Iceland's hydro tunnel bonanza

The final decision on whether to build the 630MW Kárahnjúkar hydroelectric powerplant in Iceland will be made next month according to an official spokesman for the state-owned power company Landsvirkjun. The project will include the boring of some 65km of tunnels.

Discussions for the much debated project are currently ongoing between the government of Iceland, Landsvirkjun and the US-based aluminium producer Alcoa.

With the bid closing date on the 28th November, tenders for the massive tunnelling construction contract have been invited from: Impregilo; Balfour Beatty Major Projects; a consortium comprising NCC International, Hochtief, and Icelandic Prime Contractors; and a consortium including Pihl & Son, Istak (Icelandic) and Vinci Construction.

The successful tunnelling bid should be announced at the beginning of February 2003, when it is hoped the contract will be signed between Landsvirkjun and Alcoa.

A 190m high, 750m long rockfill dam will be built on the Jökulsá á Dal, along with two smaller saddle dams, to create a 57km² Hálslón reservoir that will extend 27km. The 1km² Ufsarlón reservoir will be created with a 32m high, 675m long dam on the Jökulsá í Fljótsda river to regulate flows from the Hálslón.

A 40km long, 7m diameter headrace tunnel will carry water from the Hálslón to a valve chamber and pressure shafts located above the underground powerhouse in the Fljótsdalur valley. The two pressure shafts will be steel lined, and a surge tunnel will be located off the headrace tunnel about 100m upstream of the pressure shafts.

Road construction is already underway, ready for drill and blast adit construction to begin in April 2003. If the project is green-lighted, as expected, it is thought that the tunnels could be completed by September 2006.

The project cost will be some US$1bn, with the construction of the dams and tunnels taking up around 60% of the total.

The majority of the headrace tunnel, and some of the other 25km of tunnels, will be constructed using hard rock TBMs, while the rest will be by drill and blast through the rock, a basalt lava, similar to that found at Lesotho, Africa.

The successful contractor will be responsible for purchasing the TBMs, and will be consulted on the final design of the tunnels.

The project has been designed to supply power to an aluminium smelting plant in Reydarfjordur and has been seen as an important move for Iceland away from its dependency on the country's traditional fishing industry.

Related Files
The planned route of the headrace tunnel from the 57km2 Halslon reservoir to the Karahnjukar hydroelectric powerplant in Iceland