Tens of millions of dollars have been spent to control Tamarix (saltcedar) trees along waterways in the Southwestern United States for the purpose of increasing streamflow yet no increase in streamflow has been demonstrated. The Pecos River Ecosystem Project (PREP) served as a case study to characterize surface and groundwater interaction along the Pecos River in Texas, assess the influence of saltcedar transpiration on stream stage and water table fluctuations, and evaluate the impacts of large-scale saltcedar control on baseflows. This is the first study that has investigated the influence of saltcedar transpiration on surface and groundwater interaction and the first to provide a mechanistic explanation for the lack of measurable increase in streamflow. Neither saltcedar transpiration nor saltcedar removal influenced hydraulic gradients, streambank seepage, or stream elevations. The results of the plot scale studies indicate saltcedar transpiration along the Pecos River is lower than reported elsewhere and therefore may not yield detectable increases in baseflow. To extend the study to a much larger scale, we analyzed annual baseflows at the downstream end of 340 km river reach from 1999 (pretreatment) through 2009. Surprisingly, baseflows declined for four years after the project began despite additional acreages of saltcedar treatment each year. However, baseflow surged in 2005 and remained higher than the pretreatment year (1999) through 2009. Additional detailed analyses of reservoir release and delivery records and rainfall are needed to better understand contributions of rainfall and flow regulation to this increase. Tracer based studies to determine the relative contributions of releases and groundwater would also enable a better interpretation of the change in baseflows. We did not investigate any other reported benefits, such as restoration of native plant species, or reduced soil salinity, of saltcedar control.

Seepage direction is crucial for understanding the critical state and development of piping erosion. A stress-controlled apparatus was designed to investigate the piping behavior of cohesionless soil under upward flow condition. The components of the new apparatus included a loading chamber, a vertical and confining loading system, an upstream water supply device, a soil-water separating system, and a water collecting system. The loading chamber provides space for a soil specimen setting and loading. The combination of a vertical and a confining loading system was designed to apply complex stresses to a soil specimen. Under the stresses, the specimen was then eroded by the gradually increasing hydraulic head supplied by the water supply system. The eroded particle and spilling water were collected and detected by the soil-water separating system and the water collecting system. A series of experiments were carried out using the new apparatus. Results demonstrated the repeatability experiments and usefulness of the apparatus. The new apparatus allowed us to investigate the piping behavior under different stress states and hydraulic gradients. With this new apparatus and experiments, we found that lower and high critical hydraulic gradients (CHGs) should be included as the criteria of piping development based on the relationship between the hydraulic gradient and the seepage response. In addition, the stress state on the CHG and the particle erosion rate played important roles in the piping development. The outer pressure on the specimen can retard the development of erosion. In contrast, the hydraulic gradient was found to be positively correlated to the erosion rate. Results also indicated that a specimen would collapse once the amount of eroded small particles exceeds the critical value of 46.5 % of the soil.

No description available.

Slurry wall is a geotechnical engineering application to control the migration of contaminants by retarding groundwater flow. Sand-bentonite slurry walls are commonly used as levees and containment liners. The performance of bentonite slurry in sand-bentonite slurry walls was investigated by studying the rheological properties of bentonite suspensions, the penetration length of bentonite slurry into clean sand, and stability of the trench under in-situ hydraulic gradients. In this study, the rheological parameters of bentonite suspensions were measured at various bentonite fractions by weight from 6 to 12% with 0-3% of sodium pyrophosphate; an ionic additive to control the rheological properties of the bentonite slurries. The penetrability of the bentonite slurries through Ottawa sand was studied by injecting the slurries into sand columns at different bentonite fractions. The injection tests were performed with the permeameters having different diameters to eliminate any bias on test results due to the different size of permeameter. An empirical correlation for predicting the penetration length of bentonite slurry based on apparent viscosity, yield stress, effective particle size, relative density, and injection pressures was updated by taking into account the effects of the permeameter diameter size. Moreover, the stability of sand-bentonite slurry walls was inspected by studying the hydraulic performance of sand permeated with bentonite suspensions under increasing hydraulic gradients. The critical hydraulic gradient at which washing out of bentonite suspensions is initiated was examined. For specimens with bentonite contents less than the threshold value, the flow occurred through the sand voids and minimal washing out occurred. On the other hand, when the bentonite content was high enough to fill up all the void space between the sand particles, the flow was controlled by the clay void ratio. In this case, washing out did occur with increasing gradients accompanied by an increase in hydraulic conductivity. Accordingly, a relation between the yield stress of bentonite suspensions and the critical hydraulic conductivity was developed. / text

Seepage-related erosion is one of the predominant mechanisms responsible for incidents and failures of dams and levees. Current geotechnical engineering practice consists of comparing expected exit gradients with the critical gradient of the soil at the seepage exit point. The critical gradient is generally considered as the ratio of soil buoyant unit weight and the unit weight of water, suggesting that the critical gradient only depends on the void ratio and specific gravity of the solids. However, in the field and in research, it has been observed that piping can initiate at average gradients much lower than unity due to concentrations in flow and non-vertical exit faces. Therefore, there is a need for deeper understanding of the granular scale mechanisms of the piping erosion process. This thesis presents the results of a laboratory study to assess the effects that soil properties and exit face configurations have on the potential for initiation of piping and the piping mechanisms. By using a laboratory device designed and constructed specifically for this study, the critical gradients needed to initiate piping in a variety of sandy soils were measured to assess the effects that parameters such as gradation, grain size, and grain shape have on the critical gradients. The tests are also used to observe the grain scale mechanisms of piping erosion initiation. The ultimate goal of the study is to develop an empirical, but mechanism-based, grain-scale model that can take into account the effects of converging flows, non-horizontal exit faces, and soil properties while assessing the potential for piping erosion to occur.

Le bassin du Merguellil, en Tunisie centrale, fournit un exemple illustratif des processus hydrologiques profondément modifiés par l’action humaine. L’oued Merguellil, le principal cours d’eau du bassin, a vécu une évolution socio-hydrologique extrêmement marquée. En effet, son état actuel est l’héritage d’une longue histoire d’interactions entre l’homme et son milieu. Il est actuellement intermittent sur la majeure partie de son cours, or les dires des riverains et les documents anciens révèlent qu’il n’en était pas ainsi au début du siècle dernier. Le recours aux informations anciennes issues des documents d’archives a montré que l’oued Merguellil était autrefois soutenu principalement par le déversement de la nappe captive de Bouhefna. Durant les années 1974-1975 et afin de transférer les eaux souterraines du bassin du Merguellil vers les régions côtières, une stratégie politique a été mise en place pour rabattre le niveau de la nappe de Bouhefna de manière à pouvoir réduire ‘’les pertes’’ par évaporation dans l’oued Merguellil et minimiser l’écoulement souterrain vers la nappe voisine de Haffouz d’intérêt hydrogéologique moins important. Comme prévu, cela a induit une inversion du gradient hydraulique oued-nappe inférant le tarissement des sources de déversement, la vidange de la nappe d’accompagnement et la disparition du débit de base de l’oued Merguellil à partir de 1976-1978. La modélisation hydrodynamique établie dans cette thèse suggère que le flux souterrain qui transitait vers l’oued par drainance verticale avant l’inversion du gradient hydraulique est de l’ordre de 9 hm3. Désormais c’est les crues de l’oued qui alimentent la nappe alluviale et les nappes superficielles. Le flux moyen infiltré lors de la propagation des crues est estimé à 17 hm3 dans la section de l’oued entre la station de Haffouz et barrage El Haouareb pour l’année 2013-2014.Toutefois, le schéma de gestion de la nappe de Bouhefna a été basé exclusivement sur des considérations hydrodynamiques sans tenir compte de l’évolution des usages. En effet, la disparition de l’étiage de l’oued a contraint les riverains à abandonner les canaux d’irrigation traditionnels et à opter pour l’installation de motopompes et la mise en place des forages profonds. Cette rétroaction face au changement de régime d’écoulement de l’oued a contribué à perturber davantage l’équilibre hydrologique. Cela s’est traduit par une exploitation excessive des eaux souterraines avec une baisse actuelle observée de la piézométrie supérieure à 1m/an et une inversion du gradient entre la nappe de Bouhefna et la nappe de Haffouz. La modélisation hydrodynamique suggère que les flux moyens échangés par drainance verticale sont passés de 8 hm3 en 1970 à 2 hm3 en 2015. Dans le sens inverse, les flux transitant depuis la nappe de Haffouz vers la nappe de Bouhefna sont évolués de 1 hm3 en 1970 à 6 hm3 en 2015, imposant ainsi un risque de salinité à long terme.Le transfert des eaux de Bouhefna vers les régions côtières, même s’il est largement contesté par les populations locales, n’a jamais été mis en avant comme facteur explicatif des évolutions hydrologiques vécues localement, les travaux de cette thèse permettent pourtant de montrer à quel point ce transfert d’eau a influencé le régime hydrologique de l’oued. Toutefois, en n’omettant pas leurs propres responsabilités dans ces dynamiques, les agriculteurs font preuve de lucidité. En effet, le modèle hydrodynamique suggère que la part cumulée des volumes en eau souterraine mobilisés par ces derniers après la disparition de l’étiage de l’oued est comparable à celle destinée à l’eau potable. Les résultats de cette thèse rejoignent les recherches en socio-hydrologie qui appellent à intégrer les aspects sociaux dans les schémas de gestion pour garantir un développement durable des ressources en eaux. / The Merguellil basin in central Tunisia provides an illustrative example of hydrological processes profoundly modified by human action. The Wadi Merguellil, the main river of the basin, has experienced an extremely marked socio-hydrological evolution. Its current state is the legacy of a long history of interactions between man and his environment. Truly, it is currently intermittent over most of its course, but the statements of farmers and archival records reveal that this was not the case at the beginning of the last century. The use of ancient information from archival documents has shown that the Wadi Merguellil was supported mainly by the overflow of the confined aquifer of Bouhefna. During the years 1974-1975 and in order to transfer groundwater resources from the Merguellil basin to the coastal regions, a management plan was put in place. The aim of this plan was to reduce the level of the Bouhefna aquifer so as to reduce '' losses '' by evaporation in the Wadi Merguellil and minimize the groundwater flow towards the nearby Haffouz aquifer. As expected, this strategy led to a reversal of the hydraulic gradient inferring the drying up of the overflow springs, the emptying of the alluvial aquifer and the disappearance of the Wadi Merguellil baseflow during the period 1976-1978. The hydrodynamic model established in this thesis suggests that the averaged groundwater flow that was feeding the Wadi before the hydraulic gradient reversal is around 9 hm3. Currently, it is rather the floods of the Wadi that feed the alluvial aquifer and the shallow aquifers. The average flow infiltrated during the propagation of flood events is estimated at 17 hm3 in the section of the wadi between the Haffouz station and El Haouareb dam for the year 2013-2014.Though, the exploitation management plan of the Bouhefna aquifer was based exclusively on hydrodynamic considerations without taking into account the evolution of hydro-agricultural practices. Indeed, the disappearance of the baseflow of the Wadi Merguellil has forced farmers to abandon traditional irrigation canals and opt for the installation of motor pumps and the establishment of deep wells. This feedback on the change in the Wadi flow regime has further disrupted the hydrological balance. This resulted in an excessive exploitation of the groundwater with an observed current decrease of the piezometry higher than 1m/year and a reversal of the hydraulic gradient between the Bouhefna aquifer and the Haffouz aquifer. The hydrodynamic model suggests that the average flow exchanged by vertical drainage has decreased from 8 hm3 in 1970 to 2 hm3 in 2015. In the opposite direction, the average flow transiting from the Haffouz aquifer to the Bouhefna aquifer has increased from 1 hm3 in 1970 to 6 hm3 in 2015, imposing a risk of salinity in the long term.The transfer of water from Bouhefna to the coastal regions, even though it is widely disputed by the local populations, has never been put forward as a factor explaining the hydrological evolution experienced locally. The work of this thesis allows to show how much this transfer of water has influenced the hydrological regime of the wadi. However, by not omitting their own responsibilities in these dynamics, farmers are lucid. Indeed, the hydrodynamic model suggests that the cumulative part of groundwater volumes mobilized by the latter after the disappearance of the Wadi baseflow is comparable to that for drinking water. The results of this thesis are in line with research in socio-hydrology that calls for integrating social aspects into management plans to ensure sustainable development of water resources.

This study is focused on characterization of the hardrock environment in surroundings of Sazava river. It is based on the archival data of groundwater table in boreholes, results of pumping tests from Geofond database and topographic data (DMR , watercourse, etc.). ArcMap 10.1 and Excel were used for data processing. The relations between the groundwater table depth, water table gradient, specific yield, transmissivity and variety of topographic parameters (distance from a watercourse, elevation, relative elevation above the nearest watercourse, the terrain gradient, etc.) were studied. Close linear relationship exists between the gradient of the terrain and groundwater table (rxy 0.96) in the study area. Groundwater table gradient is on average 88 % of terrain gradient. Mean groundwater table gradient is 10 % (6). The average transmissivity in the area is 1.27 x 10-4 m2 /s, specific yield is usually between 0.01 and 0.1 l/s m. This corresponds to the low and very low transmissivity class. Variability of transmisivity values is high. The difference between transmisivity in discharge and recharge zone, assumed by previous authors, was not confirmed in the study area. Specific base flow calculated from mean transmissivity, terrain/ water table gradient and river network density based on Krásný and...

La côte ouest irlandaise située dans les comtés de Clare et Galway est depuis récemment affectée par une augmentation de la fréquence des inondations et une montée du niveau marin. L'impact de ces changements climatiques se fait particulièrement ressentir au niveau des aquifères karstiques côtiers de ces régions, tel que le bassin karstique de Bell Harbour (~50 km²) sélectionné dans le cadre de ce projet: le positionnement d'un biseau salé dans cet aquifère est clairement dû à l'interaction entre sa recharge liée aux événements pluvieux et la forte influence de la marée. Des données (niveaux d'eau et conductivités spécifiques) ont été collectées à l'aide de sondes, à deux sources côtières, six forages, trois lacs et au milieu de la baie durant des périodes prolongées. Trois types d'environnement hydrodynamiques (conduits, fissures et matrices) ont été définis pour chacun des six forages en comparant deux méthodes qui se sont avérées cohérentes entre-elles. Les variations des conductivités spécifiques combinées à la chimie des eaux des six forages et de lacs ont permis d'évaluer l'étendue du biseau salé dans l'aquifère en fonction de la recharge de l'aquifère et des cycles de marée haute/basse et vives eaux/basses eaux: l'étendue du biseau salé dépend des propriétés hydrodynamiques de l'aquifère mais aussi de l'influence relative de la recharge et de la marée sur les niveaux piézométriques, induisant chacun des comportements opposés. Ainsi, la compétition entre la recharge et la marée contrôle l'intrusion d'eau de mer dans l'aquifère, ce qui explique les changements spatio-temporels du biseau salé dans l'aquifère. Les fortes amplitudes de marée semblent être le moteur des brèves intrusions salines dans l'aquifère proche de la rive alors que la position du niveau piézométrique semble influencer l'intensité de cette augmentation de la salinité. La recharge karstique de la région est suffisamment importante tout au long de l'année pour que le biseau salé ne s'étende pas plus loin qu'un kilomètre de la rive. La diminution des précipitations durant l'été (~10 %) ainsi que l'augmentation du niveau marin prévues pour les prochaines décennies, contribueront certainement à une intrusion plus importante du biseau salé dans l'aquifère. / Low-lying coastal areas in the west of Ireland, such as the Galway and Clare coasts, have seen recent increases in flooding frequencies coupled with overall increases in sea level. The impacts of these changes are most strongly felt in coastal karst catchments and this study focuses on one such area, the Bell Harbour catchment (~50 km²), where there is a clear interaction between rainfall inputs and tidal influences, to create a terrestrial salt water wedge. Data (specific conductivity and water levels) have been collected at two coastal springs, six boreholes, three lakes, and from discrete locations in the middle of the bay, using dedicated loggers over extended periods. Two approaches that provided consistent results were used to explain the different hydrodynamic behaviours identified in the boreholes (conduits, fissures and matrix flows). Specific conductivity variations and water chemistry measured inland allowed for assessment of the spatial extent of the saltwater wedge into the aquifer as a function of both karst recharge and tidal movements at high/low and neap/spring tidal cycles. The extent of the saltwater wedge depends on the intrinsic properties of the aquifer but also on the relative influence of the recharge and the tide on groundwater levels, which induce opposite behaviours. This dynamic between recharge and the tide thus controls the seawater inputs, hence explaining temporal and spatial changes in the saltwater wedge in this coastal karst aquifer. Strong tidal amplitudes seems to be the motor of sudden saltwater intrusion observed in the aquifer near the shore while the relative elevation of the groundwater appears to influence the intensity of the salinity increase. The magnitude of annual recharge in the area is high enough to limit saltwater intrusion to no more than about one kilometre inland from the shore. Given the anticipated decreases in summer precipitation (~10 percent), coupled with anticipated sea level rises, the extent of the saltwater wedge into the aquifer is likely to increase in coming decades.

In the case of soil structures and/or subsoil of the water structures, filtration deformation can occur due to the effects of water seepage. One of the possible phenomena that can occur in water structures due to filtration deformation is external suffusion / heave, which ocure on the air side of the structure in the case of ascending external seepage, where soil particles are gradually subject to ascending seepage forces. The possibility of heave can be assessed using the method of partial factors, for which individual partial factors are needed, which are not specified in more detail in the literature. The aim of this work is to determine the partial reliability factor for failure due to heave based on the evaluation of laboratory experiments on uniform grain materials with non-uniformity number CU

This hydrogeophysical field experiment evaluated the ability of high frequency (450 & 900 MHz) ground penetrating radar (GPR) to characterize the release of gasoline over an annual cycle of in situ conditions. In August 2008, 200 liters of E10 gasoline were released into the unconfined sand aquifer at CFB Borden. The 900 MHz profiling clearly shows the development of shallow (i.e., above 10 ns) high reflectivity in the vicinity of the trench immediately after the release. Additional lateral extension of high reflectivity zone was observed over the following 20 days until the seasonal water table low stand occurred, after which no further lateral movement was observed. Throughout the remainder of the monitoring, the 900 MHz profiling observed a long-term dimming of reflectivity at the periphery of the impacted zone. While direct imaging of the shallow impacted zone by the 450 MHz antennas was significantly obscured by the superposition with the direct air-ground wave arrival; its improved depth of penetration allowed the measurement of a velocity “pull-up” of an underlying stratigraphic interface resulting from the displacement of low velocity water by high velocity gasoline. The maximum pull-up was observed during the water table low stand. The ongoing changes in the pull-up magnitude during the remainder of the observation period suggest the continued redistribution of fluids in the impacted zone. Because of the shallow depth of the gasoline impacted zone, the effects of freezing during the winter period were observed in the GPR imaging. The presence of the gasoline impacted zone appears to have affected the depth of freezing, causing a depression of the frozen soil base. The dimming of the direct air-ground wave complex indicates that the contaminant phase brought to the surface by the water table fluctuations have impacted the nature of the near-surface freezing.