Gibraltar runoff: a steep challenge for decommissioning

Much of the British government's water supply in Gibraltar over the last century was achieved by fixing corrugated iron sheeting on steep sand slopes flanking the rocky peninsula to catch rainfall. However, introduction of desalination plant has rendered the massive catchments redundant. Over the past 30 years they had also started to become a liability, with large sheets becoming detached in high winds and two major landslides resulting from concentrated wetting of underlying sand. This paper describes the challenging design and construction of a decommissioning scheme for the east-side Ministry of Defense catchments, involving removing 13 ha of sheeting, installing 78 km of stabilising ground anchors, placing a temporary coir matting and seeding with indigenous plants—and all on a 250 m high, 34° slope.