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1
Zhang, Jing. "Modeling considerations for vadose zone soil moisture dynamics." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0001982.
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2
Ausland, Hayden Willis. "Vadose zone denitrification enhancement by poplars during dormancy." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/4566.
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3
Dickinson, Jesse, and Jesse Dickinson. "Filtering of Cyclical Infiltration Forcings in the Vadose Zone." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/623171.
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Infiltration and downward percolation of water in the vadose zone are important processes that define the availability of water resources in many areas of the world. Flow in the vadose zone can vary spatially and temporally because of the complex exchange of water and energy between the land surface and atmosphere. Precipitation and infiltration forcings at the surface are filtered in the vadose zone in terms of the lag time between the forcing at the land surface and a response at any depth, and the damping of the magnitude of flux variability with depth. Climate projections call for changes in both the timing and magnitude of precipitation and land surface forcings, which increases the importance of understanding how the vadose zone filters these forcings to predict the impacts of climate variability and change on groundwater resources. This dissertation research presents a theoretical framework for assessing how cyclical variations in one-dimensional, vertical flow are filtered in the vadose zone. The filtering properties are described using analytical and numerical solutions. The analytical solution linearizes Richards equation by representing the diffusive properties of the soil as constant through time. The numerical solution uses the full Richards equation. Three implications for filtering in the vadose zone using a linearized and full Richards equation are investigated in three modeling experiments. In the first experiment, the analytical solution is used to identify subregions of aquifers where infiltration variations are sufficiently damped so that recharge can be approximated to be steady through time. The linearized solution overestimates the diffusive properties of soils, thus the amount of damping and the area of subregions of steady recharge are both under predicted. In the second experiment, the linearized analytical solution is superimposed vertically to represent the lag time and damping in layered soils. The superposed linearized solutions do not represent transitions of soil-water properties that occur between real soil layers. As a result, the filtering can be over or under predicted because of systematic errors in the estimated water capacity in the analytical solution. The filtering in homogenous and layered soils (first and second experiments) is more accurate when the water content and diffusivity variations are small, and when soil layers are relatively thick compared to the depth over which the damping occurs. In the third configuration, a numerical solution which solves the full Richards equation is used to evaluate how multiple asynchronous infiltration cycles interfere constructively and destructively in homogeneous soil. A new cyclical variation in infiltration is generated within the vadose zone through the nonlinear interaction of cycles with similar frequencies. The emergent cycle may result in prolonged periods of both enhanced and decreased recharge.
4
Nakajima, Hideo. "Centrifuge modeling of LNAPL movement in the vadose zone /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.
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5
Rossi, Matteo. "Non invasive hydrogeophysical techniques for vadose zone hydrological characterization." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3427485.
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Hydrogeophysics is a discipline that emerged and had a great development in the last two decades. The aim of this discipline is the subsurface hydrological and hydrogeological characterization via non-invasive geophysical techniques. Conventional sampling techniques, for characterizing or monitoring the shallow subsurface, are typically sparsely distributed or acquired at an inappropriate scale. Non-invasive geophysical datasets can provide more dense 2D/3D information. The present work focused on the hydrological characterization of the vadose zone, as it is a challenging issue that may be more deeply and extended understood.
The dependence of the geophysical response on changes in soil moisture content, e.g. via changes in electrical resistivity or dielectric properties, is the key mechanism that permits the use of non-invasive techniques to monitor the vadose zone in time-lapse mode, i.e. via repeated measurements over time. The use of these techniques in different configurations in the shallow and deep vadose zones can provide high-resolution images of hydrogeological structures and a detailed assessment of dynamic processes in the subsurface environment. The data from non-invasive techniques can subsequently be used to calibrate physical-mathematical models of water flow in the unsaturated zone. The understanding of fluid-dynamics is the key to all hydrologically-controlled environmental problems. The hydrogeophysical approach is based on links that can be established between geophysical quantities and hydrological variables, such as water content and solute concentration, generally in the form of empirical or semi-empirical petrophysical relationships.
The classical hydrogeophysical approach in hydraulic parameters evaluation starts from the measured geophysical data to estimate the hydrological state, albeit careful is need at this step: essential is the knowledge achievable from field data and the relative accuracy in the physical translation. Anyway this is the starting point for the hydrological simulation. Subsequently the hydrological modelled parameters may be compared and evaluated with the hydrological quantities obtained from geophysics through the petrophysical relationships. This approach can lead to erroneous parameter inference, if the spatial resolution of the geophysical techniques is not taking into account.
A different approach can be proceed, to overcome this issue. In spite of translating geophysical parameters in hydrological quantities, the comparison may be done directly on the not-inverted geophysical data. The geophysical surveys can be simulated with a forward model, starting from the hydrological modelled properties distribution and applying the petrophysical relationship to reconstruct the geophysical spatially-distributed parameters. At this point geophysical measured and simulated data can be compared, with the aim of calibrate and validate the hydrological model under examination. This second approach, not requiring geophysical inversions, is able to overcome artefacts deriving from the inversion procedure; but the resolution of the surveys must be considered, because an hydrological state should not be reproduced from geophysical methodologies, even if the two datasets, both simulated and measured, are in a perfect fitting.
The work is divided in two complementary parts. The first part is centred on the hydrological quasi-steady state characterization from cross-hole radar measurements. In many studies cross-borehole zero offset profiles (ZOP) are used to infer subsoil moisture content, which are a key topic in hydrological modelling and consequently in hydraulic parameters estimation. The principal aim of this work is to have a more complete view of how boreholes GPR ZOP measurements are informative of the subsoil geometry and distribution of relative permittivity. This is essential in moisture content estimation, uncertainty quantification and in the initial setting of parameters necessary for starting an hydrological model. For this purpose three different ZOP datasets are analysed: a synthetic dataset and two field-measured datasets.
The second part of the work is the hydrogeophysical inversion of a tracer test in the vadose zone, conducted at the Hatfield site (near Doncaster, UK). The path of a tracer in vadose zone may be masked from the variations of the physical status surrounding the dispersive plume; this could lead to erroneous interpretations of the evolving plume. The load of the new water, that moves under gravitational forces, produces the raising of the degree of saturation in the media just below the plume. This incidental effect could significantly contribute to geophysical signals and hydrological characterizations. The aim of this study is the recognition and distinction of the paths of the new injected fluid from the groundwater, already present in the system and activated from pressure variations, in a sort of “piston” effect. The discrimination between the new percolating water and the old pushed-down water is a key issue in aquifer vulnerability and soil pollution migrations, which can affect the vadose zone. In this second part the hydrogeophysical inversion is conducted: the simulated hydrological quantities are used to obtain a geophysical forward model of ZOP surveys, that should be compared with measured ZOP soundings. An estimation of the goodness of the hydrological model is then possible. A particle tracking code is then run to detect the exact evolution of the tracer plume in the subsurface. A comparison with the results from the inverted geophysical datasets is able to discriminate the tracer fluid from the old water of the system and to individuate where the geophysical imaging could be deceptive and misleading.
The present work is an example of the hydrogeophysical inversion methods, where great emphasis is focused on the characterization of the hydraulic state preceding the tracer injection test. Anyway the system must be stressed under artificial hydraulic states to force the parameters estimation and to limit the range of probable hydrological models.L’idrogeofisica è una disciplina che è emersa ed ha avuto un importante sviluppo nelle ultime due decadi. Lo scopo di questa disciplina è la caratterizzazione idrologica ed idrogeologica del sottosuolo attraverso tecniche geofisiche non invasive. Le tecniche di campionamento convenzionali sono di norma spazialmente distribuite ed acquisite ad una scala impropria. Le tecniche geofisiche invece permettono indagini spazialmente più fitte in 2D o 3D. Il presente lavoro si focalizza sulla caratterizzazione idrologica della zona vadosa. I dati ottenuti dalle tecniche geofisiche possono essere utilizzati per calibrare modelli fisico matematici del flusso nella zona del non-saturo. Tale approccio idrogeofisico è basato su relazioni petrofisiche che legano le quantità geofisiche con le variabili idrologiche. Il classico approccio idrogeofisico parte dalle misure geofisiche per ottenere una stima di parametri idrologici, che a loro volta vengono impiegati in modelli idraulici in grado di fornire ulteriori proprietà del sistema idraulico del sottosuolo. I modelli idrologici vengono successivamente validati e calibrati con i risultati delle inversioni geofisiche in time-lapse. Questo approccio prevede l’inversione del dato geofisico, metodo che può portare ad immagini del sottosuolo che contengono artefatti e che non tengono conto della risoluzione della tecnica applicata. Un approccio differente prevede che ai parametri stimati dai modelli idraulici siano applicate le relazioni petrofisiche, al fine di tradurre le quantità idrologiche in quantità geofisiche. A questo punto la simulazione di modelli geofisici diretti permette un confronto immediato con i dati misurati, senza l’ausilio dell’inversione geofisica. Il presente lavoro è suddiviso in due parti. La prima parte è centrata sulla caratterizzazione idrologica dello stato stazionario iniziale attraverso misure radar (GPR). Lo scopo principale del lavoro è quello di quantificare quanto le misure GPR a zero offset profiling (ZOP) siano informative delle geometrie del sottosuolo e delle relative condizioni di contenuto idraulico dei materiali. Questo lavoro è essenziale per ottenere una stima del contenuto idrico del sottosuolo e della relativa incertezza che ne deriva, poiché tali stime sono il punto di partenza delle simulazioni idrauliche. La seconda parte del lavoro è focalizzata sulla inversione idrogeofisica di un test con tracciante salino condotto ad Hatfield (UK). L’approccio idrogeofisico adottato è quello di simulare misure geofisiche direttamente dalla distribuzione dei parametri idrologici calcolati, per ottenere una calibrazione di quelle quantità idrologiche scopo della metodologia applicata. La ricostruzione dell’evoluzione di un plume iniettato nella zona vadosa è interessante ai fini di identificare i possibili percorsi di un contaminante nel sottosuolo. A tale scopo un codice di particle tracking è stato applicato ai risultati dell’inversione idrologica. Il codice di partcle tracking è in grado di distinguere i percorsi dell’acqua iniettata dall’acqua già presente nel sistema e movimentata del cambiamento di pressione in atto, ‘effetto pistone’. Le inversioni delle misure geofisiche non permettono di distinguere il fluido tracciante dai cambiamenti del contenuto idrico dei materiali adiacenti al plume iniettato.
6
Lookingbill, Scott David, and Scott David Lookingbill. "Effects of concentration-dependent surface tension on vadose zone instrumentation." Thesis, The University of Arizona, 1997. http://hdl.handle.net/10150/626774.
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Many of the organic compounds of environmental interest which are commonly found
at contaminated sites have the effect of lowering the surface tension of water in proportion
to their aqueous concentration. Laboratory studies were conducted to investigate the
effects of reduced surface tension on instruments commonly used to measure pressure
head in the vadose zone. Gypsum block electrical resistance sensors and heat dissipation
probes were calibrated in tap water and in butanol solutions. A scaling relationship was
used to correct pressure head measurements taken in liquids of reduced surface tension.
The results indicate that the these measurements would be in error in that they would
underestimate pressure head for solutions of lower surface tension to the same factor by
which surface tension was reduced. This would result in pressure head gradient and flux
being underestimated as well. Therefore, surface tension effects on these instruments
should be considered when measuring pressure head in soils contaminated with organic
compounds.
7
Unc, Adrian. "Transport of faecal bacteria from manure through the vadose zone." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40445.pdf.
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8
Bashir, Rashid Smith James E. Stolle Dieter. "Quantification of surfactant-induced unsaturated flow in the vadose zone." *McMaster only, 2007.
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9
Dippenaar, Matthys Alois. "Assessment of vadose zone hydrology : concepts, methods, applications and guidelines." Thesis, University of Pretoria, 2014. http://hdl.handle.net/2263/43319.
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Vadose
zone
hydrology
is
a
developing
science
influenced
by
earth
scientists
(soil
scientists,
pedologists,
hydrogeologists,
engineering
geologists
and
geomorphologists)
and
engineers
(geotechnical).
However,
problems
faced
are
associated
with
lack
of
agreement
between
basic
concepts,
different
approaches
and
definitions,
and
difficulty
in
communicating
findings
to
other
technical
or
non-‐technical
audiences.
The
need
for
better
cross-‐disciplinary
dialogue
and
understanding
subsequently
becomes
increasingly
important,
notably
given
the
sensitivity
of
investigation
related
to
ephemeral
wetlands,
contamination
and
water
impacting
infrastructure
development.
This
thesis
therefore
aims
to
address
basic
concepts,
accepted
methodologies
and
highly
variable
and
sensitive
case
studies
in
order
to
minimise
risk
in
the
assessment
of
the
vadose
zone.
Terminologies,
quantification,
methods
and
existing
guidelines
are
critically
appraised
and
validated
based
on
three
case
studies.
Findings
are
reported
in
order
to
improve
investigation
techniques
and
to
minimise
risk.
Final
recommendations
are
made
regarding
a
proposed
vadose
zone
assessment
protocol
to
ensure
compliance
to
a
set
of
minimum
requirements
for
vadose
zone
assessment.
It
is
hoped
that
such
a
methodology
will
be
implemented
towards
protection
of
the
natural
environment,
notably
in
urban
areas,
as
well
as
to
prevent
damage
to
infrastructure.Thesis (PhD)--University of Pretoria, 2014.
lk2014
Geology
PhD
Unrestricted
10
Patton, Erik Mark. "Modeling vadose zone wells and infiltration basins to compare recharge efficiency in unconfined aquifers." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/38217.
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Master of ScienceDepartment of Geology
Saugata Datta
In specific lithologic and hydrogeological settings, Managed Aquifer Recharge (MAR) projects using vadose zone wells have the potential to outperform infiltration basins in terms of volume of water recharged. Numerical modeling can assist in determining which recharge method is most efficient in infiltrating water to unconfined alluvial aquifers of differing unsaturated zone lithologic complexities. The Sagamore Lens Aquifer (SLA) in Cape Cod, Massachusetts is an example of an aquifer with minimal lithologic complexity while the Hueco Bolson Aquifer (HBA) near El Paso, Texas has greater lithologic complexity. This research combines two U.S. Geological Survey numerical models to simulate recharge from infiltration basins and vadose wells at these two locations. VS2DTI, a vadose zone model, and MODFLOW-2005, a saturated zone model, were run sequentially at both sites and with both vadose well and infiltration basin recharge methods simulated. Results were compared to determine the relative effectiveness of each method at each location and to determine the effects of vadose zone complexity on recharge. At the HBA location, soil samples were tested for conductivity and grain size distribution and a microgravity survey was begun to constrain the models. The infiltration basin structure proved to be more efficient, infiltrating more water volume at both locations. Lithologic complexity formed perched conditions in the HBA model, significantly affecting infiltration rates from both infiltration methods at that location. Methods and conclusion from this study can assist in the modeling and design of future MAR projects, especially in locations with thick or lithologically complex vadose zones.
11
Shah, Nirjhar. "Vadose zone processes affecting water table fluctuations : conceptualization and modeling considerations." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002260.
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12
Yeh, T. C. Jim. "Scale issues of heterogeneity in vadose zone hydrology and practical solutions." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1996. http://hdl.handle.net/10150/615702.
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Hydrological properties of the vadose zone often exhibit a high degree of spatial variability
at various scales due to the heterogeneous nature of geological formations. For laboratory scale
problems (i.e., small cores, soil columns, and sand boxes), variation in pore size, pore geometry, and
tortuosity of pore channels are the major source of heterogeneity. They are called laboratory-scale
heterogeneity. Microstratification, foliation, cracks, and roots are also some possible heterogeneities
at this scale. As our observation scale increases to a field, stratification or layering in a geologic
formation becomes the dominant heterogeneity, which is often classified as field-scale heterogeneity.
At an even larger observation scale, the regional-scale heterogeneity represents the variation of
geologic formations or facies. Variations among sedimentary basins are then categorized as the
global-scale heterogeneity.
Fundamental theories for flow and solute transport through porous media are essentially
derived for the laboratory-scale heterogeneity. When we attempt to apply these theories to the
vadose zone, comprising heterogeneities of many different scales, we encounter the scale problem.
To resolve this problem two approaches have evolved in the past: the system approach and the
physical approach. The former approach treats the vadose zone as a low pass filter and its governing
principle is determined by the relationship between its input and output histories (e.g., Jury et al.,
1986). The latter approach however relies on upscaling the laboratory-scale theories to the vadose
zone. While the system approach has been widely used by soil scientists, it is often criticized for its
empiricism and the lack of physical principles. Besides, it is known to be limited to nonpoint source
problems or those related to the integrated behavior of a system (for example, the average
concentration of nitrate in the irrigation return flow at irrigation drains or their breakthrough at the
water table beneath an irrigation field). Since this approach requires the knowledge of input and
output histories and model calibrations, flow and tracer experiments must be carried out at a given
site prior to prediction. Further, a calibrated system model for the vadose zone at a given depth under
a given condition is often found unsuitable for different depths and conditions (e.g., Butters et al.,
1989; Butters and Jury, 1989; Roth et al., 1991).
While such system approaches are practical tools for predicting water flow and pollutant
transport through thin vadose zones to the water table or to irrigation drains at agricultural fields,
their utility for general hydrogeological problems is limited. Hydrogeological problems involve
vadose zones of tens and hundreds of meters in thickness. Input sources to these vadose zones are
small compared with the scale of hydrogeological settings. Yet, groundwater hydrologists have to
focus on the spatial and temporal evolution of flow and spread of solutes over the vadose zone and
regional aquifers (Stephens, 1996). Because of these above- mentioned reasons, the following
discussion will concentrate on the physical approach that has been widely used by groundwater
hydrologists. Moreover, the discussion will present only the author's point of view about the scale
issue and approaches to the heterogeneity in the vadose zone.
13
Yeh, T. C. Jim, Jirka Simunek, and Genuchten Martinus Th Van. "Stochastic fusion of information for characterizing and monitoring the vadose zone." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 2002. http://hdl.handle.net/10150/615767.
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Inverse problems for vadose zone hydrological processes are often being perceived as ill -
posed and intractable. Consequently, solutions to inverse problems are often subject to
skepticism. In this paper, using examples, we elucidate difficulties associated with inverse
problems and the prerequisites for such problems to be well -posed so that a unique solution
exists. We subsequently explain the need of a stochastic conceptualization of the inverse
problem and, in turn, the conditional- effective -parameter concept. This concept aims to resolve
the ill -posed nature of inverse problems for the vadose zone, for which generally only sparse data
are available. Next, the development of inverse methods for the vadose zone, based on a
conditional -effective -parameter concept, is explored, including cokriging, the use of a successive
linear estimator, and a sequential estimator. Their applications to the vadose zone inverse
problems are subsequently examined, which include hydraulic /pneumatic and electrical
resistivity tomography surveys, and hydraulic conductivity estimation using observed pressure
heads, concentrations, and arrival times. Finally, a stochastic information fusion technology is
presented that assimilates information from unsaturated hydraulic tomography and electrical
resistivity tomography. This technology offers great promise to effectively characterize
heterogeneity, to monitor processes in the vadose zone, and to quantify uncertainty associated
with vadose zone characterization and monitoring.
14
Vermaak, Jan Johannes Gerhardus. "Geotechnical and hydrogeological characterization of residual soils in the vadose zone." Thesis, Pretoria : [s.n.], 2000. http://upetd.up.ac.za/thesis/available/etd-12042006-15912.
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15
Ponciano, Isaac de Matos. "Simulação da extração da solução do solo pela cultura do milho utilizando modelo SWAP." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/11/11152/tde-03052016-164616/.
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A modelagem da dinâmica de solutos no solo tem se mostrado uma ferramenta essencial, pois permite simular cenários e prever impactos ao meio ambiente associados ao manejo inadequado de fertilizantes agrícolas. Na zona radicular das culturas a parametrização do transporte de solutos, bem como a parametrização física do solo, são de difícil determinação tornando a sua modelagem onerosa e imprecisa. Portanto, a presente pesquisa teve como objetivo avaliar a performance do modelo SWAP (Soil, Water, Atmosphere and Plant), em simular a extração da solução do solo pela cultura do milho, em ambiente protegido. O ambiente de estudo ficou restrito à rizosfera da cultura do milho ao longo de seu ciclo de desenvolvimento, mediante a aplicação de uma solução de nitrato de potássio via água de irrigação. Para isso, conduziu-se um experimento em ambiente protegido, cujo cultivo do milho foi feito em 18 lisímetros de drenagem de 500L com plantio de duas covas por lisímetro (plantio em 22/11/2014 e colheita em 22/02/2015). Os valores de umidade volumétrica do solo e de condutividade elétrica da solução do solo foram registrados pela TDR (Time Domain Reflectometry), sendo monitorados em 4 profundidades ao longo da secção transversal das raízes (5, 15, 25 e 35 cm). Também foram monitoradas variáveis agrometeorológicas a fim de se descrever as condições experimentais. Os valores simulados pelo modelo SWAP foram confrontados com os dados observados, registrados pela TDR. A avaliação da performance do modelo foi feita pelo emprego do índice de concordância (Id), índice de avaliação de modelos (E), raíz quadrada média do erro (RMSE) e coeficiente de determinação. Diante dos resultados obtidos, percebeu-se pelo monitoramento agrometeorológico que o ciclo da cultura se deu em condições de anomalias climáticas, isso de certa forma influenciou na extração de água pela cultura. A simulação da extração de água na rizosfera do milho pelo modelo SWAP demonstrou uma satisfatória performance do modelo, o qual apresentou resultado pelos índices de avaliação valores superiores a 0,7 e índices de concordância superiores a 0,9 para todas as camadas monitoradas. O erro quadrático médio foi inferior a 0,009 cm3 cm-3 para todas as camadas, apesar de ter nas camadas mais profundas uma atenuação qualitativa na simulação. O movimento da extração da solução do solo na rizosfera, em especial, nas camadas superficiais apresentaram resultados satisfatórios com índices de avaliação de modelos de 0,659 e 0,596 e índices de concordância de 0,913 e 0,834, respectivamente, para as camadas de 5 e 15 cm de profundidade. Já para as camadas mais profundas não se observou boa aderência do valor simulado aos dados. O coeficiente de extração relativa da solução do solo pelo milho apresentou valor de 16%. Assim, o modelo SWAP mostrou-se satisfatório na simulação do movimento da solução do solo na zona radicular da cultura do milho, mesmo sob condições atmosféricas extremas. Não obstante, seu desempenho foi prejudicado para as simulações em camadas inferiores, onde foi observada uma baixa variação do conteúdo de água e concentração de sais no solo.The modeling of solute dynamics in soil is an essential tool for simulating scenarios and predicting environment impacts associated with inadequate management of fertilizers. Solute transport parameter and soil physical parameters in the vadose zone are difficult to determine, causing modeling to be expensive and imprecise. This research, therefore, was set up to evaluate the effectiveness of the SWAP (Soil, Water, Atmosphere and Plant) model to simulate soil solution uptake by corn under controlled environmental conditions. The study consisted of applying a potassium nitrate solution in irrigation water to maize rhizosphere throughout its development cycle. The experiment was conducted in a greenhouse, in which maize was planted on 11/22/2014 and harvested on 02/22/2015 in eighteen 500L drainage lysimeters.The soil moisture values and electrical conductivity of soil solution were registered by TDR (Time Domain Reflectometry) at four depths (5, 15, 25 and 35 cm) along the cross-section of the root. Environmental variables were also monitored in order to characterize the experimental conditions. Values simulated by the SWAP model were compared with observed data recorded by the TDR. Model performance was evaluated by the use of the Concordance Index (Id), the Model Assessment Index (E), Root Mean Square Error (RMSE), and Coefficient of Determination. As the experiment was conducted under controlled conditions, the water uptake patterns might not be reflective of uptake patterns under normal weather conditions. The simulation of water extraction in the rhizosphere of corn by SWAP model matched observed values, with indices greater than 0.7 and concordance rates of over 0.9, for all monitored layers. The RMSE was less than 0.009 cm3 cm-3 for all layers. The concentration of extracts of the soil solution in the rhizosphere, in particular in the top two layers, were satisfactorily simulated with model evaluation indexes of 0.659 and 0.596, and concordance rates of 0.913 and 0.834, respectively, for the 5 and 15 cm layers. For the deeper layers, there was little correlation between the observed and simulated value. The relative extraction coefficient of soil solution for corn was 16%. Thus, the SWAP model satisfactorily simulated soil solution movement in the upper layers of the vadose zone of maize, even under extreme weather conditions. However, the model did not perform as well in the lower layers performance was impaired for the simulations in lower layers, which had low variation in the observed water content and salt concentration in the soil.
16
Cockett, Archa Rowan B. "A framework for geophysical inversions with application to vadose zone parameter estimation." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/64162.
Full textAbstract:
Inverse modeling is a powerful tool for extracting information about the subsurface from geophysical and hydrologic data. Geophysical inverse problems are inherently multidisciplinary, requiring elements from the relevant physics, numerical simulation, and optimization, as well as knowledge of the geologic setting, hydrologic processes, and a comprehension of the interplay between all of these elements. Increasingly geoscientists are tackling complex problems that require integration of multiple types of information in order to better characterize the subsurface. However, many of the sub-fields of geophysics are developing simulation and inversion approaches, algorithms, and supporting software in isolation. This isolation is a barrier to quantitative integration and leads to inefficiencies in advancing interdisciplinary research. Greater efficiencies, and higher quality outcomes, could be achieved if (hydro)geophysicists had a common framework to accelerate an integrated approach. The main goal of my thesis is to organize the components of (hydro)geophysical simulations and inverse problems, and synthesize these into a comprehensive, modular framework.
The development of a geophysical framework requires considering a number of disciplines and geophysical problems (e.g. electromagnetics and potential fields) to ensure generality as well as extensibility. However, the goal is also to have the framework work outside of geophysics and most notably in hydrogeology; vadose zone fluid flow is used as a model problem. Fluid flow in the vadose zone is governed by the Richards equation; it is parameterized by hydraulic conductivity, which is a nonlinear function of pressure head. The computational scalability of the Richards equation inversion is a significant challenge for three dimensional inversions in hydrogeophysics. Existing work explicitly calculates the sensitivity matrix using finite difference or automatic differentiation, however, for large-scale problems these methods are constrained by computation and memory. This dissertation provides an implicit sensitivity algorithm that enables large-scale inversion problems for distributed parameters in the Richards equation to become tractable on modest computational resources.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Zimmerlund, Benjamin Wayne, and Benjamin Wayne Zimmerlund. "Vadose zone characterization pertaining to artificial groundwater recharge, Southern Avra Valley, Arizona." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/626931.
Full textAbstract:
The City of Tucson plans to construct a groundwater recharge and recovery
facility in southern Avra Valley to infiltrate Central Arizona Project (CAP) water. The
Southern Avra Valley Recharge and Recovery Project (SA VSARP) will initially recharge
up to 60,000 acre-feet of CAP water per year. Characterization of the vadose zone is
important in understanding the behavior of recharged water. Using grain-size distribution
data from well cuttings, three lithologic units are defined and a 2-D vertical cross-section
is developed in the area of predominant recharge. Soil samples representing each defined
lithologic unit are laboratory tested for saturated and unsaturated flow parameters. Soil
moisture retention data is fit to the van Genuchten equation to obtain unsaturated flow
model parameters. A 1-D unsaturated flow model is developed using VSAFT2 to
simulate infiltration of CAP water through the vadose zone.
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Demirkanli, Deniz I. "Modeling long-term plutonium transport in the Savannah River Site vadose zone." Connect to this title online, 2006. http://etd.lib.clemson.edu/documents/1173995114/.
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Holm, Rochelle Hales. "Comparison of three drilling technologies to characterize the vadose zone, Hanford Site." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Summer2007/r_holm_062107.pdf.
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Haile, Sosina Shimeles. "VS2DRT: Variably saturated two dimensional reactive transport modeling in the vadose zone." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-107821.
Full textAbstract:
Contaminate transport in vadose is a huge concern since the vadose zone is the main passage way for ground water recharge. Understanding this process is crucial in order to prevent contamination, protect and rehabilitate ground water resources. Reactive transport models are instrumental for such purposes and there are numerous solute transport simulation programs for both ground water and vadose zone but most of this models are limited to simple Linear, Langmuir and Freundlich sorption models and first order decay and fail to simulate more complex geochemical reactions that are common in the vadose zone such as cation exchange, surface complexation, redox reaction and biodegradation. So it is necessary to enhance capabilities of solute transport models by incorporating well tested hydrogeochemical models like PHREEQC in to them to be able closely approximate the geochemical transport process in the subsurface.
In this PhD research a new reactive transport model called VS2DRT was created by coupling existing public domain solute and heat transport models VS2DT, VS2DH with hydro-chemical model PHREEQC using non-iterative operator splitting technique. VS2DRT was compiled using MinGW compiler using tools like autotools and automake. A graphical user interface was also created using QT creator and Argus ONE numerical development tools. The new model was tested for one dimensional conservative Cl transport, surface complexation, cation exchange, dissolution of calcite and gypsum, heat and solute transport as well as for two dimensional cation exchange cases. Their results were compared with VS2DT, VS2DH, HP1 and HP2 models and the results are in good agreement.
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Bravo-Lopez, Ana Ivonne. "The fate of petrol oxygenates and BTEX compounds in the vadose zone." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409144.
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Yeh, T. C. Jim, and Jinqi Zhang. "A Geostatistical Inverse Method for Variably Saturated Flow in the Vadose Zone." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1995. http://hdl.handle.net/10150/614185.
Full textAbstract:
A geostatistical inverse technique utilizing both primary and secondary information is
developed to estimate conditional means of unsaturated hydraulic conductivity parameters (saturated
hydraulic conductivity and pore -size distribution parameters) in the vadose zone. Measurements of
saturated hydraulic conductivity and pore -size distribution parameters are considered as the primary
information, while measurements of steady -state flow processes (soil -water pressure head and degree
of saturation) are regarded as the secondary information. This inverse approach relies on the classical
linear predictor (cokriging) theory and takes the advantage of the spatial cross- correlation between
soil -water pressure head, degree of saturation, saturated hydraulic conductivity, and pore -size
distribution parameter. Using an approximate perturbation solution for steady, variably saturated
flow under general boundary conditions, the cross- covariances between the primary and secondary
information are derived. The approximate solution is formulated based on a first -order Taylor series
expansion of a discretized finite element equation. The sensitivity matrix in the solution is evaluated
by an adjoint state sensitivity approach for flow in heterogeneous media under variably saturated
conditions. Through several numerical examples, the inverse model demonstrates its ability to
improve the estimates of the spatial distribution of saturated hydraulic conductivity and pore -size
distribution parameters using the secondary information.
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Zhang, Jinqi, and T. C. Jim Yeh. "An Iterative Geostatistical Inverse Method For Steady-Flow In The Vadose Zone." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1996. http://hdl.handle.net/10150/614010.
Full textAbstract:
An iterative stochastic inverse technique utilizing both primary and secondary
information is developed to estimate conditional means of unsaturated hydraulic conductivity
parameters (saturated hydraulic conductivity and pore -size distribution parameters) in the
vadose zone. Measurements of saturated hydraulic conductivity and pore -size distribution
parameter are considered as the primary information, while measurements of steady -state flow
processes (soil -water pressure head and degree of saturation) are regarded as the secondary
information. This inverse approach is similar to the classical geostatistical approach, which
utilizing a linear estimator that depends on the cross- covariance and covariance functions of
unsaturated hydraulic conductivity parameters and flow processes. The linear estimator is,
however, improved successively by solving the governing flow equation and by updating the
residual covariance and cross- covariance functions, in an iterative manner. Using an
approximate perturbation solution for steady, variably saturated flow under general boundary
conditions, the covariances of secondary information and the cross -covariance between the
primary and secondary information are derived. The approximate solution is formulated based
on a first -order Taylor series expansion of a discretized finite element equation. The
sensitivity matrices in the solution are evaluated by an adjoint state sensitivity approach for
flow in heterogeneous media under variably saturated conditions. As a result, the nonlinear
relationships between unsaturated hydraulic conductivity parameters and flow processes are incorporated in the estimation. Through some numerical examples, the iterative inverse model
demonstrates its ability to improve the estimates of the spatial distribution of saturated
hydraulic conductivity and pore -size distribution parameters compared to the classical
geostatistical inverse approach. In addition, the inconsistency problem existing in classical
geostatistical inverse approach is alleviated. The estimated fields of unsaturated hydraulic
conductivity parameters and flow fields not only retain their observed values at sample
locations, but satisfy the governing flow equation as well.
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Zacharias, Sebastian. "Modeling Spatial Variability of Field-Scale Solute Transport in the Vadose Zone." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30775.
Full textAbstract:
Spatial heterogeneity in the soil system has a profound influence on the flow of water and chemicals in the unsaturated zone. Incorporating intrinsic soil variability and extrinsic variability into root zone leaching models will provide a better representation of pollutant distribution in natural field conditions.
In this study, a stochastic framework (SF) was developed to represent spatial variability of soil properties in one-dimensional solute transport models, and implemented with two existing root zone leaching models, Opus and GLEAMS. The accuracy of soil water, bromide and pesticide transport predictions from Opus-SF and GLEAMS-SF was evaluated using field-measured soil water content, bromide and pesticide mass data from a 3.9-ha agricultural field in the Dougherty Plain of Georgia and a 0.05-ha field plot in Nomini Creek watershed in Virginia. Results from the rate-based Opus-SF and capacity-based GLEAMS-SF were compared to determine if there were significant differences in their predictions.
In the stochastic approach, the heterogeneous field is conceptualized as a collection of vertical, non-interacting soil columns differing in soil properties. The horizontal variations of soil hydraulic and retention properties in each horizon are treated as random functions of zero transverse spatial correlation length, after accounting for any spatial trends. The spatially variable parameters were generated using the Latin hypercube sampling method, and the stochastic simulation of the model was performed using Monte-Carlo simulation techniques.
Statistical tests indicated that Opus-SF and GLEAMS-SF did not predict the central tendency and distribution of depth-averaged soil water content and total pesticide mass observed in the field on most sampling dates. But their predictions were sufficiently accurate for most management-type applications. Soil hydraulic and retention properties derived from texture data at the Nomini Creek site substantially reduced the variability in soil water content predictions from both models, but had less impact on bromide and pesticide mass predictions from both models.
The mean values predicted by Opus-SF and GLEAMS-SF were similar, but not equal to those predicted by the deterministic version of the models. Soil water and solute transport predictions from Opus-SF and GLEAMS-SF were not substantially different from corresponding results from the traditional Monte-Carlo approach, although soil water predictions from the two modeling approaches were significantly different for the first 150 days of simulation. Comparison between results from Opus-SF and GLEAMS-SF showed that the distributions and medians of soil water content predicted by the two models were significantly different on most sampling dates. The distributions and medians of pesticide mass predicted by the two models were closer than soil water content, but were significantly different on more than half of the field sampling dates.
The more functional GLEAMS-SF model was able to simulate depth-averaged soil water content in the root zone better than the more physically based Opus-SF, although GLEAMS-SF was not able to simulate the depth distribution of soil water as accurately as Opus-SF. GLEAMS-SF was also able to predict solute movement at least as well as Opus-SF. GLEAMS-SF was able to simulate spatial variations of depth-averaged soil water content and pesticide mass in the field with reasonable accuracy employing fewer parameters that exhibit relatively lesser spatial variability.Ph. D.
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Bushnell, Tanner Hans. "Parameter Importance of an Analytical Model for Transport in the Vadose Zone." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1728.pdf.
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Merideth, Johnny. "Vadose Zone Hydrology near the Vicinity of Edna's Dome, Mammoth Cave, Kentucky." TopSCHOLAR®, 2009. http://digitalcommons.wku.edu/theses/65/.
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Morrison, Candice N. "Innovative Methods for Characterizing Chlorinated Volatile Organic Compounds in the Vadose Zone." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/333041.
Full textAbstract:
Chlorinated solvents, such as tetrachloroethene (PCE), trichloroethene (TCE), and carbon tetrachloride (CT), are primary contaminants of concern for a vast majority of federal and state Superfund sites in the US due to their prior widespread use as solvents for numerous industrial and commercial applications. Source-zones containing large quantities of contaminant are typically present at sites contaminated by chlorinated solvents. Particularly in regions such as the SW US, these source zones reside, at least in part, in the extensive vadose zones typical of these regions. There are two primary concerns associated with sites that contain vadose-zone contaminant sources. First, discharge of contaminant vapor from the vadose-zone source may impact the underlying groundwater. This could contribute to overall risk posed by the site, and delay attainment of groundwater cleanup goals. Second, contaminant vapor from the vadose-zone source may migrate to the land surface and transfer into buildings, thereby causing vapor intrusion. The focus of this research is the development and application of innovative methods for characterizing vadose-zone contamination. Phytoscreening is a new, rapid, and relatively low-cost characterization technology that can be used to screen an area for the presence of select contaminants such as chlorinated VOCs. Phytoscreening is based on the sampling and analysis of plant tissues (branch, trunk, leaf, seed, needle) to detect the presence of contamination in soil and groundwater. Phytoscreening is applied to three sites in Arizona to evaluate its use in semi-arid environments. In addition, all available field data sets have been compiled to examine potential correlations between contaminant concentrations measured for tree tissue and those for groundwater. Contaminant concentrations were detected in tree tissue samples collected from two of the three Arizona sites. A review of the field site data suggests that a correlation exists between PCE and TCE concentrations measured for tree tissue and those measured in groundwater. The correlation can be used to estimate vegetation concentrations when groundwater concentrations are known. The reasonable degree of correlation supports the use of phytoscreening as a robust screening tool to provide a first-order characterization of anticipated concentrations of contaminants in groundwater. This tool can also be used to screen an area for vapor intrusion potential. A sampling method for the determination of chlorinated contaminant vapor concentrations present in the vadose zone, specifically trichloroethene (TCE), has been developed, and was applied at the Tucson International Airport Authority (TIAA) Superfund site. The method was modified from the NIOSH Manual of Analytical Methods (NMAM) # 1022 for TCE, and is targeted to situations requiring cost effective sample collection, particularly for cases when concentrations are at or below maximum contaminant levels (MCLs). In the modified NIOSH method, TCE vapor is sampled using a solid sorbent cartridge containing coconut shell charcoal arranged into primary and secondary sections. Gas Chromatography with Mass Spectrometry is used to confirm and quantify the presence of TCE. The results of laboratory tests demonstrate a maximum TCE vapor load of approximately 22 mg before breakthrough to the secondary section, and a recovery of approximately 97%. The results of a performance comparison test conducted in the field demonstrated that results obtained with the cartridge samplers were similar to those obtained with the use of standard Summa canisters. Landfill waste often serves as a long-term source of volatile organic compounds (VOCs) in the vadose zone. In turn this contamination can have a significant impact on groundwater and on residential or commercial indoor air quality through vapor intrusion. Sulfur hexafluoride (SF₆) was used as the non-reactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well, and analyzed for SF₆, CH₄, CO₂, and VOCs. The travel times determined for SF₆ from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate only gas phase diffusion. In addition, significant concentrations of CH₄ and CO₂ were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF₆ are caused by advective transport associated with landfill gas generation. A method termed vapor-phase tomography has recently been proposed to characterize the distribution of volatile organic contaminant mass in vadose-zone source areas, and to measure associated three-dimensional distributions of local contaminant mass discharge. The method is based on measuring the spatial variability of vapor flux, and thus inherent to its effectiveness is the premise that the magnitudes and temporal variability of vapor concentrations measured at different monitoring points within the interrogated area will be a function of the geospatial positions of the points relative to the source location. A series of flow-cell experiments was conducted to evaluate this premise. A well-defined source zone was created by injection and extraction of a non-reactive gas (SF₆). Spatial and temporal concentration distributions obtained from the tests were compared to simulations produced with a mathematical model describing advective and diffusive transport. Tests were conducted to characterize both areal and vertical components of the application. Decreases in concentration over time were observed for monitoring points located on the opposite side of the source zone from the local-extraction point, whereas increases were observed for monitoring points located between the local-extraction point and the source zone. The results illustrate that comparison of temporal concentration profiles obtained at various monitoring points gives a general indication of the source location with respect to the extraction and monitoring points.
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Buchner, Jens Stefan [Verfasser], and Kurt [Akademischer Betreuer] Roth. "Constructive Inversion of Vadose Zone GPR Observations / Jens Stefan Buchner. Betreuer: Kurt Roth." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1061054411/34.
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Ross, Stephanie Danielle, and Stephanie Danielle Ross. "Characterization of residual NAPL in the vadose zone using gas-phase partitioning tracers." Thesis, The University of Arizona, 2000. http://hdl.handle.net/10150/626884.
Full textAbstract:
The purpose of the field experiment conducted at City of Tucson Fire Station
Number 10 (Fire Station) was to conduct a gas-phase tracer test in the vadose zone in
order to help determine the nature and extent of non-aqueous phase liquid (NAPL)
contamination at the Thomas 0. Price Service Center (TPSC) Fire Station site. Current
methods for characterization of NAPL saturation, such as soil-gas analysis and core
sampling provide data only at discrete points and can be limited in their effectiveness.
Gas-phase partitioning tracers can sample a larger volume of the vadose zone, allowing
the location and amount ofresidual NAPL to be determined more accurately.
A gas-phase partitioning tracer experiment was conducted at the Fire Station to
evaluate the use of partitioning tracers in determining NAPL saturation in the vadose
zone. Well R-032A was used as the injection well and well R-047A was used as the
extraction well. The tracer test yielded a global retardation of 1.23, which indicates
NAPL presence. A swept volume of approximately 770 m3 was contacted by the tracer
and approximately 2.8m3 volumetric NAPL content was measured. However, a majority
of the retention of the partitioning tracer is associated with recovery from early travel
times, seen in the first peak of the breakthrough curve. Analysis of only the first peak
yields a retardation factor of 1.26, a swept volume of 260 m3, and a total volumetric
NAPL content of 1.lm3.
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Joshi, Bhaskar. "Estimation of diffuse vadose zone soil-water flux in a semi-arid region." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23996.pdf.
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Elzahabi, Malak. "The effect of soil pH on heavy metal transport in the vadose zone /." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36804.
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This research study provides the experimental information necessary for numerical analyses, structured to account for vadose zone transport of heavy metals. Particular attention is payed to the effect of degree of saturation, the presence of carbonate, soil pH and heavy metals concentrations. In addition, attention is directed to an evaluation of the coupled solute-water transport mechanisms. A method that fully describes the coupling effects on the transport coefficient based on experimental evidence provides successful predictions of the rate of transport of the heavy metals through the unsaturated soil in a pH-controlled environment.In the experimental part of this research, one dimensional solute and moisture flow (leaching) tests, using different heavy metal permeants, were conducted on an unsaturated illitic soil at varying pH values. Experimental results showed that the retention and migration of heavy metals are highly dependent on the soil pH, the presence of carbonates, the degree of saturation, the influent concentration and the time duration. At high soil pH and carbonate content, heavy metals were retained in the soils if the buffering capacity was high enough to resist the acidic input solution, and sorption processes will prevail in the carbonate phase. As the soil pH decreases, the dissolution of carbonates increases and cation exchange capacity becomes the more dominant process in heavy metals retention.
The numerical study developed a model to analyse and predict the transport of the contaminant in unsaturated clayey soils in which some of the species were adsorbed on clay particles surfaces. The proposed mathematical model was based on the postulates of irreversible thermodynamics and is also applicable in a one-dimensional case. In this model, various solute transport mechanisms such as diffusion and sorption were considered. Results indicated that the diffusion coefficient is necessary to provide a good agreement between the experimentally measured and the theoretically predicted values of contaminant transport through the soil. The numerical results of the coupled solute and moisture equations showed that the transport coefficients strongly and accurately depend on solute and volumetric content. (Abstract shortened by UMI.)
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Karim, Rezaul. "Nutrient and pesticide dynamics through the vadose zone in the wet tropics, Australia." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/210631/1/Rezaul_Karim_Thesis.pdf.
Full textAbstract:
This thesis involves the implementation of a vadose zone monitoring system (VMS), which has not previously been installed in Australia or in the Wet Tropical environments. Using this VMS, the fluctuations of water content at various layers was found correlating with the magnitude of the rain events, plant uptake and the site lithology. It also enables the characterization of pesticide migration with respect to rainwater infiltration, sugar cane growing phase and pesticide application. The possible nutrient dynamics (ammonium, nitrite, nitrate and vice versa) with respect to their application regime, local rain patterns and infiltration dynamics are also defined.
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White, Bradley A. "Physical Investigation of Field Scale Groundwater Recharge Processes in the Virginia Blue Ridge Physiographic Province." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/36297.
Full textAbstract:
Physical and geophysical data collected at the Fractured Rock Research Site in Floyd County, Virginia indicate that recharge rates to the subsurface are controlled by a small scale thrust fault associated with regional thrust faulting within the Blue Ridge Province. Recharge rates appear to be correlated to spatial variation in the hydraulic conductivity of the regolith, which has been influenced by weathering rates and the metamorphic and structural history of the underlying parent material. Previous studies conducted at the Fractured Rock Research Site suggest that recharge potential can be separated into two regions: one over a vertically oriented shear zone associated with the small scale thrust fault, and the other overlying a thrust fault hanging wall. The angle of dip of the thrust fault shear zone and the fracturing within the crystalline rock adjacent to the fault plane appear to serve as geologic controls that preferentially direct infiltrated meteoric water to a deeper confined aquifer. The structural competence of the granulite gneiss thrust fault hanging wall appears to act as a barrier to deeper groundwater recharge, causing the formation of a shallow semi-confined aquifer within the overlying regolith.
In-situ analysis of matric potential and moisture content shows two distinctly different recharge processes that are spatially correlated with the structure of the shallow subsurface (regolith overlying the vertically oriented shear zone and regolith overlying the thrust fault hanging wall), and have been shown to have strong temporal correlations with the dynamics of the underlying saturated conditions.
Recharge flux estimates within the regolith overlying the thrust fault hanging wall are uncharacteristically high, and appear to be offset within the monitored region by the upward hydraulic gradient associated with the potentiometric surface of the underlying semi-confined aquifer. Because of the influence exerted by the upward hydraulic gradient on matric potential within the unsaturated regolith overlying the semi-confined aquifer, accurate recharge estimates could not be obtained from the matric potential data recorded by the tensiometers along this portion of the transect. Recharge flux within the regolith overlying the vertically oriented shear zone is strongly controlled by the orientation and aerial extent of the thrust fault shear zone, and highlights the importance of accurate delineation of recharge areas in crystalline rock aquifer systems.
Master of Science
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Tirado-Corbala, Rebecca. "A Lysimeter Study of Vadose Zone Porosity and Water Movement in Gypsum Amended Soils." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290111537.
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MIHOPOULOS, PHILIP G. "ANAEROBIC BIOVENTING FOR TREATMENT OF VADOSE ZONE SOILS CONTAMINATED WITH HIGHLY CHLORINATED ORGANIC COMPOUNDS." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin981746418.
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Smith, Devin Foster. "Water cycling on cultivated land: an investigation of hydrological separation in the vadose zone." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555524914120314.
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Fisher, Jason C. "A coupled systems approach to solute transport within a heterogeneous vadose zone-groundwater environment." Diss., Restricted to subscribing institutions, 2005. http://proquest.umi.com/pqdweb?did=954067931&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Williams, Benjamin Deeter. "Uranium contamination of vadose zone sediments from the Hanford U single shell tank farm." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Fall2009/B_Williams_112709.pdf.
Full textAbstract:
Thesis (M.S. in environmental science)--Washington State University, December 2009.Title from PDF title page (viewed on Jan. 26, 2010). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 48-51).
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Seidemann, Rick Hugh 1960. "Gaseous transport in the vadose zone : computer simulations using the discrete state compartment model." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/191978.
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Past disposal practices of TricNoroethylene (ICE) and other halogenated hydrocarbons have resulted in the contamination of groundwater in part of the Tucson Basin, Tucson, Arizona. At the Carranza site, known to overlie a ICE groundwater contamination plume, a nest of gas sampling piezometers was constructed to measure the vertical distribution of TCE vapor in the vadose zone. The distribution of TCE vapor in the vadose zone was found to be nonmonotonically decreasing from the water table to the atmosphere. To investigate this ICE concentration profile, simulation studies were performed using the Discrete State Compartment model to test various hypotheses concerning the transport mechanisms of TCE vapor in the vadose zone. The studies showed that unless a high permeable column by which diffusing gas could by-pass low permeable layers was included in the simulation molecular diffusion alone could not produce the concentrations measured at the Carranza site. The simulation also showed that a nonmonotonic concentration profile similar to the measured concentration profile could be produced if multiple sources are assumed in the vadose zone. Soil gas advection by barometric pressure fluctuations was shown to increase concentrations at all depths in the vadose zone but the effect was minor compared with the effect of the high permeability column bypass for TCE diffusional transport.
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Paras, Ben Krisanto Yap, and Ben Krisanto Yap Paras. "Evaluation of Passive Capillary Wick Samplers for Measuring Deep Infiltration at The Jemez River Basin Critical Zone Observatory." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/626383.
Full textAbstract:
Passive capillary wick samplers (PCAPs) are primarily used to sample water from the vadose zone. PCAPs use fiberglass wicks to form a hanging water column that exerts suction on the surrounding soil. Although PCAPs have been used to estimate soil water flux, the accuracy with which PCAPs can estimate flux comes into question due to over/undersampling caused by this applied flux. I used numerical models to explore the effects of a PCAP on flow through the vadose zone. Specifically, I used a two-dimensional axisymmetric flow model of a PCAP embedded in a medium based on HYDRUS. Both steady-state and transient conditions were simulated through the application of various precipitation rates and periods across several soil textures. In this study, I examine soil hydraulic properties, across the soil texture triangle, subject to a range of precipitation events. Results show that the PCAP does over/underestimate water flux. The degree of error is quantified by defining a capture efficiency, which is the ratio of the flux into the plate and the flux that would occur at the same depth with no PCAP present. Higher fluxes and longer time periods resulted in increased convergence of flux into the PCAP, while lower fluxes and shorter durations resulted in divergence of flux from the PCAP. The goal of the study is to understand the behavior of PCAPs under different conditions and to use that knowledge to interpret field measurements in the Jemez River Basin Critical Zone Observatory.
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Yeh, T. C. Jim, and J. T. McCord. "REVIEW OF MODELING OF WATER FLOW AND SOLUTE TRANSPORT IN THE VADOSE ZONE: Stochastic Approaches." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1994. http://hdl.handle.net/10150/614147.
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Hydrologic properties of the vadose zone are heterogeneous at many different scales. An
accurate prediction of water flow and solute transport in the vadose zone requires detailed
information about spatial distributions of the properties. Collecting such detailed spatial distribution
of hydrologic properties of geological formations is a formidable task. As a result, hydrologic
modelers face a difficult challenge: to make the best prediction with little information. During the
past few decades many approaches and theories based on stochastic concepts have been developed
in an attempt to overcome this difficulty. These stochastic approaches and theories provide ways not
only to predict flow and transport processes in large -scale, heterogeneous vadose zones, but also to
assess uncertainties in our predictions. One widely -investigated stochastic approach involves the use
of effective flow and transport properties. The effective property approach essentially represents a
generalization of the well -known equivalent homogeneous media approach discussed in most
hydrology textbooks (e.g., using the arithmetic mean conductivity and harmonic mean conductivity
for flow parallel to and normal to stratification, respectively, in layered media). This approach is a
valuable tool in many practical situations but it predicts the ensemble behavior of a system which can
be quite different from reality. To obtain predictions at higher resolutions than the effective property
approach, many heterogeneous approaches have also been developed. This paper presents an
overview of the stochastic theories related to both equivalent homogeneous media and
heterogeneous approaches, it highlights their applications, and it discusses some of their deficiencies.
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Hardin, Ernest Lauriston 1956. "Uranium-234 in vadose zone and perched waters of the Apache Leap Tuff, Central Arizona." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/191210.
Full textAbstract:
Natural enrichment of ²³⁴U with respect to ²³⁸U was investigated in perched water, vadose zone pore waters, and secondary minerals. The activity ratio (AR) for dissolved ²³⁴U increased from about 1.4 in runoff to >6 in perched water. The AR in the vadose zone increased sharply at a transition that correlated with increased magnetic susceptibility and decreasing hydraulic conductivity. This was evidently caused by auto—oxidative selective leaching controlled by matrix saturation. The direct recoil fractionation mechanism has been proposed for tuffs on the Nevada Test Site, and could imply enhanced retardation of U. Direct recoil was evaluated using a steady state isotopic mass balance formulated to represent matrix pore water, and including first order sorption and selective leaching. Matrix sorption parameters were estimated by selectively leaching intact core with hydroxylamine. Much U was recovered, fractionated similarly to pore water. Interpreting this as isotopic exchange limited by Fickian transport within a sorbent layer, the rate constant and distribution coefficient were estimated. Uranium—series analysis of fracture—lining MnO₂ indicated that isotopic exchange was operant. The isotopic mass balance showed that direct recoil is a minor contribution to fractionation, so the predominant mechanism is selective leaching. This result depends mainly on the sorption rate constant, and where direct recoil is likely such as in roll—front deposits, it implies that the rate constant is smaller than in typical oxidizing waters. Extrapolating matrix properties to formation scale transport, an upper bound on formation scale sorption was inferred from the isotopic mass balance. Formation scale sorption is greater where the perched water table lies in more porous, permeable tuff. The layer diffusion model predicts that the effective sorption rate constant decreases significantly for thicker sorbent layers. Thus although fracture lining MnO₂ minerals are common at Yucca Mountain, U retardation may be strongly rate limited. Elevated AR's (>5) generally signify conditions favorable to U retardation, based on hydraulic isolation from recharge. Elevated vadose zone AR's do not necessarily signify the former presence of perched water, but could be interpreted that way at Yucca Mountain if similar fractionation is not found where past perching is unlikely.
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Tidwell, Vincent Carroll 1962. "Determination of the equivalent saturated hydraulic conductivity of fractured rock located in the vadose zone." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/191974.
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A method with which to estimate the equivalent saturated hydraulic conductivity and its associated spatial distribution in fractured rock situated in the vadose zone has been developed. Conductivity is estimated in part from outflow rates, induced by a constant hydraulic head, monitored over three meter intervals in boreholes which are oriented in a manner so as to intersect the major fracture sets of a field site. Outflow rates are monitored by means of a falling-head flowmeter while borehole intervals are isolated with a single inflatable packer. Upon collection of the field data, hydraulic conductivity values are estimated by means of two analytical solutions. The solutions are adapted to meet the special conditions posed by variable borehole orientations and multiple test intervals from existing solutions associated with borehole permeability tests. The developed methodology is subsequently utilized to determine the saturated hydraulic conductivity and the associated spatial variability of fractured tuff located near Superior, Arizona.
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Vogel, Mie. "Effects of Model Spin-Up on Simulated Recharge Using the Hydrus-1D Vadose Zone Model." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-385590.
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Groundwater is a crucial part of the hydrological cycle and is an important source for drinking water, irrigation and industry, particularly during droughts. With climate change, the hydrological variability is predicted to increase, making predictions for recharge and groundwater storage even more important to implement and to maintain sustainable water use. This study examines the importance of model spin-up in simulating recharge using the Hydrus-1D computer model. The focus is on two previously made Hydrus-1D models that represent end members in climate and hydrology; one which is a natural grassland in a semi-arid climate, while the other is a low impact development (LID) bioswale site in a Mediterranean climate. The main goal of this study is to characterize the range and causes of spin-up behavior as well as to analyze the extent of the effects that the spin-up process has on the recharge simulations. Although there has been some research on spin-up behavior for surface-water models, there is still a knowledge gap regarding the effects of model spin-up on vadose zone models simulating recharge. The initial conditions varied using three parameters for each of the two models: time (3, 15 and 30 years), initial moisture (θ = 0.1, 0.2 and 0.3) and precipitation (25% drier than historical data, historical 30-year data, 25% wetter than historical data). The output from these spin-ups were then used as initial conditions in simulating recharge using the 15-year models. The study found that the impact of spin-up is significant in the natural grassland site where there is a slow response between atmospheric forcings and recharge and where there is a relatively thick vadose zone. Especially spin-up time showed great variability and there is an inverse relationship between spin-up time and magnitude of recharge, where the longer spin-ups had lower recharge rates. Initial water content and precipitation did not result in different recharge amounts for the LID model. Length of spin-up only had very small differences in recharge for the LID models, indicating they are less sensitive to changes in initial spin-up parameters.
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Law, Stacey E. "A Numerical and Statistical Analysis of the Fractured Rock Aquifer System in Ploemeur, France to Quantify Local and Regional Recharge." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/93140.
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Groundwater recharge is an essential metric for understanding and protecting groundwater resources. Quantifying this parameter remains extremely challenging due to the uncertainties associated with the extent to which the vadose zone affects groundwater movement and the highly heterogeneous nature of the aquifer systems being monitored.
The difficulty surrounding recharge quantification is compounded when considering a fractured rock aquifer system, where classification and modeling is complicated by highly complex structural geology. However, the ability to distinguish the character and geometry of fractured rock aquifers is indispensable for quantifying recharge to evaluate sustainable yields, as well as for implementing protective measures to manage these systems.
The primary intention of this study is to assess the hydrogeologic properties that have led the unique recharge signals within the fractured crystalline-rock aquifer system near Ploemeur, France. Infiltration and groundwater movement are characterized via time-series hydraulic head and precipitation data collected at daily, monthly, yearly, and at decadal intervals. In spite of the nearly one million cubic meters of groundwater extraction, measured drawdowns are marginal, suggesting that local and regional recharge plays a significant role in moderating water-level declines and raising questions as to the origins of the substantial inflow required to sustain this complex system. A roughly two-month lag has been observed between seasonal water level and monthly precipitation at Ploemeur, which has previously been attributed solely to slow vertical migration of water through the low-permeability micaschist layer to the fractured contact zone and interconnected fault. However, results from this study suggest that a significant portion of the observed lag can be attributed to vadose-zone processes, particularly the thickness of the vadose zone. This investigation also reveals a recharge signal that continues throughout the calendar year, departing from the traditional simplified concept that recharge quantity is essentially equivalent to the value of evapotranspiration subtracted from infiltration.Master of Science
Groundwater recharge is the amount of water added to underground water sources, called aquifers. This occurs as precipitation falls to the ground, moves downward through the unsaturated subsurface, and accumulates at the top of the saturated zone, deemed the water table. The saturated zone is so named because all pore spaces between sediment grains or crevices in rocks are fully filled with water. Understanding groundwater recharge is important to the protection of groundwater resources, but is hard to estimate due to the lack of knowledge about water movement in the unsaturated zone and the uncertainties related to the systems being studied. Aquifers forming within fractured rocks are even more challenging to investigate, because the complex geological structures are difficult to replicate with computer modeling. However, fractured rock aquifers are an important groundwater resource, and understanding them is the first step in estimating recharge within the system. Recharge estimates are used to calculate how much water can be safely removed from the aquifer for years to come, so that the resource can remain protected. The aim of this investigation is to assess the aquifer properties that lead to the unique recharge signal in a fractured crystalline-rock aquifer in Ploemeur, France, where nearly 1 million cubic meters of water have been removed each year since 1991 but water table levels have not fallen significantly. This behavior raises questions about the water returned to the system as recharge that is sustaining such a highly productive resource. This site also shows a roughly two-month lag between seasonal precipitation falling and the reflection of that precipitation recorded in the water level of the aquifer. It was previously thought that the lag occurred because water travelled slowly through the mica-schist layer, which has little pore space for water to move, and into the contact zone and interconnected fault. However, this study shows instead that a majority of the lag is associated with the unsaturated zone properties and processes, particularly thickness. This investigation also shows recharge entering the aquifer system throughout the calendar year, a departure from earlier studies conceptualizations.
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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.
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Sidoli, Pauline. "Processus hydrodynamiques et de rétention dans le transfert des pesticides dans la zone non saturée : Epérimentations et modélisations avec le glyphosate, le S-métolachlore et leurs métabolites dans les solides fluvio-glaciaires de l'Est lyonnais." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSET003/document.
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La zone non saturée joue un rôle clé sur le transfert des pesticides et la qualité des eaux souterraines. Les connaissances sur les processus d’écoulement et de rétention dans les matériaux géologiques de la zone non saturée au-delà des sols sont toutefois parcellaires. Le transfert du glyphosate et du S-métolachlore (SMOC), et de leurs métabolites AMPA, ESA-métolachlore (MESA) et OXA-métolachlore (MOXA) est étudié en colonne pour deux matériaux fluvio-glaciaires issus d’un aquifère de l’Est lyonnais : un sable, S-x, et un mélange bimodal de graviers et de sables, Gcm,b. Pour des conditions de non-saturation en eau, l’écoulement dans les colonnes est fractionné en deux zones, eau mobile et eau immobile, d’importance variable suivant le solide. La sortie du SMOC est retardée par rapport au traceur de l’eau ; son bilan de masse déficitaire traduit une rétention de la molécule lors de son transfert. A l’inverse, le MESA et le MOXA se comportent comme le traceur de l’eau. Le glyphosate et l’AMPA sont très peu mobiles dans la colonne de Gcm,b (seul matériau étudié) avec des quantités éluées inférieures à 1% de la quantité appliquée. La modélisation montre que le transfert des molécules est affecté de manière variable suivant le matériau par la cinétique physique d’échange entre les zones d’eau mobile et immobile et par la cinétique chimique des molécules. Cette cinétique chimique est décrite par des expérimentations complémentaires de sorption en batch. La caractérisation des matériaux révèle la présence d’oxydes et de minéraux argileux qui pourrait expliquer leur forte réactivité, qui s’avère parfois supérieure à celle des sols de la zone d’étudeVadose zone play a key role in pesticides transfer and groundwater quality. Knowledge’s about leaching and retention processes in the vadose zone below the shallow soil zone are still poorly understood. Transfer of glyphosate, S-metolachlor (SMOC), and their metabolites AMPA, ESA-metolachlor (MESA) and OXA-metolachlor (MOXA) is studied in unsaturated columns filled with two glaciofluvial materials collected in the East of Lyon: a sand, S-x, and a bimodal gravel, Gcm,b. Experiments show water fractionation into mobile and immobile compartments with variable importance according to material column. SMOC outflow is delayed compared to the conservative tracer. SMOC mass balance is in deficit revealing retention in columns. At the opposite, complete mass elution associated with retardation factors close to unity shows that there is no adsorption of MESA and MOXA in either lithofacies. Glyphosate and AMPA mobility is very low in the one Gcm,b column studied with amounts in leachates inferior to 1% of applied. Modelling show pesticides and metabolites transfer is affected by both flow regionalisation and non-equilibrium sorption. Chemical kinetic of sorption mechanisms is studied with complementary batch experiments. The high glaciofluvial materials reactivity, in some cases upper than soil reactivity from the study site, could be attributed to oxides and clay minerals
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Sánchez-Cañete, Enrique P., Cecilio Oyonarte, Penélope Serrano-Ortiz, Yuste Jorge Curiel, Oscar Pérez-Priego, Francisco Domingo, and Andrew S. Kowalski. "Winds induce CO 2 exchange with the atmosphere and vadose zone transport in a karstic ecosystem." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/621994.
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Research on the subterranean CO2 dynamics has focused individually on either surface soils or bedrock cavities, neglecting the interaction of both systems as a whole. In this regard, the vadose zone contains CO2-enriched air (ca. 5% by volume) in the first meters, and its exchange with the atmosphere can represent from 10 to 90% of total ecosystem CO2 emissions. Despite its importance, to date still lacking are reliable and robust databases of vadose zone CO2 contents that would improve knowledge of seasonal-annual aboveground-belowground CO2 balances. Here we study 2.5 years of vadose zone CO2 dynamics in a semiarid ecosystem. The experimental design includes an integrative approach to continuously measure CO2 in vertical and horizontal soil profiles, following gradients from surface to deep horizons and from areas of net biological CO2 production (under plants) to areas of lowest CO2 production (bare soil), as well as a bedrock borehole representing karst cavities and ecosystem-scale exchanges. We found that CO2 followed similar seasonal patterns for the different layers, with the maximum seasonal values of CO2 delayed with depth (deeper more delayed). However, the behavior of CO2 transport differed markedly among layers. Advective transport driven by wind induced CO2 emission both in surface soil and bedrock, but with negligible effect on subsurface soil, which appears to act as a buffer impeding rapid CO2 exchanges. Our study provides the first evidence of enrichment of CO2 under plant, hypothesizing that CO2-rich air could come from root zone or by transport from deepest layers through cracks and fissures.
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Valdes-Abellan, Javier. "Study of impacts on the vadose zone deriving from use of brackish inland aquifers desalted water." Doctoral thesis, Universidad de Alicante, 2013. http://hdl.handle.net/10045/84087.
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El uso de agua desalada en agricultura es una actividad cada vez más extendida, debido a la disminución de los recursos convencionales y al aumento de eficiencia de los procesos de desalación. La desalación no se limita ya únicamente al agua de mar, en los últimos tiempos está aumentando la desalación de agua procedente de acuíferos salinos continentales. El objetivo principal de esta tesis es evaluar el impacto que el uso prolongado de esta agua puede tener sobre la zona no saturada del terreno y sus propiedades hidráulicas. En el marco de este trabajo se ha establecido una parcela experimental en el campus de la Universidad de Alicante donde se han cultivado especies cespitosas regadas con agua desalada procedente del acuífero salobre continental de San Vicente del Raspeig. La gestión de la parcela se ha realizado según prácticas habituales realizadas en la zona. Se ha llevado un control del contenido de agua y succión del terreno durante un periodo de 20 meses, bajo dos sistemas de monitorización alternativos: uno manual y otro automático. La experiencia ha sido completada con un ensayo de trazador mediante el empleo de BrLi controlado durante un periodo de 160 días. Asimismo, se ha realizado en laboratorio la caracterización hidráulica de muestras extraídas de la propia parcela experimental. A partir de los datos adquiridos, de manera manual y automática, se ha elaborado un modelo de flujo con el programa HYDRUS 1D para cada una de los sets de datos, el cual se ha calibrado y validado para diferentes periodos. Por otro lado, el ensayo de trazador (transporte conservativo), también simulado mediante HYDRUS 1D, además de validar el modelo de flujo, ha permitido derivar parámetros de transporte (dispersividad) a escala de campo. Finalmente, se ha creado un modelo predictivo de transporte de masa reactivo que implementa procesos geoquímicos y cambios asociados en los parámetros hidráulicos de la zona no saturada, para largos periodos de tiempo (30 años). Este último modelo se elaboró mediante la aplicación HP1, que combina los códigos HYDRUS 1D y PHREEQC. Además del modelo predictivo bajo las condiciones actuales, otros tres escenarios, según varios criterios, han sido considerados. Los dos modelos de flujo resultantes, a partir de datos adquiridos manualmente y automáticamente, han descrito adecuadamente la dinámica del flujo en la zona no saturada, concluyendo que ambas estrategias son válidas para obtener tendencias generales del flujo. No obstante, la estrategia automática es más adecuada para detectar posibles cambios en las propiedades hidráulicas debido a su mayor sensibilidad y frecuencia en la toma de datos. Para la obtención de parámetros de transporte, la combinación en el ensayo de trazador de la determinación de Br total mediante rayos X, junto con la parametrización por método inverso, ha resultado ser un método rápido y fiable. Los modelos predictivos han puesto de manifiesto un proceso de disolución continuo del yeso contenido en el suelo, así como procesos de disolución (en la zona radicular) y posterior precipitación (bajo ésta) de la calcita en el terreno. Los resultados de la simulación indican cambios en la porosidad que supondrán cambios de conductividad hidráulica en un factor mayor de 2. Finalmente, el estudio de los diferentes escenarios resalta que: la ausencia de riego reduce los cambios esperados en el terreno; la ausencia de yeso en el terreno producirá una reducción de la conductividad hidráulica bajo la zona radicular; y la disminución de la presión parcial de CO2 en la zona radicular disminuye drásticamente las disoluciones de las especies carbonatadas participantes.
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Zhang, Yonggen, Marcel G. Schaap, Alberto Guadagnini, and Shlomo P. Neuman. "Inverse modeling of unsaturated flow using clusters of soil texture and pedotransfer functions." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/622504.
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Characterization of heterogeneous soil hydraulic parameters of deep vadose zones is often difficult and expensive, making it necessary to rely on other sources of information. Pedotransfer functions (PTFs) based on soil texture data constitute a simple alternative to inverse hydraulic parameter estimation, but their accuracy is often modest. Inverse modeling entails a compromise between detailed description of subsurface heterogeneity and the need to restrict the number of parameters. We propose two methods of parameterizing vadose zone hydraulic properties using a combination of k-means clustering of kriged soil texture data, PTFs, and model inversion. One approach entails homogeneous and the other heterogeneous clusters. Clusters may include subdomains of the computational grid that need not be contiguous in space. The first approach homogenizes within-cluster variability into initial hydraulic parameter estimates that are subsequently optimized by inversion. The second approach maintains heterogeneity through multiplication of each spatially varying initial hydraulic parameter by a scale factor, estimated a posteriori through inversion. This allows preserving heterogeneity without introducing a large number of adjustable parameters. We use each approach to simulate a 95 day infiltration experiment in unsaturated layered sediments at a semiarid site near Phoenix, Arizona, over an area of 50 x 50 m(2) down to a depth of 14.5 m. Results show that both clustering approaches improve simulated moisture contents considerably in comparison to those based solely on PTF estimates. Our calibrated models are validated against data from a subsequent 295 day infiltration experiment at the site.