Morganza Spillway
Encyclopedia
The Morganza Spillway or Morganza Control Structure is a flood-control structure in the U.S. state
of Louisiana
along the western bank of the Mississippi River
at river mile 280, near Morganza
in Pointe Coupee Parish. The spillway stands between the Mississippi and the Morganza Floodway, which leads to the Atchafalaya Basin
and the Atchafalaya River
in south-central Louisiana
. Its purpose is to divert water from the Mississippi River during major flood
events by flooding the Atchafalaya Basin, including the Atchafalaya River and the Atchafalaya Swamp. The spillway and adjacent levee
s also help prevent the Mississippi from changing its present course through the major port cities of Baton Rouge and New Orleans to a new course down the Atchafalaya River to the Gulf of Mexico
. The Morganza Spillway, operated by the U.S. Army Corps of Engineers, was opened during the 1973 and 2011 Mississippi River floods
.
was the most destructive river flood in the history of the United States
, in large part due to the Mississippi River
swelling to 80 miles (128.7 km) wide in spots. To prevent a repeat of the Great Flood of 1927, and better control river flooding in general, Congress passed the Flood Control Act of 1928
to authorize the United States Army Corps of Engineers
to build the Bonnet Carre Spillway
(located 33 miles (53.1 km) above New Orleans and completed in 1931), the Birds Point floodway in Missouri
, and the Morganza Floodway as part of the 1928 Mississippi River and Tributaries Project.
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 and subsequently became incorporated into the Mississippi River Commission's 1956 project design flood
, which added the Old River Control Structure
(ORCS) in 1963 to the protections used to prevent Mississippi River flood. The Flood Control Act of 1965
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
ing of the land behind the bays."
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
, two sluice
gates, seventeen scour indicators, and 125 gated openings which can allow up to 600000 cuft/s 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
cross the structure.
The Corps of Engineers maintains the structures and, in times of flood, monitors their piers for scouring and stability. To lift and lower the flood gates, the Corps of Engineers maneuvers a movable crane along the spillway to the particular opening.
, overtopping its banks. The Corps of Engineers considers opening the Morganza Spillway when the flow of the Mississippi at Red River Landing, Louisiana
, is greater than 1500000 cuft/s and rising.
Water from the Mississippi is normally diverted into the Atchafalaya Basin at only one place, the Old River Control Structure
(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 30 miles (48.3 km) 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, 20 miles (32.2 km) long and 5 miles (8 km) wide, includes a stilling basin, an approach channel, an outlet channel, and two guide levee
s. From there, diverted water enters the Atchafalaya River Basin Floodway near Krotz Springs, Louisiana
, 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 Atchafalaya Basin
. 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
, 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
can also be opened to help protect New Orleans, many parts of which are below sea level. The Bonnet Carré Spillway, built after the Great Mississippi Flood of 1927
, is located well downstream of Morganza, where the Mississippi River approaches Lake Pontchartrain
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; see "Risk of major course change in the Lower Mississippi River" for further discussion.
running across the spillway was closed, and the Corps of Engineers built a 12 feet (3.7 m) 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 Baton Rouge reached 10600000 gal (10600000 gal) per second. However, the flow rate never reached the threshold of 11200000 gal (11200000 gal) per second for opening Morganza, and residents of Sicily Island, Louisiana
, 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 still occurred in part of the Morganza floodway when the Mississippi River crested higher than levees near the spillway. Local residents and National Guard troops attempted to add height to the permanent levee by building a supplemental sandbag
levee on top of it. However, additional rainfall raised the flood crest higher than even the supplemental sandbags, sending floodwaters over these levees into 3000 acres (1,214.1 ha) of cropland located within the floodway.
The 2011 Mississippi River floods began to become serious in April. In response, the Corp 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%).
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 Governor
of Louisiana, Bobby Jindal
, had meanwhile sent a letter on May 4, 2011, to Robert Gates
, the United States Secretary of Defense
, requesting that the National Guard be deployed under Title 32 of the United States Code
status to respond to record water levels in Louisiana, where there was "a significant probability that the U.S. Army Corps of Engineers [would] 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 125000 cuft/s 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. See Army Engineers Open Morganza Spillway for a video of the opening of the first gate, and Morganza Spillway Fish Jumping through Gates for a video of the diversion, as seen from the highway over the spillway.
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 114000 cuft/s. However, on May 25, new estimates from the U.S. Geologic Survey (USGS) described a much higher rate of 172000 cuft/s, 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 120000 cuft/s.. 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 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 45 feet (13.7 m) anticipated on Tuesday, May 17, 2011, which must remain below 1500000 cuft/s of water per second through Baton Rouge to ensure the integrity of the levee system. Since Morganza never operated above 172000 cuft/s, the flooding in the Atchafalaya Basin was considerably lower than had been anticipated during the initial estimates of 300000 cuft/s. By May 29, the Corps had also opened 330 of the 360 bays of the Bonnet Carré Spillway
located near New Orleans.
For other images of the Morganza Control Structure in operation during the 2011 flood, see the U.S. Army Corps of Engineers Flickr page.
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
of Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
along the western bank of the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
at river mile 280, near Morganza
Morganza, Louisiana
Morganza is an incorporated village near the Mississippi River in Pointe Coupee Parish, Louisiana, United States. The population was 659 at the 2000 census. It is part of the Baton Rouge Metropolitan Statistical Area. The village's zip code is 70759...
in Pointe Coupee Parish. The spillway stands between the Mississippi and the Morganza Floodway, which leads to the Atchafalaya Basin
Atchafalaya Basin
The Atchafalaya Basin, or Atchafalaya Swamp, is the largest swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atchafalaya River and the Gulf of Mexico converge. The river stretches from near Simmesport in the north...
and the Atchafalaya River
Atchafalaya River
The Atchafalaya River 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....
in south-central Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
. Its purpose is to divert water from the Mississippi River during major flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
events by flooding the Atchafalaya Basin, including the Atchafalaya River and the Atchafalaya Swamp. The spillway and adjacent levee
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
s also help prevent the Mississippi from changing its present course through the major port cities of Baton Rouge and New Orleans to a new course down the Atchafalaya River to the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. The Morganza Spillway, operated by the U.S. Army Corps of Engineers, was opened during the 1973 and 2011 Mississippi River floods
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 DeSoto's party was passing through a village at the confluence of the Mississippi River and Arkansas River on March 18...
.
History
The Great Mississippi Flood of 1927Great Mississippi Flood of 1927
The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States.-Events:The flood began when heavy rains pounded the central basin of the Mississippi in the summer of 1926. By September, the Mississippi's tributaries in Kansas and Iowa were swollen to...
was the most destructive river flood in the history of the United States
History of the United States
The history of the United States traditionally starts with the Declaration of Independence in the year 1776, although its territory was inhabited by Native Americans since prehistoric times and then by European colonists who followed the voyages of Christopher Columbus starting in 1492. The...
, in large part due to the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
swelling to 80 miles (128.7 km) wide in spots. To prevent a repeat of the Great Flood of 1927, and better control river flooding in general, Congress passed the Flood Control Act of 1928
Flood Control Act of 1928
The Flood Control Act of 1928 authorized the U.S. Army Corps of Engineers to design and construct projects for the control of floods on the Mississippi River and its tributaries as well as the Sacramento River in California. It was sponsored by Sen. Wesley L. Jones of Washington and Rep. Frank R...
to authorize the United States Army Corps of Engineers
United States Army Corps of Engineers
The United States Army Corps of Engineers is a federal agency and a major Army command made up of some 38,000 civilian and military personnel, making it the world's largest public engineering, design and construction management agency...
to build the Bonnet Carre Spillway
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 thence into the Gulf of Mexico...
(located 33 miles (53.1 km) above New Orleans and completed in 1931), the Birds Point floodway in Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
, and the Morganza Floodway as part of the 1928 Mississippi River and Tributaries Project.
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 and subsequently became incorporated into the Mississippi River Commission's 1956 project design flood
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....
, which added the Old River Control Structure
Old River Control Structure
The Old River Control Structure is a floodgate system located in a branch of the Mississippi River in central Louisiana. It regulates the flow of water leaving the Mississippi into the Atchafalaya River, thereby preventing the Mississippi river from changing course. Completed in 1963, the...
(ORCS) in 1963 to the protections used to prevent Mississippi River flood. The Flood Control Act of 1965
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 and Vicinity, Louisiana Hurricane Protection Project...
provided further regulation over the Morganza Spillway's role in Mississippi River flood prevention. A concrete pit called a stilling basin
Hydraulic jump
A hydraulic jump is a phenomenon in the science of hydraulics which is frequently observed in open channel flow such as rivers and spillways. When liquid at high velocity discharges into a zone of lower velocity, a rather abrupt rise occurs in the liquid surface...
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
Bridge scour
Bridge scour is the removal of sediment such as sand and rocks from around bridge abutments or piers. Scour, caused by swiftly moving water, can scoop out scour holes, compromising the integrity of a structure....
ing of the land behind the bays."
Design and construction
The Morganza Spillway, a 4159 feet (1,267.7 m) controlled spillwaySpillway
A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy...
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
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
, two sluice
Sluice
A sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...
gates, seventeen scour indicators, and 125 gated openings which can allow up to 600000 cuft/s 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
Louisiana Highway 1
Louisiana Highway 1 is a state highway in Louisiana. At 436.20 miles , 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 northwest corner of the state, north of Shreveport.The...
) and the Kansas City Southern Railway
Kansas City Southern Railway
The Kansas City Southern Railway , owned by Kansas City Southern Industries, is the smallest and second-oldest Class I railroad company still in operation. KCS was founded in 1887 and is currently operating in a region consisting of ten central U.S. states...
cross the structure.
The Corps of Engineers maintains the structures and, in times of flood, monitors their piers for scouring and stability. To lift and lower the flood gates, the Corps of Engineers maneuvers a movable crane along the spillway to the particular opening.
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 stageFlood stage
Flood stage is the level at which the surface of a river, creek, or other body of water has risen to a sufficient level to cause damage or affects use of man-made structures...
, 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, 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....
, is greater than 1500000 cuft/s and rising.
Water from the Mississippi is normally diverted into the Atchafalaya Basin at only one place, the Old River Control Structure
Old River Control Structure
The Old River Control Structure is a floodgate system located in a branch of the Mississippi River in central Louisiana. It regulates the flow of water leaving the Mississippi into the Atchafalaya River, thereby preventing the Mississippi river from changing course. Completed in 1963, 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 30 miles (48.3 km) 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, 20 miles (32.2 km) long and 5 miles (8 km) wide, includes a stilling basin, an approach channel, an outlet channel, and two guide levee
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
s. From there, diverted water enters the Atchafalaya River Basin Floodway near Krotz Springs, Louisiana
Krotz Springs, Louisiana
Krotz Springs is a town in St. Landry Parish, Louisiana on the Atchafalaya River. The population was 1,219 at the 2000 census. It is part of the Opelousas–Eunice Micropolitan Statistical Area.-History:...
, 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 Atchafalaya Basin
Atchafalaya Basin
The Atchafalaya Basin, or Atchafalaya Swamp, is the largest swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atchafalaya River and the Gulf of Mexico converge. The river stretches from near Simmesport in the north...
. 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
Morgan City, Louisiana
Morgan City is a city in St. Martin and St. Mary parishes in the U.S. state of Louisiana. The population was 12,404 at the 2010 census....
(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
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
, 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
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 thence into the Gulf of Mexico...
can also be opened to help protect New Orleans, many parts of which are below sea level. The Bonnet Carré Spillway, built after the Great Mississippi Flood of 1927
Great Mississippi Flood of 1927
The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States.-Events:The flood began when heavy rains pounded the central basin of the Mississippi in the summer of 1926. By September, the Mississippi's tributaries in Kansas and Iowa were swollen to...
, is located well downstream of Morganza, where the Mississippi River approaches Lake Pontchartrain
Lake Pontchartrain
Lake Pontchartrain is a brackish estuary located in southeastern Louisiana. It is the second-largest inland saltwater body of water in the United States, after the Great Salt Lake in Utah, and the largest lake in Louisiana. As an estuary, Pontchartrain is not a true lake.It covers an area of with...
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; see "Risk of major course change in the Lower Mississippi River" for further discussion.
Flood events and the Morganza Spillway
Since its completion in 1954, the Morganza Spillway has been opened twice (in 1973 and 2011), and considered for opening during four 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 flowrate 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, and 2008
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 1Louisiana Highway 1
Louisiana Highway 1 is a state highway in Louisiana. At 436.20 miles , 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 northwest corner of the state, north of Shreveport.The...
running across the spillway was closed, and the Corps of Engineers built a 12 feet (3.7 m) 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 Baton Rouge reached 10600000 gal (10600000 gal) per second. However, the flow rate never reached the threshold of 11200000 gal (11200000 gal) per second for opening Morganza, and residents of Sicily Island, Louisiana
Sicily Island, Louisiana
Sicily Island is a village in Catahoula Parish, Louisiana, United States. The population was 453 at the 2000 census.-Geography:Sicily Island is located at ....
, 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 still occurred in part of the Morganza floodway when the Mississippi River crested higher than levees near the spillway. Local residents and National Guard troops attempted to add height to the permanent levee by building a supplemental sandbag
Sandbag
A sandbag is a sack made of hessian/burlap, polypropylene or other materials that is filled with sand or soil and used for such purposes as flood control, military fortification, shielding glass windows in war zones and ballast....
levee on top of it. However, additional rainfall raised the flood crest higher than even the supplemental sandbags, sending floodwaters over these levees into 3000 acres (1,214.1 ha) of cropland located within the floodway.
Second opening of gates (2011)
The 2011 Mississippi River floods began to become serious in April. In response, the Corp 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 300000 cuft/s of water.
- Scenario 1a: Open the Morganza Spillway to one-quarter (25%) of its maximum capacity, which would divert 150000 cuft/s 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 ORCS somewhat more, which would divert an extra 150000 cuft/s 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 Governor
Governor
A governor is a governing official, usually the executive of a non-sovereign level of government, ranking under the head of state...
of Louisiana, Bobby Jindal
Bobby Jindal
Piyush "Bobby" Jindal is the 55th and current Governor of Louisiana and formerly a member of the United States House of Representatives. He is a member of the Republican Party....
, had meanwhile sent a letter on May 4, 2011, to Robert Gates
Robert Gates
Dr. Robert Michael Gates is a retired civil servant and university president who served as the 22nd United States Secretary of Defense from 2006 to 2011. Prior to this, Gates served for 26 years in the Central Intelligence Agency and the National Security Council, and under President George H. W....
, the United States Secretary of Defense
United States Secretary of Defense
The Secretary of Defense is the head and chief executive officer of the Department of Defense of the United States of America. This position corresponds to what is generally known as a Defense Minister in other countries...
, requesting that the National Guard be deployed under Title 32 of the United States Code
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.—Organization—Personnel—Training—Service, Supply, And Procurement—Homeland Defense Activities-External links:...
status to respond to record water levels in Louisiana, where there was "a significant probability that the U.S. Army Corps of Engineers [would] 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 125000 cuft/s 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. See Army Engineers Open Morganza Spillway for a video of the opening of the first gate, and Morganza Spillway Fish Jumping through Gates for a video of the diversion, as seen from the highway over the spillway.
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 114000 cuft/s. However, on May 25, new estimates from the U.S. Geologic Survey (USGS) described a much higher rate of 172000 cuft/s, 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 120000 cuft/s.. 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 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 45 feet (13.7 m) anticipated on Tuesday, May 17, 2011, which must remain below 1500000 cuft/s of water per second through Baton Rouge to ensure the integrity of the levee system. Since Morganza never operated above 172000 cuft/s, the flooding in the Atchafalaya Basin was considerably lower than had been anticipated during the initial estimates of 300000 cuft/s. By May 29, the Corps had also opened 330 of the 360 bays of the Bonnet Carré Spillway
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 thence into the Gulf of Mexico...
located near New Orleans.
For other images of the Morganza Control Structure in operation during the 2011 flood, see the U.S. Army Corps of Engineers Flickr page.
See also
- West Atchafalaya FloodwayWest Atchafalaya FloodwayThe West Atchafalaya Floodway is a flood control structure of the Mississippi River and Tributaries Project located in the Lower Atchafalaya Basin in south-central Louisiana. It has a project design flood flow capacity of .-Atchafalaya Basin floodways:...
- The "Atchafalaya" section of the book The Control of Nature by John McPheeJohn McPheeJohn Angus McPhee is an American Pulitzer Prize-winning writer, widely considered one of the pioneers of creative nonfiction....
. ISBN 0374128901.