Forecasts call for lower crest as Morganza Spillway opening set

Residents should not expect any changes in the levels of the Bayou Teche as a result of the opening of the Morganza Spillway later this week, but those with property or camps in the Atchafalaya should be vigilant and prepare as the gates at the floodway’s control structure are opened in coming days, according to Iberia Parish Director of Homeland Security and Emergency Preparedness Prescott Marshall. The Army Corps of Engineers postponed the opening of the gates from Sunday to Thursday because of lower than forecast water levels on the Mississippi River.

The Army Corps of Engineers announced last week that the Morganza Spillway would be opened Thursday, four days later than originally scheduled. But for many in the Teche Area, the implications of that opening are not clear.

The spillway was last opened eight years ago, on May 14, 2011. Despite fears at the time that the water would inundate areas of St. Martin and St. Mary parishes, the effects were far milder.

“The difference in 2011 is that we had a really scary forecast,” Iberia Parish Director of Homeland Security and Emergency Preparedness Prescott Marshall said. “It was also really dry that spring, so much of the vegetation and soil soaked up some of the water. Obviously we had a very wet spring this year, but even with that the expectation is far less than that this season.”

Marshall said the last forecast he has received was on Friday morning. At that point, officials with the Corps of Engineers, the National Weather Service and the Governor’s Office of Homeland Security were projecting a crest almost a foot and a half lower than 2011.

“The forecast this time is for a crest at Bayou Sorrel, with a worst case on June 11 of about 1.4 feet lower than 2011,” Marshall said. “After that call, the Corps of Engineers announced delaying the opening of the spillway until June 11 at the earliest due to lower than expected water levels on the Mississippi River. So our expected crest of June 11 won’t happen. It will be later.”

The main areas the flooding of the spillway will threaten are north and south of Iberia Parish. In St. Martin Parish, the Butte La Rose area is within the Atchafalaya Basin, making it very exposed to any extremely high water. If the water rises above 28 feet at that point, it could come back around the levee wall, causing flooding outside the basin.

“Right now, parish government is watching developments very closely,” Marshall said. “We have conference calls three times a week for updates. Barring any major changes, this should not be a major issue in Iberia Parish, unless someone has property or a camp in the Atchafalaya Basin. Unlike our adjoining neighbors to the north and south, we don’t have the same exposure they have.”

The only way the Morganza opening could affect the levels in the Bayou Teche or Vermilion River is if that backwater flooding occurs or if there were a levee breach that allowed water to flow out of the Atchafalaya Basin.

In St. Mary Parish near Morgan City, a barge was sunk this weekend to prevent backflow of water through Bayou Chene that could bypass levees and cause flooding to Morgan City, Amelia and Stephensville in Lower St. Martin Parish. Work is continuing to surround the sunken barge with sheet pile and rocks to block Bayou Chene prior to the opening of the Morganza.

The Army Corps of Engineers initially expected the Mississippi River to reach a depth of 60 feet at the spillway’s control structure on June 5 in Pointe Coupee Parish, near mile 280 of the river. That date was pushed back to June 9, allowing for the later opening of the structure’s gates.

The control structure contains a concrete weir, two sluice gates, 17 scour indicators and 125 gated openings to control the flow of water from the Mississippi to the Morganza Floodway, which carries the water to the Atchafalaya.

The Morganza Floodway begins at the Mississippi River, extends southward to the East Atchafalaya River levee, and eventually joins the Atchafalaya River Basin Floodway near Krotz Springs. The 20-mile long, five-mile wide floodway consists of a stilling basin, an approach and outlet channel, and two guide levees.

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