Spillway north of New Orleans expected to close in July
The corps began opening the Bonnet Carré Spillway on May 10 to relieve stress on levees protecting New Orleans. It was the first time the spillway's been opened twice in one year.
Crews opened 168 of the spillway's 250 bays over 11 days , using cranes to pull up 20 huge timbers called needles in each bay.
Spokesman Matt Roe said Thursday that the closing will be gradual and paced to the Mississippi River's fall, just as the opening was paced to its rise. He says he doesn't know how long it will take.
"Each day the hydrologists will look at what the river is doing and match that to have a slow fall," he said.
The spillway was opened for 44 days in February, March and April and has now been open for 48 days, breaking the one-year record of 75 days in 1973. The current opening has tied the third-place mark for consecutive days. The spillway was open for 48 days in 1937 and 57 in 1945.
A corps tweet Wednesday said the closing will begin when the river falls to 15.5 feet (4.7 meters) at the Carrollton gage.
That's for safety of workers who must lower the timbers into rushing water, Roe said.
The amount of water passing through the spillway peaked May 21 and 22 at 161,000 cubic feet (4,560 cubic meters) per second. That's enough water to fill the U.S. Capitol rotunda in about 8 seconds.
The spillway's flow was down to 108,000 cubic feet (3,060 cubic meters) per second Thursday, Roe said.
The governors of Louisiana and Mississippi say freshwater has replaced brackish water in Lake Pontchartrain and left much of the Mississippi Sound far less salty than usual, killing oysters, hurting fish catches and damaging livelihoods. Both have asked the U.S. Commerce Department to declare a fisheries disaster.
Scientists say fresh water in the sound may have contributed to a high number of dolphin deaths .
Entomologists say the lake's fresh water was also the hatching ground for clouds of mosquito lookalikes that plagued people along the lakefront in New Orleans, Jefferson and St. Tammany parishes.