Boletín de la RSEHN. Sección Geológica

La Sierra de Guadarrama guarda riquezas geológicas, geomorfológicas, hidrológicas, forestales, de fauna y de paisaje en general, que la hacen merecedora de pertenecer a la Red de Parques Nacionales de España desde 2013. Sus senderos, vías pecuarias, bosques, praderas y roquedos han sido transitados, desde hace más de siglo y medio, por un público cada vez más sensibilizado y cautivado por su rico patrimonio. Presta también unos impagables servicios ecosistémicos y de bienestar a la ciudadanía. Este artículo se detiene en el agua de sus ríos y en el agua subterránea que da lugar a sus manantiales. La red fluvial obedece a tres diferentes tipos de regímenes: pluvio-nival, pluvial y nivopluvial, y de morfología de los ríos: Moros, Eresma, Pirón, Cega, Guadarrama, Manzanares, Guadalix, y Lozoya. El artículo identifica hasta nueve posibles orígenes de los manantiales de la sierra vinculados a coluviones, fallas, diques, aluviales y terrazas, procesos glaciales, etc. El conjunto de recursos hídricos constituye un rico patrimonio hidráulico y arquitectónico (viaductos, puentes, molinos, azudes, batanes, pozos de nieve…) y de usos y costumbres como lo fue en su día las maderadas en el valle de Valsaín. Todo ello confiere a la Sierra de Guadarrama valores notables que requieren ser protegidos y dotarles así de una garantía de sostenibilidad ambiental que pasa por la formación y sensibilización de la ciudadanía.

The Guadarrama mountain range, situated very close to Madrid and Segovia – and with more than 6.5 million inhabitants-, is home to important geological, geomorphological, hydrological, forestry, wildlife and general landscape features, that make it worthy of being integrated into the Spanish Network of National Parks by the Law 7/2013 (Fig. 1). Students from grade school to university level are also using this entire natural heritage for educational purposes. Paths, trails, forests, grasslands, rocks and lands have been visited for over a century and half, by an increasingly aware public, captivated by its rich heritage. It also provides priceless ecosystem services and welfare to citizens. The geological uniqueness of the Park is due to its lithological constitution, composed almost exclusively of hard rocks (igneous and metamorphic with very low permeability), the development of landscapes characterized by granitic rocks and forms (La Pedriza), and glacial and periglacial modeling at high summits (Peñalara Lake). Its highest elevations and deep valleys are due to a combination of horst and graben (Figs. 2, 6). This article is devoted mainly to rivers and springs, that is, to blue water. The water quality is excellent both from the springs and from the upper basin of the rivers. The main meteorological characteristics have an average annual temperature of 6.9 ºC and an average precipitation of 1,220 mm/year (Figs. 3, 4, 5 and Table I). In addition, the water dividing line produces the existence of rivers that drain into the Duero basin on the northern slope, the Tagus in the southern part, provides the water necessary to support winter sport facilities relatively close to Madrid, and a large storage of solid water that feeds the rivers thanks to the snow regime. The river network obeys three different types of regimes: rain-snow, rain, and snow-rain that form the rivers of the Segovia slope; Moros, Eresma, Cega and Pirón; the Madrid slope; Manzanares, Guadalix, Lozoya and their tributary streams (Figs. 7, 8). Surface water collected in reservoirs is used to provide for more than six million people (Fig. 9 and Table II). These reservoirs are located at strategic points in a basin that takes advantage of a series of features like the impervious terrains, a significant rainfall, pristine waters, and a high altitude. This, in turn, facilitates water transport by gravity to the consumption points. This paper identifies nine possible origins of the Guadarrama mountain range springs (Fig. 10) linked to: colluvium, discontinuities and faults, dykes, foliation, alteration and weathering, alluvial formations, terrace deposits that break the permeability between lithologies, and finally, springs associated with glacial and periglacial processes. These springs are highly appreciated by visitors to the National Park. The entire set of water resources of the Guadarrama is has a rich hydraulic and architectural heritage (aqueducts, bridges, Fig. 11). This also includes water infrastructure whose remains can still be found today such as mills, weirs, snow storage wells and uses and customs like the maderadas in the Valsaín valley (Fig. 12). All this gives the Guadarrama mountain range features to be protected under the legal figure of The National Park Service to guarantee environmental sustainability in the future based on training and awareness of citizenship values.