2011 Mississippi River floods: Difference between revisions

2011 Mississippi River floods

100 populated locations were experiencing major or moderate flooding on May 8, 2011. Source: National Weather Service
Date	April 4, 2011 to present
Location	Mississippi River Valley, United States
Deaths	Unknown
Property damage	US$2 to 4 billion

The Mississippi River floods in April and May 2011 are among the largest and most damaging along the U.S. waterway in the past century, rivaling major floods in 1927 and 1993. In April 2011, two major storm systems dumped record rainfall on the Mississippi River watershed. Rising from springtime snowmelt, the river and many of its tributaries began to swell to record levels by the beginning of May. Areas along the Mississippi itself experiencing flooding include Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana. U.S. President Barack Obama declared the western counties of Kentucky, Tennessee, and Mississippi federal disaster areas. For the first time in 37 years, the Morganza Spillway has been opened, deliberately flooding 4,600 square miles (12,000 km²) of rural Louisiana to save most of Baton Rouge and New Orleans.

Fourteen people were killed in Arkansas, with at least 383 killed across seven states in the preceding storms. Thousands of homes were ordered evacuated, including over 1,300 in Memphis, Tennessee, and more than 24,500 in the state of Mississippi. Up to 13% of U.S. petroleum refinery output is expected to be disrupted by flood levels exceeding historical records in several locations, with gasoline prices expected to rise. The flood crested in Memphis on May 10 and is expected to crest in southern Louisiana by May 23. The Army Corps of Engineers stated that an area in Louisiana between Simmesport and Baton Rouge is expected to be inundated with 20–30 feet (6.1–9.1 m) of water. Baton Rouge, New Orleans, and many other river towns are threatened, but officials stress that they should be able to avoid catastrophic flooding.

Rainfall totals within the United States for the week ending April 29.

From April 14–16, the storm system responsible for one of the largest tornado outbreaks in U.S. history also produced large amounts of rainfall across the southern and midwestern United States. Two more storm systems, each with heavy rain and tornadoes, hit in the third week of April. In the fourth week of April, from April 25–28, another, even more extensive and deadly storm system passed through the Mississippi Valley dumping more rainfall resulting in deadly flash floods. This latter storm produced over 250 tornadoes, killing at least 340 people in the deadliest tornado outbreak since 1925. Combined, the storms killed at least 383 people and caused an estimated $5 billion dollars in damage. The unprecedented extensive rainfall from these two storms, combined with springtime snow melt from the Upper Midwest, created the perfect situation for a 500-year flood along the Mississippi.

Flood stages and effects by state

As flood waters have proceeded down the Lower Mississippi from the St. Louis area (where the Missouri River and the Mississippi River converge), they have affecting in turn Missouri and Illinois, then Tennessee, Arkansas, Mississippi, and Louisiana.

Missouri and Illinois

This image shows the resultant flooding of farmland west of the Mississippi 32 kilometres south of the deliberate levee breach near Cairo, Illinois.

On May 3, the Army Corps of Engineers blasted a two-mile hole in the levee protecting the Bird's Point-New Madrid floodway, flooding 130,000 acres (530 km²) of farmland in Mississippi County, Missouri, in an effort to save the town of Cairo, Illinois and the rest of the levee system, from record-breaking flood waters. The breach displaced around 200 residents of Missouri's Mississippi and New Madrid counties, who were forced to evacuate after a court approved the Corps of Engineers plan to breach the levee.

Tennessee

Flooding along Beale Street in downtown Memphis, Tennessee

Dyersburg, a city in northwestern Tennessee, experienced the worst flooding with over 600 homes and businesses inundated as the Forked Deer River, a tributary of the Mississippi, flowed backwards into southern areas of the city. In Memphis, Tennessee, the up-scale neighborhood of Harbor Town, located along the river on Mud Island in Downtown Memphis, evacuated its 5,200 residents as flood waters rose to record levels. On May 5, the river reached 44 feet 2 inches (13.5 m), the highest level reached at Memphis since 1927, when the river there reached a record 48.7 feet (14.8 m). Many local rivers spilled their banks, including Big Creek, the Loosahatchie River, and the Wolf River. Subsequent flooding occurred in Millington, as well as suburban areas of Frayser, Bartlett, and East Memphis.

Arkansas

Interstate 40, connecting Memphis and Little Rock, experienced flooding west of Memphis along the White River between Hazen and Brinkley, where lanes in both directions were closed. Brinkley itself also experienced flooding. Eight people died in Arkansas as a result of flooding.

Mississippi

Mississippi counties declared federal disaster areas.

In Tunica County, nine casinos located on stationary river barges have been closed. The hotel portion of the casinos are located on adjacent, low-lying land, and have begun to flood with the rising waters. On May 5, the Harrah's Tunica has reported nearly 6 feet (1.8 m) of water inside the ground floor of the hotel tower. Near Vicksburg, Highway 465 in Warren and Issaquena counties was closed on May 5 due to high flood waters.

In anticipation of major flooding, Governor Haley Barbour announced on May 5 that the federal government had declared eleven counties along the Mississippi River federal disaster areas. Gov. Barbour requested to have additional counties added, and by May 7, thirteen counties were listed: Adams, Bolivar, Claiborne, Coahoma, Desoto, Issaquena, Jefferson, Sharkey, Tunica, Warren, Washington, Wilkinson, and Yazoo. The governor urges holdouts to head for higher ground saying "The biggest danger is that they choose not to evacuate assuming there'll be someone to rescue them," Barbour said, noting that emergency teams could be endangered as well. More than anything else, save your life and don't put at risk other people who might have to come in and save your lives."

Projected crest levels at Vicksburg and Natchez are above the record 1927 level. On May 11, water levels exceeded this level in Natchez and continue to rise. As of 6:00 pm CDT, the river has reached 60.41 ft (18.41 m).

Louisiana

Following the Great Mississippi Flood of 1927, much effort has been invested in building defenses to withstand a flood of three million cubic feet per second just upstream from the Old River Control Structure. The US Army Corps of Engineers refers to this design goal as Project Flood. the expected flow will be on the high side, but still within that maximum capacity, assuming everything works as expected.

Morganza Spillway

On May 14, 2011, a single floodgate of the Morganza Spillway was opened. Diversion of 125,000 cubic feet per second (3,500 cubic metres per second) of water from the Mississippi River to the Atchafalaya Basin is planned there, with the structure operating at about 21% of its capacity. This diversion was deemed necessary to protect levees and prevent major flooding in Baton Rouge and New Orleans, with the tradeoff of creating severe flooding in the Atchafalaya Basin, and will also reduce floodwater stress on the Old River Control Structure upstream. This was the first opening of the spillway since a 1973 flood.

Prior to this decision, the Corps studied four flooding scenarios, all of which assumed the Bonnet Carré Spillway near New Orleans would be concurrently operating at full capacity (100%).

United States Army Corps of Engineers 2011 Louisiana Flooding Scenarios

• 
  Anticipated inundation from Scenario 1
• 
  Anticipated inundation from Scenario 1a
• 
  Anticipated inundation from Scenario 2
• 
  Anticipated inundation from Scenario 3

• Scenario 1: Open the Morganza Spillway to half (50%) of its maximum capacity, which would divert 300,000 cubic feet per second (8,500 cubic metres per second) of water.
• Scenario 1a: Open the Morganza Spillway to one-quarter (25%) of its maximum capacity, which would divert 150,000 cubic feet per second (4,200 cubic metres per second) of water.
• Scenario 2: Do not open the Morganza spillway, and keep the Old River Control Structure at its routine operating level of only 30% of the Mississippi's flow; no additional water would be diverted
• Scenario 3: Do not open the Morganza spillway, and open the Old River Control Structure somewhat more, which would divert an extra 150,000 cubic feet per second (4,200 cubic metres per second) of water.

Following this analysis, which showed that extensive flooding is expected in the Atchafalaya Basin regardless of the choice made regarding the Morganza Spillway, the Corps decided to start the 2011 diversion by opening the spillway a bit less than described in scenario 1a (21%, not 25%)

Baton Rouge

Engineers intend to keep the Baton Rouge river levels at 45 feet or below, which is three feet below the state capitol's primary levees but five feet above the "major" flood stage. Shipping, industrial, and agricultural interests along the waterfront and further beyond the West side of the river are significantly impacted, and unprotected low lying areas are flooded. Opening of the spillways has caused an early artificial crest, and additional spillway floodgates will be opened as needed to limit the river level.

Bonnet Carré Spillway

The Bonnet Carré Spillway, near New Orleans, was built to divert water from the Mississippi River to Lake Ponchatrain, and from there to the Gulf of Mexico, reducing water levels and flow near New Orleans. On May 14, 2011, 300 of this structure's 349 bays were opened due to rising water levels otherwise anticipated to jeopardize levees protecting New Orleans.

Waterford Nuclear Generating Station

The Waterford Nuclear Generating Station, about 25 miles west of New Orleans, was restarted May 12, after a refueling shutdown on April 6. if the river exceeds 27 feet downstream from the Bonnet Carre Spillway, the plant would be forced to shut down because a circulating water system that drives the turbine would not be able to operate.

New Orleans

Open spillways are holding the river level at New Orleans, Louisiana around the 17 foot beginning of the flood stage, which is three feet below the levees which protect the city. Navigation and docking are difficult, but refinery and other industrial operations are continuing. However, production will be impacted by the inundation of 589 oil and gas wells in the Atchafalaya Basin producing 19,300 barrels of oil and 252.6 million cubic feet of gas per day.

Risk of major course change in the Lower Mississippi River

Over geologic time, the lower Mississippi River has used different pathways as its main channel to the Gulf of Mexico across the delta region. Left to its own devices, about every 1000 years a new main channel forms through the natural process of delta switching (technically known as "river avulsion"). Geologists consider such a change now overdue. Either of two new routes — through the Atchafalaya Basin or through Lake Ponchartrain — might become the Mississippi's main channel if control structures are overtopped or severely damaged during a severe flood, such as the 2011 event.

If the Mississippi changes course to the Gulf, it would probably happen at one of four locations, three involving the Atchafalaya, and one involving Lake Ponchartrain. As of 11 May 2011, the following scenarios are plausible but still hypothetical possibilities. So far there have not been any official reports of on-the-ground observations regarding weakening or design flaws in any of the flood control systems designed to prevent a course change, and the expected 2011 flood flow approaches but is still below the maximum design capacity of the flood-control system.

Atchafalaya Basin

Failure of the Old River Control Structure, the Morganza Spillway, or nearby levees would likely re-route the main channel of the Mississippi down the Atchafalaya River to reach the Gulf of Mexico south of Morgan City in southern Louisiana, greatly reducing water flow to its present channel through Baton Rouge and New Orleans. Through human intervention, this has so far been prevented, but during any major flood the risk of such an event is still present.

Old River Control Structure

The Old River Control Structure complex. View is to the east-southeast, looking downriver on the Mississippi, with the three dams across channels of the Atchafalaya River to the right of the Mississippi. Concordia Parish, Louisiana is in the foreground, on the right, and Wilkinson County, Mississippi, is in the background, across the Mississippi on the left.

The Old River Control Structure sits at the normal water elevation and normally diverts 30% of the Mississippi's flow to the Atchafalaya River. There is a steep drop away from the Mississippi's main channel. If this facility were to fail during a major flood, there is a strong concern the water would scour and erode the river bottom enough to capture the Mississippi's main channel. The structure was nearly lost during the 1973 flood, but repairs and improvements were made after engineers studied the forces at play. In particular, the corps made many improvements and constructed additional facilities for routing water through the vicinity. These additional facilities give the corps much more flexibility and potential flow capacity than they had in 1973, which further reduces the risk of a catastrophic failure in this area. Jeff Masters of the Weather Underground noted that failure of the Old River Control Structure "would be a serious blow to the U.S. economy, and the great Mississippi flood of 2011 will give [this structure] its most severe test ever."

Morganza Spillway

Because the Morganza Spillway is located at slightly higher elevation well back from the river, it is normally dry on both sides. Even if this structure were to fail at the crest during a severe flood, the flood waters would have to cause a significant amount of erosion, down to normal water levels, before the Mississippi could permanently jump channel at this location. {{citation}}: Empty citation (help) The Army Corps of Engineers has decided to open the Morganza Spillway at 1/4 of its capacity to allow 150,000 ft³/sec flood the Morganza and Atchafalaya floodways. In addition to reducing the crest downstream, this will also reduce the chances of a channel-change, by reducing stress on the other elements of the control system.

Levees upriver of the Old River Control Structure

Some geologists have observed that the possibility for course change exists in the area north of the Old River Control Structure. Army Corps of Engineers geologist Fred Smith once stated, "The Mississippi wants to go west. 1973 was a forty-year flood. The big one lies out there somewhere—when the structures can't release all the floodwaters and the levee is going to have to give way. That is when the river's going to jump its banks and try to break through."

Lake Pontchartrain

The area currently occupied by the Bonnet Carré Spillway, between the Mississipppi River and Lake Pontchartrain, is also a candidate for a new Mississippi River channel to develop. The spillway's major function is to reduce the level of the Mississippi downstream during flooding periods. "A secondary function of the Bonnet Carré Spillway is to prevent the Mississippi River from changing course. Both the Mississippi River and Lake Pontchartrain are at sea level, and the majority of the land in the area varies between one and three feet above sea level. The only thing holding back the Mississippi River is a ridge that runs along the east bank of the river that is 12 to 16 feet high. That ridge and the levee system are all that keeps the great river in check. In fact, in past floods, the Mississippi River would overflow this ridge and drain part of its flow into Lake Pontchartrain. In the mid-1800's, the Mississippi River flowed into the Lake for 6 months following a flood. The result is that a number of small channels had been cut over the years between the river and the lake. The spillway normally blocks the Mississippi River from flowing into Lake Pontchartrain, but provides a controlled outlet for this water when needed."

See also

• 2011 Red River Flood
• 2011 Assiniboine River Flood
• April 25–28, 2011 tornado outbreak
• Atchafalaya River
• Bird's Point, Missouri
• Great Mississippi and Missouri Rivers Flood of 1993
• Great Mississippi Flood of 1927
• Ohio River flood of 1937
• Old River Control Structure

External links

• Before and after satellite images
  • NASA; The Weather Channel, May 4, 2011
  • before and after images from IBTimes.com, May 12, 2011
  • animated javascript version from HuffingtonPost.com, May 12, 2011
• Satellite images of flooding from NASA Earth Observatory
• Advanced Hydrologic Prediction Service - NOAA
• Mississippi river flood gauges (National Weather Service)
• US Army Corps of Engineers Mississippi River Flood Fight
• Photos: Mississippi River flooding at The Big Picture, Boston.com
• Interactive satellite and topographic maps from the Old River Control Structure to the Gulf