the Army Corps of Engineers had bui

the Army Corps of Engineers had built a system of levees and seawalls to keep the city from flooding. The levees along the Mississippi River were strong and sturdy, but the ones built to hold back Lake Pontchartrain, Lake Borgne and the waterlogged swamps and marshes to the city’s east and west were much less reliable. Even before the storm, officials worried that those levees, jerry-built atop sandy, porous, erodible soil, might not withstand a massive storm surge. Neighborhoods that sat below sea level, many of which housed the city’s poorest and most vulnerable people, were at great risk of flooding.