The levees, which have been provisionally repaired, will be shored up further in the months to come, although their long-term fate is unclear. Better levees would probably have prevented most of the flooding in the city center. To provide further protection, a mobile dam system, much like a storm surge barrier in the Netherlands, could be used to close off the mouth of Lake Pontchartrain. But most experts agree that these are short-term fixes.

　　The basic problem for New Orleans and the Louisiana coastline is that the entire Mississippi River delta is subsiding and eroding, plunging the city deeper below sea level and removing a thick cushion of wetlands that once buffered the coastline from wind and waves. Part of the subsidence is geologic and unavoidable, but the rest stems from the levees that have hemmed in the Mississippi all the way to its mouth for nearly a century to prevent floods and facilitate shipping. As a result, river sediment is no longer spread across the delta but dumped into the Gulf of Mexico. Without a constant stream of fresh sediment, the barrier islands and marshes are disappearing rapidly, with a quarter, roughly the size of Rhode Island, already gone.