Dolinas de colapso en el Valle de Alcedo (León): ¿un impacto geomorfológico/ambiental inducido por los Túneles de Pajares? Estudio preliminar Sinkhole development in Alcedo Valley (León): a geomorphological/environmental impact from Pajares Tunnels? A preliminary study

A section of the Pajares high speed railway tunnels were drilled over 450 meters depth below Alcedo Valley, in the Cantabrian Mountains (Leon, N. Spain). The tunnels cross a complex geological area characterized by an alternation of lithologies with very different mechanical and hydrogeological behaviours, some of which represent fractured and karstics aquifers. In 2009, Alcedo stream was canalized to avoid water infiltration. In the bottom of the valley, some subsidence and collapse evidences have been appearing from 2009 to present, also affecting the canal. The tunnels drainage after the excavation has caused the drop of the groundwater level in karstified Lancara limestone bedrock. This explains the development of sinkholes in the overlying quaternary fluvial and coluvial deposits, which work as infiltration areas of surficial water, drying up all the water of Alcedo stream. Now the process is active and it is predicted to continue progressing in the future.