Many densely populated US regions face the threat of flooding as disastrous as after Hurricane Katrina, due to urban spread into river floodplains, scientists warn.
An earthquake or even a moderate flood could destroy the levee system protecting towns and cities along the Sacramento and San Joaquin rivers in northern California, said Jeffrey Mount of the University of California.
"The probability of a catastrophic levee failure in the Sacramento-San Joaquin Delta in the next 50 years is two in three," Mount said on the sidelines of the American Association for the Advancement of Science (AAAS) annual conference.
Mount gave a worrying presentation to the conference entitled "The Sacramento/San Joaquin Delta: the next New Orleans?"
He said one of the frequent earthquakes in California could destroy the levee system that has been built up since the middle of the 19th century, sending flood water over a wide area.
Mount said it could have a similar impact to the Asian tsunami in 2004.