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Tesi sul tema "Groundwater Mathematical models"
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1
MORANDA, ARIANNA. "Mathematical models for reactive contaminants in groundwater". Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/930210.
Testo completoAbstract (sommario):
Abstract
The mass transport of contaminants in porous media is of great importance both in the field of research and in the applied field.
Today's respect for the environment and the safeguarding of resources has greatly increased the need to monitor and prevent environmental pollution.
Of great importance are the mathematical models that allow us to describe the concentration distribution in space and time of a pollutant in groundwater.
This research is focused on the study and modeling of pollutants in groundwater.
Bibliographic research and a subsequent in-depth study of 1D, 2D and 3D ADE models and their applications were conducted to examine the state of the art and possible areas for model development.
Emphasis was placed on the development of a new one-dimensional solution.
A variety of conditions were examined including the release of the source with step function, the decay of contaminants with consecutive reactions and the production and decay of the source concentration
From the one-dimensional model, it was possible to extend the model to three-dimensions with the exact integral solution and approximate solution in closed form.
A solution in approximate form was also obtained for a known solution in the Literature characterized by exponential decay at the source.
A comparative simulation analysis was performed on the models based on Literature data.
2
Khatibi, Rahman Haghi. "Mathematical open channel flow models and identification of their friction parameters". Thesis, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263145.
Testo completoAbstract (sommario):
This thesis l concerned with the mathematical modelling of open channel flows governed by the Saint-Venant equations, which are used as a prediction or identification tools. A survey of the literature in these fields identified the problems in need of Immediate research. Numerical test runs were then devised which led to projecting a clear picture as follows. The performance of twn widely used Implicit finite difference schemes, the 4-point box and 6-point staggered schemes were compared In a wide range of circumstances. it is concluded that both schemes produce 'very close results, but the staggered scheme is prone to convergence problems In some extreme cases. It was also noted that a sharp change in geometric configuration of compound channels produced discontinuous features on the aim ulated depth and discharge hydrographs. The inability of the staggered scheme In handling a head-discharge relationship as a downstream boundary condition was tackled by proposing and implementing a scheme of second order accuracy. As model data are generally corrupted withh errors and noise, their effects together with that of other factors on the Identified friction parameters we Investigated. The results demonstte the paramount Importance of the effect of a choice of objective function on the Identified parameters. While the individual values of the identified M2nning n may vary from one flood event to another, their mean is shown both numerically and rigorously to be dependent upon the choice of objective function. It is shown that an objective function formulated by using absolute errors performs ideally and produces reliable results even in the presence of autocorrelated Gaucian noise samples. The mean of the Identified parameters is also found to be adversely affected if the observation station is affected by localized disturbances. Sensitivity of objective functions to the variation In the value of the friction parameter Is also found to be an Important factor, as Insensitivity leads to ill-conditioning.
3
Cuifeng, Wei. "Improved Finite Analytic Methods for Solving Advection-dominated Transport Equation in Highly Variable Velocity Field". PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/4922.
Testo completoAbstract (sommario):
Solute transport studies frequently rely on numerical solutions of the classical advection-diffusion equation. Unfortunately, solutions obtained with traditional finite difference and finite element techniques typically exhibit excessive numerical diffusion or spurious oscillation when advection dominates, especially when velocity field is highly variable. One recently developed technique, the finite analytic method, offers an attractive alternative. Finite analytic methods utilize local analytic solutions in discrete elements to obtain the algebraic representations of the governing partial differential equations, thus eliminating the truncation error in the finite difference and the use of approximating functions in the finite element method. The finite analytic solutions have been shown to be stable and numerically robust for advection-dominated transport in heterogeneous velocity fields. However, the existing finite analytic methods for solute transport in multiple dimensions have the following disadvantages. First, the method is computationally inefficient when applied to heterogeneous media due to the complexity of the formulation. Second, the evaluation of finite analytic coefficients is when the Peclet number is large. Third, the method introduces significant numerical diffusion due to inadequate temporal approximation when applied to transient problems. This thesis develops improved finite analytic methods for two-dimensional steady as well as unsteady solute transports in steady velocity fields. For steady transport, the new method exploits the advantages of the existing finite analytic and finite difference methods. The analytically difficult diffusion terms are approximated by finite difference and numerically difficult advection and reaction terms are treated analytically in a local element in deriving the numerical schemes. The new finite analytic method is extended to unsteady transport through application of Laplace transformation. Laplace transformation converts the transient equation to a steady-state expression that can be solved with the steady version of the improved finite analytic method. Numerical inversion of the transformed variables is used to recover solute concentration in the physical space-time domain. The effectiveness and accuracy of the new finite analytic method is demonstrated through stringent test examples of two dimensional steady-state transport in highly variable velocity fields. The results clearly demonstrated that the improved finite analytic methods are efficient, robust and accurate.
4
Blue, Julie Elena. "Predicting tracer and contaminant transport with the stratified aquifer approach". Diss., The University of Arizona, 1999. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1999_426_sip1_w.pdf&type=application/pdf.
Testo completo
5
Javed, Ijaz. "Groundwater development and management at Fordwah Eastern Sadiqia (South) Project, Bahawalnager, Punjab, Pakistan". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/MQ44189.pdf.
Testo completo
6
Ritzi, Robert William. "The use of well response to natural forces in the estimation of hydraulic parameters". Diss., The University of Arizona, 1989. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1989_119_sip1_w.pdf&type=application/pdf.
Testo completo
7
Schmid, Wolfgang. "A farm package for MODFLOW-2000 simulation of irrigation demand and conjunctively managed surface-water and ground-water supply /". Diss., The University of Arizona, 2004. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_2004_287_sip1_w.pdf&type=application/pdf.
Testo completo
8
Samper, Calvete F. Javier(Francisco Javier) 1958. "Statistical methods of analyzing hydrochemical, isotopic, and hydrological data from regional aquifers". Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/191115.
Testo completoAbstract (sommario):
This dissertation is concerned with the development of mathematical aquifer models that combine hydrological, hydrochemical and isotopic data. One prerequisite for the construction of such models is that prior information about the variables and parameters be quantified in space and time by appropriate statistical methods. Various techniques using multivariate statistical data analyses and geostatistical methods are examined in this context. The available geostatistical methods are extended to deal with the problem at hand. In particular, a three-dimensional interactive geostatistical package has been developed for the estimation of intrinsic and nonintrinsic variables. This package is especially designed for groundwater applications and incorporates a maximum likelihood cross-validation method for estimating the parameters of the covariance function. Unique features of this maximum likelihood cross-validation method include: the use of an adjoint state method to compute the gradient of the likelihood function, the computation of the covariance of the parameter estimates and the use of identification criteria for the selection of a covariance model. In addition, it can be applied to data containing measurement errors, data regularized over variable lengths, and to nonintrinsic variables. The above methods of analysis are applied to synthetic data as well as hydrochemical and isotopic data from the Tucson aquifer in Arizona and the Madrid Basin in Spain. The dissertation also includes a discussion of the processes affecting the transport of dissolved constituents in groundwater, the mathematical formulation of the inverse solute transport problem and a proposed numerical method for its solution.
9
El, Didy Sherif Mohamed Ahmed 1951. "Two-dimensional finite element programs for water flow and water quality in multi-aquifer systems". Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/191110.
Testo completoAbstract (sommario):
Multiple aquifer systems similar to those that exist at coal gasification sites are complicated groundwater situations. In these types of systems, the aquifers are separated by aquitards through which interaction between aquifers can occur. The movement of the products of combustion into the coal seam and adjacent aquifers is a serious problem of interest. This dissertation presents two-dimensional finite element models for water flow and water quality in multiple aquifer systems. These models can be applied for general problems as well as the problems associated with the burned cavities in coal gasification sites. The Galerkin weightedresidual method is used in both models. Eight-noded isoparametric elements are used. Spatial numerical integration is performed using Gaussian quadrature. A weighted finite difference scheme is used, in both of them, for time integration. The two models are written in FORTRAN V for the CDC CYBER 175. They are applicable to one- or two-dimensional problems involving steady-state or transient flow. Each aquifer can have different initial conditions and boundary conditions. Boundary conditions, pumping rates, and the recharge can be specified as a function of time. The output of the flow program-nodal heads and velocity components is used as an input to the quality program. The numerical models were validated for simple problems that have available analytical solutions.
10
Ahmad, Faheem. "Numerical modelling of transport of pollutant through soils". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08182009-040239/.
Testo completo
11
Vionnet, Leticia Beatriz, e Leticia Beatriz Vionnet. "Investigation of stream-aquifer interactions using a coupled surface water and groundwater flow model". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187414.
Testo completoAbstract (sommario):
A finite element numerical model is developed for the modeling of coupled surface-water flow and ground-water flow. The mathematical treatment of subsurface flows follows the confined aquifer theory or the classical Dupuit approximation for unconfined aquifers whereas surface-water flows are treated with the kinematic wave approximation for open channel flow. A detailed discussion of the standard approaches to represent the coupling term is provided. In this work, a mathematical expression similar to Ohm's law is used to simulate the interacting term between the two major hydrological components. Contrary to the standard approach, the coupling term is incorporated through a boundary flux integral that arises naturally in the weak form of the governing equations rather than through a source term. It is found that in some cases, a branch cut needs to be introduced along the internal boundary representing the stream in order to define a simply connected domain, which is an essential requirement in the derivation of the weak form of the ground-water flow equation. The fast time scale characteristic of surface-water flows and the slow time scale characteristic of ground-water flows are clearly established, leading to the definition of three dimensionless parameters, namely, a Peclet number that inherits the disparity between both time scales, a flow number that relates the pumping rate and the streamflow, and a Biot number that relates the conductance at the river-aquifer interface to the aquifer conductance. The model, implemented in the Bill Williams River Basin, reproduces the observed streamflow patterns and the ground-water flow patterns. Fairly good results are obtained using multiple time steps in the simulation process.
12
Sorooshian, Soroosh, e Vijai Kumar Gupta. "Improving the Reliability of Compartmental Models: Case of Conceptual Hydrologic Rainfall-Runoff Models". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1986. http://hdl.handle.net/10150/614011.
Testo completo
13
Rotzoll, Kolja. "Hydraulic Parameter Estimation Using Aquifer Tests, Specific Capacity, Ocean Tides, and Wave Setup for Hawai'i Aquifers". Thesis, Water Resources Research Center, University of Hawaii at Manoa, 2007. http://hdl.handle.net/10125/22265.
Testo completoAbstract (sommario):
The islands of Hawaii face increasing ground-water demands due to population growth in the last decades. Analytical and numerical models are essential tools for managing sustainable ground-water resources. The models require estimates of hydraulic properties, such as hydraulic conductivity and storage parameters. Four methods were evaluated to estimate hydraulic properties for basalts on the island of Maui. First, unconventional step-drawdown tests were evaluated. The results compare favorably with those from classical aquifer tests with a correlation of 0.81. Hydraulic conductivity is log-normally distributed and ranges from 1 to 2,500 m/d with a geometric mean of 276 m/d and a median of 370 m/d. The second approach developed a simplified parameter-estimation scheme through an empirical relationship between specific capacity and hydraulic parameters that utilized Hawaii's state well database. For Maui's basalts, the analysis yields a geometric-mean and median hydraulic conductivity of 423 and 493 m/d, respectively. Results from aquifer tests and specific-capacity relationships were used to generate island-wide hydraulic-conductivity maps using kriging. The maps are expected to be of great benefit in absence of site-specific field assessments. In the third approach, ocean-tide responses in the central Maui aquifer were used to estimate an effective hydraulic diffusivity of 2.3 x 10^7 m^2/d. The position of the study area necessitated refining the existing analytical solution that considers asynchronous and asymmetric tidal influence from two sides in an aquifer. Finally, measured ground-water responses to wave setup were used to estimate hydraulic parameters. Setup responses were significant as far as 5 km inland and dominated barometric-pressure effects during times of energetic swell events. The effective diffusivity estimated from setup was 2.3 x 10^7 m^2/d, matching that based on tides. Additionally, simple numerical ground-water flow models were developed to assess the accuracy of results from analytical solutions for step-drawdown tests, dual-tides and wave setup, and to evaluate sediment-damping effects on tidal propagation. The estimated mean hydraulic conductivities of the four methods range between 300 and 500 m/d for basalts in Maui. The results of different methods are consistent among each other and match previous estimates for basalts.USGS Pacific Island Water Science Center
14
Zhang, Dongxiao. "Conditional stochastic analysis of solute transport in heterogeneous geologic media". Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186553.
Testo completoAbstract (sommario):
This dissertation develops an analytical-numerical approach to deterministically predict the space-time evolution of concentrations in heterogeneous geologic media conditioned on measurements of hydraulic conductivities (transmissivities) and/or hydraulic heads. Based on the new conditional Eulerian-Lagrangian transport theory by Neuman, we solve the conditional transport problem analytically at early time, and express it in pseudo-Fickian form at late time. The stochastically derived deterministic pseudo-Fickian mean concentration equation involves a conditional, space-time dependent dispersion tensor. The latter not only depends on properties of the medium and the velocity but also on the available information, and can be evaluated numerically along mean "particle" trajectories. The transport equation lends itself to accurate solution by standard Galerkin finite elements on a relatively coarse grid. This approach allows computing without using Monte Carlo simulation and explicitly the following: Concentration variance/covariance (uncertainty), origin of detected contaminant and associated uncertainty, mass flow rate across a "compliance surface", cumulative mass release and travel time probability distribution across this surface, uncertainty associated with the latter, second spatial moment of conditional mean plume about its center of mass, conditional mean second spatial moment of actual plume about its center of mass, conditional co-variance of plume center of mass, and effect of non-Gaussian velocity distribution. This approach can also account for uncertainty in initial mass and/or concentration when predicting the future evolution of a plume, whereas almost all existing stochastic models of solute transport assume the initial state to be known with certainty. We illustrate this approach by considering deterministic and uncertain instantaneous point and nonpoint sources in a two-dimensional domain with a mildly fluctuating, statistically homogeneous, lognormal transmissivity field. We take the unconditional mean velocity to be uniform, but allow conditioning on log transmissivity and hydraulic head data. Conditioning renders the velocity field statistically nonhomogeneous with reduced variances and correlation scales, renders the predicted plume irregular and non-Gaussian, and generally reduces both predictive dispersion and uncertainty.
15
Liao, Boshu. "Analytical and numerical analysis of LNAPL migration and LNAPL thickness estimation in unconfined aquifers". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/32846.
Testo completo
16
Hendrickson, Jene Diane, e Soroosh Sorooshian. "CALIBRATION OF RAINFALL-RUNOFF MODELS USING GRADIENT-BASED ALGORITHMS AND ANALYTIC DERIVATIVES". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/614186.
Testo completoAbstract (sommario):
In the past, derivative-based optimization algorithms have not
frequently been used to calibrate conceptual rainfall -riff (CRR)
models, partially due to difficulties associated with obtaining the
required derivatives. This research applies a recently- developed
technique of analytically computing derivatives of a CRR model to a
complex, widely -used CRR model. The resulting least squares response
surface was found to contain numerous discontinuities in the surface
and derivatives. However, the surface and its derivatives were found
to be everywhere finite, permitting the use of derivative -based
optimization algorithms. Finite difference numeric derivatives were
computed and found to be virtually identical to analytic derivatives.
A comparison was made between gradient (Newton- Raphsoz) and
direct (pattern search) optimization algorithms. The pattern search
algorithm was found to be more robust. The lower robustness of the
Newton-Raphsoi algorithm was thought to be due to discontinuities and a
rough texture of the response surface.
17
Vionnet, Leticia Beatriz, e Thomas Maddock. "Modeling of Ground-Water Flow and Surface/Ground-Water Interaction for the San Pedro River Basin Part I Mexican Border to Fairbank, Arizona". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1992. http://hdl.handle.net/10150/614152.
Testo completoAbstract (sommario):
Many hydrologic basins in the southwest have seen their perennial streamflows
turn to ephemeral, their riparian communities disappear or be jeopardized, and their
aquifers suffer from severe overdrafts. Under -management of ground -water exploitation
and of conjunctive use of surface and ground waters are the main reasons for these
events.
18
Kalin, Robert M. "The hydrogeochemical evolution of the groundwater of the Tucson Basin with application to 3-dimensional groundwater flow modelling". Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186609.
Testo completoAbstract (sommario):
This work examines the hydrogeochemical evolution of Tucson basin groundwater, including isotope hydrology, geochemistry and age determinations. Results of mineralogic investigation on basin fill were used to constrain water-rock geochemical reactions. Examination of 45 years of water quality data shows that groundwater mining has affected water quality. Stable isotopes of carbon, oxygen, hydrogen, sulfur, and chlorine and radiocarbon, tritium and radon determinations refine the interpretation of hydrogeochemical evolution of Tucson basin groundwater as modelled with NETPATH. Two distinct sampling periods, the first in 1965 and the second between 1984 and 1989, resulted in the determination of groundwater ages for water mined two decades apart. Isotope hydrology and geochemical modelling suggest that much of the water presently mined from the Tucson basin has a component recharged during the last 50 years. Increased sulfate concentrations suggest that heavy pumping in the northeastern basin may have induced increased leakage from lower units. Results of geochemical modelling indicate an average of 5 percent mountain-front recharge to the Ft. Lowell Formation along the northern aquifer margin. An increase in dissolved solids along the basin margin implies that this component to recharge has increased in the past decade. The radiocarbon age of the basin groundwater was compared with the temporal movement of water as modelled with MODFLOW and PATH3D. In general, the hydrologic simulation agrees with both the distribution of tritium and the exponentially modelled water age, as determined with bomb-derived radiocarbon, for areas of the Tucson basin that contain water less than 50 years in age. Hydrologic modelling failed to predict the antiquity of recently sampled water in the central basin but is similar to age determinations on waters collected in 1965.
19
Zhang, You-Kuan. "A quasilinear theory of time-dependent nonlocal dispersion in geologic media". Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185039.
Testo completoAbstract (sommario):
A theory is presented which accounts for a particular aspect of nonlinearity caused by the deviation of plume "particles" from their mean trajectory in three-dimensional, statistically homogeneous but anisotropic porous media under an exponential covariance of log hydraulic conductivities. Quasilinear expressions for the time-dependent nonlocal dispersivity and spatial covariance tensors of ensemble mean concentration are derived, as a function of time, variance σᵧ² of log hydraulic conductivity, degree of anisotropy, and flow direction. One important difference between existing linear theories and the new quasilinear theory is that in the former transverse nonlocal dispersivities tend asymptotically to zero whereas in the latter they tend to nonzero Fickian asymptotes. Another important difference is that while all existing theories are nominally limited to situations where σᵧ² is less than 1, the quasilinear theory is expected to be less prone to error when this restriction is violated because it deals with the above nonlinearity without formally limiting σᵧ². The theory predicts a significant drop in dimensionless longitudinal dispersivity when σᵧ² is large as compared to the case where σᵧ² is small. As a consequence of this drop the real asymptotic longitudinal dispersivity, which varies in proportion to σᵧ² when σᵧ² is small, is predicted to vary as σᵧ when σᵧ² is large. The dimensionless transverse dispersivity also drops significantly at early dimensionless time when σᵧ² is large. At late time this dispersivity attains a maximum near σᵧ² = 1, varies asymptotically at a rate proportional to σᵧ² when σᵧ² is small, and appears inversely proportional to σᵧ when σᵧ² is large. The actual asymptotic transverse dispersivity varies in proportion to σᵧ⁴ when σᵧ² is small and appears proportional to σᵧ when σᵧ² is large. One of the most interesting findings is that when the mean seepage velocity vector μ is at an angle to the principal axes of statistical anisotropy, the orientation of longitudinal spread is generally offset from μ toward the direction of largest log hydraulic conductivity correlation scale. When local dispersion is active, a plume starts elongating parallel to μ. With time the long axis of the plume rotates toward the direction of largest correlation scale, then rotates back toward μ, and finally stabilizes asymptotically at a relatively small angle of deflection. Application of the theory to depth-averaged concentration data from the recent tracer experiment at Borden, Ontario, yields a consistent and improved fit without any need for parameter adjustment.
20
Sheng, Jopan. "Multiphase immiscible flow through porous media". Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/53630.
Testo completoAbstract (sommario):
A finite element model is developed for multiphase flow through soil involving three immiscible fluids: namely air, water, and an organic fluid. A variational method is employed for the finite element formulation corresponding to the coupled differential equations governing the flow of the three fluid phase porous medium system with constant air phase pressure. Constitutive relationships for fluid conductivities and saturations as functions of fluid pressures which may be calibrated from two-phase laboratory measurements, are employed in the finite element program. The solution procedure uses iteration by a modified Picard method to handle the nonlinear properties and the backward method for a stable time integration. Laboratory experiments involving soil columns initially saturated with water and displaced by p-cymene (benzene-derivative hydrocarbon) under constant pressure were simulated by the finite element model to validate the numerical model and formulation for constitutive properties. Transient water outflow predicted using independently measured capillary head-saturation data agreed well with observed outflow data. Two-dimensional simulations are presented for eleven hypothetical field cases involving introduction of an organic fluid near the soil surface due to leakage from an underground storage tank. The subsequent transport of the organic fluid in the variably saturated vadose and ground water zones is analysed.Ph. D.
21
Wang, Maili. "Approximate method for solving two-stage stochastic programming and its application to the groundwater management". Diss., The University of Arizona, 1999. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1999_068_sip1_w.pdf&type=application/pdf.
Testo completo
22
Xiao, Liang. "Evaluation of groundwater flow theories and aquifer parameters estimation". University of the Western Cape, 2014. http://hdl.handle.net/11394/4366.
Testo completoAbstract (sommario):
Philosophiae Doctor - PhDThis thesis deals with some fundamental aspects of groundwater models. Deterministic mathematical models of groundwater are usually used to simulate flow and transport processes in aquifer systems by means of partial differential equations. Analytical solutions for the deterministic mathematical models of the Theis problem and the transient confined-unconfined flow in a confined aquifer are investigated in the thesis. The Theis equation is a most commonly applied solution for the deterministic mathematical model of the Theis problem. In the thesis, a most simplified similarity transformation method for derivation of the Theis equation is proposed by using the Boltzmann transform. To investigate the transient confined-unconfined flow towards a fully penetrating well in a confined aquifer, a new analytical solution for the deterministic mathematical models of interest is proposed in the thesis. The proposed analytical solution considers a change of hydraulic properties (transmissivity and storativity) during the confined-unconfined conversion. Based on the proposed analytical solution, a practical method to determine distance of the conversion interface from pumping well and diffusivity of the unconfined region is developed by using a constant rate test. Applicability of the proposed analytical solution is demonstrated by a comparison with previous solutions, namely the MP and the Chen models. The results show that the proposed analytical solution can be used to assess the effect of the change of diffusivity on the transient confined-unconfined flow. The MP model is only accepted if the transmissivity during the confined-unconfined conversion is constant. The Chen model, given as a special case of the proposed analytical solution, is limited to the analysis of the transient confined-unconfined flow with a fixed diffusivity. An important application of groundwater models is to estimate parameters, such as hydraulic properties and flow dynamics, of groundwater systems by assessing and analysing field data. For instance, the pumping and the hydrochemistry and environmental tracer tests are two effective ways to obtain such data. To evaluate hydraulic properties of aquifer systems by derivative interpretation of drawdown data from pumping tests, a new diagnostic analysis method is proposed based on a lg-lg drawdown derivative, dlgs/dlgt, and the differentiation algorithm namely Lagrange Interpolation Regression (LIR) in the thesis. Use of a combined plot of dlgs/dlgt and a semi-lg drawdown derivative (ds/dlgt) is made to identify various flow segments during variable discharge tests with infinite conditions, constant rate tests in bounded aquifers and tests involving double-porosity behaviours. These can be applied to further characterize pumped aquifers. Compared to traditional diagnostic analysis method using plot of ds/dlgt alone, the combined drawdown derivative plot possesses certain advantages identified as: (1) the plot of dlgs/dlgt is strikingly sensitive for use in unveiling differences between pumping and its following recovery periods in intermittent variable discharge tests; (2) storativity (S) of pumped aquifers can be evaluated by using the combined plot; and (3) quantitative assessments of double-porosity behaviours can also be achieved. Based on two case studies, advantages and disadvantages of uses of the LIR and other existing differentiation methods in calculations of numerical drawdown derivative are demonstrated in practice. The results suggest that the LIR is a preferred method for numerical differentiation of drawdown data as it can be used to effectively minimise noisy effects. The proposed derivative approach provides hydrologists with an additional tool for characterizing pumped aquifers. Use of hydrochemistry and environmental tracer tests to assess flow dynamics of groundwater systems is demonstrated via a case study in the dolomite aquifer of South Africa. An emphasis is on determining mean residence times (MRTs) of the dolomite aquifer by means of an appropriate box model with time series of 14C values of dissolved inorganic carbon (14C-DIC) and initial 14C activities of spring samples during 1970s and 2010s. To obtain the calibrated 14C MRTs, 13C values of dissolved inorganic carbon (δ13C-DIC) of the spring samples are applied to estimate mineral dissolution in the dolomite aquifer and calculate the initial 14C activities. The results indicate that the spring samples have about 50%-80% initial 14C activities. By using the appropriate box model, the calibrated 14C MRTs of the spring system are given within a range from ≤ 10 to 50 years. Additionally, the flow dynamics, including the recharge source and area, the effect of climate change on the temporal trend of the groundwater MRTs and the groundwater flow circulation, of the dolomitic spring system are also discussed for further possible management interventions in the dolomite aquifer.
23
Sande, Leif Andrew. "Experimental Studies on Infiltration/Soil-Water Movement Processes and Green-AMPT Modeling". Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29329.
Testo completoAbstract (sommario):
Experimental studies on infiltration/soil-water movement processes are vital to
better understanding movement of soil-water in the vadose zone. The objective of this
experimental research was to investigate infiltration/soil-water movement processes
utilizing laboratory experiments and computer modeling. Small scale laboratory soil box
infiltration experiments were conducted and utilized for the improved parameterization of
the Green-Ampt (GA) saturated moisture content parameter to produce an effective
moisture content parameter (Be) for utilization in a modified GA model. By incorporating ?e
values into GA modeling, modeling results showed greatly improved wetting front
prediction across different soil conditions. A new soil packing method was proposed for
replicating complex microtopographical surfaces with uniform bulk densities in laboratory
soil box experiments which proved efficient and effective at accomplishing both objectives.
A rainfall simulator and an instantaneous-profile laser scanner were used to simulate
rainfall and quantify surface microtopography for experiments. The results clearly show the
effect of microtopography on infiltration and soil-water movement characteristics. This
offers valuable insight into infiltration/soil-water movement processes as affected by
different soil and surface microtopographic conditions.National Science Foundation (Grant No. EAR-0907588)
24
Vionnet, Leticia Beatriz, Thomas III Maddock e David C. Goodrich. "Investigations of stream-aquifer interactions using a coupled surface-water and ground-water flow model". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1997. http://hdl.handle.net/10150/615700.
Testo completoAbstract (sommario):
A finite element numerical model is developed for the modeling of coupled
surface-water flow and ground-water flow. The mathematical treatment of subsurface
flows follows the confined aquifer theory or the classical Dupuit approximation for
unconfined aquifers whereas surface-water flows are treated with the kinematic wave
approximation for open channel flow. A detailed discussion of the standard approaches to
represent the coupling term is provided. In this work, a mathematical expression similar
to Ohm's law is used to simulate the interacting term between the two major hydrological
components. Contrary to the standard approach, the coupling term is incorporated
through a boundary flux integral that arises naturally in the weak form of the governing
equations rather than through a source term. It is found that in some cases, a branch cut
needs to be introduced along the internal boundary representing the stream in order to
define a simply connected domain, which is an essential requirement in the derivation of
the weak form of the ground-water flow equation. The fast time scale characteristic of
surface-water flows and the slow time scale characteristic of ground-water flows are
clearly established, leading to the definition of three dimensionless parameters, namely, a
Peclet number that inherits the disparity between both time scales, a flow number that
relates the pumping rate and the streamflow, and a Biot number that relates the
conductance at the river-aquifer interface to the aquifer conductance.
The model, implemented in the Bill Williams River Basin, reproduces the observed
streamflow patterns and the ground-water flow patterns. Fairly good results are obtained
using multiple time steps in the simulation process.
25
Agyei, Eugene Osei. "Groundwater modeling and management using the finite element method and evolutionary optimisation techniques /". Title page, synopsis and contents only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09pha284.pdf.
Testo completo
26
Bailey, Mark A(Mark Alexander) 1970. "Improved techniques for the treatment of uncertainty in physically-based models of catchment water balance". Monash University, Dept. of Civil Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/8271.
Testo completo
27
Perraton, Etienne. "Hydrogeologic and agroclimatic considerations for the development of a water management model for the Tlacolula subbasin, Oaxaca, Mexico". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0016/NQ44553.pdf.
Testo completo
28
Chavez, Rodriguez Adolfo 1951. "Modeling mountain-front recharge to regional aquifers". Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/191124.
Testo completoAbstract (sommario):
The estimation of mountain-front recharge to regional aquifers is approached from a hydroclimatic standpoint. Analytical models of the seasonal water yield and streamflow are developed in this dissertation. These models are specialized for hard-rock mountainous watersheds where deep percolation occurs through fractures exclusively. Input variables are considered to be stochastic, and a relationship between precipitation and surface runoff is derived by using a deterministic physical process. Streamflow models for the summer and winter rainy seasons are developed separately in terms of known parameters of the storm process and unknown parameters of the physical process. The winter model considers the generation of surface runoff from both rainfall and snowmelt. These models include the long-term effective subsurface outflow from the mountainous watershed, or mountain-front recharge, as one of the parameters to be identified. The parameter estimation problem is posed in the framework of maximum likelihood theory, where prior information about the model parameters and a suitable weighting scheme for the error terms in the estimation criterion are included. The issues of model and parameter identifiability, uniqueness and stability are addressed, and strategies to mitigate identifiability problems in our modeling are discussed. Finally, the seasonal streamflow models are applied to three mountainous watersheds in the Tucson basin, and maximum likelihood estimates of mountain-front recharge and other model and statistical parameters are obtained. The analysis of estimation errors is performed in both the eigenspace and the original space of the parameters.
29
Wang, Jinjun. "Sensitivity and uncertainty analyses of contaminant fate and transport in a field-scale subsurface system". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22562.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008.Committee Chair: Aral, Mustafa; Committee Member: Guan, Jiabao; Committee Member: Kim, Seong Hee; Committee Member: Luo, Jian; Committee Member: Uzer, Turgay.
30
Orr, Shlomo. "Stochastic approach to steady state flow in nonuniform geologic media". Diss., The University of Arizona, 1993. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1993_409_sip1_w.pdf&type=application/pdf.
Testo completo
31
Lang, Patrick T., e Thomas III Maddock. "SIMULATION OF GROUND-WATER FLOW TO ASSESS THE EFFECTS OF PUMPING AND CANAL LINING ON THE HYDROLOGIC REGIME OF THE MESILLA BASIN: Dona Ana County, New Mexico & El Paso County, Texas". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1995. http://hdl.handle.net/10150/617628.
Testo completoAbstract (sommario):
This study, which is to provide information to a settlement over the rights to water
resources in the Mesilla Basin, uses a groundwater model to estimate how pumping in the
basin affects the hydrologic regime.
32
Lingen, Carl, e Nathan Buras. "Dynamic Management of a Surface and Groundwater System on Both Sides of the Lower Yellow River". Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/614178.
Testo completoAbstract (sommario):
This paper analyzes the management problem of the conjunctive use of
surface and ground water in an irrigation system on both sides of the Lower
Yellow River. For this purpose, a stochastic dynamic programming model is
developed. In the model, the statistical characteristics of seasonal rainfall
within 2 years are considered; groundwater level control is also emphasized in
order to prevent soil salinity and waterlogging. Through computer calculations,
optimal operation policies are obtained for efficient conjunctive use
of surface and groundwater. These policies take into account the interactions
between pumping groundwater by farmers, canal diversions by irrigation system
managers, and the physical response of the stream- aquifer system, and minimize
the total operation costs.
In this paper, we take an irrigation district, the People's Victory Canal
System, as an example to illustrate the development and solution of the model.
At the same time, the effects of system parameters, including surface irrigation
efficiency and rainfall recharge coefficient, on the optimal policies or
total operation costs, are discussed. The analytical results in this example
indicate that the variation in optimal operation costs caused by the proportion
of rainfall infiltrated is small, but the effect of surface irrigation
efficiency on the costs is significant. Hence, the surface irrigation efficiency
must be increased as much as possible. Then, efficient conjunctive use
of surface and groundwater can be attained with the optimal policies.
33
Shrestha, Surendra Prakash. "An effective medium approximation and Monte Carlo simulation in subsurface flow modeling". Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/38642.
Testo completo
34
Bandeen, Reid Francis 1957. "Simulations of dry well recharge in the Tucson Basin, Arizona". Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276654.
Testo completoAbstract (sommario):
The variably saturated flow model Unsat 2 was used for three case study simulations of dry well recharge in the Tucson Basin, Arizona. Dry well design, and rainfall/runoff and vadose zone conditions representative of the locality were assumed in the simulations to address travel time to the regional aquifer, rates and extent of radial flow, and relative degree of solute attenuation by sorption and dilution with regional groundwater. Soil specific surface was used to estimate relative degree of sorption among the three cases. One case of uniform soil composition and two cases of layered soil composition were simulated. Clay content had the greatest influence on specific surface. Hydraulic conductivity had the greatest influence on soil water velocities and degree of radial flow. The presence of layered subsurface conditions that included strata of low hydraulic conductivity enhanced the degree of subsurface solute attenuation by sorption and dilution.
35
Rucker, Dale Franklin. "Improved analysis of borehole ground penetrating radar to monitor transient water flow in the vadose zone". Diss., The University of Arizona, 2003. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_2003_320_sip1_w.pdf&type=application/pdf.
Testo completo
36
Woods, Juliette Aimi. "Numerical accuracy of variable-density groundwater flow and solute transport simulations". Title page, contents and abstract only, 2004. http://web4.library.adelaide.edu.au/theses/09PH/09phw8941.pdf.
Testo completo
37
Melo, Davi de Carvalho Diniz. "Estimativa de impacto de mudanças climáticas nos níveis do aquífero livre em zona de recarga do sistema Aquífero Guarani". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-31072013-110008/.
Testo completoAbstract (sommario):
A exploração acelerada das águas subterrâneas pode acarretar em problemas de disponibilidade de água. Esse problema tende a ser acentuado devido as mudanças no clima previstas para as próximas décadas. Nesse contexto, este trabalho buscou avaliar os possíveis impactos das mudanças climáticas e do uso do solo sobre níveis de água subterrânea em zona de afloramento do Sistema Aquífero Guarani. Foram utilizadas simulações de Modelos de Circulação Global (MCG) como dados de entrada para um modelo transiente de fluxo hídrico subterrâneo, visando avaliar o comportamento dos nveis de água sob diferentes condições climáticas. Este modelo foi calibrado utilizando dados de níveis freáticos em seis poços localizados na bacia do Ribeirão da Onça (BRO). A partir de dados climáticos observados, estimou-se a recarga, usada como input no modelo matematico, em diversos tipos de cultura por meio do balanço hídrico. As maiores alterações nas médias pluviométricas mensais foram projetadas, pela maioria dos modelos climáticos, para ocorrer no perodo seco. No perodo chuvoso, as previsões indicaram que essas médias devem diminuir em torno de 50%. Quase 70% dos cenários climáticos geraram, no modelo transiente, variações dos nveis freáticos abaixo daqueles medidos no monitoramento entre 2004 e 2011. Em setores da área de estudo, o rebaixamento da superfície potenciométrica, simulada sob condições climáticas mais extremas previstas por alguns modelos, ultrapassou 10 m. Os cenários mais otimistas, embora tenham resultado em elevações dos níveis de água em mais metade da BRO, também geraram rebaixamentos de até 5 m. Os resultados reforçam a necessidade do contínuo monitoramento hidrogeológico, principalmente em áreas de recarga do SAG, e do desenvolvimento de outros trabalhos que quantiquem os impactos das mudanças climáticas, aplicando diferentes métodos de estimativa de recarga e downscaling.The unsustainable use groundwater in many countries might cause water availability restrictions. Such issues are likely to worsen due to changes in climate, predicted for the incoming decades. In this context, the objective of this work was to assess possible climate and land use changes impacts on groundwater levels in the Guarani Aquifer System\'s (GAS) outcrop zone. Global Climate Models\' (GCM) outputs were used as inputs in a transient ux groundwater model. Thus, groundwater table uctuation could be evaluated under distinct climatic conditions. Six monitoring wells, located in the Ribeir~ao da Onca basin (ROB), provided water table measurements to calibrate the groundwater model. Using observed climatic data, a water budget method was applied to estimate recharge in dierent types of land uses. Statistically downscaled future climate scenarios were used as inputs in that same recharge model, which provided the inputs for SPA. Most of the GCMs used here predict temperature arises over 2°C. Major monthly rainfall mean changes are projected by the GCM great majority to take place in the dry season. During wet seasons, the predictions indicate those means might experience around 50% decrease. Water table variations, derived from the transient model under almost 70% of the climate scenarios, were below of those measured between 2004 and 2011. Few GCM predicted more extreme climate scenarios. In some regions of the study area and under these conditions, groundwater surface would decline more than 10 m. Although more optimistic scenarios resulted in an increase of groundwater levels in more than half of ROB, these would cause up to 5 m water table decline. The results reinforce the need for a permanent hydrogeological monitoring, mainly in the GAS recharge areas, along with the development of other climate change impacts assessment works using dierent downscaling and recharge estimates methods.
38
Simpson, Matthew. "An analysis of unconfined ground water flow characteristics near a seepage-face boundary". University of Western Australia. Centre for Water Research, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0025.
Testo completoAbstract (sommario):
A quantitative understanding of ground water flow characteristics in unconfined aquifers is important because of the prevalence of abstraction from, and pollution of these systems. The current understanding of ground water flow in unconfined aquifers is limited because of the dominance of horizontal flow modelling strategies used to represent unconfined flow processes. The application of horizontal flow principles leads to an ignorance of seepage-face formation and can not predict the complicated three-dimensional nature of the ground water flow that dominates at the ground water-surface water interface. This study aims to address some of these deficiencies by exploring the true three-dimensional nature of ground water flow including the formation of seepage faces at the ground water-surface water interface using numerical and laboratory techniques. A finite element model for simulating two-dimensional (vertical) variably saturated flow is developed and benchmarked against standard laboratory and field-scale solutions. The numerical features of the finite element model are explored and compared to a simple finite difference formulation. The comparison demonstrates how finite element formulations lead to a broader spatial averaging of material properties and a different method for the representation of specified flux boundaries. A detailed comparison analysis indicates that these differences in the finite element solution lead to an improved approximation to the partial differential equation governing two-dimensional (vertical) variably saturated flow. A laboratory analysis of unconfined ground water flow and associated solute transport characteristics was performed. The analysis focused upon unconfined flow towards a pumping well. The laboratory observations were reliably reproduced using a three-dimensional (axi-symmetric), variably saturated ground water flow model. The model was benchmarked against the ground water flow characteristics such as the seepage-face height and total flow rate. In addition, the model was shown to reliably reproduce the solute transport features such as travel times and streamline distributions. This is the first time that a numerical model has been used to reliably reproduce the solute transport characteristics near a seepage-face boundary where the three-dimensional flow effects are prevalent. The ability to reliably predict solute transport patterns in the seepage-face zone is important since this region is known to support vital microbially facilitated reactions that control nutrient cycling and contaminant attenuation. The three-dimensional travel time distribution near the seepage-face was compared to that predicted using a horizontal flow modelling approach derived from the basic Dupuit-Forchheimer equations. The Dupuit-Forchheimer based model indicated that horizontal flow modelling would under-estimate the total residence time near a seepage-face boundary, thereby introducing a considerable source of error in a solute transport analysis. For this analysis, a new analytical solution for the steady travel time distribution in an unconfined aquifer subject to a single pumping well was derived. The analytical model has identified, for the first time in the hydrogeology literature, the use of the imaginary error function. The imaginary error function is a standard transcendental function and an infinite series approach to evaluate the function was successfully proposed. The two-dimensional (vertical) ground water flow model was extended to handle the case where the flow is driven by density gradients near the ground water-surface water interface. The unsteady, two-dimensional, Galerkin finite element model of density-dependent ground water flow in variably saturated porous media is rigorously presented and partially benchmarked under fully saturated (confined) conditions. The partial benchmarking involved reproducing solutions to the standard Henry salt-water intrusion and the Elder salt-convection problems. The model was used in a standard density-coupled and a new density-uncoupled mode to elucidate the worthiness of the Henry and Elder problems as benchmark standards. A comparison of the coupled and uncoupled solutions indicates that the Henry salt-water intrusion problem has limited worthiness as a benchmark as the patterns of ground water flow are relatively insensitive to density-coupled effects. Alternatively, the Elder problem is completely dependent upon a correct representation of the density-coupled flow and solute transport processes. The coupled versus uncoupled comparison is proposed as a new test of the worthiness of benchmark standards. The Henry salt-water intrusion problem was further analysed in an attempt to alleviate some of the difficulties associated with this benchmark problem. The numerical model was tested against a re-evaluated version of Henry's semi-analytical solution for the coupled solute concentration distribution. The numerical model was used to propose a modified version of the Henry problem where the importance of density-coupled processes was increased. The modified problem was shown to have an improved worthiness as compared to the standard solution. The numerical model results were benchmarked against a new set of semi-analytical results for the modified problem. Certain advantages in using the modified problem as a test case for benchmarking the results of a numerical model of density-dependent ground water flow are identified. A numerical investigation of the patterns of density-driven ground water flow at the ground water-surface water interface was undertaken. The numerical model is shown to produce grid-independent results for a finely discretised domain. The pattern of discharge is controlled, in part, by two parameters. One describes the recharge applied to the aquifer, and the second describes the magnitude of the density differences between the fresh recharging fluid and the saline receiving fluid. The influence of dense intrusions upon the formation of seepage-face boundaries at the ground water-surface water interface under steady-state conditions was also investigated. Dense intrusions are shown to dominate the pattern of ground water flow only under mild recharge conditions, while seepage faces dominate the outflow pattern under strong recharge conditions. Therefore, the formation of seepage-face boundaries and dense intrusions are unlikely to coincide under the conditions examined in this study.
39
Faborode, Jumoke O. "Predictive modeling of sulfide removal in tray aerators". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4633.
Testo completoAbstract (sommario):
Hydrogen sulfide is commonly found in many Florida potable groundwater supplies. Removing sulfur species, particularly hydrogen sulfide is important because if left untreated, sulfide can impact finished water quality, corrosivity, create undesirable taste and odor, and oxidize to form visible turbidity and color. This document presents the results of a study designed to investigate the removal efficiencies of a variety of tray aerators in Central Florida in order to develop a predictive mathematical model that could be used to determine tray effectiveness for sulfide removal. A literature review was performed that indicated there was limited information regarding the removal of hydrogen sulfide using conventional tray aerators, and no information regarding the removal of total sulfide from tray aerators. There was significantly more information available in the literature regarding the usefulness of sulfide removal technologies from water supplies. Consequently, the lack of literature regarding sulfide removal using tray aerators suggested that there was a need for additional research focused on sulfide removal from water flowing thru tray aerators. Several water purveyors that relied on tray aerators as a part of their water treatment operations were contacted and requested to participate in the study; three water purveyors agreed to allow the University of Central Florida (UCF) to enter their secured sites to collect samples and conduct this study. The three facilities included the UCF‘s water treatment plant located in Orlando and situated in eastern Orange County, the City of Lake Hamilton‘s water treatment plant located in west-central Polk County, and the Sarasota-Verna water treatment plant located in western Sarasota County. An experimental plan was developed and field sampling protocols were implemented to evaluate sulfide removal in commonly used tray aerators at the three drinking water treatment facilities. Total sulfide concentrations passing through the trays were determined in the field at each site using a standard iodometric analytical technique. In addition, other water quality parameters collected included dissolved oxygen, pH, temperature, conductivity, turbidity, alkalinity, hardness, total dissolved solids and total suspended solids; these samples were collected and analyzed either in the field or at the UCF laboratory. A first-order empirical model was developed that predicted sulfide removal in tray aerators. The model‘s constant was evaluated with respect to the water‘s proton concentration [H+], the tray aerator‘s surface area, and hydraulic flow rate thru the trays. The selected model took the form of C[sub]=C[sub]0 (10[super]-kn) where C[sub]n is the sulfide remaining after aeration in mg/L, C[sub]0 is the sulfide entering the distribution tray in mg/L, n is the number of tray stages in the aerator, and k=(0.00248)(H+)[super]-0.397(Area0[super]0.584(Flow)[super]-1.17. From the empirical model, it was shown that sulfide removal was negatively impacted as the proton concentration (H+) decreased, and flow increased. Conversely, it was observed that increased sulfide removal occurred as the available tray aerator surface area increased. The combined parameters of proton concentration, flow rate, and area were statistically evaluated and used to develop an empirical constant that could be used in a first order model to predict sulfide removal in tray aerators. Using a site-specific derived experimental (empirical) constant, a water purveyor could use the developed model from this work to accurately predict sulfide removal in a tray aerator by simply measuring the total sulfide content in any raw groundwater supply and then providing the desired number of tray stages available for treatment.ID: 029050889; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2010.; Includes bibliographical references (p. 83-87).
M.S.
Masters
Department of Civil, Environmental, and Construction Engineering
Engineering and Computer Science
40
Jang, Wonyong. "Unsteady Multiphase Flow Modeling of In-situ Air Sparging System in a Variably Saturated Subsurface Environment". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7517.
Testo completoAbstract (sommario):
In order to preserve groundwater resources from contamination by volatile organic compounds and to clean up sites contaminated with the compounds, we should understand fate and transport of contaminants in the subsurface systems and physicochemical processes involving remediation technologies. To enhance our understanding, numerical studies were performed on the following topics: (i) multiphase flow and contaminant transport in subsurface environments; (ii) biological transformations of contaminants; (iii) in-situ air sparging (IAS); and, thermal-enhanced venting (TEV). Among VOCs, trichloroethylene (TCE) is one of the most-frequently-detected chemicals in the contaminated groundwater. TCE and its daughter products (cis-1,2-dichloroethylene (cDCE) and vinyl chloride (VC)) are chosen as target contaminants.
Density-driven advection of gas phase is generated by the increase in gas density due to vaporization of high-molecular weight contaminants such as TCE in the unsaturated zone. The effect of the density-driven advection on fate and transport of TCE was investigated under several environmental conditions involving infiltration and permeability.
Biological transformations of contaminants can generate byproducts, which may become new toxic contaminants in subsurface systems. Sequential biotransformations of TCE, cDCE, and VC are considered herein. Under different reaction rates for two bioreaction kinetics, temporal and spatial concentration profiles of the contaminants were examined to evaluate the effect of biotransformations on multispecies transport.
IAS injects clean air into the subsurface below the groundwater table to remediate contaminated groundwater. The movement of gas and the groundwater as a multiphase flow in the saturated zone and the removal of TCE by IAS application were analyzed. Each fluid flow under IAS was examined in terms of saturation levels and fluid velocity profiles in a three-dimensional domain. Several scenarios for IAS systems were simulated to evaluate remedial performance of the systems.
TEV was simulated to investigate its efficiency on the removal of a nonaqueous phase liquid in the unsaturated zone under different operational conditions.
For numerical studies herein, the governing equations for multiphase flow, multispecies transport, and heat energy in porous media were developed and solved using Galerkin finite element method. A three-dimensional numerical model, called TechFlowMP model, has been developed.
41
Weatherford, Jonathan Michael. "Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon". PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2479.
Testo completoAbstract (sommario):
The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption.
A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components.
The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components.
42
Purczel, Carl Leslie. "Evaluating and applying contaminant transport models to groundwater systems /". Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09SM/09smp9854.pdf.
Testo completo
43
Clemente, Roberto Sulit. "A mathematical model for simulating pesticide fate and dynamics in the environment (PESTFADE) /". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70275.
Testo completoAbstract (sommario):
A one-dimensional transient mathematical model which can predict simultaneous movement of water and reactive solutes through homogeneous soil systems under saturated/unsaturated conditions is developed. The physically-based numerical model, called PESTFADE, considers the interactive processes/mechanisms such as mass flow, plant uptake, adsorption/desorption, dispersion, volatilization, chemical/microbial degradation and runoff in the simulation.The PESTFADE model employs SWACROP, a model developed in the Netherlands, to simulate transient water flow in the unsaturated zone; evaluates non-equilibrium sorption in macropores, analyzes soil heat flow to to model microbial degradation, calculates pesticide partitioning in runoff/sediment as affected by agricultural management practices, and describes first order degradation and sorption kinetics. The governing partial differential equation describing the various processes is solved numerically via the Numerical Method of Lines (NMOL) technique, and the computer programs are written in FORTRAN 77. The resulting computer code (PESTFADE), is run on a microcomputer and has been implemented for interactive simulation on IBM PC or compatible microcomputers.
The model was tested and validated using actual data measured from field plot experiments involving herbicide atrazine which was post-emergently applied in a corn field on a loam soil. Various analytical solutions were used to check the accuracy of the different components of PESTFADE, and parametric sensitivity analyses were performed to determine how the model output reacts to changes in some selected input parameters.
Results indicate that model predictions generally agreed with measured concentrations of atrazine and compared closely with the analytical solutions. Moreover, model performance tests showed that predicted values are within acceptable ranges of model accuracy and bound of experimental uncertainties. It was also found that the model is very sensitive to degradation rate constant (k), sorption coefficient (K$ sb{ rm d})$ and soil temperature and slightly sensitive to management practice (CN) and sorption site fraction (F). Finally, the various field scenarios and pathways for non-point source contamination evaluated in the study have demonstrated the wide applicability and flexibility of PESTFADE.
44
Petrula, Lubomír. "Hodnocení kontaminace podzemních vod v oblasti Letiště Přerov". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265335.
Testo completoAbstract (sommario):
The main goal of this work is to assess ground water contamination at the Přerov airport as a consequence to oil products leakage. For this purpose a flow and transport model was created. Another goal is to create and assess several variations of unfavorable scenarios in terms of water quality. The final goal is to create a set of recommendations for the entire area.
45
Rasser, Paul Edward. "Calibration of numerical models with application to groundwater flow in the Willunga Basin, South Australia". 2001. http://thesis.library.adelaide.edu.au/public/adt-SUA20030414.111541/index.html.
Testo completoAbstract (sommario):
Bibliography: 80-82. Electronic publication; full text available in PDF format; abstract in HTML format. The process of calibrating a numerical model is examined in this thesis with an application to the flow of groundwater in the Willunga Basin in South Australia. The calibration process involves estimating unknown parameters of the numerical model so that the output obtained from the model is comparable with data that is observed in the field. Three methods for calibrating numerical models are discussed, these being the steepest descent method, the nonlinear least squares method, and a new method called the response function method. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.
46
Umetsu, Chieko. "Spatial water allocation under conjunctive use". Thesis, 1995. http://hdl.handle.net/10125/9225.
Testo completo
47
Dietrich, Claude Ren{u00E9}. "Identification of hydrogeological systems via inverse procedures". Phd thesis, 1988. http://hdl.handle.net/1885/114574.
Testo completoAbstract (sommario):
This thesis is concerned with three topics. The first two comprise the
development of a new model of salinity transport in a stream connected to a
salty aquifer and the derivation of a new method for the identification of
transmissivity in an aquifer. A third topic interwoven with the first two is
the analysis of ill-posedness often associated with the identification of
hydrological systems.
The salinity transport model is derived from basic mass conservation
equations and from the representation of the stream-aquifer interaction by
a convolution integral. In order to restrict model complexity to a level
compatible both with the available data and with the objectives of the
modelling exercise, several simplifying assumptions are invoked and
result in a model linear in the parameters. The identification procedure is
performed via recursive instrumental variable techniques. The
ill-posedness associated with the deconvolution of the stream-aquifer
system is addressed through the choice of a low level of parameterization
for the kernel of the convolution. The salinity transport model is tested on a
207 km stretch of the River Murray.
The identification of transmissivity in a confined and steady aquifer is
carried out via the use of a direct approach based on a weak formulation of
the aquifer flow equation. The approach leads to a natural discretization by
a Galerkin method via the use of spectral expansions for the piezometric
head, the sink/source flow and the transmissivity over subregions of the
aquifer. The ill-posedness of the problem is counteracted by inclusion of a
smoothing constraint involving the linearized curvature of the unknown
transmissivity. The computation of the regularizing parameter is
perfomed by generalized cross-validation. The method provides guides to
assess the amount of information truly present in the data. In addition, it
is amenable to error analysis. Results based on synthetic data are provided.
The general question of ill-posedness encountered in inverse problems
is addressed in detail. Furthermore, a review of the work reported in recent
years in the mathematical literature and relevant to the identification of
hydrological systems is presented. Finally, an analysis of the conditioning
of the geo statistical approach to aquifer identification is provided.
48
Brown, Theresa Jean. "Modeling the effects of aerosols on groundwater systems". Thesis, 1989. http://hdl.handle.net/2152/21321.
Testo completoAbstract (sommario):
Just as children eventually learn that covering their eyes does not make them invisible, we as adults have realized that just because harmful substances are "out-of-site" it does not necessarily mean they are gone for good. As we expanded our ability to think abstractly we began to consider how our actions affect our future and the lives of future generations. For example, we established procedures for the handling and disposal of high level radioactive waste and other hazardous materials because of the threat such materials pose to the environment. To date, however, the effect of atmospheric pollutants on groundwater supplies has been virtually ignored. Atmospheric pollution sources include, but are not limited to, smoke stack emissions, releases from power plants, weapons testing and manufacturing, fires, explosions, and deflation from tailings, spills and playas. This study evaluates the potential for groundwater to be contaminated by a point-source atmospheric emission. Pollutant concentrations in groundwater are estimated using a Gaussian model of atmospheric transport, a transfer function model for transport through the unsaturated zone, and a two-dimensional groundwater flow model based on Darcy's law to simulate transport in the saturated groundwater system. A sensitivity analysis of the composite atmospheric-groundwater transport model suggests that the most important factors influencing the susceptibility of a groundwater system to contamination by an aerosol source are: the concentration of the source, the amount of recharge, the depth to the water-table, and the velocity distribution in the unsaturated zone. This study indicates a significant potential for pollution of groundwater systems by aerosols. Shallow aquifers are especially vulnerable; however, deeper aquifers where rapid travel times through the unsaturated zone exist are also susceptible to aerosol contamination.text
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Jayanti, Shekhar. "Modeling tracers and contaminant flux in heterogeneous aquifers". Thesis, 2003. http://wwwlib.umi.com/cr/utexas/fullcit?p3116345.
Testo completo
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Kaucner, Christine E. Civil & Environmental Engineering Faculty of Engineering UNSW. "Factors influencing overland mobility of Cryptosporidium Oocysts". 2007. http://handle.unsw.edu.au/1959.4/40609.
Testo completoAbstract (sommario):
The mechanisms responsible for overland transport of faecal pathogens, particularly Cryptosporidium oocysts, from animal sources to water bodies are not fully understood. Surface properties of microbes, such as electrostatic charge and hydrophobicity, are thought to contribute to their aggregation and attachment to solid surfaces. There is conflicting evidence that methods used to purify Cryptosporidium oocysts from faecal material may affect the oocyst surface, leading to biased conclusions from transport studies. By studying oocyst surface properties, aggregation and soil attachment, this thesis addressed whether oocyst purification methods influence overland transport studies, and whether oocysts are likely to be associated with particles during transport. When using the microbial adhesion to hydrocarbon (MATH) assay with octane, oocyst hydrophobicity was shown to be method and isolate dependent, with oocysts displaying moderate to high hydrophobicity in 0.01 M KNO3. There was no observed attachment, however, to the hydrophobic octyl-SepharoseTM bead ligands when using the same suspension solution. Oocyst age did not appear to influence their hydrophobicity. A small but statistically significant proportion of oocysts displayed a net negative surface charge as observed by their attachment to an anion exchange ligand (DEAE). There was no difference in hydrophobicity or surface charge observed between purified oocysts and oocysts that had been extracted without the use of harsh chemicals and solutions with dehydrating properties. Purified oocysts did not aggregate at pH values between 3.3 and 9.0, nor in solutions lower than 0.59 M in ionic strength at a pH 2.7 which is approaching the reported isoelectric point of oocysts. This finding suggests that oocysts may not form aggregates under general environmental conditions. The association of purified oocysts with soil particles was observed in settling columns. Attachment to soil particles was not conclusive since the settling of the soil particles may have entrained single oocysts. Nonetheless, approximately 27% of oocysts were estimated to be unbound to soil or associated with small soil particles. Hence models for oocyst overland transport should consider a significant fraction as single entities or associated with soil particles less than about 3 μm in size.