The study focuses on the adjacent Tenthill and Ma Ma catchments which converge onto the heavily cultivated alluvial plain of Lockyer Creek. Groundwater extracted from the alluvial aquifers is the primary source of water for intensive irrigation. Within the study the hydrogeology is investigated, a conceptual groundwater model produced and a numerical groundwater flow model is developed from this. The hydrochemistry and stable isotope character of groundwater are also investigated to determine processes such as recharge and evaporation. Examination of bore logs confirms the Quaternary alluvium comprises a laterally continuous gravel aquifer with an average thickness of 4.5 m, overlain by mixed sands and clays which form a semi-confining layer with an average thickness of 22 m. Variations in long term groundwater hydrographs indicate the aquifer changes from confined to unconfined in some locations as water levels drop, while bores adjacent to creek banks display a rapid response to a flood event. Pump testing of bores screened in the gravel produces estimates of hydraulic conductivity ranging from 50-80 m/day and storativity of 0.00166 which are both within realistic bounds for this aquifer material. Major ion chemistry of surface water collected during a flood is Mgdominated, similar to alluvial groundwater in the Tenthill catchment and the Lockyer plain, suggesting a strong connection between surface and groundwater in these locations. Alluvial groundwater salinity in Tenthill catchment is typically less than 3500 ìS/cm but may approach 6000ìS/cm on the Lockyer plain. By contrast Ma Ma catchment alluvial groundwater is Na-dominated with conductivity up to 12000 ìS/cm and more associated with groundwater from the underlying sandstone bedrock. Stable isotope analyses of alluvial groundwater from throughout both catchments and the Lockyer plain are compared with basalt and sandstone groundwater. A range of processes have been identified including recharge to alluvium from basalt groundwater and evaporated surface water; and alluvial-bedrock groundwater mixing at some locations. Integration of the components of the study enabled the production of a conceptual hydrogeological model of the Lockyer alluvial plain, proposing two hydrostratigraphic units; the gravel aquifer and the overlying mixed sand and clay which acts as a semi confining unit. Hydrochemical and stable isotopic evidence suggests seepage from creek channels as the dominant recharge process. A single layer groundwater flow model using MODFLOW was developed, based on groundwater extraction data, to represent flow in the gravel aquifer. The model was calibrated to transient conditions with groundwater fluctuations, incorporating both drought and flood conditions. A sensitivity analysis for each of the aquifer properties demonstrates the model is insensitive to variations within realistic bounds for the gravel aquifer material, however, the model is highly sensitive to changes in the chosen boundary conditions. Predictive simulations with several annual extraction scenarios ranging from 1.75 to 0.5 ML/ha indicate the resulting minimum saturated aquifer thickness ranges from 0.03 to 1.4 m.

Le diagnostic du SAGE Loire au niveau de la plaine du Forez (42) relate une dégradation du potentiel hydrogéologique et une pollution des nappes superficielles par les nitrates et les pesticides. Ces problèmes nécessitent une gestion durable et équilibrée de la ressource en eau. Une partie de la demande en eau est assurée par la ressource souterraine. Les eaux souterraines exploitées sont : les eaux des formations alluviales superficielles pour l’irrigation et l’AEP ; et les eaux minérales des niveaux aquifères profonds du bassin sédimentaire sous-jacents aux alluvions pour le thermalisme et de mise en bouteille.La synthèse des connaissances disponibles a révélé des insuffisances dans la description des aquifères superficiels. En effet, elles ne permettent pas d’appréhender comment fluctue la ressource dans le temps et ne prennent pas en compte l’origine de la recharge des aquifères superficiels. Ainsi, le travail de thèse se focalise sur ces deux points particuliers :- l’identification du fonctionnement transitoire des aquifères est abordée par caractérisation physique des écoulements s’appuyant sur l’analyse de 4 points de suivi piézométrique permanent et la modélisation numérique des écoulements permettant de reproduire les fluctuations piézométriques observées.- l’origine de la recharge des aquifères alluviaux est abordée par caractérisation géochimique des écoulements (analyses en ions majeurs et isotopes δ180, δ2H, δ13C et A14C). Cette approche a mis en évidence des apports d’eaux profondes alimentant localement les aquifères superficiels.La méthodologie proposée, couplée physique et géochimie, permet de mieux préciser la vulnérabilité des aquifères investigués, en vue d’une meilleure gestion future. / The Water Management Scheme in the Forez plain (France 42) has concluded to a degradation of the water resources and a serious pollution of the shallow aquifers by nitrogen and pesticides. These issues require a sustainable and balanced management of the water resources. A part of the water demand is met by groundwater. The exploited groundwater come from: shallow alluvial formations exploited for irrigation and drinking water and deep aquifers in sedimentary basin under the alluvium. Mineral waters from the deep aquifers are exploited for thermo-mineral activities and bottling.The analysis of the data available in the studied area revealed a lack of knowledge in the understanding of the groundwater flow in the shallow aquifers. Is not sufficient to explain how the water resource varies with time and the origin of the recharge of the shallow aquifers. As consequence, this thesis work will focus on these two main topics: - Identification of the transient functioning of the aquifers based on a physical characterization of groundwater flow. This method is based on piezometric head analysis carry out on 4 stations with continuous measurements and numerical modeling to compare with the observed piezometric fluctuations.- Identification of the origin of the recharge of the alluvial aquifers through a geochemical characterization of groundwater flow (major ions and isotopes δ180, δ2H, δ13C and A14C). This approach established the partial contribution of the deep aquifers to the groundwater flow in the shallow alluvium. This methodology based on a coupled geochemical and physical approach allows to assess the vulnerability of the studied aquifers and contributes to improve the future water resources management in this area.

From the Proceedings of the 1972 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - May 5-6, 1972, Prescott, Arizona / The distribution of transmissivity within the Tucson basin aquifer, as determined by pumping tests and reviewed in the construction of a digital model of the aquifer, was not totally random in space. Data tended to be distributed normally or log-normally for biased samples of developed wells. A frequency distribution of transmissivity derived from a calibrated digital model is more nearly representative of the real world because the aquifer sample is without bias as the sample constitutes the entire aquifer. Geohydrologic setting, electric analog, and digital models of the basin are discussed. The theory of transmissivity distribution in an arid land alluvial aquifer is developed from Horton's laws of exponential relationship between stream order and drainage network parameters. It is hypothesized that there is an exponential relationship between transmissivity of an alluvial aquifer. A statistical study was made of values derived from the digital model to test the probability density function hypothesized for transmissivity. The mean value is a function of climate and drainage area. These hypotheses require further validation.