With Mississippi River rising, Bonnet Carré Spillway is tested in case LA needs flood protection (2025)

The U.S. Army Corps of Engineers ran a test opening of the Bonnet Carre Spillway Monday morning following weeks of rising Mississippi River waters that could prompt the floodway to be used for the first time since 2020.

Current weather forecasts show the river hitting just around the threshold that triggers at least a partial opening of the diversion, which eases pressure on South Louisiana levees as water flows to Lake Pontchartrain.

The Corps has not yet announced whether the agency plans to open the spillway, and says they are monitoring the forecast before making a recommendation. According to National Weather Service projections Monday morning, the river will crest in New Orleans at 16.5 feet April 30 and then gradually drop in the following days.

The spillway, located in St. Charles Parish, opens when the river flow rate hits 1.25 million cubic feet per second, which usually corresponds to around 17 feet on the Carrollton gauge in New Orleans, or around 17 feet above sea level. But at this phase in the flood cycle, higher flow rates are translating to slightly lower elevation, said Matt Roe, a spokesperson for the New Orleans district of the Army Corps. An opening might be triggered at 16.5 or 16.6 feet.

On Monday morning, Army Corps members, nearby fishers and curious spectators gathered before the Bonnet Carre as crane operators and other workers pulled 20 timber beams from the massive structure, allowing water to temporarily rush through a single compartment, or bay. The test run is really a training exercise, Roe said, that relies on high water levels.

"We have to wait for the water to get high because water actually seeps through the structure by design," Roe said. "When we have water against the structure like we do today, that stimulates real-world conditions of when we'd operate it."

With the spillway fully closed, the seepage rate of water through the beams Monday morning was 2,000 cubic feet per second. While the single bay was briefly opened, the flow rate of the released water was 260 cfs.

'Everybody needs to see'

The crew individually pulled each timber beam, called a needle, from the structure amid the push and pull of the water. A single timber beam weighs around 600 pounds, according to the Army Corps. Each bay contains 20 beams, and 350 bays compose the structure, which was built 96 years ago after the 1927 flood.

Jimmy Bordelon, 56, drove down from St. Amant in Ascension Parish to watch the test opening with his two young grandsons. He's watched the spillway opening several times and wanted the five- and seven-year-old boys to learn about the river and the protection of South Louisiana, he said.

"It's something that everybody needs to see," Bordelon, 56, said.

Two different crews of around a dozen workers ran the test exercise. But after the first test opening, water poured through the spillway, filling shoes and sending spectators home or to higher ground.

In recent weeks, the rising water levels have led to a good fishing environment. Tim Yang, who has fished in the area for over 15 years, left the spillway with a drum, and other fishers walked away with coolers full of fresh catch.

While opening the Bonnet Carre alleviates pressure on the levee system, the rush of fresh water to the lake can also imperil commercial shrimp and oyster fisheries. The spillway was last opened in 2020.

If a spillway opening does happen, it is not likely to be long, as forecasts indicate river levels will fall in the days immediately after cresting. That would be a big difference from 2019, when the spillway had to be opened twice for a record amount of time.

The Mississippi Sound Coalition, representing local governments, fishers and the tourism industry, sent a letter to the Corps last week calling on it to limit any spillway opening as much as possible due to the potential harms.

"Operations of the Bonnet Carre Spillway in flood years like 2011 and 2019 have caused extreme adverse effects on the oyster reefs, dolphins, fisheries and natural resources of the Mississippi Sound," it said in a statement. "The openings in 2019 alone essentially wiped out many natural oyster reefs in the Sound."