Iceland is the country with the highest renewable energy quotas in the world (as much as 99%), with a huge quota generated by hydroelectric sources (80% of the available electricity).

The project for the exploitation of the water resources in the area near Mount Karahnjukar covers the northeastern plateaus of Iceland, some 300 km from Reykjavik, Iceland's capital, and less than 200 km from the Arctic Circle. Its implementation was made possible thanks to the collaboration between the Icelandic government and the aluminum multinational Alcoa: after being approved by a popular referendum, the project entered its operational phase in 2003, and a contract was awarded to Salini Impregilo for construction of the dam and diversion tunnel.

The work includes a concrete-faced rockfill dam, the tallest in the Nordic regions and the first European one of the rockfill type. The glacial waters from the Jökulsá a Dal river are collected into the reservoir of Halslòn, and diverted to an underground power station with an headrace tunnel almost 40 km long that took three Tunnel-Boring Machines to excavate. The dam is 193 m high, with a crest length of approximately 730 m and a rockfill volume of 8.9 million m³.

The river diversion works comprise two tunnels with lengths of 764 m and 845 m respectively, excavated using traditional methods. The bottom outlet consists of a 60 m high, 5 m diameter surge shaft, discharging into one of the two diversion tunnels.

The headrace tunnel is approximately 40 km long, of which a section of 35.3 km excavated using three full-face TBMs, two with a diameter of 7.20 m and the third with a diameter of 7.60 m; the remaining 3.7 km section was excavated with traditional methods. Additionally, three adits were excavated, as well as a secondary headrace tunnel and drainage tunnel (overall length 16.6 km) and two valves chambers for a total volume of 13,425 m³.

Client: LANDSVIRKJUN – Iceland’s National Power Company