Síntesis hidrogeológica y modelización regional de la Cuenca Media del Tajo asistida por un SIG

Abstract

This work resumes the results obtained from the application of a numerical code for hydrogeologic modelization (NCHM) assisted through a Geographic information System (GIS) to an area of 20,952 km2 of the middle part of the Tajo basin; it includes both the tertiary basins of Campo Arañuelo and Madrid and the igneous-metamorphic massif until a depth of 5,500 m. The cities of Madrid, Toledo and Talavera de la Reina are located in the selected area and the Jerte fault and the confluence area of the rivers Tajo and Tietar constitute its westemmost part. The objectives of this work are for one side to study the problem related with the integration of several hidrogeologic formations of differentiated characteristics in one single model and for the other, to push forward in the regional knowledge from an integrated and multidisciplinary perspective. One isotropic and five anisotripic models were performed. In the anisotropic ones, the influence in the flow of the water of 3 different sets of fractures -N 105, N 142.5 y N 168.75- and a regional esquistosity of N 140, was considered. The calibration of the models rests upon both restored piezometric levels and the base yield of the hydrographic network. Different values of the calibrated parameters were obtained according to each model. The quality of the adjustments is acceptable; each one of the models shows a better adjustment respect the others in those areas where the features that are represented fix with those in the real system. The evolution of the permeability with the depth fix with the expected one, being kx/kz = ky/kz = 1, for the first 200 m and 0.1 for the rest. A calibrated recharge of 3 % of the precipitation was obtained for the tertiary, 2 % in the Guadarrama-Gredos system and 0.5 % in Montes de Toledo range. Information from different sources, either doctoral thesis or studies from ENRESA CEDEX, CHT and DGOH and the SIGMA project was integrated and contrasted to perform the model. The chosen confiuration ARC/INFO-IDRISIVISUAL MODFLOW has shown its usefulness and versatility to face the modelization of this area, which is characterized for its complexity and big extension.