The most representative images of the current drought in the internal basins of Catalonia are most likely those of the Sau reservoir, on the Ter river, but in the Llobregat, historically the main source of supply to most of the city of Barcelona, the situation is even worse.
The Baells reservoir, the largest reservoir in this river that officially originates in Castellar de n'Hug, is this week at 23% of its capacity. The percentage may seem reassuring when compared to the 11% of the Sau swamp, but the total volumes are in this case more important than the percentages. Thus, according to data from the Catalan Water Agency (ACA), the Sau-Susqueda system (reservoirs with which the Ter is regulated in a coordinated manner) accumulates 64.6 cubic hectometres of water this week. Meanwhile, 25.2 hm³ are now preserved in the Baells. Even adding to the Baells the waters of the Llosa del Cavall and Sant Ponç (reservoirs both in the Cardener river), the whole of the Llobregat basin adds up to 46.7 hm³ this week.
The Baells reservoir is in fact experiencing the fourth most serious drought episode in its 47-year history (the dam was built between 1973 and 1976), only behind the records of April 1990 (18%, historical minimum). April 2002, September 2005 and April 2008, according to Aleix Villegas, the technician responsible for this hydraulic installation owned by the ACA.
The lack of rain in recent months has exposed some of the buildings in the town of Sant Salvador de la Vadella covered by water four decades ago and terraced areas that were formerly forested near the gorge that gave its name to the reservoir. On the great wall of Baells, water and its absence have been leaving signs in the form of stripes and colors, but none of this natural graffiti is necessary to verify the spectacular nature of the work.
If the Sau dam may look like an inverted elongated pyramid, the Baells has the shape of a gigantic concave-convex lens. A structure 102.35 meters high (in the central part, on the foundations), 27 meters thick in the plinth (lower part) and 302.28 meters long in the crown (upper part, between the abutments).
Technically, Sau is a dam with a gravity arch (the wall is straight, perpendicular to the mass of water) while the Baells forms a double curvature arch, a much more complex design but which allows reducing the volume of concrete necessary to secure the work. Despite its relative lightness, 400,000 cubic meters of concrete were injected in the construction of Baells, a mass that, although it may not seem like it, is pierced by an extensive network of galleries.
"In a total tour, round trip through all the galleries, we have calculated that we can take about 10,000 steps," explains Aleix Villegas, recalling the brand that became popular a few years ago as a daily goal to improve cardiovascular health.
It may not reach 7 km (equivalent to 10,000 steps) because Baells has an elevator, but five days a week a technician walks through each and every one of the galleries, corridors and flights of stairs inside this work. "We have a lot of very advanced surveillance equipment but, in addition, we want to make sure that everything is in order with our own eyes," explains Villegas.
The general public can also verify that the Baells is a solid and safe work because this is one of the few reservoirs in Catalonia where guided tours can be made inside the dam. The organized routes include a walk through the cloister (semi-covered gallery just below the crown) and part of two galleries on the upper levels. Hydrological tourists can thus verify the grandeur and aesthetic beauty of the work, in addition to receiving detailed information on its history and structure in a careful collection of photographs and graphics.
Baells also occupies a prominent place for the surveillance and security equipment installed. Among the most notable is a network made up of four seismographs and a set of 8 pendulums that hang in small wells drilled in the concrete (the largest of which is 80 meters deep), with which you can observe in detail the most minimum displacement that occurs in the dam wall.
In this case, technology plays an important role in the safety of the construction site, but its operation is only perfect with the help of human intelligence. In this sense, Aleix Villegas remembers two occasions in which the pendulum system launched its alerts. "In one case, one of the devices indicated that the dam was moving and forced us to do an exhaustive check until we discovered that the pendulum was twisting because a fungus was growing in its base." "On another occasion, the alarm of another pendulum went off because it had touched a small fragment of the resin that infiltrates the joints of the concrete blocks," recalls this ACA technician among the very few incidents in this hydraulic infrastructure. which now guarantees the maintenance of the scarce water resources of the Llobregat basin.
