Spring could bring big floods
by Wally Northway
Published: March 4,2010
The National Weather Service (NWS) has issued its “Flood Potential Outlook,” and it raises concerns for serious flooding in Mississippi this spring. Just a little ill-timed rain – here or to the north – and the state could be facing another serious natural disaster.
“The ground is already saturated, which does not allow water to run off,” said Jackson-based NWS hydrologist Marty Pope. “The biggest threat is along the Mississippi River. We have a lot of snow to melt in the Upper Mississippi region as well as in the Ohio Valley,” said Jackson-based NWS hydrologist Marty Pope.
The NWS report stated that an above average spring flood potential exists on Pascagoula River Basin (which includes the Leaf and Chickasawhay rivers), the Pearl River Basin, the Yazoo, Big Black and Homochitto river basins as well as the Lower Mississippi River Basin from Arkansas City, Ark., to Natchez.
The synopsis for North Central, Central and much of South Mississippi, reads: “Over the past three months, temperatures have generally run below normal…while precipitation has been above normal. Cold weather and periods of excessive precipitation during the fall and winter has resulted in long-term soil moisture contents being above normal…”
Pope is especially concerned about the Mississippi River. It is common for the state to be facing a serious flood threat due to snow in the Ohio Valley or the Upper Mississippi River. However, this year the snow has been heavy in both regions.
Upstream, snow depths ranged from 12 to 40 inches over Iowa and Minnesota while Illinois and Missouri have snow depths of less than six inches. Snow water equivalents across Iowa and Minnesota ranges from two to seven inches and less than one inch in Missouri and Illinois.
Snow depths over the Ohio Valley range from six to 20 inches with snow water equivalents running from one to three inches.
The report noted that as of late February, moderate to major falls were taking place along the Lower Ohio Valley and Lower Mississippi River Basin. However, the river was well above flood stage already. The Mississippi River at Vicksburg registered 139 percent above normal, historical streamflows while Natchez recorded a flow 177 percent.
Pope said weather patterns over the next few weeks would be the critical factor. At press time, a series of rain-producing fronts were expected across the state and nation. But, Pope said that is a good thing. His fear is that a front could stall over the state, or worse, to our north.
“If we get a stalled weather pattern, or they get big rains in the north, we could be in trouble,” said Pope, who pointed out that the Mississippi River reached a depth of 57.41 feet at Greenville in the spring of 2008, triggering flooding along the river and its tributaries. “Excessive rains could trigger a major snow melt, and that water will come our way in a hurry. A gradual melt is what we need.”
The Mississippi Levee Board maintains that the levee is capable of holding back any spring flooding this year. Peter Nimrod, the Greenville-based chief engineer with the Levee Board, pointed out that the Mississippi River levees have been tested by high water recently, and there were few problems.
In 2008, when the river came within a foot of the crest registered by the great flood of 1973, Nimrod said there were some issues with sand boils. In 2009, the river hit 52.9 feet at Greenville, and the levee system handled that volume without any incident.
He added that the system has a project design flood of 72 feet, meaning the levees should hold up against the river at that depth. And, there is an extra three feet built above that. So, theoretically the levees should contain the river at a depth of 75 feet.
The U.S. Army Corps of Engineers reevaluated the project design flood after the 1973 event, and determined that 69 miles of levee were insufficient. Improvements are complete on roughly 32 miles of the levee, and another eight miles are currently being strengthened.
Mississippi’s other rivers are not affected by snow melt. Those waterways are impacted only by local conditions – rain and soil moisture. The Pearl River has historically been prone to flooding, the last major event being 1979 when communities in Central Mississippi, especially Jackson, where only rooftops of homes were showing in some neighborhoods.
Late last month, the U.S. Army Corps of Engineers announced that it had tested the Pearl River levees in Hinds and Rankin counties, and certified that the system is capable of withstanding a 100-year flood. However, the Corps said the certification does not mean the levees completely reduce flood risks. It is recommending extending the existing levee system by approximately 22 miles.
This is one concern of Mike Womack, executive director of the Mississippi Emergency Management Agency (MEMA). Unlike the Mississippi River levee system, the Pearl River levees are inadequate to hold back the water along the length of the nearly 500-mile-long river.
However, Womack’s bigger concern is in Washington and the suspension of the National Flood Insurance Program (NFIP). The NFIP expired Feb. 28 when Congress failed an extension of the program.
Womack said it is vital that the program be restarted. His primary advice to businesses is to ensure they have adequate flood insurance. Here, he recommends that businesses splurge.
“If you have insurance that protects against a 100-year flood event, look at purchasing insurance to insure against a 500-year event,” he said.
Womack said he is confident that MEMA is well prepared for a spring flood. The agency received extra federal and state assistance post-Katrina that added more resources and personnel, and that those resources would be on the ready if needed.
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