The construction of a drainage tunnel as part of glacial lake hazard mitigation at Hualcán, Cordillera Blanca, Peru

Abstract

At Hualcán in the Cordillera Blanca is a high-altitude glacier lake dammed by a moraine. Local glaciers regularly produce ice avalanches. In 1988 it was confirmed that the moraine was ice-cored. The rate of melting of the ice was sufficiently fast that, unless mitigation measures had been undertaken rapidly, the moraine would have collapsed. This would have resulted in the inundation downstream of Carhuaz, a town with a population of 25000 people. Following the successful installation of siphons in 1988–89 to reduce the water level by 8 m, it was decided to undertake more permanent engineering works to ensure that the lake could never again pose a threat. It was proposed to construct a 2-m diameter tunnel, 155 m long beneath a rock bar below the moraine dam, to lower the lake level by a further 20 m. This would create sufficient freeboard to contain possible displacement waves.