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The intense 'Dana' (cold drop) storms in Malaga province in October and November clogged the bottom spillways of the Casasola dam, located in Almogía. The main function of this reservoir is to protect Malaga from the flooding of the Campanillas river, a tributary of the Guadalhorce. Since it was necessary to unclog this critical safety component of the dam, an emergency operation was commissioned using special excavator machines (clamshells). The divers had no visibility.
Then came the next 'dana', on 28 February, and the work had to be postponed. The reservoir began to fill up again. As the bottom spillway was blocked, Junta de Andalucía technicians had to let the water rise to the upper spillway.
It was urgent to return the dam to the safety threshold. It wasn't possible to lower the water volume using only the spillway, which functions only when a certain level is exceeded. It is, to put it simply, a slot through which water flows down like a slide once it reaches a specific height.
Then, before Easter, when the relentless storms had calmed down, the technicians assessed the situation. They drew up a quick plan: to build a by-pass pipe to drain water and mud. It was ready in a week and the dam continued to drain through this emergency pipe. In addition, they were going to introduce underwater drones and machines to try to make a bathymetry of the seabed.
What the technicians are working on right now is the installation of a system called air-lift, which is used in places such as sewage treatment plants to extract the sludge and pass it through treatment. Additionally, the technicians have calculated a serious silting up in Casasola: a third of its volume is sludge, which seriously compromises the efficacy of the reservoir. In addition, long-term plans must be drawn up to avoid excessive silting.
"With the emergency work on the by-pass, it has been possible to recover the maximum level in the reservoir, as defined by the dam's operating regulations at this time of year. Once the maximum level has been reached, work can be carried out on the installation of the air-lift sludge extraction equipment , which will begin to operate in the next few days," technical sources from the regional ministry of agriculture told SUR.
According to the regional ministry's calculations, some 7 million cubic metres of sludge have already been removed, which still leaves the remaining 14 million cubic metres - an equivalent of a barrier of almost 9 metres in height.
"The work of the divers is scheduled for this summer, in order to check the intake of the bottom drains, once we are done with the removal of the sludge," the technicians said.
On 18 March, the reservoir exceeded 115% of its full capacity and broke the 25-million-cubic-metre barrier. It now stands at 14 million cubic metres.
On 17 May, the rise of the Campanillas river once again prompted the emergency evacuation of residents. Fortunately, the flood did not cause any major damage to property.
It is very common for reservoirs in Spain to lose a lot of capacity due to siltation. It varies a lot depending on the terrain and the basins. The accumulation of sediment affects the outflow organs and the reservoir itself, reducing storage capacity. All this significantly alters the efficacy of the facility.
For this reason, planning is key and Casasola is the clearest example in the province. The reservoir was inaugurated in 2000 with 23.64 million cubic metres. Its capacity has decreased over the years and now stands at 21.72 million cubic metres, although this may vary, as we have seen, because the limits are set by the spillways, but the reservoir can actually hold more than 25 million cubic metres.
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