New Costa del Sol storm tank will collect more than 3 million litres of water and help prevent flash flooding

Mijas is building a 135-metre-long storm tank which will be capable of storing more than three million litres of water and help prevent flash flooding in the event of heavy downpours.

A massive hole has been created in the ground on Avenida de Andalucía where the 10-metre-wide tank will be located. It is also set to prevent landslides from occurring during heavy rainfall when it is finished, expected to be around September 2025. It will benefit some 15,000 residents in three areas of Mijas: Lagunas Norte, Lagunas Sur and the area of the Fuengirola river plain.

Work is currently under way after nearly five years of planning the infrastructure, with construction involving technicians of the area's insurance compensation board, town hall and Acosol.

How does a storm tank work?

Fernando Jiménez Rojas, head of the infrastructures and works department at Mijas council and civil engineer said: "This is an urban water infrastructure, designed to relieve the sewage networks when it rains". "Often when it rains, the sewage network mixes with rainwater and that is what causes the pipes to overflow and manholes to lift. In other words, the typical image when a storm comes is manholes starting to spew water outwards, causing pools of water to form in the street," he added.

Once the storm tank is in operation, "if the flow in the pipe is very full, the surplus will pour into the tank, which will gradually fill up and the sewage system will continue to function as if it were not raining".

In the event of a heavy rainfall, such as the 'Dana' storm last week, it could happen that the tank fills up to the top. In such a case, the water would be discharged into the Fuengirola river, "but it would be filtered and not contaminated", Jiménez pointed out.

The Mijas storm tank will have filters so that rubbish or faeces does not make its way into the river. If it fills up with the 3.2 million litres it can hold and has to drain into the river, these filters will ensure that all the dirt sticks to the bottom and only the clean water flows out. And once it stops raining, "the rest of the flow will be pumped progressively into the sewage network so that the treatment plant can gradually and progressively treat the wastewater", avoiding the collapse of the sewage network.

"If the amount of water mixed with rainwater and sewage were to reach the treatment plant all at once, the plant would have to open floodgates and use its spillways without first having treated it. What the storm tank achieves is to discharge in a non-polluting way into the public watercourses," Jiménez said.

Once it is finished and in operation, the tank will not be visible and will be under Avenida de Andalucía. This exact spot was chosen due to its proximity to the water treatment plant.

The cost of the tank's construction, about four million euros, will be assumed by the private developers of this urban sector, through the insurance compensation board, and at the request of Mijas town hall. The work is being carried out by Naxfor Ingeniería e Infraestructuras.