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1.
The active region model (ARM) has been developed as a practical and effective approach for characterizing and representing
preferential flow patterns in unsaturated soils. However, studies on methods to determine the ARM parameter (γ) are very limited. The major objective of this work was to refine the methods for determining the ARM parameter (γ) using the data from field-scale dye staining experiments. For this purpose, 13 field-scale dye staining experiments were
conducted in silty clay, loam and sand with various initial and boundary conditions. The distributions of soil water content
and fraction of stained region were measured to determine the ARM parameter (γ). Three determination methods of ARM parameter (γ) were presented according to the different distribution patterns of the soil water content of stained region. The efficiency
of these approaches was demonstrated with the results from 13 field-scale dye staining tests that were directly related to
preferential flow patterns. Impacts of soil texture on soil water redistribution, and effects of initial soil water content
and infiltration amount on the preferential flow heterogeneity were also discussed in this research. 相似文献
2.
The application of road salts as deicing agents contributes to the anthropogenic loading of chloride (Cl−) on the environment. Using a 2D solute model, the potential of the unsaturated zone to serve as a reservoir and the mechanisms
controlling the movement of Cl− were examined. Physical properties and initial pore-water Cl− concentrations were derived from an array of soil borings. Initial pore-water concentrations show the presence of a Cl− “slug” approximately 0.75 m below the surface. Simulations show that within the unsaturated zone, Cl− transport is predominantly vertical, driven by molecular diffusion. After a 1-year simulation, a Cl− slug similar to the background observation was noted. While Cl− is retained in the unsaturated zone, a net loss of Cl− from the unsaturated zone was simulated for the first 10 years. In year 11, an equilibrium between the Cl− input and output is achieved. The presence of Cl− in the unsaturated zone becomes a long-term source of chloride to the groundwater, which eventually discharges into the surface
water. Historically, surface water chemistry data support the continual discharge of chloride to the surface water in the
area, further supporting the hypothesis that the unsaturated zone serves as a Cl− reservoir. 相似文献
3.
S. A. Mirbagheri S. A. Hashemi Monfared H. R. Kazemi 《Environmental Earth Sciences》2009,59(2):287-296
A one-dimensional mathematical model based on convection–dispersion equation in unsaturated porous media is presented to compute
inorganic total solid concentration in the soil column under the Shiraz landfill. In addition, a dynamic mathematical model
is formulated to simulate concentrations of ions such as Ca2+
, Mg2+, Fe2+, K+, Na+, Cl−, SO4
2− and HCO3
− as well as PH and EC in soil profile under the Shiraz landfill. Leachw model was applied to simulate water flow, water content
and hydraulic conductivity in soil depth. The model was calibrated and verified by using different sets of data collected
from several segments of soil depth in the study area. The numerical solution obtained using finite element method. The simulated
values for the parameters were compared with measured values as well as analytical solution. The simulated results are in
good agreement with measured values. This model could be applied to field scale problems for the landfill management. 相似文献
4.
Comparison of numerical simulation of solute transport with observed experimental data in a silt loam subsoil 总被引：1，自引：0，他引：1
Solute transport experiments were conducted on loamy soils of north-eastern Iowa, USA, and the results were compared with
a numerical solution of a classical advection-dispersion transport model developed in this study. Flow experiments in the
laboratory on undisturbed soil columns showed a flow rate of water much higher than was estimated from the soil properties
and grain-size analysis data, suggesting preferential flow regime in the soil. In contrast, the relative concentration peaks
of Cl– and Br– in the effluent were only approximately 70% of those predicted by the classical advection-dispersion equation (ADE). In addition,
the experimental breakthrough curves (BTCs) showed greater tailings of these ions than the model solution. These observations
suggest a loss of solute mass during transport from the dynamic flowing regions to a stagnant, immobile water phase in the
soil matrix. Experiments in small disturbed soil columns showed that movement of Cl– and Br– is in good agreement with predictions of the classical ADE when the tracers are applied as a continuous source. However,
in the case of a pulse source, the BTCs of Cl– and Br– matched the model only in the ascending part of the curves. Such variation indicates greater retardation of these ions than
that of simulation, probably caused by the decrease in soil permeability due to cation exchange reactions in the soil involving
monovalent and divalent cation pairs such as K+–Ca2+ and K+–Mg2+. In addition, retardation occurred as a result of the continuous saturation of soil columns which seemed to have caused an
expansion of clay minerals, thus resulting in decreased soil permeability. In both the continuous and the pulse-source experiments,
K+ was not detected in the effluent samples, which seemed to have been lost in exchange reactions and adsorption.
Received: 20 November 1998 · Accepted: 19 July 1999 相似文献
5.
6.
土壤中优势流的几个基本问题研究 总被引：4，自引：0，他引：4
优势流是指土壤在整个入流边界上接受补给,但只通过少部分土体的快速运移,优势流是一种普遍存在的现象,而不是一种特例,它受许多因素的控制,如土壤中的大空隙,土壤结构,土壤质地,土壤水分含量,土壤初始水分含量,水和溶质的施加速率及溶质的施加方法等,优势流的产生机理主要有两种,一种是由土壤介质的非均质所驱动的优势流;另一种是湿润锋的不稳定性所驱动的优势流,目前优势流的监测方法主要取土壤原状土,实验室内的土 相似文献
7.
Eva Pacioni Marco Petitta Ezio Burri Maria Fanelli Piero Mazzeo Fabrizio Ruggieri 《Environmental Earth Sciences》2010,61(1):201-216
This paper analyses flow and transport of pesticides from the unsaturated zone to groundwater so as to predict concentration
of those contaminants in the Fucino Plain’s groundwater, by site investigations and numerical simulations. Pesticides were
detected in surface water (peaks of 13 μg L−1) and groundwater (peaks of 0.37 μg L−1). Modelling tools made it possible to identify that pattern of precipitation, organic matter content, and root thickness
are the key factors involved in vertical seepage of pesticides. Numerical simulations indicated that a significant fraction
of contaminants is leached from the most surficial soil layers through runoff, while only a secondary fraction is mobilised
towards groundwater. Likelihood of contaminating deep groundwater is fairly low, whereas surface waters show higher susceptibility.
Results of the proposed conceptual hydrogeological model show that pesticides are more likely to be entrained by mixing of
stream water with shallow groundwater in periods of high water exploitation from shallow wells. 相似文献
8.
Displacement studies on leaching of potassium (K+) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and
25 cm long). Pulses of K+ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl2) at a rate of 18 mm h−1. The movement of K+ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM
CaCl2. The Ca2+ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K+ was displaced with the distilled water, K+ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow
and lack of K+ sorption. The application of gypsum and CaCl2 in the reclamation of sodic soils would be expected to leach K+ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca2+ concentration can also lead to leaching of K+ from soil. Average effluent concentration of K+ during leaching period was 30.2 and 28.6 mg l−1 for the gypsum and CaCl2 treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation
(12 mg K+ l−1). 相似文献
9.
10.
地球化学作用是影响岩土类多孔介质中流体流动、传质、传热的重要因素之一。基于Fredlund所提出的非饱和土四相理论,将地球化学作用所产生的溶解/沉淀视为一个独立相,在一定的假设基础上,利用溶质浓度对介质孔隙度、含水率进行修正,从而建立起传质过程与介质水力性质之间的关系,改进了传统模型中传质过程与流体密度、黏度之间单一的耦合关系;并以此为基础建立了考虑地球化学作用下饱和-非饱和介质中多组分、多相流体渗流场-浓度场-温度场耦合的数学模型。通过在实验室内对反应性煤矸石进行渗透实验的结果对笔者所建模型进行了验证,结果表明：综合考虑溶解作用时所测点处渗流速度与未考虑耦合作用的结果相比增大0.58倍;单独考虑溶解/沉淀相时,所测点处渗流速度与未考虑密度耦合作用时的结果相比增大0.44倍。水流的实际渗透速度与在使用考虑溶解/沉淀相计算模型时的结果吻合较好。 相似文献
11.
Environmental geochemistry and quality assessment of surface and subsurface water of Mahi River basin, western India 总被引：4，自引：3，他引：1
The hydrogeochemical study of surface and subsurface water of Mahi River basin was undertaken to assess the major ion chemistry,
solute acquisition processes and water quality in relation to domestic and irrigation uses. The analytical results show the
mildly acidic to alkaline nature of water and dominance of Na+ and Ca2+ in cationic and HCO3
− and Cl− in anionic composition. In general, alkaline-earth elements (Ca2+ + Mg2+) exceed alkalis (Na+ + K+) and weak acids (HCO3
−) dominate over strong acids (SO4
2+ + Cl−) in majority of the surface and groundwater samples. Ca2+–Mg2+–HCO3
− is the dominant hydrochemical facies both in surface and groundwater of the area. The weathering of rock-forming minerals
mainly controlled the solute acquisition process with secondary contribution from marine and anthropogenic sources. The higher
concentration of sodium and dissolved silica, high equivalent ratios of (Na+ + K+/TZ+), (Na+ + K+/Cl−) and low ratio of (Ca2+ + Mg2+)/(Na+ + K+) suggest that the chemical composition of the water is largely controlled by silicate weathering with limited contribution
from carbonate weathering and marine and anthropogenic sources. Kaolinite is the possible mineral that is in equilibrium with
the water, implying that the chemistry of river water favors kaolinite formation. Assessment of water samples for drinking
purposes suggests that the majority of the water samples are suitable for drinking. At some sites concentrations of TDS, TH,
F−, NO3
− and Fe are exceeding the desirable limit of drinking. However, these parameters are well within the maximum permissible limit
except for some cases. To assess the suitability for irrigation, parameters like SAR, RSC and %Na were calculated. In general,
both surface and groundwater is of good to suitable category for irrigation uses except at some sites where high values of
salinity, %Na and RSC restrict its uses. 相似文献
12.
Suspended sediment concentration is a major variable influencing soil erosion and loss, study on which at different spatial
scales is of great meaning to understand soil erosion mechanism and sediment transport process. Based on data from 4 sloping
surfaces and 7 basins ranging from 0.0003 to 187 km2 in area, the suspended sediment concentration in flood season (SSC) with drainage area is studied. With increasing drainage
area on the slope surfaces, the mean suspended sediment concentration in flood season (MSSC) enhances continuously until a
peak value of 685 kg m−3 occurs at the whole slope surface No. 7 runoff plot resulting from harder and harder erosion forms downslope. Entering basin
systems, the diluted action of subsurface water on the toeslope on MSSC and small water flow power Ω make a minimum MSSC value
of 568 kg m−3 occur in the first-order basin system Tuanshangou basin at an area of 0.18 km2, and then from Tuanshangou basin to larger basins, the positive feedback function among drainage density, water flow energy,
and hyperconcentrated flow as well as its reduction of settling velocity of coarser particles generates continuously increasing
MSSC with drainage area. 相似文献
13.
Effects of entrapped residual air bubbles on tracer transport in heterogeneous soil: Magnetic resonance imaging study 总被引：1，自引：0，他引：1
Vladimira Jelinkova Michal SnehotaAndreas Pohlmeier Dagmar van DusschotenMilena Cislerova 《Organic Geochemistry》2011,42(8):991-998
Magnetic resonance imaging (MRI) was used to study the process of infiltration and solute transport in an undisturbed soil sample of coarse sandy loam. The sample was subjected to the recurrent ponded infiltration (RPI) experiment, which was carried out in order to assess the changes in the entrapped air volume and its impact on steady state flow rates and solute breakthrough. The main stages of the first and second experimental RPI runs were monitored using an MRI sequence that follows both water density and magnetic relaxation. In a steady state stage of each experimental run a nickel nitrate pulse was injected in order to visualize the solute breakthrough. Effluent from the sample was collected for chemical analysis and a breakthrough curve of the nickel was constructed. To obtain information about the soil structure and to reveal potential preferential pathways, the soil sample was scanned using computed tomography. The local nickel ion transport breakthrough was evaluated from MR images in a series of local observation points distributed along the selected preferential pathways.The preferential flow instability phenomenon with the emphasis on air bubble formation was shown by detecting a 60% decrease of the steady state infiltration rate. The detailed analyses of MRI measurements at observation points revealed air bubble formation, producing a flow rate decrease accompanied by redirection of nickel ion transport trajectories. By analyzing M0 maps it was found that the volumetric water content decrease was 2.2%. 相似文献
14.
B. Trček 《Environmental Geology》2008,55(2):269-276
The role of the unsaturated zone in the karst aquifer hydraulic behaviour was brought into focus in these studies of the catchment
of the Hubelj spring (SW Slovenia). The variations of natural tracers in precipitation and in groundwater during a summer
storm event made it possible to trace local flow and solute transport in the observed aquifer. The results produced data on
the aquifer recharge, storage and discharge processes, as well as on mechanisms that affected them, which reflects a karst
groundwater dynamics also at a regional scale. They point out the significance of effects of the fast preferential flow—epiflow
that is the main factor controlling solute/contaminant transport towards the aquifer saturated zone. Numerous arguments indicate
that the karst aquifer flow and solute transport mechanisms depend on the hydraulic behaviour of the epikarst zone. 相似文献
15.
16.
Samuel Boateng 《Hydrogeology Journal》2001,9(6):543-554
A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils.
The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability
distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables
are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are
used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along
the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content,
van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to
the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant
uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet
clay loam. Saturated water content is most significant for the dry clay loam.
Electronic Publication 相似文献
17.
In this paper, a simple scenario and probabilistic approach is used to assess the potential groundwater risk due to proposed
overdraft remedial actions in cone of depression, Jining City, China. Focusing on the concentrations of Chloride ions (Cl−) and total hardness (TH), the impact of artificial recharge and reduced pumping on groundwater quality and quantity is analysed
by using the three-dimensional finite difference groundwater flow and transport model, Visual MODFLOW, to simulate groundwater
flow and transport within the study area based on scenarios, and utilizes SURFER software to map risk levels. Although 5,
10 or 15% reduced pumping with artificial recharge leads to more decrease in Cl− and TH concentrations than the 25%, less volume increase is achieved for the remediation of land subsidence and other environmental
problems in the cone of depression. The Cl− concentrations in recovered groundwater are within the desired concentration of 200 mg/l; however, TH in some cases are above
the maximum permissible limit of 500 mg/l, with an exceedence probability of about 0.67 for recharge and recharge with reduced
pumping at 25%. The presence of fractures and hydrogeological complexity greatly determines impacts of remediation, and the
22% reduced pumping with artificial recharge offers an optimum strategy for overdraft remediation in the Jining cone of depression. 相似文献
18.
A Fully Coupled Chemo-Poroelastic Analysis of Pore Pressure and Stress Distribution around a Wellbore in Water Active Rocks 总被引：1，自引：0，他引：1
Water active rocks consist of minerals that hold water in their crystalline structure and in pore spaces. Free water from
drilling fluid can be attracted by the formation depending on the potential differences between pore space and drilling fluid.
The fluid movement into the formation or out of the formation can lead to a change in effective stress, thus causing wellbore
failures. In all previous studies it is found that the solute transport from or to the formation is primarily controlled by
diffusion process and the effect of advection on solute transfer is negligible for a range of very low permeable shale formations
(>10−5 mD). In this study a range of permeable shale formations (10−5 to 10−3 mD) commonly encountered in drilling oil and gas wells are considered to investigate the solute transfer between drilling
fluid and formation due to advection. For this purpose a finite element model of fully coupled chemo-hydro-mechanical processes
was developed. Results of this study revealed that the solute transfer between the drilling fluid and the shale formation
is controlled primarily by permeability of the shale formations. For the range of shale formations studied here, there exists
a threshold permeability below which the solute transfer is dominated by diffusion process and above which by fluid in motion
(fluid flow). Results from the numerical experiments have shown that when the permeability of shales is greater than this
threshold permeability, the chemical potential gradient between the pore fluid and drilling fluid reaches equilibrium faster
than that when the permeability of shales is below this threshold value. Also it has been found that when advection is taken
into account, effective radial and tangential stresses decrease around the wellbore, particularly near the wellbore wall where
the solute concentration has reached near equilibrium. 相似文献
19.
Vincent Cloutier René Lefebvre Martine M. Savard René Therrien 《Environmental Earth Sciences》2010,59(5):977-994
The objective of this study was to identify geochemical processes and Quaternary geological events responsible for the variations
in groundwater geochemistry observed in a sedimentary rock aquifer system, including brackish to saline groundwater. Inorganic
constituents and environmental isotopes were analyzed for 146 groundwater samples. Dissolution of carbonates dominates in
recharge areas, resulting in Ca-, Mg-HCO3 groundwater. Further along flow paths, under confined conditions, Ca2+–Na+ ion exchange causes groundwater evolution to Na-HCO3 type. Na-Cl groundwater is also found and it falls on a seawater mixing line. Using conservative tracers, Cl− and Br−, the original Champlain Sea water is shown to have been, in the region, a mixture of about 34% seawater and 66% freshwater,
a composition still retained by some groundwater. Na-Cl groundwater thus results from mixing with former Champlain Sea water
and also from solute diffusion from overlying marine clay. The system is thus found to be at different stages of desalinization,
from the original Champlain Sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions
in parts, where more flow occurs, especially in recharge zones. The geochemical processes are integrated within the hydrogeological
context to produce a conceptual geochemical evolution model for groundwater of the aquifer system. 相似文献
20.
Environmental research of groundwater in the urban and suburban areas of Attica region,Greece 总被引：4，自引：0，他引：4
G. D. Bathrellos H. D. Skilodimou A. Kelepertsis D. Alexakis I. Chrisanthaki D. Archonti 《Environmental Geology》2008,56(1):11-18
In this study, 92 groundwater samples were collected from the Attica region (Greece). Moreover, geographical information system
database, geochemistry of groundwater samples and statistics were applied. These were used for studying the chemical parameters
(NO3
−, Mg2+, Ca2+, Cl−, and Na+) and conductivity spatial distribution and for assessing their environmental impact. The ranges of chemical parameters of
the water samples (in mg L−1) are: NO3
− 1–306, Mg2+ 2–293, Ca2+ 3–453, Cl− 5–1,988, and Na+ 4–475. The elevated concentrations of sodium, Mg2+, Cl− are attributed to natural contamination (seawater intrusion). On the other hand, NO3
− elevated concentrations are attributed to anthropogenic contamination (nitrate fertilizers). The results of the GIS analysis
showed that elevated values of Na+, Mg2+, Cl− are related to shrubby and sparsely vegetated areas, while elevated values of NO3
− are connected with urban and agricultural areas. 相似文献