Rozprawy doktorskie na temat „Groundwater Interaction”

Underground constructions below the water table may be problematic if the role of groundwater is not properly acknowledged. Difficulties worsen in urban environments. Two aspects should be taken into account in the interaction between underground constructions and groundwater, 1) the impacts caused by the construction in the aquifers and 2) the difficulties that groundwater causes during the construction. Therefore, the design of an underground construction must be minimize the impacts in the underground environment as well as guaranteeing the safety of the workers and the integrity of adjacent structures. The adopted measures must not complicate the development of the construction and must not increase the total cost. To sum up, the construction must be efficient. These questions arose during the construction of the High Speed Train (HST) tunnel in Barcelona, which passes next to the Sagrada Familia. This thesis proposes answers to the questions which came up. Two problems may arise when a construction intersects an aquifer, the drain and the barrier effect. While the former has been widely studied, the second has not been adequately formalized and this is the first aim of the thesis. Analytical solutions are obtained to compute the head variations caused by an underground impervious structure. The solutions allow computing of the impact under different circumstances and to design corrective measures. The proposed equations were verified by using the data from real underground constructions. Subsidence caused by dewatering processes of deep excavations is feared. This fact affects the design. One option to reduce subsidences consist on deepen the enclosures (diaphragm walls, piles, jet-grouting piles) in order to avoid or minimise the dewatering. The second objective is to discuss the effectiveness of this measure, which rise the cost of the constructions, since drawdown caused by pumping are usually small and less dangerous (poorly differential) than is expected. Moreover, the pumping stabilizes the bottom of excavations. Therefore, to deepen the enclosures may be less efficient than combining short enclosures with deep pumping wells. Both alternatives must be compared. Thus, a number of dewatering scenarios, where the depth of the enclosures and the pumping wells are varied, are compared considering the safety, the outside affectations and the cost. Results show that combining deep pumping wells with short enclosures can become the most efficient method to perform excavations in preconsolidated soils. ii Regardless of the method used to perform an excavation, the enclosure, always, plays an important role since it guarantees the stability of the excavation walls and prevents the entrance of lateral flow. The presence of small defects may lead to disastrous consequences, which would invalidate all the previous work oriented to develop an efficient construction. Therefore, given that the defects are relatively common, that the techniques used to detect defects are limited and that the groundwater behaviour taking into account underground structures can be predicted, the third objective of the thesis is to develop hydraulic methods to assess the state of an enclosure. These methods, specifically the Watertightness Assessment Test (WTAT), are used as much to estimate the effective parameters of the enclosure as to locate the defects. Finally, the steps followed during the construction of the HST tunnel in Barcelona demonstrate the importance of the geological characterisation. If the soil is well known, all the aspects associated with the construction can be predicted accurately, which is crucial for designing an efficient underground construction. The geology, the hydrogeology and the historical processes suffered by the soil must be characterized accurately.
Las construcciones subterráneas realizadas por debajo del nivel piezométrico pueden ser problemáticas si no se reconoce el papel del agua subterránea. Las dificultades aumentan en ambientes urbanos. La interacción con el agua subterránea tiene lugar en las dos direcciones 1) los impactos causados por la construcción sobre el acuífero y 2) las dificultades que, durante la construcción, causará la presencia de agua subterránea. Por ello, el diseño de una construcción subterránea debe minimizar los impactos en el medio subterráneo y garantizar la seguridad de los trabajadores y la integridad de las estructuras adyacentes. Las medidas adoptadas no deben complicar en exceso el desarrollo de las obras ni sobrecargar el coste total de la obra. En resumen, la construcción debe ser eficiente. Estas preguntas surgieron durante la construcción del túnel para el Tren de Alta Velocidad (HST) en Barcelona, adyacente a la Sagrada Familia. En esta tesis se proponen respuestas a las mismas. Los impactos sobre el acuífero pueden ser de dos tipos: el efecto dren y el efecto barrera. Mientras que el primero ha sido ampliamente estudiado, el segundo no ha sido formalizado adecuadamente, lo que constituye el primer objetivo de esta tesis. Para calcular las variaciones de nivel causadas por una estructura subterránea impermeable, se derivan ecuaciones para diversas condiciones de obra y para medidas correctoras. Se han verificado con datos de construcciones reales. La subsidencia causada por el drenaje de excavaciones profundas es uno de los temores más condicionantes del diseño. Una de las maneras de reducirla, consiste en profundizar los recintos (pantallas, pilotes, columnas de jet-grouting) con el fin de evitar o minimizar el bombeo. El segundo objetivo de esta tesis es cuestionar la eficacia de estas medidas, que aumentan el coste de la construcción, ya que los asientos causados por el bombeo suelen ser pequeños y menos peligrosos (poco diferenciales) de lo temido. Además, el bombeo estabiliza la base de las excavaciones. Por ello realizar recintos más profundos puede ser menos eficiente que combinar recintos cortos y pozos de bombeo profundos. Es obvio que ambas alternativas deben compararse adecuadamente. Para ello, se han estudiado una serie de escenarios de drenaje que son comparados teniendo en cuenta la seguridad, las afecciones externas y el coste. Las variaciones entre los diferentes escenarios son las profundidades de los recintos y de los pozos de bombeo. Los resultados muestran que combinar pozos de bombeo profundos con recintos cortos es el método más eficiente para llevar a cabo excavaciones en suelos preconsolidados. Independientemente del método utilizado para llevar a cabo una excavación, el recinto, siempre juega un papel importante, ya que garantiza la estabilidad de las paredes de la excavación y evita la entrada de flujo lateral. La presencia de pequeños defectos puede tener consecuencias desastrosas, lo que haría inútil todo el trabajo previo orientado a desarrollar una construcción eficiente. Por lo tanto, dado que los defectos son relativamente comunes, que las técnicas utilizadas para detectar defectos son limitadas y que el comportamiento del agua subterránea puede ser predicho teniendo en cuenta las estructuras subterráneas existentes. El tercer objetivo de la tesis es desarrollar métodos hidráulicos para evaluar el estado del recinto de una excavación. Se muestra que estos métodos y, en particular, el ensayo de caracterización de impermeabilización permiten tanto estimar los parámetros efectivos del recinto como localizar los defectos. Por último, los pasos seguidos durante la construcción del túnel para el Tren de Alta Velocidad en Barcelona evidencian la importancia de una buena caracterización geológica. Si el suelo es bien conocido, todos los aspectos asociados con la construcción pueden ser estimados con precisión, lo que resulta crucial para diseñar una construcción subterránea eficiente. La geología, la hidrogeología y los procesos históricos sufridos por el suelo deben ser bien conocidos.
Les construccions subterrànies realitzades sota el nivell piezométric poden ser problemàtiques si no es reconeix el paper de l'aigua subterrània. Les dificultats augmenten en ambients urbans. La interacció amb l'aigua subterrània té lloc en els dos sentits 1) els impactes causats per la construcció sobre l'aqüífer i 2) les dificultats que, durant la construcció, causarà la presència d'aigua subterrània. Per això, el disseny d'una construcció subterrània ha de minimitzar els impactes al medi subterrani i garantir la seguretat dels treballadors i la integritat de les estructures adjacents. Les mesures adoptades no han de complicar en excés el desenvolupament de les obres ni sobrecarregar el cost total de l'obra. En resum, la construcció ha de ser eficient. Aquestes preguntes van sorgir durant la construcció del túnel per al Tren d'Alta Velocitat a Barcelona, adjacent a la Sagrada Família. En aquesta tesi es proposen respostes a les mateixes. Els impactes sobre l'aqüífer poden ser de dos tipus: l'efecte dren i l'efecte barrera. Mentre que el primer ha estat àmpliament estudiat, el segon no ha estat formalitzat adequadament, la qual cosa constitueix el primer objectiu d'aquesta tesi. Per calcular les variacions de nivell causades per una estructura subterrània impermeable, es deriven equacions per a diverses condicions d'obra i per a mesures correctores. S'han verificat amb dades de construccions reals. La subsidència causada pel drenatge d'excavacions profundes és un dels temors més condicionants del disseny. Una de les maneres de reduir-la, consisteix a aprofundir els recintes (pantalles, pilotis, columnes de jet-grouting) amb la finalitat d'evitar o minimitzar el bombament. El segon objectiu d'aquesta tesi és qüestionar l'eficàcia d'aquestes mesures, que augmenten el cost de la construcció, ja que els seients causats pel bombament solen ser petits i menys perillosos (poc diferencials) del temut. A més, el bombament estabilitza la base de les excavacions. Per això realitzar recintes més profunds pot ser menys eficient que combinar recintes curts i pous de bombament profunds. És obvi que ambdues alternatives han de comparar-se adequadament. Per a això, s'han estudiat una sèrie d'escenaris de drenatge que són comparats tenint en compte la seguretat, les afeccions externes i el cost. Les variacions entre els diferents escenaris són les profunditats dels recintes i dels pous de bombament. Els resultats mostren que combinar pous de bombament profunds amb recintes curts és el mètode més eficient per dur a terme excavacions en sòls preconsolidats. vi Independentment del mètode utilitzat per dur a terme una excavació, el recinte, sempre juga un paper important, ja que garanteix l'estabilitat de les parets de l'excavació i evita l'entrada de flux lateral. La presència de petits defectes pot tenir conseqüències desastroses, la qual cosa faria inútil tot el treball previ orientat a desenvolupar una construcció eficient. Per tant, atès que els defectes són relativament comuns, que les tècniques utilitzades per detectar defectes són limitades i que el comportament de l'aigua subterrània pot ser predit tenint en compte les estructures subterrànies existents. El tercer objectiu de la tesi és desenvolupar mètodes hidràulics per avaluar l'estat del recinte d'una excavació. Es mostra que aquests mètodes i, en particular, l'assaig de caracterització d'impermeabilització (WTAT) permeten tant estimar els paràmetres efectius del recinte com localitzar els defectes. Finalment, els passos seguits durant la construcció del túnel per al Tren d'Alta Velocitat a Barcelona evidencien la importància d'una bona caracterització geològica. Si el sòl és ben conegut, tots els aspectes associats amb la construcció poden ser estimats amb precisió, la qual cosa resulta crucial per dissenyar una construcció subterrània eficient. La geologia, la hidrogeologia i els processos històrics soferts pel sòl han de ser ben coneguts.

L'evidenza riconosciuta del riscaldamento globale richiede una valutazione del ciclo dell'acqua presente e futuro in Europa e nel mondo. Recentemente, è stata documentata l'evidenza di un regime idrologico modificato nelle Alpi sotto il cambiamento climatico. Tuttavia, secondo il quinto rapporto di valutazione dell'IPCC, è ancora necessario approfondire la nostra comprensione dell'impatto del cambiamento climatico e dell'uso del suolo sullo stoccaggio delle acque sotterranee nei bacini idrografici alpini. Una delle maggiori limitazioni all'analisi dell'interazione tra acque superficiali e sotterranee nei terreni alpini è la difficoltà di acquisizione dei dati e la limitata presenza di stazioni meteorologiche. Questi due fattori aumentano considerevolmente l'incertezza di una rappresentazione olistica dei processi idrologici e una stima affidabile della ricarica delle acque sotterranee. Lo scopo di questo lavoro di ricerca è quello di migliorare le attuali conoscenze sull'interazione tra le acque superficiali e gli acquiferi poco profondi e di definire un metodo per una modellazione integrata delle principali componenti del ciclo dell'acqua a scala di bacino da utilizzare come input per la modellazione delle acque sotterranee. La raccolta e l'uso di dati e metodi che permettono la massima discretizzazione dell'eterogeneità degli elementi coinvolti è il filo conduttore di questo lavoro. L'approccio scientifico è dimostrato per un caso di studio complesso, la valle della Valtellina (Italia settentrionale), per indagare l'interazione tra le componenti del ciclo idrogeologico e le loro proiezioni future secondo le dinamiche climatiche. Questa valle potrebbe essere considerata un perfetto caso di studio perché è caratterizzata da un sistema attivo che reagisce rapidamente alle variazioni meteorologiche e climatiche. Ciò è visibile dalla fluttuazione delle acque sotterranee e del fiume principale, l'Adda, durante eventi estremi di precipitazione e con lo scioglimento della neve durante i periodi di primavera/estate. La tesi è divisa in tre sezioni principali. La prima fornisce una descrizione dell'idrostratigrafia della pianura alluvionale della Valtellina. Questa sezione include il modello di flusso delle acque sotterranee in condizione stazionaria, sviluppato utilizzando FeFlow 7.2, e il relativo processo di calibrazione automatica della parametrizzazione idrogeologica. La seconda mostra la quantificazione del volume di stoccaggio stagionale delle acque sotterranee secondo il metodo del bilancio idrico residuo per due anni idrologici. Per la stima delle componenti principali (Precipitazione, Evapotraspirazione e Snow Water Equivalent), vengono testati nuovi promettenti database e metodi satellitari. L'ultimo capitolo descrive il modello di flusso transitorio delle acque sotterranee sviluppato con condizioni limite dinamiche ottenute dai metodi satellitari. Infine, il modello di flusso è stato utilizzato per valutare l'impatto sulle acque sotterranee di possibili scenari di cambiamento climatico.
The recognized evidence of global warming demands assessment of the present and future water cycle in Europe and worldwide. Recently, evidence of modified hydrological regime in the Alps under climate change has been documented. However, according to the IPCC Fifth Assessment Report, it is still necessary to deepen our understanding of the impact of climate change and land use on groundwater storage in the alpine catchment areas. A major limitation to the analysis of the surface water-groundwater interaction in alpine terrain are the difficultly of data acquisition as well as the limited presence of meteorological stations. These two factors considerably increase the uncertainty of a holistic representation of the hydrological processes and a reliable estimation of groundwater recharge. The aim of this research work is to improve the current knowledge on the interaction between surface water and shallow aquifers and to define a method for an integrated modelling of the main components of the water cycle at the catchment scale to be used as input for groundwater modelling. The collection and use of data and methods that allow for the maximum discretisation of the heterogeneity of the elements involved is the guiding thread of this work. The scientific approach is demonstrated for a complex case study, the Valtellina valley (northern Italy), to investigate the interaction among the components of hydrogeologic cycle and their future projections according to climate dynamics. This valley could be considered a perfect case study because it is characterized by an active system that rapidly reacts to meteorological and climatic variations. This is visible by the fluctuation of the groundwater and of the main river, Adda River, during extreme precipitation events and with snow melts during the spring/summer periods. The thesis is divided into three main sections. The first provides a description of hydro-stratigraphy of the Valtellina valley floodplain. This section includes the groundwater flow model in a steady state condition, developed by using FeFlow 7.2, and the relative automatic calibration process for the hydrogeologic parametrization. 5 The second shows the quantification of seasonal groundwater storage volume according to the residual water budget method for two hydrologic years. For the estimation of the main components (Precipitation, Evapotranspiration and Snow water equivalent), new promising satellite-based database and methods are tested. The last one describes the tranFinally, the flow model has been used to evaluate the impact on groundwater of possible climate change scenarios.sient groundwater flow model developed with dynamic boundary conditions obtained from satellite-based methods.

The modular three-dimensional finite-difference groundwater flow model (MODFLOW) was used to study the hydrology of Upper Cienega Creek. The geological and hydrological characteristics of the basin indicate that the groundwater is contained in an unconfined aquifer. The study focuses on the interaction between groundwater and surface water in Upper Cienega Creek Basin and the surrounding basins (Sonoita and Bobocamari). The steady state analysis simulated the predevelopment conditions of the aquifer, and the transient state analysis, conducted between 1989 and 2002, predicted the response of the aquifer to future stresses. The location of pumpage and the volume of water pumped during the entire transient period resulted in a minimum reduction (1%) of the Cienega Creek stream flow. However, a drawdown of 200 ft located in Sonoita and Elgin area was predicted in the transient simulation. Capture calculations show that the reduction in evapotranspiratiou partially balanced the volume of water lost as result of pumping.

Integrated Catchment Management (ICM), defined as the design of intervention strategies encompassing and integrating the fields of hydrology, environmental, social and economic science, is vital in order to reach sustainable solutions on a catchment basis. Modelling lies at the core of the ICM process as it supports baseline studies and enables analysis of proposed intervention measures both for present day conditions and under future scenarios. Its core role in ICM leads to the need to develop modelling into a more comprehensive activity within which the design of a modelling approach, selection of tools and need for linkages can be thoughtfully matched to the requirements of ICM. Initial research revealed a gap in this area, leading to development of a Framework for Catchment Modelling Studies (FCMS) intended to create a staged and systematic approach that could be used as a template for development of modelling exercises that strike the right balance between ICM needs, project costs and the availability of human and technical resources. To demonstrate the utility of the FCMS and populate it with application guidance, practical techniques and examples, technical research was focused on analysis of groundwater-surface water interaction in the Rio Salado Basin. This flatland of 175,000km2, is located in the Buenos Aires Province of Argentina and features widespread groundwater-surface water interaction as the key driver of the flooding in vast areas of the basin. This flooding currently limits the potential for agricultural and livestock development of what is, economically, most important region of the country. Research revealed that use of uncoupled groundwater-surface water models was inadequate to simulate observed flooding in a test area of the Rio Salado Basin, and a new program - iSISMOD - was developed by coupling MODFLOW (McDonald and Harbaugh, 1988) with ISIS (HR Wallingford and Halcrow, 1995) to permit dynamic coupling of both systems and support improved flood probability mapping. The research concludes that adoption of an FCMS approach would provide scientists and engineers with a systematic basis from which to think through technical issues involved in the modelling cycle, and would facilitate improved decision making on key issues, such as when uncoupled models must be replaced by coupled models. This systematic approach is not only resource-effective, it is more importantly essential to support development of integrated catchment management plans that are sustainable.

A number of problems, e.g. sudden inflows are encountered during tunneling under the piezometric level, especially when the excavation crosses high transmissivity areas. These inflows may drag materials when the tunnel crosses low competent layers, resulting in subsidence, chimney formation and collapses. Moreover, inflows can lead to a decrease in head level because of aquifer drainage. Tunnels can be drilled by a tunnel boring machine (TBM) to minimize inflows and groundwater impacts, restricting the effect on the tunnel face. This method is especially suitable for urban tunneling where the works are usually undertaken near the ground surface. The aim of the thesis is to elucidate the tunneling difficulties arising from hydrogeology, and to determine groundwater impacts. The following approaches were adopted to achieve these objectives. First, a methodology that characterizes hydrogeologically the medium crossed by the TBM is proposed. Two important aspects that are often overlooked are: variable groundwater behavior of faults (conduit, barrier, conduit-barrier), and role of groundwater connectivity between fractures that cross the tunnel and the rest of the rock massif. These two aspects should be taken into account in the geological and groundwater characterization to correct the tunnel design and minimize hazards. A geological study and a preliminary hydrogeological characterization were carried out in a granitic sector during the construction of Line 9 of the Barcelona subway (B-20 area). The hydrogeological conceptual model was constructed using a quasi-3D numerical model, and different scenarios were calibrated. Faults and dikes show a conduit-barrier behavior, which partially compartmentalized the groundwater flow. The barrier behavior, which is the most marked effect, is more prominent in faults, whereas conduit behavior is more notable in dikes. The characterization of groundwater media entailed a dewatering plan and changes in the tunnel course. Second, a methodology to locate and quantify the inflows in the tunnel face of the TBM was adopted. Unexpected high water inflows constitute a major problem because they may result in the collapse of the tunnel face and affect surface structures. Such collapses interrupted boring tasks and led to costly delays during the construction of the Santa Coloma Sector of L9 (Line 9) of the Barcelona Subway. A method for predicting groundwater inflows at tunnel face scale was implemented. A detailed 3D geological and geophysical characterization of the area was performed and a quasi-3D numerical model with a moving tunnel face boundary condition was built to simulate tunnel aquifer interaction. The model correctly predicts groundwater head variations and the magnitude of tunnel inflows concentrated at the crossing of faults and some dikes. Adaptation of the model scale to that of the tunnel and proper accounting for connectivity with the rest of the rock massif was crucial for quantifying the inflows. This method enables us to locate the hazardous areas where dewatering could be implemented. Third, the hydrogeological impacts caused by tunneling with TBM were characterized. The lining in tunnels reduces water seepage but could cause a barrier effect because of aquifer obstruction. Analytical methods were employed to calculate the gradient and permeability variation after tunnelling. The uses of pumping tests allow determinate the barrier effect and the changes in groundwater connectivity due to tunnelling. These approaches were adopted to help overcome the main hydrogeological problems encountered during the construction of tunnels with the TBM. Numerical models proved useful in quantifying and forecasting tunnel water inflows and head variations caused by tunnelling. A better understanding of these scenarios enabled us to find the correct solutions and to minimize the consequences of tunnel-groundwater interaction.
La construcción de túneles bajo el nivel piezométrico puede comportar problemas constructivos cuando la excavación atraviese zonas muy transmisivas donde puede haber entradas repentinas de agua. Estas entradas pueden generar arrastres cuando se crucen capas muy poco competentes, llegando a provocar hundimientos, creación de chimeneas subsidencia del terreno. Además estas entradas de agua pueden provocar el descenso del nivel freático por drenaje del acuífero. Para minimizar las entradas de agua y los impactos asociados a la excavación se realizan perforaciones con tuneladoras (TBM) que restringen las afectaciones por drenaje al frente de perforación. Este método es especialmente adecuado en medios urbanos donde el túnel se sitúa cerca de la superficie. El objetivo de esta tesis será abordar las dificultades constructivas relacionadas con la hidrogeología que existen al construir túneles con tuneladora así como determinar los impactos que estas pueden producir. En primer lugar, se busca una metodología que permita caracterizar hidrogeológicamente el terreno que será atravesado por la tuneladora ya que esta maquinaria es sensible a los cambios repentinos de medio y condiciones de terreno. Hay dos aspectos que normalmente no se tienen en cuenta: el comportamiento hidrogeológico de las fallas (conducto, barrera, conducto-barrera) y la importancia de la conectividad hidrogeológica entre las fracturas que cruzadas por el túnel y el resto del macizo rocoso. Estos dos aspectos han sido tenidos en cuenta en la caracterización geológica e hidrogeológica con el fin de corregir el diseño del túnel y minimizar riesgos geológicos. Una investigación geológica con caracterización hidrogeológica preliminar (que incluyó la revisión del estado hidrogeológico previo y ensayos de bombeo de interferencia) fue realizada en una zona granítica de la Línea 9 del metro de Barcelona (zona de la B-20). El modelo hidrogeológico conceptual fue construido usando un modelo numérico quasi-3D, donde fueron calibrados diverso escenarios. Las fallas y diques mostraron un comportamiento de conductobarrera que compartimentaliza parcialmente el flujo. El comportamiento de barrera es el efecto mas marcado, aunque en los diques aparece comportamiento de conducto. La caracterización del medio hidrogeológico ha permitido realizar un plan de drenaje y los cambios necesarios en el diseño del túnel. En segundo lugar, se busca una metodología que permita localizar y cuantificar las entradas de agua que pueda haber en el frente de excavación de un túnel construido con tuneladora. Entradas de agua repentinas constituyen un problema importante porque pueden provocar un colapso del túnel que afecte estructuras superficiales. Un método para predecir las entradas de agua en el frente de túnel fue implementado en el sector de Santa Coloma de la Línea 9 del metro de Barcelona. Una caracterización geológica y geofísica 3D del área fue realizada y los resultados fueron implementados en un modelo numérico quasi-3D, donde una condición de contorno de frente de túnel móvil se ha insertado para simular la interacción con el acuífero. El modelo predice correctamente la variación de los niveles piezométricos y la magnitud de las entradas de agua concentrados en las zonas de falla y diques. La adaptación de la escala del modelo al túnel y a la conectividad con el resto del macizo ha sido crucial para cuantificar las entradas de agua. Este método permite localizar las zonas peligrosas donde el dewatering debería ser implementado. En tercer lugar, se caracterizan los impactos que provoca la construcción de un túnel construido con tuneladora. Aunque el efecto dren que suelen producir la mayoría de túneles es minimizado en los túneles perforados con tuneladora con el sostenimiento que se instala después de la acción perforadora de la maquina, la construcción de esta estructura lineal impermeable puede producir una obstrucción del acuífero o efecto barrera. Se cuantifica la variación de gradientes piezométricos antes y después de la construcción de un túnel, esto se realizará con el uso de métodos analíticos que comparen los cambios reales observados. Además se cuantificaran los cambios de conectividad que provoca la construcción de un túnel comparando la variación de comportamiento observada en una serie de ensayos de bombeo realzados antes y después de la construcción de l túnel. Todos estos enfoques permiten abordar los principales problemas hidrogeológicos que se encontraran los túneles construidos con tuneladora así como los impactos que provocan. El uso de modelos numéricos se convierte en una herramienta robusta para cuantificar y predecir las entradas de agua en el frente de túnel y las variaciones de nivel provocadas por el mismo túnel. El conocimiento de estos escenarios permitirá encontrar las mejores soluciones para minimizar las consecuencias de la acción del medio hidrogeológico sobre el túnel o viceversa.
La construcció de túnels sota el nivell piezomètric pot comportar problemes constructius quan l’excavació travessi zones molt transmissives on pot haver-hi entrades sobtades d’aigua . Aquestes entrades poden arrossegar materials quan es creuin capes poc competents, arribant a provocar enfonsaments, xemeneies I subsidència del terreny. D’altra banda aquestes entrades d’aigua poden provocar el descens del nivell d’aigua per drenatge de l’aqüífer. Per minimitzar les entrades d’aigua I els impactes associats a la excavació es perforen túnels amb tuneladores (TBM) que restringeixen les afeccions per drenatge al front de perforació. Aquest mètode es especialment adequat en medis urbans on el túnel es proper a la superfície. L’objectiu d’aquesta tesi serà abordar les dificultats constructives relacionades amb la hidrogeologia que existeixen al construir túnels amb tuneladora així com determinar els impactes que aquestes poden produir. En primer lloc, es busca una metodologia que permeti caracteritzar hidrogeològicament el terreny que ha de travessar la tuneladora ja que aquestes són sensibles als canvis sobtats de medi i condicions de terreny. Hi ha dos aspectes important que normalment no son tinguts en compte: El comportament hidrogeològic de les falles (conducte, barrera, conducte-barrera) i la importància de la connectivitat hidrogeològica entre les fractures que son creuades pel túnel y la resta del massís rocós. Aquests dos aspectes han estat tinguda en compte en la caracterització geològica i hidrogeològica amb el fi de corregir el disseny del túnel i minimitzar riscos geològics. Una investigació geològica amb caracterització hidrogeològica preliminar (que va incloure la revisió de l’estat hidrogeològic previ i assaigs de bombeig d’interferència) va ser realitzada en una zona granítica de la Línia 9 del metro de Barcelona (zona de la B-20). El model hidrogeològic conceptual va ser construït fent servir un model numèric quasi-3D, on van ser calibrats diferents escenaris. Les falles i els dics van mostrar un comportament de conducte barrera que compartimentalitza el flux parcialment. El comportament de barrera es l’efecte mes marcat i es mentre que en els dics apareix el comportament de conducte. La caracterització del medi hidrogeològic ha permès realitzar un pla de drenatge i els canvis necessaris en el disseny del túnel. En segon lloc, es troba una metodologia que permeti trobar el lloc i quantificar les entrades d’aigua que hi pot haver en el front d’excavació d’un túnel construït amb tuneladora. Les entrades d’aigua sobtades en el túnel constitueixen un problema important perquè poden provocar un col·lapse del túnel que afecti a les estructures superficials. Un mètode per predir les entrades d’aigua en el front de túnel ha estat implementat en el sector de Santa Coloma de la Línia 9 del metro de Barcelona. Per aconseguir-ho es va realitzar una caracterització geològica i geofísica 3D, aquests resultats van ser implementats en un model numèric quasi-3D, on una condició de contorn de front de túnel mòbil ha estat inserida per simular la iteració amb l’aqüífer. El model prediu correctament la variació de nivells piezomètrics i la magnitud de les entrades d’aigua concentrades en les zones de falla i dics. L’adaptació de l’escala del model al túnel i a la connectivitat amb la resta del massís han estat clau per poder quantificar les entrades d’aigua. Aquest mètode permet localitzar les zones perilloses on el dewatering hauria de ser implementat. En tercer lloc, es caracteritzen els impactes hidrogeològics que provoca la construcció d’un túnel construït amb tuneladora. Malgrat que l’efecte dren que acostumen a originar la majoria de túnels es minimitza per l’acció del sosteniment que s’instal·la just després de la maquina, la construcció d’aquesta estructura lineal impermeable pot produir una obstrucció de l’aqüífer o efecte barrera. Es quantifica la variació de gradient abans i desprès de la construcció d’un túnel, això es farà amb mètodes analítics que es comparen amb el canvi de gradient observat. A mes a mes es quantifiquen els canvis de connectivitat que provoca la construcció del túnel comparant la variació de comportament observada en una sèrie d’assaigs de bombeigs realitzats abans i després de la construcció del túnel. Tots aquests enfocaments permeten abordar els principals problemes hidrogeològics que es trobaran els túnels construïts amb tuneladora així com els impactes que provoquen. L’ús de models numèrics esdevé una eina robusta per poder quantificar i predir les entrades d’aigua en el front del túnel i les variacions de nivell provocades pel mateix túnel. El coneixement d’aquests escenaris permetrà trobar les solucions adients o minimitzar les conseqüències de l’acció de medi hidrogeològic sobre el túnel o a l’inrevés.

Sinusoidal variations in recharge can induce cyclical flows in surface water and groundwater. In this thesis, such time-dependent flows are explored in a coupled lakeaquifer system. The modelling extends previous steady state results and introduces new flow-visualisation techniques. Local responses in a 2D vertical section are illustrated for lakes within a 1D regional groundwater mound. The theory employs complex variables to decouple the periodic groundwater flows into separate steady state and fluctuating components. The time dependent behaviour causes the lake-aquifer flow to change between flowthrough, recharge and discharge regimes. Corresponding fluctuations between inflow and outflow across the lakebed allow interchange of lake water with the aquifer (recycling and recapture). This also gives rise to sinuous flowpaths that can result in apparent dispersion; the number and size of waves, cusps and loops is characterised by a nondimensional waviness ratio. Streakline plots are introduced and provide an intuitive impression of the time-dependent groundwater motion. Such plots are enhanced by animation and illustrate the complex and potentially dispersive nature of the flows. Interplay between the steady state and fluctuating responses determines the type and strength of flow regime transition. Importantly, there is an inverse relationship between head and flow in the fluctuating response. This is characterised by a dimensionless response time; a function of the aquifer geometry, hydraulic properties and period of fluctuation. During fast response, the recharge propagates mainly as fluctuation in flow, with small phase lags; particle trajectories form elliptical paths in the visualised flows. With a slower aquifer response, variation in recharge is manifest mostly as fluctuation in water level; cyclical perturbations in the flows are small and flows are nearly in steady state. The position of a lake within the regional setting, size of the lake, and ratio of lake to aquifer recharge are important to the steady state response. Flow-through regimes occur throughout the regional setting, but dominate when the lake is lower in the system and groundwater flow is greater. Discharge and recharge regimes occur higher in the flow system, when the ratio of lake to aquifer recharge is large in magnitude.

This research investigates the nature and controls of surface water–groundwater interaction at the watershed scale, and investigates how mechanisms which control this interaction during baseflow conditions might best be represented within an integrated surface-subsurface numerical model. The study site is the 46 km² Bertrand Creek Watershed, which is situated in a glaciated landscape in southern western British Columbia. A conceptual model of surface water–groundwater interaction along Bertrand Creek is developed based on a field data collection program conducted during the dry seasons of 2006 and 2007. The investigation relies on a suite of field techniques to characterize the nature of the interaction, including hydrologic measurements, stream water chemistry, and point-based measurements of streambed flux. These measurements are complemented by an assessment of topographic slope over the alluvial aquifer to infer the groundwater flow direction. Results indicate that topography adjacent to the stream is a principal control on water exchange between Bertrand Creek and the underlying aquifer. Topography influences the direction of groundwater flow adjacent to the stream and determines the persistence and magnitude of groundwater discharge along the channel. The conceptual model is used to develop an integrated numerical model of Bertrand Creek Watershed using HydroGeoSphere. HydroGeoSphere is a three-dimensional physics-based model that simulates overland flow, unsaturated flow, and groundwater flow in a fully integrated manner. The watershed model is calibrated using field data collected in 2007, including measured streamflows, groundwater contributions to streamflow, hydraulic heads, soil moisture contents, and change in surface water height in a pond. The calibrated watershed model is then evaluated against, and suitably represents, hydrologic data collected in 2006. Simulating baseflows and the seasonal hydrologic response requires that features controlling the spatial distribution of recharge, such as surficial soils and topography, are adequately characterized and represented within the model. Model results further demonstrate that evapotranspiration, particularly transpiration within the riparian zone, is a significant control of baseflows in Bertrand Creek. Finally, the calibrated model is used as a predictive tool to assess the impact of groundwater withdrawals on streamflow depletion.

Chalk streams are of high ecological value and are dependent upon groundwater discharge to support flows. This study investigates chalk stream-aquifer interaction, focusing on a near-natural catchment; the River Lambourn of the West Berkshire Downs. The topographic catchment of the Lambourn is 234km², principally underlain by Upper Chalk. The river has a perennial length of c.16km, and a 7.5km seasonal section. Temporal dynamics of the recharge-storage-discharge sequence are investigated using linear regression techniques to identify the lag between recharge and discharge. The effective maximum duration of groundwater flow is 9.1 months, which is used with regional hydraulic gradients to calculate a bulk (interfluve) hydraulic conductivity of 114m/d (using Sy=1%), suggesting that interfluve permeability has been historically underestimated. Spatial flow accretion on the Lambourn is defined from 12 reaches (each 1-2km long), exhibiting mean accretion rates between -0.019 and 0.211 cumecs/km. The accretion rate profile approximates a sinusoidal pattern (λ=12km) suggesting a catchment scale litho-structural control. However, local topography and lithology also exert influence. High accretion rate reaches are associated with major dry valley intersections and elevated valley floor permeability, whilst the presence of Chalk Rock at shallow depths restricts local accretion.

Salinisation is a major global environmental concern especially in semi-arid regions such as Australia. Dryland salinity is caused by capillary rising or discharging saline groundwater, which adversely impacts natural environments and infrastructure. It is important to understand salinisation processes to reduce these adverse impacts. This thesis uses a focus catchment (Muttama creek catchment, NSW) to explore salinisation mechanisms at a catchment scale. Three particular aspects are the focus of this thesis: (i) The variation in time and space of the groundwater salinity in the Muttama catchment; (ii) The nature and origin of the groundwater salinity in the catchment; and (iii) how the groundwater salinity influences water quality in Muttama creek. A statistical random forest model of historical groundwater data demonstrated that spatial variation of groundwater salinity in the Muttama catchment is mostly caused by spatial factors and underlying lithology. Although the temporal effect on groundwater salinity appears small, past (lagged) rainfall has a great influence on the variation in groundwater salinity. The hydrogeochemical analysis of groundwater reveals that this is NaCl dominant and cyclic salts are most likely the primary source. Weathering inputs contribute a further 50% of the salt load. Study of multiple techniques (hydrogeochemistry, stable isotopes and radon) indicates that discharge of Na-Cl dominant groundwater into Muttama creek is most likely relatively higher in the lower catchment and these connections are mainly in winter. Surface runoff might contribute significant salt in the upper catchment. Thus, this thesis improves the understanding of the salinisation mechanism in the Muttama catchment and highlights that salt output of the catchment can be efficiently reduced by applying more focused saline groundwater discharge management options.

Sinusoidal variations in recharge can induce cyclical flows in surface water and groundwater. In this thesis, such time-dependent flows are explored in a coupled lakeaquifer system. The modelling extends previous steady state results and introduces new flow-visualisation techniques. Local responses in a 2D vertical section are illustrated for lakes within a 1D regional groundwater mound. The theory employs complex variables to decouple the periodic groundwater flows into separate steady state and fluctuating components. The time dependent behaviour causes the lake-aquifer flow to change between flowthrough, recharge and discharge regimes. Corresponding fluctuations between inflow and outflow across the lakebed allow interchange of lake water with the aquifer (recycling and recapture). This also gives rise to sinuous flowpaths that can result in apparent dispersion; the number and size of waves, cusps and loops is characterised by a nondimensional waviness ratio. Streakline plots are introduced and provide an intuitive impression of the time-dependent groundwater motion. Such plots are enhanced by animation and illustrate the complex and potentially dispersive nature of the flows. Interplay between the steady state and fluctuating responses determines the type and strength of flow regime transition. Importantly, there is an inverse relationship between head and flow in the fluctuating response. This is characterised by a dimensionless response time; a function of the aquifer geometry, hydraulic properties and period of fluctuation. During fast response, the recharge propagates mainly as fluctuation in flow, with small phase lags; particle trajectories form elliptical paths in the visualised flows. With a slower aquifer response, variation in recharge is manifest mostly as fluctuation in water level; cyclical perturbations in the flows are small and flows are nearly in steady state. The position of a lake within the regional setting, size of the lake, and ratio of lake to aquifer recharge are important to the steady state response. Flow-through regimes occur throughout the regional setting, but dominate when the lake is lower in the system and groundwater flow is greater. Discharge and recharge regimes occur higher in the flow system, when the ratio of lake to aquifer recharge is large in magnitude.

Sinusoidal variations in recharge can induce cyclical flows in surface water and groundwater. In this thesis, such time-dependent flows are explored in a coupled lakeaquifer system. The modelling extends previous steady state results and introduces new flow-visualisation techniques. Local responses in a 2D vertical section are illustrated for lakes within a 1D regional groundwater mound. The theory employs complex variables to decouple the periodic groundwater flows into separate steady state and fluctuating components. The time dependent behaviour causes the lake-aquifer flow to change between flowthrough, recharge and discharge regimes. Corresponding fluctuations between inflow and outflow across the lakebed allow interchange of lake water with the aquifer (recycling and recapture). This also gives rise to sinuous flowpaths that can result in apparent dispersion; the number and size of waves, cusps and loops is characterised by a nondimensional waviness ratio. Streakline plots are introduced and provide an intuitive impression of the time-dependent groundwater motion. Such plots are enhanced by animation and illustrate the complex and potentially dispersive nature of the flows. Interplay between the steady state and fluctuating responses determines the type and strength of flow regime transition. Importantly, there is an inverse relationship between head and flow in the fluctuating response. This is characterised by a dimensionless response time; a function of the aquifer geometry, hydraulic properties and period of fluctuation. During fast response, the recharge propagates mainly as fluctuation in flow, with small phase lags; particle trajectories form elliptical paths in the visualised flows. With a slower aquifer response, variation in recharge is manifest mostly as fluctuation in water level; cyclical perturbations in the flows are small and flows are nearly in steady state. The position of a lake within the regional setting, size of the lake, and ratio of lake to aquifer recharge are important to the steady state response. Flow-through regimes occur throughout the regional setting, but dominate when the lake is lower in the system and groundwater flow is greater. Discharge and recharge regimes occur higher in the flow system, when the ratio of lake to aquifer recharge is large in magnitude.

South Florida has transformed from a natural to a managed ecosystem upon channelization of Kissimmee River and the wetlands in the 1960’s. The drainage has resulted in fast transport of water and nutrient, and subsequently eutrophication of the downstream water bodies. The intervention required: intensive management of the shallow groundwater to balance ecological water requirement; and nutrient removal, namely phosphorus, to minimize eutrophication. The study was set to examine and develop an operational prediction method for groundwater-phosphorus interactions to support the wetlands management. Accordingly, a point scale and a spatio-temporal groundwater level was simulated using sequence based Markovian stochastic analysis and dynamic factor analysis methods respectively. A root mean square error of 0.12m and 0.15m was observed for a point and spatio-temporal groundwater prediction. Soluble and sequestered phosphorus were also simulated at 13% error using a watershed based model called ArcWAM. A spatial analysis on simulated soluble phosphorus and groundwater level indicated similarity of patterns (spatial correlation) 99% of the time. A geographically weighted multivariate analysis of soluble phosphorus using predictors of groundwater level, total phosphorus of surficial water, and distance from Kissimmee River showed a goodness of fit (R2 ) of 0.2 – 0.7. Amongst the factors, the groundwater explained 70% of the soluble phosphorus variability. In summary, an increase in soluble phosphorus was observed with groundwater rise and a decrease during groundwater recession. A reversed relationship was identified for the total phosphorus. Presumably, organic matter in the root zone has contributed to increased soluble phosphorus with the rise in groundwater. On the other hand, solubility of calcium carbonate from the karst aquifers seems to fix and precipitate phosphorus during recession of groundwater. The least sequestration of phosphorus, observed in oversaturated wetlands also suggested that nutrient removal on karst hydrogeology could be risky unless a check is made using vegetation strip to enhance phosphorus uptake. The study concluded that phosphorus could be operationally predicted associated with forecasting of groundwater fluctuation. Further research is recommended to explore factors that could be derived either empirically or from satellite data for prediction of soluble phosphorus at minimum cost.

A field study was conducted in 1994 and 1995 to understand the interaction of groundwater and surface water in the Raisin River watershed, near Cornwall, Ontario. The Raisin River lies within an agricultural region which relies heavily on groundwater use. The regional groundwater supply is predominantly from a limestone aquifer which underlies various surficial deposits (primarily glacial till). Groundwater movement appears to be in a southeasterly direction, towards the St. Lawrence River. Seepage meters, mini-piezometers, and a falling head permeameter were used to (i) measure the flux of groundwater into (positive seepage) or out (negative seepage) of the Raisin River, and (ii) measure the hydraulic conductivity of the Raisin River sediments. Measurements were made at thirteen sites within the watershed. To identify the source of groundwater and study processes of streamflow generation during storm runoff, surface water, groundwater, and rainwater samples were collected for environmental isotopes (oxygen-18 and deuterium). Raisin River discharge data were also analysed. Seepage measurements and hydraulic conductivities exhibit significant variability. The coefficients of variation for seepage measurements ranged from 20.3 to 392%, and for hydraulic conductivity from 0 to 161%, depending on the site. Seepage flux ranges from $2.23\times10\sp{-6}$ to $\rm{-}9.82\times10\sp{-9}m\sp3m\sp{-2}s\sp{-1},$ and hydraulic conductivity ranges from 10$\sp{-6}$ to 10$\sp{-9}$ ms$\sp{-1}$ (a negative seepage flux indicates groundwater flow from the aquifer to the river). Environmental isotope analyses indicate that meteoric water is the source of local groundwater with a mean residence time of approximately 4 months. After a storm event, groundwater composed 63% of total stream discharge. The peak response in the river is approximately two days after a storm event. These variables indicate that groundwater/surface water relationships should be taken into account if decisions are made with respect to water quality or quantity. (Abstract shortened by UMI.)

>Magister Scientiae - MSc
The present study investigated the application of a multi-method approach to determine groundwater-surface water (GW-SW) interactions to quantify and characterize the quality of water resources in a fractured rock aquifer system in upper catchment of the Berg River (G10A). Demonstrating methods for improved understanding of groundwater and surface water interactions is important for informing development of strategies that ensure effective utilization and management of water resources. Applying a single method to inform innovative strategies for water resources has proved futile. The current study shows how the use of several methods can provide the basis for devising practical strategies for water resource utilization and management. The three methods were applied as follows: First, the base flow separation was used whereby the Chapman and Lynne & Hollick digital filter algorithms were applied to time-series streamflow data from four stream gauging stations in the catchment. The computation from algorithms on three sites (gauging stations) showed that the mean Base Flow Index (BFI) value ranged between 7%-8% for the 2012-2014 periods. This means that discharges from subsurface water storages dominate stream flows throughout the study period. Secondly, the quality of groundwater and surface water was sampled using standard methods. Piper Diagrams generated on Aquachem™ software and radial charts were used to identify the predominant hydrochemical facies. Results showed that Na-Cl was the predominant GW and SW water-type. This means that both GW and SW are mainly influenced by recharging surface water as well as interaction occurring between the rock matrices and infiltrating water. Multivariate statistical analyses were used to evaluate the factors controlling GW and SW chemistry in the upper Berg River catchment and the results showed that GW and SW are influenced by natural processes. Two main factors (a. & b.) were extracted which explained 71.8% of the variation in both GW and SW physicochemical parameters. These factors include water-rock interactions and the recharge of surface water. Cluster Analysis extracted four major clusters that grouped sites with similar physicochemical characteristics together. Finally, differential stream gauging was applied to a 600m reach above the Berg River Dam. Three 200m sub-reaches were used to compute differences in flows between sub-reaches. Stream flow at each sub-reach was estimated using mass balance equations with electrical conductivity measurements during instant salt tracer injection tests. Results indicated that during both the wet season (high flow) dry season (low flow), the river continuously lost water to the subsurface. This was demonstrated by the 0.91m³/s and 2.24m³/s decrease in stream flow along the 600m reach. Dry season flow decreases were less than wet season flow decreases, indicated by markedly lower flow loss in respect to the wet season. This confirms results of the analysis of base flow separation, which indicated that discharges from subsurface storages dominate stream flows during low flow periods. The differential stream gauging approach did not provide distinct points along the selected stream reach where GW-SW interaction occurred; rather it provided a holistic representation of seasonal flow variations along the selected reach. This study showed that upper Berg River catchment is dependent on discharges from subsurface water storages to maintain dry season flows. Furthermore, this study showed that infiltration of surface water and discharge of subsurface water transfers the respective chemical signature of the contributor, meaning that the transfer of water of suitable quality will reduce contamination in the receiving water body (i.e. surface water). Transfer of water between subsurface and surface water contributed an average of 8% of the gauged flows in the catchment between 2012 and 2014, suggesting that the groundwater recharge process dominates this catchment.

Thesis: Ph. D. in Environmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Contamination of groundwater with geogenic arsenic is widespread throughout much of South and Southeast Asia and poses a serious health risk to the millions of individuals who consume this water. It is widely agreed that the dominant mechanism of arsenic mobilization is reductive dissolution of arsenic-bearing iron-oxides coupled to the oxidation of organic carbon. However, it is unclear why dissolved arsenic concentrations have reached the high levels currently observed in aquifers throughout the region. In particular, the influence of surface water recharge on arsenic contamination remains unresolved. To address this issue we studied the hydrogeology and geochemistry of two arsenic contaminated sites: one site in Vietnam and another site in Bangladesh. Our field site in Vietnam is located adjacent to the Red River and has been impacted by intensive groundwater pumping for decades. The aquifer now receives net recharge from the river. We conducted a hydrogeologic and geochemical investigation to determine the influence of riverine recharge on groundwater arsenic concentrations. We determined that rates of arsenic mobilization in freshly deposited riverbed sediments are up to 1000 times those of inland aquifer sediments and measured arsenic concentrations in riverbed porewaters that exceeded the aquifer concentrations. We found the effect of riverine recharge is controlled by the geomorphic setting of the river-aquifer interface. Aquifers inland of freshly deposited river reaches are highly contaminated with dissolved arsenic, whereas aquifers inland of non-depositional river reaches host low arsenic groundwater. At our Bangladesh field site the aquifer has been impacted by the construction of man-made ponds, which provide 40% of aquifer recharge. To investigate the role of ponds on groundwater arsenic levels we constructed and instrumented a pond, installed a network of 100 wells, performed laboratory experiments, and collected sediment and water samples over three years. Our characterization of the pond physical hydrology and the pond and aquifer geochemistry reveals that arsenic mobilization within the aquifer is primarily driven by sedimentary organic matter. While ponds contribute substantial aquifer recharge our results suggest that high arsenic concentrations in Bangladesh are not driven by surface water recharge and likely emerged prior to anthropogenic perturbations to the hydrology.
by Mason Odell Stahl.
Ph. D. in Environmental Engineering

Thesis (MA)--Stellenbosch University, 2005.
ENGLISH ABSTRACT: The Table Mountain Group (TMG) Aquifer System is a regional fractured aquifer system with a large potential as a source of future water supplies in the Western and Eastern Cape. This system is currently under consideration for large-scale water abstraction. Many terrestrial ecosystems, however, are dependent on these groundwater resources for survival. Exploitation of ground water resources at a rate exceeding the rate of natural recharge would result in a lowering of the water table and the drying up of seeps. The main objective of this study was to determine if satellite remote sensing data can be used for the detection of groundwater-dependent wetlands, and secondly, to use multi-temporal imagery for estimating seasonal changes experienced in wetland communities in relation to surrounding vegetation. The Kogelberg Biosphere Reserve, situated approximately 30km to the east of Cape Point in the Western Cape, South Africa, was selected for investigation. To accomplish the objectives, three Landsat 7 ETM+ images (path/row: 175/84) captured on 22 September 2001, 18 May 2002 and 23 September 2002 were acquired. Image fusion of the multispectral bands (30m resolution) with the panchromatic band (15m resolution) provided 15m multispectral images for analysis purposes. Geometric correction, radiometric normalisation and atmospheric corrections was performed in order to ensure pixel-level comparability between images. Once comparability between images was guaranteed, vegetation indices and tasselled cap components were derived to provide threshold values of moisture stress indicators and productivity estimations of wetland communities in relation to surrounding non-wetland communities. Additionally, change vector analysis on these transformations provided the ability to detect and assess the seasonal changes experienced by these communities during an annual cycle. The results of these transformations were combined in a rule-based image classifier in order to assist in estimating the seasonal dependency of observed wetland communities. The ability to use Landsat 7 images and the abovementioned image processing procedures to identify wetland communities with a high probability of groundwater interaction was demonstrated with a high degree of accuracy (78%). It is recommended that future studies concentrate on increasing classification accuracies, while focusing on incorporating these techniques into a remote monitoring system for assessing the impacts of groundwater extraction on the groundwater-dependent wetland communities.
AFRIKAANSE OPSOMMING: Die Tafelberg Groep (TBG) Akwifer is 'n regionale verskuiwingsakwifer sisteem met groot potensiaal as toekomstige waterbron vir die Wes- en Oos-Kaap. Grootskaalse grondwateronttrekking uit hierdie sisteem word tans ondersoek. Baie terrestriële ekosisteme is egter vir oorlewing van grondwaterbronne afhanklik. Grondwaterontginning teen 'n tempo hoër as die natuurlike aanvultempo sal die watertafel laat daal en syfersones laat opdroog. Die hoofdoel van die studie was om te bepaal of satellietbeelde gebruik kan word om grondwater-afhanklike vleilande waar te neem, en om 'n tydsreeks van beelde te gebruik om die seisoenale verandering in vleilandgemeenskappe relatief tot omliggende plantegroei te raam. Die Kogelberg Biosfeer Reservaat, ongeveer 30km oos van Kaappunt, is as studiegebied geïdentifiseer. Drie Landsat 7 beelde (baan/ry: 175/84) van 22 September 2001, 18 Mei 2002 en 23 September 2002 is ontleed. Die Landsat 7 multispektrale bande (30m resolusie) is met behulp van beeld-fusietegnieke met die panchromatiese band (15m resolusie) gekombineer om multispektrale beelde te lewer met 15m grondresolusie. Geometriese korreksie, radiometriese normalisering en atmosferiese korreksie is op elk van die beelde toegepas om beeld-selvlak vergelykings tussen beelde 'n moontlikheid te maak. Met beeldvergelykbaarheid verseker, is plantegroei-indekse en 'tassled cap' transformasies gebruik om afsnywaardes vir vleiland-identifikasie te bereken. Verder is veranderingsvektoranalises op die transformasies bereken om die seisoenale veranderinge oor die jaarsiklus in vleilande te bepaal. Die resultate hiervan is vervat in 'n reël-gebaseerde beeldklassifiseerder waarmee vleilande se seisoenale grondwater afhanklikheid geraam is. Die vermoë om vleilande met 'n hol! waarskynlikheid van grondwater interaksie uit Landsat 7 beelde te identifiseer is met 'n hol! vlak van totale akkuraatheid (78%) gedemonstreer. Die aanbeveling is dat toekomstige studies moet fokus op die verhoging van hierdie klassifikasie akkuraathede. Die tegnieke moet toegespits word op die ontwikkeling van 'n afstandswaarnemingstelsel om die

It is widely recognized that topographically-driven groundwater flow can perturb conductive thermal regimes. High-relief topography amplifies the impact of factors controlling groundwater flow and advective heat transfer. A finite element method is developed to model the influence of geology, climate, surface topography and regional heat flux on steady groundwater flow and heat transfer. Because fluid viscosity (hence fluid flux) depends upon temperature, groundwater flow is influenced by the regional heat flux. As a consequence, isothermal approaches to modeling deep groundwater flow in mountains may be inappropriate. Using a free-surface approach, the water table is represented as an internal characteristic of the groundwater flow system, rather than the upper boundary for fluid flow. Thick unsaturated zones are expected in high-permeability terrain (greater than 10⁻¹⁵ m²) with arid climate, or where groundwater recharge is restricted by extensive alpine glaciers. Only vertical fluid flow is assumed to occur in the unsaturated zone, therefore, heat transfer above the water table is represented by one-dimensional advection and two-dimensional conduction. Simulation results indicate that water table elevations are highly sensitive to changes in the controlling factors, but have little impact on the thermal regime. Conductive thermal regimes are predicted in low-permeability terrain (less than 10⁻¹⁸ m²) or in high-permeability terrain with arid climate (recharge rates less than 10⁻¹¹ m/sec). Strong advective heat transfer masks the regional heat flux when permeability exceeds 10⁻¹⁶ m² in terrain with relief of 2 km over a horizontal distance of 6 km. Less than one percent of typical mean annual precipitation is transmitted through deep groundwater flow systems under these conditions. Asymmetric surface topography complicates efforts to interpret chemical and thermal data collected near the valley floor. Fracture zones outcropping at the valley floor can capture a large percentage of groundwater flowing through the system and a significant percentage of the basal heat flux. Maximum spring temperatures are indicated when bulk permeability is between 10⁻¹⁷ m² and 10⁻¹⁵ m². Outside this range, spring temperatures approach ambient air temperature. Topographically driven groundwater flow can distort and obliterate free-convection cells that might otherwise develop within a mountain massif.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Gasoline spills are sources of groundwater contamination. In the event of a spill, timely remediation efforts can advert most of the potential groundwater contamination due to the immiscibility of gasoline in water. Ethanol functions as a cosolvent that can increase the solubility of gasoline in water. Therefore, the risk of groundwater contamination in the event of a fuel spill increases as the ethanol content in automobile fuels increases. This study examines the effect fuel spill size and ethanol content has on the quantities of toluene, ethylbenzene, m-xylene and o-xylene (TEMO) that dissolve into the aqueous phase at equilibrium. Laboratory experiments were preformed to determine the mass fractions of TEMO in waters that were in contact with various volumes of gasoline and ethanol. UNIFAC is a model capable of predicting the concentrations of TEMO in the aqueous phase of a gasoline-ethanol-water system at equilibrium. In this study, the generalized UNIFAC-LLE method, designed for chemical engineering applications, was used to model the laboratory experiments. New UNIFAC-LLE parameters were developed to improve the model's accuracy in predicting the solubilities of aromatic species in ethanol-water mixtures. The new UNIFAC-LLE parameters were also used to model the laboratory experiments. The modeled results were compared to the analogous laboratory experiments. The UNIFAC-LLE parameters developed in this study improved the model's accuracy in predicting the solubilities of TEMO when the aqueous ethanol mass fraction was between 0.114 and 0.431.

Benzene and toluene are known groundwater contaminants . Male CD-I mice were continuously exposed to 0, 31, 166, and 790 mg/ L benzene and 0, 17, 80, and 405 mg/L toluene, respectively, in drinking water for four weeks. Benzene caused a reduction of leukocytes, lymphocytes and erythrocytes, and resulted in a macrocytic anemia. Lymphocyte response to both B- and T-cell mitogens, mixed lymphocyte response to alloantigens, and the ability of cytotoxic lymphocytes to lyse tumor cells were enhanced at the lowest dose of benzene and depressed in the higher dosage animals. Benzene at doses of 166 and 790 mg/L decreased the number of sheep red blood cell (SRBC) -specific plaque-forming cells, the level of serum anti-SRBC antibody, and the activity of interleukin-2 (IL -2). Benzene treatment increased endogenous concentrations of the brain biogenic amines norepinephrine (NE), dopamine (DA) and serotonin (5-HT), and concomitantly, elevated the levels of their respective major metabolites vanillymandelic acid (VMA), 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA), in several brain regions . In most cases, the changes were dose related; in several instances, maximum effects occurred at the 166 mg/L benzene dose. Toluene did not adversely affect the hematological parameters. Depression of immune function was evident at the highest dose (405 mg/L), except for mitogeneses. Increased neurochemical concentrations caused by toluene displayed a dose-dependent biphasic manner which began at a dose of 17 mg/L, peaked at 80 mg/L, and decreased at 405 mg/L. Toluene treatment had more selective effects on NE, 5-HT ,VMA and 5-HIAA, than DA, DOPAC and HVA. Both compounds, by increasing concentrations of the hypothalamic NE and its major metabolite VMA, stimulated the hypothalamic-pituitary-adrenocortical axis activity, resulting in an elevated plasma adrenocorticotropic hormone and serum corticosterone which had an additive adverse effect on IL-2 synthesis. Toluene, 325 mg/ L, completely inhibited benzene-induced cytopenia and immunosuppression when it was coadministered with benzene (166 mg/L). The low dose of toluene (80 mg/L ) did not antagonize benzene immunotoxicity. Mice given the combined exposures exhibited raised levels of regional neurochemicals when compared to the untreated controls. Increased levels of monoamine metabolites in several brain regions were greater in the combined treatments of benzene and toluene than when either chemical was used alone. The results of the interaction studies support the known metabolic interaction mechanisms of benzene and toluene.

Regions of surface water and groundwater exchange are major sites for the transfer and transformation of solutes and nutrients between stream and subsurface environments. Conventional stream and groundwater exchange investigations are limited by methodologies that require intensive field investigations and/or the set-up of expensive infrastructure. These difficulties are exacerbated where hydraulic gradients are very low and stream discharge highly variable. This thesis uses a suite of environmental tracers (Cl-, Rn-222, H-2 & O-18, Sr-87/Sr-86) to characterise the extent of stream and groundwater exchange between a sand bed stream and adjacent alluvial aquifer in a subtropical catchment (the Wollombi Brook) of eastern Australia. The aims were to identify sources and relative contributions of different sources of groundwater to stream discharge and specifically to improve the methodology of using Rn-222 to obtain quantitative estimate of groundwater fluxes. The sensitivity of the Rn-222 technique for identifying groundwater discharge based on the Rn-222 concentration in stream water was improved via an iterative numerical approach to account for Rn-222 loss from stream water via turbulent gas exchange and radioactive decay. Optimal distances between stream sampling points for defining the magnitude of groundwater discharge to stream flow based on Rn-222 concentrations in stream water is a function of average stream velocity and water depth. The maximum allowable distance between sampling points for determining the magnitude of groundwater discharge to the Wollombi Brook was 2 km. This work showed that groundwater discharged to all reaches of the Wollombi Brook during baseflow and flood recession conditions. Alluvial groundwater contributed less than 30% of water to stream flow in the mid Wollombi Brook catchment. Dilution of steady-state Rn-222 concentrations measured in transects from the stream to the alluvial sediments showed that significant surface water and groundwater exchange occurs even when gradients between surface water and groundwater are low. Lateral stream water influx to the adjacent alluvial aquifer was more extensive in the lowland areas of the Wollombi Catchment during low flow than flood recession conditions. Extensive stream water influx to the adjacent alluvial aquifer occurs contrary to the net direction of surface water and groundwater flux (as indicated by hydraulic gradients toward the stream channel). The rate of stream and groundwater exchange within the adjacent alluvial aquifer appears to be greatest during baseflow conditions. Fresh alluvial groundwater appeared to provide a buffer against higher salinity regional groundwater discharge to the alluvial aquifer in some reaches of the Wollombi Brook catchment. Pumping of the alluvial aquifer and diversions of surface water may jeopardise the water quality and volume of the alluvial aquifer and induce water flow from the regional aquifer toward the stream, potentially salinising the fresh alluvial aquifer and subsequently the stream. The change in the Cl- concentration and the variation in slope of the deuterium � oxygen-18 line between consecutive stream sampling points could be used to differentiate between regional and alluvial groundwater discharge to stream flow. Incorporating this information with three-component end-member mixing using [Sr2+] and Sr-87/Sr-86 showed that stream and alluvial groundwater exchange within the stream channel was highest in the lowland floodplains during low flow conditions. The least stream and alluvial groundwater exchange occurred in the low streambed gradient mid reaches of the Wollombi Brook regardless of stream stage. The greatest difference in the degree of stream and alluvial groundwater exchange between high and low stream stages occurred in the lowland floodplains of the Wollombi Brook.

Thesis (Ph. D.)--School of Computing and Engineering and Dept. of Geosciences. University of Missouri--Kansas City, 2008.
"A dissertation in engineering and geosciences." Advisor: Anil Misra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Sept. 12, 2008. Includes bibliographical references (leaves 234-236). Online version of the print edition.

Highly acidic and metal-rich runoff from coal storage facilities can have a dramatic impact on local surface and ground water quality. In order to identify important reactions governing metal transport within subsurface environments subject to infiltration of coal pile runoff, samples of uncontaminated subsoil and aquifer materials adjacent to the D-Area coal stockpile runoff containment basin at the Department of Energy's Savannah River Site were collected and subjected to leaching with the acidic, metalliferous coal pile runoff. Columns were packed to bulk densities of 1.5 Mg m³ and subjected to steady, saturated flows of 0.2 and 1.3 cm h⁻¹, Effluent was collected and multicomponent transport through the subsoil and aquifer materials evaluated. Observed transport was then related to soil chemical and mineralogical properties. Mass balance calculations, a sequential dissolution scheme in which column leaching was terminated and elements partitioned to aqueous, M NH₄CI, and ammonium oxalate in the dark (Ox)-extractable phases, and mineralogical and surface chemical analyses were used to identify important chemical processes and mineralogical alterations.
Ph. D.

The main goal of this research is to develop and test a groundwater recharge estimation method that can address some of the key research priorities in groundwater. In this context use is made of various modelling tools including ArcGIS, field data (in situ observations of soil temperature and soil moisture), and soil physics as represented by a physically based vadose zone hydrologic model (HYDRUS-1D). The research is conducted in a pilot watershed in north Okanagan, Canada. The public version of HYDUS-1D and another version with detailed freezing and thawing module are first used to investigate seasonal distribution of heat and water movement in the vadose zone. Model performance is evaluated in different scales by using field data, the gradient-based optimization algorithm of HYDRUS-1D, and ROSETTA derived prior information about soil hydraulic parameters. The latter are fitted to statistical distributions and used in Monte-Carlo experiments to assess the potential uncertainty in groundwater recharge due to model parameters. Next, the significance of the recharge estimation method for catchment scale transient groundwater modelling is demonstrated by applying uniform and variable flux boundary condition to a saturated zone transient groundwater model, MIKESHE. The results showed that the traditional uniform recharge assumption can lead to misleading decisions related to water resources management and pumping well network design. The effect of pumping well network and the provincial Water Act on water resources sustainability are further examined in an evolving climate. The results suggest potential water resource problem in the basin, which can possibly be attributed to the previously installed pumping well network (depth and screen level), and the provincial water use policy. The findings of this study demonstrate that such problems related to inappropriate well network and water resource management can greatly be minimised with the use of the recharge estimation method developed in this study.

>Magister Scientiae - MSc
Assessing groundwater-surface water interaction as a decision-making tool licensing water use South Africa: Case study area of Gevonden Farm is the title of the current study with the context that arises from the use of GRAII methodology which uses quaternary catchment boundaries for groundwater abstraction water use licence application assessment during decision making. The problem is that the quaternary catchment scale approach does not provide the scientific bases for site specific scale. The current study argues that such approach provides realistic, practical information at site specific scale and therefore informs the issuing of licences more accurately. The aim of the current study is to improve understanding of how the assessment of groundwater abstraction water use licence should be carried out at a site specific scale to improve decision making during licence issuance. The objective of the study is to outline the scientific study and demonstrate how the investigation that leads to the decision making can be conducted. The study was carried out using hydraulic methods such as pumping test and geochemical analysis method. Hydraulic properties were determined and chemical elements were analysed for and compared with the SANS 241 water quality standards for domestic and agricultural use. Hydraulic properties such as hydraulic conductivity (K), transmissivity (T), yield and storativity (S) were determined. Major and minor ions that are required to be analysed for domestic and agricultural water use were analysed. Piper diagrams and FC method were used to analyse data. The piper diagrams plotted indicated that surface water is mixing with groundwater and that means there is connection between groundwater and surface water. The chemical elements analysed for were compared with SANS 241 water quality standards for domestic and agricultural use. The water quality on the investigated site can be categorized as having good water quality. A sustainable yield estimated from the two boreholes (BH03 and BH05) which was 1.02 Ɩ/s. The available drawdown estimated with reference to the boreholes water strikes that were determined by EC profiling were 135 mbgl from both boreholes. The study recommends the issuance of water use licence with conditions that chemistry of water should be analysed for once a quarter and boreholes water levels should be analysed for once a month.

This dissertation puts in place a risk-cost-benefit analysis for waste management facilities that explicitly recognizes the adversarial relationship that exists in a regulated market economy between the owner-operator of the facility and the government regulatory agency under whose terms the facility must be licensed. The risk-cost-benefit analysis is set up from the perspective of the owner-operator. It can be used directly by the owner-operator to assess alternative design strategies. It can also be used by the regulatory agency to assess alternative regulatory policies, but only in an indirect manner, by examining the response of an owner-operator to the stimuli of various policies. The objective function is written in terms of a discounted stream of benefits, costs, and risks over an engineering time horizon. Benefits are in terms of revenues for services provided; costs are those of construction and operation of the facility. Risk is defined as the expected cost associated with failure, with failure defined as a groundwater contamination event that violates the licensing requirements set forth by the regulatory agency. Failure requires a breach of the containment structure and contaminant migration through the hydrogeological environment to a compliance surface. Reliability theory is used to estimate the probability of breaching and Monte Carlo finite-element simulations are used to simulate advective contaminant transport. The hydraulic conductivity values in the hydrogeological environment are defined stochastically. The probability of failure is reduced by the presence of a monitoring network established by the owner-operator. The level of reduction in the probability of failure can be calculated from the stochastic contaminant transport simulations. While the framework is quite general, the development in this dissertation is specifically suited for a landfill in which the primary design feature is one or more synthetic liners and in which contamination is brought about by the release of a single, nonreactive species in an advective, steady-state, horizontal flow field. The risk cost benefit analysis is applied to 1) an assessment of the relative worth of alternative containment-construction activities, site-investigation activities, and monitoring activities available to the owner-operator, 2) an assessment of alternative policy options available to the regulatory agency, and 3) two case histories. Sensitivity analyses designed to address the first issue show that the allocation of resources by the owner-operator is sensitive to the stochastic parameters that describe the hydraulic conductivity field at a site. For the cases analyzed, the installation of a dense monitoring network is of less value to the owner-operator than a more conservative containment design. Sensitivity analyses designed to address the second issue suggest that from a regulatory perspective, design standards should be more effective than performance standards in reducing risk, and design specifications on the containment structure should be more effective than those on the monitoring network. Performance bonds posted before construction have a greater potential to influence design than prospective penalties to be imposed at the time of failure. Sitting on low-conductivity deposits is a more effective method of risk reduction than any form of regulatory influence. Results of the case histories indicate that the methodology can be successfully applied at field sites, and that the risks associated with groundwater contamination may be small when compared to the owner-operators' benefits and costs.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Through the application of downhole logging techniques an innovative assessment of density dependent groundwater flow has been undertaken that highlights the limitations of water level measurements for assessing groundwater flow in coastal environments. The method utilises an EM39 bulk conductivity log to calculate fluid conductivity/fluid density that was then used to convert measured point water head to freshwater head/environmental head to improve the understanding of groundwater flow at the creek. This method of assessing density dependent flow is unique and has not previously been demonstrated. The converted water levels showed that interpretation of groundwater flow is critically dependent on a detailed knowledge of both head and density. An assessment of the potential error in the conversion process indicated that, for the low gradients at the study site, misinterpretation of flow could occur due to errors inherent in the process. As a result, it is recommended that pressure transducers and loggers be used to monitor pressure in variable density systems so that Darcy???s equation can be used directly to calculate groundwater flow and direction. The thesis also presents the results of high-resolution geophysical mapping of the distribution of saline groundwater beneath a tidal creek. The mapping was used to develop a detailed conceptual model of the salinity distribution at a tidal creek that included: the presence of saline intrusion beneath the creek; saline groundwater overlying fresh groundwater due to surface flooding in extreme tide events; concentrated discharge of groundwater (comprised of brackish water due to mixing in the aquifer) at the creek banks; and, significant changes in the distribution of saline groundwater according to rainfall events and only minor changes over a tidal cycle. The conceptual model, geophysical site assessment, water level analysis and numerical modelling represents a multi-disciplinary approach to the assessment of the interaction of saline and fresh groundwater that has not previously been undertaken. Significant anisotropy was inferred from geophysical observations that indicated vertical flow in the borehole annulus. This observation is particularly significant and implies that even relatively short (1.0 to 2.0 m) screened wells may not yield accurate fluid conductivity and head values in variable density systems.

The relationship between shallow groundwater levels and Avon River baseflow upstream of Gloucester Street has been investigated. Avon River baseflow is supplied by shallow groundwater-fed springs. Historical and anecdotal information indicate that since European settlement of the Christchurch area in the 1850's, Avon River baseflow has declined. The baseflow decline is attributed to the progressive lowering of the Christchurch area watertable which has caused downstream migration of headwater spring positions and a reduction in spring discharge. Prior to this study minimal historical Avon River flow data existed, and a quantitative estimation of the decline in baseflow is not possible. A management plan for maintaining acceptable baseflow levels in the Avon River is currently being developed by the Canterbury Regional Council. The aim of this study was to provide information on the relationship between Avon River baseflow and shallow groundwater levels to aid baseflow management. The Christchurch groundwater system is characterised by a watertable aquifer that overlies a series of layered confined aquifers. Direct groundwater discharge into the Avon River is considered to be from both the watertable aquifer and upper most confined aquifer. Groundwater was found to enter the river system by two different mechanisms; seepage through stream bed gravel and artesian spring discharge. Groundwater seepage through streambed gravel occurs where the stream channel intersects the watertable aquifer. Artesian springs occur where water-bearing gravels are overlain by between approximately 1 to 10 m of finer-grained confining sediment. Artesian spring water is thought to flow from both the watertable aquifer and the uppermost confined aquifer. Pipes through the confining sediment connect the spring vent to the underlying water-bearing gravels. When the hydraulic head of the underlying gravel aquifer is above the stream stage artesian spring flow will occur. Tributary baseflow and shallow groundwater data were collected for the 11 month period, February 1992 to January 1993. In addition, baseflow was separated from the Avon River flow record. Available flow data indicate that mean A von River baseflow at Gloucester Street from 1980 to 1992 was approximately 1700 1/s. In March 1993 Avon River baseflow was 50% of that in March 1980. Large rainfall events in late-August 1992 caused Avon River baseflow in January 1993 to increase to approximately 77% of the March 1980 value. Regression analysis established a relationship between both hydraulic head in the upper most confined aquifer and unconfined watertable levels, to Avon River baseflow (R² > 0.8). The flow hydrograph showed that the daily abstraction of shallow groundwater from beneath the catchment caused an associated reduction in flow. Seasonal fluctuations in spring discharge and baseflow were found to be greater in the western tributaries than the eastern tributaries. This is attributed to the greater seasonal fluctuation of shallow groundwater levels in the western area of the catchment than in the eastern area. From available data the peak in seasonal groundwater levels occurred throughout the study area during the period of 24-27 October 1992. No observable time delay occurred between the seasonal peaks in shallow groundwater levels and Avon River baseflow at Gloucester Street. In order to sustain acceptable rates of Avon River baseflow, shallow groundwater levels need to be maintained in areas of the catchment were groundwater enters the river. As a first step, the Canterbury Regional Council has placed restrictions on the abstraction of groundwater in areas where springs occur. The information presented in this study on the relationship between shallow groundwater levels and Avon River baseflow confirms the need for management of shallow groundwater levels in areas where groundwater contributes to baseflow. To ascertain the effectiveness of remedial measures continued monitoring of A von River baseflow and shallow groundwater levels are necessary.

The interaction between earthquakes and crustal fluids is a very complex topic due to several mechanisms that are involved and which influence each other. Some phenomena, like the alterations of springs discharge rates and fluid flow, liquefaction and changing of the water levels in phreatic wells are largely documented in the literature, but their explanation is not yet fully clear. Furthermore, these phenomena can greatly change with the rock type, the earthquake magnitude and the observation distance from the fault. Within a distance of a few fault lengths from the epicenter, an earthquake can alter both the regional stress field and the hydraulic properties of the rocks, influencing the underground fluid distribution. In this thesis, I apply the numerical simulator TOUGH2 to represent the changes in water level of some wells after the ML 5.9 earthquake that took place in Italy in 2012. The model shows that the wells response to the seismic event can be represented imposing a static stress change and highlights the role of the soil stratigraphy. This zone is also well known for localized methane seepages associated with anomalous soil temperatures. I simulate the process and draw some conclusions on the nature of this phenomenon and on the possible interactions with the local seismicity. Finally, I study the earthquake-fluid interaction from the opposite point of view: looking at how fluids can promote seismicity. I present the results obtained by coupling the TOUGH2 geothermal simulator with a stochastic seed model of seismicity. The coupled simulation could capture the main characteristics of the seismicity induced by the fluid injection in a seismically active area.
L'interazione tra terremoti e fluidi crostali è un argomento molto complesso per via dei numerosi meccanismi che sono coinvolti e che si influenzano a vicenda. Alcuni fenomeni, come l'alterazione delle sorgenti e del flusso di fluidi, la liquefazione e il cambiamento del livello d'acqua nei pozzi freatici, sono largamente documentati in letteratura, tuttavia la loro spiegazione non è ancora del tutto chiara. Oltretutto, questi fenomeni possono cambiare sensibilmente in base al tipo di roccia, alla magnitudo del terremoto e alla distanza dalla faglia. Entro una distanza di poche lunghezze di faglia dall'epicentro, un terremoto può modificare sia il campo di sforzo regionale che le proprietà idrauliche della roccia, influenzando la distribuzione dei fluidi nel sottosuolo. In questa tesi utilizzo il simulatore numerico TOUGH2 per rappresentare la variazione del livello d'acqua di alcuni pozzi successivamente al terremoto di magnitudo ML5.9 che avvenne in Italia nel 2012. Il modello mostra che la risposta dei pozzi al terremoto può essere rappresentata imponendo una variazione di stress statico ed evidenzia l'importanza della stratigrafia del sottosuolo. Questa zona è ben nota anche per emissioni di metano localizzate, associate a riscaldamenti anomali del sottosuolo. In questa tesi presento delle simulazioni per rappresentare questo processo e traggo alcune conclusioni circa la natura di questo fenomeno e sulle sue possibili interazioni con la sismicità locale. In ultimo, studio la relazione tra fluidi e terremoto dal punto di vista opposto: come I fluidi possono facilitare la sismicità. Presento i risultati ottenuti accoppiando il simulatore geotermico TOUGH2 con un modello sismico, stocastico, a “seed”. La simulazione accoppiata è in grado di catturare le caratteristiche principali della sismicità indotta dall'iniezione di fluidi in un'area sismicamente attiva.

The interaction between earthquakes and crustal fluids is a very complex topic due to several mechanisms that are involved and which influence each other. Some phenomena, like the alterations of springs discharge rates and fluid flow, liquefaction and changing of the water levels in phreatic wells are largely documented in the literature, but their explanation is not yet fully clear. Furthermore, these phenomena can greatly change with the rock type, the earthquake magnitude and the observation distance from the fault. Within a distance of a few fault lengths from the epicenter, an earthquake can alter both the regional stress field and the hydraulic properties of the rocks, influencing the underground fluid distribution. In this thesis, I apply the numerical simulator TOUGH2 to represent the changes in water level of some wells after the ML 5.9 earthquake that took place in Italy in 2012. The model shows that the wells response to the seismic event can be represented imposing a static stress change and highlights the role of the soil stratigraphy. This zone is also well known for localized methane seepages associated with anomalous soil temperatures. I simulate the process and draw some conclusions on the nature of this phenomenon and on the possible interactions with the local seismicity. Finally, I study the earthquake-fluid interaction from the opposite point of view: looking at how fluids can promote seismicity. I present the results obtained by coupling the TOUGH2 geothermal simulator with a stochastic seed model of seismicity. The coupled simulation could capture the main characteristics of the seismicity induced by the fluid injection in a seismically active area.
L'interazione tra terremoti e fluidi crostali è un argomento molto complesso per via dei numerosi meccanismi che sono coinvolti e che si influenzano a vicenda. Alcuni fenomeni, come l'alterazione delle sorgenti e del flusso di fluidi, la liquefazione e il cambiamento del livello d'acqua nei pozzi freatici, sono largamente documentati in letteratura, tuttavia la loro spiegazione non è ancora del tutto chiara. Oltretutto, questi fenomeni possono cambiare sensibilmente in base al tipo di roccia, alla magnitudo del terremoto e alla distanza dalla faglia. Entro una distanza di poche lunghezze di faglia dall'epicentro, un terremoto può modificare sia il campo di sforzo regionale che le proprietà idrauliche della roccia, influenzando la distribuzione dei fluidi nel sottosuolo. In questa tesi utilizzo il simulatore numerico TOUGH2 per rappresentare la variazione del livello d'acqua di alcuni pozzi successivamente al terremoto di magnitudo ML5.9 che avvenne in Italia nel 2012. Il modello mostra che la risposta dei pozzi al terremoto può essere rappresentata imponendo una variazione di stress statico ed evidenzia l'importanza della stratigrafia del sottosuolo. Questa zona è ben nota anche per emissioni di metano localizzate, associate a riscaldamenti anomali del sottosuolo. In questa tesi presento delle simulazioni per rappresentare questo processo e traggo alcune conclusioni circa la natura di questo fenomeno e sulle sue possibili interazioni con la sismicità locale. In ultimo, studio la relazione tra fluidi e terremoto dal punto di vista opposto: come I fluidi possono facilitare la sismicità. Presento i risultati ottenuti accoppiando il simulatore geotermico TOUGH2 con un modello sismico, stocastico, a “seed”. La simulazione accoppiata è in grado di catturare le caratteristiche principali della sismicità indotta dall'iniezione di fluidi in un'area sismicamente attiva.

In situ chemical oxidation (ISCO) is a leading-edge technology for soil and groundwater remediation, and involves injecting a chemical oxidant (e. g. , permanganate, hydrogen peroxide, or persulfate) into the subsurface to deplete contaminant mass through oxidation. Since the delivery of the chosen oxidant to the target treatment zone must occur in situ, the interaction between the injected oxidant and the aquifer material is a key controlling factor for a successful ISCO application. While many published ISCO studies have focused on the interaction between an oxidant and target contaminants, many questions still remain on the interaction between a potential oxidant and the aquifer material. Through a series of bench-scale experiments with aquifer materials collected from 10 sites throughout North America, the research presented in this thesis provides insight into the interaction between these aquifer materials and two widely used ISCO oxidants; permanganate and hydrogen peroxide.

The investigation into the interaction between aquifer materials and permanganate consisted of three series of bench-scale experiments: (1) long-term batch experiments which were used to investigate permanganate consumption in response to fundamental geochemical properties of the aquifer materials, (2) short-term batch experiments which were designed to yield kinetic data that describe the behavior of permanganate in the presence of various aquifer materials, and (3) column experiments which were used to investigate permanganate transport in a system that mimics the subsurface environment. The long-term experiments which involved more than 180 batch reactors monitored for ~300 days showed that the unproductive permanganate consumption by aquifer materials or natural oxidant demand (NOD) is strongly affected by the initial permanganate concentration, permanganate to solid mass ratio, and the reductive components associated with each aquifer material. This consumption cannot be represented by an instantaneous reaction process but is kinetically controlled by at least a fast and slow reactive component. Accordingly, an empirical expression for permanganate NOD in terms of aquifer material properties, and a hypothetical kinetic model consisting of two reaction components were developed. In addition, a fast and economical permanganate NOD estimation procedure based on a permanganate COD test was developed and tested. The investigation into short-term permanganate consumption (time scale of hours) was based on the theoretical derivation of the stoichiometric reaction of permanganate with bulk aquifer material reductive components, and consisted of excess permanganate mass experiments and excess aquifer material mass experiments. The results demonstrated that permanganate consumption by aquifer materials can be characterized by a very fast reaction on the order of minutes to hours, confirming the existence of the fast reaction component of the hypothetical kinetic model used to describe the long-term permanganate NOD observations. A typical experimental column trial consisted of flushing an aquifer-material packed column with the permanganate source solution until sufficient permanganate breakthrough was observed. The permanganate column results indicated the presence of a fast and slow consumption rate consistent with the long-term batch test data, and an intermediate consumption rate affecting the shape of the rising limb of the breakthrough curve. Finally, a comparison of the experimental results between batch and column systems indicated that permanganate NOD was significantly overestimated by the batch experiments; however, permanganate consumption displayed some similarity between the batch and column systems and hence an empirical expression was developed to predict permanganate consumption in physically representative column systems from batch reactor data.

The interaction between hydrogen peroxide and aquifer materials was also investigated with both batch and column experiments. A series of batch experiments consisting of a mixture of 2% hydrogen peroxide and 15 g of aquifer materials was used to capture the overall hydrogen peroxide behavior in the presence of various aquifer materials. The results indicated that the decomposition of hydrogen peroxide in the presence of various aquifer materials followed a first-order rate law, and was strongly affected by the content of amorphous transition metals (i. e. , Fe and Mn). Although hydrogen peroxide decomposition is related to the total organic carbon (TOC) content of natural aquifer materials, the results from a two-week long exposure to hydrogen peroxide suggests that not all forms of natural organic matter contributed to this decomposition. A multiple linear regression analysis was used to generate predictive relationships to estimate hydrogen peroxide decomposition rate coefficients based on various aquifer material properties. The enhanced stability of hydrogen peroxide was investigated under six scenarios with the addition of chelating reagents. The impact of a new green chelating reagent, S,S'-ethylenediaminedisuccinate (EDDS), on the stability of hydrogen peroxide in the presence of aquifer materials was experimentally examined and compared to that of the traditional and widely used chelating reagent, Ethylenediaminetetraacetic (EDTA). The results demonstrated that EDDS was able to significantly increase the stability of hydrogen peroxide, especially for aquifer materials with low TOC contents and/or high dissolvable Fe and Mn contents. Finally, to complement and expand the findings from the batch experiments, column experiments were conducted with aquifer materials from five representative sites. Each column was flushed with two types of source solutions (with or without EDDS addition) at two flow rates. The column experiments showed that the use of EDDS resulted in an earlier breakthrough and a higher stable concentration of hydrogen peroxide relative to the case without the addition of EDDS. The hydrogen peroxide decomposition rate coefficients generated from the column data were significantly higher than those generated from the batch test data and no correlation between hydrogen peroxide decomposition coefficients obtained from column and batch experiments was observed. Based on the column experimental results, a one-dimensional transport model was also calibrated to capture the hydrogen peroxide breakthrough process.

Data from bench-scale tests are routinely used to support both ISCO design and site screening, and therefore the findings from this study can be used as guidance on the utility of these tests to generate reliable and useful information. In general, the behavior of both permanganate and hydrogen peroxide in the presence of aquifer materials in batch and the column systems clearly indicates that the use of batch test data for ISCO system design is questionable since column experiments are believed to mimic in situ conditions better since column systems provide more realistic aquifer material contact. Thus the scaling relationships developed in this study provide meaningful tools to transfer information obtained from batch systems, which are widely employed in most bench-scale studies, to column systems.

Abstract Water resources management calls for methods to simultaneously manage groundwater (GW) and surface water (SW) systems. These have traditionally been considered separate units of the hydrological cycle, which has led to oversimplification of exchange processes at the GW-SW interface. This thesis studied GW hydrology and the previously unrecognised connection of the Rokua esker aquifer with lakes and streams in the area, with the aim of identifying reasons for lake water level variability and eutrophication in the Rokua esker. GW-SW interactions in the aquifer were first studied with field methods. Seepage meter measurements showed substantial spatial variability in GW-lake interaction, whereas transient variability was more modest, although present and related to the surrounding aquifer. Environmental tracers suggested that water exchange occurs in all lakes in the area, but is of varying magnitude in different lakes. Finally, GW-SW interaction was studied in peatland catchments, where drainage channels in the peat soil presumably increased groundwater outflow from the aquifer. Amount and rate of GW recharge were then estimated with a simulation approach developed explicitly to account for the physical characteristics of the Rokua esker aquifer. This produced a spatially and temporally distributed recharge estimate, which was validated by independent field techniques. The results highlighted the impact of canopy characteristics, and thereby forestry management, on GW recharge. The data collected and the new understanding of site hydrology obtained were refined into a fully integrated surface-subsurface flow model of the Rokua aquifer. Simulation results compared favourably to field observations of GW, lake levels and stream discharge. A major finding was of good agreement between simulated and observed GW inflow to lakes in terms of discharge locations and total influx. This thesis demonstrates the importance of using multiple methods to gain a comprehensive understanding of esker aquifer hydrology with interconnected lakes and streams. Importantly, site-specific information on the reasons for water table variability and the trophic status of Rokua lakes, which is causing local concern, is provided. As the main outcome, various field and modelling methods were tested, refined and shown to be suitable for integrated GW and SW resource management in esker aquifers
Tiivistelmä Vesivarojen hallinnassa tarvitaan menetelmiä pohja- ja pintaveden kokonaisvaltaiseen huomioimiseen. Pohja- ja pintavesiä tarkastellaan usein erillisinä osina hydrologista kiertoa, mikä on johtanut niiden välisten virtausprosessien yksinkertaistamiseen. Tässä työssä selvitettiin Rokuan pohjavesiesiintymän hydrologiaa ja hydraulista yhteyttä alueella oleviin järviin ja puroihin. Tutkimuksessa pyrittiin osaltaan selvittämään syitä harjualueen järvien pinnanvaihteluun ja veden laatuongelmiin. Kenttätutkimuksissa todettiin voimakasta alueellista vaihtelua järven ja pohjaveden vuorovaikutuksessa. Pohjaveden suotautumisen ajallinen vaihtelu puolestaan oli vähäisempää, mutta havaittavissa, ja kytköksissä järveä ympäröivän pohjavesipinnan vaihteluihin. Merkkiaineet vesinäytteistä viittasivat vastaavan vuorovaikutuksen olevan läsnä myös muissa alueen järvissä, mutta suotautuvan pohjaveden määrän vaihtelevan järvittäin. Turvemailla tehdyt mittaukset osoittivat pohjaveden purkautuvan ojaverkostoon ja ojituksen mahdollisesti lisäävän ulosvirtaamaa pohjavesiesiintymästä. Pohjaveden muodostumismäärää ja -nopeutta tutkittiin numeerisella mallinnuksella, joka kehitettiin huomioimaan harjualueelle ominaiset fysikaaliset tekijät. Mallinnus tuotti arvion ajallisesti ja alueellisesti vaihtelevasta pohjaveden muodostumisesta, joka varmennettiin kenttämittauksilla. Tuloksissa korostui kasvillisuuden, ja sitä kautta metsähakkuiden, vaikutus pohjaveden muodostumismääriin. Hydrologiasta kerätyn aineiston ja kehittyneen prosessiymmärryksen avulla Rokuan harjualueesta muodostettiin täysin integroitu numeerinen pohjavesi-pintavesi virtausmalli. Mallinnustulokset vastasivat mittauksia pohjaveden ja järvien pinnantasoista sekä purovirtaamista. Työn merkittävin tulos oli, että mallinnetut pohjaveden purkautumiskohdat ja purkautumismäärät alueen järviin vastasivat kenttähavaintoja. Tämä työ havainnollisti, että ymmärtääkseen pohjaveden ja siitä riippuvaisten järvien ja purojen vuorovaikutusta harjualueella on käytettävä monipuolisia tutkimusmenetelmiä. Työ toi lisätietoa Rokuan harjualueen vesiongelmien syihin selittäen järvien vedenpinnan vaihtelua ja vedenlaatua pohjavesihydrologialla. Väitöstyön tärkein anti oli erilaisten kenttä- ja mallinnus-menetelmien soveltaminen, kehittäminen ja hyödylliseksi havaitseminen harjualueiden kokonaisvaltaisessa pinta- ja pohjavesien hallinnassa

The need to consider groundwater and surface water as a single resource has fostered the interest of the scientific community on the interactions between surface water and groundwater. The region below and alongside rivers where surface hydrology and subsurface hydrology concur is the hyporheic zone. This is the region where water exchange determines many biogeochemical and ecological processes of great impact on the functioning of rivers. However, the complex processes taking place in the hyporheic zone require a multidisciplinary approach. The combination of innovative point and distributed techniques originally developed in separated disciplines is of great advantage for the indirect identification of water exchange in the hyporheic zone. Distributed techniques using temperature as a tracer such as fiber-optic distributed temperature sensing can identify the different components of groundwater-surface water interactions based on their spatial and temporal thermal patterns at the sediment-water interface. In particular, groundwater, interflow discharge and local hyporheic exchange flows can be differentiated based on the distinct size, duration and sign of the temperature anomalies. The scale range and resolution of fiber-optic distributed temperature sensing are well complemented by geophysics providing subsurface structures with a similar resolution and scale. Thus, the use of fiber-optic distributed temperature sensing to trace flux patterns supported by the exploration of subsurface structures with geophysics enables spatial and temporal investigation of groundwater-surface water interactions with an unprecedented level of accuracy and resolution. In contrast to the aforementioned methods that can be used for pattern identification at the interface, other methods such as point techniques are required to quantify hyporheic exchange fluxes. In the present PhD thesis, point methods based on hydraulic gradients and thermal profiles are used to quantify hyporheic exchange flows. However, both methods are one-dimensional methods and assume that only vertical flow occurs while the reality is much more complex. The study evaluates the accuracy of the available methods and the factors that impact their reliability. The applied methods allow not only to quantify hyporheic exchange flows but they are also the basis for an interpretation of the sediment layering in the hyporheic zone. For upscaling of the previous results three-dimensional modelling of flow and heat transport in the hyporheic zone combines pattern identification and quantification of fluxes into a single framework. Modelling can evaluate the influence of factors governing groundwater-surface water interactions as well as assess the impact of multiple aspects of model design and calibration of high impact on the reliability of the simulations. But more importantly, this modelling approach enables accurate estimation of water exchange at any location of the domain with unparalleled resolution. Despite the challenges in 3D modelling of the hyporheic zone and in the integration of point and distributed data in models, the benefits should encourage the hyporheic community to adopt an integrative approach comprising from the measurement to the upscaling of hyporheic processes.

The Upper Roper River is one of the Australia’s unique tropical rivers which have been largely untouched by development. The Upper Roper River catchment comprises the sub-catchments of the Waterhouse River and Roper Creek, the two tributaries of the Roper River. There is a complex geological setting with different aquifer types. In this seasonal system, close interaction between surface water and groundwater contributes to both streamflow and sustaining ecosystems. The interaction is highly variable between seasons. A conceptual hydrogeological model was developed to investigate the different hydrological processes and geochemical parameters, and determine the baseline characteristics of water resources of this pristine catchment. In the catchment, long term average rainfall is around 850 mm and is summer dominant which significantly influences the total hydrological system. The difference between seasons is pronounced, with high rainfall up to 600 mm/month in the wet season, and negligible rainfall in the dry season. Canopy interception significantly reduces the amount of effective rainfall because of the native vegetation cover in the pristine catchment. Evaporation exceeds rainfall the majority of the year. Due to elevated evaporation and high temperature in the tropics, at least 600 mm of annual rainfall is required to generate potential recharge. Analysis of 120 years of rainfall data trend helped define “wet” and “dry periods”: decreasing trend corresponds to dry periods, and increasing trend to wet periods. The period from 1900 to 1970 was considered as Dry period 1, when there were years with no effective rainfall, and if there was, the intensity of rainfall was around 300 mm. The period 1970 – 1985 was identified as the Wet period 2, when positive effective rainfall occurred in almost every year, and the intensity reached up to 700 mm. The period 1985 – 1995 was the Dry period 2, with similar characteristics as Dry period 1. Finally, the last decade was the Wet period 2, with effective rainfall intensity up to 800 mm. This variability in rainfall over decades increased/decreased recharge and discharge, improving/reducing surface water and groundwater quantity and quality in different wet and dry periods. The stream discharge follows the rainfall pattern. In the wet season, the aquifer is replenished, groundwater levels and groundwater discharge are high, and surface runoff is the dominant component of streamflow. Waterhouse River contributes two thirds and Roper Creek one third to Roper River flow. As the dry season progresses, surface runoff depletes, and groundwater becomes the main component of stream flow. Flow in Waterhouse River is negligible, the Roper Creek dries up, but the Roper River maintains its flow throughout the year. This is due to the groundwater and spring discharge from the highly permeable Tindall Limestone and tufa aquifers. Rainfall seasonality and lithology of both the catchment and aquifers are shown to influence water chemistry. In the wet season, dilution of water bodies by rainwater is the main process. In the dry season, when groundwater provides baseflow to the streams, their chemical composition reflects lithology of the aquifers, in particular the karstic areas. Water chemistry distinguishes four types of aquifer materials described as alluvium, sandstone, limestone and tufa. Surface water in the headwaters of the Waterhouse River, the Roper Creek and their tributaries are freshwater, and reflect the alluvium and sandstone aquifers. At and downstream of the confluence of the Roper River, river water chemistry indicates the influence of rainfall dilution in the wet season, and the signature of the Tindall Limestone and tufa aquifers in the dry. Rainbow Spring on the Waterhouse River and Bitter Spring on the Little Roper River (known as Roper Creek at the headwaters) discharge from the Tindall Limestone. Botanic Walk Spring and Fig Tree Spring discharge into the Roper River from tufa. The source of water was defined based on water chemical composition of the springs, surface and groundwater. The mechanisms controlling surface water chemistry were examined to define the dominance of precipitation, evaporation or rock weathering on the water chemical composition. Simple water balance models for the catchment have been developed. The important aspects to be considered in water resource planning of this total system are the naturally high salinity in the region, especially the downstream sections, and how unpredictable climate variation may impact on the natural seasonal variability of water volumes and surface-subsurface interaction.

Decision makers' conflicts about the validity of a single simulation model and inefficiencies of existing response matrix methods (RMM) hinder adopting successful groundwater management plans. We speed up the process by proposing a hybrid RMM that is most efficient for situations in which optimizable stimuli can vary through consecutive periods of uniform duration interspersed with periods of different duration. We use the hybrid RMM within Simulation-Optimization (S-O) models to develop optimal water management strategies. For the tested problems, the hybrid RMM requires as much or 63-89% less computation time than other RMMs. Second, we propose Multi-Conceptual Model Optimization (MCMO) that can help stakeholders reach a compromise strategy instead of agreeing on the validity of a single model. MCMO computes optimal strategies that simultaneously satisfy analogous constraints and bounds in multiple numerical models differing by more than parameter values. Applying MCMO to Cache Valley (Utah, USA) reveals that protecting local ecosystem limits the increased groundwater pumping to satisfy only 40% of projected water demand increase using two models. To successfully and sustainably manage Cache Valley aquifer, we evaluate sustained yield strategies (SYS) and quantify the resilience of a computed SYS. We maximize the number of new residents who can have their indoor and outdoor uses satisfied, subject to constraints on aquifer-surface waters conditions, and limiting new residents to projected increases in population (PIiP). furthermore, we examine the effect of optimization approach and sequiencing, temporally-lagged spatially distributed return flow that is a function of optimal groundwater use, and the acceptability time evaluation on the optimal yield strategy. Cache Valley aquifer can sustainably satisfy the outdoor water demand of 74%-83% and the indoor water demand of 83%-100% of the PIiP. We quantify deterministic resilience Rd(A,T,SV)=P to evaluate how completely an aquifer condition (SV) recovers after the end of climatic anomaly (A), by recovery time (T). Simulation predicts that Cache Valley aquifer system resiliences to a 2-year drought are Rd(2YD, 3 yrs, Overall) = 93% and Rd (2YD,≥8,Overall) ≥ 95%. Proportionally reducing pumping rates by 25% through the time horizon of the simulation increases the overall resilience to 96% within 3 years.

Geochemical mixing methods utilizing ²²²Rn and chloride and statistical hydrograph separation techniques were carried out in an attempt to understand baseflow dynamics in a section of the Kern River in the Sierra Nevada of Southern California. ²²²Rn has become a valuable tool for evaluating groundwater inflow to a river, particularly when groundwater and surface water have similar major ion geochemistry. When using geochemical methods it is important to minimize uncertainty through comparison with separate tracers and techniques, though this is complicated in this setting. Snow melt discharge and regulation of natural river flow cause hydrograph-based techniques to suffer from inaccuracies. Geochemical mixing using major ions and stable isotopes are complicated by the chemical similarity between surface water and groundwater. ²²²Rn is a powerful tool to elucidate this relationship in this setting if major uncertainties, like rate of radon degassing and parafluvial and hyporheic radon production can be constrained.

>Magister Scientiae - MSc
Over half of total flows in the global river network are composed of non-perennial rivers. This indicates the importance of non-perennial river systems in supporting the biodiversity. It has been established that groundwater is one of the elements that control the flow regimes and classification (whether perennial or not) of a river system. However, the use of hydrogeological characteristics to establish the influence of groundwater on non-perennial river systems remain to be widely unpublished. This study, therefore, intends to conceptualize and explain the role of hydrogeological characteristics in non-perennial rivers, using the Heuningnes catchment in the Western Cape Province of South Africa as a case study. The study has argued that thorough characterization of aquifers is essential in order to adequately establish the extent of aquifer-river connectivity and how groundwater influences flows and chemical loading in non-perennial river systems. The study has three objectives namely: (i) to determine the aquifer characteristics (ii) to characterise the aquifer-river interaction and (iii) to conceptualize the groundwater flow system. Records review, field, analytical and laboratory-based methods were used to collect and interpret geological, groundwater level, pumping test, hydro-chemical and environmental stable isotopic data in order to characterise groundwater occurrence, flow system and its interaction with the rivers of the study area. Water samples were taken from groundwater, surface water and rainfall during both dry and wet periods. Results show that the study area has a topography-controlled water table with shallow depth to groundwater levels ranging on average from 3 - 10 m, which result into largely a local groundwater flow system. Transmissivity values determined from constant rate pumping test range between 0.17 and 1.74 m2/day. Results exhibit that the low transmissivity values are associated with the weathered nature of the Table Mountain sandstone and the unfractured Bokkeveld shale formations. Hydrochemical data results indicate that both groundwater and river samples in the upstream part of the study area are characterised as fresh water with TDS values of less than 1000 mg/l while the downstream part has saline waters with TDS ranging from 2000 – 35000 mg/l. Results also show that Na-Cl is the dominant water composition for both groundwater and river water. The order of major ion dominance is similar for the two water sources, with concentration ranges from high to low in the order of Na+>Mg2+>Ca2+>K+ and Cl->SO42->HCO3- for cations and anions respectively. The similar patterns and trends in salinity and major ion data suggest the connectivity between the aquifer and the river. Environmental stable isotope data indicate river samples in upstream areas having depleted δ18O (-4.3 to -5.12‰) and δ2H (-22.9 to -19.3‰) signatures similar to groundwater indicating a stable and continuous groundwater contribution to the river flows. Meanwhile, high evaporative enrichment of δ18O (1.13 to 7.08‰) and δ2H (38.8 to 7.5‰) is conceived in river samples from downstream areas. Ionic ratios and isotope-salinity relationships suggest that groundwater chemistry is derived from sea sprays, evaporation and dissolution of Bokkeveld shale host rock. Geological, hydrogeological, hydrochemical and environmental stable isotope data were used to develop a conceptual hydrogeological model which explains the role of groundwater in non-perennial river systems. Results indicate that the North East – South West fault on the north-eastern part of the study area seem to act as a conduit to groundwater flow thereby supplying water to the upstream rivers while the East -West fault in the northern part seem to act as a barrier to groundwater flow resulting into a hydraulic discontinuity between upstream and downstream areas. Meanwhile, the relatively low conductive formation in the downstream areas coupled with a relatively low hydraulic gradient (0.000843) suggests there is slow Darcian groundwater flows resulting in less flushing and high salinization of groundwater. Eventually, in the downstream part of the study area there is slow and minimal groundwater discharge to the rivers resulting into groundwater failing to maintain the river flows and pools. In general, rivers of the study area largely gain water from groundwater although the amount of groundwater discharge varies from one river segment to another in both upstream and downstream parts. The conceptual model has led to the development of a proposed optimum management of non-perennial rivers including the effects of groundwater abstraction on the river flows.
2022-09-01

Streams and groundwaters interact in distinctly different ways during flood versus base flow periods. Recent research in the Upper San Pedro River using isotopic and chemical data shows that (1) near-stream, or 'riparian,' groundwater recharged during high streamflow periods is a major contributor to streamflow for the rest of the year, and (2) the amount of riparian groundwater derived from this flood recharge can vary widely (10-90%) along the river. Riparian groundwater in gaining reaches is almost entirely basin groundwater, whereas losing reaches are dominated by prior streamflow.This description of streamflow gives rise to the questions of (1) how much flood recharge occurs at the river-scale, and (2) subsequently, what is the relative importance of flood recharge and basin groundwater in maintaining the hydrologic state of the riparian system. To address these questions, a coupled hydrologic-solute model was constructed for 45 km of the Upper San Pedro riparian system.

The aim of this thesis is to determine the sources, controls and risk aspects of fluoride in surface water and groundwater in a region of southeastern Sweden where the fluorine-rich 1.45 Ga circular Götemar granite (5 km in diameter) crops out in the surrounding 1.8 Ga granites and quartz monzodiorites (TIB rocks). The materials of this thesis include both primary data, collected for the purpose of this thesis, and a large set of secondary data, retrieved from the Swedish Nuclear Fuel and Waste Management Co., the Swedish Geological Survey and the Kalmar County Council. A characteristic feature of the area is high fluoride concentrations in all kinds of natural waters, including surface waters (such as streams) and groundwater in both the Quaternary deposits (regolith groundwater) and bedrock fractures (fracture groundwater). A number of potential sources and controls of the high fluoride concentrations were investigated, including a variety of geological, mineralogical, mineral-chemical and hydrological features and processes. For the stream waters and regolith groundwater, high fluoride concentrations were correlated with the location of the Götemar granite. This finding is explained by the discharge of fluoride-rich groundwater from fractures in the bedrock and/or the release of fluoride due to the weathering of fluorine-bearing minerals in the Quaternary deposits; however, the Quaternary deposits had considerably lower fluoride concentrations than the underlying bedrock. The high fluoride concentrations in the fresh fracture groundwater (up to 7.4 mg/L) in the TIB-rocks are proposed to be the result of long residence times and the alteration/dissolution of fluorine-bearing primary and secondary minerals along the fracture walls. In terms of risk aspects, this thesis shows that fluoride can add to the transport and inorganic complexation of aluminium in humic-rich, acidic streams. Additionally, 24 % of the children in households with private wells in Kalmar County were assessed to be at risk of excess fluoride intake based on the WHO drinking water guideline value (1.5 mg/L). However, the risk increased significantly when instead the US EPA reference dose (0.06 mg/kg-day) was used, both when all relevant exposure pathways were taken into account as well as water consumption alone. Hence, it is shown that the risk of an excess intake of fluoride is strongly dependent on the basis for evaluation.