Major

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

s along the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

in April and May 2011 were among the largest and most damaging recorded along the U.S. waterway in the past century, comparable in extent to the

Great Mississippi Flood of 1927 The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States, with inundated in depths of up to over the course of several months in early 1927. The period cost of the damage has been estimate ...

and

Great Flood of 1993 The Great Flood of 1993 (or Great Mississippi and Missouri Rivers Flood of 1993) was a flood that occurred in the Midwestern United States, along the Mississippi River, Mississippi and Missouri River, Missouri rivers and their tributaries, from ...

. In April 2011, two large storm systems deposited record levels of rainfall on the Mississippi River

drainage basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...

. When that additional water combined with the springtime

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...

, the river and many of its

tributaries A tributary, or an ''affluent'', is a stream or river that flows into a larger stream ('' main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which the ...

began to swell to record levels by the beginning of May. Flooding occurred in

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

Mississippi Mississippi ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South regions of the United States. It borders Tennessee to the north, Alabama to the east, the Gulf of Mexico to the south, Louisiana to the s ...

, and

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

. U.S. President

Barack Obama Barack Hussein Obama II (born August 4, 1961) is an American politician who was the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, he was the first African American president in American history. O ...

declared the western counties of Kentucky, Tennessee, and Mississippi federal disaster areas. For the first time in 37 years, the Morganza Spillway was opened on May 14, deliberately flooding of rural Louisiana to save most of

Baton Rouge Baton Rouge ( ; , ) is the List of capitals in the United States, capital city of the U.S. state of Louisiana. It had a population of 227,470 at the 2020 United States census, making it List of municipalities in Louisiana, Louisiana's second-m ...

and

New Orleans New Orleans (commonly known as NOLA or The Big Easy among other nicknames) is a Consolidated city-county, consolidated city-parish located along the Mississippi River in the U.S. state of Louisiana. With a population of 383,997 at the 2020 ...

."Rural Louisiana flooded to save New Orleans"
''(CBS News/Associated Press)'' May 14, 2011 Fourteen people were killed in Arkansas, with 348 killed across seven states in the preceding storms. Thousands of homes were ordered evacuated, including over 1,300 in Memphis, and more than 24,500 in Louisiana and Mississippi, though some people disregarded mandatory evacuation orders. The flood crested in Memphis on May 10 and artificially crested in southern Louisiana on May 15, a week earlier than it would have if spillways had not been opened. The

United States Army Corps of Engineers The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil wo ...

stated that an area in Louisiana between Simmesport and Baton Rouge was expected to be inundated with of water.Estimated Inundation
(US Army Corps of Engineers) Baton Rouge, New Orleans, and many other river towns were threatened, but officials stressed that they should be able to avoid catastrophic flooding. Pcpnweekending04292011

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. The unprecedented extensive rainfall from these four storms, combined with springtime snow melt from the

Upper Midwest The Upper Midwest is a northern subregion of the U.S. Census Bureau's Midwestern United States. Although the exact boundaries are not uniformly agreed upon, the region is usually defined to include the states of Iowa, Michigan, Minnesota and Wi ...

, created the perfect situation for a 500-year flood along the Mississippi.

Flood stages and effects by state

As flood waters proceeded down the Lower Mississippi from the

St. Louis St. Louis ( , sometimes referred to as St. Louis City, Saint Louis or STL) is an independent city in the U.S. state of Missouri. It lies near the confluence of the Mississippi and the Missouri rivers. In 2020, the city proper had a populatio ...

area (where the

Missouri River The Missouri River is a river in the Central United States, Central and Mountain states, Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Moun ...

and the Mississippi River converge), they affected

and

, then

, and

Missouri and Illinois

On May 3, using the planned procedures for the Birds Point-New Madrid Floodway, the Corps of Engineers blasted a two-mile (3 km) hole in the

levee A levee ( or ), dike (American English), dyke (British English; see American and British English spelling differences#Miscellaneous spelling differences, spelling differences), embankment, floodbank, or stop bank is an elevated ridge, natural ...

protecting the floodway, flooding of farmland in

Mississippi County, Missouri Mississippi County is a County (United States), county located in the Missouri Bootheel, Bootheel of the U.S. state of Missouri, with its eastern border formed by the Mississippi River. As of the 2020 United States census, 2020 census, the popu ...

, in an effort to save the town of

Cairo, Illinois Cairo ( , sometimes ) is the southernmost city in the U.S. state of Illinois and the county seat of Alexander County, Illinois, Alexander County. A river city, Cairo has the lowest elevation of any location in Illinois and is the only Illinoi ...

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 plan to breach the levee.

Tennessee

Dyersburg, a city in northwestern Tennessee, experienced the worst flooding with over 600 homes and businesses inundated as the

Forked Deer River The Forked Deer River system is the main drainage of the central portion of West Tennessee. Locals pronounce the first word of the river's name with two syllables, as in “Forkéd” (). The Forked Deer consists of various streams designated ...

, a tributary of the Mississippi, flowed backwards into southern areas of the city. On May 10, the river reached , the highest level reached at Memphis since 1937, when the river there reached a record , and the second highest level ever recorded, even surpassing the 1927 flood. Many local rivers spilled their banks, including Big Creek, the Loosahatchie River, and the Wolf River along with Nonconnah Creek. Subsequent flooding occurred in Millington, as well as suburban areas of Frayser, Bartlett, and

East Memphis East Memphis is a region of Memphis, Tennessee with several defined and informal subdivisions and neighborhoods such as Colonial Acres, White Station, Memphis, White Station-Yates, Memphis, Yates, Sherwood Forest, Memphis, Sherwood Forest, Nor ...

Arkansas

2011 Flooding From Mississippi River Levee Breach

Interstate 40 Interstate 40 (I-40) is a major east–west transcontinental Interstate Highway System, Interstate Highway in the Southeastern United States, southeastern and Southwestern United States, southwestern portions of the United States. At a leng ...

, connecting Memphis and

Little Rock Little Rock is the List of capitals in the United States, capital and List of municipalities in Arkansas, most populous city of the U.S. state of Arkansas. The city's population was 202,591 as of the 2020 census. The six-county Central Arkan ...

, 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

In Tunica County, nine casinos located on stationary river barges were closed most of May. The hotel portion of the casinos are located on adjacent, low-lying land, and began to flood with the rising waters, some up to . Near Vicksburg, Highway 465 in Warren and Issaquena counties was closed on May 3 due to high flood waters. North-south access to and from Vicksburg was cut off for more than two weeks. U.S. Highway 61 between Vicksburg and

Port Gibson Port Gibson is a city and the county seat of Claiborne County, Mississippi, United States. The population was 1,567 at the 2010 United States Census, 2010 census. It is bordered on the west by the Mississippi River. The first European settlers i ...

was closed by backwater flooding along the Big Black River on May 12; it reopened June 1. Another portion of U.S. Highway 61 near

Redwood Sequoioideae, commonly referred to as redwoods, is a subfamily of Pinophyta, coniferous trees within the family (biology), family Cupressaceae, that range in the Northern Hemisphere, northern hemisphere. It includes the List of superlative tree ...

was closed by backwater flooding along the

Yazoo River The Yazoo River is a river primarily in the U.S. state of Mississippi. It is considered by some to mark the southern boundary of what is called the Mississippi Delta, a broad floodplain that was cultivated for cotton plantations before the Ame ...

on May 13 and was closed until June 3. In anticipation of major flooding, the U.S. federal government declared 14 counties along the Mississippi River, the Thames River: Adams, Bolivar, Claiborne, Coahoma, DeSoto, Humphreys, Issaquena, Jefferson, Sharkey, Tunica, Warren, Washington, Wilkinson and Yazoo. The Flood of 2011 set new record stages at Vicksburg and Natchez. The peak streamflow at Vicksburg, , exceeded both the estimated peak streamflow of the

, , and the measured peak streamflow of the 1937 flood, . The Project Design Flood predicts that a flowrate at Vicksburg of would still be within the limits of the downstream capacities, meaning that the May 17-18 peak flow was about 85% of the acceptable flowrate for Vicksburg.

Louisiana

Following the

, 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 Old River Control Structure is a floodgate system in a branch of the Mississippi River in central Louisiana. It regulates the flow of water from the Mississippi into the Atchafalaya River, thereby preventing the Mississippi River from chang ...

. 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 and Atchafalaya Basin

On May 14, a single floodgate of the Morganza Spillway was opened in order to divert of water from the Mississippi River to the

Atchafalaya Basin The Atchafalaya Basin, or Atchafalaya Swamp (; Louisiana French: ''Atchafalaya'', ), is the largest wetland and swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atch ...

. This diversion was deemed necessary to protect levees and prevent major flooding in Baton Rouge and New Orleans, with the tradeoff of exacerbating 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 the 1973 flood. By May 15, a total of nine gates had been opened by the Corps of Engineers. The Corps had estimated that it would take opening one-fourth of the spillway's 125 bays—or 31 bays—to control the flow of the river through Baton Rouge in response to a forecast crest of anticipated on May 17, which must remain below of water per second through Baton Rouge to ensure the integrity of the levee system. Prior to the decision to open more gates on the spillway, 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%). *Scenario 1: Open the Morganza Spillway to half (50%) of its maximum capacity, which would divert of water. **Scenario 1a: Open the Morganza Spillway to one-quarter (25%) of its maximum capacity, which would divert 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 of water. Following this analysis, which showed that extensive flooding was 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%) The Corps of Engineers subsequently released a map showing the estimated times it would take the flood waters to reach the various communities in the Atchafalaya Basin over eight days. File:NO District Inundation Spring May 2011.jpg, Anticipated inundation from Scenario 1 File:NODInundationMay2011Scenario1a.jpg, Anticipated inundation from Scenario 1a File:NODInundationMay2011Scenario2.jpg, Anticipated inundation from Scenario 2 File:NODInundationMay2011Scenario3.jpg, Anticipated inundation from Scenario 3 ;Source: United States Army Corps of Engineers Image:Morganza-spillway-times.jpg, Atchafalaya Basin floodwater travel times from the Morganza Spillway. Image:May 2011 Morganza Spillway Opens in Louisiana.jpg, Natural-colour satellite image of the Floodway on May 15, 2011. Image:May 2011 Morganza Spillway Opens in Louisiana (False Colour).jpg, False colour satellite image of the Floodway on May 15, 2011.

Waterford Nuclear Generating Station

The

Waterford Nuclear Generating Station The Waterford Steam Electric Station, Unit 3, also known as Waterford 3, is a nuclear power plant located on a plot in Killona, Louisiana, in St. Charles Parish, about west of New Orleans. This plant has one Combustion Engineering two-loop ...

, about west of New Orleans, was restarted May 12, after a refueling shutdown on April 6.

Bonnet Carré Spillway and Lake Pontchartrain

The

Bonnet Carré Spillway The Bonnet Carré Spillway is a Flood#Flood defences, planning, and management, flood control operation in the Lower Mississippi River, Mississippi Valley. Located in St. Charles Parish, Louisiana, about west of New Orleans, it allows floodwat ...

, near New Orleans, was built to divert water from the Mississippi River to

Lake Pontchartrain Lake Pontchartrain ( ; ) is an estuary located in southeastern Louisiana in the United States. It covers an area of with an average depth of . Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about from w ...

, and from there to the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, reducing water levels and flow near New Orleans. On May 23, 330 of the structure's 350 bays were opened due to rising water levels otherwise anticipated to jeopardize levees protecting New Orleans. The Army Corps of Engineers began closing the spillway gates on June 12 as the river level began to fall and the last of the gates were closed on June 20.

Climate factors

The

Gravity Recovery and Climate Experiment The Gravity Recovery and Climate Experiment (GRACE) was a joint mission of NASA and the German Aerospace Center (DLR). Twin satellites took detailed measurements of Earth's gravity field anomalies from its launch in March 2002 to the end of it ...

(GRACE) satellites indicated a continued water storage increase over the Missouri River Basin (MRB) prior to the 2011 flood event. A 2014 study examined what climate forcing conditions preceded the long-term changes in these variables. It was found that precipitation over the MRB undergoes a profound modulation during the transition points of the Pacific quasi-decadal oscillation and associated

teleconnection Teleconnection in atmospheric science refers to climate anomalies being related to each other at large distances (typically thousands of kilometers). The most emblematic teleconnection is that linking sea-level pressure at Tahiti and Darwin, Aust ...

s. The results infer a prominent teleconnection forcing in driving the wet/dry spells in the MRB, and this connection implies persistence of dry conditions for the next 2 to 3 years.

Risk of major course change in the Lower Mississippi River

During the 2011 floods, concerns were raised that the Mississippi might divert its main channel into the Atchafalaya Basin if the Old River Control Structure, the Morganza Spillway, or nearby levees failed, or into Lake Pontchartrain if the

or adjacent levees failed. Jeff Masters of the ''

Weather Underground The Weather Underground was a far-left Marxist militant organization first active in 1969, founded on the Ann Arbor campus of the University of Michigan. Originally known as the Weathermen, or simply Weatherman, the group was organized as a f ...

'' 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 his structureits most severe test ever." During the 2011 floods, the Army Corps of Engineers decided to open the Morganza Spillway at 1/4 of its capacity to allow to enter the Morganza and Atchafalaya floodways. In addition to reducing the 2011 flood crest downstream, this reduced the chances of a channel change by reducing stress on the other elements of the control system.

References

NOAA The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with forecasting weather, monitoring oceanic and atmospheric conditions, charting the seas, conducting deep-sea exploratio ...

Mississippi river flood gauges
(

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

)
US Army Corps of Engineers Mississippi River Flood Fight
* Photos

at The Big Picture, Boston.com
Interactive satellite and topographic maps from the Old River Control Structure to the Gulf

General Weather Conditions and Precipitation Contributing to the 2011 Flooding in the Mississippi River and Red River of the North Basins, December 2010 through July 2011

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

Streamflow Characterization and Summary of Water-Quality Data Collection During the Mississippi River Flood, April through July 2011

{{DEFAULTSORT:Mississippi River Floods, 2011 Flood,Mississippi

2011 The year marked the start of a Arab Spring, series of protests and revolutions throughout the Arab world advocating for democracy, reform, and economic recovery, later leading to the depositions of world leaders in Tunisia, Egypt, and Yemen ...

Flood,2011,Mississippi

2011 Mississippi River floods Major floods along the Mississippi River in April and May 2011 were among the largest and most damaging recorded along the U.S. waterway in the past century, comparable in extent to the Great Mississippi Flood of 1927 and Great Flood of 19 ...

Flood,2011,Mississippi Flood,2011,Mississippi Flood,2011,Mississippi Flood,2011,Mississippi Floods in Louisiana 2011 in Arkansas 2011 in Illinois 2011 in Kentucky 2011 in Mississippi 2011 in Missouri 2011 in Louisiana 2011 in Tennessee May 2011 in the United States June 2011 in the United States