Disaster-proofing Marbella's reservoir: La Concepción will have new sensor, communications and monitoring systems

Everything must be checked, documented and prepared for in case of an incident. Every sensor, every spillway, every gauge, every communication system, the list goes on. This is especially true for a type A dam, as is La Concepción, located between Marbella and Istán.

This category includes all dams whose rupture or malfunction could result in loss of life. This obliges the authorities to have early detection mechanisms and immediate intervention tools in place. This is the key to the contract recently awarded by the Junta's regional ministry for agriculture.

La Concepción came into service more than half a century ago in 1972 and has never had any significant problems, other than its insufficient capacity to store all the water that flows into it (from the Verde river and the Guadaiza-Guadalmina-Guadalmansa triple transfer system).

This winter, had it not reached its safe operating level on several occasions and had to release up to 62 million cubic metres, it would have filled up twice over. There have been serious attempts to increase the dam's capacity. The most recent, a preliminary project from 2016, was eventually shelved. The idea was to practically triple the reservoir's current capacity of 56 million cubic metres.

Safety regulations were tightened in 2021 via royal decree. A project to upgrade the reservoir's safety systems was already underway. The construction contract had to be modified and the work, budgeted at 2.1 million euros, has been awarded to the Sando-Ofiteco-HCC consortium.

The deadline for completion is nine months. The project is based on the technical design from HGM and Inproes, led by engineer José Antonio Remesal and drafted by Rafael Garrote. The project includes a comprehensive modernisation of the monitoring, communications and early warning systems for the local population.

Located on the Verde river, 5.5 kilometres from its mouth and west of Marbella, the dam is a gravity dam (its own weight resists the water's flow and prevents drift towards the abutments and side walls). It is made of concrete and its imposing height above the foundations is 89.55 metres. Its reservoir floods an area of 215 hectares at the normal maximum level (104.90 metres above sea level), allowing it to reach a maximum volume of 62.09 million cubic metres, a threshold that is not usually reached due to the aforementioned operating regulations.

Its primary function is to regulate flow rates to guarantee the water supply to the entire association of municipalities of the Western Costa del Sol (Mancomunidad de Municipios de la Costa del Sol Occidental).

The core of the new project focuses on replacing traditional analogue methodologies with automated systems that send real-time data to both the dam control centre and the Andalusian Mediterranean basins control centre in Malaga. Until now, infrastructure control depended on periodic manual measurements. For example, seepage measurements were done manually on a weekly basis at eight specific control points distributed along the longitudinal concrete galleries.

The project envisions modernising motion control through the automatic monitoring of its five forward and three reverse pendulums. Structural movements of the block joints, currently measured weekly by eleven mechanical gauges distributed across the four upper galleries, will also be integrated into the digital control system. Meteorological measurements and reservoir level monitoring, which currently rely on a combination of manually-readable scales, an ultrasonic sensor and a hydraulic scale connected to the bottom outlet, will be unified for continuous monitoring.

The implementation of the emergency plan includes the deployment of a redundant communications system designed to withstand the most adverse environmental conditions or possible power outages. The communications system at La Concepción dam will link the dam's new emergency room at the dam itself to the Malaga control centre via four transmission channels (mobile, radio, fibre optic and satellite).

This telecommunications network will govern the revamped public warning system, consisting of several siren stations distributed throughout the municipality and the affected areas downstream of the Verde river. The control centre will be equipped with advanced siren remote control software that will allow alerts to be activated remotely. The equipment the river basin control centre in Malaga will be completely renewed and specific training and outreach programmes will be developed so that both operators and the public are familiar with the protocols.

Beyond the technological deployment, there is a significant budget allocation for carrying out complementary civil engineering work. The most important is the complete renovation of the dam's internal drainage network, a key element for dissipating the interstitial pressures exerted by seepage of the filtered water inside the concrete structure.

The dam's service road is also being improved. This road, which begins at a roundabout at kilometre marker 5+300 on the local A-7176 (Istán-A-7) road, is about five kilometres long. Its renovation will ensure the safe passage of heavy vehicles and emergency equipment.

There will also be a geotechnical research campaign that will include taking soil samples to assess the state of the foundations after almost half a century of active use.