Modelo y simulación hidrogeológica para la sostenibilidad del acuífero libre de los Montes Torozos

Resumo

The availability of water resources in equal quantity and quality for the required uses, has become the target milestone of any economic or social proposal for an entrepreneurship development. Under these assumptions, there has been lately different perception experiences concerning the evaluation of water resources and therefore a variety of management paradigms. This social change has allowed to propose new management scenarios, which be able to include more and different parameters such as: climate change, emerging contaminants, or virtual water. In this research, The Montes Torozos' aquifer has been characterized hydrogeologically, taking into account the typical parameters: precipitation, evapotranspiration, infiltration, groundwater level, permeability, transmissivity, inertia response, exhaustion curve, extractions, runoff, alpha coefficient. The recharge, inputs and outputs were summarized on a water budget. All of them contributed to the conception of an organizational model. Facing the conceptual model design, the recharge and drainage parameters, and their spatial placement, have been employed to archive the assessment of the resources and their reserves. On the other hand, the environmental characterization of the field workspace (physical and environmental characteristics, biota, socioeconomic issues, and, finally the landscape) allowed the computation of the used hydrological balance. The volume of water in Monte Torozos aquifer belongs to the Duero river watershed and goes through the provinces of Valladolid and Palencia (Castilla y León, Spain), occupying an area of 1000 km2. It extends between levels 750 and 880 m above sea level, and has got a population that exceeds 47000 habitants distributed in 57 municipalities. It is a region with an aged population, settlements have a low density and are far from each other, usually they located on the border of moorland or its slopes, close to the water springs. The mainly land uses historically are agriculture and Mediterranean forest, but in the last 60 years agriculture is the most extended. For this reason, it is addressed vulnerability integration, in relation to policy, specifically in risk evaluation and risk–benefit considerations focusing the requirements of the European Community’s Water Framework Directive 2000/60/EC and the Groundwater Directive 2006/118/EC. Contamination of groundwater is a complex process and full of uncertainty in regional scale. In fact, has been developed of an integrated vulnerability assessment methodology, that can be useful to effectively manage (including prioritization of limited resource allocation to monitor high risk areas) and protect this valuable freshwater source. A geographic information system (GIS) was established for the territorial analysis, together with hydrogeological and geostatistical simulation methodologies (the used software was the SpaceStat, 4.08). The results, allows their spatial analysis and visualization, as well as its evolution over the last 50 years. Land-use temporal evolution mapping was performed using a remote sensing based methodology, taking into account the aerial frames of the historical flights of 1956/59 and 1977/83 and CORINE (Coordination of information on the environment) Land Cover (1990, 2000 and 2006) as spatial information. Geomorphologically this moorland is a morph structural unit, that was originated by sedimentary process in the center of the Duero basin during the Tertiary, with a slight influence of the Neotectonics process. Montes Torozos is a karstic unconfined aquifer. This feature turns the aquifer particularly vulnerable to the emission of external pollutants. The vulnerability assessment was the preliminary and most important, to the estimation of the system’s susceptibility (extrinsic vulnerability) and vulnerability (intrinsic vulnerability). The international indices used were, for the intrinsic vulnerability assessment the DRASTIC and the susceptibility index (SI) for the specific vulnerability. The research insights suggest that the establishment of a pattern of effective governance is mandatory as the future highway, the prison and the airport are overlaying the most vulnerable areas of the aquifer and therefore provide policy makers guidance in overcoming urban water governance challenges. The obtained results indicates that the Torozos Limestone aquifer is unconfined and a hydrogeological isolated structure. It is a Messinian (Pontiense) subhorizontal limestone, slightly wedge shaped, with a slope of about two thousandths southwest. The main stream, which is built by the aquifer’s slope and thickening, has the same direction. Geologically, could be considered as a horizontal limestone strata laying on a detrital mixed formation of evaporate facies of the Facies Cuestas. The Facies Cuestas is the lower substrate formed by limestone and a series of soft clay loam-gypsum materials. The limestones are grey, hard and showing a microcrystalline structure in banks of varying thickness separated by marly intercalations. The area corresponds to a tectonic zone only modified by diagenetic fracturation, allowing the development of karst channels. The aquifer is included in the Watershed’s Management Plan 2009 like Body Water of Páramo de los Montes Torozos. Its overall thickness is approximately 6-10 meters, but can reach 30 meters promptly. The body water recharge’s system is primarily kept in line by the fracture network. A karstic fracturation system was adjusted simulating the sinkhole system alignments NE, SW and SE-NW. The alignment of the surface found on the moor allows that the water erosion and the river network drains the moor towards the SW and almost parallel and generating large valleys. Therefore, this preferential flow towards South-west has determined the course of the hydrographic network, likewise coherent by the fracture network. Direction. Drainage and piezometry parameters, together with the aquifer border conditions, have been subsequently embedded in a hydrodynamic flow model for which was used the software "Visual Modfow". The drainage network of this model is interactive, which facilitates its use as a management and planning tool in the development of a water resources system, based on an attempt/error methodology. To estimate the model's parameters of the aquifer has been used geostatistical methodologies, namely Gaussian kriging with backtransform, allowed the reconstruction of the moor's piezometric level, smoothing the outliers and a representation in the original variable unit. It was possible to distinguish two zones with different structural behavior in the aquifer. On the other hand piezometric level, extraction system and water spring distribution, allowed the aquifer behavior simulation such as flow steady and transient state. The results validated a dominant flow towards the SO. The hydrological budget is positive and allows to increase withdrawals without overexploitation risk. The recharged is directly due to rainfall and drawn by: a) hydrographic radial net, b) trickle drainage between limestone and clays, and c) pumping wells. The watershed shows an annual inertia of four months and a water renovation period of two years. The aquifer environmental characteristics are defined by its intrinsic characteristics as well as the anthropogenic activities. Montes Torozos' aquifer Shows high values of intrinsic and extrinsic vulnerability. Whoever is a highly vulnerable aquifer to pollutant discharges, mostly the ones from agricultural and livestock activities along the full surface of the moor. Together with the discharges of de-icing and anti-icing substances (typically road salt) and/or leaking fuel tanks along the N-601 constitutes the main hazards to forthcoming monitoring and control. There are physical and chemical water parameters exceeding the legal allowed limits. For this reason most of this water is unfit for human consumption, mostly due to the high nitrate concentrations, twice the maximum allowed in many places. Despite the existence of enough water volume it must be stressed its low quality since there are strong restrictions on its use and management. Being an unconfined aquifer is extremely vulnerable to direct emission of pollutants from topical and diffuse. The sustainability of the water body is good, primarily due to its high resilience and viability management. Validated models (quantity and quality) allow us to estimate the sustainability of current and potential uses of the system. The flow model calibration is fairly good. For this reason, model can be used for scenarios predictions for different management situations.. Sustainability has been achieved using the following indicators: the assurance of water resources available, the resilience of aquifer after pollutant episode, the vulnerability and risks of likelihood of contamination, the environmental integrity of system (legislation, evolution, cross-compliance, and spatial planning), the equity in water distribution, and the economic viability of extraction. Should be stressed that those variables are core topics in the vulnerability assessment and water quality classification. Hence the steps proposed aims the system’s conservation and special attention is needed on the monitoring of those variables related to the aquifer protection measures and risk minimization such as emission and/or others that could increase vulnerabilities therefore improving the accuracy for further feasibility solutions.