FADE under the conditions of step input and steady state flow. Data sets of adsorbing contaminants Cd and NH4+-N transport in short homogeneous soil columns and conservative solute NaCI transport in a long homogeneous soil column, respectively were used to estimate the transport parameters both by FADEMain and the advection-dispersion equation (ADE) based program CXTFIT2.1. Results indicated that the concentration simulated by FADE agreed well with the measured data. Compared to the ADE model, FADE can provide better simulation for the concentration in the initial lower concentration part and the late higher concentration part of the breakthrough curves for both adsorbing contaminants. The dispersion coefficients for ADE were from 0.13 to 7.06 cm2/min, while the dispersion coefficients for FADE ranged from 0.119 to 3.05 cm1.856/min for NaCI transport in the long homogeneous soil column. We found that the dispersion coefficient of FADE increased with the transport distance, and the relationship between them can be quantified with an exponential function. Less scale-dependent was also found for the dispersion coefficient of FADE with respect to ADE. 相似文献
14.
Junhong Bai Rong Xiao Xiaofei Ye Denghua Yan Haifeng Gao Junjing Wang 《洁净——土壤、空气、水》2013,41(5):473-477
Ammonium transport was simulated in horizontal soil columns from an inland alkaline wetland (Fulaowenpao wetland) of Northeast China. The primary objectives of this work are to investigate the changes in ammonium transport rate with increasing distances along horizontal soil column and to determine the effects of water diffusion rate and volumetric water content on ammonium transport rate. Our results showed that water diffusion coefficient was the lowest at the soil layer of 10–20 cm, followed by the 0–10 cm soil layer, and the highest value occured at the soil layer of 20–60 cm. The highest ammonium transport rate also appeared at the soil layer of 20–60 cm, while the lowest value was observed at the soil layer of 10–20 cm. Ammonium transport rates decreased with increasing distances along horizontal soil columns. The ammonium transport rates showed higher values at the distance from 0 to 6 cm and then decreased rapidly from 6 to 18 cm. However, they nearly kept constant and approached to zero after exceeding the distance of 18 cm. Ammonium transport rates increased exponentially with increasing volumetric water contents and water diffusion rates. The alkaline wetland soils prevented ammonium from horizontal diffusion at all soil layers under drying conditions. 相似文献
15.
Jack C. Parker 《Ground Water Monitoring & Remediation》2003,23(1):107-120
A model is presented for estimating vapor concentrations in buildings because of volatilization from soil contaminated by non- aqueous phase liquids (NAPL) or from dissolved contaminants in ground water. The model considers source depletion, diffusive- dispersive transport of the contaminant of concern (COC) and of oxygen and oxygen-limited COC biodecay. Diffusive-advective transport through foundations and vapor losses caused by foundation cross-flow are considered. Competitive oxygen use by various species is assumed to be proportional to the product of the average dissolved-phase species concentration and a biopreference factor. Laboratory and field data indicate the biopreference factor to be proportional to the organic carbon partition coefficient for the fuel hydrocarbons studied. Predicted indoor air concentrations were sensitive to soil type and subbase permeability. Lower concentrations were predicted for buildings with shallow foundations caused by flushing of contaminants by cross-flow. NAPL source depletion had a large impact on average exposure concentration. Barometric pumping had a minor effect on indoor air emissions for the conditions studied. Risk-based soil cleanup levels were much lower when biodecay was considered because of the existence of a threshold source concentration below which no emissions occur. Computed cleanup levels at NAPL-contaminated sites were strongly dependent on total petroleum hydrocarbon (TPH) content and COC soil concentration. The model was applied to two field sites with gasoline-contaminated ground water. Confidence limits of predicted indoor air concentrations spanned approximately two orders of magnitude considering uncertainty in model parameters. Measured contaminant concentrations in indoor air were within model-predicted confidence limits. 相似文献
16.
Barry J. Allred 《Ground Water Monitoring & Remediation》2012,32(2):81-95
Agricultural subsurface drainage waters containing nutrients (nitrate/phosphate) and pesticides are discharged into neighboring streams and lakes, frequently producing adverse environmental impacts on local, regional, and national scales. On‐site drainage water filter treatment systems can potentially prevent the release of agricultural contaminants into adjacent waterways. Zero valent iron (ZVI) and sulfur‐modified iron (SMI) are two types of promising filter materials that could be used within these treatment systems. Therefore, water treatment capabilities of three ZVI and three SMI filter materials were evaluated in the laboratory. Laboratory evaluation included saturated falling‐head hydraulic conductivity tests, contaminant removal batch tests, and saturated solute transport column experiments. The three ZVI and the three SMI filter materials, on average, all had a sufficient hydraulic conductivity greater than 1 × 10–3 cm/s. Batch test results showed a phosphate decrease of at least 94% for all tests conducted with the ZVI and SMI. Furthermore, the three SMI filter materials removed at least 86% of the batch test nitrate originally present, while batch tests for one of the ZVI filter materials exhibited an 88% decrease in the pesticide, atrazine. Saturated solute transport column experiments were carried on the best ZVI filter material, or the best SMI filter material, or both together, in order to better evaluate drainage water treatment effectiveness and efficiency. Results from these column tests additionally document the drainage water treatment ability of both ZVI and SMI to remove the phosphate, the ability of SMI to remove nitrate, and the ability of a select ZVI material to remove atrazine. Consequently, these findings support further investigation of ZVI and SMI subsurface drainage water treatment capabilities, particularly in regard to small‐ and large‐scale field tests. 相似文献
17.
The late tail of the breakthrough curve (BTC) of a conservative tracer in a regional-scale alluvial system is explored using Monte Carlo simulations. The ensemble numerical BTC, for an instantaneous point source injected into the mobile domain, has a heavy late tail transforming from power law to exponential due to a maximum thickness of clayey material. Haggerty et al.'s (2000) multiple-rate mass transfer (MRMT) method is used to predict the numerical late-time BTCs for solutes in the mobile phase. We use a simple analysis of the thicknesses of fine-grained units noted in boring logs to construct the memory function that describes the slow decline of concentrations at very late time. The good fit between the predictions and the numerical results indicates that the late-time BTC can be approximated by a summation of a small number of exponential functions, and its shape depends primarily on the thicknesses and the associated volume fractions of immobile water in "blocks" of fine-grained material. The prediction of the late-time BTC using the MRMT method relies on an estimate of the average advective residence time, t(ad). The predictions are not sensitive to estimation errors in t(ad), which can be approximated by L/v , where v is the arithmetic mean ground water velocity and L is the transport distance. This is the first example of deriving an analytical MRMT model from measured hydrofacies properties to predict the late-time BTC. The parsimonious model directly and quantitatively relates the observable subsurface heterogeneity to nonlocal transport parameters. 相似文献
18.
Occurrences of pharmaceutically active compounds in surface water and sewage water have been widely reported. Investigations show the presence of several classes of pharmaceuticals such as antirheumatics (e.g., diclofenac), analgesics (e.g., propyphenazone), and blood lipid regulators (clofibric acid), even in ground water. Compared to their occurrences in surface water, however, the reported incidences of drugs in ground water are much rarer. This may be due to the input, but also to transport processes and degradation in the aquifer. In field studies investigating ground water sampled at a bank infiltration site at Lake Tegel, Berlin, Germany, clofibric acid was found at concentrations up to 290 ng/L, and propyphenazone up to 250 ng/L, whereas concentrations of diclofenac were around the detection limit. The aim of this study was to investigate the ground water transport behavior of the pharmaceuticals clofibric acid, propyphenazone, and diclofenac with a laboratory soil column experiment. Results show that clofibric acid exhibits no degradation and almost no retardation (Rf = 1.1). Diclofenac (Rf = 2.0) and propyphenazone (Rf = 1.6) are retarded, whereas significant degradation was not observed for both pharmaceuticals under the prevailing conditions in the soil column. We conclude that the concentration distribution of the pharmaceuticals at the bank filtration site at Lake Tegel is controlled by sorption, desorption, and input variation, rather than by degradation. 相似文献
19.
The transport of bromide (Br) under matric heads of 0, ?2, ?5, and ?10 cm using undisturbed soil columns was investigated for understanding the solute transport in arid soils. Undisturbed soil cores were collected at ground surface, directly below where tension infiltrometer measurements were made in the Amargosa Desert, Nevada, United States. Laboratory experiments were conducted by introducing water containing Br tracer into a soil column maintained at steady‐state conditions. The observed data of breakthrough curves (BTC) were well fitted to an one‐region model, except for the cores at saturation, and a core at the matric head of ?5 cm, from which the observed data were better fitted to a two‐region model. Fitted pore water velocities with the one‐region model ranged from 1.2 to 56.6 cm/h, and fitted dispersion coefficients (D) ranged from 2.2 to 100 cm2/h. Results for the core analyzed with the two‐region model indicated that D ranged from 27.6 to 70.9 cm2/h at saturation, and 25.7 cm2/h at the matric head of ?5 cm; fraction of mobile water (β) ranged from 0.18 to 0.65, and mass transfer coefficient (ω) ranged from 0.006 to 0.03. In summary, the water fluxes and Br dispersion coefficients at investigated matric heads were very high due to the coarseness of the soils and possibly due to preferential flow pathways. These high water fluxes and Br dispersion coefficients would lead to a higher risk of deeper leaching accumulating nitrate nitrogen to the groundwater, and have significant effects on the desert ecosystem. 相似文献
20.
《水文科学杂志》2013,58(6)
Abstract Using the Monte Carlo (MC) method, this paper derives arithmetic and geometric means and associated variances of the net capillary drive parameter, G, that appears in the Parlange infiltration model, as a function of soil texture and antecedent soil moisture content. Approximate expressions for the arithmetic and geometric statistics of G are also obtained, which compare favourably with MC generated ones. This paper also applies the MC method to evaluate parameter sensitivity and predictive uncertainty of the distributed runoff and erosion model KINEROS2 in a small experimental watershed. The MC simulations of flow and sediment related variables show that those parameters which impart the greatest uncertainty to KINEROS2 model outputs are not necessarily the most sensitive ones. Soil hydraulic conductivity and wetting front net capillary drive, followed by initial effective relative saturation, dominated uncertainties of flow and sediment discharge model outputs at the watershed outlet. Model predictive uncertainty measured by the coefficient of variation decreased with rainfall intensity, thus implying improved model reliability for larger rainfall events. The antecedent relative saturation was the most sensitive parameter in all but the peak arrival times, followed by the overland plane roughness coefficient. Among the sediment related parameters, the median particle size and hydraulic erosion parameters dominated sediment model output uncertainty and sensitivity. Effect of rain splash erosion coefficient was negligible. Comparison of medians from MC simulations and simulations by direct substitution of average parameters with observed flow rates and sediment discharges indicates that KINEROS2 can be applied to ungauged watersheds and still produce runoff and sediment yield predictions within order of magnitude of accuracy. 相似文献