Thesis (M.Sc.)--University of Adelaide, Dept. of Geology and Geophysics, 2003. / Includes bibliographical references (leaves 112-115).

L’île de La Réunion a été couverte par une vaste campagne de géophysique héliportée en 2014. Le dispositif SkyTEM a permis de cartographier l’anomalie du champ magnétique et la résistivité électrique du sous-sol jusqu’à 300 m de profondeur, et ce, sur l’ensemble de l’île. L’acquisition de ce jeu de données met en évidence la problématique de l’interprétation des données électromagnétiques héliportées à l’échelle régionale. L’interprétation d’un modèle 3D de résistivité d’une superficie 2 500 km2 nécessite la mise en place de méthodologies innovantes pour le confronter aux données géologiques, climatiques et hydrogéologiques. L’objectif de la thèse est de valoriser ce jeu de données géophysique à l’échelle régionale en intégrant l’analyse hydrogéologique à différentes échelles spatiales. Pour répondre à ces problématiques, cette thèse s’organise autour d’une méthodologie hydrogéophysique multi-échelle qui permet d’étudier la répartition et le fonctionnement des aquifères à des échelles inédites jusqu’alors. Pour interpréter les 350 000 sondages électromagnétiques de la campagne, une approche statistique a été développée pour synthétiser une information sur les contrastes 3D en 2D. Les résultats, cohérents avec les connaissances géologiques et hydrogéologiques de l’île, ont permis d’analyser l’impact des paramètres géologiques et climatiques régionaux sur la répartition des aquifères et les processus d’altération. Sur le littoral, les données de résistivité sont confrontées à des logs de conductivité électrique de l’eau souterraine afin de valider l’interprétation de la géophysique. Le modèle de résistivité permet ainsi de cartographier et d’analyser les paramètres de contrôle du phénomène d’intrusion saline à l’échelle de l’île. En altitude, l’utilisation conjointe des données électromagnétiques et magnétiques héliportées permet de caractériser la géométrie des structures géologiques et d’imager les profils et paléo-profils d’altération météorique. / In 2014, Reunion Island was covered by a vast airborne geophysics campaign. The SkyTEM device mapped magnetic anomalies and bulk resistivity at an extra 300 m depth throughout the island. The resulting dataset revealed the issue of interpreting airborne electromagnetic data at the regional scale. The interpretation of a 3D resistivity model wrapping 2 500 km2 requires the implementation of innovative methodologies to compare it with geological, climatic and hydrogeological data. The aim of the thesis is to enhance this geophysical dataset at the regional scale by integrating hydrogeological analysis at different spatial scales. To answer these issues, this thesis revolves around a multi-scale hydrogeophysical methodology, which allows to analyze how aquifers are distributed and their behaviors on unprecedented scales. A statistical approach has been developed to synthesize 3D geo-electrical contrasts in 2D to interpret the 350 000 soundings. All outcomes are consistent with the geological and hydrogeological knowledge of the island, enabling us to study how regional geological and climatic parameters impact the distribution of aquifers and weathering processes. In the coastal zone, resistivity data are compared with groundwater electrical conductivity logs to validate the interpretation of geophysics. Thus, the resistivity model helped mapping saltwater intrusion and analyzing its control parameters at the island scale. Inland, the combined use of airborne electromagnetic and magnetic data made it possible to characterize the geometry of geological structures and to image weathering profiles and paleo-profiles. Combining results gathered on various scales allows the analysis of weathering impact on aquifers of shield volcanoes. On the coastal zone, un-weathered and highly permeable lithological units (up to 10-1 m/s) are subject to saltwater intrusion, even with recharge rates up to 6 to 8 m per year. With decreasing transmissivity, aquifers become less exposed to saltwater intrusion. According to geophysics outcomes, the contacts between different eruptive phase products at high altitude are characterized by specific weathering paleo-profiles which create permeability contrasts conducive to perched aquifers establishment. Examining the geophysical response in different areas of the island made it possible to analyze the dynamics of weathering processes, initially controlled by the age of the formations and secondly, by the rainfall rates and the temperature. These results showed that weathering and structure of basaltic volcanoes depend on their age and on windward/leeward slopes. Thus, our research helped improve the accuracy of the conceptual hydrogeological model including geological structuring and time evolution of basaltic volcanic aquifers in an insular environment.

Groundwater is often the most important source of drinking water. In recent decades, the environmental threats to this resource have increased dramatically, because of pollution, over usage and disturbed water balances. Climate change will affect the groundwater in coastal areas by sea-level rise and changes in precipitation and temperature. If seasonal variations in groundwater recharge and groundwater reservoirs changes it could lead to problems for drinking water supplies.  In coastal areas and archipelagos, there is a general lack of groundwater because of thin soil covers and limited storage capacities within the bedrock aquifers. When water abstraction in a well is too large in relation to the formation of groundwater the area can be affected by saltwater intrusion. More people are settling permanently in former summer-house areas, which mean higher pressure on groundwater as a drinking water resource. This development is under way on the island Tynningö in the Stockholm archipelago. Saltwater intrusion in wells has been investigated in collaboration with Södra Roslagens Miljö- och Hälsoskyddskontor (SRMH). The aim was to find out how many of the wells that have enhanced chloride concentrations (≥50 mg/l) and how different parameters affect the concentrations. The study is limited to houses where people live permanently. Water samples from 67 wells have been analyzed for chloride concentrations. Parameters that may affect the risk of saltwater intrusion, for example how deep the well is and its distance to the shoreline, are used to interpret the measured chloride concentrations. A comparison with previous chloride measurements is also made to evaluate how the problem has changed over time. Furthermore, measures to reduce water consumption and possibilities for the municipality to prevent problems with saltwater intrusion are discussed. The results show that 24 % of the wells have an enhanced chloride concentration (≥50 mg/l), which is in harmony with results from earlier studies in Tynningö and similar areas. This survey was conducted during winter; chloride concentrations in summer may therefore be higher. The result shows that all the investigated parameters have an influence on the chloride concentrations. Wells with enhanced chloride concentrations are slightly deeper, older, lower in the terrain, closer to the shoreline and the well bottom is located deeper below sea level. The number of people using the well also affects the risk of saltwater intrusion. / Grundvatten utgör ofta den viktigaste källan till dricksvatten. De senaste årtiondena har miljöhoten mot denna resurs ökat kraftigt till följd av föroreningar, överutnyttjande och rubbad vattenbalans. Klimatförändringarna kommer att påverka grundvattnet i kustområden genom havsnivåhöjning och förändrad nederbörd och temperatur. Om grundvattenbildningen och grundvattenmagasinens årstidsvariationer förändras kan det leda till problem för den enskilda dricksvattenförsörjningen. I kust- och skärgårdsområden råder det i allmänhet brist på grundvatten på grund av tunna jordtäcken och små lagringsmöjligheter i berggrunden. När vattenuttaget i en brunn blir för stort i förhållande till nybildningen av grundvatten kan området drabbas av saltvatteninträngning. I många tidigare fritidshusområden bosätter sig fler permanent, vilket innebär ett större tryck på grundvattnet. På Tynningö i Stockholms skärgård pågår en sådan utveckling och saltvatteninträngning i enskilda brunnar har därför undersökts i samarbete med Södra Roslagens Miljö- och Hälsoskyddskontor (SRMH). Syftet har varit att ta reda på hur många av brunnarna som har förhöjda kloridhalter (≥50 mg/l) samt hur olika parametrar påverkar kloridhalten. Undersökningen är avgränsad till permanentboenden och vattenprover från 67 brunnar har analyserats för klorid. Parametrar som kan påverka risken för saltvatteninträngning, t.ex. brunnens djup och dess avstånd till strandlinjen, har sedan använts för att analysera de uppmätta kloridhalterna. En jämförelse med tidigare kloridmätningar har även gjorts för att utvärdera hur problemet har förändrats över tid. Vidare har åtgärder för att minska vattenförbrukningen samt kommunens möjligheter att förebygga problem med saltvatteninträngning diskuterats. Resultatet visar att 24 % av brunnarna har en förhöjd kloridhalt (≥50 mg/l), vilket stämmer överrens med resultat från tidigare undersökningar på Tynningö och i liknande områden. Denna undersökning genomfördes under vintern. Eftersom kloridhalten påverkas av årstid kan kloridhalterna sommartid komma att bli högre. Resultatet visar att samtliga undersökta parametrar har en påverkan på kloridhalten. Brunnar med förhöjda kloridhalter är något djupare, äldre, ligger lägre i terrängen och närmare stranden och brunnsbottens nivå ligger djupare under havsnivån. Även antal personer som använder brunnen påverkar risken för saltvatteninträngning.

Bactérias quitinolíticas são autóctones do ecossistema marinho e tem um importante papel no processo de degradação de quitina. Relativamente pouco é conhecido sobre a diversidade e potencial enzimático de bactérias quitinolíticas isoladas de ambientes tropicais costeiros. Amostras de água do mar e de plâncton foram coletadas no Canal de São Sebastião, Baixada Santista e Ubatuba. As bactérias quitinolíticas foram enumeradas e isoladas em meio mínimo contendo quitina coloidal e caracterizadas através de métodos fenotípicos e genotípicos. As maiores contagens de bactérias quitinolíticas foram observadas em amostras de água do mar e plâncton coletadas na Baixada Santista. A diversidade de bactérias quitinolíticas e o potencial de produção de quitinases foram influenciados pelo nível de contaminação fecal presente no ecossistema marinho. Uma maior diversidade foi encontrada em ambiente com médio e baixo impacto antropogênico, mas bactérias quitinolíticas isoladas de ambiente com alta atividade antropogênica mostraram os maiores valores de produção de quitinases. / Chitinolytic bacteria are autochthonous in marine ecosystems and have an important role in chitin degradation process. A very little is know about the diversity and enzymatic potential of chitinolytic bacteria isolated from coastal tropical environments. Seawater and plankton samples were collected at Canal de São Sebastião, Baixada Santista and Ubatuba. Chitinolytic bacteria were counted and isolated in minimal media containing colloidal chitin and characterized using phenotypic and genotypic methods. Highest counts of chitinolytic bacteria were observed in seawater and plankton samples collected at Baixada Santista. The diversity of chitinolytic bacteria and the potential of chitinases production were influenced by the level of fecal contamination present in the marine ecosystem. Highest diversity was found in environment with medium and low anthropogenic impact, but chitinolytic bacteria isolated from environment with high anthropogenic influences showed highest chitinases production.

O arsênio é um importante contaminante estudado em toxicologia, pois pode estar presente em alimentos e no meio ambiente. Seus efeitos nocivos para humanos depende da forma química, onde os arsenicais trivalentes apresentam maior toxicidade e as formas inorgânicas são melhor absorvidas pelo organismo. Seus efeitos tóxicos podem envolver os sistemas respiratórios, gastrointestinal, cardiovascular, nervoso e hematopoiético. O arsênio pode ser encontrado em alguns gêneros alimentícios em concentrações menores que 1 mg/Kg. Em frutos do mar, tais como peixes pode conter teores que vão desde 1 a mais de 100 mg/Kg e em outros alimentos à base de peixe podem chegar à algumas miligramas por quilo, predominantemente na forma orgânica. A quantidade de arsênio ingerido pelo homem está diretamente influenciada pelo consumo de alimentos marinhos incluídos na dieta. Este trabalho tem por objetivo comparar duas técnicas: a colorimétrica, com o método do dietilditiocarbamato de prata e por absorção atômica com gerador de hidratos (HGAAS) e com isso avaliar a presença de arsênio em amostras de cação comercializadas na cidade de São Paulo. O método colorimétrico do dietilditiocarbamato de prata, baseia-se na transformação das diversas formas orgânica ou inorgânica de arsênio presentes nos alimentos, em pentóxido de arsênio e sua redução final à arsina, através do meio ácido e da presença de hidrogênio nascente liberado na reação do ácido com zinco metálico. No segundo método as amostras são mineralizadas e quantificadas no Absorção Atômica com gerador de hidretos(HGAAS).O método do dietilditiocarbamato de prata apresentou limite de detecção e quantificação de 0,05 e 0,1 µg/mL, respectivamente. A linearidade obtida com massas de 5 a 20 µg apresentou um coeficiente de determinação de 0,9970. Por este método foram analisadas 18 amostras de cação com níveis entre 0,17 à 3,79 mg/Kg. Com a técnica por HGAAS foi analisado MRC de ostra e foi obtido recuperação em torno de 94%. Foi encontrado limite de detecção de 0,93 µg/L e limite de quantificação de 1,49 µg/L. Foram analisadas 9 amostras por ambas as técnicas e 89% delas continham teores de arsênio total acima de 1 mg/Kg, que é o limite admitido pela legislação brasileira. / Arsenic is an important pollutant studied in toxicology, due to the fact that it can be present in food and in the environment. Its toxicity for humans depends on its chemical structure where trivalent arsenicals show higher toxicity and inorganic forms are better absorbed by the organism. Its toxicant effects can involve the respiratory, gastrointestinal, cardiovascular, nervous and blood systems. The arsenic can be found in some foods in smaller concentrations than 1 mg/Kg. Fish and crustaceous may contain 1 to 100 mg/Kg, in some cases, marine fishes may show amounts of As up to milligrams per killogram, predominantly in the organic form. The amount of arsenic ingested by man is directly influenced by the consumption of marine food included in the diet. This present work compare two techniques: the colorir11etric, with the method of the silver dietylditiocarbamate and the atomic absorption with hydride generator (HGAAS) aiming the evaluation of total arsenic present in samples of fish marketed in the city of São Paulo. The method using silver dietylditiocarbamate, is based on the transformation of all organic or inorganic forms of arsenic present in edible parts of fish, in arsenic pentoxide and its final reduction to arsine. In the second method the samples are mineralized and quantified by atomic absorption with hydride generator. The first method showed limit of detection and quantification of 0,05 and 0,1 µg/mL, respectively. Linearity obtained with masses of 5 to 20 µg showed a coefficient of determination of 0,9970. By this method 18 fish samples ware analyzed showing levels of 0,17 to 3,79 mg/Kg. By HGAAS method oyster certified reference material was analyzed and it was obtained a recovery of 94%, limit of detection of 0,93 µg/L and limit of quantification of 1,49 µg/L. Nine samples were analyzed by both techniques and 89% of them have As content higher than 1 mg/Kg, which is the limit admitted by the Brazilian legislation.

The impact of natural disasters is often exacerbated by a disparity between resources for relief and recovery. When the barrio of Punta Santiago in Puerto Rico was devastated by Hurricane Maria in September of 2017, many of its residents lived in the remains of their homes for over a year while they rebuilt from wind damage and flood waters that rose over 6 feet. As climate change leads to an even more constrained timeline for response with increasingly frequent and intense storms, the future of Punta Santiago and other coastal communities worldwide will necessitate strategies ranging from nature-based shore protection systems, coastal setbacks, and managed retreat. This thesis investigates the time disparate processes of disaster relief, recovery, and climate adaptation through the lens of their impact upon the interdependent identities of people and place as informed by theorists and designers including J.B. Jackson and Patrick Geddes. My approach works from the scale of the Antón Ruíz watershed to the delta to uncover the historical and contemporary processes that knit people in the region to the land. I identify commonalities in the immediate recovery needs and long-term resiliency of the community and ecosystems, and seek to support ongoing globally significant research of the rare coastal systems surrounding Punta Santiago. The proposed design, a causeway linking the coast to the hills, dovetails disaster relief and recovery with climate adaptation by providing a persistent connection that restores and reveals the dynamic coastal landscape. / Master of Landscape Architecture / Global warming is correlated with an increase in sea level rise, atmospheric moisture (water content in the air), and surface sea temperatures. The body of research around the complex interaction of these factors is growing, but current projections are that warmer seas will cause more intense hurricanes. Coastal communities, particularly those with fewer economic resources, bear the brunt of this trend and recovery is more difficult with each passing storm. After Hurricane Maria struck in September 2017, many residents of the barrio of Punta Santiago in Puerto Rico lived in the remains of their homes for over a year with little resources to rebuild from the severe wind damage and flood waters that rose over 6 feet. Recovery is still underway almost two years later. A sustainable way forward for Punta Santiago and other coastal communities worldwide necessitates strategies ranging from natural shore stabilization techniques like mangrove buffers and living reefs to restrictions on coastal development, and even the relocation of communities. This thesis investigates the time disparate processes of disaster relief, recovery, and climate adaptation through the lens of their impact upon the interdependent identities of people and place as informed by theorists and designers including J.B. Jackson and Patrick Geddes. My approach works from the scale of the Antón Ruíz watershed to the delta to uncover the historical and contemporary land use that knit people in the region to the land. I identify commonalities in the immediate recovery needs and long-term resiliency of the community and ecosystems, and seek to support ongoing globally significant research of the rare coastal systems surrounding Punta Santiago. The proposed design, a causeway linking the coast to the hills, dovetails disaster relief and recovery with climate adaptation by providing a persistent connection that restores and reveals the dynamic coastal landscape.

This paper presents an overview of the concepts and strategies in the original composition, The Harbour of Incense, a cycle of three movements for different groups of instruments. Each movement addresses an aspect of the musical cultures of Hong Kong. The first movement Taan Go for Harp Solo explores the sound world of the folk genre saltwater song; the second movement Jat1 Wun2 Sai3 Ngau4 Naam5 Min6 for Flute and Piano highlights the musicality of Cantonese language; the third movement Daa Zaai for Oboe, Clarinet in B-flat, Bassoon, and Percussion, is inspired by the keyi music used in the Taoist funeral. The paper discusses how to bring together Southeast Asian aesthetics and contemporary Western compositional techniques, as well as how to communicate this unique cultural experience to performers and audiences from other backgrounds. It provides the transcriptions of two saltwater songs and an excerpt of keyi music, and illustrate how they inform the structures, textures, and melodic gestures of the composition. The nine tones of Cantonese language are also explored for generating melodic materials, metric plans, and articulation writing.

Le thème de cette thèse est l'identification de paramètres tels que la conductivité hydraulique, K, pour un problème d'intrusion marine dans un aquifère isotrope et libre. Plus précisément, il s'agit d'estimer la conductivité hydraulique en fonction d'observations ou de mesures sur le terrain faites sur les profondeurs des interfaces (h, h₁), entre l'eau douce et l'eau salée et entre le milieu saturé et la zone insaturée. Le problème d'intrusion marine consiste en un système à dérivée croisée d'edps de type paraboliques décrivant l'évolution de h et de h₁. Le problème inverse est formulé en un problème d'optimisation où la fonction coût minimise l'écart quadratique entre les mesures des profondeurs des interfaces et celles fournies par le modèle. Nous considérons le problème exact comme une contrainte pour le problème d'optimisation et nous introduisons le Lagrangien associé à la fonction coût. Nous démontrons alors que le système d'optimalité a au moins une solution, les princcipales difficultés étant de trouver le bon ensemble pour les paramètres admissibles et de prouver la différentiabilité de l'application qui associe (h(K), h₁(K₁)) à K. Ceci constitue le premier résultat de la thèse. Le second résultat concerne l'implémentation numérique du problème d'optimisation. Notons tout d'abord que, concrètement, nous ne disposons que d'observations ponctuelles (en espace et en temps) correspondant aux nombres de puits de monitoring. Nous approchons donc la fonction coût par une formule de quadrature qui est ensuite minimisée en ultilisant l'algorithme de la variable à mémoire limitée (BLMVM). Par ailleurs, le problème exact et le problème adjoint sont discrétisés en espace par une méthode éléments finis P₁-Lagrange combinée à un schéma semi-implicite en temps. Une analyse de ce schéma nous permet de prouver qu'il est d'ordre 1 en temps et en espace. Certains résultats numériques sont présentés pour illustrer la capacité de la méthode à déterminer les paramètres inconnus. Dans la troisième partie de la thèse, nous considérons la conductivité hydraulique comme un paramètre stochastique. Pour réaliser une étude numérique rigoureuse des effets stochastiques sur le problème d'intrusion marine, nous utilisons les développements de Wiener pour tenir compte des variables aléatoires. Le système initiale est alors transformé en une suite de systèmes déterministes qu'on résout pour chaque coefficient stochastique du développement de Wiener. / This thesis is concerned with the identification, from observations or field measurements, of the hydraulic conductivity K for the saltwater intrusion problem involving a nonhomogeneous, isotropic and free aquifer. The involved PDE model is a coupled system of nonlinear parabolic equations completed by boudary and initial conditions, as well as compatibility conditions on the data. The main unknowns are the saltwater/freshwater interface depth and the elevation of upper surface of the aquifer. The inverse problem is formulated as the optimization problem where the cost function is a least square functional measuring the discrepancy between experimental interfaces depths and those provided by the model. Considering the exact problem as a constraint for the optimization problem and introducing the Lagrangian associated with the cost function, we prove that the optimality system has at least one solution. The main difficulties are to find the set of all eligible parameters and to prove the differentiability of the operator associating to the hydraulic conductivity K, the state variables (h, h₁). This is the first result of the thesis. The second result concerns the numerical implementation of the optimization problem. We first note that concretely, we only have specific observations (in space and in time) corresponding to the number of monitoring wells, we then adapt the previous results to the case of discrete observations data. The gradient of the cost function is computed thanks to an approximate formula in order to take into account the discrete observations data. The cost functions then is minimized by using a method based on BLMVM algorithm. On the other hand, the exact problem and the adjoint problem are discretized in space by a P₁-Lagrange finite element method combined with a semi-implicit time discretization scheme. Some numerical results are presented to illustrate the ability of the method to determine the unknown parameters. In the third part of the thesis we consider the hydraulic conductivity as a stochastic parameter. To perform a rigorous numerical study of stochastic effects on the saltwater intrusion problem, we use the spectral decomposition and the stochastic variational problem is reformulated to a set of deterministic variational problems to be solved for each Wiener polynomial chaos.

Le thème de cette thèse est l'analyse mathématique de modèles décrivant l'intrusion saline dans les aquifères côtiers. On a choisi d'adopter la simplicité de l'approche avec interface nette : il n'y a pas de transfert de masse entre l'eau douce et l'eau salée (resp. entre la zone saturée et la zone sèche). On compense la difficulté mathématique liée à l'analyse des interfaces libres par un processus de moyennisation verticale nous permettant de réduire le problème initialement 3D à un système d'edps définies sur un domaine, Ω, 2D. Un second modèle est obtenu en combinant l'approche 'interface nette' à celle avec interface diffuse ; cette approche est déduite de la théorie introduite par Allen-Cahn, utilisant des fonctions de phase pour décrire les phénomènes de transition entre les milieux d'eau douce et d'eau salée (respectivement les milieux saturé et insaturé). Le problème d'origine 3D est alors réduit à un système fortement couplé d'edps quasi-linéaires de type parabolique dans le cas des aquifères libres décrivant l'évolution des profondeurs des 2 surfaces libres et de type elliptique-parabolique dans le cas des aquifères confinés, les inconnues étant alors la profondeur de l'interface eau salée par rapport à eau douce et la charge hydraulique de l'eau douce. Dans la première partie de la thèse, des résultats d'existence globale en temps sont démontrés montrant que l'approche couplée interface nette-interface diffuse est plus pertinente puisqu'elle permet d'établir un principe du maximum plus physique (plus précisèment une hiérarchie entre les 2 surfaces libres). En revanche, dans le cas de l'aquifère confiné, nous montrons que les deux approches conduisent à des résultats similaires. Dans la seconde partie de la thèse, nous prouvons l'unicité de la solution dans le cas non dégénéré, la preuve reposant sur un résultat de régularité du gradient de la solution dans l'espace Lr (ΩT), r > 2, (ΩT = (0,T) x Ω). Puis nous nous intéressons à un problème d'identification des conductivités hydrauliques dans le cas instationnaire. Ce problème est formulé par un problème d'optimisation dont la fonction coût mesure l'écart quadratique entre les charges hydrauliques expérimentales et celles données par le modèle. / The theme of this thesis is the analysis of mathematical models describing saltwater intrusion in coastal aquifers. The simplicity of sharp interface approach is chosen : there is no mass transfer between fresh water and salt water (respectively between the saturated zone and the area dry). We compensate the mathematical difficulty of the analysis of free interfaces by a vertical averaging process allowing us to reduce the 3D problem to system of pde's defined on a 2D domain Ω. A second model is obtained by combining the approach of 'sharp interface' in that with 'diffuse interface' ; this approach is derived from the theory introduced by Allen-Cahn, using phase functions to describe the phenomena of transition between fresh water and salt water (respectively the saturated and unsaturated areas). The 3D problem is then reduced to a strongly coupled system of quasi-linear parabolic equations in the unconfined case describing the evolution of the DEPTHS of two free surfaces and elliptical-parabolic equations in the case of confined aquifer, the unknowns being the depth of salt water/fresh water interface and the fresh water hydraulic head. In the first part of the thesis, the results of global in time existence are demonstrated showing that the sharp-diffuse interface approach is more relevant since it allows to establish a mor physical maximum principle (more precisely a hierarchy between the two free surfaces). In contrast, in the case of confined aquifer, we show that both approach leads to similar results. In the second part of the thesis, we prove the uniqueness of the solution in the non-degenerate case. The proof is based on a regularity result of the gradient of the solution in the space Lr (ΩT), r > 2, (ΩT = (0,T) x Ω). Then we are interest in a problem of identification of hydraulic conductivities in the unsteady case. This problem is formulated by an optimization problem whose cost function measures the squared difference between experimental hydraulic heads and those given by the model.

Dans ce travail, nous étudions un schéma élément fini que nous appliquons à un modèle décrivant l'intrusion saline dans les aquifères côtiers confinés et libres. Le modèle est basé sur l'approche hydraulique qui consiste à moyenner verticalement le problème initial 3D, cette approximation repose sur une hypothèse d'écoulement quasi-hydrostatique qui, loin des épontes et des sources, est vérifiée. Pour modéliser les interfaces entre l'eau douce et l'eau salée (respectivement entre la zone saturée et la zone sèche), nous combinons l'approche 'interface nette' à l'approche avec 'interface diffuse' ; cette approche est déduite de la théorie de champ de phase, introduite par Allen-Cahn, pour décrire les phénomènes de transition entre deux zones. Compte tenu de ces approximations, le problème consiste en un système fortement couplé d'edps quasi-linéaires de type parabolique dans le cas des aquifères libres décrivant l'évolution des profondeurs des 2 surfaces libres et de type elliptique-prabolique dans le cas des aquifères confinés, les inconnues étant alors la profondeur de l'interface eau salée/eau douce et la charge hydraulique de l'eau douce. Dans la première partie de la thèse, nous donnons dans le cas d'un aquifère confiné, des résultats d'estimation d'erreur d'un schéma semi-implicite en temps combiné à une discrétisation en espace de type élément fini Pk Lagrange. Ce résultat utilise entre autre un résultat de régularité du gradient de la solution exacte dans l'espace Lr(ΩT), r > 2, ce qui permet de traiter la non-linéarité et d'établir l'estimation d'erreur sous des hypothèses de régularité raisonnables de la solution exacte. Dans la seconde partie de la thèse, nous généralisons l'étude précédente au cas de l'aquifère libre. La difficulté principale est liée à la complexité du système d'edps paraboliques mais à nouveau, grâce au résultat de régularité Lr(ΩT), r > 2 établi pour les gradients des surfaces libres, nous montrons que le schéma est d'ordre 1 en temps et k en espace pour des solutions suffisamment régulières. Nous concluons ce travail par des simulations numériques dans différents contextes (impact de la porosité et de la conductivité hydraulique sur l'évolution de l'interface, pompage et injection d'eau douce, effet des marées) validant ainsi le modèle et le schéma. Puis nous comparons les résultats à ceux obtenus avec un schéma volume fini construit à partir d'un maillage structuré. / In this work, we study a finite element scheme we apply to a model describing saltwater intrusion into coastal aquifers confined and free. The model is based on the hydraulic approach of vertically averaging the 3D original problem, this approximation is based on a quasi-hydrostatic flow hypothesis which, instead of the walls and springs, is checked. To model the interface between freshwater and salt water (respectively between the saturated zone and dry zone), we combine the approach net interface (approach with the diffuse interface) ; This approach is derived from the phase field theory introduced by Allen-Cahn, to describe the phenomena of transition between two zones. Given these approximations, the problem consists of a strongly couple to edps parabolic quasi-linear system in the case of unconfined aquifers describing the evolution of the depths of two free surfaces and elliptical-parabolic type in the case confined aquifer, the unknowns being then the depth of salt water / fresh water and the hydraulic load of fresh water. In the first part of the thesis, we give in the case of a confined aquifer, error estimation results of a semi-implicit scheme in a combined time discretization space finite element type Pk Lagrange. This result among other uses a regularity result of the gradient of the exact solution in the space Lr(ΩT), r > 2, which can handle the non-linearity and to establish the error estimate under assumptions reasonable regularity of the exact solution. In the second part of the thesis, we generalize the previous study to the case of the free aquifer. The main difficulty is related to the complexity of the system of parabolic edps but again, thanks to regularity result Lr(ΩT), r > 2 gradients established for the free surfaces, we show that the scheme is of order 1 time and space k for sufficiently regular solutions. We conclude this work by numerical simulations in different contexts (impact of porosity and hydraulic conductivity of the evolution of the interface, and pumping fresh water injection, tidal effects) thus validating the model and diagram. The we compare the results with those obtained using a finite volume scheme constructed from a structured mesh.