Hydrogeomorphic impact of the Peñalén (Guadalajara) mines and spoil heaps on the Upper Tagus Natural Park

Abstract

The Peñalén municipality (Guadalajara Province) houses a series of derelict kaolin mines. The environmental impact of these mined lands upon the close Upper Tagus Natural Park is subject to constant discussion. This works shows a characterization of the geomorphic setting of the mines, as a main determining factor of the hydrological impact. In addition, an evaluation of the soil erosion rates of the Peñalén catchment was carried through RUSLE 1.06, to identify the main sediment sources. Additionally, sediment yield quantification was feasible from the evaluation of the stored sediments at a check-dam located at the the Peñalén catchment’s mouth. Finally, a descriptive analysis of the erosive landforms at these mined areas has been made both from field work and a combination of oblique aerial photos of different times. The higher erosion rates obtained by RUSLE 1.06 are: highwall (202.54 Mg ha-1 year-1); highwall’s debris slope deposits (87.55 Mg ha-1 year-1); outslope spoil heaps (86.12 Mg ha-1 year-1) and natural gullies (197.93 Mg ha-1 year-1). The quantification from the check-dam sedimentation offers a realistic value of the sedi-ments that are being emitted from the Peñalén catchment to the Tagus River (approximately 3200 Mg year-1). Finally, the geomorphic analysis from oblique aerial photos and field work shows that the outslope spoil heaps of Santa Engracia mine are the main source of sediments, in contradiction with the RUSLE 1.06. From these results, three evidences are noticeable: (i) the derelict mined areas of Peñalén are located in very vulnerable topographical positions to the hydric erosion; (ii) these mined areas are subject to very high erosion rates; (iii) there is a direct hydrological connection between the sediment sources of these mined areas and the Tagus River within the protected area, and therefore a permanent and severe ecohydrologic impact is taking place.