Since Hurricane Katrina, the federal government has spent $14.5 billion on levees, pumps, seawalls, floodgates and drainage that provide enhanced protection from storm surges and flooding in New Orleans and surrounding suburbs south of Lake Pontchartrain.
The system is a 350-mile network of levees, floodwalls, canals, 24 pumping stations and 99 pumps within the city of New Orleans – suburbs have their own pump systems.
Levees are made from compacted soil, whereas floodwalls are erected from man-made materials, usually metal and cement.
The National Hurricane Center forecasts between 10 to 15 feet of floodwaters in the West Bank area, which lies east of the main part of the city (the area is named for its position on the Mississippi River) – the upper range of that estimate would ‘overtop’ most of the southwest-facing levee walls facing the Gulf of Mexico in that area.
The average height of the levee walls facing southwest, according to NOLA.com, is 14 feet.
If forecasted flood levels prove true, floodwaters will rise over levees for the first time since the system was upgraded post-Hurricane Katrina. In 2005, over 50 levees failed throughout New Orleans, leaving 80 percent of the city underwater.
A car sits parked on a levee close to New Orleans, amid fears the flood defenses could be overcome by Hurricane Ida
The Gulf Intracoastal Waterway West Closure Complex in Belle Chasse, Louisiana, is pictured on July 13 of 2019
The surge is predicted to weaken as it flows over the marshes and land of southern Jefferson Parish, shrinking in height and intensity as it moved further inland and toward the levees surrounding the communities near the Mississippi River. Exactly how much of an effect that would have, however, is not clear.
‘Armoring,’ a new strategy applied to the levee system since Hurricane Katrina, involves strategically planting grass and laying mats along the inside of the levees – this prevents floodwaters that flow over the walls from eroding soil at the levee’s base, which could cause the structure to collapse.
However, because water has never made it over the retaining walls before, this erosion-prevention system has never been tested in practice.
Southeast Flood Protection Authority – West Region Director Nicholas Calli, whose agency oversees the levees, said to NOLA.com that he was confident that the system would work as designed.
This forecast from the National Hurricane Center shows just how high storm surges could rise – with up to 16 feet forecast for the mouth of the Mississippi River
Authorities predict that the rest of the system, lining the Mississippi River to the north of the city of New Orleans, is not expected to be overwhelmed by high water levels.
A surge of storm water, in theory, would be slowed and lowered in height as it flowed over the marshes and land of southern Jefferson Parish, putting the walls protecting the communities near the Mississippi River – it is unclear how much, however.
Water that overtakes the levees would be pumped out by the same water pumps used to divert rainwater that falls within the levee’s walls outside of its perimeter.
Parts of the $2billion of drainage equipment installed since 2005 can pump out as much as 4.7 inches of rainwater each three hours, according to the Army Corps of Engineers. Combined, the Corps said, the pumps have a capacity of over 50,000 cubic feet per second (CFS), or 400,000 gallons of water.
Authorities urged residents on Friday to clean leaves and detritus around storm drains to prevent the system from clogging and, therefore, slowing the removal of water.
While some of the pumps were built more recently, according to New Orleans Sewerage & Water Board Executive Director Ghassan Korban, some are antiques. Officials tried to bring an electrical turbine online on Friday in an attempt to provide a back-up power source for less reliable pumps.
Three of the 99 pumps are not operation, an obstacle that Korban said will be solved by the ‘redundancy’ of the system and its back-ups.
Just weeks ago, on August 6, the Army Corps of engineers recommended $1.7billion dollars in renovations to the system to ensure that it will work reliably until 2078. Among proposed changes were raising the height of 99 miles of the levees, replacing over a mile of floodwalls and building an additional 3.2 miles of additional flood walls.