The Morganza Spillway or Morganza Control Structure is a flood-control structure in the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sover ...

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...

. It is located along the western bank of the

Lower Mississippi River The Lower Mississippi River is the portion of the Mississippi River downstream of Cairo, Illinois. From the confluence of the Ohio River and Upper Mississippi River at Cairo, the Lower flows just under 1000 miles (1600 km) to the Gulf of ...

at river mile 280, near Morganza in

Pointe Coupee Parish Pointe Coupee Parish ( or ; french: Paroisse de la Pointe-Coupée) is a parish located in the U.S. state of Louisiana. As of the 2010 census, the population was 22,802; in 2020, its population was 20,758. The parish seat is New Roads. Pointe ...

. The spillway stands between the Mississippi and the Morganza Floodway, which leads to the

Atchafalaya Basin The Atchafalaya Basin, or Atchafalaya Swamp (; Louisiana French: ''L'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 Atc ...

and the

Atchafalaya River The Atchafalaya River ( french: La Rivière Atchafalaya, es, Río Atchafalaya) is a distributary of the Mississippi River and Red River in south central Louisiana in the United States. It flows south, just west of the Mississippi River, and ...

in south-central

. Its purpose is to divert water from the Mississippi River during major

flood A flood is an overflow of water ( 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 an area of study of the discipline hydrol ...

events by flooding the Atchafalaya Basin, including the Atchafalaya River and the Atchafalaya Swamp. The spillway and adjacent

levee A levee (), dike (American English), dyke (English in the Commonwealth of Nations, Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually soil, earthen and that often runs parallel (geometry), parallel to ...

s also help prevent the Mississippi from changing its present course through the major port cities of

Baton Rouge Baton Rouge ( ; ) is a city in and the capital of the U.S. state of Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-sma ...

and

New Orleans New Orleans ( , ,New Orleans
Merriam-Webster. ; french: La Nouvelle-Orléans , es, Nuev ...

to a new course down the Atchafalaya River to the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. The Morganza Spillway, operated by the

U.S. Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

, was opened during the

1973 Events January * January 1 - The United Kingdom, the Republic of Ireland and Denmark enter the European Economic Community, which later becomes the European Union. * January 15 – Vietnam War: Citing progress in peace negotiations, U.S. ...

and

2011 File:2011 Events Collage.png, From top left, clockwise: a protester partaking in Occupy Wall Street heralds the beginning of the Occupy movement; protests against Libyan dictator Muammar Gaddafi, who was killed that October; a young man celebrate ...

Mississippi River floods The Mississippi River and its tributaries have flooded on numerous occasions. This is a list of major floods. Flood of March 1543 Hernando de Soto's party was passing through a village at the confluence of the Mississippi River and Arkansas Ri ...

History

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 uninflated cost of the damage has been estimat ...

was the most destructive river flood in the

history of the United States The history of the lands that became the United States began with the arrival of Settlement of the Americas, the first people in the Americas around 15,000 BC. Native American cultures in the United States, Numerous indigenous cultures formed ...

. This was in large part due to the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...

swelling to wide in spots. To prevent a repeat of the Great Flood of 1927, and to have better control over river flooding in general,

Congress A congress is a formal meeting of the representatives of different countries, constituent states, organizations, trade unions, political parties, or other groups. The term originated in Late Middle English to denote an encounter (meeting of a ...

passed the

Flood Control Act of 1928 The Flood Control Act of 1928 (FCA 1928) ( 70th United States Congress, Sess. 1. Ch. 569, enacted May 15, 1928) authorized the U.S. Army Corps of Engineers to design and construct projects for the control of floods on the Mississippi River and it ...

. This authorized the

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

to build the

Bonnet Carre Spillway A Bonnet is a variety of headgear, hat or cap Specific types of headgear referred to as "bonnets" may include Scottish * Blue bonnet, a distinctive woollen cap worn by men in Scotland from the 15th-18th centuries And its derivations: ** Fea ...

, the Birds Point floodway in

Missouri Missouri 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 is bordered by eight states (tied for the most with Tennessee ...

, and the Morganza Floodway as part of the 1928

Mississippi River and Tributaries Project The United States Army Corps of Engineers Mississippi Valley Division (MVD) is responsible for the Corps water resources programs within 370,000-square-miles of the Mississippi River Valley, as well as the watershed portions of the Red River ...

Construction of the levees that make up part of the Morganza Spillway began in the late 1930s. The Morganza Control Structure portion of the project was completed in 1954. It subsequently became incorporated into the

Mississippi River Commission The United States Army Corps of Engineers Mississippi Valley Division (MVD) is responsible for the Corps water resources programs within 370,000-square-miles of the Mississippi River Valley, as well as the watershed portions of the Red River ...

's 1956

project design flood The project design flood is a hypothetical "maximum probable" flood of the Mississippi River used by the United States Army Corps of Engineers to aid in the design and execution of flood protection in the Mississippi Valley. The current project ...

, which added 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 ...

(ORCS) in 1963 to the protections used to prevent Mississippi River flood. The

Flood Control Act of 1965 The Flood Control Act of 1965, Title II of , was enacted on October 27, 1965, by the 89th Congress and authorized the United States Army Corps of Engineers to design and construct numerous flood control projects including the Lake Pontchartrain a ...

provided further regulation over the Morganza Spillway's role in Mississippi River flood prevention. A concrete pit called a stilling basin was added at the Morganza Spillway in 1977 "to provide erosion protection after the velocity of water pouring through the open bays during a 1973 flood caused severe

scour Scour may refer to: Hydrodynamic processes * Hydrodynamic scour, the removal of sediment such as sand and silt from around an object * Bridge scour, erosion of soil around at the base of a bridge pier or abutments via the flow of air, ice, or ...

ing of the land behind the bays."

Design and construction

The Morganza Spillway, a ''controlled''

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

using a set of flood gates to control the volume of water entering the Morganza Floodway from the Mississippi River, consists of a concrete

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

, two

sluice Sluice ( ) is a word for a channel controlled at its head by a movable gate which is called a sluice gate. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway and can be considered ...

gates, seventeen scour indicators, and 125 gated openings which can allow up to of water to be diverted from the Mississippi River into the Atchafalaya Basin during major floods. The project was completed in 1954. A highway ( Louisiana Route 1) and the

Kansas City Southern Railway The Kansas City Southern Railway Company is an American Class I railroad. Founded in 1887, it operates in 10 midwestern and southeastern U.S. states: Illinois, Missouri, Kansas, Oklahoma, Arkansas, Tennessee, Alabama, Mississippi, Louisiana and ...

cross the structure. The Corps of Engineers maintains the structures and, in times of flood, monitors their piers for scouring and stability. The Corps of Engineers has two 25-ton cranes used to lift and lower the flood gates. The cranes roll on special tracks next to the roadway, enabling the operators to open or shut any spillway gate or perform maintenance while the roadway is in use.

Operation during floods

The land on both sides of the Morganza Control Structure is above normal river water levels, and usually dry. In order for water to reach the spillway, the Mississippi must first rise well above its

flood stage Flood stage is the water level or stage at which the surface of a body of water has risen to a sufficient level to cause sufficient inundation of areas that are not normally covered by water, causing an inconvenience or a threat to life and property ...

, overtopping its banks. The Corps of Engineers considers opening the Morganza Spillway when the flow of the Mississippi at

Red River Landing, Louisiana Red River Landing was the name of a community located in northern Pointe Coupee Parish, Louisiana, United States. The community was located near the Red River and the Mississippi River, adjacent to the current location of Louisiana State Penitent ...

, is greater than and rising. 1986 Design Flows

Water from the Mississippi is normally diverted into the Atchafalaya Basin at only one place, the

(ORCS), in use since 1963, where floodgates are routinely used to redirect the Mississippi's flow into the Atchafalaya River such that the volume of the two rivers is split 70%/30%, respectively, as measured at the latitude of Red River Landing. During the 1973 Mississippi flood, the ORCS was being damaged due to high flow rates, leading to the opening of the Morganza Spillway to help relieve this pressure. Subsequently, the nearby Old River Control Auxiliary Structure (ORCAS) was constructed, adding additional floodgates for use during major floods. The Morganza Spillway, about downriver from ORCS and ORCAS, is designed for emergency use to divert additional water from the Mississippi River into the Morganza floodway, which merges downstream with the Atchafalaya floodway before entering the Gulf. Diversion of water from the Mississippi's main channel has the effect of lowering water level in the Mississippi downstream of the spillway, helping to relieve stress on levees and other flood control structures both upstream and down. Besides controlling flooding in a given event, the system is also designed to prevent the Mississippi River from permanently altering course down the Atchafalaya River, bypassing Baton Rouge and New Orleans. Water that passes the Morganza Spillway first enters the Morganza Floodway, which extends from the spillway at the Mississippi River south to the East Atchafalaya River levee. The floodway, long and wide, includes a stilling basin, an approach channel, an outlet channel, and two guide

s. From there, diverted water enters the Atchafalaya River Basin Floodway near

Krotz Springs, Louisiana Krotz Springs is a town in St. Landry Parish, Louisiana, United States, on the Atchafalaya River. The population was 1,198 at the 2010 census, down from 1,219 in 2000. It is part of the Opelousas–Eunice Micropolitan Statistical Area. Hi ...

, and continues to the Gulf of Mexico. In an extreme flood event, a major release of water from the Morganza Spillway into the Morganza Floodway and Atchafalaya Basin inundates not only the floodways themselves (between their levees), but extensive additional areas of southern Louisiana throughout the

. In such an event, the water level of the Mississippi, high enough to overtop the Spillway, would already be flooding some areas in the Basin downstream of the spillway, due to increased flow through the ORCS and the ORCAS, as well as possible overtopping of levees near the spillway. This flooding, plus any additional water from a Morganza Spillway release, together determine the total extent of flooding throughout the Atchafalaya Basin during a major Mississippi River flood. At risk in the Atchafalaya Basin are Morgan City (population 13,500), various smaller populated places, many farms, thousands of oil and gas wells, and considerable swampland. Inhabitants know that the region is a natural

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

, and the Corps of Engineers issues written notices annually to all interests reminding them of the possibility that it might open the spillway and flood the area. Any decision to open the spillway must be carefully planned to give ample warning and protect life and property. Part of that planning process includes the Corps' preparation of maps known as "inundation scenarios" so that interested parties can discuss how much water, if any, should be allowed through the spillway. During both moderate and severe floods of the Mississippi, the

Bonnet Carré Spillway The Bonnet Carré Spillway is a flood control operation in the Lower Mississippi Valley. Located in St. Charles Parish, Louisiana, about west of New Orleans, it allows floodwaters from the Mississippi River to flow into Lake Pontchartrain and ...

can also be opened to help protect New Orleans, many parts of which are below sea level. The Bonnet Carré Spillway, built after the

, is located well downstream of Morganza, where the Mississippi River approaches

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 west ...

near New Orleans. The Corps uses Bonnet Carré to divert floodwaters into the lake in order to protect the levees near New Orleans. Integrity of the Morganza Spillway, the Old River Control Structure, and nearby levees is essential to prevent the Mississippi from diverting its main channel into the Atchafalaya Basin.

Flood events and the Morganza Spillway

Since its completion in 1954, the Morganza Spillway has been opened twice, in 1973 and 2011. The Morganza Spillway was also considered for opening during other major floods of the Lower Mississippi River.

First opening of gates (1973)

On April 17, 1973, in order to lower the water level of the Mississippi River and relieve pressure on the Old River Control Structure, the Corps of Engineers opened 42 of the 125 steel gates of the Morganza Spillway for the first time since its completion, allowing about half of its maximum designed flow rate to pass from the Mississippi into the Atchafalaya Basin. The spillway received minor scouring and slight damage to the stilling basin, and substantial flooding occurred in the Atchafalaya Basin. After the 1973 flood, the structure was restored to its original condition.

Gates left closed in floods of 1983, 1993, 1997, 2008, and 2016

The issue of opening the gates to keep the Mississippi in its current place was next raised in May 1983. Although the gates were not opened,

Louisiana Highway 1 Louisiana Highway 1 (LA 1) is a state highway in Louisiana. At , it is the longest numbered highway of any class in Louisiana. It runs diagonally across the state, connecting the oil and gas fields near the island of Grand Isle with the no ...

running across the spillway was closed, and the Corps of Engineers built a ring dike and put a blanket of earth across a section of the spillway to contain water pouring underneath it. During the Great Mississippi and Missouri Rivers Flood in 1993, officials decided to leave the gates of the Morganza Floodway closed. In March 1997, the river water flow at

reached () per second. However, the flow rate never reached the threshold of () per second for opening Morganza, and residents of

Sicily Island, Louisiana Sicily Island is a village in Catahoula Parish, Louisiana, United States. The population was 336 at the 2020 census. Geography Sicily Island is located in northeastern Catahoula Parish at (31.846573, -91.658925). U.S. Route 425 passes through ...

, became angry that the spillway was not opened to prevent flooding in their homes. In March–April 2008, officials considered but declined to open the spillway gates. While the spillway gates remained closed then, flooding occurred in the Morganza forebay when the Mississippi River crested higher than the potato ridge levee at the forebay entrance. Local residents and

National Guard National Guard is the name used by a wide variety of current and historical uniformed organizations in different countries. The original National Guard was formed during the French Revolution around a cadre of defectors from the French Guards. Nat ...

troops attempted to add height to the permanent levee by building a supplemental

sandbag A sandbag or dirtbag is a bag or sack made of hessian (burlap), polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification in trenches and bunkers, shielding gl ...

levee on top of it. However, additional rainfall raised the flood crest higher than even the supplemental sandbags, sending floodwaters over these levees into of cropland located within the floodway.Water Over the Levee in Louisiana: 3,000 acres of wheat acres hurt
, ''Midsouth Farmer'', April 8, 2008. In the spring of 2016, the Corps considered opening the spillway but the forecast was lowered for the crest of the Mississippi River at Red River Landing, so the gates were left closed.

Second opening of gates (2011)

The 2011 Mississippi River floods began to become serious in April. In response, the Corps first analyzed the flooding, and then opened the spillway in a controlled manner. The Corps studied four flooding scenarios, all of which assumed the Bonnet Carré Spillway 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 (ORCS) 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 ORCS 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%)
/ref> The

Governor A governor is an administrative leader and head of a polity or political region, ranking under the head of state and in some cases, such as governors-general, as the head of state's official representative. Depending on the type of political ...

of Louisiana,

Bobby Jindal Piyush "Bobby" Jindal (born June 10, 1971) is an American politician who served as the 55th Governor of Louisiana from 2008 to 2016. The only living former Louisiana governor, Jindal also served as a member of the U.S. House of Representatives a ...

, had meanwhile sent a letter on May 4, 2011, to

Robert Gates Robert Michael Gates (born September 25, 1943) is an American intelligence analyst and university president who served as the 22nd United States secretary of defense from 2006 to 2011. He was originally appointed by president George W. Bush an ...

, the

United States Secretary of Defense The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high ranking member of the federal cabinet. DoDD 5100.1: Enclosure 2: a The s ...

, requesting that the

be deployed under

Title 32 of the United States Code Title 32 of the United States Code outlines the role of the United States National Guard in the United States Code. It is one of two ways the National Guard can be activated by the US Federal Government. Under Title 32, National Guard remains u ...

status to respond to record water levels in Louisiana, where there was "a significant probability that the U.S. Army Corps of Engineers

ould Ould is an English surname and an Arabic name ( ar, ولد). In some Arabic dialects, particularly Hassaniya Arabic, ولد‎ (the patronymic, meaning "son of") is transliterated as Ould. Most Mauritanians have patronymic surnames. Notable p ...

open the Morganza Spillway for the first time since 1973." The second opening of the Morganza Spillway began with the lifting of a single floodgate on May 14, 2011. Diversion of of water from the Mississippi River to the Atchafalaya Basin was planned during this event, 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 possibly severe flooding in the Atchafalaya Basin. By May 18, 2011, a total of 17 gates (the largest number for the 2011 event) had been opened by the Corps of Engineers. The Corps estimated the flow rate at . However, on May 25, new estimates from the U.S. Geologic Survey (USGS) described a much higher rate of , resulting in the closure of 3 bays by May 26, and additional closures by May 29, bringing the total to 11 bays with an estimated diversion rate of . The Corps continued to evaluate the flow and close additional bays as appropriate. By June 6, the number of open gates had been reduced to seven, and by June 8, only two gates were still open. All bays were closed on July 7, 2011. The Corps had estimated that it would take opening 31 of the Spillway’s 125 bays to control the flow of the river through Baton Rouge in response to a forecast crest of anticipated on Tuesday, May 17, 2011, which must remain below of water per second through Baton Rouge to ensure the integrity of the levee system. Since Morganza never operated above , the flooding in the Atchafalaya Basin was considerably lower than had been anticipated during the initial estimates of . By May 29, the Corps had also opened 330 of the 350 bays of the

located near New Orleans. Image:Morganza Floodway opened in Louisiana seen from Air.jpg, Aerial photograph of the first bay opening on the Morganza Floodway on 14 May 2011. The Mississippi River is in the upper left background, and the Atchafalaya Floodway to the right. Image:Morganza Floodway Travel Times May 2011.jpg, Water travel time down the Morganza Floodway after the May 14, 2011 opening. 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.

Third opening of gates (2019; cancelled)

On Wednesday May 22, 2019, the U.S. Army Corps of Engineers announced that, due to the extended flood event on the Mississippi River, which had been above flood stage since January 2019, they were anticipating the third opening of the Morganza Spillway. The further anticipated river rise stoked fears that the waters would overtop the spillway, which would destroy the structure. On Monday May 27, 2019, the Army Corps of Engineers officially announced it would open Morganza on Sunday, June 2, 2019. However, the US Army Corps of Engineers New Orleans issued a press release on May 30, 2019, announcing the postponement of the Spillway opening until June 6, 2019. The opening was later postponed again to June 9, then indefinitely.

Notes

References

External links

Morganza Spillway Fish Jumping through Gates
* For other images of the Morganza Control Structure in operation during the 2011 flood, see th
U.S. Army Corps of Engineers Flickr page
{{coord, 30.7766, -91.6199, region:US-LA_type:landmark, display=title Buildings and structures in Pointe Coupee Parish, Louisiana United States Army Corps of Engineers Spillways Mississippi River