Flooding: Morganza Spillway May Soon be Opened

May 13, 2011; 6:26 AM ET
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The Old River Control Structure, which allows water from the Mississippi River to enter the Morganza Spillway and Atchafalaya Basin, is seen from the air in Morganza, La., Monday, May 9, 2011. The Army Corps of Engineers has asked the Mississippi River Commission for permission to open the Morganza Spillway north of Baton Rouge to help alleviate pressure on river levees. It hasn't been opened since 1973. (AP Photo/Patrick Semansky)

According to Louisiana Governor Bobby Jindal, in a recent news conference, the Morganza Spillway will be opened as the slow-moving natural disaster along the Mississippi River continues.

The move would impact an additional 25,000 people, agricultural and wildlife areas with flooding.

The Morganza Spillway, completed in 1954, is a flood control option that can be used when the flow of the Mississippi River at Red River Landing, reaches a certain threshold.

That point was getting close Friday morning with the water near 1.48 million cubic feet per second. According to the U.S. Army Corps of Engineers, the trigger for opening the spillway is 1.50 million cubic feet per second and rising and is forecast by National Weather Service hydrologists to be reached this weekend.

Meanwhile, in the path of the spillway waters, crews were busy shoring up levees around multiple communities. A secondary levee was being constructed around Krotz Springs and a refinery located there.

The crews and residents were hoping for a few extra days before the spillway is opened, slowly releasing water from the Mississippi.

Levels along the lower Mississippi is surpassing marks set back in 1973, 1937 and 1927.

If the Morganza Spillway is activated an area nearly the size of Connecticut will be flooded in central and southern Louisiana. However, the move would take pressure off levees around nearby Baton Rouge and the downstream port of New Orleans, lowering flow rates and river levels in those and other areas.

The Bonnet Carre spillway was partially opened on Monday to lower river levels and flow rates around New Orleans. The move at Bonnet Carre is expected barely to keep the river below the tops of the 20-foot levees.

Late this week, the Army Corps of Engineers opened more of the Bonnet Carre's bays in an attempt to allow shipping to continue for a while longer along the river.

If the flow becomes too strong on Old Man River, boats cannot steer.

A record crest of 47.5 feet is forecast on May 22 at Baton Rouge, but this does not account for the opening of the Morganza Spillway.

The Morganza Spillway directs some of the flow from the Mississippi River into the Atchafalaya Basin.

If opened, water would slowly flood the parishes of St. Landry, St. Martin, Iberia, Morgan City and St. Mary with up to 25 feet of water.


This map shows the approximate areas that would be flooded (bright colored areas). A larger view of this map is available at the U.S. Army Corps of Engineers Website.

Direct and indirect flooding (water backing up into bayous and lakes) could affect approximately 25,000 people and agricultural areas.

Some communities within this zone are protected by ring levees.

Fortunately, since the flooding process along the Mississippi is very slow, it is giving people time to move valuables, take preventative measures and simply get out of the way in case evacuation orders are given.

The river flooding is not like a flash flood or tsunami, which can overwhelm communities in seconds and minutes.

Unfortunately, the agonizingly drawn-out nature of the flooding will have many areas under water and levees holding back the water for weeks.

The battle and worrying will go beyond the point of crest and the the patrol for boils and breaches will continue for weeks.

Boils are caused when water travels under a levee and comes to the surface on the side that is being protected. If not dealt with in a timely manner, the boils can continue to undermine a levee, leading to failure.

The levees along the lower Mississippi River are deemed the strongest in the nation and are largely constructed of nearly impenetrable clay.

Some rain and locally drenching thunderstorms will swing through the lower Mississippi Valley and the Delta region into early Saturday. Not enough rain is forecast to fall over a large enough area to impact the major river flooding.

Enough rain will fall at the local level to cause urban and flash flooding incidents in parts of the Midwest and the South over the next five days.

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