La nappe de la craie du Nord de la France est actuellement confrontée à des concentrations en nitrates qui dépassent les limites fixées par la directive européenne sur les nitrates. Dans le secteur de Lens (Pas-de-Calais), l’alimentation en eau potable se fait principalement dans cette nappe, où les concentrations en nitrates peuvent atteindre 100 mg/l. A quelques kilomètres au Nord (17 km de Lens), la nappe de la craie devient captive et il se produit une dénitrification naturelle qui assure une bonne qualité de l'eau. La gestion de la ressource en eau dans le secteur de Béthune, nécessite la réalisation d’une modélisation numérique qui s’est avérée comme un outil très performant pour comprendre le fonctionnement hydrodynamique des aquifères.L’utilisation de Systèmes d'Information Géographique (SIG) offre une plate-forme intégrée de gestion, d’analyse, de modélisation, d'affichage et d’aide à la décision. Une méthodologie basée sur la combinaison des SIG, la modélisation hydrogéologique, la modélisation hydrodispersive et les réseaux de neurones artificiels (RNA), a été adoptée pour orienter la gestion des eaux souterraines. Un modèle hydrodynamique a été créé par le code Modflow à l’aide d’un SIG. Un modèle conceptuel de données MCD préparé selon la méthode HBDS a permis de visualiser les liens qui existent entre les différents phénomènes étudiés. Le modèle physique de données MPD représenté par les geodatabases, a été réalisé pour structurer l'information spatiale (géographique) et/ou aspatiale (thématique). Le traitement, la manipulation et la création des données d’entrée ont été réalisés à l’aide d’un modèle conçu dans ArcGIS. Deux simulations ont été faites, en régime permanent pour caler le modèle, puis en régime transitoire pour étudier l’impact de prélèvements dans deux puits situés à Béthune. Le but recherché était de définir les débits optimums de prélèvements d'eau dans ces puits de manière à fournir une alimentation en eau potable dans secteur de Lens tout en préservant la capacité de dénitrification de l'aquifère exploité. Des scénarios de prélèvements, simulés par Modflow et à l’aide du RNA, ont été définis et testés pour des années sèches et humides au cours de la période 1972-2008. Un modèle de transport de nitrates a été créé par le code MT3D, et comparé avec un autre modèle basé sur un couplage entre le (RNA) et le (SIG) pour la prédiction spatiale de pollution par les nitrates des eaux souterraines. Ce modèle couplé permet la création de cartes de distribution spatiale des concentrations en nitrates à différentes échelles de temps, sans création de modèles de transport qui s'appuient sur des équations mathématiques complexes et nécessitent beaucoup de données d'entrée. Afin de mettre à profit les résultats des modèles créés dans cette étude, un outil de consultation et de gestion des données (GWMV) a été créé dans ArcGIS en VBA (Visual Basic for Applications). Cet outil contient des interfaces qui sont crées dans le cadre de la gestion de l’aquifère de Béthune. L’utilisateur peut consulter les bases de données en entrées et en sorties de manière simple et efficace.Ces travaux, bien qu'appliqués à l’aquifère de Béthune, sont génériques. La méthodologie suivie peut être appliquée à plusieurs types d’aquifères. De même, les travaux de modélisation, d'analyses, de simulation, et de création des interfaces sont adaptables à des problématiques différentes. / The chalk aquifer of northern France is currently facing nitrate concentrations above the levels specified in the European Nitrates Directive. In the urban area of Lens, the drinking water resource occurs mainly in this chalk aquifer, but its nitrate concentrations can reach 100mg/l. This modeling study focuses on the chalk aquifer located in Béthune (17 km from Lens), which provides natural denitrification and ensures a good drinking water quality The management of Béthune’s aquifer requires the implementation of a numerical modeling that has proven to be a powerful tool for understanding the hydrodynamic behaviour of this chalk aquifer. Geographic Information Systems (GIS) offers an integrated platform of management, analysis, modeling, display and decision support. In this research, a methodology, based on the combination of GIS, hydrogeological modeling by Modflow, transport modeling by MT3D and Artificial Neural Networks model (ANN), was adopted to support groundwater management. A numerical flow model was created by the code “Modflow” using a Geographic Information System. A conceptual data model CDM has been prepared according to HBDS method and this is to visualize the relationships between the different studied phenomena. The physical data model PDM presenting by geodatabases has been made mainly in order to structure spatial (geographic) and/or no spatial (thematic) information, treatment, handling and creating input data were performed with a model designed in ArcGIS 9.3.1 software. Two simulations were done, steady state simulation in order to calibrate the model and transient simulation to define an optimum level of water use from two wells located in Béthune’s aquifer so as to supply Lens with drinking water without reducing the aquifer’s denitrification capacity. Water usage scenarios are defined and tested (in Modflow and using RNA) for dry and for wet years over the period 1972-2008. A nitrate transport model has been created by the code MT3D, and compared with another model based on a coupling between ANN and Geographic Information Systems (GIS) which build for spatial nitrate prediction of groundwater. This coupled model allows to create spatial distribution maps of nitrates at different time scales without creating transport models that rely on complex mathematical equations and that require a lot of input data. To get better the results of models created in this study, a tool of consulting and data management (GWMV) was created in ArcGIS using the VBA. This tool provides interfaces that are created for Bethune‘s aquifer management. The user can view and consult the inputs and outputs data in a more simple and effective way.

No description available.

A importância do estudo de aqüíferos livres e rasos se evidencia quando se leva em conta que tais aqüíferos são altamente vulneráveis a contaminação e que em geral se encontram em regiões densamente povoadas. Com o objetivo de melhor compreender a dinâmica do fluxo de água subterrânea na zona saturada destas formações aqüíferas, foi construído e calibrado um detalhado modelo tridimensional e transiente para representar o fluxo subterrâneo em uma porção de um aqüífero livre e raso que ocorre no Parque Ecológico do Tietê, no Município de São Paulo. Este modelo, baseado em dados de cargas hidráulicas de 81 poços de monitoramento instalados em uma área de 320m2 medidas diariamente, em valores diários de precipitação na área e em 75 determinações de condutividades hidráulicas, foi construído e executado através do software Visual MODFLOW e calibrado por meio do software PEST, através de um método de regressão não linear. Os resultados gerados por este modelo para um evento de recarga rápida indicam que a distribuição de cargas hidráulicas na área de estudo é governada pela recarga regional, pela distribuição das condutividades hidráulicas horizontais e pelas vazões específicas das camadas superiores da formação, mas é praticamente independente da intensidade e distribuição temporal da recarga local, que influencia apenas os níveis mais rasos da formação. Além disso, verifica-se o caráter extremamente dinâmico do fluxo, que responde rapidamente ao evento de recarga regional, apresentando alterações significativas de intensidade e direção no intervalo de apenas alguns dias. Tais resultados, verificados apenas por meio de um modelo tão detalhado como o produzido neste trabalho, sugerem que estratégias comuns de avaliação podem não ser capazes de avaliar suficientemente bem o comportamento deste tipo de aqüífero. / The importance of studying unconfined and shallow aquifers is verified when taking into account that these aquifers are highly vulnerable to contamination and that they are often located under heavily populated regions. A detailed three-dimensional and transient model, which represents the groundwater flow in an area of an unconfined and shallow aquifer at the Parque Ecológico do Tietê, in the Municipality of São Paulo, Brazil, was created and calibrated with the objective of enhancing the comprehension of the dynamics of the groundwater flow in the saturated zone of these formations. This model was based on hydraulic head data of 81 monitoring wells, which were installed in an area of 320 m2 and measured on a daily basis, on daily values of precipitation occurring in the area and 75 determinations of hydraulic conductivities. The model was created and run using the software Visual MODFLOW and calibrated using the software PEST, based on a non-linear regression method. The results generated by this method for an event of rapid recharge indicate that the distribution of the horizontal hydraulic conductivities and by the specific yield of the upper layers of the formation, but it is mostly disconnected from the intensity and temporal distribution of the local recharge, that only influences the shallowest levels of the formation. Furthermore, the extremely dynamic character of the flow can be verified, which responds rapidly to the regional recharge event, presenting significant changes of intensity and direction within only a few days. These results, which were only observable through a very detailed model such as the one produced and presented in this study, suggest that commonly employed evaluation strategies may not be capable of evaluating this kind of aquifer in a satisfactory way.

Conventional methods of groundwater modeling are based on applying laminar flow condition in the aquifer and assuming primary porosity to be present in the aquifer. But in cases where conduits, caves, springs and sinks characterize the aquifer as in karst, this assumption is inappropriate. In addition to Darcian flow condition in matrix portion of aquifer there should be consideration for dealing with non-Darcian flow in the conduits where high velocity of flow occurs. Presence of conduit network in the aquifer greatly affects the potentiometric heads within the aquifer. Hence the necessity of different modeling method has long been realized for karst aquifers. MODFLOW-Conduit Flow Process (CFP) has the capability to simulate both turbulent and laminar groundwater flow condition present in caves and conduits portion of karst aquifers. This study examined the cases where a sub-regional model was used to simulate discharge of springs and heads both with and without considering the presence of conduit network in the aquifer using MODFLOW-CFP 2005 and MODFLOW 2005 respectively. Comparison of results showed that the potentiometric head in the area consisting conduit network were unrealistically low when conduit network was not considered to be present in the matrix. This study also introduces and uses a program called CONGEN to generate conduit flow process file for CFP Mode 1. Furthermore this study also carried out the benchmark testing to examine the capability of MODFLOW-CFP to simulate both laminar and turbulent pipe flow in the conduits for a sub-regional scale. Results from transient state simulation indicate that, although MODFLOW-CFP considers both laminar and turbulent flow conditions in the pipe like conduits in the karst, it underestimated the peak discharge of the springs in this study.

In this study the saltwater intrusion in coastal aquifers is briefly described and the prevention techniques are discussed. By using two computer models SWI and SHARP, the movement of freshwater and saltwater is analyzed on hypothetical cases and on one real aquifer in Marmaris in the coast of Mediterranean Region. Artificial recharge and subsurface barrier techniques are applied to hypothetical cases as means of controling the saltwater intrusion. The performance of strip recharge and subsurface barrier in reducing the salt water intrusion is analyzed by simulation of the groundwater flow with the codes mentioned above. The results obtained are compared with each other. The results of hypothetical cases are relatively in good agreement. For the real aquifer the results show discrepancy that cannot be ignored.

As groundwater models are being used increasingly in the area of resource allocation, there has been an increase in the level of complexity in an attempt to capture heterogeneity, complex geometries and detail in interaction between the model domain and the outside hydraulic influences. As models strive to represent the real world in ever increasing detail, there is a strong likelihood that the boundary conditions will become nonlinear. Nonlinearities exist in the groundwater flow equation even in simple models when watertable (unconfined) conditions are simulated. This thesis is concerned with how these nonlinearities are treated numerically, with particular focus on the MODFLOW groundwater flow software and the nonlinear nature of the unconfined condition simulation. One of the limitations of MODFLOW is that it employs a first order fixed point iterative scheme to linearise the nonlinear system that arises as a result of the finite difference discretisation process, which is well known to offer slow convergence rates for highly nonlinear problems. However, Newton's method can achieve quadratic convergence and is more effective at dealing with higher levels of nonlinearity. Consequently, the main objective of this research is to investigate the inclusion of Newton's method to the suite of computational tools in MODFLOW to enhance its flexibility in dealing with the increasing complexity of real world problems, as well as providing a more competitive and efficient solution methodology. Furthermore, the underpinning linear iterative solvers that MODFLOW currently utilises are targeted at symmetric systems and a consequence of using Newton's method would be the requirement to solve non-symmetric Jacobian systems. Therefore, another important aspect of this work is to investigate linear iterative solution techniques that handle such systems, including the newer Krylov style solvers GMRES and BiCGSTAB. To achieve these objectives a number of simple benchmark problems involving nonlinearities through the simulation of unconfined conditions were established to compare the computational performance of the existing MODFLOW solvers to the new solution strategies investigated here. One of the highlights of these comparisons was that Newton's method when combined with an appropriately preconditioned Krylov solver was on average greater than 40% more CPU time efficient than the Picard based solution techniques. Furthermore, a significant amount of this time saving came from the reduction in the number of nonlinear iterations due to the quadratic nature of Newton's method. It was also found that Newton's method benefited more from improved initial conditions than Picard's method. Of all the linear iterative solvers tested, GMRES required the least amount of computational effort. While the Newton method involves more complexity in its implementation, this should not be interpreted as prohibitive in its application. The results here show that the extra work does result in performance increase, and thus the effort is certainly worth it.

Submitted by Anderson Luiz dos Santos Safre (andersonsafre@hotmail.com) on 2018-07-04T15:38:25Z No. of bitstreams: 1 ALSS_dissertacao.pdf: 7390849 bytes, checksum: 6fd7ac960f9c7465831ca92b09f0bbd3 (MD5) / Approved for entry into archive by Maria Lucia Martins Frederico null (mlucia@fca.unesp.br) on 2018-07-04T16:17:18Z (GMT) No. of bitstreams: 1 safre_als_me_botfca.pdf: 7390849 bytes, checksum: 6fd7ac960f9c7465831ca92b09f0bbd3 (MD5) / Made available in DSpace on 2018-07-04T16:17:18Z (GMT). No. of bitstreams: 1 safre_als_me_botfca.pdf: 7390849 bytes, checksum: 6fd7ac960f9c7465831ca92b09f0bbd3 (MD5) Previous issue date: 2018-05-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os usos de técnicas de modelagem em águas subterrâneas vêm sendo amplamente utilizado para entender a variabilidade e as incertezas associadas às condições hidrodinâmicas dos aquíferos. Os modelos numéricos de fluxo das águas subterrâneas são utilizados para representar a distribuição da carga hidráulica, bem como a velocidade e volume de escoamento da água no aquífero. O Estado de São Paulo possui algumas unidades de conservação de proteção integral, chamadas de Estações Ecológicas. Na região hidrográfica do Médio Paranapanema (UGRHI-17), destaca-se a Estação Ecológica de Santa Barbara (EEcSB), localizada sob uma transição do Sistema Aquífero Bauru (SAB) e o Sistema Aquífero Serra Geral (SASG). A principal atividade econômica na região é a agricultura, onde as águas subterrâneas e superficial são captadas para a irrigação. A demanda excessiva pode ameaçar os recursos hídricos e os ecossistemas da região. Desse modo, foi analisado nesse estudo qual o papel da EEcSB como área de garantia de recarga, utilizando a modelagem do fluxo das águas subterrâneas a partir da plataforma FREEWAT, que utiliza o código MODFLOW de diferenças finitas para simulação numérica. Gerou-se uma camada de espessura variada, representado o SAB. A discretização horizontal foi de 7.789 células ativas, com extensões de 100 m x 100 m. Foram utilizados 23 poços de observação, distribuídos por entre as microbacias da EEcSB, para calibração do modelo. A recarga foi dívida em duas zonas para representar a EEcSB ou outros usos da terra no entorno. Os valores variaram entre 15% de recarga da precipitação média. As duas formações do SAB contidas na EEcSB (Adamantina e Marilia) foram representadas por zonas com diferentes condutividades hidráulicas, a primeira com 1,75 m/d e a segunda com 0,9 m/d. A análise de sensibilidade foi realizada automaticamente pelo módulo UCODE_2014 e demonstrou que os parâmetros com maior sensibilidade foram a condutividade hidráulica na zona 1 e a recarga. A calibração teve um erro médio quadrático residual de 0,52 m. O valor total de afluxo simulado pelo modelo em regime permanente é de 66.893,882 m³/d, onde 59.079 m³/d correspondem ao volume escoado pelos drenos, e 7.813 m³/d ao valor de saída pela evapotranspiração. Foram observados três padrões principais de fluxo, com um divisor de águas subterrâneas no centro do domínio simulado. Um padrão de fluxo possui sentido Oeste em direção ao Rio Capivari, apresentando segmentações nas direções de fluxo próximas aos córregos afluentes (Divisa, Santana, Guarantã e Boi). Foram simulados dois cenários, o primeiro com a remoção de 50% da área e o segundo com remoção total da EEcSB. O primeiro cenário apresentou redução de 53,6% no volume da recarga e 47,5% no volume das drenagens, com quedas de até 11m no nível freático. O segundo cenário apresentou uma redução de 61,68% na recarga e de 77,79% na vazão das drenagens com rebaixamentos de até 14m no nível freático. / The uses of groundwater modeling techniques have been widely applied to understand the variability and uncertainties associated with the hydrodynamic conditions of aquifers. Numerical groundwater models are used to represent the hydraulic head distribution, as well as the velocity and volumetric flow. The São Paulo State has some Conservation Units of integral protection, called Ecological Stations. In the Médio Paranapanema Hydrographic region (UGRHI-17), stands out the Santa Bárbara Ecological Station (EEcSB), located under a transition from the Bauru Aquifer System (BAS) and the Serra Geral Aquifer System (SGAS). The main economic activity in the region is agriculture, where the groundwater and surface water are extracted for irrigation. The excessive demand of water threatens the region’s water resources and ecosystems. Thus, in this study, the role of EEcSB as a recharge guarantee area, was analyzed through groundwater flow modeling through the FREEWAT platform, that uses the MODFLOW finite difference code for numerical approximation. One layer of varied thickness, representing the BAS was generated. The horizontal discretization was made of 7,789 active cells, with 100 m x 100 m extension. Twenty three observation wells were used, distributed among EEcSB micro-basins for calibration. The recharge was divided in two zones, to represent the EEcSB and the other land uses in the environment. Recharge values varied around 15% of average rainfall. The two BAS formations (Adamantina and Marillia) at EEcSB were represented by two zones with different hydraulic conductivity, the first with 1.75 m.d-1, and the second with 0.9 m.d-1. The sensitivity analysis was performed automatically by UCODE_2014 module and showed that the parameters with the highest sensitivity were the hydraulic conductivity at zone 1 and the recharge. The calibration had a mean square residual error of 0.52 m. The total value of simulated inflow by the steady state model is 66,893,882 m³.d-1 where outflow was 59,079 m³.d-1 by the leakage into the drains, and 7,813 m³.d-1 by evapotranspiration. Three main flow patterns were observed, with a groundwater divide at the center of the simulated domain. A flow pattern runs westward toward the Capivari Rver, showing segmentations in the flow directions near the tributaries (Divisa, Santana, Guarantã and Boi). Two scenarios were simulated, the first with the removal of 50% of the area and the second one with total removal of the EEcSB. The first scenario presented a reduction of 53.6% in the recharge volume and 47.5% in the drainage volume, with decreases up to 11 m in the water table. The second scenario presented a reduction of 61.685 in recharge and 77.79% n drainage flow with decreases up to 14 m in the water table.

During the 1950's and 1960's a railroad yard located in Oneida, Tennessee, was used as a creosote treatment facility for railroad ties. After the cross-ties were treated with creosote, the excess creosote was stored in an holding pond located about 100 feet north of Pine Creek (Fetterolf 1998). In 1990, during a creek modification project, creosote was discovered seeping through the banks of Pine Creek. The creosote had leached through the bottom of the pond and migrated towards the creek. In 1997, the Tennessee Department of Environment and Conservation authorized a remedial strategy prepared by Geraghty & Miller, Inc (Fetterolf 1998). The strategy involved the use of phytoremediation and a previously installed interception trench system. The primary goals of the phytoremediation plan are to stimulate biodegradation and to decrease groundwater flow, thus minimizing the migration of the contaminant into Pine Creek. Poplar trees were selected for the phytoremediation plan and were planted in two sections. The objectives of this report involved analyzing the hydrogeology of the Oneida, Tennessee site and organizing the collected data for the purpose of evaluating the impact of the phytoremediation and interception trench systems on the aquifer. The water level data was used to evaluate water level and hydraulic gradient changes due to evapotranspiration, rainfall, and groundwater extraction. It was obvious from the water level and rainfall comparison plots that the rainfall has a measurable effect on the water table elevation (i.e. groundwater flow). Some areas may be less affected because the coal layer has a tendency to decrease recharge. Meanwhile, the interception trench lowers the water level around the trench. The decrease in head occurs before and after the trench, thus the water level forms a "v-shape" at the trench. This "v-shape" lends to the notion that the hydraulic gradient also slopes towards the trench in both directions. As for the phytoremediation, there was not sufficient evidence to suggest that the water levels were being lowered by evapotranspiration. This was expected since the poplar trees were had only completed their second growing season. GMS MODFLOW was used to predict the effects on the water table due to the phytoremediation and the interception trench systems. The calibrated model did an adequate job in simulating the site when the interception trench was not in operation and the trees were not in their growing season. By using variable recharge in some areas, the results are expected to improve. For example, it is important to know the location of the coal layer so this area can be given a lower recharge value than the other areas in the model. As for the trench model, the simulated heads were much lower than the observed heads, which emphasizes that using wells is not the best method to simulate the interception trench. In the future, a transient model should be used to simulate the site with the trench operation, and the drain package could be used to model the trench itself. Meanwhile, the ET model was a valuable simulation, because it illustrates how effective the poplar trees can be even under conservative conditions. With an assumed root zone of just 3 feet and a maximum potential evapotranspiration rate of 4.6 gallons per day per tree, the majority of the site will experience the dry conditions expected. / Master of Science

Wetland ecological function greatly depends on the wetland hydrology. As a result, correctly estimating the wetland water budget, is essential to the success of created wetlands. A wetland water budget model, Wetbud, was developed by collaborators from Virginia Tech, Old Dominion University, and the Technical University of Crete for estimating wetland water budgets to assist wetland design in the Virginia Piedmont. The Wetbud model has basic and advanced modules. The basic module uses level pool routing to compute average monthly water levels. Based on the groundwater model MODFLOW, the advanced module estimates groundwater interactions and vegetative resistance to surface flows on a daily timestep. The overall goal of this research was to assess Wetbud as an uncalibrated design model for mitigation wetland water budget estimation in the Virginia Piedmont. Specific objectives were to compare predictions using the basic and advanced modules and to compare the Thornthwaite and the FAO-56 Penman-Monteith potential evapotranspiration estimation methods for the design of created wetlands. The Wetbud model was tested using data from two existing mitigation wetlands. Both modules produced reasonable results; however, the basic module did not accurately predict drawdown occurring during dry periods. Results showed that the Wetbud advanced module produced more accurate and detailed results when compared to the basic module: Nash-Sutcliffe model efficiency ratings for the advanced module ranged from to 0.44 to 0.63. Potential evapotranspiration estimates by the FAO-56 Penman Monteith method were more accurate than those from the Thornthwaite method in nearly every model scenario / Master of Science

No description available.