Bonnet Carré Spillway
Encyclopedia
The Bonnet Carré Spillway is a flood control operation in the Lower Mississippi Valley
. Located in St. Charles Parish, Louisiana
- about 12 miles (19.3 km) west of New Orleans
- it allows floodwaters from the Mississippi River
to flow into Lake Pontchartrain
and thence into the Gulf of Mexico
. The construction of the spillway was completed in 1931.
which extends for over a mile and a half parallel to the river. When opened, the control structure slightly restricts the flow of the river (at the structure’s location) toward its main channel, thereby causing it to rise in elevation just high enough to flow into the diversion channel; and, with sufficient elevation (or head), to carry the overflow volume into Lake Pontchartrain. The lake’s opening to the gulf is sufficient to absorb and dissipate any conceivable volume of flood flow. Thus, the flood surcharge portion of the water from the Mississippi is divided between the main river and the diversion channel; with the surcharge bypassing the New Orleans metropolitan area, resulting in the Mississippi being lower (through that area) than it could have been; and reducing the stress on the area's levee
s that line the river. Confined by guide levees, the floodway stretches nearly six miles (10 km) to Lake Pontchartrain, with a design capacity of 250000 cuft/s. The spillway is crossed by U.S. 61
and Interstate 10.
The spillway was built in response to the Great Mississippi Flood of 1927
that inundated much of the Mississippi River basin. It was first opened during the flood of 1937
, and nine times thereafter through 2011 to lower river stages at New Orleans. The most recent opening began on May 9, 2011, when river levels in New Orleans approached the flood stage of 17 feet (5.2 m).
The spillway is part of the United States Army Corps of Engineers
' multi-state plan, called the Mississippi River and Tributaries Project (MR&T), providing flood
protection for the alluvial valley between Cape Girardeau, Missouri
and the mouth of the river near Venice
, Louisiana. Due to the wide expanse of the project and the complex problems involved, the plan contains an array of features. The MR&T Project provides for levees to contain flood flows, floodways such as the Bonnet Carré to redirect excess flows away from the Mississippi and has other aspects such as channel improvement and river bank stabilization for efficient navigation and protection of the levee system. It also involves reservoirs and pumping plants for flood control drainage.
era, clay extracted from the spillway will be crucial to raising the levees in St. Charles Parish
and east Jefferson Parish
.
Once the excavation is complete, the pits will be filled with water and stocked with bluegill
, largemouth bass
and other fish
to enhance the area's secondary function: a recreational haven for boaters, hikers, hunters and fishers.
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...
. Located in St. Charles Parish, Louisiana
St. Charles Parish, Louisiana
St. Charles Parish is a parish located in the U.S. state of Louisiana. The parish seat is Hahnville. In 2010, its population was 52,780. In the eighteenth and nineteenth century, this was part of the German Coast, an area along the Mississippi River settled by numerous German pioneers in the...
- about 12 miles (19.3 km) west of New Orleans
New Orleans, Louisiana
New Orleans is a major United States port and the largest city and metropolitan area in the state of Louisiana. The New Orleans metropolitan area has a population of 1,235,650 as of 2009, the 46th largest in the USA. The New Orleans – Metairie – Bogalusa combined statistical area has a population...
- it allows floodwaters from 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...
to flow into 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...
and thence into 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 construction of the spillway was completed in 1931.
Overview
The Bonnet Carré Spillway consists of two basic components: a control structure along the east bank of the Mississippi River and a floodway that transfers the diverted flood waters to the lake. The control structure is a mechanically controlled concrete weirWeir
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...
which extends for over a mile and a half parallel to the river. When opened, the control structure slightly restricts the flow of the river (at the structure’s location) toward its main channel, thereby causing it to rise in elevation just high enough to flow into the diversion channel; and, with sufficient elevation (or head), to carry the overflow volume into Lake Pontchartrain. The lake’s opening to the gulf is sufficient to absorb and dissipate any conceivable volume of flood flow. Thus, the flood surcharge portion of the water from the Mississippi is divided between the main river and the diversion channel; with the surcharge bypassing the New Orleans metropolitan area, resulting in the Mississippi being lower (through that area) than it could have been; and reducing the stress on the area's 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 that line the river. Confined by guide levees, the floodway stretches nearly six miles (10 km) to Lake Pontchartrain, with a design capacity of 250000 cuft/s. The spillway is crossed by U.S. 61
U.S. Route 61
U.S. Route 61 is the official designation for a United States highway that runs from New Orleans, Louisiana, to the city of Wyoming, Minnesota. The highway generally follows the course of the Mississippi River, and is designated the Great River Road for much of its route. As of 2004, the highway's...
and Interstate 10.
The spillway was built in response to 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...
that inundated much of the Mississippi River basin. It was first opened during the flood of 1937
Ohio River flood of 1937
The Ohio River flood of 1937 took place in late January and February 1937. With damage stretching from Pittsburgh to Cairo, Illinois, one million persons were left homeless, with 385 dead and property losses reaching $500 million...
, and nine times thereafter through 2011 to lower river stages at New Orleans. The most recent opening began on May 9, 2011, when river levels in New Orleans approached the flood stage of 17 feet (5.2 m).
The spillway is part of 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...
' multi-state plan, called the Mississippi River and Tributaries Project (MR&T), providing 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...
protection for the alluvial valley between Cape Girardeau, Missouri
Cape Girardeau, Missouri
Cape Girardeau is a city located in Cape Girardeau and Scott counties in Southeast Missouri in the United States. It is located approximately southeast of St. Louis and north of Memphis. As of the 2010 census, the city's population was 37,941. A college town, it is the home of Southeast Missouri...
and the mouth of the river near Venice
Venice, Louisiana
Venice is an unincorporated community in Plaquemines Parish, Louisiana, United States. It is 130 km south of New Orleans on the west bank of the Mississippi River at . It is the last community down the Mississippi accessible by automobile, and is the southern terminus of the Great River Road...
, Louisiana. Due to the wide expanse of the project and the complex problems involved, the plan contains an array of features. The MR&T Project provides for levees to contain flood flows, floodways such as the Bonnet Carré to redirect excess flows away from the Mississippi and has other aspects such as channel improvement and river bank stabilization for efficient navigation and protection of the levee system. It also involves reservoirs and pumping plants for flood control drainage.
Natural Resource Management
In 2007, extraction operations began on a 42 acres (169,968.1 m²) square section of spillway property. The 7600 acres (30.8 km²) spillway, designed to divert rising water out of the Mississippi River during flooding seasons, long has been a major source of sand and clay that is used in construction projects throughout the area. But in the post-KatrinaHurricane Katrina
Hurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...
era, clay extracted from the spillway will be crucial to raising the levees in St. Charles Parish
St. Charles Parish, Louisiana
St. Charles Parish is a parish located in the U.S. state of Louisiana. The parish seat is Hahnville. In 2010, its population was 52,780. In the eighteenth and nineteenth century, this was part of the German Coast, an area along the Mississippi River settled by numerous German pioneers in the...
and east Jefferson Parish
Jefferson Parish, Louisiana
Jefferson Parish is a parish in Louisiana, United States that includes most of the suburbs of New Orleans. The seat of parish government is Gretna....
.
Once the excavation is complete, the pits will be filled with water and stocked with bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
, largemouth bass
Largemouth bass
The largemouth bass is a species of black bass in the sunfish family native to North America . It is also known as widemouth bass, bigmouth, black bass, bucketmouth, Potter's fish, Florida bass, Florida largemouth, green bass, green trout, linesides, Oswego bass, southern largemouth...
and other fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
to enhance the area's secondary function: a recreational haven for boaters, hikers, hunters and fishers.
History of openings
Years when the spillway was opened, number of days it remained open, and peak number of bays opened- 1937 48 days, 285 bays opened
- 1945 57 days, all 350 bays opened
- 1950 38 days, all 350 bays opened
- 1973 75 days, all 350 bays opened
- 1975 13 days, 225 bays opened
- 1979 45 days, all 350 bays opened
- 1983 35 days, all 350 bays opened
- 1997 31 days, 298 bays opened
- 2008 31 days, 160 bays opened
- 2011 42 days, 330 bays opened