The Arno River in Italy intermittently inundates large areas of the Arno River basin. This paper investigates flood phenomena and evaluates some of the proposals that have been made to alleviate the flood hazard using procedures developed at the IBM Pisa Scientific Center.On the morning of November 4, 1966, the residents of Florence, Italy, awoke to find themselves the victims of a major flood. Thirty‐six people were drowned in Florence, and replaceable real property damage has been estimated at $640,000,000 (C. Pandolfi, personal communication, 1977). In addition, art treasures of inestimable value were lost, and the cleanup operation attracted worldwide attention, sympathy, and help [Judge, 1967]. As an illustration of the amount of damage caused by this catastrophic flood, we have reproduced a photograph of Ponte Vecchio (Figure 1) taken on the morning of November 5, 196