December's rains could mean water is released from Marbella reservoir for safety reasons

The increase in water reserves in Malaga province has been spectacular since the December rains. Reservoirs are well over half full. The end of the year has provided water to meet practically a full year's demand for Malaga city. The provincial system has gone from 277 million cubic metres to over 314 (a 52% increase). Of all the reservoirs, the most striking rise is that of La Concepción, located between Marbella and Istán.

The increase is such that the dam is already approaching the safety limit, which means that a new release of water might be necessary very soon, less than a year after the previous release (March 2025).

In just a few days, the reservoir, which receives the inflows from the Verde and the triple transfer Guadaiza-Guadalmina-Guadalmansa, has gone from 37 million cubic metres to 45.8 on 1 January (79.5% of capacity). The safety threshold for the winter months is 48 million cubic metres. The floodgates have to be opened if this level is reached.

The safety threshold varies according to the month and the time of year. A reservoir's full capacity in the summer is different from the safety level set when there is a risk of heavy rainfall. In fact, heavy rain is expected in this part of the province again over the first weekend of the year.

La Concepción reached 57.62 million cubic metres in May 2025, 0.08 above the theoretical capacity. It was at 104.94 above sea level. A couple of months earlier, on 7 March, the reservoir had to open its floodgates with flows that reached 60 cubic metres per second, due to the heavy storms taking turns in the province. In the entire hydrological year, it would have filled at least one and a half times if it had had that capacity.

Between the months of October and April, the safety buffer is left at approximately 100 metres above sea level, which is 48 million cubic metres. May allows for the 104.90 level. From then on, the spillways can begin to operate.

Obviously, there is always a safeguard. The historical maximum of the reservoir was reached in 2010 - 62.5 million cubic metres.

The regional government of Andalucía is also actively working to update the entire obsolete reservoir system for situations of extreme drought such as that of 1995.

The work will cost around one and a half million euros. Work on La Concepción returned to the technical and political agenda in 2001, with its inclusion in the Malaga plan.

Both the expansion of the reservoir and a new dam, which were part of the preliminary project, have since been abandoned. Instead, the Gibralmedina dam project has been drawn up (on the Guadiaro, between Cadiz and Malaga), from which up to 15 million cubic metres of water will be sent to the coast every year. This is an expensive project (780 million euros with the pipelines) and even the best-case scenario foresees at least a decade of work.

The preliminary project for the expansion of La Concepción was officially completed in 2016. However, it didn't even reach the environmental processing stage, although the reason has never been made clear to the public, apart from speculations about technical and environmental issues.

Opponents pointed to the environmental impact associated, for example, with sourcing aggregates. Around 3.5 million cubic metres of material would have had to be extracted from Sierra Blanca, requiring the opening of a new quarry on the edge of the ZEC (special area of conservation). It would sit below the quarry used from 1966 to build the current dam and above that of Nagüeles, where the Starlite festival is held.