Enhancing water management by using glacial lakes: examples of opportunities and risks from deglaciated Cordillera Negra, Peru

Peruvian Cordillera Negra (8°40’ – 10°30’ S; 77°20’ – 78°30’ W) is characterised by dry semi-arid climate and a general lack of water, especially during the dry season (April – October). Numerous glacial lakes – remnants of the past glaciation of this currently glacier ice-free mountain range – thus represent an important water reservoirs. Glacial lakes sustain environmental flows during dry season, store water for grazing animals as well as simple agricultural irrigation. At the same time, climate change and socio-economic development drive increasing pressure on water resources in the region.

To further enhance potential of glacial lakes in water management, hundreds of glacial lakes of the Cordillera Negra have been equiped by damming structures in order to: (i) increase the volume of retained water; (ii) manage the outflow throughout the seasons of the year. Two general types of dams are distinguished: (i) traditional dams (built by local communities from stones, turf and clay); and (ii) modern dams (concrete or embankment earth- or rock-filled). While these dams help to retain water and the idea is promising, the implementation and dam management lag behind.

During the field visit conducted in 2019, many of the visited dams (both traditional and modern) were documented to leak through; attempts to retain as much water as possible also led to the intentional blocking of spillways, reducing dam freeboard to only tens of cm in some cases. In the worst case, these unacceptable management practices might result in dam overtopping or dam failure. Despite the uppermost part of the Cordillera Negra is not densely settled, some of the glacial lakes are located upstream mining areas, so that there is a risk of environmental pollution and contamination in case of flood. These observations suggest that glacial lakes can successfully be used in water mangement, however, they need to be managed properly and continuously.