Las aguas subterráneas del Parque Nacional de la Sierra de Guadarrama.

Abstract

The Guadarrama Range National Park covers about 1000 km 2 of the highest areas of this mountain range in the provinces of Madrid and Segovia. The most abundant lithologies are igneous and metamorphic rocks (hard rocks) except in the sedimentary basin in the High Valley of Lozoya. These rocks are practically impervious but can host small local, shallow and low-resource aquifers by processes of surface alteration, fracturing, and recent deposits of small size such as colluviums, alluviums, moraines and talus cones. Works on the tunnel for the high speed train that crosses beneath the Park, confirm the almost null permeability in depth but show the possibility of the existence of a deep flow through the set of discontinuities within the rock massif that may correspond to the model proposed by Toth in the 1960s. Limestone in the Lozoya basin give rise to a water table and karstic aquifer, which has been somewhat forgotten in previous hydrogeological studies, but it has water points with flow at rates of tens L/s. In spite of the poor water resources of hard rocks, local aquifers have played a significant role in the drinking water supply to localities in the area, enabling recreational activities with drinking fountains throughout the Park, supplying water to the livestock, and playing a key ecological role in maintaining water bodies during the summer. There are several springs of sulphurous waters resulting from deep groundwater flow, while the good quality water in the shallow aquifers has allowed the establishment of some bottling plants of natural mineral waters.