“The summer of 2023 will be different from last year: river flows have increased and, apart from a critical area in the Piacenza area, the water tables have been restored throughout the basin,” explains Alessandro Bratti, secretary of the Po River District Basin Authority and former director of ISPRA.
Having just witnessed the images of flooded Romagna, on the eve of the next meeting of the Observatory on Water Uses on May 25, it seems surreal to be discussing the topic of drought, but the two phenomena go together: a few weeks ago, Bratti himself had pointed out that 16% of the banks of the Po River were in serious danger, partly due to the drought that in recent years had left them without cover for a long time.
In May, rainfall affected the entire basin, but it took on a tragic character in Romagna, where the raised embankments collapsed. What are the possible responses to these extreme events?
The embankments on the Po River, its main tributaries and the Emilia-Romagna waterways affected by the latest flood events are strategic systems for the protection of very large portions of the Po Valley. In many cases, these protective systems are inadequate to contain flood water levels, in terms of their height, shape and structure, and for this reason those territories have been identified as Areas of Potentially Significant Risk. We should stress that embankments can never guarantee absolute safety: they can’t hold when the water level rises above them; if they are overtopped, they quickly collapse, allowing a large part of the flood water volumes to flow into the territories behind them.
How can we deal with this situation?
A task that is necessary, but not sufficient, is the proper routine and extraordinary maintenance of embankment works and the adequate management of sediments and riverside vegetation. The embankments on the Po and those on other river courses in the Po Valley have reached limitations in terms of height: this can no longer be significantly increased, and there is a need to find new defensive courses of action in case of exceptional events, which are increasingly possible in times of climate change. In particular, it is a matter of giving more space to the rivers, reversing the trend that had characterized the era in which many such embankments were built: the reclaiming activity of the early 20th century, which involved recovering as much space as possible for agriculture and anthropogenic development.
Today we need to think in the opposite direction: wherever possible, the embankments should be pulled back, even creating closed floodplains just like those found on the Po. Floodplain soil levels should be lowered in the most overhanging sections of embankment compared to the surrounding ground planes; sections of embankments that can handle overflowing should be built, so that they won’t collapse if overtopped by water. These innovative interventions will have to be considered in the future, along with the completion of the expansion reservoirs currently being built, the upgrading of bridges and exposed infrastructure and the relocation of the most critical buildings and settlements and those severely damaged during the flood events.
There is fake news circulating about the Ridracoli Dam, which claims that it was opened suddenly and that was what caused the flood, when in fact it had been undergoing controlled draining in order to be able to store water from the expected rainfall. Faced with the complexity of the hydrological system, how do we help citizens understand the mechanisms that govern it?
A lot has been accomplished in terms of forecasting flood events, alerting citizens and managing emergency phases, and the floods of the past few days bear witness to this, despite their severity and exceptional character. The death toll could have been much higher. We need to continue to educate in order to make citizens aware of the risks, because people’s memories are short and they often tend to forget what happened even in the recent past. This is necessary in a country in which 94 percent of its municipalities are exposed to the risk of floods, landslides and coastal erosion.
In recent days, in Turin, the Po River flooded the Murazzi area, something that happens frequently now. Do we need an extraordinary plan to ensure the habitability of the Po Valley? If so, what are the priorities?
The plans already exist. For example, the Hydrogeological Structure Master Plan for the Po River was approved back in the late 1990s, and it already contains the zoning of the areas next to the river and the land use regulations – and urban planning, which is in the hands of the regions and municipalities, will have to conform to this.