What has been done in the last fifty years to minimize the risk of flooding in Florence? How great a risk is flooding to the city today? In what circumstances could we be faced with a catastrophe along the lines of 1966?
To seek answers to these questions, The Florentine spoke with Enio Paris, professor of hydraulics at the Department of Civil and Environmental Engineering at the University of Florence, who analyses and monitors the Arno River on a regular basis, and Carlo Francini, manager of the UNESCO Office of the Municipality of Florence and site manager of the UNESCO World Heritage site “The Historic Centre of Florence”.
Giovanni Giusti: What can be done to lower the risk of flooding in Florence?
Enio Paris: 50 years after the 1966 flood, our knowledge of the Arno River are still not sufficiently adequate to face the risks deriving from flooding, which has always occurred in the past and which will continue to occur in the future. The damage caused to persons and property by catastrophic events cannot ever be nullified. Damage can be reduced, however, through structural interventions, through dams, detention basins and laminated reservoirs), by the local government (city planning, ground use, infrastructure), civil protection (warning systems, civil protection plans) and risk awareness (training, information and education).
GG: What has been accomplished to date among these measures aimed at reducing the risk and damage of a future flood?
EP: Not much in actual fact. In terms of structural interventions, in the Seventies the foundation slabs of the Ponte Vecchio and Ponte Santa Trinita bridges were lowered by a metre to increase the river’s capacity through the city. According to the physical model made by the University of Bologna in 1972, lowering the foundations upped the maximum capacity from 2,800 m3/sec to 3,200 m3/sec (approx. +15%), but this figure has still to be verified. The first of four detention basins in the Valdarno is expected to open in the next few days; the remaining three should be implemented within the next couple of years. The detention basins are located in areas where they can collect the river’s excess water to avoid uncontrolled overflow. Other smaller interventions have been introduced like raising the parapets in Gavinana, but nothing crucial. In 2014, a survey of the river bed was conducted using a multibeam and laser scanning, which provided a 3D map of the waterway, showing the morphology of the underwater part.
GG: What were the advantages of this survey?
EP: Several. Firstly, comprehensive knowledge of the river’s geometry and the surface and underwater engineering. Then there’s the opportunity to monitor the state of disrepair of the bed and walling. For instance, through this survey we observed the undermining of the foundation of the left pillar of Ponte Vespucci. The City of Florence restricted the circulation of heavy traffic and introduced additional surveys around the foundation in order to gain invaluable knowledge to strengthen the bridge. Lastly, the survey forms the database to construct mathematical and physical models to predict risks.
GG: What’s the status quo in terms of education and awareness?
EP: The University of Florence, with numerous other public and private associations, institutions and organizations, is a member and supporter of the Firenze2016 Project, which aims to learn from the 1966 flood to obtain concrete results for the future: to improve prevention and increase protection for persons and property. With the Firenze 2016 Project, the fiftieth anniversary of the Florence flood intends not only to be a chance to remember but also to be a pivotal moment to promote ideas, projects and new know-how to face the future.
A view of lungarno Vespucci, Florence, on a stormy November day, 2016
GG: Tell me about the Management Plan of the Historic Centre of Florence and potential flooding.
Carlo Francini: The projects undertaken and added to the Management Plan of the Historic Centre of Florence aim to reduce possible damage to fixed and movable cultural heritage caused by flooding through citizen awareness of the effects of a flood about the areas that could be affected and behaviour to be adopted during a warning. Back in 2010 a memorandum of understanding was approved to secure Florence’s cultural heritage if the Arno River were to overflow. The project included surveying the buildings of cultural interest in the Historic Centre of Florence in an area potentially subject to overflow.
GG: Is the Arno a risk or a resource?
CF: The Arno River has always been an important resource for the Historic Centre of Florence, associated with the city’s history, its culture, environment and society. Our intention is to spark to a new vision of the Arno, a more proactive approach, which views the river as a resource to be looked after, promoted and lived. By starting with a greater awareness of the importance of the Arno we can plan future measures to secure citizens, visitors and the monumental and artistic heritage of Florence, whilst making the river usable, accessible and appealing.
To have a broad overview of the actions taken since 1966 and the present-day criticalities about the flood risk in Florence, download the report written by an international committee of independent experts, titled the International Technical and Scientific Committee of Florence 2016. The judgment made by the committee is critical without reserve:
“Since 1966, some actions have been taken to reduce the risk to flooding, however, these actions have not been sufficient to provide the standards that one would expect for a city like Florence. […] The ITSC concluded that Florence remains at risk to significant flooding and this risk grows each day. It is not a question of whether a flood of the magnitude of 1966 or greater will occur, but when. In fact, the level of protection that exists in Florence at the present time does not yet provide the risk reduction needed for the city and is not on a level appropriate to the citizens and treasures that rest within the city. If, under current conditions, a 1966-like flood occurred, the consequences to human lives, treasures, other properties and community infrastructure could be much more catastrophic than they were in 1966”.