Seite - 583 - in Book of Full Papers - Symposium Hydro Engineering

know the risks and the possible effects when operating reservoirs in this area of Peru. Recent research ([4], [5], [6] and [7]) shows an overall glacier loss of 46% between 1930 and 2016 with an increasing melting rate for the glaciers in the Cordillera Blanca based on climate change effects. In the present paper, the potential risk of ice blocks falling into a reservoir in the Andean region causing an impact wave, overtopping of the dam and provoking a dam break with significant damages downstream is analyzed. Eighteen glacier blocks with danger of detachment due to the melting and retreat of the glacier because of climate effects were identified based on a glaciological hazards analysis. Furthermore, adapted operation of the reservoir, which is located directly downstream of the Huantsán glacier, is presented. 2. INVESTIGATION ENVIRONMENT AND BASIC DATA The lagoon with a volume of 29 Mio m3 and a maximum depth of 90 m is located at the base of the snowcapped Huantsán glacier on the western slopes of the Cordillera Blanca at an altitude of 4,290 meters. The basin includes the Pariac creek and belongs to the province of Huaraz of the Ancash department (see Fig. 1). The ovoid-shaped reservoir corresponds to a very deep depression of glacier origin. The volume of the former glacier lake was augmented by the construction of an earth dam (HDam = 23 m) above the former moraine allowing a controlled operation of the lagoon. The 5.5 m wide crest of the dam is located at 4294.5 m.a.s.l. and covered with a concrete slab. The dam has a spillway with a fixed concrete overflow crest at 4290.88 m.a.s.l. and a width of 3.0 m. Fig. 1 Lagoon and Huantsán glacier (left; view from down- to upstream) and dam & spillway (right) Lagon et glacier de Huantsán (à gauche - vue de l'amont vers l'aval) et barrage et évacuateur de crue (à droite) The bottom outlet is located at 4271.00 m.a.s.l. and consists of a pipe running from the intake at the reservoir to the control house at the bottom of the dam. The rocky buttresses surrounding the reservoir correspond to the Chicama Formation (Js-ch), which consists of shales and fine sandstones, forming rather steep slopes, greater than 45 °. 583