Genoa flood: why a stream like the Bisagno could be so dangerous?

Many people after the Genoa’s flood of a few days ago asked how is possible that a little stream like the Bisagno (not a river, a stream!), dry almost all the year, could make all those damages and become so dangerous?

First, we have to notice that the most damages, in which many people died, has been caused by the Rio Fereggiano, another stream, affluent of the Bisagno, but less important.

Then, the overflowing of the Bisagno luckily caused only material damages, but this was enough to paralyze the city and flood it.

Over the exceptional rains (>500 mm of rains in only 3h) there’s, of course, also a wrong management of the territory and of the same hydrography: the Bisagno, in this way, is a very particular case, as explained in this very interesting article (only in italian: http://www.terranews.it/news/2011/11/una-foce-non-puo-diventare-un-porto ) that we’re trying to explain you.

Indeed, the Bisagno isn’t new to similar situations: unfortunately, after the Second World War we had several overflowing, due to a particular management of the same stream that, after the “building boom” in the 60s’ has been “tombed”, covered in its terminal part (that one close to the sea): yes, you understood, that street that you’re seeing now, called Viale Brigate Partigiane, is the covering of the Bisagno, a stream transformed to a street.

If then we add to this situation that at the mouth has been built the International Fair with attached a little touristic harbor, increasing the cement, reducing the slope and putting away the same mouth… the situation doesn’t appear so unforeseeable as the the Authorities are saying.

In the years, a lot of alternative solutions have been proposed to solve the problem and make safe the Bisagno but with scarce results: maybe the only valid solution would be “re-open” the Bisagno, restoring its original flow and demolishing the buildings that the men built around, in front and (even) above.