Corps begins to close spillway

• By JOE GYAN JR.
• Advocate New Orleans bureau
• Published: May 1, 2008 - Page: 1A - UPDATED: 12:30 a.m.

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NORCO — With the swollen Mississippi River in a slow fall, the U.S. Army Corps of Engineers on Wednesday began slowly closing the Bonnet Carré Spillway control structure and said the process should be completed by mid-May.

The corps opened 38 of the structure’s 350 bays on April 11 — marking the ninth time it had been opened since 1937 and the first since 1997 — and eventually opened 160 bays.

Corps spokesman Eric Hughes said 10 of the 20-foot-wide bays were closed Wednesday. The flow in the river and the daily drop in river stage will determine how many bays are closed each day over the next two to three weeks, he added.

“Hooray! Hallelujah!’’ Lake Pontchartrain Basin Foundation Executive Director Carlton Dufrechou said of the corps’ decision.

The foundation, as well as commercial and recreational fishing and seafood interests that use the lake, said the shorter the spillway is open, the better it is for the lake, its marine inhabitants and those who make a living on its waters.

Dufrechou said the muddy river water has turned the freshwater lake “pretty chocolate looking.’’

“It’s brown. The salinities are near zero everywhere,’’ he said, noting that the onslaught of river water has pushed the fresh water to the eastern reaches of the lake.

The fertilizer-laden river water is expected to trigger an algae bloom in the lake this summer when the water heats up, which could kill seafood and fish in the lake.

“Only time and the climate will determine that,’’ Dufrechou said.

The corps is working with its partners on various studies — new and ongoing — to understand and address the impacts that the spillway’s opening will have on the local environmental and economic industry, Hughes said.

Peak river flows passing through the 1.3-mile Bonnet Carré structure reached about 119,000 cubic feet per second, he said, well below its design capacity of 250,000 cfs — or about 187,000 gallons per second.

The Bonnet Carré— about 30 miles above New Orleans — is opened to prevent Mississippi River flows at New Orleans from exceeding 1.25 million cfs, thus relieving pressure on local levees, lowering river stages at communities south of the structure and reducing the velocity of the river current — a plus for ships and barges.

The corps estimates the river would have crested at 17.8 feet at the Carrollton Gauge in New Orleans had the spillway not been open. The river crested at 16.96 feet in the city April 24. Flood stage there is 17 feet.