Wednesday March 3. 2004

More than half a century has passed since the idea of harnessing the power of some of east Iceland’s great glacial rivers was first raised, and it is now almost three decades since proposals were first made for the introduction of power-intensive industry to the region. With the coming of the Karahnjukar project, both are now a reality.

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 both rivers simultaneously and linked together. This means that a proposed reservoir at Eyjabakkar could be omitted, and that a single large reservoir, Hálslón, handles the seasonal storage for both rivers.   

An extensive Environmental Impact Assessment (EIA) on the Kárahnjúkar hydropower project was completed in 2001. Following a final positive ruling by the Ministry for the Environment, legislation authorising the project was passed with a sizable majority by the Icelandic Parliament, the Althing, in 2002. Later the same year, the Ministry for Industry issued the necessary permit, and the local municipalities concerned then issued a construction permit in February 2003. 

 
Electricity generated at the Kárahnjúkar power plant will be transmitted to the Fjarðaál aluminium smelter, which will be built in the port of Reyðarfjörður 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 US multinational Alcoa in March, 2003. Once the contract had been signed, building work on the Kárahnjúka

Project arrangement and construction

The dams
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. In places extremely low-lying, the Fljótsdalur valley traverses the highland plateau north of Vatnajökull, creating ideal conditions for power production. As a result, the project is based on a head, or drop, of about 600 metres. 
The installed power of the Kárahnjúkar project is 690 MW, produced in six generating units.

Maximum flow is 144 m3 per second, and the annual generating capacity is about 4,600 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 metres long and 193 metres high.

The structure is of the concrete-faced rock fill dam (CFRD) type, 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 quarried just upstream of the dam in the reservoir area, and is placed in compacted layers. During construction, the river flows through two diversion tunnels under the western bank of the dam. 

The reservoir
Completing the trio are two smaller saddle dams which will also be built at Kárahnúkar. These are the Desjarárstífla dam to the east, and Sauðárdalsstífla dam to the west. Both will 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 625 metres 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 Kárahnjúkastífla dam down to the edge of the Hafrahvammar canyon, and from there via a 90 metre-high waterfall down to the canyon floor.

 
On the east side of the mountain Snæfell, 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 has been named Ufsarlón, and water from three tributary rivers on the eastern side of the Jökulsá is also diverted into it. 

The tunnels
From the Hálslón reservoir, the water runs through a tunnel under the Fljótsdalsheiði moor to a junction with another tunnel running from the Ufsarlón pond, 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, and they vary in average depth from 100-200 metres. 

 
Two steel-lined vertical pressure shafts lead the water from the intake to the underground powerhouse. Each shaft is 420 metres high, and the total head of the project is 599 metres. The powerhouse houses six Francis turbines, each with a rated output of 115 MW. When water exits the powerhouse, a tailrace tunnel and canal take it to the course of the Jökulsá í Fljótsdal river at a point just east of the farm Valþjófsstaður, which lies at a height of 26 metres above sea level. 
The total length of the tunnels involved in the Kárahnjúkar project is about 73 km.

The headrace tunnels and parts of the access adit tunnels will be drilled using three full-face (TBM) boring machines, while the remainder will be excavated by drilling and blasting. Each TBM machine requires about 3 MW of electricity to drive it, and the crushed rock the drills produce will be transported on electrically driven conveyor belts to disposal areas near the adits. The estimated average rate of drilling for each machine is about 25 metres per day. 

Water will begin filling the Hálslón reservoir in September 2006. Electricity from the first generating unit will begin to flow in April 2007, and the project is scheduled to be fully completed in 2009.