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1.
Monte Carlo simulations are conducted to evaluate microbial-mediated contaminant reactions in an aquifer comprised of spatially variable microbial biomass concentrations, aquifer hydraulic conductivities, and initial electron donor/acceptor concentrations. A finite element simulation model is used that incorporates advection, dispersion, and Monod kinetic expressions to describe biological processes. Comparisons between Monte Carlo simulations of heterogeneous systems and simulations using homogeneous formulation of the same two-dimensional transport problem are presented. For the assumed set of parameters, physical aquifer heterogeneity is found to have a minor effect on the mass of contaminant biodegraded/transformed when compared to a homogeneous system; however, it noticeably changes the dispersion, skewness, and peakness of contaminant concentration distributions. Similarly, for low microbial growth rate, given favorable microbial growth characteristics, biological heterogeneity has minor effect on the mass of contaminant biodegraded/transformed when compared to a homogeneous system. On the other hand, when higher effective growth rates are assumed, biological heterogeneity and spatial heterogeneities in essential electron donor/acceptors reduce the efficiency of biotic contaminant reactions; consequently, model simulations derived from heterogeneous biomass distributions predict remediation time scales that are longer than those simulated for homogeneous systems. When correlations between physical aquifer and biological heterogeneities are considered, the assumed correlation affects predicted mean and variance of contaminant concentration and biomass distributions. For example, an assumed negative correlation between hydraulic conductivity and the initial biomass distribution produces a plume where less efficient biotic contaminant reactions occur at the leading edge of the plume; this is consistent with less degradation/transformation occurring over regions of higher groundwater velocities. However, the presence and absence of these correlations do not appear to affect the efficiency of microbial-mediated contaminant attenuation. 相似文献
2.
A finite element 2D Monte Carlo approach is used to evaluate the sensitivity of groundwater contaminant discharges to a Damkohler number ω and spatial variability in aquifer hydraulic conductivity, initial microbial biomass concentrations, and electron acceptor/donor concentrations. Bioattenuation is most sensitive to spatial variations in incipient biomass and critical electron donors/acceptors for ω ≥ 1 (i.e., when pore-water residence times are high compared to the time needed for microbial growth or contaminant attenuation). Under these conditions, critical reaction processes can become substrate-limited at multiple locations throughout the aquifer; which in turn increases expected contaminant discharges and their uncertainties at monitored transects. For ω ≤ 0.2, contaminant discharge is not sensitive to incipient biomass variations. Physical heterogeneities expedite plume arrival and delay departure at transects and in turn attenuate peak discharges but do not affect cumulative contaminant discharges. Physical heterogeneities do, however, induce transect mass discharge variances that are bimodal functions of time; the first peak beings consistently higher. A simple stream tube model is invoked to explain the occurrence of peaks in contaminant discharge variance. 相似文献
3.
T. N. NARASIMHAN 《水文科学杂志》2013,58(1):70-83
ABSTRACT A Ratio Method is presented, which dispenses with the classical curve-matching procedure for computing characteristics of Ideal, Leaky and Bounded aquifers. This simple method consists of selecting any three values of observed drawdown, (t0, s0), (t1, s1) and (t2, S2), such that t1 = 2 t0 and t2 = 100 t0. Then, using the ratios, s0/s 1 and s0/s2, the values of u0, W(u0) as well as r/B (in the case of leaky aquifers) and ri (in the case of aquifers with one boundary) are extrapolated from the charts presented. The extrapolated values are substituted in the standard equations to determine the aquifer characteristics. The Ratio Method may also have useful application in other branches of science where the curve-matching procedure is employed for calculation of parameters. (Key Words: Ratio Method; Aquifer characteristics; Ideal aquifer; Leaky aquifer; Bounded aquifer) 相似文献
4.
Generalized inversion of the S-wave amplitude spectra from the strong-motion network data in the East-Central Iran has been used to estimate simultaneously source parameters, site response and the S-wave attenuation (Qs). In this regard, 190 three-component records were used corresponded to 40 earthquakes with the magnitudes M3.5–M7.3. These earthquakes were recorded at 42 stations in the hypocentral distance range from 9 to 200 km. The inverse problem was solved in 20 logarithmically equally spaced points in the frequency band from 0.4 to 15 Hz. The frequency-dependent site amplification was imposed, as a constraint, on two reference site responses in order to remove the undetermined degree of freedom in the inversion and obtain a unique inverse solution. Also, a geometrical spreading factor was assumed for removing the trade-off between geometrical spreading and anelastic attenuation. Different source parameters, such as seismic moment (M0), seismic energy (Es), corner frequency (fc) and Brune stress drop (Δσ), were estimated for each event by fitting an ω2 model to the spectra obtained from the inversion. The stress drop values of earthquakes, obtained in this research, are in good agreement with those of other studies. Also average site response values were correlated to the average shear wave velocities in the uppermost 30 m, in high and low frequency bands. The peak frequencies of site amplifications, estimated by the generalized inversion method, where in good agreement with those of horizontal to vertical (H/V) spectral ratios for the S-wave portion of records. However, no perfect matching in amplitude was obtained due to the deficiencies of the H/V ratio technique. By supposing a free shape for Q factor, a frequency dependent function was found, the logarithm of which could be approximated by a linear function, Q(f)=151f0.75. The uncertainties of model parameters have been evaluated by covariance matrix of least-square fit. The residuals were also analyzed in order to assess the validity of the model. The analysis of residuals with respect to magnitude and distance indicates that they are distributed normally with approximately zero mean. The robustness of the results has been studied concerning their sensitivities to the omission of different datasets, selected randomly from original database. The results obtained here can be used in predicting ground-motion parameters applying stochastic methods. 相似文献
5.
We compare two methods for determining the upscaled water characteristics and saturation-dependent anisotropy in unsaturated hydraulic conductivity from a field-scale injection test. In both approaches an effective medium approximation is used to reduce a porous medium of M textures to an equivalent homogenous medium. The first approach is a phenomenological approach based on homogenization and assumes that moisture-based Richards’ equation can be treated like the convective–dispersive equation (CDE). The gravity term, dKz(θ)/d(θ), analogous to the vertical convective velocity in the CDE, is determined from the temporal evolution of the plume centroid along the vertical coordinate allowing calculation of an upscaled Kz(θ). As with the dispersion tensor in the CDE, the rate of change of the second spatial moment in 3D space is used to calculate the water diffusivity tensor, D(θ), from which an upscaled K(θ) is calculated. The second approach uses the combined parameter scale inverse technique (CPSIT). Parameter scaling is used first to reduce the number of parameters to be estimated by a factor M. Upscaled parameters are then optimized by inverse modeling to produce an upscaled K(θ) characterized by a pore tortuosity–connectivity tensor, L. Parameters for individual textures are finally determined from the optimized parameters by inverse scaling using scale factors determined a priori. Both methods produced upscaled K(θ) that showed evidence of saturation dependent anisotropy. Flow predictions with the STOMP simulator, parameterized with upscaled parameters, were compared with field observations. Predictions based on the homogenization method were able to capture the mean plume behavior but could not reproduce the asymmetry caused by heterogeneity and lateral spreading. The CPSIT method captured the effects of heterogeneity and anisotropy and reduced the mean squared residual by nearly 90% compared to local-scale and upscaled parameters from the homogenization method. The Pacific Northwest National Laboratory is operated for the US Department of Energy by Battelle under Contract DE-AC05-76RL01830. 相似文献
6.
While tomographic inversion has been successfully applied to laboratory- and field-scale tests, here we address the new issue of scale that arises when extending the method to a basin. Specifically, we apply the hydraulic tomography (HT) concept to jointly interpret four multiwell aquifer tests in a synthetic basin to illustrate the superiority of this approach to a more traditional Theis analysis of the same tests. Transmissivity and storativity are estimated for each element of a regional numerical model using the geostatistically based sequential successive linear estimator (SSLE) inverse solution method. We find that HT inversion is an effective strategy for incorporating data from potentially disparate aquifer tests into a basin-wide aquifer property estimate. The robustness of the SSLE algorithm is investigated by considering the effects of noisy observations, changing the variance of the true aquifer parameters, and supplying incorrect initial and boundary conditions to the inverse model. Ground water flow velocities and total confined storage are used as metrics to compare true and estimated parameter fields; they quantify the effectiveness of HT and SSLE compared to a Theis solution methodology. We discuss alternative software that can be used for implementing tomography inversion. 相似文献
7.
This study proposes an inverse solution algorithm through which both the aquifer parameters and the zone structure of these parameters can be determined based on a given set of observations on piezometric heads. In the zone structure identification problem fuzzy c-means (FCM) clustering method is used. The association of the zone structure with the transmissivity distribution is accomplished through an optimization model. The meta-heuristic harmony search (HS) algorithm, which is conceptualized using the musical process of searching for a perfect state of harmony, is used as an optimization technique. The optimum parameter zone structure is identified based on three criteria which are the residual error, parameter uncertainty, and structure discrimination. A numerical example given in the literature is solved to demonstrate the performance of the proposed algorithm. Also, a sensitivity analysis is performed to test the performance of the HS algorithm for different sets of solution parameters. Results indicate that the proposed solution algorithm is an effective way in the simultaneous identification of aquifer parameters and their corresponding zone structures. 相似文献
8.
Aquifer Properties Determined from Two Analytical Solutions 总被引：3，自引：0，他引：3
In the analysis of pumping test data, the quality of the determined aquifer parameters can be greatly improved by using a proper model of the aquifer system. Moench (1995) provided an analytical solution for flow to a well partially penetrating an unconfined aquifer. His solution, in contrast to the Neuman solution (1974), accounts for the noninstantaneous decline of the water table (delayed yield). Consequently, the calculated drawdown in these two solutions is different under certain circumstances, and this difference may therefore affect the computation of aquifer properties from pumping test data. This paper uses an inverse computational method to calculate four aquifer parameters as well as a delayed yield parameter, α1 from pumping test data using both the Neuman (1974) and Moench (1995) solutions. Time-drawdown data sets from a pumping test in an unconfined alluvial aquifer near Grand Island, Nebraska, were analyzed. In single-well analyses, horizontal hydraulic conductivity values derived from the Moench solution are lower, but vertical hydraulic conductivity values are higher than those calculated from the Neuman solution. However, the hydraulic conductivity values in composite-well analyses from both solutions become very close. Furthermore, the Neuman solution produces similar hydraulic conductivity values in the single-well and composite-well analyses, but the Moench solution does not. While variable α1, seems to play a role in affecting the computation of aquifer parameters in the single-well analysis, a much smaller effect was observed in the composite-well analysis. In general, specific yield determined using the Moench solution could be slightly higher than the values from the Neuman solution; however, they are still lower than the realistic values for sand and gravel aquifers. 相似文献
9.
Paul M. Bradley 《Ground Water Monitoring & Remediation》2011,31(4):50-55
Chlororespiration is common in shallow aquifer systems under conditions nominally identified as anoxic. Consequently, chlororespiration is a key component of remediation at many chloroethene‐contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products is interpreted as evidence that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene‐contaminated shallow aquifer systems, however, nonconservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms and is consistent with contaminant degradation to nondiagnostic mineralization products like CO2. While anoxic mineralization of chloroethene compounds has been proposed previously, recent results suggest that oxygen‐based mineralization of chloroethenes also can be significant at dissolved oxygen concentrations below the currently accepted field standard for nominally anoxic conditions. Thus, reassessment of the role and potential importance of low concentrations of oxygen in chloroethene biodegradation are needed, because mischaracterization of operant biodegradation processes can lead to expensive and ineffective remedial actions. A modified interpretive framework is provided for assessing the potential for chloroethene biodegradation under different redox conditions and the probable role of oxygen in chloroethene biodegradation. 相似文献
10.
The attenuation characteristics of the Kinnaur area of the North West Himalayas were studied using local earthquakes that occurred during 2008–2009. Most of the analyzed events are from the vicinity of the Panjal Thrust (PT) and South Tibetan Detachment Thrust, which are well-defined tectonic discontinuities in the Himalayas. The frequency-dependent attenuation of P and S waves was estimated using the extended coda normalization method. Data from 64 local earthquakes recorded at 10 broadband stations were used. The coda normalization of the spectral amplitudes of P and S waves was done at central frequencies of 1.5, 3, 6, 9, and 12 Hz. Q p increases from about 58 at 1.5 Hz to 706 at 12 Hz, and Q s increases from 105 at 1.5 Hz to 1,207 at 12 Hz. The results show that the quality factors for both P and S waves (Q p and Q s) increase as a function of frequency according to the relation Q?=?Q o f n , where Q o is the corresponding Q value at 1 Hz frequency and “n” is the frequency relation parameter. We obtained Q p?=?(47?±?2)f (1.04±0.04) and Q s?=?(86?±?4)f (0.96±0.03) by fitting power law dependency model for the estimated values of the entire study region. The Q 0 and n values show that the region is seismically very active and the crust is highly heterogeneous. There was no systematic variation of values of Q p and Q s at different frequencies from one tectonic unit to another. As a consequence, average values of these parameters were obtained for each frequency for the entire region, and these were used for interpretation and for comparison with worldwide data. Q p values lie within the range of values observed for some tectonically active regions of the world, whereas Q s values were the lowest among the values compared for different parts of the world. Q s/Q p values were >1 for the entire range of frequencies studied. All these factors indicate that the crust is highly heterogeneous in the study region. The high Q s/Q p values also indicate that the region is partially saturated with fluids. 相似文献
11.
An inverse method is developed to simultaneously estimate multiple hydraulic conductivities, source/sink strengths, and boundary conditions, for two-dimensional confined and unconfined aquifers under non-pumping or pumping conditions. The method incorporates noisy observed data (hydraulic heads, groundwater fluxes, or well rates) at measurement locations. With a set of hybrid formulations, given sufficient measurement data, the method yields well-posed systems of equations that can be solved efficiently via nonlinear optimization. The solution is stable when measurement errors are increased. The method is successfully tested on problems with regular and irregular geometries, different heterogeneity patterns and variances (maximum Kmax/Kmin tested is 10,000), and error magnitudes. Under non-pumping conditions, when error-free observed data are used, the estimated conductivities and recharge rates are accurate within 8% of the true values. When data contain increasing errors, the estimated parameters become less accurate, as expected. For problems where the underlying parameter variation is unknown, equivalent conductivities and average recharge rates can be estimated. Under pumping (and/or injection) conditions, a hybrid formulation is developed to address these local source/sink effects, while different types of boundary conditions can also exert significant influences on drawdowns. Local grid refinement near wells is not needed to obtain accurate results, thus inversion is successful with coarse inverse grids, leading to high computation efficiency. Furthermore, flux measurements are not needed for the inversion to succeed; data requirement of the method is thus not much different from that of interpreting classic well tests. Finally, inversion accuracy is not sensitive to the degree of nonlinearity of the flow equations. Performance of the inverse method for confined and unconfined aquifer problems is similar in terms of the accuracy of the estimated parameters, the recovered head fields, and the solver speed. 相似文献
12.
A. Ugalde L. G. Pujades J. A. Canas A. Villaseñor 《Pure and Applied Geophysics》1998,153(2-4):685-702
—Northeastern Venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short-period seismic network. The studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters. Coda-Q ?1 (Q c ?1) has been obtained using the single-scattering theory. The contribution of the intrinsic absorption (Q i ?1) and scattering (Q s ?1) to total attenuation (Q t ?1) has been estimated by means of a multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Results show significant spatial variations of attenuation the estimates for intermediate depth events and for shallow events present major differences. This fact may be related to different tectonic characteristics that may be due to the presence of the Lesser Antilles subduction zone, because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc. 相似文献
13.
The results of solving the inverse problem of forced nutations and free oscillations of the Earth by decomposing the Q-factor and small depth variations in density in a system of orthogonal functions are considered. These functions are determined by orthogonalization of the functional derivatives of the observed parameters with respect to the depth distributions of the sought parameters (assuming there are no distributions of the velocities of body seismic waves V p and V S with depth and unchanged total mass M and inertia moments I of the Earth). The examples are presented to illustrate the numerical solution of the inverse problem on finding the density distributions in the mantle and core of the Earth using orthogonalization of the integral constraints for the probable depth distributions of density describing the conditions of unchanged M and I, as well as the constraints posed by the data on the periods of the free low-order oscillations of the Earth. 相似文献
14.
Walter A. Illman 《Ground water》2014,52(5):659-684
Fractured rocks have presented formidable challenges for accurately predicting groundwater flow and contaminant transport. This is mainly due to our difficulty in mapping the fracture‐rock matrix system, their hydraulic properties and connectivity at resolutions that are meaningful for groundwater modeling. Over the last several decades, considerable effort has gone into creating maps of subsurface heterogeneity in hydraulic conductivity (K) and specific storage (Ss) of fractured rocks. Developed methods include kriging, stochastic simulation, stochastic inverse modeling, and hydraulic tomography. In this article, I review the evolution of various heterogeneity mapping approaches and contend that hydraulic tomography, a recently developed aquifer characterization technique for unconsolidated deposits, is also a promising approach in yielding robust maps (or tomograms) of K and Ss heterogeneity for fractured rocks. While hydraulic tomography has recently been shown to be a robust technique, the resolution of the K and Ss tomograms mainly depends on the density of pumping and monitoring locations and the quality of data. The resolution will be improved through the development of new devices for higher density monitoring of pressure responses at discrete intervals in boreholes and potentially through the integration of other data from single‐hole tests, borehole flowmeter profiling, and tracer tests. Other data from temperature and geophysical surveys as well as geological investigations may improve the accuracy of the maps, but more research is needed. Technological advances will undoubtedly lead to more accurate maps. However, more effort should go into evaluating these maps so that one can gain more confidence in their reliability. 相似文献
15.
Igor B. Morozov 《Pure and Applied Geophysics》2010,167(10):1131-1146
Variability of the Earth’s structure makes a first-order impact on attenuation measurements which often does not receive adequate attention. Geometrical spreading (GS) can be used as a simple measure of the effects of such structure. The traditional simplified GS compensation is insufficiently accurate for attenuation measurements, and the residual GS appears as biases in both Q 0 and η parameters in the frequency-dependent attenuation law Q(f) = Q 0 f η . A new interpretation approach bypassing Q(f) and using the attenuation coefficient χ(f) = γ + πf/Q e(f) resolves this problem by directly measuring the residual GS, denoted γ, and effective attenuation, Q e. The approach is illustrated by re-interpreting several published datasets, including nuclear-explosion and local-earthquake codas, Pn, and synthetic 50–300-s surface waves. Some of these examples were key to establishing the Q(f) concept. In all examples considered, χ(f) shows a linear dependence on the frequency, γ ≠ 0, and Q e can be considered frequency-independent. Short-period crustal body waves are characterized by positive γ SP values of (0.6–2.0) × 10?2 s?1 interpreted as related to the downward upper-crustal reflectivity. Long-period surface waves show negative γ LP ≈ ?1.9 × 10?5 s?1, which could be caused by insufficient modeling accuracy at long periods. The above γ values also provide a simple explanation for the absorption band observed within the Earth. The band is interpreted as apparent and formed by levels of Q e ≈ 1,100 within the crust decreasing to Q e ≈ 120 within the uppermost mantle, with frequencies of its flanks corresponding to γ LP and γ SP. Therefore, the observed absorption band could be purely geometrical in nature, and relaxation or scattering models may not be necessary for explaining the observed apparent Q(f). Linearity of the attenuation coefficient suggests that at all periods, the attenuation of both Rayleigh and Love waves should be principally accumulated at the sub-crustal depths (~38–100 km). 相似文献
16.
The attenuation of P- and S-waves in Southeastern Sicily was estimated by applying two different methods in time and frequency domains. We analyzed waveforms from about 290 local events (0.6≤ML≤4.6) recorded at a three-component digital network.By applying the pulse broadening method to the first P-wave pulse, we found an average Qp value of ca. 140. The application of the frequency decay method provided a Qp value of ca. 120, in the low-frequency band (3-9 Hz). Conversely, in the high frequency range (16-27 Hz) the average Qp is significantly larger (ca. 640). The frequency decay method was also applied to S-waves spectra. In the low frequency range (2-5 Hz) the estimated average Qs is ca. 190. As for Qp, also Qs, in the high frequency range (16-27 Hz), is larger (ca. 700). These results evidenced a frequency dependence of both the quality factors Qp and Qs, as commonly observed in tectonically active zones characterized by high degree of heterogeneity. 相似文献
17.
An Electron-Balance Based Approach to Predict the Decreasing Denitrification Potential of an Aquifer
Numerical models for reactive transport can be used to estimate the breakthrough of a contaminant in a pumping well or at other receptors. However, as natural aquifers are highly heterogeneous with unknown spatial details, reactive transport predictions on the aquifer scale require a stochastic framework for uncertainty analysis. The high computational demand of spatially explicit reactive-transport models hampers such analysis, thus motivating the search for simplified estimation tools. We suggest performing an electron balance between the reactants in the infiltrating solution and in the aquifer matrix to obtain the hypothetical time of dissolved-reactant breakthrough at a receptor if the reaction with the matrix was instantaneous. This time we denote as the advective breakthrough time for instantaneous reaction (τinst ). It depends on the amount of the reaction partner present in the matrix, the mass flux of the dissolved reactant, and the stoichiometry. While the shape of the reactive-species breakthrough curve depends on various kinetic parameters, the overall timing scales with τinst . We calculate the latter by particle tracking. The effort of computing τinst is so low that stochastic calculations become feasible. We apply the concept to a two-dimensional test case of aerobic respiration and denitrification. A detailed spatially explicit reactive-transport model includes microbial dynamics. Scaling the time of local breakthrough curves observed at individual points by τinst decreased the variability of electron-donor breakthrough curves significantly. We conclude that the advective breakthrough time for instantaneous reaction is efficient in estimating the time over which an aquifer retains its degradation potential. 相似文献
18.
《Advances in water resources》1998,22(3):273-284
A series of multi-step outflow experiments was carried out to identify the unsaturated hydraulic properties of two homogeneous coarse-textured porous media (glass beads and sand). Because of the measured sharp fronts of water content decrease during these experiments the hydraulic functions are assumed to be represented by the complete van Genuchten–Mualem closed-form expressions with variable coefficients α, n, m and θr. The values of θs and Ks were measured directly. A sensitivity analysis with respect to α, n, and m shows that conditions of local identifiability are satisfied if measurements of water content at some inner points inside the column are considered. The inverse modelling technique consists of two steps: first, computation of objective function values based on water content data responses to obtain initial parameter estimations, and second, a more detailed parameter determination using a Levenberg–Marquardt scheme. In both steps a numerical model incorporating the hydraulic functions is utilized to simulate theoretical pressure head and water content distributions along the column. For both porous media unique solutions of the inverse problem could be obtained, and afterwards, the corresponding hydraulic functions were verified from additional drainage experiments.©1998 Elsevier Science Limited. All rights reserved 相似文献
19.
Z. J. Kabala H. K. El-Sayegh H. P. Gavin 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(6):399-424
Logarithmic sensitivities and plausible relative errors are studied in a simple no-crossflow model of a transient flowmeter
test (TFMT). This model is identical to the model of a constant-rate pumping test conducted on a fully penetrating well with
wellbore storage, surrounded by a thick skin zone, and situated in a homogeneous confined aquifer. The sensitivities of wellbore
drawdown and wellface flowrate to aquifer and skin parameters are independent of the pumping rate. However, the plausible
relative errors in the aquifer and skin parameters estimated from drawdown and wellface flowrate data can be proportionally
decreased by increasing the pumping rate. The plausible relative errors vary by many orders of magnitude from the beginning
of the TFMT. The practically important flowrate and drawdown measurements in this test, for which the plausible relative errors
vary by less than one order of magnitude from the minimum plausible relative errors, can begin approximately when the dimensionless
wellface flowrate exceeds q
D
=q/Q≈0.4. During most of this stage of the test, the plausible relative errors in aquifer hydraulic conductivity (K
a
) are generally an order of magnitude smaller than those in aquifer specific storativity. The plausible relative errors in
the skin hydraulic conductivity (K
s
) are generally larger than the plausible relative errors in the aquifer specific storativity when the thick skin is normal
(K
s
>K
a
) and smaller when the thick skin is damaged (K
s
<K
a
). The specific storativity of the skin zone would be so biased that one should not even attempt to estimate it from the TFMT.
We acknowledge Wiebe H. van der Molen for recommending the De Hoog algorithm and sharing his code. This research was partially
supported by the US Geological Survey, USGS Agreement #1434-HQ-96-GR-02689 and North Carolina Water Resources Research Institute,
WRRI Project #70165. 相似文献
20.
《Advances in water resources》2007,30(6-7):1571-1582
It has been widely observed in field experiments that the apparent rate of bacterial attachment, particularly as parameterized by the collision efficiency in filtration-based models, decreases with transport distance (i.e., exhibits scale-dependency). This effect has previously been attributed to microbial heterogeneity; that is, variability in cell–surface properties within a single monoclonal population. We demonstrate that this effect could also be interpreted as a field-scale manifestation of local-scale correlation between physical heterogeneity (hydraulic conductivity variability) and reaction heterogeneity (attachment rate coefficient variability). A field-scale model of bacterial transport developed for the South Oyster field research site located near Oyster, Virginia, and observations from field experiments performed at that site, are used as the basis for this study. Three-dimensional Monte Carlo simulations of bacterial transport were performed under four alternative scenarios: (1) homogeneous hydraulic conductivity (K) and attachment rate coefficient (Kf); (2) heterogeneous K, homogeneous Kf; (3) heterogeneous K and Kf with local correlation based on empirical and theoretical relationships; and (4) heterogeneous K and Kf without local correlation. The results of the 3D simulations were analyzed using 1D model approximations following conventional methods of field data analysis. An apparent decrease with transport distance of effective collision efficiency was observed only in the case where the local properties were both heterogeneous and correlated. This effect was observed despite the fact that the local collision efficiency was specified as a constant in the 3D model, and can therefore be interpreted as a scale effect associated with the local correlated heterogeneity as manifested at the field scale. 相似文献