Bre Parra stood alongside the Bonnet Carre Spillway on Thursday, her toddler nursing a bottle in his stroller and her older daughter darting among the few hundred people gathered there.

Parra and three other parents from her Paradis-Houma home schooling group brought a total of 12 children to watch workers begin to open the spillway, a massive 1930s structure that remains a key part of the federal government's efforts to manage the might of the Mississippi River.

"My family is from Wisconsin and Iowa" along the upper part of the river, Parra said. "We have seen up there what the river can do."

Video: Bonnet Carre Spillway opens to ease flooding concerns along Mississippi River

This was Parra's first time to see the spillway opened, and she planned to tell her Midwestern relatives. "This is what we can do to relieve the pressure," she said.

Relieving pressure is exactly what the federal officials began to do Thursday by opening eight of the spillway's 350 bays, diverting some of the rising river's water into Lake Pontchartrain a few miles away.

As the volume of water moving downriver increases, more gates will be opened, said David Ramirez, a water management official with the U.S. Army Corps of Engineers, which operates the spillway. The Corps also controls other flood-protection structures along the lower Mississippi River, including the Morganza Spillway near Baton Rouge and the Old River Control Structure in central Louisiana, where the Red River flows into the Mississippi.

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The first timber is removed from the Bonnet Carre Spillway as it is opened by U.S. Army Corps of Engineers in Norco, La. Thursday, March 8, 2018, to relieve flooding risk down river in New Orleans where the Mississippi River is expected to reach flood stage at 17 feet later in the week. Eight bays with twenty creosoted timbers each will be opened Thursday with possibly more of the 350 bays being opened through out the week. The Mississippi River is the third largest drainage basin in the world draining 41 percent of the water from the contiguous 48 United States. Heavy rain hundreds of miles away can cause the river to rise down in New Orleans.

Currently, the river is flowing at a rate of just above 1.25 million cubic feet per second, which is the threshold to trigger the opening of the spillway, Ramirez said. That volume is deemed to be the maximum that the levees in New Orleans can safely withstand.

Current forecasts show the river, left to itself, would crest at about 1.4 million cubic feet per second. Such a flow would lead to the opening of between 150 and 175 bays. The Corps currently expects to have bays opened for about 20 days, Ramirez said, though he cautioned that is always subject to change.

Thursday's opening — as it is every time the spillway is called into service — was a spectator event, attended by not just Corps officers but also local officials and hundreds of spectators.

One of those was Emmet Cedotal, a 67-year old retired boilermaker who lives in Bucktown. 

"I come every year to see it," he said, stubbing out a cigarette. Cedotal was there when the Corps opened the spillway in 2011 and 2016. He missed the 2008 opening.

With river level rising in New Orleans, Bonnet Carre Spillway to open sooner than expected

Cedotal was keeping a keen eye on the area just below the spillway structure where, he said, one can often see fish — many times invasive carp — jumping after being sucked through into the spillway.

"We'll come out and watch when they open more gates," he said.

Even though the spillway was officially opened Thursday, about 8,000 cubic feet of water per second already was leaking through the structure, according to Col. Mike Clancy of the Corps. Thursday's eight gates will increase that amount by about 5,000 cubic feet per second, he said.

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Water seeps through the timbers of the Bonnet Carre Spillway before it is opened by U.S. Army Corps of Engineers in Norco, La. Thursday, March 8, 2018, to relieve flooding risk down river in New Orleans where the Mississippi River is expected to reach flood stage at 17 feet later in the week. Eight bays with twenty creosoted timbers each will be opened Thursday with possibly more of the 350 bays being opened through out the week. The Mississippi River is the third largest drainage basin in the world draining 41 percent of the water from the contiguous 48 United States. Heavy rain hundreds of miles away can cause the river to rise down in New Orleans.

Out in the spillway, two Corps airboats idled as the "needles" — long wooden timbers — were pulled out one by one. The crews in those boats were there to watch for any pallid sturgeon, an endangered fish that lives in the river. If any sturgeon fall through the spillway, the crews will attempt to capture, measure and tag them before releasing them back into the river.

The sturgeon watchers are just a part of an extensive environmental monitoring effort that ramps up when the bays are opened. Agencies will carefully watch as the river's sediment-laden fresh water spills into the lake, pushing out the brackish water and bringing an injection of new nutrients into the system. Those nutrients provide fresh breeding grounds for algae, which can deplete the oxygen levels in the lake and kill fish.

Past openings have shown that the freshwater displaces the saltwater after just a couple of weeks. But once the spillway is closed, the lake "returns to normal" after a few months, said John Lopez of the Lake Pontchartrain Basin Foundation.

Officials will also watch freshwater rivers and bayous around the lake for signs of carp or other invasive species, he said.

This year's opening is not the earliest the spillway has ever been opened, but it is early, Clancy said. 

"Typically, April or May is the high river period," he said.

Heavy rains in the Ohio River valley could mean that the river will stay high for a long period this year, but officials at this time do not believe that it will be necessary to open the Morganza Spillway northwest of Baton Rouge, which has been opened only twice, in 1973 and 2011. 

This is the fourth time the Bonnet Carre has been opened since 2008. It was opened only eight times between 1931 and 2007, but four times from 1973 until 1983. 

The spillway is part of the broader system that helps govern the flow of the Mississippi River south of Cairo, Illinois, where the Ohio River flows into the Mississippi, said Maj. Gen. Richard Kaiser, the commanding officer of the Mississippi Valley Division, which oversees the entire system.

Kaiser said the system helps protect 4.5 million people and agricultural land that produces $51 billion in crops every year.

Walter Dunbar, a retired shipbuilder, said he had interrupted his normal fishing trip to watch the spillway's opening.

"It's an experience to see," he said. "It's not an everyday event."

Follow Faimon A. Roberts III on Twitter, @faimon.