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The Junta de Andalucía's regional ministry of agriculture is currently facing a complicated situation of managing the Casasola dam in Malaga. Besides the setback of having to face a whole train of Atlantic storms with continuous rainfall that sometimes fell intensely in short periods of time, there is also the problem that all the silt and sediment have caused to the lower drainage outlet of the reservoir. Basically, this prevents water from being released in a controlled manner when needed, as is currently being done, for example, in recent days for the reservoirs of La Concepción (near Marbella), the Tajo de la Encantada and the Conde de Guadalhorce. After several meetings with the engineering and technical experts, it has been decided to contract emergency work that will be added to the attempts already being made to remove whatever is clogging up the overflow outlets at Casasola.
According to SUR sources, the maintenance crew had been carrying out other emergency work for weeks because the drainage system had been damaged by all the debris that was washed into the reservoir following the 'Dana' weather events last autumn. Work has been carried out with clamshell dredgers that move slowly and carefully so as not to remove, nor stir up, too much sediment.
However, the weather afforded them no respite and the current train of storms arrived. The extreme turbidity of the water coming into the reservoir has made it impossible to see where the blockage is. The divers are unable to work with a minimum guarantee of safety.
The extraction pump was tried a few days ago and it was found to still be working. However, something is blocking the outlet.
So what will be done? A complementary outflow pipe will be built, which will add 3 million cubic metres per week of discharge capacity. This will allow the level to fall at an adequate and controllable rate and the filling volume to remain within safe margins, especially as this is a flood abatement dam, designed to defend Malaga city against flooding. This does not prevent Emasa (the municipal water company), during periods of drought and problems in the Guadalhorce canal, breakdowns or water turbidity, from drawing heavily on this resource, which is connected to the network via the Pilones system. In fact, according to technical sources, all emergency operations are being consulted and shared with the city's water company.
At the same time the strategy of deploying special dredgers and doing a new bathymetric measurement of the bottom of the reservoir will be pursued. The latter will provide an exact knowledge of the reservoir floor and how much sediment is there.
The idea is that the emergency work, which has already been commissioned, will be ready just before Easter. If they do not manage to release the spillway sooner, this work will allow the reservoir level to be lowered so that divers and dredgers can work in better conditions,
Once the dammed water is below the spillways, the dam will stop draining and will not be able to make voluntary discharges until the spillways are restored. If it had been possible, it would have been released during the weekend before Storm Laurence hit to increase the guarantees, given that the river was then stable.
The release system that has been running since last Saturday has been done to relieve the pressure on the dam. There are three outlet points in the body of this dam. The central one is lower (6.5 metres below the crest level) and is the one that drains first with the water sliding down the face in the form of a slide. The two lateral ones are 2.5 metres higher. These three openings operate independently of each other.
Casasola is therefore a fixed-lip dam whose construction was completed in the autumn of 2000. According to FCC, which built it: "The dam is 76 metres high from its foundations, with its crest at an elevation of 160. The crest width is nine metres, which corresponds to seven metres of roadway and two one-metre pavements, the latter being cantilevered. The volume of the reservoir at the normal, maximum level is 23.64 million cubic metres."
The volume of water that has entered this reservoir located in Almogía has exceeded in just a few days what came down during the entirety of the two 'Dana' storms last autumn. At midnight on Andalusia Day, which marked the start of the train of consecutive storm fronts from which we have not yet emerged, the reservoir stored just over 11 million cubic metres. On the night of discharging the excess, from Monday to Tuesday, it exceeded 25. It reached 115% of its capacity. The inflow to the reservoir went from 5 cubic metres per second to almost a hundred times more: 470, to be exact.
The flow downstream towards Campanillas reached 351 cubic metres per second at eight o'clock in the morning. That was 100 more than the basin can hold. It was more than 5 metres deep. In any case, the dam itself was never at risk: the problem was downstream, as Junta spokesperson Antonio Sanz commented.
In any case, complete safety will not be achieved until the river is fully channelled, for which the first projects are being carried out. The big stumbling block is the high cost of the project. In any case, if the dam were not in place and did not meet its flood control capacity, all that water going downstream would have been a disaster. In November last year this dam prevented the Campanillas river from rising three times as much as it eventually did.
At the time of publication, the reservoir was holding around 22 million cubic metres. Its safe capacity is 21.72.
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