Natural drainage basins as fundamental units for mine closure planning: Aurora and Pastor I quarries

The vast majority of the Earth’s ice-free land surface has been shaped by fluvial and related slope geomorphic processes. Drainage basins are consequently the most common land surface organization units. Mining operations disrupt this efficient surface structure. Therefore, mine restoration lacking stable drainage basins and networks, “blended into and complementing the drainage pattern of the surrounding terrain” (in the sense of SMCRA 1977), will be always limited. The pre-mine drainage characteristics cannot be replicated, because mining creates irreversible changes in earth physical properties and volumes. However, functional drainage basins and networks, adapted to the new earth material properties, can and should be restored. Dominant current mine restoration practice, typically, either lacks a drainage network or has a deficient, non-natural, drainage design. Extensive literature provides evidence that this is a common reason for mined land reclamation failure. These conventional drainage engineered solutions are not reliable in the long term without guaranteed constant maintenance. Additionally, conventional landform design has low ecological and visual integration with the adjoining landscapes, and is becoming rejected by public and regulators, worldwide. For these reasons, fluvial geomorphic restoration, with a drainage basin approach, is receiving enormous attention. Its origin is the US SMCRA of 1977, followed by scarce but continued literature on the topic from the US, Canada, Australia and Spain. This literature claimed for the need of replicating the patterns and complexity that stable landforms have in natural catchments. However, that option has not been viable until the development of, still few, fluvial geomorphic design methods and software. This contribution summarizes the lessons learned from the application of one of them (GeoFluv-Natural Regrade) in Spain. Although the overall results are truly positive, two issues need attention: the stability of fluvial channels when additional runoff connects with designed channels and the difficulties for implementing the geomorphic designs as planned.