The work is actually a reading of what was published by the Spanish Ministry of Ecological Transition in 2021. This work was carried out by the College of Engineers of Ports, Canals and Roads, but given its complexity the City Hall of Sangüesa requested a report to Ingeotyci, now published.

The final recommendation in the report is very clear. He says that even today there are displacements on the right side, that the observations currently made are limited and that uncertainty about the slope dynamics is significant, which does not guarantee the necessary security in situations that can be caused by earthquakes or other events. Consequently, it is not appropriate to change the water level in this area and it is therefore recommended that the Yesa reservoir should not be kept to the level required by the extension.

Problems since 1928

The report begins with a historical review of the reservoir and recalls that since the beginning of its construction in 1928 it has given problems to the slopes on the right. In fact, immediately after its beginning, the works were paralyzed due to the great movements suffered. Then came the Civil War and eventually the reservoir began to work in 1959.

Between 2003 and 2011, for example, the fin had a movement of 15 millimeters. In 2006, there was also another big movement on the hillside, it was concealed, but the press did. Also in 2013, as a result of the heavy flooding, two landslides changed the landscape and had to evict the urbanizations Tranquility and Observatory of Yesa. In 2014, the Spanish government expropriated the land of the urbanizations and nobody lives there anymore.

Instability is inherent in its compliance and emptying

According to the report, when the work of expansion of the reservoir began, the capacity of the right slope to withstand the works and their permeability was analyzed, but it was not considered to study its geomorphological evolution. Due attention has also not been paid to the movements of the nails holding the dam: “Current measurements have significant deficiencies and automatic auscultation tools must be put in place that provide continuous records.”

Although geologists acknowledge that important works have been carried out on the hillside, they consider that the hillside is still unstable, it must be taken into account that the filling and emptying processes of the reservoir are intrinsically responsible for instability and retest the hillside even without seismic movements.

The reservoir currently has a capacity of 446 cubic hectometers, an increase of 1,525 hectares. Work on extending the reservoir began in 2003 with a budget of EUR 113 million and has already exceeded EUR 500 million. This station is one of the most water collected by Esa, but this week it has only 219 cubic hectometers, which accounts for 48% of its capacity. In addition to the risks of the hillside, many experts believe that it is not worth expanding the reservoir because, among other things, the scarcity of rainfall will make it difficult to comply with it.