The images have flooded social networks this weekend: the Aldeadávila dam “turbinating at full capacity” with the Duero river descending with enormous force, or the Iznájar reservoir recovering its splendor in a matter of days. They are hypnotic images that hide a much more tense and calculated reality. While the citizen sees natural spectacles, the engineers see a fight against the disaster.
In the midst of this “festival” of storms that has shaken the peninsula this month of February, One phrase sums up the situation better than any other. It is pronounced by José María Sanz de Galdeanodirector of Hydrological Planning and Works of the Basque Water Agency (URA): “The dams were not designed for floods, but today they are key to cushioning them.” These infrastructures, designed decades ago so that water comes out when you turn on the tap or to turn on the light, have become—almost by historical accident—the last line of defense between the perfect storm and the safety of the populations downstream.
A winter concentrated in a few days. To understand the magnitude of the event, we must first look at the Basque Country, where the orography and intense rains have tested the system. As explained by Sanz de Galdeano in the SER ChainEuskadi has faced a winter marked by episodes of very intense rain concentrated in very few days.
The situation has forced the activation of the two major Basque regulatory systems. On the one hand, the Zadorra system composed of the Ullibarri-Gamboa reservoir and the Urrunaga dam. On the other hand, the Añarbe system is responsible for supplying the Donostialdea area.
It is not a local phenomenon. It is a symptom of a broader hydrometeorological pattern that has affected the entire peninsula. While in the Tormes system, reservoirs like Santa Teresa are close to 80% and release water preventively to defend the city of SalamancaIn the south the situation has been even more drastic.
In Andalusia, the Iznájar reservoir—the giant of the community— has doubled its reserves in just two weeks, going from a critical 25% to exceeding 50%, something that had not been seen in a decade. The intensity has been such that the AEMET even warned of scenarios of soil saturation with impacts “some of the highest in the world”, causing water to gush directly from the ground in places like Grazalema (Cádiz). forcing preventive evacuations.
From supply to “lamination”. The relevant thing about these weeks is not only that it has rained, but how we have managed that rain. Sanz de Galdeano puts his finger on the sore: “These infrastructures were built primarily for water supply, not specifically to laminate avenues.” However, its immense storage capacity has made it possible to change its function on the fly. Dams have acted as giant shock absorbers. “They have sufficient volume to play with reserves, create space and retain water at the most critical moments,” says the director of URA.
Sanz de Galdeano’s warning has scientific support. A study on the effectiveness of dams in the face of climate change confirms that infrastructure designed with “historical data” They are operating blind to the new reality. Old models did not account for this extreme variability; under severe warming scenarios, the risk of large dams overflowing could multiply by up to 17 compared to historical records. The conclusion is technical but terrifying: the effectiveness of a dam decreases dramatically under extreme hydrological regimes if adaptive management is not applied.
This excess water has had an unexpected side effect on the energy market: Spain’s “battery” it’s so loaded (117% more stored hydroelectric energy than last year) that nuclear energy is no longer competitive. The Trillo plant, for example, has been disconnected from the grid because, given such an abundance of turbineable water, the numbers simply “did not add up.”
Choreography of floodgates. The precision mathematics that decides how much water reaches your home. The management of these crises is a precision choreography that Sanz de Galdeano graphically defines as working “with one eye on the river and another on the sky.” The technical key lies in the “reservoir”: the empty space that is deliberately left in the reservoir before the rain arrives in order to swallow the flood.
The director of URA details how it is applied this differently depending on the capacity of each system:
- In the Zadorra (High regulation): These dams control 60% of the upstream basin. This allows for drastic intervention. The figures from Sunday night are the best example: 260 cubic meters per second of furious water entered the system, but the floodgates only let out 54. That difference (more than 200 m³/s retained) is the flood that was avoided.
- In Añarbe (Less regulation): Here the dam only controls 23% of the basin. Most of the river water circulates freely, so there is less room for maneuver. Even so, the strategy is the same: when the river goes high, floodgates are closed to retain “as much as possible.”
All this is done under administrative coordination complex but fluid between URA, the Ebro Hydrographic Confederation and that of the Cantabrian Sea.
Not all barriers are the same. In this context of saving dams, a reasonable question arises: why then are some dams on Basque rivers being demolished? Sanz de Galdeano makes a crucial distinction between large regulatory infrastructures and small weirs. “These are not large infrastructures like those of Zadorra, but rather low-rise structures that have no real capacity to manage avenues,” he clarifies. The elimination of these small obstacles responds to two logics:
- Environmental: they allow fish and fauna to ascend the river, improving ecological health.
- Hydraulics: Although it may seem contradictory, these small walls can raise the water table in local floods, worsening the problem instead of solving it.
However, large dams have their own silent enemy: sediment. Experts and organizations like Greenpeace warn that torrential rains They drag tons of mud that accumulate at the bottom of the reservoirs, subtracting their real capacity (that “hole” that Galdeano spoke of) and blocking the bottom drains, vital for safety. The scientific study above corroborates this risk: sedimentation reduces effective storage capacity and compromises the long-term flood control function, shortening the functional useful life of the dam.
This month’s lesson. This episode has served as a large-scale “stress test” for the Spanish water infrastructure. We have seen how dams designed with data and needs from the 20th century are being forced to adapt to the climate reality of the 21st century.
José María Sanz de Galdeano summarizes the philosophy that has averted disaster this week: “We stop the flood by retaining the flow that reaches them in the dams.” A maneuver that seems simple on paper, but requires constant vigilance and robust infrastructure. Because although the water today is too much for us and turn off nuclear power plantsthe ability to manage it—whether to save it or stop it—remains the line that separates resource from catastrophe.
Image | Pexels
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