| Large dams Gouvães Dam Alto Dam


Alto Tâmega powerhouse is equipped with two 80MW turbine units. These units have a combined installed capacity of 160 MW, capable of generating approximately 139 GWh of electricity annually. This significant power output contributes to Portugal’s renewable energy goals and helps meet the country’s growing electricity demands. The dam’s design incorporates advanced flood control measures, featuring two lateral spillways with a combined discharge capacity of 1,825m3


/sec. This impressive flow rate


ensures the dam’s safety during high water events, protecting both the structure itself and downstream areas from potential flooding. Construction of the Alto Tâmega Dam has been a massive undertaking, requiring approximately 220,000m3


of concrete. This


substantial amount of material reflects the scale and complexity of the project. The dam’s crest length of 335m further emphasizes its imposing presence in the landscape.The Alto Tâmega project is part of a larger hydroelectric complex developed by Iberdrola under a 70-year concession agreement signed with the Portuguese government in July 2014. This agreement covers the design, construction, and operation of three interconnected projects: Alto Tâmega, Daivões, and Gouvães dams. The construction of the Alto Tâmega Dam has been a significant undertaking, employing a peak workforce of almost 1,000 workers on site. This project not only contributes to Portugal’s energy infrastructure but also has provided substantial employment opportunities in the region.


Daivões Dam


The Daivões Dam is classified as an arch- gravity concrete dam, combining the structural advantages of both arch and gravity dam designs. It stands at a height of 77.5m and stretches 264m in length across the river valley. This substantial structure required approximately 240,000 cubic meters of concrete during its construction, highlighting the scale of the engineering involved. The reservoir created by the Daivões Dam covers a surface area of 176 hectares, serving as a crucial water storage facility for power generation. This reservoir not only supports the dam’s own power generation capabilities but also plays a vital role in the operation of the larger Tâmega complex.


Daivões Dam


At the heart of the Daivões project is its powerhouse, which is semi-buried to minimize environmental impact. The generating unit consists of two Francis turbines, each with a capacity of 59MW, giving the dam a total installed capacity of 118 MW. These turbines are designed to handle a maximum flow rate of 220m3


/sec,


enabling the dam to produce approximately 159 GWh of electricity annually. One of the key features of the Daivões Dam is its spillway, which is located over the dam body. The spillway consists of four radial gates, each measuring 11.5m in width and 9m in height. This configuration allows for a maximum discharge capacity of 3,400m3


/sec, ensuring


the dam’s safety during high water events and providing effective flood control for downstream areas. The Daivões Dam also serves a crucial role in the operation of the larger Tâmega complex. It functions as the lower reservoir for the 880MW Gouvães Hydroelectric Pumped Power Station. This interconnection allows for efficient energy storage and management within the complex, enhancing the overall flexibility and reliability of the system.


Construction of the Daivões Dam was a significant undertaking, involving not only the dam structure itself but also associated infrastructure. The project included the construction of a bridge approximately 200m long and 35m high, more than 5km of power lines, over 7km of roads, and two sewage treatment plants. These additional components highlight the comprehensive nature of the project and its impact on local infrastructure. The first filling of the Daivões reservoir was completed in March 2021, marking a significant milestone in the project’s development. This event paved the way for the subsequent testing and commissioning phases of the power generation equipment.


The Gouvães Dam is a 35m-high rockfill dam constructed on the River Torno, a tributary of the Tâmega River. Its reservoir covers a substantial surface area of 340 hectares, serving as the upper reservoir for the complex’s pumped storage system. This large body of water not only supports power generation but also provides opportunities for efficient energy storage and management within the larger Tâmega complex.


At the heart of the Gouvães project is its underground powerhouse, a marvel of engineering designed to minimize environmental impact. The generating unit is housed in a cavern measuring 120m in length, 20m in width, and 44m in height. Adjacent to this is a transformer hall with dimensions of 80m by 17m by 14m. This underground configuration allows for a significant power generation capacity while preserving the natural landscape above ground. The Gouvães power plant is equipped with four reversible turbine units, each with a capacity of 220MW, giving the facility a total installed capacity of 880MW. These Francis turbines are impressive in scale, with a runner diameter of 3500mm and operating at a speed of 600 rpm. The plant is designed to handle a maximum head of 700m, showcasing the significant elevation difference utilized for power generation. The dam’s spillway, located on the left side of the structure, has a maximum discharge capacity of 67 cubic meters per second, ensuring effective flood control and dam safety. The project also includes 6.5km of tunnels and a 750m shaft, highlighting the complex underground infrastructure required for this type of hydroelectric facility. A notable feature of the Gouvães project is its penstock - a concrete tunnel with a length of 4.7km and a diameter of 7.3m. This massive conduit is responsible for conveying water between the upper reservoir and the powerhouse, playing a crucial role in both generation and pumping modes. Construction of the Gouvães Dam was a massive undertaking, estimated to be completed in 47 months. The project required approximately 660 tonnes of steel, part of the total 2,440 tonnes used across the entire Tâmega complex.


Gouvães Dam www.waterpowermagazine.com | September 2024 | 47


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