Ravenna, 8 May 2024 – In the weeks following the double flood of May 2023, municipalities such as Brisighella and Casola Valsenio earned the nickname – like nearby Modigliana – of ‘towns of 200 landslides’.
The flood in Sant’Agata sul Santerno in a photo from May 2023
A picture that today would seem optimistic: the number of landslides recorded by the special post-flood plan, presented a few days ago by the commissioner structure and the Region, contains the most frightening fact of all; there are 6,200 landslides in the municipality of Brisighella, 5,500 in Casola Valsenio, 2,000 in Riolo Terme. In the two mountain municipalities, 3.9% and 5% of the municipal territory respectively collapsed: this means 7.6 square kilometers of landslides in Brisighella and five in Casola.
An apocalypse that takes on even more dramatic contours when you focus your attention on everything around the landslide: in Casola there are over 100 buildings included within the five meter perimeter of the so-called ‘mapped landslide polygons’, 300 are within the twenty meter perimeter of a landslide.
In both cases it means that over one building in ten, among those judged to be at risk in Emilia Romagna, it is located in the municipality of Casola. There are as many as 300 interferences between roads and landslides recorded in the small Apennine municipality.
But if the mountain cries, the plain does not laugh: subsidence in some parts of the province of Ravenna will remain an element of risk; the area at the mouth of the United Rivers is in the spotlight (“with maximum subsidence of around 15 millimeters per year”) and “a large area east of Faenza between the Lamone and the Montone, at the height of the motorway”. Lowerings attributable in the first case to the extraction of hydrocarbons and in the second to the withdrawal of groundwater, which could respectively “exacerbate marine intrusion” and “slow down the outflow of floods”.
In the plains the special post-flood plan identifies what is a corollary of problems to be solved: in particular, the following include “inadequacy of reclamation works in artificially drained territories”, “changed hydrological and meteorological conditions compared to the design period”, “inadequacy of drainage systems”, “volumes of reservoirs available in the reclamation network which are now chronically insufficient”, “soil waterproofing” and “silting of canals”.
The work to be done outlines a real Marshall plan: and the most complex situations, as regards the rivers of the area, are linked to Lamone and Senio. For the first “areas may be identified where to evaluate controlled overflows even in the stretch between Via Emilia and the A14″.
As for instead the Marzeno, which is a tributary of the Lamone, the implementation of lamination works in the section upstream of the confluence, in Faenza, is reiterated as a priority. A complicated situation also for the Senio river, which flooded Castel Bolognese a year ago, and from there the water continued its course across the plain: “Local structural interventions will be implemented to defend Riolo Terme and the hamlet of Isola; completion is a priority of the Cuffiano expansion tank”.
But it’s not enough: it’s also useful a “defensive system that protects on the one hand the town of Castel Bolognese, and on the other favors the capacity for lamination even through closed floodplains”. While for the Fiumi Uniti the expansion tanks will have to see the light upstream of Forlì, for the Savio it will be necessary to “increase the volume of lamination also upstream of Castiglione”.
Channels of the territory are not doing better: “On 50% of the Ravenna network it is necessary to restore the hydraulic efficiency. The Canala-Via Cupa-Valtorto, Fosso Ghiaia, Lama Superiore and Inferiore, Fossatone, Rio Cosina, Madonna del Pino basins need to be strengthened “.
It is also necessary “make up for the insufficiencies of the water pumping systems, also through the installation of new generators”. Finally, the connection of the Canala and via Cerba water pumping systems is defined as “of particular interest in Ravenna, with lightening of the hydraulic node of the Lama system at the Longana sewer, with outlet into the Ronco River”.
