They were designed twenty years agowith return times of two hundred years. «And luckily we have them», say the experts. The object is i lamination basinssmall and large, who saved the Veneto from the torrential rains of February and permission to contain the damage in the wave of bad weather of recent days. Yet, although recently built (the one in Caldogno in the Vicenza area was put into operation for the first time in December 2020), limitations are already emerging, including insufficient dimensions to contain heavy rainfall. «There are more and more extreme events and the return times no longer match – explains Andrea Crestani, director of Anbi Veneto -, every time the bar is raised, it’s worrying. It would have been worse without basins and it is It is essential to continue with the 2010 regional plan.” Which predicts thirteen morethe sizing of which precedes the approval of the plan.
Dated projects
«The design of Caldogno was developed on data from twenty years ago”, says Marco Marani, professor of the Engineering department and head of the Center for studies on climate impacts in Rovigo of the University of Padua.
Although the assessments were made on scenarios that took into account data, statistics and forecasting models that were even worse than the estimates, “the bar” has, in fact, been raised. Precisely for this reason, for the future, “strategic quantitative assessments must be made, starting from what has already been achieved to define what to do”, adds the teacher. At the center of the debate, the issue of climate change (Veneto, just as it is not at year zero on the rolling front, neither is it on this: there is the Rovigo study centre). «We have rainfall measurements, for example in Padua there is a series measured since 1,725 - underlines Marani -, there you can see how in the eighteenth and nineteenth centuries there are oscillations while since the 1950s the increases in events have been systematic.”
Coordination and maintenance
When updating hydraulic protection interventions, «The complexity of the territory must also be considered – observes Crestani – dried up and torn from the sea, it rapidly degrades in a complicated hydraulic balance”. For it to work the mosaic pieces must adhere perfectly to each other. «We have the larger basins and the smaller ones created by the reclamation consortia to defend small urban centers and at the same time we have the network of canals». In all, 18,500 kilometers of rainwater drainage system which connects to the lifting systems that discharge onto the rivers and, therefore, into the sea. «But maintenance is needed — he specifies —. An intervention plan in this sense is necessary otherwise we fill the basins, then when they discharge onto the rivers the banks cannot hold and break”. In the Lower Padua area it happened in recent days: «Seven thousand hectares of countryside – adds Crestani – have been transformed into basins precisely for this reason». Marani reprimands: «But don’t get the idea that there is no maintenance. The consortia do them and, thanks to the Pnrr, a lot is being done.”
Strategies for the present and future
The question of questions remains: what to do for the future. «Given that zero risk does not exist – says the teacher -, what is the residual risk must be defined an analysis of costs and benefits at community level must be carried out on the interventions to be implemented”. That is, if a basin disliked by the inhabitants of the area where it is to be built is fundamental, it is a good idea to continue with the work without hesitation. «With the awareness that not all problems can be solved, laminations should be planned carefully – explains Marani – and at the same time we work on non-structural strategies, that is plan what to do in the event of a major flood by establishing the selective opening of embankments where less damage is caused: the models indicate it.” Finally, to those who put concrete construction at the top of the causes of flooding, the expert reminds: «There has been land consumption, but it is necessary to quantify the impact. It was done in Romagna and in last year’s flood the impact was minimal.”
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