By June 1, 2011, 89% of the System perimeter construction will defend against a storm with a 1% chance of occurring in any given year. The remaining 11% of the System perimeter includes the HSDRRS levees co-located with the Mississippi River levees on the west bank, where construction is suspended until high river stages recede.
86% of the System perimeter is constructed to 100-year design criteria. 2% of the System perimeter is constructed using temporary engineered interim structures which meet the 100-year criteria and are temporary in nature, to be replaced by permanent features. 1% of the System perimeter has engineered construction closures on-site to be used, should a hurricane threaten the area, to close discrete access points that are under construction, such as railroad/highway crossings.
The 100-year elevations were determined from data developed through extensive modeling using the most advanced technology available. A team of scientists, engineers, members of academia, and other experts used a comprehensive surge modeling system to determine storm surges for an event that has a 1% chance of occurrence in any given year. The required 100-year elevations vary throughout the system based on individual hydrological requirements.
The map emphasizes the re-design of the System perimeter, blocking storm surge at the mouths of outfall canals, the Inner Harbor Navigation Canal at Lake Borgne and Seabrook and the West Closure Complex. These structures remove over 60 miles of levees and floodwalls from direct exposure to storm surge resulting in 30% less perimeter to defend.
The Corps has strengthened and improved 133 miles of levees, floodwalls, gated structures and pump stations, forming the new Greater New Orleans perimeter system.
Funded at almost $15 billion, the HSDRRS is the Corps’ largest civil works program ever, and the Corps’ number one domestic priority.