Bonnet Carré Spillway
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The Bonnet Carré Spillway is a
flood control Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and ru ...
operation in the Lower
Mississippi Valley 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 ...
. Located in
St. Charles Parish, Louisiana St. Charles Parish () is a parish located in the U.S. state of Louisiana. At the 2020 census, its population was 52,549. The parish seat is Hahnville and the most populous community is Luling. The parish was established in 1807, following t ...
, about west of
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 ...
, it allows floodwaters from 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 ...
to flow into
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 thence into 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 ...
. The spillway was constructed between 1929 and 1931, following 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 has been designated as a
National Historic Civil Engineering Landmark __NOTOC__ The following is a list of Historic Civil Engineering Landmarks as designated by the American Society of Civil Engineers since it began the program in 1964. The designation is granted to projects, structures, and sites in the United Stat ...
by the
American Society of Civil Engineers The American Society of Civil Engineers (ASCE) is a tax-exempt professional body founded in 1852 to represent members of the civil engineering profession worldwide. Headquartered in Reston, Virginia, it is the oldest national engineering soci ...
.


History

The
Bonnet Carré Crevasse The Bonnet Carré Crevasse (1871) was one of several levee breaches in the Bonnet Carré area in the mid-to-late 19th century. Bonnet Carré was approximately from New Orleans, Louisiana. The breach occurred when excess water from the Missis ...
was one of several levee breaches in the Bonnet Carré area in 1871. Local drainage systems were unable to contain the floodwater and strong winds caused the water to enter Lake Pontchartrain and surrounding urban areas. The river levee was not restored until 1883. The spillway was built in response 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 ...
that inundated much of the Mississippi River basin. It was first opened during the flood of 1937. In 2007, extraction operations began on a square section of spillway property. The 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- Katrina era, clay extracted from the spillway will be crucial to raising the levees in St. Charles Parish and east
Jefferson Parish Jefferson Parish () is a parish in the U.S. state of Louisiana. As of the 2020 census, the population was 440,781. Its parish seat is Gretna, its largest community is Metairie, and its largest incorporated city is Kenner. Jefferson Parish i ...
. The several openings of the spillway have had a significant effect on marine fisheries in the
Mississippi Sound The Mississippi Sound is a sound along the Gulf Coast of the United States. It runs east-west along the southern coasts of Mississippi and Alabama, from the mouth of the Pearl River at the Mississippi-Louisiana state border to the Dauphin Islan ...
, which resulted in a federal award of damages in 2011 and ongoing federal litigation over the management of the spillway. The 2019 opening began February 27, 2019, when river levels were predicted to rise to minor flood stage in New Orleans on March 19, 2019. The Army Corps of Engineers initially opened 38 of the 350 bays and increased this number to 206 bays when the flood crest arrived later in March. The Army Corps of Engineers closed the spillway on April 11, 2019, only to reopen it again on May 10, 2019. This marks the first time in the spillway's history that it was opened twice in one year. In April 2020 the Spillway was again opened from April 3, 2020, until May 1, 2020, a total of 29 days.


Description

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, located between the towns of Montz and Norco, is a mechanically controlled 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 water level. Weirs are also used to control the flow of water for outlets of l ...
that extends for over a mile and a half parallel to the river. When opened, the control structure allows overflow volume to flow 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 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 ...
s that line the river. Confined by guide levees, the floodway stretches nearly to Lake Pontchartrain, with a design capacity of . The spillway is crossed by U.S. 61 and
Interstate 10 Interstate 10 (I-10) is the southernmost transcontinental highway in the Interstate Highway System of the United States. It is the fourth-longest Interstate in the country at , following I-90, I-80, and I-40. It was part of the origina ...
. The spillway's secondary function is as a recreational area. It is used for off-road vehicles, biking, boating, hiking, hunting, and fishing. It is designated a protected
wildlife management Wildlife management is the management process influencing interactions among and between wildlife, its Habitat, habitats and people to achieve predefined impacts. Wildlife management can include wildlife conservation, population control, gamekeepi ...
area by the
Louisiana Department of Wildlife and Fisheries The Louisiana Department of Wildlife and Fisheries (LDWF) is a state agency of Louisiana that maintains state wildlife and fishery areas. The agency is headquartered in the capital city of Baton Rouge. Mission The Louisiana Department of Wildlife ...
. To enhance fishing in the spillway, the clay extraction pits were filled with water and stocked with
bluegill The bluegill (''Lepomis macrochirus''), sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose", is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and wetlands ea ...
,
largemouth bass The largemouth bass (''Micropterus nigricans'') is a carnivorous, freshwater fish, freshwater, ray-finned fish in the Centrarchidae (sunfish) family, native to the eastern United States, eastern and central United States, southeastern Canada an ...
, and other
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
.


Structure & multi-state plan

The floodgate inlet is offset into the Mississippi River bank, at a location that had seen natural flooding for at least two centuries. The concrete structure has been designed to reduce settling into the riverbank. The opening and closing of the spillway is done by lifting out up to 7000 wooden ' needles' (8" x 12" wooden beams) arranged in 350 linear bays. This is done by two rail-mounted gantry cranes atop the spillway. The number of needles removed determines the water flow into the spillway. Gaps built into each bay allow limited seepage anytime the river level reaches the bottom of the bays. Removal of all 7000 needles takes about 36 hours but is usually done over a period of several days. The spillway is part of 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 ...
' multi-state plan, called the Mississippi River and Tributaries Project (MR&T), providing
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 ...
protection for the alluvial valley between
Cape Girardeau, Missouri Cape Girardeau ( , ; colloquially referred to as "Cape") is a city in Cape Girardeau County, Missouri, Cape Girardeau and Scott County, Missouri, Scott Counties in the U.S. state of Missouri. At the 2020 United States census, 2020 census, the ...
. and the mouth of the river near
Venice Venice ( ; ; , formerly ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 islands that are separated by expanses of open water and by canals; portions of the city are li ...
, Louisiana. Because of the wide expanse of the project and the complex problems involved, the plan contains an array of features. The MR&T Project provides for
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 ...
s to contain flood flows, floodways such as the Bonnet Carré to redirect excess flows away from the Mississippi, and 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 stations for flood control drainage.


List of openings

The following chart shows the years when the spillway was opened, number of days it remained open, peak number of bays opened, percent of maximum flow at peak, and peak flow rate. The spillway has a design capacity of 250,000 cu ft/s when all 350 bays are fully open, or approximately 714 cu ft/s per bay.


Kugler and Kenner Cemeteries

There are two cemeteries located in the spillway. The cemeteries contain the remains of enslaved persons of African descent and free African-Americans, and the historic ground surface is under several feet of sediment. When the spillway gates are opened, the cemeteries are flooded. The location of the gravesites was a mystery until May 1975, when the US Army Corps of Engineers excavated a ditch in the spillway. During that process, a tombstone and casket were discovered. In 1986, the corps ordered a historical study of the spillway and discovered a second cemetery. The two cemeteries were placed on the
National Register of Historic Places The National Register of Historic Places (NRHP) is the Federal government of the United States, United States federal government's official United States National Register of Historic Places listings, list of sites, buildings, structures, Hist ...
in 1987. The artifacts discovered during the 1986 study included coffin furniture, coffins, grave markers, cultural remains, and human remains. The Kenner and Kugler Cemeteries Archeological District consists of the two cemeteries. Additional research on the cemeteries was done in 2002–2005 and archaeological investigations in 2008–2009. The cemeteries, named the Kenner Cemetery and the Kugler Cemetery, are
black Black is a color that results from the absence or complete absorption of visible light. It is an achromatic color, without chroma, like white and grey. It is often used symbolically or figuratively to represent darkness.Eva Heller, ''P ...
burial plots which appear to date from the early 1800s and were in use until 1929. Several African-American US Army Civil War veterans were moved from the spillway cemeteries to Chalmette National Cemetery in 1930. The total number of burials in either cemetery is unknown. The sites adjoin 19th- and early 20th-century
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...
plantations Plantations are farms specializing in cash crops, usually mainly planting a single crop, with perhaps ancillary areas for vegetables for eating and so on. Plantations, centered on a plantation house, grow crops including cotton, cannabis, tobacco ...
in St. Charles Parish. According to oral histories and as confirmed by GIS analysis, both cemeteries were located in the midst of the cane fields of their respective plantations. The Kenner Cemetery, located on the former Roseland Plantation, was reported to be marked by iron and wooden crosses during its period of use. No such markers were confirmed archaeologically, but one granite US veteran headstone was recovered from the site. The Kugler Cemetery, located on the former Hermitage Plantation, was reported to contain iron crosses and a metal fence. One such iron cross and remnants of what could have been the fence were recovered during the 1986 archaeological investigations. At present, the cemetery sites have been demarcated by young
live oak Live oak or evergreen oak is any of a number of oaks in several different sections of the genus ''Quercus'' that share the characteristic of evergreen foliage. These oaks are generally not more closely related to each other than they are to o ...
trees.


Diversion projects

The success of the Caernarvon Freshwater and the Davis Pond Freshwater Diversions, especially concerning wetlands maintenance more than wetlands building, has led to studies for more fresh water diversion projects. Caernarvon and Davis Pond diversions have limits, because of laws governing their operation, aimed at limiting the flow of freshwater to minimize damage to oysters. The ''Bonnet Carré Spillway diversion'' would be built within the spillway, on the east bank of the Mississippi, allowing up to 25,000 c.f.s. (i.e. ft3/s) of fresh water and sediment diversion into
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 the
Mississippi Sound The Mississippi Sound is a sound along the Gulf Coast of the United States. It runs east-west along the southern coasts of Mississippi and Alabama, from the mouth of the Pearl River at the Mississippi-Louisiana state border to the Dauphin Islan ...
. The diversion would slow or stop
subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...
, reducing marsh loss by 10,500 acres in the next 50 years, providing fish and wildlife protection, as well as further storm surge protection. The diversion was authorized by the Water Resources Development Act of 1988 (WRDA 1988), and Congress (1990) split the cost and maintenance between the Federal Government at 75%, Louisiana at 20% and Mississippi at 5%. Louisiana and Mississippi must agree to a final project design, but in July 1996, Louisiana withdrew as a sponsor, and as of 2016 an agreement has not been reached.USACE brochure: ''Bonnet Carré Spillway diversion''
Retrieved 2016-08-07


See also

*
CNR Bonnet Carré Spillway-Baton Rouge Bridge The CNR Bonnet Carré Spillway-Baton Rouge Bridge is a 1.3 mile (2,092 m or 6,864 ft) wooden trestle bridge that carries a Canadian National Railway rail line over the Bonnet Carré Spillway in St. Charles Parish. Its length once had it in ...
*
CNR Bonnet Carré Spillway-McComb Bridge The CNR Bonnet Carré Spillway-McComb Bridge is a 1.3 mile (2,092 m or 6,864 ft) bridge that carries Canadian National Railway tracks over the Bonnet Carré Spillway and a portion of Lake Pontchartrain in St. Charles Parish and St. Jo ...
*
Kansas City Southern Bonnet Carré Spillway Bridge The Kansas City Southern Bonnet Carré Spillway Bridge is a bridge that carries a Canadian Pacific Kansas City rail line over the Bonnet Carré Spillway in St. Charles Parish. At 1.8 miles (2,896 m or 9,504 ft), its length once had it included o ...
*
I-10 Bonnet Carré Spillway Bridge The I-10 Bonnet Carré Spillway Bridge is a twin concrete trestle bridge in the U.S. state of Louisiana. With a total length of , it is one of the longest bridges in the world. The bridge carries Interstate 10 over the Bonnet Carré Spillway ...
* U.S. 61 Bonnet Carré Spillway Bridge * Birds Point-New Madrid Floodway *
Morganza Spillway The Morganza Spillway or Morganza Control Structure is a flood-control structure in the U.S. state of Louisiana. It is located along the western bank of the Lower Mississippi River at river mile 280, near Morganza in Pointe Coupee Parish. The sp ...
*
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 ...


References


External links


U.S. Army Corps of Engineers Bonnet Carré Spillway Official Site

"New Orleans Flood Valve Finished", March 1931, Popular Science
{{DEFAULTSORT:Bonnet Carre Spillway * Mississippi River United States Army Corps of Engineers Protected areas of St. Charles Parish, Louisiana Tributaries of Lake Pontchartrain Tourist attractions in St. Charles Parish, Louisiana Landforms of St. Charles Parish, Louisiana 1931 establishments in Louisiana Historic Civil Engineering Landmarks Spillways