Kárahnjúkar Hydroelectric Project, Hálslón Reservoir

The development of the Kárahnjúkar Power Station entails the harnessing of the glacial rivers Jökulsá á Dal and Jökulsá í Fljótsdal in northeastern Iceland. These rivers originate in the northeastern region of the Vatnajökull ice cap and run in a northeast direction through the Jökuldalur and Fljótsdalur valleys to their common estuary in the Héradsflói Bay.

The hydropower station will have an installed capacity of 630 megawatts, a harnessed flow rate of 126 cubic meters per second, and a power generating capacity of 4,450 gigawatt hours per year. The hydropower project involves the damming of the glacial river Jökulsá á Dal at Mt. Fremri Kárahnjúkar and the creation of the water storage reservoir Hálslón. Another small reservoir, Ufsarlón, will be created by damming the glacial river Jökulsá í Fljótsdal.

From the Hálslón reservoir, water is conveyed through an underground head race tunnel eastward and joins another tunnel from the Ufsarlón reservoir. The water is then carried in a single tunnel northeastward to the Teigsbjarg escarpment, where it drops through two steep penstocks to an underground powerhouse. There the water enters six generating units in the powerhouse and travels through a tailrace tunnel and canal into the course of the glacial river Jökulsá í Fljótsdal.