There was a horrible flood in Paris in 1910, so bad that the Seine overflowed its banks, bringing the city to a near standstill. At its peak, the Seine was some 20 feet above its normal level. The Zouave who stands below the Pont de l'Alma was literally up to his neck in water. Some 20,000 buildings housing 200,000 people were affected.
Today the Seine sits so low relative to the banks that it's hard to imagine that it ever approached the level of the quais. But there are still reminders of this natural disaster. Last week, I noticed this mark on a building on rue de Bellechasse, just a block or so from the Musee d'Orsay in the 7th arrondissement. During the flood, the Orsay (then a train station) was completely flooded, its tracks under water.
Despite a hundred years of technological progress, the authorities say that it could happen again. Better have your boots ready.