See also: Sacramento, which dealt with frequent winter/spring flooding back when it was first founded because the founders built the city right up against the river. The city adapted by effectively converting all the first floors into basements and raising the city's "ground" (most of it all got filled in with dirt or otherwise lost with time, but some of it's still preserved in the so-called "Old Sacramento Underground").

Venice will likely have to take similarly-drastic measures, and they're a lot harder to take given that modern-day Venice is much bigger than 1850's-1860's Sacramento.