Kárahnjúkar HEP

By Richard High20 March 2008

The Kárahnjúkastífla dam will have a maximum height of 193 m and is constructed using 8,5 million m3

The Kárahnjúkastífla dam will have a maximum height of 193 m and is constructed using 8,5 million m3 of fill materials

First mooted 50 years ago the € 2,5 billion Kárahnjúkar Hydro-Electric Project (HEP) will harness the power of east Iceland's glacial rivers. However, the weather, a remote location, difficult geological conditions and intense media interest are proving formidable obstacles to delivering the project on time and on budget. Richard High reports.

Sitting in a site office with winds reaching 180 km/hour and temperatures well below freezing for a large part of the year may not be everyone's idea of the perfect working environment but for Richard Graham, chief engineer at Impregilo, it's just another day at the office.-

While Mr Graham concedes Impregilo hadn't really thought too much about the wind – “We concentrated on the cold” – it did mean using any kind of equipment, especially cranes, was “extremely difficult”.

“Winter, as you can imagine, is very severe, which means everything has to be covered and heated. You have to build a tent every time you do a concrete pour, for example. We did the face slab of the main dam in winter, which was quite an achievement,” said Mr Graham.

The remote location has also had a major impact on parts and labour. “Iceland is a small country in terms of its labour pool and resources. In Reykjavik you get the impression everything is there, but noone has any stock or spare parts so we made the decision early on to import everything.

“Wear and tear is no more than anywhere else, but things that you'd normally expect to buy locally just don't exist here. Those small workshops that can offer support services also don't exist, and if they do they are very, very expensive,” added Mr Graham.

Impregilo has had 36 different nationalities working at Kárahnjúkar. But because of the harsh working conditions and the fact its workers have to live in labour camps miles from anywhere, staff turnover was very high at the beginning. “But once we sorted out the personnel we really took off,” said Mr Graham.

Impregilo's four labour camps currently house around 800 workers, who go through 0,5 tonnes of food a day, all of which, like the construction equipment, has to be imported into the camps. And transport costs are high, again something Mr Graham said Impregilo hadn't anticipated.

Mr Graham told CE that almost 95% of its workforce is foreign, where normally he would expect that figure to be 5 to 10% on a project of this size. “The government wasn't keen on us doing this but Icelanders didn't want to work here because the economy is so strong.

“Some people thought bringing in foreign workers was a tax dodge,” he added, “with the result that we've even had TV cameras here filming us handing over cash to some of our workers.”

Contracts

At present there are almost 1800 men in total at Kárahnjúkar, which Mr Graham believes is one of the largest infrastructure projects currently under construction in Western Europe.

Work, which started in 2003 following an Environmental Impact Assessment in 2001, and the passing of legislation authorising the project in 2002, is currently expected to finish in 2009.

Earlier plans had proposed two separate developments to harness the Jökulsá í Fljótsdal and Jökulsá á Dal glacial rivers, both of which originate in the north-east of the Vatnajökull ice cap and run through the Jökuldalur and Fljótsdalur valleys to a common coastal estuary.

According to Sigurður St Arnalds, public relations manager at national power company Landsvirkjun, a project of this size would normally require two separate storage reservoirs.

However, Kárahnjúkar links both rivers, meaning only a single large reservoir, Hálslón, will handle seasonal storage for both.

Electricity generated at the Kárahnjúkar HEP will be transmitted to the Fjarðaál aluminium smelter being built in Reyðarfjördur on Iceland's east coast.

Access roads and other preparatory work began in late 2002, and a 40-year contract to provide power for the smelter was signed with US-based Alcoa in March 2003, allowing construction to start in the spring of 2003.

Impregilo won the lion's share of the project, the tunnels and the construction of the largest dam, Kárahnjúkastífla, in terms of value and size (55 to 60%).

Both contracts were won on a lowest bid basis and were awarded to Impregilo because no single Icelandic contractor was capable of undertaking the work.

“Each contract was awarded separately and the philosophy was that while some of the work was suited to Icelandic contractors, such as the earthworks, the buildings, access roads and the smaller saddle dams, two parts were too big for them to handle,” said Mr Arnalds.

While Impregilo is handling construction, supervision of the Kárahnjúkar dams and headrace tunnels is by a consortium from Iceland and France led by the UK's Mott MacDonald. The project also includes architects, engineers, designers and contractors from Switzerland, the US, Norway, Germany, Denmark, Austria and Hungary.

Natural Resources

Mr Arnalds told CE the key to the development of Kárahnjúkar lies in the region's topography and geographical conditions. In places extremely low-lying, the Fljótsdalur valley traverses the highland plateau north of Vatnajökull, creating ideal conditions for power production. As a result, said Mr Arnalds, the project will have a head of about 600 m.

“This is what makes the project so economical. We are using these natural resources to create an export industry. About 80% of the power will go to outside companies, mainly Alcoa, so power has become a major export because the electricity will be turned into aluminium, which is exported.

The installed power of the Kárahnjúkar HEP will be 690 MW. Maximum flow is 144 m3 per second, and the annual generating capacity is about 4600 GWh.

To generate this energy, the Jökulsá á Dal river is dammed by three dams at Fremri Kárahnjúkur. The largest, Kárahnjúkastífla, is located at the southern (upper) end of the Hafrahvammar canyon and is about 730 m long and 193 m high.

It 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 was quarried just upstream of the dam in what is now the Hálslón reservoir, and placed in compacted layers. During construction, the river flows through two diversion tunnels under the western bank of the dam.

Reservoir and Tunnels

Completing the trio of dams at Kárahnúkar are two smaller saddle dams. These are the Desjarárstífla to the east, and the Sauðárdalsstífla to the west. Both are rock-filled with an earthen core. All three will combine to feed the main 57 km2 Hálslón storage reservoir, which when full will have a water level 625 m above sea level and reach the edge of the Brúarjökull glacier.

It is expected Hálslón will be filled by late summer in most years. Surplus water will then be diverted through a spillway at the western end of the Kárahnjúkastífla dam down to the edge of the Hafrahvammar canyon, and from there via a 90 m-high waterfall to the canyon floor.

On the east side of the Snæfell mountain, the Jökulsá í Fljótsdal river is dammed about 2 km downstream of the Eyjabakkafoss waterfall on the north side of the Eyjabakkar wetlands. The intake pond this creates, the Ufsarlón, will also take water from three tributary rivers on the eastern side of the Jökulsá.

From the Hálslón reservoir, the water runs through a tunnel under the Fljótsdalsheiði moor to a junction with another tunnel running from Ufsarlón, and from there is carried north-east through a combined headrace tunnel to an intake at the Valþjófsstaðafjall escarpment. The total length of the headrace tunnels is 53 km, which vary in depth from 100 to 200 m.

Two steel-lined vertical pressure shafts will take the water from the intake to the underground powerhouse. Each shaft is 420 m high, and the total head of the project is 599 m.

“The creation of these two vertical shafts has been extremely difficult,” said Mr Arnalds, “not least because joining the steel sections is very critical. To overcome too much deviation the contractor first drilled a 1 m bore and then pulled a 4 m diameter rotary drill up from the bottom. The result was a bore that deviated less than 150 mm from top to bottom.”

The powerhouse will house six 115 MW Francis turbines, with water exiting via a tailrace tunnel and canal that will take it to the Jökulsá í Fljótsdal river at a point just east of Valþjófsstaðafjall, 26 m above sea level.

The total length of the tunnels involved in the project is about 73 km, with the headrace tunnels and parts of the access adit tunnels constructed using three full-face tunnel boring machines (TBMs). The remainder is being excavated by drilling and blasting.

“Water is the main problem in the tunnels,” said Mr Graham. “The other is the geological conditions, which slowed progress of one of the TBMs right down. We spent almost six months in one tunnel to advance just 70 m because of large cracks in the rock. There have also been lots of design revisions because it's a seismic area.”

Home Stretch

At the time of CE 's visit water had begun filling the Hálslón reservoir and electricity from the first generating unit had also started to flow. Most of the construction is on schedule, although the tunnels are a little behind due to the geological faults encountered.

Despite all these difficulties, and the added problem of one major contractor pulling out “at the last minute”, and no mobilisation period – “we signed the contract in February and spent most of 2003 mobilising and working at the same time, which meant doing things a little differently than normal” – Mr Graham told CE he would do very little differently.

“It's big, it's impressive, but it's all about logistics and supply, the actual work is a piece of cake,” he said.

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