The Tamega River hydropower complex is being developed on the Tamega River in northern Portugal, by Iberdrola Generación.

The project is part of the Portuguese National Programme for Dams with High Hydroelectric Potential (PNBEPH), which was approved by the Government of Portugal in 2007.

Iberdrola won the concession from the Government of Portugal to develop four dams namely Gouvães, Daivões, Alto Tâmega and Padroselos at an estimated total cost of €1.5bn ($1.74bn) in January 2009. Padroselos dam was, however, reproved by the PNBEPH in 2012.

The Tamega River hydroelectric complex will comprise three dams named Gouvães, Daivões and Alto Tâmega with a capacity of 880MW, 118MW and 160MW respectively. It will have a gross capacity of 1.158GW and an operational life of 65 years.

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The estimated construction cost of the Gouvães dam is €80m ($93m), while that of Daivões dam is €90m ($105m) and that of Alto Tâmega dam is €110m ($128m).

Construction work on the Tamega River hydroelectric complex began in 2015. The Gouvães dam is expected to be operational in 2021, followed by Daivões dam in 2022 and Alto Tâmega dam in 2023.

The annual generating capacity of the project is estimated to be 1,760GWh, which will add up to 6% to the total electricity production of Portugal.

The Tamega River hydroelectric complex will electrify 300,000 Portuguese households and generate 13,500 jobs during the construction phase.

Gouvaes dam and generating unit details

Gouvães is a 35m-high rockfield dam being built on River Torno, a tributary of River Tamega. The total reservoir surface area of the dam will be 340ha.

The dam will consist of an underground generating unit with a length of 120m, width of 20m and height of 44m. It also includes an 80mx17mx14m transformer hall.

The generating unit of the Gouvães plant will consist of four 220MW reversible turbine units with a runner diameter of 3,500mm and speed of 600rpm. The total electricity generation from the plant will be 1,468GWh a year.

"The Tamega River hydroelectric complex will comprise three dams named Gouvães, Daivões and Alto Tâmega."

The maximum discharge capacity of the spillway located on the left of Gouvães dam will be 67m³/s. The dam will also include 6.5km tunnels along with a 750m shaft. The penstock will be a concrete tunnel with a length and diameter of 4.7km and 7.3m respectively.

Daivoes dam and generating unit details

Daivões will be a 77.5m-high and 264m-long arch-gravity concrete dam located on the Tamega River. The total reservoir surface area for the dam will be 176ha.

The dam will consist of semi-buried machine hall installed with two 59MW Francis turbines with a maximum flow rate of 220m³/s. It will produce 159GWh of electricity a year.

The spillway for Daivões dam will be located over the dam body and will consist of four radial gates with a width of 11.5m and height of 9m each. The maximum discharge capacity of spillway will be 3,400m³/s.

Alto Tamega dam and generating unit details

Alto Tâmega will be 106.5m-long double-curvature concrete dam with the height of 334m. The total reservoir surface area for the dam will be 740ha.

The generating unit of the dam will consist of two 80MW turbine units with a maximum flow rate of 200m³/s and will produce 139GWh of electricity a year.

The dam will contain two spillways with discharge capacities of 1,510m³/s and 300m³/s, which will protect the dam from over-topping. It will also include 1.2km of tunnels with a 40m shaft.

Tamega River hydropower complex construction

The Tamega River is being diverted through the construction of a 400m-long tunnel and a 71m-long weir with a height of 10.5m, located 2.2km downstream of the Daivões dam. The excavation work for the diversion tunnel was completed in January 2017. It included the removal of approximately 136,000m³ of rock.

The construction of Gouvães dam is estimated to be completed in 47 months, followed by that of Daivões in 56.5 months.

The entire power plant complex is expected to require approximately 2,440t of steel including 1,000t for Alto Tâmega, 780t for Daivões and 660t for Gouvães.

Financing for the Tamega hydropower complex

European Investment Bank (EIB) is providing €650m ($759m) for the construction of the Tamega River hydroelectric complex . The first tranche of the funding amounting to €500m ($584m) was provided to Iberdrola in July 2018.

Contractors involved with Tamega project

Iberdrola awarded a contract worth €92.2m ($107.7m) to a consortium of Ferrovial Agroman (50%) and MSF Construction (50%) for the construction of the Daivões dam in May 2016. The same consortium was awarded the civil engineering and construction contracts worth €79.2m ($92.8m) and €80m ($93.4m) respectively for the Gouvães dam.

A joint venture of ACCIONA, Mota Engil and Edivisa (Visabeira Group) was awarded a €110m ($128m) contract for the construction of the Alto Tâmega dam. The JV was also awarded a contract worth €50m ($58.4m) for the construction of penstock for the Gouvães dam.

Andritz Hydro was awarded the engineering, procurement and construction contract worth €140m ($163m) for the electro-mechanical equipment along with the penstocks for the Gouvães dam in 2016. The company is also supplying hydro-mechanical equipment including hydraulic machines, radial and roller gates for the three dams, under a contract awarded in June 2017.

EFACEC was awarded the contract worth €11m ($12.8m) for the manufacture and supply of transformers for all the three dams in July 2017.

NRV Norvia, EPTISA Engineering, Coba Group, CEMOSA, AQUALOGUS-Engenharia E Ambiente and TPF Consultores are some of the other contractors involved in the Tamega River hydropower complex project.