Hydroelectric generation on the River Thjórsá
Preparatory work on new hydroelectric installations on the River Thjórsá below the Búrfell hydropower station has been in progress for some years. Three new hydropower stations are planned to harness the head down to sea level.
The most upstream project is the Hvammur Hydropower Project (HPP), then come Holta and Urridafoss HOPs. The Hvammur HPP will have an installed capacity of around 80 MW, and its power-generating capacity will be about 630 GWh/year. Its intake reservoir, named Hagalón, will be formed by a dam on the River Thjórsá above Minnanúpshólmi and dykes along the river's east bank. The powerhouse will be located near the north end of Mt Skardfjall, on land belonging to Hvammur Farm in the Landsveit district. The water will run through a 400 m headrace tunnel to the power plant, and then through a tailrace tunnel and later in an open canal back to the River Thjórsá below Ölmódsey.
Holt HPP will have an installed capacity of around 50 MW, and its power-generating capacity will be about 390 GWh/year. Its intake reservoir, named Árneslón, will be formed by damming the River Árnedkvísl near Akbraut in Holt, and by dykes in Árnes. A diversion system will be constructed at Búdarfoss, near Árnes, which will redirect most of the River Thjórsá into the River Árneskvísl. The powerhouse will be located at the end of the dam, close to Akbrautarholt. From there, a tailrace canal will run to a point below Árnesspord, mostly excavated in the river bed of the eastern branch of the River Thjórsá.
Urridafoss HPP will have an installed capacity of around 125 MW, and its power-generating capacity will be about 930 GWh/year. The plant's intake reservoir, Heidarlón, will be formed by a dam in the River Thjórsá at Heidartangi, and dykes along the river's west bank. The intake facility will be at Heidartangi, and the powerhouse will be located underground, close to Thórsártún. A tailrace tunnel will run from the powerhouse and out into the River Thjórsá below Urridafoss.