Spain has 1,226 dams for its geography. Or he had them, since these last 20 years have demolished more 100. The goal is for the rivers to return to their channels and the truth is that the majority of demolished dams were small, they did not fulfill their functions and were not in operation. Of those that are still standing, the most imposing is between Salamanca and Zamora.
This is the Almendra dam, a concrete giant that is not only the highest dam in Spain, but an intelligent electric battery.
Concrete mole. Located on the Tormes River in Salamanca, Almendra’s is a colossal wall of 202 meters high and 567 meters long. Its construction was carried out between 1964 and 1970 and it was necessary to make an excavation at the height: 1.5 million cubic meters to house both the construction and the 8,650 hectares that would be covered by water.
It is estimated that more than 2,400,000 cubic meters of concrete were used for its construction, being one of the most pharaonic works in the country, and with a cost that is difficult to determine. Between 4,000 million pesetas and 10,000 million, according to the newspapers of the time, which adjusted to inflation would be between 312 and 780 million euros.
A straw in the Duero. The dam is of a vault type with double curvature and two side dikes that, if we include them in the dimensions of the “wall”, add up to a length of 3.5 kilometers. But a dam is much more than what is seen with the naked eye, and something fundamental in Almendra’s is the tube that connects with the Duero and with the hydroelectric power plant.
It is a pressure gallery with a length of 15 kilometers and a diameter of 7.5 meters that was excavated in the rock and covered by more concrete. Towards the end, it is divided into two galleries five meters in diameter and, each, in two other 2.8 meters to increase water pressure. This gallery saves a 30 -meter unevenness and is the one that carries the water from the turbine reservoir of its associated hydroelectric plant, Villarino.
Each group contains six Francis R turbines that work in a double way: they revolve to produce electricity, but they can also do it on the contrary to pump water. They can move 232,000 liters per second and is key to feedback with another large close reservoir: that of Aldeadávila in El Duero. Thus, Almendra’s is like a great reserve to contain the Duero in its floods, but it also supplies it in times of more drought.
Leading the European Top-10. To put in context its importance, although compared to the rest of Spanish dams, Almendra’s is colossal, if we put the eye in Europe … it is not so much. Switzerland takes the palm in this regard, with dams like the large dixence 285 meters high. Georgia has that of Unguri with 271 meters high, but beyond that pair and two other Swiss dams (Mauvoisin and Luzzone), the rest of the list of the highest is starring Spanish dams.
Almendra’s is the fifth at European level and is followed by channels with 156 meters, that of Canelles with 151 meters, that of Portas with its 141 meters, that of Aldeadávila with 139 meters and that of Barasona with a height of 133 meters.
An ocean. Although it is huge, its capacity is not the largest in the country. It doesn’t even come. Its reservoir has a capacity of more than 2,600 cubic hectometers, far from the 3,162 h3 of the Alcántara dam in Cáceres or the 3,220 h3 of the La Serena dam in Badajoz, which is not only the largest reservoir in Spain, but the third largest in Europe.
And, like other reservoirs, Almendra’s allows the development of recreational activities, with hiking routes or maritime activities such as expeditions in kayak. But it is evident that the most important role of the dam is not to create an ocean in the middle of Castilla y León, but to generate electricity.
Not so striking production. The huge turbines we described some lines allow the installed power of the plant to be 810 MW, which implies an annual production of more than 1,300 GWh. It is one of the dams that help Castilla y León be one of the communities with the most installed power in renewable energy, but the years do not pass in vain and there are prey that are much more striking than those of Almendra in this area.
With an installed power of 1,720 MW, that of Cortes-La Muela in Valencia has an annual production of more than 1,600 GWh. That of José María Oriol-Alcántara II in Cáceres has 915 MW and a production of 1,750 GWh and that of Aldeadávila in Salamanca, with an installed power of 1,139 MW, it has an estimated production of 2,400 GWh per year.
And there are already projects like Conso II in Ourense with a power of 1,800 MW that will allow up to 4,000 GWh per year or the planned of Llumaigua in Tarragona that will have the whopping of 3,124 MW with productions between 4,160 GWh and 7,000 GWh, something that is still in the air.
Demographic impact. But of course, next to the rivers there are usually peoples and, with 8,500 hectares of surface, it is evident that the reservoir took some ahead. The beginning of the construction was an economic bubble for Villarino of the air and almond. Populated were built to house workers and the population peak because it was evident. In 1970, Almendra had 807 registered inhabitants, Villarino had 2,130 registered. Both locations came from decades of gradual depopulation, so the dam meant an unusual demographic rebound.
In 2024, Almendra had 130 inhabitants and Villarino of the air with 739, and in both cases, just after completing the work, the population reached the level prior to it, which has also been decreasing aggravated with the rural depopulation of recent years. And to that loss of population in the area, we must add the 400 inhabitants of the town of Argusino that was engulfed by the reservoir.
Today, the Almendra dam only holds the honor of being the highest in the country, but although its production is not the largest, for the work controlling the Duero and what it contributes to the hydraulic generation in Castilla y León, this colossal works with half a century behind it remains relevant.
Images | Airpicimagen, Piutus from Salamanca
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