Karahnjúkar Hydroelectric Power Station

The Kárahnjúkar Hydroelectric Power Station is located in eastern Iceland. The plant produces electricity for Alcoa’s aluminum smelter in Reydarfjordur. Kárahnjúkar is the largest power plant in Iceland with a capacity of 690 MW. The plant harnesses two glacial rivers, and the complex comprises a 200 m. high concrete face rock-fill dam (CFRD) as well as several smaller rock-fill dams, 72 km of tunnels and an underground power station with six Francis turbines.


Kárahnjúkar Hydroelectric Power Station - Mannvit.is

Technical data:

  • Installed capacity: 690 MW
  • Turbines: 6 Francis units, vertical axis
  • Rated capacity: Discharge of 144 m³/s at a power of 690 MW
  • Gross head: Max gross head of 600 m.
  • Kárahnjukar dam: Length 700 m; height 198 m.
  • Water reservoir: Hálslon reservoir; 625 - 575 m.a.s.l.;
  • Storage capacity: 2100 million m³
  • Headrace tunnel: 40 km, ø7.2-7.6 m.
  • Other tunnels: 11 tunnels totaling 32 km in length, ø6.5-9.0 m.
  • Pressure shafts: 2 vertical pressure shafts; ø3.4 m; length 400 m.
  • Generating capacity: 4600 GWh year


  • Site investigation
  • EIA report
  • Civil works design of diversions (dams and tunnels)
  • Structural and mechanical design for diversions
  • Cost estimates for diversions
  • Tender documents and evaluation of tenders for diversions
  • Project planning
  • Site supervision of power station 
  • Testing and start-up
  • Commissioning
  • Pre-design and site supervision of the 400 kV transmission lines
Gross head
2100 million  m³ 
Reservoir capacity
4600 GWh 
Generation capacity

The plant is owned and operated by Landsvirkjun. Construction work at Kárahnjúkar began in 2003 until the Fljótsdalur Power Station reached full operational capacity in 2007. The River Jökulsá á Dal is dammed at Fremri Kárahnjúkar with the largest of the Kárahnjúkar dams. Two smaller saddle dams were built at Kárahnjúkar, Desjará dam to the east and Saudárdalur dam to the west. Together, the three dams form the Hálslón Reservoir which covers an area of 57 km². Kárahnjúkar dam is the tallest concrete-faced rockfill dam in Europe and among the largest of its kind in the world. In the powerhouse, which is located underground, the water drives six Francis turbines and then flows through a tailrace tunnel and canal into the river Jökulsá in Fljótsdalur.