Lawrence Williams reports on the current state of play at the construction of Iceland’s Kárahnjúkar hydro power project
A remote wilderness region of eastern Iceland is the scene of the Kárahnjúkar hydro power project, Europe’s latest major hydro scheme expected to cost around US$1.4B. It involves the construction of one large dam and several smaller ones, some 73km of tunnels, what are thought to be the world’s deepest steel lined vertical pressure shafts and an underground power plant housing six Francis 115MW turbines.
The power plant is being constructed by Fosskraft, a consortium led by Hochtief of Germany, and also including E. Pihl of Denmark and two Icelandic groups, Istak and Íslenskir adalverktakar, while the main Kárahnjúkar dam and tunnels are being constructed by Impregilo of Italy.
Contracts for the two smaller saddle dams went to Icelandic contractor Sudurverk, while the dam contracts for the eastern extension of the project are still to be awarded. The client is Iceland’s national power company, Landsvirkjun.
Landsvirkjun was established on 1 July 1965 to step up the harnessing of hydro power through the development of power intensive industries as well as meeting rapidly growing demand from the ordinary market. Initially owned jointly by the city of Reykjavík and the Icelandic state, its task was to supply electricity to the south and west of Iceland.
A new law was enacted in 1983, entrusting it with the task of supplying electricity to the whole of Iceland. In the same year, Akureyri – the largest town in north Iceland – acquired a share in the company. Present ownership is divided between the state, which has 50%, Reykjavík which has 45% and Akureyri with 5%.
Landsvirkjun produces, distributes and sells wholesale electricity to local public utilities and, under special agreements, to power intensive industries as in this case. Its task is to promote the greater use of Iceland’s hydroelectric and geothermal energy resources (there are no fossil fuel power plants in the country) and ensure that electricity supply is always sufficient to meet demand.
The Kárahnjúkar hydro power project is economically viable as the bulk of its power output is to be purchased under a long term, 40 year agreement by US aluminium giant Alcoa for the new Fjardaál aluminium smelter it will build in the fjord of Reydarfjördur on the east coast, which will generate hundreds of jobs and provide a major boost to the economy of the region.
The idea of harnessing the power of some of east Iceland’s great glacial rivers was first raised over half a century ago, and it is now almost thirty years since proposals were first made for the introduction of power intensive industry to the region.
Earlier plans proposed two separate developments to harness the Jökulsá í Fljótsdal and Jökulsá á Dal glacial rivers, both of which originate in the north-east segment of the Vatnajökull ice cap and run through the Jökuldalur and Fljótsdalur valleys to a common estuary at the coast.
While a development of this type would have required two separate storage reservoirs, one in the Eyjabakkar wetland area in the east, and one at the more westerly Háls area, the project currently under construction includes harnessing the hydro potential of both rivers simultaneously by linking them together. This means that the proposed reservoir at Eyjabakkar could be omitted, and that a single large reservoir, Hálslón, will be used to handle the seasonal storage for both rivers.
An extensive environmental impact assessment on the Kárahnjúkar project was completed in 2001. Following a final positive ruling by the ministry for the environment, legislation authorising the project was passed with a sizeable majority by the Icelandic parliament, the Althing, in 2002. Later that year, the ministry for industry issued the necessary permit, and the local municipalities concerned issued a construction permit in February 2003.
Yet there has been environmental opposition to the project. The Icelandic Nature Conservation Association (INCA) and three other plaintiffs challenged the environment minister’s decision to allow the project to go ahead, firstly in the Reykjavik District Court and then in the Supreme Court when its initial challenge was rejected. Subsequently, in January this year, the Icelandic Supreme Court ruled in favour of Landsvirkjun and the final project hurdle was overcome.
Some of the environmental reporting on the project, including the despoliation of a previously unspoilt area and the destruction of local flora and fauna, appears to be misleading. The area in question is only a fraction of the relatively barren wilderness area in the region and it is felt that there will be no lasting damage to the sparse local wildlife, while much of the ground to be covered by the reservoirs is not covered by vegetation.
As for the construction itself, the major facilities will be underground, while temporary access roads will be returned to their natural state once the project construction is complete. Few people have visited this difficult-to-access region in the past, but tourism is now likely to increase given that vehicular access will be vastly improved by the new permanent road.
Electricity generated at the Kárahnjúkar power plant will be transmitted to the Fjardaál aluminium smelter, which will be built at Reydarfjördur on Iceland’s east coast. Road construction and other preparatory work began in the second half of 2002, and a 40-year contract to provide power for the plant was concluded with Alcoa in March 2003. Once the contract had been signed, the major construction work on the Kárahnjúkar dam and associated works was able to proceed.
The Fjardaál smelter is being designed to be one of the most environmentally friendly and competitive aluminium production facilities in the world. It will have an annual capacity of 322,000t and is expected to cost US$1.1B over the next four years. The smelter will also be supported by the construction of a new harbour facility at Mjoeyri by the Fjardabyggd Harbour Fund. The combined project is the most extensive investment ever undertaken in Iceland.
The key to the economical development of the Jökulsá í Fljótsdal and Jökulsá á Dal glacial rivers lies in the region’s topography and geographical conditions. The Fljótsdalur valley, which traverses the highland plateau north of Vatnajökull, is extremely low-lying in places, creating ideal conditions for power production. As a result, the project is based on a head of about 600m.
The installed capacity of the six generating units at Kárahnjúkar will be 690MW. Maximum flow will be 144m3/sec, and the annual generating capacity is to be about 4600GWh.
To generate this energy, the Jökulsá á Dal river is being dammed by three dams in the vicinity of Mt. Fremri Kárahnjúkur. The largest, the Kárahnjúkar dam itself, is located at the southern (upper) end of the Hafrahvammar canyon and will be about 730m long and 193m high.
The structure is a concrete faced rock fill dam and, when complete, will be the highest of its kind in Europe and among the highest in the world. The rock fill used in its construction is being quarried just upstream of the dam in the reservoir area, and is being placed in compacted layers, currently by truck, but there will also be an overland conveyor delivering crushed and screened material for the dam.
The concrete face will be constructed in 15m wide panels by slip forming. The spillway is an engineering challenge due to the high head. The high head is also an engineering challenge for the various hydraulic gates in the project.
During dam construction, the river is being diverted through two tunnels under the western bank of the dam. These diversion tunnels have already been completed so main dam construction is now under way and, at the time of writing almost 400,000m3 of the 8.5Mm3 of rock fill has already been placed.
Completing the trio are the two smaller saddle dams, which will also be built at Kárahnúkar. These are the Desjarár dam to the east, and Saudárdals dam to the west. Both will also be rock-fill dams with an earthen core, and together the three will combine to feed the main 57km2 Hálslón storage reservoir. When full, its water level will reach a height of 625m above sea level, and its shores will reach the edge of the Brúarjökull glacier.
It is estimated that the Hálslón reservoir will be filled by late summer in most years. Surplus water will be then diverted through a spillway chute at the western end of the Kárahnjúkar dam down to the edge of the Hafrahvammar canyon, and from there via a 90m-high waterfall down to the canyon floor.
On the east side of Mt. Snæfell, the Jökulsá í Fljótsdal river is to be dammed about 2km downstream of the Eyjabakkafoss waterfall on the north side of the Eyjabakkar wetlands. The intake reservoir this creates has been named Ufsarlón, and water from three tributary rivers on the eastern side of the Jökulsá is also diverted into it (the Jökulsárveita diversion). Most of the diversion will be conveyed by tunnel. The dam in the Kelduá river is the largest at 26m high, and will change Folavatn lake into an 8km2 reservoir. Other dams belonging to the diversion are much smaller and surface disturbance will therefore be slight.
Tunnels and shafts
From the Hálslón reservoir, the water runs through a headrace tunnel under the Fljótsdalsheidi moor to a junction with another tunnel running from the Ufsarlón reservoir, and from there is carried north-east through a combined headrace tunnel to an intake at the Valdjófsstadafjall escarpment. The total length of these headrace tunnels is 53km, and they vary in average depth from 100–200m. The headrace tunnel junction represents something of an engineering challenge as the water heads from each reservoir could be at different pressures.
Two steel lined vertical pressure shafts (thought to be the world’s deepest steel lined shafts) will lead the water from the intake to the underground power house. Each shaft is 420m deep, and the total head of the project at this point is 599m. The power house will contain six Francis turbines, each with a rated output of 115MW. When water exits the power house, a tailrace tunnel and canal will take it back to the course of the Jökulsá í Fljótsdal river at a point that lies at a height of 26m above sea level.
Landsvirkjun signed a contract with va-tech Escher Wyss GmbH for the power house electromechanical equipment in January this year. The contract is for the design, manufacturing, testing, delivery, erection and commissioning of the six generating units including all accessories. Site installation will start in early 2005 and the first unit is scheduled to start operation in April 2007. The contract amount is US$8.6M, inclusive of value added tax. Another German company, DSD Stahlbau, will supply the steel linings for the two pressure shafts.
The total length of the tunnels involved in the Kárahnjúkar project is about 73km. The greater part of the headrace tunnels and parts of the access adit tunnels will be bored using three full-face tunnel boring machines (TBMs) supplied by US hard rock TBM specialist Robbins, while the remainder will be excavated by drilling and blasting. Each TBM requires about 3 MW of electricity to drive it, and the crushed rock the machines produce will be transported on conveyor belts, supplied by Continental Conveyor, to disposal areas near the adits. The estimated average rate of boring for each TBM is about 25m per day. Two of the machines are fitted with 7.2m diameter cutterheads and the third a 7.6m diameter head.
State of play
With the Fljótsdalur valley access tunnel rapidly reaching its full length, attention has already begun to turn to the area deep in the Valthjófsstadarfjall mountain where blasting work will soon begin on the massive cavern which will house the power house and transformer room for the project. Work on the Fljótsdalur cable tunnel has continued to proceed slowly due to the need to reinforce the rock face.
Elsewhere on the site, the first TBM has reached the mouth of adit 3, and work is now in progress on connecting its component parts, which include a workshop, canteen and other facilities. The last piece of equipment to be installed will be the conveyor belts from Continental Conveyor which will be used to remove rubble from the tunnel, and boring operations were set to commence after Easter.
Icelandic transport company Landflutningar-Samskip completed delivery at the beginning of April of the second of the three TBMs which will be used, and work will shortly commence on the construction of the prefabricated hangar/workshop which will house the unit during its construction at adit 2 near the Axará river. Total weight of the load which made the134km journey in a convoy by road from the port of Reydarfjördur was 1000t, with the largest single piece weighing in at an impressive 67t.
At the time of writing, the third and final machine was due to come onshore at Reydarfjördur on 18–20 April, and will be transported in the same way to its site at the Teigsbjarg escarpment in the Fljótsdalur valley.
While the main headrace tunnel from the Kárahnjúkar dam will be bored at 7.2–7.6m, the Jökulsá tunnel from the smaller Ufsarlón reservoir will only be bored at 6.5m diameter and one of the TBMs will have to be altered at the end of its first drive to undertake this task.
The balance of the tunnels will be driven by drill and blast. The headrace sections will be part of the Impregilo contract, while the power station area tunnels are being constructed by the Fosskraft joint venture. Both contractors are primarily using Sandvik Tamrock computerised Axera drill rigs manufactured in Finland. Currently the Fosskraft tunnels are running well ahead of schedule with completion now planned for the end of 2004 rather than the originally planned first half of 2005.
At the time of writing, the contract KAR-21 for the excavation of a 3.4km drill/blast section of the Jökulsá tunnel at 6m in diameter, and construction of the Ufsarlón power intake and the intake canal was out for bidding with a deadline for bid receipt of 4 May.
Water is due to begin filling the Hálslón reservoir in September 2006. Electricity from the first unit will be generated in April 2007, and the project is scheduled to be fully completed in 2009.
Lawrence Williams is a technical writer based in the UK.
The writer would like to thanks, in particular, Sigurdur Arnalds of Landsvirkjun for checking the data in the article and helping with illustrations and photographs. Much of the article is based on material drawn from the extremely comprehensive Landsvirkjun and Karahnjukar websites and permission to use this data is acknowledged.