Hurricane Ida blasted ashore Sunday as one of the most powerful storms ever to hit the U.S., knocking out power to all of New Orleans, blowing roofs off buildings and reversing the flow of the Mississippi River as it rushed from the Louisiana coast into one of the nation’s most important industrial corridors.
Data from the U.S. Geological Survey shows a storm gauge just south of New Orleans recorded a “negative flow” on the Mississippi River, which flows into the Gulf of Mexico, as storm surge from Ida pushed inland.
In the six days before Ida's arrival, the river had a discharge rate of around 300,000 cubic feet per second. However, on Sunday, it was moving nearly 40,000 cubic feet per second of water upriver during peak reversal.
USGS supervising hydrologist Scott Perrien told CNN that the reversal is “extremely uncommon.”
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“I remember, offhand, that there was some flow reversal of the Mississippi River during Hurricane Katrina, but it is extremely uncommon,” Perrien said.
The storm surge caused the river level to rise about seven feet at the USGS gauge in Belle Chasse, Louisiana, according to Perrien.
Ida weakened into a tropical storm overnight as it pushed inland over Mississippi with torrential rain and shrieking winds.
Rescuers set out in hundreds of boats and helicopters Monday to reach people trapped by floodwaters and utility crews mobilized after a furious Hurricane Ida swamped the Louisiana coast and made a shambles of the electrical grid in the sticky, late-summer heat.
Interstate 10 between New Orleans and Baton Rouge — the main east-west route along the Gulf Coast — was closed because of flooding, with the water reported to be 4 feet deep at one spot, officials said.
Preliminary measurements showed Slidell, Louisiana, got at least 15.7 inches of rain, while New Orleans received nearly 14 inches, forecasters said. Other parts of Louisiana and Mississippi, Alabama and Florida got 5 to 11 inches.
Amid the maze of rivers and bayous around the New Orleans area, people retreated to their attics or rooftops and posted their addresses on social media with instructions for search-and-rescue teams on where to find them.
The Louisiana National Guard said it activated 4,900 Guard personnel and lined up 195 high-water vehicles, 73 rescue boats and 34 helicopters. Local and state agencies were adding hundreds of more.