Alqueva Dam

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The Alqueva Dam is a large arch dam on the Guadiana River in southern Portugal, forming the Alqueva Reservoir, also known as Grande Lago. It is the centerpiece of the Alqueva Multi-Purpose Project, built to provide water for supply and irrigation, generate electricity, and support tourism.

Construction started in 1995 and the dam was completed in 2002 at a cost of about US$1.7 billion. The floodgates were closed on February 8, 2002, and the reservoir reached its planned level in 2010. When full, the lake covers about 250 square kilometers and can hold around 4.15 billion cubic meters of water. The shoreline can stretch up to about 1,200 kilometers, and the maximum depth reaches around 100 meters. The project is the largest dam and artificial lake in Western Europe.

The dam is 96 meters tall and 458 meters long, with a crest width of about 7 meters. The surrounding area is used to regulate water for regional use, support irrigation, and generate power. A well-developed marina near Amieira serves boating and tourism needs.

Power generation comes from a 518.4 MW pumped-storage plant. It was built in two stages: the first in 2004 and the second in 2013. The plant uses four reversible Francis turbines, each about 129.6 MW. These turbines can generate electricity when demand is high, and later pump water back into the reservoir during low-demand periods, storing energy for later use.

The Alqueva project also includes Pedrógão Dam downstream, about 23 kilometers away, which helps create a lower reservoir to balance flows and supply water for the region. Water is moved through a network of pumping stations, including Álamos and Pedrógão Left Bank and Right Bank stations, to distribute water for the Alqueva system and its subsystems.

In 2023, a 5 MW floating solar facility was added to the reservoir. It covers about four hectares with nearly 12,000 solar panels and is designed to produce around 7.5 GWh per year. This solar installation is part of Portugal’s move toward renewable energy and could eventually supply energy to a large portion of the southern region's people, with room to expand up to 70 MW.

The project has had significant environmental and cultural impacts. The dam flooded areas that included prehistoric engravings and wildlife habitats for species such as eagles, kites, wild boars, and the Iberian lynx, and it submerged a Roman fort. Archaeological work has surveyed about 1,200 cultural heritage sites. Critics argue that the irrigation system’s profitability is limited, noting that some studies suggest only a portion of the irrigated land is economically viable. To address these effects, the project includes mitigation plans and ongoing studies while balancing regional needs for water, energy, and development.