The US Army Corps of Engineers exploded a large section of a Mississippi River levee on Monday in a desperate attempt to protect an Illinois town from rising floodwaters.
The corps said the break in the Birds Point levee would help tiny Cairo by diverting up to 1.2m of water off the river.
Just before Monday night’s explosions, river levels at Cairo were at historic highs and creating pressure on the floodwall protecting the town.
For the Missouri side, the blasts were likely unleashing a muddy torrent into empty farm fields and around evacuated homes in Mississippi County.
Brief but bright orange flashes could be seen above the river as the explosions went off just after 10:00pm. The blasts lasted only about two seconds.
Darkness kept reporters, who were more than 800m off the river, from seeing how fast the water was moving into the farmland.
Engineers carried out the blast after spending hours pumping liquid explosives into the levee. More explosions were planned for overnight and midday Tuesday, though most of the damage was expected to be done by the first blast.
But questions remain about whether breaking open the levee would provide the relief needed, and how much water the blast would divert from the Mississippi River as more rain was forecast to fall on the region on Tuesday.
The seemingly endless rain has overwhelmed rivers and strained levees, including the one protecting Cairo, at the confluence of the Ohio and Mississippi rivers.
Flooding concerns also were widespread on Monday in western Tennessee, where tributaries were backed up due to heavy rains and the bulging Mississippi River.
Streets in suburban Memphis were blocked, and some 175 people filled a church gymnasium to brace for potential record flooding.
The break at Birds Point was expected to do little to ease the flood dangers there, Tennessee officials said.
The Ohio River at Cairo had climbed to more than 18.5m as of Monday, a day after eclipsing the 1937 record of 18.1m.
The river was expected to crest late Wednesday or early Thursday at 19.2m − just 30cm below the level that Cairo’s floodwall is built to hold back − before starting a slow decline by Friday.
The high water has raised concerns about the strain on the floodwalls in Cairo and other cities. The agency has been weighing for days whether to blow open the Birds Point levee, which would inundate 52,000ha of Missouri farmland.
Engineers believe sacrificing the levee could reduce the water levels at Cairo by about 1.2m in less than two days. A National Weather Service spokesman put the figure closer to 1.5m.
“These are uncharted territories, but it would be very fast,” she said.