Louisiana's top hurricane experts have rejected the official explanations for the floodwall collapses that inundated much of New Orleans, concluding that Hurricane Katrina's storm surges were much smaller than authorities have suggested and that the city's flood- protection system should have kept most of the city dry. With the help of computer models and visual evidence, scientists at Louisiana State University's Hurricane Center have concluded that Katrina's surges did not come close to overtopping those barriers. * * * * Ivor van Heerden, the Hurricane Center's deputy director, said the real scandal of Katrina is the "catastrophic structural failure" of...