Rain fall-runoff response in temperate humid headwater catchments is mainly controlled by hydrolo gical processes at the hillslope scale. Applied tracer experiments with fluore scent dye and salt tracers are well known tools in groundwater studies at the large scale and vadose zone studies at the plot scale, where they provide a means to characterise subsurface flow. We extend this approach to the hillslope scale to investigate saturated and unsaturated flow path s concertedly at a forested hill slope in the Austrian Alps. Dye staining experiments at the plot scale revealed that crack s and soil pipe s function as preferential flow path s in the fine-textured soils of the study area, and these preferenti al flow structures were active in fast subsurface transport of tracers at the hillslope scale. Breakthrough curves obtained under steady flow conditions could be fitted well to a one-dimensional convection-dispersion model. Under natural rain fall a positive correlation of tracer concentrations to the transient flows was observed. The results of this study demon strate qualitative and quantitative effects of preferential flow feature s on subsurface stormflow in a temperate humid headwater catchment. It turn s out that / at the hill slope scale, the interaction s of structures and processes are intrinsically complex, which implies that attempts to model such a hillslope satisfactorily require detailed investigation s of effective structures and parameters at the scale of interest.

The underlying objective of this research is to improve the overall understanding of how spatial and temporal variability in macroporosity and soil hydraulic properties in the shallow subsurface influence the long term mobility of agricultural nutrients, and specifically the movement of liquid swine manure, in macroporous, tile drained soils. The principal motivation for the work was to provide insight into dynamic nutrient mobility in this type of agricultural environment in order to guide both the efficiency and environmental sustainability of nutrient management practices. The results of this work facilitate the advancement of our conceptual understanding and our ability to simulate preferential flow and transport in structured agricultural soils that are subject to seasonal hydrologic patterns similar to those found in the humid continental climate of southwestern Ontario

A major challenge to cold regions hydrology and northern water resources management lies in predicting runoff dynamically in the context of warming-induced changes to the rates and patterns of ground thaw and drainage. Meeting this challenge requires new knowledge of the mechanisms and rates of ground thaw and their implications to water drainage and storage patterns and processes. The study carries out to evaluate the concept of energy-based runoff in the perspective of ground heat flux, soil thaw and liquid moisture content, tortuosity of snow-free area, preferential flow and discharge of the hillslope. Based on field measurements, coupled energy and water flow is simulated in the Area of Interest (AOI) with a half-hour time interval by the distributed hydrological model, GEOtop. In the field, the saturated hydraulic conductivity varies exponentially between the superficial organic layer and the underlying mineral layer. In the simulation, the parameters of the soil physical properties are input by fourteen uneven layers below the ground surface. Starting from the initially frozen state, the process of soil thaw is simulated with dynamic variables such as soil liquid moisture and ice content, hydraulic conductivity, thermal conductivity and heat capacity. The simulated frost table depths are validated by 44-point measurements and the simulation of point soil temperature is also compared to data measured in an excavated soil pit. As a result, the frost table topography is dominated by both the snow-free pattern and the energy fluxes on the ground surface. The rate and magnitude of runoff derived from snow drift and the ice content of frozen soil is greatly influenced by the frost table topography. According to the simulation, the frost table depth is closely regressed with the ground surface temperature by a power function. As soil thawing progresses, ground heat flux reduces gradually and the rate of soil thaw becomes small when the frost table descends. Along with the snow-free area expanding, the average soil moisture of the AOI increases prior to that time when the average frost table is less than 25 cm deep. The snow-free patches expand heterogeneously in the AOI, which causes the spatial and temporal variation of hydraulic conductivity due to the non-uniform frost table depth. According to the simulation, the transit time of the flow through the AOI decreases to the shortest span on May 13 with the average frost table of 10 cm. Before this date, the time lag between snowmelt percolation and slope runoff is about 8-10 hours; while after this date, the time lag is no more than 5 hours. The pattern of the preferential flow in the AOI highly depends on the frost table topography. When the snow-free patches are widely scattered and the average frost table is between 0 and 10 cm, the preferential flow paths are inhibited. With soil thaw progresses, the preferential flow paths are prominent with the largest single contributing area occurring when the average frost table is between 10 cm to 15 cm. When the average frost table reaches 25 cm, the importance of preferential flow is not apparent, and matrix flow prevails.

The underlying objective of this research is to improve the overall understanding of how spatial and temporal variability in macroporosity and soil hydraulic properties in the shallow subsurface influence the long term mobility of agricultural nutrients, and specifically the movement of liquid swine manure, in macroporous, tile drained soils. The principal motivation for the work was to provide insight into dynamic nutrient mobility in this type of agricultural environment in order to guide both the efficiency and environmental sustainability of nutrient management practices. The results of this work facilitate the advancement of our conceptual understanding and our ability to simulate preferential flow and transport in structured agricultural soils that are subject to seasonal hydrologic patterns similar to those found in the humid continental climate of southwestern Ontario

A major challenge to cold regions hydrology and northern water resources management lies in predicting runoff dynamically in the context of warming-induced changes to the rates and patterns of ground thaw and drainage. Meeting this challenge requires new knowledge of the mechanisms and rates of ground thaw and their implications to water drainage and storage patterns and processes. The study carries out to evaluate the concept of energy-based runoff in the perspective of ground heat flux, soil thaw and liquid moisture content, tortuosity of snow-free area, preferential flow and discharge of the hillslope. Based on field measurements, coupled energy and water flow is simulated in the Area of Interest (AOI) with a half-hour time interval by the distributed hydrological model, GEOtop. In the field, the saturated hydraulic conductivity varies exponentially between the superficial organic layer and the underlying mineral layer. In the simulation, the parameters of the soil physical properties are input by fourteen uneven layers below the ground surface. Starting from the initially frozen state, the process of soil thaw is simulated with dynamic variables such as soil liquid moisture and ice content, hydraulic conductivity, thermal conductivity and heat capacity. The simulated frost table depths are validated by 44-point measurements and the simulation of point soil temperature is also compared to data measured in an excavated soil pit. As a result, the frost table topography is dominated by both the snow-free pattern and the energy fluxes on the ground surface. The rate and magnitude of runoff derived from snow drift and the ice content of frozen soil is greatly influenced by the frost table topography. According to the simulation, the frost table depth is closely regressed with the ground surface temperature by a power function. As soil thawing progresses, ground heat flux reduces gradually and the rate of soil thaw becomes small when the frost table descends. Along with the snow-free area expanding, the average soil moisture of the AOI increases prior to that time when the average frost table is less than 25 cm deep. The snow-free patches expand heterogeneously in the AOI, which causes the spatial and temporal variation of hydraulic conductivity due to the non-uniform frost table depth. According to the simulation, the transit time of the flow through the AOI decreases to the shortest span on May 13 with the average frost table of 10 cm. Before this date, the time lag between snowmelt percolation and slope runoff is about 8-10 hours; while after this date, the time lag is no more than 5 hours. The pattern of the preferential flow in the AOI highly depends on the frost table topography. When the snow-free patches are widely scattered and the average frost table is between 0 and 10 cm, the preferential flow paths are inhibited. With soil thaw progresses, the preferential flow paths are prominent with the largest single contributing area occurring when the average frost table is between 10 cm to 15 cm. When the average frost table reaches 25 cm, the importance of preferential flow is not apparent, and matrix flow prevails.

Cette thèse a été effectuée dans le cadre du projet ANCRES. Son rôle est d'assurer la compréhension physique du milieu récepteur, le sol, alors qu'une autre équipe étudie l'impact physico-chimique des eaux usées traitées sur le sol. Pour cela, il faut connaître ses propriétés texturales et structurales contrôlant ses fonctions d'épuration et d'évacuation. La problématique est donc de comprendre le processus de l'infiltration imposée par un dispositif d'ANC dans un sol caillouteux. D'abord, suite au positionnement du site pilote d'ANC au pied d'un versant au cœur du plateau portlandien dans le département de l'Yonne en France, on a identifié là un type de sol hétérogène et complexe, caillouteux, une colluvion qui n'était pas cartographiée sur la carte géologique BRGM de cette région et sur laquelle on focalise la thèse. Ensuite, dans le sol complexe du site pilote, on a d'abord mesuré la conductivité hydraulique du sol par l'appareil Guelph sur 15 m² de la fouille de l'ANC à une profondeur de 120 cm : au total, on a fait 15 essais d'infiltration. De plus, on a récupéré 15 échantillons du sol accompagnant ses essais de Guelph pour la caractérisation physique au laboratoire. On a mesuré la texture, l'humidité résiduelle (HR), la teneur en cailloux (Rw) et la matière organique (MO) des échantillons au laboratoire. Ensuite, pour l'étude du processus d'infiltration, on a instrumenté ce site par un dispositif de surveillance hydrique (tensiométrie, teneur en eau, piézométrie) et de prélèvement d'eau interstitielle du sol. De plus, la masse volumique (densité) apparente d'un sol hétérogène a été déterminée. Parmi les paramètres mesurés, certains sont choisis comme indicateurs pour caractériser un sol comme milieu récepteur potentiel des eaux usées traitées en ANC. Puis, en utilisant la MO et la texture des échantillons, on a estimé la masse volumique apparente de la matrice du sol du site piloteau moyen de fonctions de pédotransfert appelées BD-FPTs et on a testé la relation entre la conductivité hydraulique à saturation Ks et la texture de ce sol complexe. Pour cela, une méthodologie en quatre phases a été développée pour évaluer la capacité prédictive des fonctions Ks-FPTs. Cette méthodologie de sélection n'a pas été trouvée dans la littérature mais est élaborée pour les besoins de la thèse. On a déduit les meilleures Ks-FPTs pour ce type de sol. Enfin, avec les données d'humidité volumique et du potentiel matriciel du sol, acquises par une centrale d'acquisition des données, le régime hydrodynamique du sol sous le massif filtrant de l'ANC a été étudié et on a mis en évidence l'écoulement préférentiel dans un sol caillouteux. Les résultats ont montré que dans la colluvion, bien que la matrice du sol soit fine, la conductivité hydraulique mesurée est plus élevée qu'attendu. Cela démontre que la fraction des cailloux dans le sol joue un rôle essentiel en accélérant l'évacuation des eaux usées traitées et aussi l'eau pluviale vers les couches sous-jacentes, et finalement vers la nappe. Cette propriété serait un point fort pour la fonction de transfert du sol et on peut en déduire une méthode pour améliorer la capacité de transfert de l'eau des sols lourds dans les projets d'aménagement urbain ou périurbain : l'ajout de graviers et graves calcaires par mélange au sol en place. On conclut que cette expérimentation, unique en son genre, a été utile pour évaluer la fonction de rétention / transfert de l'eau dans le sol recevant les eaux usées traitées. On a identifié les paramètres prédicteurs pertinents et les relations empiriques qui permettent de faire l'économie de nombreux essais in situ d'eau / The soil is an essential compartment in hydrologic cycle of water in the nature. Therefore, it is clear that taking into account the properties and organization of the soil is essential to the understanding and management of flows involved in the development of the quality of groundwater and surface water. The on-site sanitation (ANC) is a management method of domestic wastewater, by which the water is sent into the soil after settling and filtration liquefaction / aerobic degradation. The second step was often provided by the top soil in place himself, and this continues to this day on many plots of on-site sanitation.This thesis was carried out under ANCRES project. Its role was to ensure the physical understanding of the receptor medium, soil, while another research team was investigating the physico-chemical impact of treated wastewater on the sol. To ensure it, we have to understand its textural and structural properties controlling its purifying power and hydrodynamic processes. So, the problematic is to understand the process of infiltration imposed by an ANC in a heterogeneous stony soil. At first, due to the positioning of the pilot ANC site, at the foot of a slope in the Yonne department in France, a type of complex and heterogeneous soil, a colluvion, was identified. This soil has not been mapped on the BRGM (Bureau de recherches géologiques et minières) geological map of the area. So, the thesis was focalised on this soil. Then, in this soil complex at a depth of the 120 cm of the excavation of the ANC, the soil hydraulic conductivity was first measured by a Guelph apparatus on 15 m². We totally made 15 infiltration tests. Furthermore, we have collected 15 soil samples with each Guelph test for physics laboratory physical characterization. Then, in order to study the soil functions, this site was instrumented by the water monitoring devices (tensiometers, water content probes, and piezometer) and the interstitial water sampling device from the soil. In addition, the bulk of this heterogeneous soil was determined. Among the measured parameters, a series of indicators chosen to characterize the soil as a potential receptor medium of treated wastewater of the ANC. Then, the bulk density of the soil matrix using pedotransfer functions called BD-FPTs was estimated and the relationship between saturated hydraulic conductivity Ks and the texture of the soil complex (by Ks-FPT function) was tested. For this aim, a four-phase methodology was developed to assess the predictive ability of Ks- FPTs functions. This methodology in four phases is not found in the literature but was prepared for the purposes of the thesis. We concluded the best Ks- FPTS for this type of soil. Finally, with the volumetric water content and soil matrix potential data acquired by a the data loggers, the hydrodynamic regime of the soil under the sand pack of the ANC has been studied and demonstrated the preferential flow in a stony soil was demonstrated. The results showed that in the colluvion, although the soil matrix is fine, the measured hydraulic conductivity is higher than expected. This shows that the stone fraction in the soil plays an important role in accelerating the evacuation of treated wastewater and also rainwater to the underlying layers, and finally to the water table. This property would be a strong point for the transfer function of the soil and we can deduce a method to improve the transfer function of heavy soils in urban or peri-urban development projects. This could be possible by adding the gravel and -limestone to soil matrix and mixing them. It has been concluded that this experiment, unique in its kind, has been useful in evaluating the function of retention / transfer of water in the soil receiving treated wastewater. In addition, the relevant predictor parameters and empirical relationships that make the economy of many water tests were identified

Dye tracer and time-lapse ground-penetrating radar (GPR) were used to image preferential flow paths in the shallow, unsaturated zone on hillslopes in two adjacent watersheds within the Susquehanna-Shale Hills Critical Zone Observatory (CZO). At each site we injected about 50 L of water mixed with brilliant blue dye (4 g/L) into a trench cut perpendicular to the slope (~1.0 m long by ~0.20 m wide by ~0.20 m deep) to create a line of infiltration. GPR (800 MHz antennae with constant offset) was used to monitor the movement of the dye tracer downslope on a 1.0 m x 2.0 m grid with a 0.05 m line spacing. The site was then excavated and the stained pathways photographed to document the dye movement. We saw a considerable difference in the pattern of shallow preferential flow between the two sites despite similar soil characteristics and slope position. Both sites showed dye penetrating down to saprolite (~0.40 m); however, lateral flow migration between the two sites was different. At the Missed Grouse field site, the lateral migration was ~0.55 m as an evenly dispersed plume, but at distance of 0.70 m a finger of dye was observed. At the Shale Hills field site, the total lateral flow was ~0.40 m, dye was barely visible until the excavation reached ~0.10 m, and there was more evidence of distinct fingering in the vertical direction. Based on laboratory and field experiments as well as processing of the radargrams, the following conclusions were drawn: 1) time-lapse GPR successfully delineated the extent of lateral flow, but the GPR resolution was insufficient to detect small fingers of dye; 2) there was not a distinct GPR reflection at the regolith-saprock boundary, but this interface could be estimated from the extent of signal attenuation; 3) the preliminary soil moisture conditions may explain differences in the extent of infiltration at the two sites; 4) rapid infiltration into the underlying saprock limited the extent of shallow lateral flow at both sites and can be seen using the mass balance calculation and the lateral extent of dye within the radargrams; and 5) variations in flow patterns were observed between sites with similar settings at Susquehanna-Shale Hills CZO. / Geology

Streams and rivers are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge excess nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biogeochemical processes which attenuate pollutants in stream corridors. The focus is hyporheic zones which form the interface between surface water and groundwater below and adjacent to stream channels, and riparian zones which form the interface between channels and adjacent uplands, both of which can attenuate pollutants. In this context, soil-pipes can dominate subsurface hydraulics. This research first employed MODFLOW and MT3D-USGS to model transient hyporheic hydraulics and nitrate transport in a length of riparian/riverbank soil to probe the effects of soil pipes on hydraulics and denitrification due to peak flow events in the channel. Findings showed that inserting just one soil pipe 1.5 m in length caused a ~75% increase in both hyporheic exchange and denitrification. A rough upscaling showed soil pipes could remove up to ~3% of nitrate along a 1-km reach. Next, the ability of soil pipes to bypass the often championed ability of riparian buffers to remove nitrate migrating from uplands to the channel was evaluated. This effort also employed MODFLOW and MT3D-USGS to simulated hydraulics and nitrate removal along a length of riparian soil. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. We posited a non-dimension parameter which governs when nitrate bypass is significant. In addition to soil pipes, dune bedforms can also enhance hyporheic exchange, primarily in the stream/riverbed. Again employing MODFLOW but now pairing with the transport code SEAM3D to simulate microbially-mediated aerobic metabolism of dissolved organic carbon and dissolved oxygen, the combined effects of dune translation and microbial growth and death were explored. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that aerobic metabolism increased with celerity. The results herein bolster knowledge of natural pollutant attenuation in stream and river corridors, and have implications for pollutant mitigation strategy and stream credit allocation. / Doctor of Philosophy / Streams are a vital part of our ecosystem. They are imperiled by human ecological activities such as urbanization, industrialization, and agriculture which discharge nitrate and other pollutants into our waterways. Here, this dissertation seeks to understand the physical and biological processes which attenuate pollutants. The hyporheic zone is the interface between surface water and groundwater below the bed and adjacent to stream banks, and can attenuate pollutants. Transient peak flow events such as a storm or snow melt raise the stream water levels, causing the water pressure in the stream channel to temporarily outweigh the water pressure in the soil pore spaces adjacent to the stream channel. This drives water into the banks subjecting it to pollutant attenuation processes. Soil pipes (long cylindrical void spaces created by decayed plant roots) are prevalent along stream banks, and they dominate subsurface hydraulics. This dissertation implemented a numerical study on a chunk of riparian soil to probe the effects of soil pipes on hydraulics and denitrification. Findings showed that inserting just one – 1.5 m soil pipe caused a ~75% increase in both water flow volume into the bank and nitrate removal. Riparian buffers are the vegetated strips adjacent to stream channels and have long been championed as stalwarts of pollutant removal. Soil pipes undermine this by acting as a bypass mechanism. A numerical study was again performed on a chunk of riparian soil to quantify the effects soil pipes on riparian bypass of nitrate. Findings showed that soil pipes increased flow of nitrate to the banks by five orders of magnitude in some cases. This means that a buffer enhancement strip with fine roots that prevent the formation of soil pipes should be installed along riparian buffers. In addition to soil pipes, dune bedforms can increase flowrate of water into the hyporheic zone. This dissertation modeled the combined effects of dune translation and microbial growth and death. Major findings include that neglecting microbial growth can lead to inaccurate modeling of biogeochemistry, and that biodegradation increases with increased dune velocity. The results herein bolster knowledge on natural pollutant attenuation in streams, and have implications in terms of pollutant mitigation strategy and stream credit allocation.

Surface coal mining has caused significant land-use change in central Appalachia in the past few decades. This landscape altering process has been shown to degrade water quality and impact aquatic communities in the mining-influenced headwater streams of this biodiverse ecoregion. Among pollutants of concern is total dissolved solids (TDS) which is usually measured via its surrogate parameter, specific conductance (SC). The SC of valley fill effluent is a function of fill construction methods, materials, and age; yet hydrologic studies that relate these variables to water quality are sparse due to the difficulty of implementing traditional hydrologic measurements in fill material. We tested the effectiveness of electrical resistivity imaging (ERI) to monitor subsurface hydrologic flow paths in valley fills. ERI is a non-invasive geophysical inverse technique that maps spatiotemporal changes in resistivity of the subsurface. When a resistance or conductive change is induced in the system, ERI can reveal both geologic structure and hydrologic flows. We paired ERI with artificial rainfall experiments to track highly conductive infiltrated water as it moved through the valley fill. The subsurface structure of two other landforms were also imaged to confirm variations between forms. Results indicate that ERI can be used to identify the subsurface geologic structure as well as track the advancing wetting front and preferential flow paths. We observed that the upper portion of a fill develops a profile that more closely resembles soil with smaller particle sizes, while the deeper profile has higher heterogeneity, with large rocks and void spaces. The sprinkling experiments revealed that water tends to pond on the surface of compacted areas until it reaches preferential flowpaths, where it infiltrates quickly and migrates deeply or laterally. We observed water moving from the surface down to a 20 meters depth in one hour and 15 minutes, and to a depth of 10 meters in just 45 minutes. We also observed lateral preferential flow downslope within 5 meters of the surface, likely due to transmissive zones between compacted layers along the angle-of-repose. Finally, when compared to other landscapes we were able to see that a filled highwall slope has larger rocks near the surface than the valley fill, but a similar degree of heterogeneity throughout; while the natural slope has less heterogeneity at depth as is expected in consolidated bedrock. ERI applications can improve understanding of how various fill construction techniques influence subsurface water movement, and in turn aid in the development of valley fill construction methods that will reduce environmental impacts. / Master of Science

Surface coal mining has altered Appalachian landscapes, affecting water quality and aquatic ecology. Valley fills created from excess overburden are prominent features of many mined landscapes. Increased total dissolved solids (TDS), as measured by its surrogate specific conductance (SC), is a significant water quality concern related to the exposure of fresh mineral surfaces to weathering in valley fills. Specific conductance levels in waters draining Appalachian mined areas are highly variable, yet the causes for this variability are not well known. Here we sought to improve understanding of such variability by investigating the interior subsurface structure and hydrologic flowpaths within a series of valley fills and relating that to valley fill characteristics such as age and construction method. We used electrical resistivity imaging (ERI) to investigate the subsurface structure of four valley fills in two dimensions. We combined ERI with artificial rainfall to investigate the location and transit time of hydrologic preferential infiltration flowpaths through the fills. Finally, we used our ERI results in conjunction with SC data from effluent streams to improve understanding of SC relationship to fill flowpaths and characteristics. ERI results indicated considerable variability in substrate type and widespread presence of preferential infiltration flowpaths among the valley fills studied. We estimated an average preferential flowpath length of 6.6 meters, average transit time of 1.4 hours, and average velocity of 5.1 m/h or 0.14 cm/s through preferential infiltration flowpaths. ERI successfully distinguished fills constructed using methods of conventional loose-dump and experimental controlled-material compacted-lift construction. Conventional fills had greater ranges of subsurface resistivity, indicating a wider range of substrate types and/or more variable moisture content. Conventional fills also showed more accumulation of water within the fill during artificial rainfall, possibly indicating more quick/deep preferential infiltration flowpaths than in the experimental fill. Relationships between other fill characteristics as well as stream effluent SC were not related in a statistically significant way to fill structure or flowpaths. ERI appears to be a robust non-invasive technique that provides reliable information on valley fill structure and hydrology, and experimental compacted-lift valley fill construction produces significantly altered hydrologic response, which in turn affects downstream SC. / MS