Junta injects cash to squeeze last possible drop of usable water out of main reservoir that serves the Costa del Sol

The regional ministry of Agriculture in Andalucía has approved a one-million-euro injection of cash that will allow utilisation of all but the last 40,000 cubic metres Marbella's La Concepción reservoir's reserves.

If no more rain falls and if necessary, only the 'dregs' of the reservoir that supplies the western strip of the Costa del Sol will remain, which are very muddy and contain more natural metals.

Experience from previous droughts in Spain has shown that the 'dead reservoir' concept is outdated: so, as a result, all the pumping and intake systems are to be upgraded. It is a slightly more complex system, but similar to the one that has already been installed at La Viñuela, in the Axarquía, which has not had to be pressed into action yet thanks to the respite from the last rains.

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A 'dead reservoir' is defined as the area of the water body that is below the intakes and which, theoretically, could not be used. Each reservoir is different because it depends on the catchment area type and the river's flow. In rocky terrain, a dead reservoir is very small. In muddy or clay soils, it is larger. Added to this is the fact that all reservoirs gradually lose capacity due to the accumulation of earth at the bottom of the basin.

In the 1960s, La Concepción reservoir began life with 61 hectometres of water. The latest bathymetry shows its capacity is around 56 hectometres, after a dead volume of five cubic hectometres was set. There is a lot of life below that level and almost all the water can be used, although its quality is constantly decreasing with more natural metals, more sediment, more organic matter and less oxygen. Sometimes the engineers find that is necessary to carry out dewatering, to help remove the sludge.

To update this entire extraction system, the Junta's regional ministry of Agriculture has approved a project valued at more than one million euros. It was approved by the regional ministers this Tuesday. Everything now has to be fine-tuned because of the drought, although the reservoir level continues to increase due to run-off after the passage of Storm Monica. During an evening status report this week, the reservoir contained 19.69 cubic hectometres — at the beginning of the year it held approximately 13 hectometres (hm³).

In a statement, the Junta de Andalucía said: "It is a pumping system that dates back to 1970 and that had become obsolete and did not provide the sufficient guarantee of supply that is required at this time. That is why it has been approved to act diligently in the modernisation of this infrastructure in order to avoid serious social and economic damage to the area."

"In addition, the asbestos cement pipe will be replaced with a carbon steel one and pumping equipment will be installed in the stilling basin downstream, allowing the flow to be pumped to the outlet channel of the dam, through the upper intake and attached to the face of the dam with a flow rate of 500 litres per second [five pumps]. In this way, the above-mentioned pumping can be combined with that of the pumps on the upstream face capable of supplying a flow of 400 litres per second up to the mouth of the intermediate intake."

Experience and improvements in various phases show that almost the entire reservoir can be used, practically down to the last drop due to several implementations during the severe droughts of 1982 and 1995.

However, at the dead reservoir level there is still a lot of water to be extracted, with pumps on platforms and other systems, and with adjustments to the physical and chemical processes making the water drinkable.

In 1982, a fibre cement pipe was connected to the lower intake and the bottom drain to supply water to the pumping station and from there to the supply canal. And, the pumping units were connected in series, to extract a further four hm³ from the five hm³ in the dead reservoir.

Thirteen years later, during the 1995 drought, a further 0.9hm³, 90% of what was left, were able to be used when three pumps, with a capacity of 300 litres per second, were installed on the face of the dam.

But that same year, by means of a water transfer pump, it was possible to use some 60,000 cubic metres (m³) of the approximately 100,000m³ that remained in the reservoir. Now, for example, in the middle of a drought, just over 47,000 cubic metres a day are leaving La Concepción to be treated — 7,000m³ more than were left at the bottom of the reservoir 29 years ago.

At the same time, important maintenance work was also been carried out on the tunnels that make up the triple Guadaiza-Guadalmina-Guadalmansa water transfer, which add their contributions to those of the River Verde which, however, have still left the reservoir with insufficient levels during the longed-for rainy season.

This summer, the water in the reservoir will be boosted by the Fuengirola and Estepona boreholes, and by a monthly supply of one cubic hectometre from the first extension of the Marbella desalination plant. In principle, Acosol is not planning to request water from the Campo de Gibraltar, despite the rains, which have also improved the situation in that region. For many summers the agreement with Arcgisa, the water and waste company in the area, has been in place.

The 11 municipalities of the Costa del Sol have authorised drastic reductions in pressure as an agreed water saving measure during the night, except on Saturdays so as not to overly affect the leisure, hospitality and catering trade.