In 1982, Ayesa won the tender to design the La Serena dam. This was to be the largest reservoir in Spain, with a capacity of 3,219 hm3, which came hand in hand with a highly unusual requirement: that the dam be built within the pre-existing Zújar dam, which would need to remain functional in order to continue servicing the subordinate irrigable area throughout the project. This was to present the challenge of building the dam within a lake which could reach depths of up to 35 metres.
We designed a dam measuring 90m in height and 600m in length. A straight-plan gravity dam design was selected, and our proposal was to make it out of rolled concrete, which was a novel technique at the time. It seemed a risky approach to project manager M. Barragan for such a complex structure, and so a compromise was reached: we put transverse ready-mixed concrete joints every 15m, adding fly ash to the cement and cooling the coarse aggregates.
Slopes of 0.05 and 0.8 were used to ensure stability with the water levels below the Zújar dam. The dam was fitted with a triple drainage system, as well as inspection and drainage galleries which were accessible by car.
The trickiest part was to design a construction system within a functioning dam. We had two diversion channels, one on each side, of 250 m3/s, and two 20m-high breakwater cofferdams, with a clay core and cement-bentonite walls. Despite the cofferdams being breached once during their construction, the diversion channels successfully drained the major flood which resulted – right in the middle of laying the dam’s foundations – whilst keeping the foundations dry. Once the slabs rose above the height of these cofferdams they were closed, and subsequent floods passed over the concrete structure with no further damage being caused. It was a great success.
The project included 80 kilometres of new road and seven large viaducts with supports reaching up to 60 metres in height.
The La Serena dam is currently fully operational, and regulates annual water provisions of 658 hm3, with a 95% guarantee.