Búðarháls hydropower plant, 94 MWe

The project's objective

Early 2008 Landvirkjun decided to review and complete the project planning of the Búðarháls HPP, that until that time had been on and off its constructions' schedule. Notwithstanding the Icelandic financial crisis in late 2008, when all three major banks in Iceland went default, Landsvirkjun remained resolute in continuing and completing the project. Early 2010 preparation for tender started and contracts were signed late that same year. Búðarháls HPP was commissioned early March 2014.

Búðarháls HPP is the last power plant constructed in a cascade that harnesses mainly the catchment area of upper Þjórsá River and Tungnaá River. Búðarháls HPP harnesses almost 40 m head between Sporðalda Reservoir, which Hrauneyjafoss HPP tailwater runs to, and Sultartangi Reservoir, which Þjórsá River and Tungnaá River run into. Sporðalda Reservoir normal water level (NWL) is 337.0 m a.s.l. (meters above sea level) and Sultartangi Reservoir NWL is 297.2 m a.s.l.

The Búðarháls HPP rated capacity is 94 MW, with two 47 MW Kaplan turbines, and its output is 585 GWh per year.

About Búðarháls HPP

Búðarháls HPP comprises of a 7 km² reservoir, a 4 km headrace tunnel through Búðarháls Ridge that ends in a surge basin, a penstock intake that sits in the surge basin downstream end, and two penstocks that lead from the intake to the powerhouse. From there lies a tailrace into Sultartangi Reservoir.

Sporðalda Reservoir is sustained by two 26 m high earthfill dams and a 170 m long spillway with a crest height of 337.3 m a.s.l. Water on the spillway runs in a new riverbed that confluences with Tungnaá River. Complex diversion works were required during the construction period so the spillway and dams could be constructed with acceptable risk. Other civil works related to the Sporðalda Reservoir, and were part of the project where: i) elevation of Road 26, Sprengisandsleið Route, where it crosses Hrauneyjafoss HPP tailrace control structure, ii) Tungnaá River diversion canal including diversion spillway leading water from Tungnaá River into Sporðalda Reservoir when the river holds water, and iii) inflow improvement canal that enhances the flow between the north and south parts of the reservoir.

The headrace tunnel

The headrace tunnel is located in a rather complicated rock mass. In the eastern part of the Búðarháls ridge, the tunnel goes through prominent series of thick basalt layers, but towards the centre of the ridge, thick conglomerate formation become more frequent and at the western exit there is a rhyolite formation. The rock mass is also affected by hydrothermal alteration, that can be related to extinct volcanoes.

The headrace tunnel is elliptical in shape, with an cross-sectional area of 140 m², 14.7 m high, widest 11.3 m and has a bottom width of 9.3 m. The tunnel connects to the Sporðalda Reservoir with more than a 400 m long headrace canal. Upstream the tunnel portal is concreted with two bulkhead openings. The headrace tunnel opens into a surge basin, which has access through 100 m long horseshoe-shaped adit, 6 m high and wide. In the centre of the adit is a concrete open plug with a bulkhead door.

At the downstream end of the surge basin is the concreted penstocks intake, 33 m high. Each penstock intake is equipped with trashracks, bulkhead and wheel gates. Downstream of the wheel gates, two concrete embedded steel penstocks connect to the intake, with an inside diameter of 5.8 m.

Between the downstream wall of the intake and the upstream wall of the powerhouse are 52 m. 

The surface powerhouse

The Búðarháls HPP surface powerhouse is traditional, 56 m long and 40.2 m high measured from bottom of draft tubes to top of machine hall roof that is 15.6 m wide. The powerhouse is widest 27.1 m on the generator floor. The powerhouse contains two turbines and generator including accessory, protection and control equipment. Underneath the powerhouse roof are two 75 tons bridge cranes. Two divided draft tubes are equipped with bulkhead gates. Free passage is around the powerhouse. Between the machine hall and the draft tubes bridge are transformer stalls, both for unit and station transformers. From the powerhouse leads a buried high voltage cable to a substation almost 100 m west from the powerhouse.

The turbine manufacturer is Voith Hydro GmbH & Co. KG. Each turbine is rated 47 MW at net head 36,1, rate discharge 140 m³/s and rotation speed 166,67 rpm.

The generator manufacturer is VG Power (Sweden). Each generator is rated 52 MVA x 0,90, 11 kV ± 5% V, Y at rotation speed 166,67 rpm.

A 500 m long tailrace leads from the powerhouse into Sultartangi Reservoir.

EFLA's role

EFLA Consulting Engineers was the managing and main consultant of Landsvirkjun for the preparation and construction of the Búðarháls HPP.

Landsvirkjun decided that the Búðarháls HPP Civil Works where to be tendered in accordance with the tendering and contract conditions of FIDIC, Conditions of Contract for Construction (first ed. 1999), which required complete revision and reconstruction of Landsvirkjun tendering and contract condition that EFLA played big part in executing.

EFLA's major tasks in the Búðarháls HPP project were:

• Project Planning of Civil Works
• Supervision and main author of Design Memoranda in cooperation with Landsvirkjun and other consultants
• Tender Design of Civil Works
• Reconstitute Landsvirkjun tendering and condition of contract for hydropower projects Civil Works
• Review and recompose work specifications for hydropower projects Civil Works
• Works Scheduling
• Estimations of Cost
• Project Risk Assessments
• Occupational Health & Safety Assessment Series (OHSAS)
• Negotiation and contract support
• Detail design
• Design coordination
• Diverse consultancy during construction
• Dispute resolution consultancy
• Including divers minor consultancy e.g. lesser contracts, finalization, etc.