The Great Mississippi Flood of 2011
As the date of the cresting of the Mississippi river approaches, the state has taken increasingly direct steps in flood control to prevent as much damage as possible to our somewhat weather-torn state. The opening of the Morganza Spillway over the weekend marked a significant point in both the flood and in the lives of Louisianans — especially the residents of the seven parishes that are most vulnerable to the floodwaters.
“It’s the most water we’ve probably seen in more than 100 years,” Louisiana Department of Agriculture and Forestry commissioner Mike Strain said in a phone interview. “We are working very hard, and we are going to fight the flood.”
As Louisiana residents have been doing for a very long time now.
The Red River and the Mississippi were once two rivers flowing parallel to one another down to the Gulf of Mexico. It’s thought that in the 15th century the Mississippi writhed its way westward, intercepting the Red River at Turnbull’s Bend. From the southern swoop of the bend, the Atchafalaya River was formed, as a distributary of the Mississippi.
In the first half of the 19th Century, Henry Miller Shreve, a steamboat captain and pioneer, fancied himself a river engineer. He cut a path through Turnbull’s neck, cutting travel time down significantly for his enterprise. As a result of his efforts, the north swoop of Turnbull’s bend slowly filled with sediment, while the southern portion continued to transport water from the Mississippi to the Atchafalaya distributary. That southern stretch, known today as the Old River, now links three rivers together: The Red River, the Atchafalaya River and the Mississippi.
The Atchafalaya river — which, until 1839, had been blocked by a logjam — was opened up after local and state officials removed the debris; the river has been eating up the Mississippi ever since. Atchafalaya grew deeper and wider over time, siphoning off more and more of the Mississippi. The Old River acted as a valve: when the water was high in the Mississippi (due to heavy snow melt, for example), water would move westward by way of the Old River to the Atchafalaya. When the Atchafalaya was high, water would move eastward through the Old River to the Mississippi. By the end of the 19th century, eastward flows of the Old River were becoming more and more rare as the Atchafalaya grew: in 1920, around 18% of the Mississippi was entering the Atchafalaya. By 1950, that percentage had jumped to 30.
After monitoring the latitude flow of water over a period of time (the amount of water that crosses a latitudinal line), the Army Corps of Engineers concluded that without preventative action, the Mississippi would change course to intercept the Atchafalaya river by 1990, in a process known as “delta switching.” It was decided that the current water levels be preserved, so that no more than 30% of the water would enter the Atchafalaya, and no less than 70% would remain in the Mississippi.
A decade later, the Old River Control Structure, which is comprised of a series of floodgates that control the amount of water that passes through the Old River into the Atchafalaya, was completed. By 1975, water levels of both the Atchafalaya and the Mississippi were completely maintained by man under “artificial control.”
Keeping the River at Bay
350 gates opened at the Bonnet Carre Spillway
photo by USACE HQ
After the Great Mississippi Flood of 1927, the US Congress ordered the Army Corps of Engineers to develop a flood control plan which would help to protect citizens living along the lower Mississippi from a sequel to the debilitating flood.
The Bonnet Carre Spillway, located around 12 miles west of New Orleans, is considered the first line of defense against rising waters of the Mississippi. It diverts about 250,000 cubic feet per second of water flow into Lake Ponchartrain. It has operated 10 times since its construction in 1931. As of press time, the Army Corp of Engineers has opened 330 of the 350 bays, but is expected to open the spillway 100% eventually.
The Morganza Spillway, located about 50 miles northwest of Baton Rouge, was opened over the weekend. Completed in 1954, the river control structure uses 125 bays to divert up to 600,000 cubic feet per second of water from the Mississippi to the Atchafalaya river basin. This is only the second time the spillway has been opened since its completion in 1954. The Army Corp of Engineers have, to date, opened only 15 bays, and are expecting to operate the spillway at 25% capacity.
The third and final floodway is called the Fuse Plug Levee. It runs east to west near the West Atchafalaya levee, and is lower than the surrounding levees. If the water reaches above Fuse Plug levee, it’s designed to quickly disintegrate, directing potentially dangerous waters away from inhabited areas. The Fuse Plug levee carries a maximum capacity of 250,000 cubic feet per second of water. It has never been used, and there is no intention of using it in the near future.
The Politics of Flood Control
The Mississippi river is a national economic concern, and consequently the flood control has forced politicians to make some unappetizing decisions. The Morganza spillway, for example, is operated under the assumption that it prevents more destruction than it causes. Diverting floodwater to the Atchafalaya, before those waters hit Baton Rouge and New Orleans, will potentially save the state millions of dollars worth of damage.
“The Mississippi river is responsible for 60 percent of transportation of this nation’s grains, coal, and ore and petroleum products,” Commissioner Strain said. “It is necessary [to operate the spillway] because failure to do so could result in catastrophic failure to the levee system.”
But that safeguard comes at the cost of incurring significant damages to areas located within the Atchafalaya basin.
“We’re looking at probably water until the end of June of the first of July in some areas,” Commissioner Strain said. “Look at Arkansas: $500 million in damages and a million acres under water; Missouri, 130,000 acres and $100 million worth of damages. We’ll see.”
Commissioner Strain requested the Federal Department of Agriculture’s Office of Risk Management to categorize the flooding resultant of the spillway as a natural disaster, instead of a man-made disaster, for the purpose of recouping some of the lost crop yields in the flood.
“A man-made designation would not allow producers to make crop insurance claims,” he said in a statement released two weeks ago. “The rising water will overtake the control structure regardless of any opening or diversion.”
Last week, the Department of Agriculture guaranteed farmers’ eligibility for crop insurance payments.
“We’re happy that USDA and FEMA have made a decision that is favorable for our producers,” Commissioner Strain said. “We’ve been pushing hard for this declaration.”
Implications of Opening Morganza’s Box
Morganza Spillway, 3 days after US Army Corps of Engineers opened 4 bays.
photo by tobo
Over the weekend, the Army Corps of Engineers opened a few bays of the Morganza Spillway to reduce the amount of water that reaches Baton Rouge and New Orleans.
“It is regrettable that we’re in this situation completely,” Commissioner Strain said. “This is the system that we have in order to control the river and the massive amount of water that is coming down, which is greater than the amount of water we saw in the Great Flood of 1927.”
Up to three million acres of land will be under water (this is roughly the size of Connecticut), and around 2,500 residents within the floodway, and another 22,500 outside the floodway, will be vulnerable to back flooding.
“You’re going to have water that will flow down to Morgan City, and between 11 and 12 and a half feet [deep],” said Commissioner Strain. The residential areas in Morgan City will be protected by 20-foot levees.
The soils of the spillway — which are particularly rich — are used for farming soybeans, wheat and rice. Farmers spent last week harvesting as much crop as they could before the gates Morganza Spillway were opened on Saturday. Up to 18,000 acres of farmland will be lost due to the flood, and while the loss of crops will have an effect on the market, the USDA’s assertion that the disaster is natural will enable farmers to file insurance claims and recoup some or all of their losses.
The Alon USA Energy refinery, located in Krotz Springs in the Atchafalaya Basin, will close as a result of opening the spillway. the refinery is projected to be surrounded by water within 14 days of opening Morganza. The company has begun constructing levees around the refinery to protect against the flood waters. The refinery accounts for approximately 80,000 barrels of oil per day.
Oyster beds located near the mouth of the Gulf will be inundated with fresh water from the Mississippi from the two spillways. Such a dramatic change in salinity will prove deadly for the oysters, potentially hurting the industry for a few months. Last week, the Department of Health and Hospitals announced the closing of two oyster harvest areas, located on the east side of the Mississippi, in addition to the relocation of some oyster beds to areas beyond the reach of the flood waters.
Governor Bobby Jindal requested a declaration of commercial fisheries failure by US Department of Commerce Secretary Gary Locke, in light of the rising Mississippi, and five other disasters experienced in the region in the last six years, including Hurricanes Katrina, Rita, and the BP Horizon oil spill.
Finally, wildlife inhabiting the land, including black bears, snakes, deer and wild hogs, will be forced into residential areas surrounding the spillway as a result of the flood waters, while wildlife in the basin near Morgan City and Pierre Part might be trapped, due to steel cofferdams that have been erected atop the Atchafalaya levee to extend it.
by USACE HQ
Note: Photos that appear on this blog were not part of the original printed story.