Drainage network evolution and reconstruction in an open pit kaolin mine at the edge of the Alto Tajo natural Park

Abstract

Landform instability of the abandoned Nuria kaolin mine, surrounding the Alto Tajo Natural Park in Spain, has caused frequent and severe environmental impacts due to deficient mining practices, environmental mismanagement and closure planning. Geomorphic instability has caused widespread soil erosion and elevated sediment yields with off-site effects. We quantified such land instability, the evolution of the resulting drainage networks and catchments, and ensuing gully processes. High Resolution Topography sources were compared with historic maps and photos. The current mine rehabilitation practices are depicted based on a geomorphic approach that introduces a sustainable drainage system designed to avoid detected risks. Our aim is reconstructing fluvial channels and related hillslopes that mimic their natural counterparts adapted to a rehabilitation of pre-existing gradient terraces. We demonstrate that: i) mining activity produced a 31–58% decrease in the original site drainage network ii) a post-mining active advancing gully is an indicator of drainage network redevelopment advancing toward an upstream pond with flash-flooding risk; iii) a geomorphic designed and constructed fluvial network and proper drainage density adapted to pre-existing gradient-terraces seeks reestablishing stability; and iv) in absence of sufficient funding for rehabilitation, public/private collaboration agreements play an important role to reinstate landscape stability of abandoned or erroneously restored mines.