Large areas of New Orleans, including many parts where people are busy rebuilding, remain at risk from flooding despite more than $1 billion in work to fix and upgrade the hurricane protection system, a new Army Corps of Engineers report released Wednesday shows. The corps released risk assessments on a block-by-block basis in the form of maps showing the estimated threat of flooding each year from hurricanes. The mapping was based on extensive modeling and statistical analysis. For example, it shows that if what the corps refers to as a 100-year storm were to hit the city, many neighborhoods in the central part of the city that were inundated during Katrina are now less likely to flood because of levee improvements since Katrina hit on Aug. 29, 2005. Other areas, however, could see as much as 2.5 meters of flooding. Nearly every part of the city, except for a sliver along the Mississippi River where the French Quarter sits, would flood under current levee conditions if a 500-year hurricane hits the area. Katrina was a 400-year storm, according to the corps.