Lake Pontchartrain - Hurricanes

Hurricanes

During hurricanes, a storm surge can build up in Lake Pontchartrain. Wind pushes water into the lake from the Gulf of Mexico as a hurricane approaches from the south, and from there it can spill into New Orleans.

A hurricane in September 1947 flooded much of Metairie, Louisiana, much of which is slightly below sea level due to land subsidence after marshland was drained. After the storm, hurricane-protection levees were built along Lake Pontchartrain's south shore to protect New Orleans and nearby communities. A storm surge of 10 feet (3.0 m) from Hurricane Betsy overwhelmed some levees in Eastern New Orleans in 1965, while storm surge funneled in by the Mississippi River – Gulf Outlet Canal and a levee failure flooded most of the Lower 9th Ward. After this the levees encircling the city and outlying parishes were raised to heights of 14 to 23 feet (4.3 to 7.0 m). Due to cost concerns, the levees were built to protect against only a Category 3 hurricane; however, some of the levees initially withstood the Category 5 storm surge of Hurricane Katrina (August 2005), which only slowed to Category 3 winds within hours of landfall (due to a last-minute eyewall replacement cycle).

Experts using computer modeling at Louisiana State University after Hurricane Katrina have concluded that the levees were never topped but rather faulty design, inadequate construction, or some combination of the two were responsible for the flooding of most of New Orleans: some canal walls leaked underneath because the wall foundations were not deep enough in peat-subsoil to withstand the pressure of higher water.