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The effects of geological heterogeneities and piezometric fluctuations on groundwater flow and chemistry in a hard-rock aquifer, southern India | L’ impact des hétérogénéités géologiques et des fluctuations piézométriques sur l’écoulement et la chimie d’un aquifère de socle du sud de l’Inde Los efectos de las heterogeneidades geológicas y de las fluctuaciones piezométricas en el flujo y química del agua subterránea en un acuífero de roca dura en el sur de la India 印度南部坚硬岩石含水层中地质非均质性和水头波动对地下水流场及水化学的影响 Efeitos das heterogeneidades geológicas e das flutuações piezométricas no fluxo e na química da água subterrânea num aquífero fraturado do Sul da Índia Texto completo
2011
Perrin, Jérôme | Ahmed, Shakeel | Hunkeler, Daniel
Crystalline aquifers of semi-arid southern India represent a vital water resource for farming communities. A field study is described that characterizes the hydrodynamic functioning of intensively exploited crystalline aquifers at local scale based on detailed well monitoring during one hydrological year. The main results show large water-table fluctuations caused by monsoon recharge and pumping, high spatial variability in well discharges, and a decrease of well yields as the water table decreases. Groundwater chemistry is also spatially variable with the existence of aquifer compartments within which mixing occurs. The observed variability and compartmentalization is explained by geological heterogeneities which play a major role in controlling groundwater flow and connectivity in the aquifer. The position of the water table within the fracture network will determine the degree of connectivity between aquifer compartments and well discharge. The presented aquifer conceptual model suggests several consequences: (1) over-exploitation leads to a drop in well discharge, (2) intensive pumping may contribute to the hydraulic containment of contaminants, (3) groundwater quality is highly variable even at local scale, (4) geological discontinuities may be used to assist in the location of drinking-supply wells, (5) modeling should integrate threshold effects due to water-table fluctuations.
Mostrar más [+] Menos [-]Heat transport in a coastal groundwater flow system near De Panne, Belgium | Transport de chaleur dans un système d’écoulement souterrain côtier près de De Panne, Belgique Transporte de calor en un sistema de flujo de agua subterránea costeras cerca De Panne, Bélgica 靠近比利时De Panne海岸地下水流动系统中的热传输 Transporte de calor num aquífero costeiro próximo de De Panne, Bélgica Texto completo
2011
Vandenbohede, Alexander | Lebbe, Luc
Temperature distribution and heat transport are studied in a coastal aquifer at De Panne in the western Belgian coastal plain. Field observations include temperature profiles of groundwater in the dunes and temperature measurements at the water table in a profile on the shore. Freshwater–saltwater distribution is known from previous studies. These are used to constrain a density-dependent model simulating the freshwater–saltwater distribution and heat transport using the SEAWAT code. The yearly fluctuation of the groundwater temperature in the phreatic aquifer under the dunes, shore and sea, and the influence of a tidal inlet in the dunes are simulated. The observations show that seawater temperature variations determine the temperature variations on the shore whereas atmospheric temperature changes determine this in the dunes. Yearly temperature fluctuations imposed at the water table propagate mainly vertically in the aquifer with only limited lateral influence. Heat transport is mainly convection dominated. Thickness of the surficial zone is determined by the amplitude of the groundwater temperature at the water table and the groundwater flow. Establishment of a tidal inlet in the dunes results in asymmetric temperature profiles under and in the vicinity of it.
Mostrar más [+] Menos [-]Système de prévision des fluctuations de niveau de nappe de versant collinaire basé sur l’information Identificación de un sistema basado en información para predecir las fluctuaciones del nivel de las aguas subterráneas de laderas 应用信息基础系统识别于山坡地地下水位扰动预测 Sistema de identificação baseado na informação para prever as flutuações do nível de água subterrânea em encostas | Information-based system identification for predicting the groundwater-level fluctuations of hillslopes Texto completo
2011
Hong, Yao-Ming | Wan, Shiuan
The analysis of pre-existing landslides and landslide-prone hillslopes requires an estimation of maximum groundwater levels. Rapid increase in groundwater levels may be a dominant factor for evaluating the occurrence of landslides. System identification—use of mathematical tools and algorithms for building dynamic models from measured data—is adopted in this study. The fluid mass-balance equation is used to model groundwater-level fluctuations, and the model is analytically solved using the finite-difference method. Entropy-based classification (EBC) is used as a data-mining technique to identify the appropriate ranges of influencing variables. The landslide area at Wushe Reservoir, Nantou County, Taiwan, is chosen as a field test site for verification. The study generated 65,535 sets of numbers for the groundwater-level variables of the governing equation, which is judged by root mean square errors. By applying cross-validation methods and EBC, limited numbers of validation samples are used to find the range of each parameter. For these ranges, a heuristic method is employed to find the best results of each parameter for the prediction model of groundwater level. The ranges for governing factors are evaluated and the resulting performance is examined.
Mostrar más [+] Menos [-]The fate and transport of nitrate in shallow groundwater in northwestern Mississippi, USA | Devenir et transport des nitrates en aquifère superficiel au Nord-Ouest du Mississippi, Etats-Unis El transporte y destino de nitratos en agua subterránea somera en el noroeste del Mississippi, EEUU 美国密西西比州西北部浅层地下水中硝酸盐的运移与归宿 O destino e transporte dos nitratos nas águas subterrâneas pouco profundas no noroeste do Mississippi, EUA Texto completo
2011
Welch, Heather L. | Green, Christopher T. | Coupe, Richard H.
Agricultural contamination of groundwater in northwestern Mississippi, USA, has not been studied extensively, and subsurface fluxes of agricultural chemicals have been presumed minimal. To determine the factors controlling transport of nitrate-N into the Mississippi River Valley alluvial aquifer, a study was conducted from 2006 to 2008 to estimate fluxes of water and solutes for a site in the Bogue Phalia basin (1,250 km2). Water-quality data were collected from a shallow water-table well, a vertical profile of temporary sampling points, and a nearby irrigation well. Nitrate was detected within 4.4 m of the water table but was absent in deeper waters with evidence of reducing conditions and denitrification. Recharge estimates from 6.2 to 10.9 cm/year were quantified using water-table fluctuations, a Cl– tracer method, and atmospheric age-tracers. A mathematical advection-reaction model predicted similar recharge to the aquifer, and also predicted that 15% of applied nitrogen is leached into the saturated zone. With current denitrification and application rates, the nitrate-N front is expected to remain in shallow groundwater, less than 6–9 m deep. Increasing application rates resulting from intensifying agricultural demands may advance the nitrate-N front to 16–23 m, within the zone of groundwater pumping.
Mostrar más [+] Menos [-]Relation entre facteurs hydrogéologiques, conditions d’oxydo-réduction de nappe et distribution temporelle et spatiale des nitrates, Centre-Est, de la San Joaquin Valley, Californie, USA Relaciones de factores hidrogeológicas, condiciones de oxidación-reducción del agua subterránea, y distribuciones espacial y temporal de nitrato, Valle Centro-Oriental de San Joaquín, California, EEUU 美国加州东区中部 San Joaquin河谷水文地质条件、地下水氧化还原条件与硝酸盐时空分布的关系 Relações dos factores hidrogeológicos, das condições redução-oxidação das águas subterrâneas e das distribuições espacial e temporal da variável nitrato na área Centro-Este do Vale de SanJoaquin, Califórnia, EUA | Relations of hydrogeologic factors, groundwater reduction-oxidation conditions, and temporal and spatial distributions of nitrate, Central-Eastside San Joaquin Valley, California, USA Texto completo
2011
Landon, M. K. | Green, Christopher T. | Belitz, Kenneth | Singleton, Michael J. | Esser, Bradley K.
In a 2,700-km2 area in the eastern San Joaquin Valley, California (USA), data from multiple sources were used to determine interrelations among hydrogeologic factors, reduction-oxidation (redox) conditions, and temporal and spatial distributions of nitrate (NO3), a widely detected groundwater contaminant. Groundwater is predominantly modern, or mixtures of modern water, with detectable NO3 and oxic redox conditions, but some zones have anoxic or mixed redox conditions. Anoxic conditions were associated with long residence times that occurred near the valley trough and in areas of historical groundwater discharge with shallow depth to water. Anoxic conditions also were associated with interactions of shallow, modern groundwater with soils. NO3 concentrations were significantly lower in anoxic than oxic or mixed redox groundwater, primarily because residence times of anoxic waters exceed the duration of increased pumping and fertilizer use associated with modern agriculture. Effects of redox reactions on NO3 concentrations were relatively minor. Dissolved N2 gas data indicated that denitrification has eliminated >5 mg/L NO3–N in about 10% of 39 wells. Increasing NO3 concentrations over time were slightly less prevalent in anoxic than oxic or mixed redox groundwater. Spatial and temporal trends of NO3 are primarily controlled by water and NO3 fluxes of modern land use.
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