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

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.

Managed Aquifer Recharge (MAR) can be conducted via wells or by spreading the water on a surface (e.g, during basin infiltration). While the former has the advantage of minimal area demand and the possibility of dual-use for groundwater abstraction, the latter usually has smaller construction costs and offers additional treatment to the water during infiltration via the vadose zone. Vadose Zone Wells (VZWs) combine many of these advantages, but as their hydraulics are more complex, infiltration rates and the degradation processes in the subsurface are more difficult to determine. Furthermore, they are prone to clogging and redevelopment has not been documented in the literature. Therefor, low-quality waters - with high content of suspended solids or dissolved contaminants/nutrients - are rarely infiltrated via VZWs. In this study, I will (1) evaluate the hydraulic advantage, VZWs can have over other vadose zone infiltration systems in a synthetical modeling study, (2) assess the spatial variability of key parameters for aerobic degradation below a VZW in a small-scale experiment, (3) determine the relationship between clogging dynamics and a well’s diameter and setup (gravel pack) in an experimental study and (4) demonstrate that the backflush of a VZW is possible - in contrast to the literature’s suggestions. All in all, VZWs appear to offer potential even for low-quality waters, and a further investigation for economical operation seems worthwhile. / Managed Aquifer Recharge' ('MAR' = 'Künstliche Grundwasseranreicherung') kann mit Brunnen oder über flächenhafte Versickerung erfolgen (z.B. durch Infiltrationsbecken). Während Brunnen wenig Platz benötigen und neben der Infiltration auch für die Grundwasserentnahme genutzt werden können, sind Becken meist günstiger in Errichtung und Erhaltung und die Versickerung durch die ungesättigte Zone kann die Wasserqualität erheblich verbessern. 'Vadose Zone Wells' ('VZWs' ≈ 'Ungesättigte Schluckbrunnen') verbinden einige dieser Vorteile, allerdings sind Infiltrations- und Abbauprozess aufgrund der ungleich komplizierteren Hydraulik schwer vorherzusagen. Darüber hinaus sind sie anfällig für Kolmation/Clogging und über ihre Regenerierung ist nach jetzigem Stande nichts bekannt. Im Allgemeinen werden deshalb Wässer mit niedriger Qualität - hohe Trübung und/oder Schad- und Nährstoffgehalte - selten durch VZWs versickert. In dieser Studie, werde ich (1) in einer synthetischen Modellstudie die hydraulichen Vorteile aufzeigen, die VZWs gegenüber anderen Versickerungsformen haben, (2) die räumlichen Unterschiede von Schlüsselparametern für den aeroben Abbau unter einem VZW in einem Laborexperiment untersuchen, (3) die Verbindung zwischen Kolmationsdynamik sowie Brunnendurchmesser und -aufbau (insb. der Kiesschüttung) herausarbeiten und (4) demonstrieren, dass eine Rückspülung von VZWs möglich ist - anders als es die Literatur nahelegt. Insgesamt, bieten VZWs ein hohes Potential - auch für Wasser niedriger Qualität, die allerdings noch durch weitere Untersuchungen bzgl. Kosten/Nutzen und Nachhaltigkeit bestätigt werden müssen.

The vadose zone is the unsaturated zone between the ground surface and water table. This zone is of much importance as it acts as a link between surface water and ground water. Knowledge of soil moisture in this zone is very much essential to understand the meteorologic, hydrologic and agronomic process. Flow and transport in the unsaturated zone are more complex compared to saturated medium, as the pores in unsaturated zone are partly filled by air and partly by water. Most of vadose zone studies are done on agricultural plots where anthropogenic activities govern the vadose zone flows. Vadose zone studies in natural pristine conditions such as in forested areas where no anthropogenic activities are present are very limited that too in Indian conditions are rare. The present research work deals with understanding of the flow behavior in the vadose zone in a small experimental forested watershed called Mule Hole. Mule Hole watershed is 4.5 km2 and located in Bandipur National Park in Chamrajnagar District of Karnataka state, in the southern part of India. The forest is of deciduous type with 3 to 4 months of leafless dry period. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The rainfall pattern is bimodal i.e. it receives rainfall during South West Monsoon (June -September) and North East Monsoon (October – December) with dominant rainfall occurring during South West Monsoon. Human activity is minimal as watershed is a part of Bandipur National Park, dedicated to wildlife and biodiversity preservation. The watershed consists of around 80 % of red soils, and black soil and saprolite covering the rest. The first part of the study involves soil moisture measurements by neutron probe and electrical resistivity measurements by geophysical method and their linking, i.e. developing volumetric soil moisture vs electrical resistivity relationship. The second part of the study involves application of neutron probe soil moisture measurement in identifying relationship between soil and erosion in the watershed. The third part involves development of two dimensional (2D) vadose zone model for watershed and validating it with measured data. The last part involves development of three dimensional model of watershed and validating it with observed data. Vadose zone is briefly described in chapter 1 along with its governing equations. Different soil moisture measurement techniques including invasive and non – invasive ones are also discussed. Different vadose zone modeling software which are public domain as well as commercial ones are also discussed. The chapter ends with organization of this thesis. Chapter 2 reviews relevant literature related to this study with focus on soil moisture measurement techniques and vadose zone flow modeling. Different soil moisture measurement techniques, their applications and limitations are reviewed. In the soil moisture measurement techniques, invasive and non – invasive types are reviewed. In the modeling part, different vadose zone models for 2D and 3D flow along with its applications and limitations are reviewed. Also a brief review about application of HYDRUS 2D/3D model is done which is used for the vadose zone modeling in this thesis. Chapter 3 introduces study area Mule Hole watershed, which is a forested watershed located in Bandipur National Park, Karnataka. India. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The watershed has average regolith thickness or vadose zone of 17 m with roots of the trees able to penetrate up to groundwater. A toposequence T1 is identified in the watershed which has red soil – black soil confluence where soil moisture measurements and electrical resistivity measurements are carried out. The toposequence consists of 8 layers with organic layer forming the top layer followed by 3 red soil layer with 2 black soil layers intruding from stream into red soil layers and sandy weathered horizon at base of red and black soil. Also a sandy horizon at the top of black soil. Soil moisture measurements with neutron probe and electrical resistivity measurements with electrical logging tool which are done on toposequence periodically for two years are explained and the data are presented in this chapter. These data are used for validation of vadose zone models. Chapter 4 discusses in detail about comparison of electrical resistivity by geophysical method and neutron probe logging for soil moisture monitoring in a forested watershed. The electrical resistivity data and soil moisture data are compared for different soils and existence of relationship between them are studied and discussed in this chapter. For the red soil, existence of relationship between volumetric soil moisture content and electrical resistivity is found. Chapter 5 discusses soil moisture measurements as a tool to study erosion processes in forested watershed. Hydrodynamic behavior of the red soil – black soil system at toposequence T1 is studied using neutron probe soil moisture measurements. Two distinctive types of erosional landforms have been identified at T1 viz, rotational slips (Type 1); seepage erosion (Type 2),which are highlighted by neutron probe soil moisture measurements. Based on the observations relative chronology of formulation of different soil horizons are studied, which guided in developing four-stage model showing the relative chronology in the recent formation of the soil cover at downslope. Chapter 6 discusses application of 2D vadose zone modeling using HYDRUS – 2D model at two experimental sites in forested watershed where soil moisture monitoring and groundwater monitoring have been conducted. At the first site, which is toposequence T1 in the forested watershed, where soil moisture measurements are done, three case studies for comparison of daily scale data with hourly scale data and effects of internal layering by clubbing red soil layers and black soil layers to equivalent red soil and black soil layers respectively are performed. The model is run for two years. In that, first year results are used for calibrating the model where measured soil moisture content data are used to get soil hydraulic parameters for all the three cases by inverse modeling using Marquardt – Levenberg algorithm which is a part of HYDRUS 2D. The parameters thus obtained fall under particular soil range and performed efficiently in predicting soil moisture content. The second year results of model run is used for validation of the model in all the three cases where simulated soil moisture content is compared with measured soil moisture content. It is found that model is performing well and match between measured and simulated soil moisture contents is good in all the three cases. It can be said that having hourly scale data with detailed layering information is always advantageous in modeling soil moisture content. But, in absence of hourly scale data or finer scale data and absence of detailed layering information, the soil moisture model can also perform well. The scale of data and detailed layering information has minimal effect on soil moisture modeling. At the second site ERT profile near the watershed outlet has five monitoring wells are available and all layering information regarding regolith and hard rock layer distribution profiles. The soil hydraulic parameters obtained at toposequence T1 for soil and sandy weathered horizon are used and tested at this site to simulate the groundwater levels. The parameter for rock layer is estimated by testing different hydraulic parameters from HYDRUS database. The results are validated using observed groundwater levels at the site. The results show significant match between observed and simulated groundwater levels. Chapter 7 discusses 3D modeling of Mule Hole forested watershed using HYDRUS – 3D model. A three layer model of Mule Hole along with its topographic details is modeled. The layering information is derived from geophysical study done at 12 Electrical Resistivity Tomography (ERT) profiles distributed in the watershed. The three layers considered are top soil layer followed by sandy weathered layer and bottom rock layer. Anisotropy in hydraulic conductivity, root water uptake and sloping water table are introduced to make the model more realistic. Soil hydraulic parameters obtained during 2D vadose zone modeling of toposequence T1 are used initially for soil and sandy weathered layers and are subsequently tuned to make model more efficient. Different scenarios are considered to test flux as well as constant head boundary conditions and effect of different porosities for rock layer. The model is run for 7 years and model simulations are validated with observed groundwater levels from monitoring wells across the watershed. The result shows good fit between simulated and observed groundwater levels especially for monitoring well which has shallow groundwater level. It is found that porosity in the rock layer is not uniform and there exist different porosities for the rock layer across the watershed. Also the distribution of sandy weathered zone requires improvement. The model is also able to predict ET closer to ET predicted by COMFORT model which was developed earlier. Also the model shows rise in groundwater fluxes as groundwater starts replenishing. Over all, the 3D model of Mule Hole watershed in HYDRUS – 3D worked well with satisfactory results and HYDRUS – 3D can be used for modeling small forested watersheds. Chapter 8 concludes the study and discusses the further scope of the work.

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.

The environmental sanitation situation in Kampala’s peri-urban areas was reviewed and investigated through field studies, structured interviews with personnel from key institutions and administration of questionnaires to households in a selected peri-urban settlement (Bwaise III Parish).  In this settlement, specific field and laboratory measurements were undertaken so as to create a better understanding of the environmental sanitation situation, anthropogenic pollution loads and their transport and impact (with a focus on Phosphorus) in Kampala’s Peri-urban areas in pursuit of interventions for improving the environmental sanitation and protecting the shallow groundwater resource there. The review revealed that the urban poor in Kampala, like elsewhere in developing countries, are faced with inadequate basic services caused by a combination of institutional, legal and socio-economic issues and that the communities’ coping strategies are in most cases detrimental to their health and well-being. Field surveys showed that excreta disposal systems, solid waste and greywater are major contributors to the widespread shallow groundwater contamination in the area. Field measurements revealed that the water table responds rapidly to short rains (48 h) due to the pervious (10-5-10-3 m/s) and shallow (<1 mbgl) vadose zone, which consists of foreign material (due to reclamation). This anthropogenically influenced vadose zone has a limited contaminant attenuation capacity resulting in water quality deterioration following rains. The only operational spring in the area is fed by regional baseflow meaning a wider protection zone. The spring discharge exhibited microbial quality deterioration after rains primarily as a result of poor maintenance of the protection structure. Subsurface phosphorus (P) transport mechanisms appeared to be a combination of adsorption, precipitation, leaching from the soil media and through macropore flow with the latter two playing an important role in the wet season. The Langmuir isotherm described the phosphorus sorption data well (R2³ 0.95) and the best prediction of Langmuir sorption maximum (Cmax) had organic carbon, Ca and available phosphorus and soil pH as significant predictors. Loosely bound P (NH4Cl-P) was the least fraction (<0.4% of total P) in all layers indicating a high binding capacity of P by the soils implying that the soils have a capacity to adsorb additional P loads. Simulation results from the preliminary numerical model built in this study based on field and laboratory measurements indicate that rainfall infiltration rates > 7x10-3 mm/s drive shallow groundwater contamination with higher intense rains of relatively longer duration (³ 70 mm within 48 h) reducing phosphorus transport. Sensitivity analysis of the model input with respect to how long it takes to pollute the subsurfacehad the phosphorus sorption coefficients as being more influential than the pore size and air entry values. There are however, key contrasts between the model simulations and field observations which are useful in guiding new efforts in data collection. The study reveals that intervention measures to improve the environmental sanitation and protect the shallow groundwater in the peri-urban settlements are of a multidisciplinary nature necessitating action research with community participation. / QC 20100917

Field-scale transport through unsaturated soil is influenced by surface and subsurface boundary conditions, and the spatial variability of state soil variables. The objective of this thesis is to examine the relative importance of the spatial redistribution of surface water versus spatial variability of soil properties on long-term transient water flow and transport under semi-arid conditions. The field-scale transport (34 yr) of a surface applied tracer (chloride), spatial variability of other pedogenic tracers, and surface water redistribution over a 19 mo fallow period were measured in a catchment basin. In 1966 and 1971, a chloride tracer (KCl) was surface applied to plots (6.1 m x 90 m, Chernozemic soil) near Saskatoon, Saskatchewan. In 2000 and 2001, 262 soil cores were taken along and perpendicular to one KCl strip. Soil layering at each core was recorded and samples were analysed for chloride concentration, electrical conductivity, bulk density and water content. Sulphate and nitrate concentrations were measured on selected cores. The site is level by common definitions, with a very slight concave depression (1.8% grade) midway along the KCl strip and a slight grade (¡Ü2.1%) perpendicular to the KCl strip. Measured water recharge indicated slight differences in surface slope had a marked effect on redistribution of water and spatial distribution of the chloride tracer. An estimated 90% of redistributed water was subsequently used by plants and 10% resulted in an increase in deep drainage. A varved layer had a strong influence on the subsurface redistribution of water and chloride below the root zone. There were sharp horizontal transitions between areas of slow and faster transport, which corresponded to sharp increases in catchment area and water recharge. Small surface depressions, which controlled pedogenic transport and soil formation, have been filled in by tillage translocation. Spatial variability of soil horizon thickness (and associated hydraulic properties) had little effect on transport of chloride after 34 yr. Computer simulations also suggest substantial surface redistribution of precipitation and snowmelt. In contrast to the measured chloride data, the model was sensitive to changes in hydraulic properties and horizon thickness in the root zone. Surface water redistribution was the primary factor controlling long-term transport.

Near-surface sediments in the vadose zone play a fundamental role in the hydrologic system. The shallow vadose zone can act as a buffer to delay or attenuate surface contaminants before they reach the water table. It also acts as a temporary soil moisture reservoir for plant and atmospheric uptake, and regulates the seasonal groundwater recharge process. Over the past few decades, geophysical methods have received unprecedented attention as an effective vadose zone characterization tool offering a range of non-invasive to minimally invasive techniques with the capacity to provide detailed soil moisture information at depths typically unattainable using conventional point-measurement sensors. Ground-penetrating radar (GPR) has received much of this attention due to its high sensitivity to the liquid water phase in geologic media. While much has been learned about GPR soil moisture monitoring and characterization techniques, it has not been evaluated across highly dynamic natural soil conditions. Consequently, GPR’s capacity to characterize a complete range of naturally occurring vadose zone conditions including wetting/drying and freeze/thaw cycles, is not yet fully understood. Further, the nature of GPR response during highly dynamic moisture periods has not been thoroughly investigated. The objective of this thesis is to examine the capacity of various surface GPR techniques and methodologies for the characterization of soil moisture dynamics in the upper few meters of vadose zone, and to develop measurement strategies capable of providing quantitative information about the current and future state of the shallow hydrologic system. To achieve this, an exhaustive soil moisture monitoring campaign employing a range of GPR antenna frequencies and survey acquisition geometries was initiated at three different agricultural field sites located in southern Ontario, Canada, between May 2006 and October 2008. This thesis represents the first attempt to evaluate multiple annual cycles of soil conditions and associated hydrological processes using high-frequency GPR measurements. Summaries of the seven major works embodied in this thesis are provided below. Direct ground wave (DGW) measurements obtained with GPR have been used in a number of previous studies to monitor volumetric water content changes in the root zone; however, these studies have involved controlled field experiments or measurements collected across limited ranges in soil moisture. To further investigate the capacity of the DGW method, multi-frequency (i.e., 225 MHz, 450 MHz and 900 MHz) common-midpoint (CMP) measurements were used to monitor a complete annual cycle of soil water content variations at three sites with different soil textures (i.e., sand, sandy loam and silt loam). CMP surveys permitted characterization of the nature and evolution of the near-surface electromagnetic wavefields, and their subsequent impact on DGW velocity measurements. GPR results showed significant temporal variations in both the near-surface wavefield and multi-frequency DGW velocities corresponding to both seasonal and shorter term variations in soil conditions. While all of the measurement sites displayed similar temporal responses, the rate and magnitude of these velocity variations corresponded to varying soil water contents which were primarily controlled by the soil textural properties. Overall, the DGW measurements obtained using higher frequency antennas were less impacted by near-surface wavefield interference due to their shorter signal pulse duration. The estimation of soil water content using GPR velocity requires an appropriate petrophysical relationship between the dielectric permittivity and volumetric water content of the soil. The ability of various empirical relationships, volumetric mixing formulae and effective medium approximations were evaluated to predict near-surface volumetric soil water content using high-frequency DGW velocity measurements obtained from CMP soundings. Measurements were collected using 225, 450 and 900 MHz antennas across sand, sandy loam and silt loam soil textures over a complete annual cycle of soil conditions. A lack of frequency dependence in the results indicated that frequency dispersion had minimal impact on the data set. However, the accuracy of soil water content predictions obtained from the various relationships ranged considerably. The best fitting relationships did exhibit some degree of textural bias that should be considered in the choice of petrophysical relationship for a given data set. Further improvements in water content estimates were obtained using a field calibrated third-order polynomial relationship and three-phase volumetric mixing formula. While DGW measurements provide valuable information within the root zone, the characterization of vertical moisture distribution and dynamics requires a different approach. A common approach utilizes normal-moveout (NMO) velocity analysis of CMP sounding data. To further examine this approach, an extensive field study using multi-frequency (i.e., 225 MHz, 450 MHz, 900 MHz) CMP soundings was conducted to monitor a complete annual cycle of vertical soil moisture conditions at the sand, sandy loam and silt loam sites. The use of NMO velocity analysis was examined for monitoring highly dynamic vertical soil moisture conditions consisting of wetting/drying and freeze/thaw cycles with varying degrees of magnitude and vertical velocity gradient. NMO velocity analysis was used to construct interval-velocity-depth models at a fixed location collected every 1 to 4 weeks. Time-lapse models were combined to construct temporal interval-velocity fields, which were converted into soil moisture content. These moisture fields were used to characterize the vertical distribution, and dynamics of soil moisture in the upper few meters of vadose zone. Although the use of multiple antenna frequencies provided varying investigation depths and vertical resolving capabilities, optimal characterization of soil moisture conditions was obtained with 900 MHz antennas. The integration of DGW and NMO velocity data from a single CMP sounding could be used to assess the nature of shallow soil moisture coupling with underlying vadose zone conditions; however, a more quantitative analyses of the surface moisture dynamics would require definitive knowledge of GPR sampling depth. Although surface techniques have been used by a number of previous researchers to characterize soil moisture content in the vadose zone, limited temporal sampling and low resolution near the surface in these studies impeded the quantitative analysis of vertical soil moisture distribution and its associated dynamics within the shallow subsurface. To further examine the capacity of surface GPR, an extensive 26 month field study was undertaken using concurrent high-frequency (i.e., 900 MHz) reflection profiling and CMP soundings to quantitatively monitor soil moisture distribution and dynamics within a sandy vadose zone environment. An analysis on the concurrent use of reflection and CMP measurements was conducted over two contrasting annual cycles of soil conditions. Reflection profiles provided high resolution traveltime data between four stratigraphic reflection events while cumulative results of the CMP sounding data set produced precise depth estimates for those reflecting interfaces, which were used to convert interval traveltime data into soil water content estimates. The downward propagation of episodic infiltration events associated with seasonal and transient conditions were well resolved by the GPR data. The GPR data also revealed variations in the nature of these infiltration events between contrasting annual cycles. The use of CMP soundings also permitted the determination of DGW velocities, which enabled better characterization of short-duration wetting/drying and freezing/thawing processes. This higher resolution information can be used to examine the nature of the coupling between shallow and deep moisture conditions. High-resolution surface GPR measurements were used to examine vertical soil moisture distribution and its associated dynamics within the shallow subsurface over a 26 month period. While the apparent ability of surface GPR methods to give high quality estimates of soil moisture distribution in the upper 3 meters of the vadose zone was demonstrated, the nature of these GPR-derived moisture data needed to be assessed in the context of other hydrological information. As a result, GPR soil moisture estimates were compared with predictions obtained from a well-accepted hydrological modeling package, HYDRUS-1D (Simunek et al., 2008). The nature of transient infiltration pulses, evapotranspiration episodes, and deep drainage patterns were examined by comparing them with vertical soil moisture flow simulations. Using laboratory derived soil hydraulic property information from soil samples and a number of simplifying assumptions about the system, very good agreement was achieved between measured and simulated soil moisture conditions without model calibration. The overall good agreement observed between forward simulations and field measurements over the vertical profile validated the capacity of surface GPR to provide detailed information about hydraulic state conditions in the upper few meters of vadose zone. A unique DGW propagation phenomenon was observed during early soil frost formation. High-frequency DGW measurements were used to monitor the seasonal development of a thin, high velocity frozen soil layer over a wet low velocity unfrozen substratum. During the freezing process, the progressive attenuation of a low velocity DGW and the subsequent development of a high velocity DGW were observed. Numerical simulations using GPRMAX2D (Giannopoulos, 2005) showed that low velocity DGW occurring after freezing commenced was due to energy leaking across the frozen layer from the spherical body wave in the unfrozen half space. This leaky phase progressively dissipated until the frozen layer reached a thickness equivalent to one quarter of the dominant wavelength in the frozen ground. The appearance of the high velocity DGW was governed by its destructive interference with the reflection events from the base of the frozen layer. This interference obscured the high velocity DGW until the frozen layer thickness reached one half of the dominant wavelength in the frozen ground. While GPR has been extensively used to study frozen soil conditions in alpine environments, its capacity to characterize highly dynamic shallow freeze-thaw processes typically observed in temperate environments is not well understood. High-frequency reflection profiles and CMP soundings were used to monitor the freezing and thawing process during the winter seasonal period at the sand and silt loam sites. Reflection profiles revealed the long-term development of a very shallow (<0.5 m) soil frost zone overlying unfrozen wet substratum. During the course of the winter season, long-term traveltime analysis yielded physical properties of the frozen and unfrozen layers as well as the spatial distribution of the base of the soil frost zone. Short-term shallow thawing events overlying frozen substratum formed a dispersive waveguide for both the CMP and reflection profile surveys. Inversion of the dispersive wavefields for the CMP data yielded physical property estimates for the thawed and frozen soils and thawed layer thickness. It was shown that GPR can be used to monitor very shallow freezing and thawing events by responding to changes in the relative dielectric permittivity of the soil water phase. The works embodied in this thesis demonstrate the effectiveness of high-frequency GPR as a non-invasive soil moisture monitoring tool under a full range of naturally occurring moisture conditions with the temporal and vertical resolution necessary to quantitatively examine shallow vadose zone moisture dynamics. Because this study encompassed an unprecedented range of naturally occurring soil conditions, including numerous short and long duration wetting/drying and freezing/thawing cycles, complex geophysical responses were observed during highly dynamic soil moisture processes. Analysis and interpretation of these geophysical responses yielded both qualitative and quantitative information about the state of the hydrologic system, and hence, provided a non-invasive means of characterizing soil moisture processes in shallow vadose zone environments. In the future, these GPR soil moisture monitoring strategies should be incorporated into advanced land-surface hydrological modeling studies to improve our understanding of shallow hydrologic systems and its impacts on groundwater resources.

Field-scale transport through unsaturated soil is influenced by surface and subsurface boundary conditions, and the spatial variability of state soil variables. The objective of this thesis is to examine the relative importance of the spatial redistribution of surface water versus spatial variability of soil properties on long-term transient water flow and transport under semi-arid conditions. The field-scale transport (34 yr) of a surface applied tracer (chloride), spatial variability of other pedogenic tracers, and surface water redistribution over a 19 mo fallow period were measured in a catchment basin. In 1966 and 1971, a chloride tracer (KCl) was surface applied to plots (6.1 m x 90 m, Chernozemic soil) near Saskatoon, Saskatchewan. In 2000 and 2001, 262 soil cores were taken along and perpendicular to one KCl strip. Soil layering at each core was recorded and samples were analysed for chloride concentration, electrical conductivity, bulk density and water content. Sulphate and nitrate concentrations were measured on selected cores. The site is level by common definitions, with a very slight concave depression (1.8% grade) midway along the KCl strip and a slight grade (¡Ü2.1%) perpendicular to the KCl strip. Measured water recharge indicated slight differences in surface slope had a marked effect on redistribution of water and spatial distribution of the chloride tracer. An estimated 90% of redistributed water was subsequently used by plants and 10% resulted in an increase in deep drainage. A varved layer had a strong influence on the subsurface redistribution of water and chloride below the root zone. There were sharp horizontal transitions between areas of slow and faster transport, which corresponded to sharp increases in catchment area and water recharge. Small surface depressions, which controlled pedogenic transport and soil formation, have been filled in by tillage translocation. Spatial variability of soil horizon thickness (and associated hydraulic properties) had little effect on transport of chloride after 34 yr. Computer simulations also suggest substantial surface redistribution of precipitation and snowmelt. In contrast to the measured chloride data, the model was sensitive to changes in hydraulic properties and horizon thickness in the root zone. Surface water redistribution was the primary factor controlling long-term transport.

Groundwater use is of fundamental importance to meet rapidly expanding urban, industrial, and agricultural water requirements, particularly in semiarid zones. To quantify the current rate of groundwater recharge is thus a prerequisite for efficient and sustainable groundwater resource management in these dry areas, where such resources are often the key to economic development. Increased groundwater recharge has been documented where native vegetation or forest/shrub land was converted to grassland or pasture, or where the land was cleared for agricultural purposes. The basic argument for increased recharge is that evapotranspiration, primarily interception and transpiration, is higher in shrublands than grasslands. Chloride mass balance (CMB) has been used to estimate ancient recharge, but recharge from recent land-use change has also been documented, specifically where vegetation has been altered and deep-rooted species replaced with shallow-rooted grasses. Chloride concentrations are inversely related to recharge rates: low Clconcentrations indicate high recharge rates as Cl- is leached from the system; high Cl concentrations indicate low recharge rates since Cl- accumulates as a result of evapotranspiration. The objectives were (1) to assess the hypothesis that removal of woody-shrub vegetation and replacement with grasses increases deep drainage, (2) to quantify the amount of deep drainage after land-use change, and (3) to provide science-based data for a better understanding of changing land-use impacts on deep drainage. Eight soils from five locations in the Central Rolling Red Plains near Abilene and Sweetwater were sampled. Each location consisted of a pair of similar soils with contrasting vegetative cover: shrubland and grassland. At each site three to five soil cores were taken as deep as possible and samples were taken by horizon, but horizons were split when their thickness exceeded 0.25 m. Soil Cl- profiles under shrubland at three sites showed that virtually no water escapes beyond the root zone. High Cl- concentrations and inventories reflect soil moisture fluxes that approached 0 mm yr-1 with depth. Evapotranspiration may be largely responsible for Cl- enrichment in those profiles. Surprisingly, soil moisture flux past 200 cm under juniper woodlands was the highest with 2.6 mm yr-1. Evapotranspirative Cl- enrichment in the upper 300 cm was not observed and may suggest a different water uptake mechanism for this plant community. Soil Cl- profiles showed increased recharge rates under grassland vegetation ecosystem. Estimated deep drainage past 200 cm of 0.1 to 1.3 mm yr-1 was observed. Low Cl- concentrations and inventories suggest a leaching environment that may be in response to changes in land use/land cover.