Landsvirkjun is planning to build the Hvammur HEP, 95 MW hydroelectric project on river Þjórsá in the lower highlands of southern Iceland on the river Þjórsá approx. 100 km east of Reykjavík.
The area is inhabited rural area, mainly with farmhouses. The Hvammur HEP will harness the fall in Þjórsá river between 116 m a.s.l. to approximately 84 m a.s.l. The average river flow is 332 m3/s, rated discharge is 352 m3/s and the estimated installed capacity 95 MW.
Landsvirkjun is an independent legal entity owned by the Icelandic State.
Landsvirkjun in their project has conducted life cycle assessments. We systematically work towards reducing our carbon emissions, supporting Iceland’s commitment to the Paris Agreement, and responding to climate change-induced challenges and opportunities. We apply carbon pricing to fossil fuels, concrete in all major tenders for construction projects and evaluate offers based on both climate impact and cost. Tenderers must submit a plan for their planned/expected greenhouse gas emissions from fossil fuels and concrete used in the project.
In order to minimize disruption to the river ecosystem, construction in the river channel will be limited to a specific period of time each year. A fish ladder will be built to ensure upstream fish migration, and a juvenile fish bypass facility will also be constructed for salmon smolts migrating downstream.
The Hvammur HEP will be divided into several contracts, the biggest will be the Civil Works (HVM10).
The Civil Works main structures includes earthfill dams, spillway structures, fishways structure, headrace canal and intake structure, excavation and embedment for penstocks, access tunnel, powerhouse, surge basin, tailrace tunnel, tailrace canal, and associated works for the Hvammur Hydro-Electric Project in Iceland.
An overview of the main structures is provided below.
The Núpur dam will be divided into the Main Dam crossing the Þjórsá river, and side dam sections on the right and left bank of the Þjórsá river.
The dams will be earth fill dams. The dams create the Hagi reservoir. The main dam across the riverbed will be about 18 m high and 200 m long with impervious central core. Main fills for the dams are taken from required excavations from the powerhouse and spillway area, and the tailrace canal excavation. Core fill will be glacial till, filter material is taken from river sediments, and wave protection fills sorted from required excavations for the powerhouse and tailrace canal.
The Þjórsá river will be kept in its pathway throughout the period of main construction of the upstream gates and structures until the river will be diverted by cofferdams and training dikes through the fully operational spillway structures.
These are concrete gravity structures for three 12 x 9,5 m (w x h) spillway radial gates, and four 20 x 4,9 m (w x h) flap gates.
200 m long concrete fish ladder structure and a juvenile fish bypass facility comprising an intake weir and a concrete chute.
The headrace canal and intake structure includes excavation and rock supports for a 140 m long headrace canal. The structure will accommodate trashracks, bulkhead gates, and radial gates with hydraulic control. A gate equipment room will be located on top of the main structure.
The Penstock works includes surface excavation and associated rock support of about 190 m long and up to 30 m deep cutting through 3-8 m thick loose overburden overlaying rock and thin loose intermediate sediment layers into the underlaying bedrock. Also, construction of concrete foundations for first stage concrete at intake and powerhouse and second stage concreting.
The surface excavation for the powerhouse will be 63 m long, 37 m wide and up to 44 m deep, consisting of 3-5 m loose sediment into rock and loose intermediate sediment layers into the underlaying bedrock. The excavation will be rock supported, with shotcrete, rock bolts and other measures as needed.
The powerhouse will be a cast-in-place reinforced concrete structure. The main roof over the generators and erection bay will comprise pre-cast and pre-stressed double-tee cassettes with concrete topping and upside-down roofing on top.
A 2000m² surge basin will be excavated downstream of the powerhouse. The tailrace access tunnel is a 380 m long, adit tunnel to the tailrace surge basin and the tailrace tunnel as well as the powerhouse construction site. The tunnel is a conventional upside-down U-shaped tunnel, 7,5 m in width and height.
The tailrace tunnel will be about 1,2 km long. The tunnel cross-section will be up to 16 m by 12 m wide elliptical shaped 177 m2. The tunnel will be excavated mainly in base bedrock (hyaloclastite). The rock support will mainly be rock bolts, sprayed concrete and sprayed concrete ribs. Grouting of the rock mass is foreseeable.
The 2,0 km tailrace canal will divert water from the tailrace tunnel back to the Þjórsá river course downstream of Ölmóðsey island. The canal is excavated through scoria and basalt. The canal cross-section is up to 33 m deep by up to 27,0 m wide at the bottom.
