NEW ORLEANS ā When it comes to water, New Orleans faces three threats: the sea, the sky and the river.
Tropical storms and hurricanes send storm surges pushing up against the cityās outer defenses. Thatās what happened in 2005 when Hurricane Katrinaās surge caused widespread levee failures and left 80% of the city under water.
The massive rainfall from Hurricane Barry will have to be pumped out, taxing the cityās ancient and historically underfunded drainage system. And the Mississippi River, which drains most of the water that falls in a vast section of the United States and even parts of Canada, is held in check by tall levees.
Hereās a look at the defenses that protect the New Orleans area and risks that remain:
BRYAN NORCROSS TALKS TROPICS: Ā Hurricane Barry's storm surge threatens Louisisana
POST-KATRINA IMPROVEMENTS
After Hurricane Katrina, billions of dollars were spent to improve the system of levees, pumps and other infrastructure that protects the city from storms coming up from the Gulf. The U.S. Army Corps of Engineers worked to raise levees several feet, install new stronger floodwalls at critical places and strengthen almost every section of the 130-mile (210-kilometer) perimeter that protects the greater New Orleans area. The system is built to hold out storm surge of about 30 feet (9 meters) where the cityās boundaries meet the swamps and lakes near the Gulf of Mexico.
The post-2005 improvements include several massive floodgates that are shut when a storm approaches. In particular, a new surge barrier and gate that closes off the Inner Harbor Navigation Canal near the Lower 9th Ward has reduced the risk of flooding in an area long viewed as the cityās Achillesā heel.
But experts note that the system was built to protect against what experts once estimated would be a 100-year level of storm surge ā a surge that has a 1% chance of happening any given year. With rising seas from climate change and subsidence in Louisianaās coast, thereās concern that these killer surges will hit more frequently.
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THE RAIN
Hurricane Barryās rainfall is a particular problem for the low-lying city. Rainwater is pumped out through a century-old system of canals, drainage pipes and pumps ā all suffering from decades of neglect, laid bare during a particularly bad August 2017 deluge that dropped as much as 9 inchesĀ in three hours.
Since then, the cityās Sewerage and Water Board, one of the key agencies responsible for drainage, has poured tens of millions of dollars into generating power to make sure thereās enough electricity to keep pumps working. And theyāve improved systems to allow operators to see in real-time how the pumps and turbines are operating. The city also has moved to clean out catch basins to make sure water flow isnāt impeded.
Ahead of Barry, officials said 118 of the cityās 120 drainage and constant-duty pumps are available. That includes major drainage pumps able to move 1,000 cubic feetĀ of water per second.
But officials also have cautioned that the system canāt prevent all flooding. An intense rainstorm or a slow-moving hurricane that sits over the city could overpower it. Theyāve also emphasized the need to do more things such as ripping up concrete, and building water retention ponds and underground cisterns. These so-called āgreenā infrastructure projects are designed to let rainwater seep slowly underground instead of pumping it out.
THE RIVER
The New Orleans area is protected from the mighty Mississippi River by levees that started going up right around the time of the cityās first settlers three centuries ago. Reinforced and strengthened over the years, they are now about 20 feet to 25 feetĀ high, and are regularly inspected for seepage or other indications that the structural integrity is compromised.
The levees have never been overtopped in the cityās modern-day history, but the river remains swollen by months of rain across the Midwest, and its flows will push against a storm surge flowing upstream from the Gulf of Mexico.
Gov. John Bel Edwards said this would be the first time a hurricane made landfall in Louisiana when the Mississippi River was already at flood stage.
The river had been expected to crest at the same height as the lowest parts of the levees, but a positive forecast Friday night showed the river cresting slightly lower, raising hopes that the water will be contained.