Jorge Pueyo Chunta, deputy of Aragonesista and Sumar, brought the matter to the Spanish Congress and called for an end to the pharaonic work. Bel Bozueta, a member of the Assembly, also asked the Ministry of Ecological Transition and the Democratic Challenge of the Spanish Government about the issue and asked it to cancel the enlargement of Esa. The Ministry’s response came at the end of December: the reservoir is safe, even greater security measures have been taken in recent years and will be filled with water as planned at the end of the works.

The history of the Esa reservoir is long, construction work began before the War of 36, in 1928, but was delayed with the war; the reservoir was completed in 1959 and filled with water in 1960. With a capacity of 460 cubic hectometers (Hm3), it was planned to irrigate 80,000 hectares of land in the Cinco Villas area of Aragón and the Bardenas of Navarra. In addition, it is mainly used for electricity generation and drinking water for Zaragoza.

In 2001, work began on the extension of the reservoir, with the following objectives: one, to increase the irrigation areas by 48,000 hectares, but this has finally been reduced to about 10,000 hectares; two, to channel drinking water to Zaragoza, however, it is said that it is not necessary at present, among others, because the water for this purpose is taken from the reservoir of La Loteta; three, to generate electricity; and four, to control the flow of water to Aragon, especially during the seasons. Those that are officially mentioned. In the shade, on the other hand, the detractors of the project often mention another: the possibility that, in the future, the waters of the Ebro could be transferred to other basins.

Work on the extension began in 2001 and it is expected that the works will be completed in 55 months. In 2025, however, the expansion is still unfinished and although the official deadline for completion is 2027, few expect it to be so. What has delayed the expansion of so many reservoirs? Mainly the movements of the slopes that support the dam, and especially of the right lap. Thus, four adaptations of the initial project have been written in response to the instability of the slopes, and the initial budget of 113 million euros already exceeds 500 million, according to Rio Aragón. Currently, this fourth arrangement approved in 2016 is being carried out, with more than 82% of the extension works completed according to the Ebro Hydrographic Confederation (CHE), while the works are almost at a standstill since the summer of 2023.

Zangozo and Zaragoza at risk
César González Cebolledo is a PhD engineer and Professor of Hydraulic Engineering at the University of Zaragoza. He made a video simulation of how this would hit Sangüesa, ten kilometers away, and so much with Zaragoza, almost 150 kilometers away from the reservoir (shown on Youtube). Zangozi would be submerged within 23 minutes of the breakage, with almost no reaction power. The water would reach Zaragoza in thirteen hours and reach a height of five meters in its Plaza Pilar and ten meters in many parts of the city. The floods caused by the rains in 1787 devastated Sangüesa and forced the town to be rebuilt, but it was built in the same place with the risk that this could pose for the future. Much of Zaragoza has also been built in the areas of the river in recent decades, as in other cities and towns. The consequences of this have been severe during the floods in Valencia. This is one of the main causes of rainfall disasters and there are many projects currently planned in areas that can be covered by river expansion, but once the disasters have passed, they are ignored.

Dr. González has been accused of being a catastrophe by the CHE and the governments, but he tells LA LUZ that, given the movements of the slopes of the Esa reservoir, this risk is real. It also provides data for this purpose: 2.2% of the reservoirs built in the world before 1950 had some type of catastrophic rupture, that is, one in 45 reservoirs. González says that the possibility of accidents in the reservoirs built later has decreased, but at the same time, due to climate change, the meteorological phenomena are even stronger. “The only safe scenario for Sangüesa,” continues the professor, “is the abandonment of the works of expansion of the reservoir. There is no zero risk, but in this case the risk is greater than what may be acceptable. Imagine that one out of every 50 constructions falls, or one out of every 50 cars explodes in the time it remains active... we wouldn’t allow it. And that’s data from the International Group of Large Reservoirs, not mine.”

The ghost of Vajonte also comes out to the phone conversation with González. “Nothing should have happened there either, and look.” The disaster of the Vajonte reservoir in Italy (1963) is well known and even there numerous geologists repeatedly reported on the movements of the land and demanded that the water not pass beyond a certain level. Those responsible ignored it, a large part of the mountain fell into the swamp and the huge wave that passed over the dam crushed several villages down the river. Nearly 2,000 people were killed.

The engineer René Petit, who was in charge of the construction of the Esa reservoir, said this in an interview for the newspaper Navarra Hoy in 1983: “The rise of Esa would be very scary for me. The current reservoir has a depth of 60 meters and we had it at the time whether or not it would withstand our ups and downs. You have to be very careful, very careful.” The documentary Los malos sueños de René Petit (The Nightmares of René Petit) was also presented by Sol Video in 2014.

In recent decades, many other experts have also expressed their fear: Pedro Arrojo, Antonio Casas, Antonio Aretxabala, Valentín Ibarra, Tomás Morales, Cesar González... there are many geologists and engineers who have asked not to expand. As in these cases, however, there are those who do not see a problem that can stop the expansion of the reservoir and/or who want to cure geogrists with engineering drugs.

In the note signed on December 30,
2024, the Spanish Transitional Government replied to Deputy Bel Pozueta that the overflow of Esa is being built according to the advice of the Technical Guidelines for the Safety of Dams 2021, so there is no impediment to the full filling of the reservoir once the works have been completed. The current reservoir has 460 Hm3 and the increased reservoir would have 1,079 Hm3.The initial project foresaw 1,500 Hm3, and even then there was no problem, but when later the earth dances began, the CHE took away a third of the amount of water just in case.

The Ministry’s note also referred to the research carried out by the City Council of Sangüesa by the geologists Valentín Ibarra and Tomás Morales, who said they would follow up on the reports they evaluated. In the report written in 2021, two experts analyzed the study carried out by the Spanish College of Engineers with the right skirt commissioned by the City Council of Zangoza. The study stated that the slopes are unstable and therefore it was recommended not to carry out the enlargement of Esa.

The Spanish Government refers in particular to the overflow channels – the channels through which water can be extracted from the reservoir – in its response, and we asked the expert on the subject, González Cebolledo: “It says that the overflow has been designed in compliance with the 2021 standards, but this is not possible since the changes that were made in 2003 were carried out in 2008. Perhaps the overflows that are now being renewed would have been done in view of the 2021 rules. Apart from that, the technical guides of the reservoirs say that the wings that support the dam must be stable, and in this case this is not guaranteed.”

As for the overflow, for González, the technical guides say that dams like this one built on land can not only have overflows like tunnels, they also need free sheet overflows – “which are like giant slides” – because they are more flexible and can draw more water from the reservoir. “The risk of these dams, like loose materials, is that the water passes over them, because the water wears the dam, so in this project the overflows are very important.” For González,
the design of the dam falls short in the face of a cold drop like that of Valencia. “For the expansion work, references have been made to the quantities of water collected by the reservoir in 1976-1995, but the period was dry, with a flow of water less than usual. The climatic phenomena of 30 years later lead to much higher amounts of water.”

When experts talk about the instability and dangers
of the slopes, they are not talking about castles built in the air, but about the many events that have already taken place. There are many and very old landslides and landslides, when the construction of the Esa reservoir began. Coming to more recent times, among the many movements, we must highlight the movements of the left slope of the reservoir in 2006 and 2007. Or those who were on the right side in 2012 and 2013. The initial project to address these movements has been modified four times, resulting in a five-fold increase in the initial budget of EUR 113 million. There is no exact current data on the evolution of the budgets, but in 2017 the funds spent on the works of the dam amounted to 430 million euros, and since then great works have been carried out, both in terms of the stability of the slopes and in the works that, as a result, have had to be carried out indirectly in the surroundings – roads, bridges... The Aragón River Association provides detailed monitoring of the budget on its website.

To cite the most significant movements, there are those that took place in 2006 and 2007 on the left wing, respectively, of Mount Mélida and La Refaya. Between them, they occupied 60 million m3 of land. In 2007, the Spanish Ministry of the Environment stopped the works and ordered geological studies. Other smaller movements and cracks that occurred in 2008 and 2012 also appeared. In general, the movements continue on this slope, but since they are not monitored, there is not much talk about them.

Most of the problems that followed have been left to the right, especially after the heavy rains of 2012 and 2013. During the rains of 2012, 294 litres of water per m2 were collected and this led to land movements to inherently unstable lands. January 2013 also left a heavy rainfall of 234 l/m2, which intensified the dance of the lands created in the previous October. The CHE admitted that in some places the earth’s movements were four centimeters per week and in one month they measured up to 20 centimeters. The measures taken were severe: The urbanizations of Tranquility and El Mirador de Yesa –104 homes– built on this right wing in the first decade of the 21st century were evacuated and discarded in subsequent years. The neighbors were compensated. Since then, many opponents of the expansion of the dam have highlighted the alleged contradiction that the slope was not safe for urbanizations, but there is a need to increase the dam.

In the cold drop of Valencia, in general, it dropped 300 l/m2, but in some villages much more, such as Chiva (445 l/m2) and Turis (630 l/m2), many of them in a few hours. Dr. González also referred to the difficulties that the Esa Reservoir would have in maintaining such a quantity of water when referring to the disaster risk. The water it receives from the Sierra de Leyre is one of the reasons for the natural instability of the right foothills, and the rains and the increase of the reservoir bring more water to the already slippery area. For this reason, if the reservoir is filled in the coming years, there will be moments of great risk, according to González, because “those are the first moments in which the slopes suffer the most the new situation”.

Over the past decade, thousands of tons of material have been removed from these right-wing plots to remove the weight from the hillside and avoid the risk of landslides. However, in the works of the geologist Antonio Aretxaina on the reservoir, it is clear that the slope is inherently unstable and there is no stabilization. After all, all the expert studies of the last ten years agree on this: the lap is unstable and moves. But to what extent? There is the nail of the matter, for some few or very few, for others many or too much. For some the movements have stabilized, for others the level of stability is not allowed to increase the reservoir. As a result of all the discussions that have taken place, the Spanish Government and the CHE have indicated that in the future work will be carried out using the observation method. That is, that they will observe the area with the appropriate equipment and will mold the construction works accordingly. “But that kind of work doesn’t work for an unstable lap,” says González. How do you deal with the part of the mountain that suddenly fell into the swamp? It can't be."

MOVEMENTS OF THE RIGHT WING OF THE SWAMP

The instability. The map shows the situation in 2019. According to observations from 2021, where it moved the most, the wing moved 1.4 millimeters per year. The largest movements occurred in 2013, reaching up to 30 centimeters throughout the year. An alert status of 1 was then set in Zangozan. In 2019, cracks reappeared after heavy rains. In 2022 the CHE indicated that the lap did not have significant movement.

A large mass divided. Underlying Rupture Area (AAA). It can reach a depth of 100 meters in different areas. This is the one with the largest area. Main Breaking Area (ANA). It affects land masses of 30-35 meters. This area is the one that moves the most and is above the previous one. In reality, everything is a large moving mass (almost 12 million m3), but it has these two fractures mentioned. The English slipping. This area of land –on the red line– is located above the concrete dam and has a maximum depth of 30 meters. It is the oldest known movement (from 1928) and is activated when the reservoir is emptied and filled.

The observer for Copernicus. Data from the European Union’s Copernicus Earth observation programme from 2023 can also be analysed and these also confirm that the slopes of the Esa reservoir are moving. According to data from Copernicus, reported by the Aragon River Association, movements occur on the surface and at a great depth, the latter could occur up to 100 meters deep. To date, experts have relied heavily on the data provided by the CHE and will henceforth be able to observe the movements themselves, at least to some extent.

THE RIGHT WING: PHOTOS OF 2012 AND 2022

Demolition of urbanizations. There is a decade between the two images and during this time the urbanizations seen in the image above (104 homes) have disappeared, Tranquility (on the left) and El Mirador de Yesa. It was due to the movements of the right wing in 2013: then the urbanization was evacuated, compensation was paid and by 2020 all the houses were demolished.

To lighten the lap. The most important landslides are mounted on top of each other, they are like two spoons lying on top of each other. They affect the following amounts of land: With an area of 237,418 m2, a depth of 117 meters and a volume of almost 12 million m3. It is estimated that a volume of 1,500.00 m3 of material has been removed to relieve the load on the skirt. This is also believed to cause movements.

FINAL SECURITY REVIEW WORK

More than 30 studies have been carried out since the beginning of the extension of the reservoir in 2001. Here we talk about what has been done in the last decade, especially those related to the safety of the right lap, where the most significant problems of recent years have been.

Government of Navarre (2016)
In December 2015, during the government of Uxue Barkos, an Interdepartmental Technical Group was created, made up of four independent members. In 2016 they presented their conclusions to the Parliament of Navarre, which considered that, due to natural and technical factors, there were serious doubts about the safety of the reservoir. It was recommended that work should be stopped until security was fully guaranteed.

Government of Navarre (Geoconsult,
2019) The Provincial Government commissioned Geoconsult in 2018 and presented its conclusions in 2019. He asserted that the skirt was in strict equilibrium, moving less than two millimeters per month, and that these movements did not condition the viability of the swamp’s expansion. He recommended that measures be taken to improve the drainage of water from the inside of the lap, stabilize the upper part of the lap and reduce the small movements that existed. It also referred to the need for further and continuous observation in order to increase security.

FNCA Foundation (October 2020) The Fundación
Nueva Cultura del Agua (FNCA in Spanish) commissioned geologists Antonio Casas and Antonio Aretxabala to report on the Esa reservoir. According to them, in 2013 the security factors fell to a minimum, and both due to the natural movements of the hillside and the works of the reservoir, the movements were reactivated. According to the experts, “the volume of land that slips or slides is so large that any surface activity will have little effect on the improvement or worsening of the situation.”

Government of Spain (2021) In
2018 the Government of Spain commissioned the study from the College of Engineers of Roads, Canals and Ports of Spain. Four years later, the official body presented its conclusions. He also paid special attention to the right wing. The report says there are moves, but that the lap is stable enough to contain the dam. However, it advises on the need for a very precise and careful protocol in the filling and emptying of the reservoir. At the same time, from now on, it is necessary to use the observation method, so that the project also adapts according to the changes that are observed in the reservoir or in the slope.

The report of the
Engineering College of Zangoza City Council (2023) was so complex that the City of Zangoza commissioned Ingeotys SL to analyze it. The geologists Valentín Ibarra and Tomás Morales were in charge of the study. The vision of the Hien is critical in many areas with the work of the College of Engineers and at the end it extends the following vision to the City of Zangoza: improvements have been made in the right slope, but while there are displacements, and in view of the significant limitations that exist to monitor them, it is recommended not to increase the reservoir of Esa.