Local Mississippi River water levels expected to hold steady
Published: Monday, May 16, 2011, 7:45 AM
By Mark Schleifstein
The opening of the Morganza Floodway on Saturday and the ratcheting up of the Bonnet Carre Spillway flow to Lake Pontchartrain to 319,000 cubic feet per second on Sunday is keeping water levels in New Orleans right at the Mississippi's official 17-foot flood stage, a level not expected to vary much during the next two weeks, according to the National Weather Service.
And a lower crest of the Mississippi River on Sunday at Arkansas City, Ark., about 100 miles above Morganza, might help the Army Corps of Engineers in its plan to reduce the amount of water needed to be funneled into the Atchafalaya River Basin, which could reduce damage to homes, businesses and residences there.
The half-foot reduction in the expected crest at Arkansas City, believed the result of the overtopping of a levee a bit upstream, has allowed the weather service's Lower Mississippi River Forecast Center to drop its May 25 crest forecast at Morgan City to 11 feet, compared to an earlier estimate of 12 to 13 feet.
On Sunday, the corps increased to nine the open gates at Morganza, allowing about 90,000 cubic feet per second to flow into the Atchafalaya River, and keeping water in the Mississippi at Baton Rouge below 1.5 million cubic feet per second.
Over the next two weeks, as much as 125,000 cubic feet per second will be moved from the Mississippi to the Atchafalaya at Morganza, joining more than 700,000 cubic feet per second diverted into the Atchafalaya through the Old River Control Structure.
Reduced estimates of water flowing into the Atchafalaya from the Red and Ouachita rivers and the corps decision to use only a quarter of the Morganza Floodway capacity, instead of half, helped lower the Morgan City estimate, said David Welch, development operations hydrologist with the forecast center.
The rising water is still expected to threaten a variety of oil and gas production facilities within the Atchafalaya Basin, according to state and federal officials. There are 589 producing oil and gas wells within areas that will be inundated with the opening of the Morganza Floodway, according to the state Department of Natural Resources, representing 19,300 barrels of oil a day and 252.6 million cubic feet of gas.
Also at risk is Alon Refining in Krotz Springs, on the banks of the Atchafalaya River, where state and local officials are beefing up an emergency levee system to protect both the refinery and other homes and businesses.
"Construction continues on the additional levee, and every indication I have is that the project is on track, " said Blake Lewis, a spokesman for the company.
"(The) refinery continues to be on normal operations and will remain that way until either a change in safe conditions is identified or the flood situation creates an unresolvable logistics issue, " he said. "I can't predict either circumstance."
The refinery processed an average 73,457 barrels of oil a day during the first quarter of 2011, according to a recent Security & Exchange Commission report. It receives petrochemicals and crude oil from major pipelines that run through the basin.
The oil and gas wells and other manufacturing facilities have been directed by both the state Department of Environmental Quality and the Louisiana Oil Spill Control Office to be prepared for the floodwaters and to secure loose equipment.
In addition to the wells, there are believed to be 97 storage tanks, 10 pipelines and 86 bulk liquid petroleum transportation facilities, as well as a number of retail, light manufacturing and other commercial sites in the path of high water.
Impact on residences
There also are about 28,000 residences within the floodway that are outside ring levees.
Officials say there also are 172 known archaeological and historic sites there.
The effects of the high water on farmland and communities in the Atchafalaya Basin is still a guessing game, in part the result of that river's successful transfer of the sediment contained in the 30 percent of the Mississippi that it normally carries to the Gulf of Mexico.
That sediment has been filling in many low spots and water bodies within the basin, especially during flood years, said Daniel Kroes, an ecologist with the U.S. Geological Survey. The survey is conducting a variety of studies during this year's high river event to track what's in the floodwaters and where it goes.
Kroes said large water bodies like Myette Point and Flat Lake have grown noticeably smaller since the first time Morganza was opened in 1973.
"People you bring out there today don't really recognize it if they haven't been watching the change, " he said. "Over the years, the river has deposited more and more sediment."
All that sediment also has created an 8.5 mile long delta at Wax Lake Outlet, just west of Morgan City, the only part of Louisiana's coastline that is growing.
The corps has requested the Geological Survey to conduct the studies, in part to help understand whether the floodwaters stay within the river channel and the crisscross of oil and gas canals that dot the basin, or whether the water and its sediment flow through all of the basin's wetland areas, Kroes said.
Researchers with Tulane University and Virginia Tech are assisting in gathering that data.
The Geological Survey's National Stream Quality Network also will be sampling what is in the water, both at the town of Melville near where it enters the floodway and to the south, in Morgan City and the Wax Lake Outlet, said George Arcement, director of the survey's Louisiana Water Science Center in Baton Rouge.
The scientists will be testing for nutrients, pesticides, suspended sediment, turbidity and alkalinity, and oil and grease, he said.
Similar sampling of materials carried by water through the Bonnet Carre Spillway also will begin in Lake Pontchartrain and last for several months, similar to research conducted after the spillway was opened in 2008, Arcement said.
Survey scientists also have deployed 57 storm surge sensors, usually put in place in advance of hurricanes, to measure water heights throughout the basin, he said.
Another 10 temporary monitors have been placed in key locations to help officials keep track with rising water as it moves down the basin. That data is available on the web at http://la.water.usgs.gov/.