Tesis doctoral de Albert Folch Sancho
Groundwater hydrodynamics in range-and-basin areas are essentially determined by their geology, including the tectonic structure and the basin sedimentary infilling. Their study requires a large-scale approach to determining the location of the recharge and discharge areas of each flow system providing the basin with water resources. Furthermore, most of these areas have undergone heavy human development that can modify groundwater quantity and/or quality in different ways. Understanding geological and human influences on groundwater flow in these areas is a key aspect in achieving an adequate water resources management and therefore its future availability. in this dissertation, the selva basin has been studied as a paradigmatic case of a range-and-basin area with severe human pressure on its groundwater resources.A conceptual hydrogeological model emphasizing the role of the main fault zones has been developed and tested using numerical flow modeling as a first step. Groundwater flow has been simulated in a range-and-basin area affected by a significant fault zone, which may drain or recharge an overlying alluvial aquifer. Various hydraulic conductivity values for the range rocks, the fault-zone, and the sedimentary infilling of the basin are considered, as well as different fault-zone widths and boundary conditions. The results show that upward and downward fluxes develop in the upper part of the fault zone controlled by the action of the alluvial aquifer, and even through the basement floor, which influence the recharge of the sedimentary infilling of the basin. second, the selva range-and-basin hydrogeological system is described using potentiometric, hydrochemical, and isotopic data (¿18o, ¿d) taken from different field surveys, in order to achieve a twofold objective: (i) to describe a hydrogeological system in which tectonic elements play a significant role in the flow dynamics, and (ii) to show the influence of groundwater exploitation on the hydrodynamics of the system. Hydraulic head data indicate the relationships between the geological formations in the range areas and the sedimentary infill of the basin. In this context, fault zones and a fracture network have a direct effect on the recharge, and allow an upward vertical flow from the basement to the sedimentary aquifers. Hydrochemical and isotopic data support this observation. The use of fluoride (up to 15 mg/l) and nitrate (up to 217 mg/l) as tracers for the contribution of deep and shallow flow systems respectively provides a detailed portrait of the effects of pumping on the flowpath distribution. Isotopic data depict seasonal trends in groundwater captured by wells. Two distinct flow systems are differentiated: a regional, large-scale, long residence time system, originating in the surrounding ranges, and a local flow system constituted by infiltration in the lower areas of the basin. The two systems contribute differently to the resources that are withdrawn, and their specific contributions define the potential for sustainable future water exploitation in the basin. the final part of this hydrogeological study is a more specific description of the geochemical processes that determine the hydrochemical characteristics of groundwater across the selva basin, based on the interpretation of major, minor and trace elements (such as fluoride, bromide, lithium, toc, and their ratios to some major elements), and isotope data (18o-h2o, d, tritium,34s-so4,18o-so4). It defines two different regional flow systems and different water qualities of local recharge anduses this specific data to corroborates the overall hydrogeologic conceptual model for the selva range-and-basin area. From a methodological perspective, this chapter explores the use of minor elements and isotopes in the interpretation of regional scale system hydrodynamics. It also discusses their use as tracers of the distinct ground water flows originating in distinct recharge areas and influenced by an intricate tectonic setting. the results of this dissertation describe the flow system of the selva basin. In this basin, structural control defines the local, intermediate and regional flow systems responsible for the large-scale hydrodynamics of the basin and, more importantly, the recovery of drawdown after the main withdrawal period (summer). The origin of the recharge of the large-scale, regional flow systems is assigned to the transversal range on the northern side and to the guilleries range, especially in the western part. These hydrogeological systems include a groundwater flow within the basement and an upward vertical recharge from the basement to the overlying neogene sedimentary layers. The local and intermediate flow systems originate in the basin itself or in the less-elevated surrounding ranges, and the fault system has a minor effect on their flowpaths. Human development modifies the flow paths mixing the different flow systems and changing the water quality along the year seasons. from a broader point of view, this highlights the value of using different methodological insights in the study of these hydrogeological systems, as well as addressing the problem of water management in complex geological environments. First, it presents the outcome of various methodologies ranging from field work to numerical modeling, together with the analysis of hydraulic head, hydrochemical and isotopical data. Second, it shows the relevance of potentiometric evolution in different geological settings, and the treatment of the hydrochemical/isotopic features and related geochemical processes that define groundwater samples and therefore each of the recharge end-members (local, intermediate, and regional) that participate in the overall flow systems. Finally, it identifies the effect of human pressures even on large-scale flow systems, as true alterations of natural behavior. The recognition of these effects, together with an integrated characterization of the hydrogeological system, provides the necessary knowledge for formulating specific strategies for assessment focusing on sustainability of water resources management in these geological contexts. in specific terms, these strategies must be based on the importance of the groundwater flow terms in the water balance for a given hydrological basin. These terms are usually overlooked, yet they play an important role, especially when groundwater resources from deep confined (or leaky) aquifers are exploited. In the case of the selva basin, identifying this contribution is fundamental in establishing potential future exploitation rates that further socio-economic developments may generate. This dissertation shows the scope of several approaches to describing this term in the water budget in range-and-basin areas in order to determine the availability of water resources therein, as a first essential step towards sustainability.
Datos académicos de la tesis doctoral «Geological and human influences on groundwater flow systems in range-and-basin areas: the case of the selva basin (catalonia, ne spain)«
- Título de la tesis: Geological and human influences on groundwater flow systems in range-and-basin areas: the case of the selva basin (catalonia, ne spain)
- Autor: Albert Folch Sancho
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 07/06/2010
Dirección y tribunal
- Director de la tesis
- Josep Mas Pla
- Tribunal
- Presidente del tribunal: mike Edmunds
- giovanni María Zuppi (vocal)
- (vocal)
- (vocal)