The most representative images of the current drought in the internal basins of Catalonia are probably those of the Sau swamp, in the Ter, but in the Llobregat, on which much of the supply to Barcelona and the metropolitan area depends, the situation is even worse
The Baells reservoir is this week at 23% of its capacity, a percentage that may seem reassuring when compared to Sau’s 11%, but total volumes are in this case more important than percentages . So, the Sau-Susqueda system (reservoirs that are regulated with the Ter in a coordinated way) accumulates this week 64.6 cubic hectometres of water. For its part, 25.2 hm³ are now preserved in the Baells. Even adding to the Baells the volumes of the Llosa del Cavall and Sant Ponç (both in the Cardener), the Llobregat basin as a whole totals only 46.7 hm³ this week.
Baells is experiencing, in fact, the fourth worst 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), in April 2002, September 2005 and April 2008, according to Aleix Villegas, technician responsible for this facility owned by the ACA.
If the Sau dam can look like an elongated inverted pyramid, the Baells has the shape of a gigantic concave-convex lens, formed by 400,000 cubic meters of concrete. A structure 102.35 meters high (in the central part), 27 meters thick at the plinth (lower part) and 302.28 meters long at the top.
“In a total tour, round trip through all the galleries, we have calculated that we can do 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 a lift, but five days a week a technician goes through all the galleries, corridors and sections of stairs inside this building. “We have a lot of very advanced surveillance equipment, but we want to make sure that everything is in order with our own eyes,” explains Villegas.
Among the most outstanding equipment is a network of four seismographs and a set of eight pendulums that hang from small wells drilled in the concrete (the largest of which are 80 meters deep), and with which it is possible to observe in detail the smallest displacement that takes place in the dam wall.
In this case, technology plays an important role in the safety of the work, but its operation is only perfect with the help of human intelligence. In this sense, Aleix Villegas remembers two occasions when the pendulum system set off its alerts. “In one case, one of the devices indicated that the dam was moving and forced us to do a thorough review until we discovered that the pendulum was twisting because a mushroom was growing on its cable.” “Another time 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 that now guarantees the maintenance of the scarce water resources of the Llobregat basin.
The concrete and mechanical equipment of a reservoir is not the most attractive or suitable habitat for wild animals, but Baells has had a notable and respected exception for some years. Hanging from the concrete, from some metal piece or on the rocks that are at the boundaries of the work, in these galleries rest about twenty specimens of the species large horseshoe bat (Rhinolophus ferrumequinum), river bat (Myotis daubentonii ) and small horseshoe bat (Rhinolophus hipposideros).
In the water, the protagonist is a less welcome species: the zebra mussel (Dreissena polymorpha), detected for the first time in 2011. This mollusc accumulates in equipment such as pipes and sluices and forces expensive and complex monitoring and cleaning. One of the few positive parts of this invasion is that, as divers in dam improvement operations have found, at the depth where zebra mussels live (which feed by filtering substances with bronchial cilia) the water is exceptionally transparent, which makes it easier to see during inspections.
