A steady trickle of water seeping through the Bonnet Carre Spillway turned into torrents Wednesday morning as the wooden beams keeping the Mississippi River in its channel were plucked one by one from their bays.

Workers methodically made their way across the span, allowing more and more of the fast-rising Mississippi’s course to be diverted into Lake Pontchartrain to keep the river below the height of the levees that protect New Orleans and other downriver communities.

It was the 13th time the spillway has been opened in its 90-year history, and the first time the structure has been needed in back-to-back years. This year’s opening was necessary because of heavy rains across the basins that feed the Mississippi and Ohio rivers, feeding a crest that is making its way downstream.

“Everything is going according to plan,” Col. Michael Clancy, head of the U.S. Army Corps of Engineers’ New Orleans district, said of the opening.

Watch live video from the opening below. Can't see video? Click here.

The spillway is opened whenever the flow in the Mississippi reaches a rate of 1.25 million cubic feet per second, a level that roughly corresponds with a river height of 17 feet above sea level and leaves it a few feet shy of the top of the levees.

Before the spillway was opened on Wednesday, the river had reached a height of just above 16 feet at the Carrollton gauge in New Orleans, but pressure from water upstream pushed it past the rate that triggers the opening, said David Ramirez, the Corps’ chief of water management.

The Corps opened 30 of the spillway’s 350 bays on Wednesday, about eight fewer than it had predicted would be necessary two days earlier. About 25,000 cubic feet of water per second poured through those openings, Ramirez said.

Each of those bays is typically closed with 20 large wooden “needles,” some of which date back to the structure’s original construction in 1931. Crews used a crane to grab the needles from bays spaced at intervals along the low structure in the same order dictated by the original manual written for the structure's operation in the 1930s.

Clancy said the Corps will continue to adjust the number of open bays to manage the river’s height and speed. At this point, the spillway is expected to remain open for at least a month, and up to 200 bays could be opened when the river crests, he said.

Onlookers lined the levees as the Corps went to work, watching and filming as bay after bay was opened and the marshy spillway was flooded with water headed toward Lake Pontchartain.

Among those watching were seniors in an environmental science class from John Curtis Christian School in River Ridge.

Their teacher, Marisa Guillie, said she turned the class’s studies to the Mississippi River two weeks ago after she heard about the downpours wracking the Midwest and began to suspect the spillway would be opened.

Chara Brown, one of Guillie’s students, said seeing the spillway’s opening helped make the lessons the class had learned about the Mississippi more concrete and drove home the scale of the river and the methods used to control it.

“To see how quickly the water from the river flows out and takes over the entirety of the area is amazing,” Brown said.

The spillway is owned by the Corps and is kept unoccupied to allow the water a channel that does not threaten people or their homes. So the primary concern with any opening is the effect a flood of fresh water will have on the normally brackish Lake Pontchartrain.

The Lake Pontchartrain Basin Foundation will monitor the lake weekly to check for changes to its salinity and oxygen levels, as well as to check on the effects on algae levels and vegetation, Executive Director Kristi Trail said. It will be particularly interesting to see how the lake reacts to two consecutive years of spillway openings, Trail said.

North of the spillway, the river is expected to come close to the flow that would trigger an opening of the Morganza Spillway, which has been used only twice in its 65-year history.

At its peak, the river is expected to reach a rate of 1.45 million cubic feet per second; the Corps typically considers opening the Morganza when its rate is 1.5 million cubic feet per second and rising.

“It’s going to be very, very close, but as we sit here today we are not planning on opening Morganza,” Clancy said.

Follow Jeff Adelson on Twitter, @jadelson.​