Landsvirkjun is preparing for the construction of three power plants in the lower section of the Þjórsá river, South Iceland.
Hvammur Power Plant
The installed capacity of Hvammur Power Plant will be approximately 82 MW, and its power-generating capacity about 665 GWh/year. The intake reservoir for Hvammur Power Plant, which will be named Hagalón, will be formed by a dam over Þjórsá river, situated above Minnanúpshólmi island, and by dykes along the east banks of the river. Located near the north end of Skarðsfjall mountain, on the estate of Hvammur farm in the Landsveit area, the powerhouse will be mostly underground. A headrace tunnel some 400 m long will lead from the intake structures at Hagalón to the power station, from which the water will run through an underground tunnel and subsequently an open ditch to Þjórsá river, below Ölmóðsey island.
Holt Power Plant
The installed capacity of Holt Power Plant will be approximately 53 MW and its power-generating capacity about 415 GWh/year. The intake reservoir of Holt Power Plant, to be named Árneslón, will be formed by a dam over Árneskvísl river, situated by Akbraut farm in the Holt area, and by dykes on Árnes peninsula. At Búðafoss waterfall, above Árnes peninsula, diversion structures will be built to divert the main part of Þjórsá river into Árneskvísl river. The powerhouse will be located at the end of the dam, by Akbrautarholt farm, with a tailrace canal that will lie from there to below Árnessporður point and be excavated for the most part out of the east branch of the Þjórsá river.
Urriðafoss Power Plant
The Urriðafoss Power Plant will have a capacity of approximately 130 MW and a power-generating capacity of some 980 GWh/year. The intake reservoir for this power plant, which will be named Heiðarlón, will be formed by a dam over the Þjórsá river, situated at Heiðartangi point, and by dykes lying along the west banks of the river. The intake structures will be at Heiðartangi point and the powerhouse will be underground, near Þjórsártún farm, while the tailrace tunnel leading from the powerhouse will open out into Þjórsá river somewhat below Urriðafoss waterfall.
Environmental impact assessment
In 2003, an environmental impact statement on power development in Þjórsá river at both Urriðafoss waterfall and Núpur mountain was submitted to the Icelandic Planning Agency for its ruling. Two alternative proposals were submitted for harnessing the Þjórsá river at Núpur: one was to harness a head of 56 m in one power station, Núpur Power Plant, while the other was to harness a head of 50-52 m in two power stations, Hvammur Power Plant (with a head of 32–34 m) and Holt Power Plant (with a head of 18 m). Landsvirkjun has now abandoned the idea of power development at a single level and intends to build Hvammur Power Plant and Holt Power Plant, in addition to Urriðafoss Power Plant farther downstream.
Ruling by the Planning Agency and Minister for the Environment on hydropower development of the Þjórsá river at Núpur mountain
On 19 August 2003, the Planning Agency issued a ruling on the environmental impact assessment regarding power development on Þjórsá river at Núpur mountain. The Agency's conclusion was to accept the proposed project, based on the proposals presented in the environmental impact statement, as well as the modification of Búrfell Line 1, but with several conditions. On 27 August 2004, the Minister for the Environment confirmed the Planning Agency ruling, adding a number of conditions:
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In consultation with the concerned land owners and local authorities, the developer shall restore wetlands in South Iceland that are at least equal in area to the wetlands disturbed or affected by the proposed construction. The developer must consult the Environment and Food Agency on the wetlands restoration plan prior to the beginning of construction.
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In consultation with the Soil Conservation Service and the Environment and Food Agency, the developer shall prevent sand from blowing in sandy and muddy areas that dry up as a result of the project.
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The developer shall monitor wave erosion and the depletion of plant cover on the shores of the reservoir throughout the operating period of the power plant, consulting with local authorities, the Environment and Food Agency and the Soil Conservation Service in regard to mitigating measures if they are needed. Prior to the start of construction, the developer must consult the Soil Conservation Service and the Environment and Food Agency on the monitoring plan.
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Prior to the start of construction, the developer shall conduct the supplementary studies on baseline conditions of the Þjórsá river biota that were proposed in the scientific report by the Institute of Freshwater Fisheries on the biota of the river and are outlined in Section 4.3.3 of the Planning Agency ruling. Based on the results of these studies, the developer shall further elaborate and implement the mitigation measures proposed in the aforementioned scientific report by the Institute of Freshwater Fisheries. When construction has been completed, the developer must follow the monitoring proposals presented in the scientific report and outlined in Section 4.3.3 of this ruling. Monitoring shall proceed for at least 10 years after the power plants have entered into operation. Further research studies, mitigation measures and monitoring procedures must be presented to and carried out in consultation with the Institute of Freshwater Fisheries.
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The developer shall comply with the mitigation measures proposed by the Archaeological Heritage Agency regarding the impact on each and every archaeological site mentioned in Section 4.2 of the Planning Agency ruling. In consultation with the Archaeological Heritage Agency, the developer must sponsor investigations into archaeological remains in the areas affected by roads, tracks, construction camps and the power line before starting any construction, and must comply with any mitigation measures proposed by the Archaeological Heritage Agency regarding archaeological remains in these areas.
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While designing the power plant, the developer shall have a risk assessment carried out to demonstrate that the local risk for people in the area will not be higher per year after construction than that considered acceptable in relation to avalanches and landslides.
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The developer shall fence off both banks of the river channel as needed and post warning signs at appropriate points in order to reduce risks due to sudden increases in flow. Sound alarm equipment shall also be installed to indicate when the dam gates are being moved for this purpose.