Malaga province reservoir is now safe from risk of flooding after months of work to clear blocked spillway
Serious problems were detected almost a year ago, after the 29 October flood, but work was delayed by further torrential rains in March
The Casasola dam, some 25km from the city, has regained its full functionality and maximum level of safety, which enables it to perform its main purpose: protect Malaga and, more specifically, the Campanillas district against flooding. The serious sedimentation that threatened the useful life of this infrastructure, which turns 25 years old in a few days, together with the materials dragged by the floods, had clogged the dam's drainage system that ensures proper management and safety. Casasola's recovery is especially important before the start of the autumn, given the increased likelihood of floods.
Prior to this year's heavy rainfall, the drains were usually cleaned at least once a month. When the dam is very full and heavy rainfall is expected, it can start getting drained beforehand. If the drainage system is clogged or not working, it is necessary to wait for the water to overflow through the spillways and flow downstream. But the desired control and prevention are lost during this process. The regional government of Andalucía has always assured the population close to Casasola that there has never been any risk of collapse, even when the reservoir reached 115% of its capacity this past March. The river then had reached a flow of 315 cubic metres per second, 100 more than the basin can withstand.
It has taken six consecutive months of hard work. Finally, the technicians have found the source of the problem - a huge concrete slab that was clogging the pipes. As confirmed by the regional ministry of agriculture, responsible for the emergency work, the drains have now been freed with the help of a boom crane.
Short-term plans
"The next tasks to be carried out are to test that the valves are functioning correctly and to design and install a grate to prevent large solids from entering the drains," the sources added.
Over the last few months, it has been necessary to work with short-, medium- and long-term plans because of the serious problem caused by sedimentation, which laps the flows of the Campanillas river. Despite it being a defensive dam, its reserves are also used by Emasa - Malaga's water company - when it is necessary to find an alternative supply from the Guadalhorce's headwater reservoirs due to breakdown, turbidity or reserve levels.
Erosion, dragging of materials and sedimentation
A third of the full reservoir has become sediment, hence the need to put long-term solutions on the table, as this greatly reduces the lifespan of the infrastructure and affects its safety and capacity. There are many possible solutions for the future: dams, reforestation, reservoir drawdowns, and removal of deposits. No immediate action will be taken, but the issue is already being considered.
History
Casasola was inaugurated in 2000 with a capacity of 23.64 million cubic metres and now has a filling limit of 21.72, although this has nuances, as was observed during the storms last winter and spring. This is the capacity marked by the first upper spillway, the one located at the lowest level. The dam actually holds more than 25 million cubic metres.
Tasks ticked off
The serious clogging problems were detected almost a year ago, after the heavy rainfall of 29 October. The regional government started emergency work with bivalves because of their resemblance to molluscs. However, excessive turbidity prevented divers from working or identifying the blockage. The work was delayed due to the continuous and torrential rains in March.
Over all these months, work has been carried out using robots, bathymetries (an imaging system that allows mapping and understanding the relief and characteristics of the reservoir bottom and determining its exact capacity), heavy machinery and divers.
An extra pipeline was also built to provide an outlet for the water and achieve an initial lowering of the level of the reservoir so that work could be carried out. This pipeline, completed around Easter, will remain a permanent feature. It allows the level to be lowered by 3 million cubic metres a week.
Up to now, the removed mud has been returned to the riverbed, leaving the area entirely clear.
The nightmare caused by storm Laurence
The reservoir can hold more than 25 million cubic metres, as was proven during the passage of storm Laurence, when the bottom floodgates could not be opened and the dam had to be allowed to overflow. During that episode, 300 families were evicted from Campanillas for one night.
On Wednesday, Casasola stored just over 12 million cubic metres (55% of its storage capacity). It ended March with more than 25. Last year, it was at a third of its current level.
