The rupture of one of the Mondego River dikes near Coimbra caused, on Wednesday, the collapse of a segment of the A1.
Here are some questions and answers about these hydraulic works designed to regulate river courses, according to experts interviewed today by the Lusa agency:
– What is a dike?
A dike is an embankment built along a river. It requires constant observation and strong maintenance. The Mondego dikes are lateral containment dikes.
– What is a dike for?
A dike serves to allow the river to drain larger flows, without flooding the marginal fields. It can be done where justified. They are normally built where there are cultivated plains or when the aim is to protect a village.
– Why does a dike break?
When building a dike, it is necessary to define the flow rate that can drain without flooding. For the Coimbra dikes, the defined value was close to 2,000 cubic meters per second.
Embankments can deform over time and require repair due to erosion.
– What can be done to prevent a dam from breaking?
To increase the protection of marginal areas, the height of the dikes must be increased, in order to drain a higher flow.
After a situation like the one that occurred at the Mondego dike, an inspection must be carried out to determine the points of weakness and assess what to do, taking into account that the floods recorded in Portugal this month, due to heavy and persistent rain, could be repeated.
Depending on the results obtained in the risk and surrounding assessment, the project must be reformulated and/or a control plan established for the entire area and factors that may contribute to changes in the soils that form the basis of the dikes.
Monitoring must cover the foundations of dikes and reservoirs, taking into account climate change, which can contribute to aggravating the risk, among other factors.
It is important that the fitting capacity of dams is respected.
– What dikes are there in Portugal?
In addition to the Mondego, the Tagus River also has dikes built on landfill.
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