The Bonnet Carre Spillway opening usually draws a crowd

The Bonnet Carre Spillway opening usually draws a crowd

(WVUE) - The rapidly rising Mississippi River will force the U.S. Army Corps of Engineers on Thursday to operate the Bonnet Carre Spillway, the giant relief value 32 miles north of New Orleans.

Thousands of wooden piles were driven during construction to support the structure (U.S. Army Corps of Engineers)

Built after the great 1927 flood, the Bonnet Carre has operated 11 times since 1937, most recently in January of 2016.

A large volume of fresh, nutrient rich fresh water pouring through the spillway into Lake Pontchartrain frequently shocks the system, resulting in algae blooms and temporary dead zones in the lake.

However, the dramatic sight of thousands of cubic feet per second pouring through the spillway bays frequently draws huge crowds to witness the opening.

Corps staff members plan to initially open 10 of the 350 bays on Thursday, and more in subsequent days depending on the river's predicted flow.

Each bay measures 20 feet in length.

To open the structure, workers will ride a rail car, hoisting large creosote timbers that block the Mississippi, 20 per bay.

Below are vitals statistics from the U.S. Army Corps of Engineers

Engineers designed gaps in the spillway to relieve the pressure on the structure.  As a result, a relatively small amount of water has poured through the still-closed bays since last week as the river’s height rose.

During just a partial opening Thursday, the river will surge through the bays, sending white water rapids toward the lake nearly six miles away.

On Tuesday at 7 a.m., the Carrollton river gauge in New Orleans read 14.37 feet, according to The National Weather Service Advance Hydrologic Prediction Service.

Forecasters expected the river to reach 15 feet later in the day and to hit 17 feet-- flood stage-- on March 14.  The river levees protect New Orleans to a height of 20 feet.

The river pours through gaps in the spillway pins, creating Louisiana waterfalls

A Corps website estimates the spillway will operate every 10 years.  However, this week's opening marks the second time the Corps has operated the Bonnet Carre in three calendar years.

The spillway will operate for the fourth time since 2008, also marking only the second time the structure has been opened in eleven calendar years