New Orleans District Sets Protocol For Closing Spillway

The New Orleans Engineer District has announced the protocol for closing the Bonnet Carré Spillway, the flood control structure on the Mississippi River almost 30 miles above New Orleans, La.

The Bonnet Carré, which diverts water from the river to Lake Pontchartrain and onward toward the Gulf of Mexico, is currently nearing the 50th day of its second opening this year. The Corps initially opened the spillway February 27 in response to a flow rate at the Carrollton Gage in New Orleans of 1.25 million cubic feet per second (cfs). That first opening of the year lasted 44 days, with a peak discharge of 213,000 cfs.

By early May, the Mississippi River was on the rise again, and the Corps reopened the spillway on May 10—marking the first time in the spillway’s 88-year history that it opened twice in a single year. Though the spillway has been open longer this time, peak discharge has been lower, reaching 161,000 cfs. on May 21.

The Bonnet Carré Spillway was first opened in 1937 and, on average, has been used every 10 years since. Swells in operation occurred in the 1970s, when the spillway was opened three times. And since 2008, the spillway has seen a significance rise in usage. Over the last decade, the spillway has been operated six times, including the past two years and three of the last four years.

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With the Carrollton Gage reading just under 16 feet the morning of June 27, it appears the current opening should be drawing to a close within two or three weeks.

“The closure of the Bonnet Carré Spillway structure will begin at a stage of 15.5 feet at the Carrollton Gage,” according to a statement released by the New Orleans District. “This will allow the crews to safely begin closing bays. Based on the forecast from the National Weather Service we anticipate the closing process to begin in the second or third week in July.

“There is still a tremendous amount of water in the river, so the closing will not be a fast operation and Mississippi River waters will not exceed 1.25 million cfs. past the Carrollton Gage,” the statement concluded.

According to the current Mississippi River forecast from the National Weather Service, the Mississippi River in New Orleans will fall to 15.5 feet around July 20.

Much of the Mississippi River Basin is in the midst of the longest-lasting flood on record. In Louisiana, Baton Route entered flood stage on January 6 and set a new record for longest duration of a flood event on May 21, according to the National Weather Service. Red River Landing entered flood stage on December 28, 2018, and set a new flood duration record on May 28. Both previous records were set in 1927.

At Bonnet Carré alone, operation of the spillway this year has smashed the previous record of 75 days set in 1975. Currently, the combined days open in 2019 will reach 100 on July 5, with at least two more weeks to follow after that, based on current forecasts.

The long operation of Bonnet Carré has caused an uproar to the east as fresh water from the Mississippi River has encroached on commercial fishing areas in Lake Pontchartrain and Lake Borgne, the Mississippi Sound and along Coastal Mississippi. Catches for shrimp and crabs are dramatically down, and oyster fishermen are seeing almost a total die-off of their harvest. A sharp increase in dolphin and sea turtle mortalities have been observed, and algae blooms along the Mississippi Gulf Coast have triggered beach closures.

The unprecedented operation of the Bonnet Carré Spillway has prompted Mississippi officials to ask for more input in future openings, and Mississippi Gov. Phil Bryant has requested a federal disaster declaration for fisheries in the state.