Old River Control Structure
Encyclopedia
Floodgate
Floodgates are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or...
system located in a branch 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...
in 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...
. It regulates the flow of water leaving the Mississippi into 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....
, thereby preventing the Mississippi river from changing course. Completed in 1963, the complex was built by the U.S. Army Corps of Engineers in a side channel of the Mississippi known as "Old River," between the Mississippi's current channel and 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...
, a former channel of the Mississippi.
Purpose
Although the Red River is currently a tributary of the Mississippi River and the Atchafalaya RiverAtchafalaya 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....
a distributary of the Red River, it has not always been that way. Up until the 15th century A.D., the Red River and Mississippi River were entirely separate rivers and more or less parallel to one another.
Beginning in the 15th century, though, the Mississippi River created a small westward loop, later renamed Turnbull’s Bend, near present-day Angola, La. This loop intercepted the Red River, and the Atchafalaya River was formed as a distributary.
In the heyday of steamboats
Steamboat
A steamboat or steamship, sometimes called a steamer, is a ship in which the primary method of propulsion is steam power, typically driving propellers or paddlewheels...
along the Mississippi River, it took a boat several hours to travel the bend’s 20 miles, and only then it had progressed a mile or so. To reduce travel time, Captain Henry M. Shreve
Henry Miller Shreve
Henry Miller Shreve was the American inventor and steamboat captain who opened the Mississippi, Ohio and Red rivers to steamboat navigation. Shreveport, Louisiana, is named in his honor....
, a river engineer and founder of Shreveport
Shreveport, Louisiana
Shreveport is the third largest city in Louisiana. It is the principal city of the fourth largest metropolitan area in the state of Louisiana and is the 109th-largest city in the United States....
, La., dug a canal in 1831 through the neck of Turnbull’s Bend. At the next high water, the Mississippi roared through this channel.
With the Mississippi River taking a new course, the Red River began emptying into the smaller Atchafalaya River. And the Atchafalaya River was force-fed by the Mississippi River at the abandoned Turnbull’s Bend, which had come to be known as "Old River.” With this extra intake of water, the Atchafalaya River wore deeper and wider throughout the 1800’s and early 1900’s.
The U.S. Army Corps of Engineers measured the amount of water flowing through the Mississippi River and compared it to the amount entering the Atchafalaya Basin by monitoring “latitude flow” at the latitude of the Red River Landing
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....
, located five miles downstream of Old River. In this case, latitude flow is a combination of the flows of the Mississippi and Atchafalaya rivers as they cross an imaginary line at that latitude.
Between 1850 and 1950, the percentage of latitude flow entering the Atchafalaya River had increased from less than 10 percent to about 30 percent. By 1953, the U.S. Army Corps of Engineers concluded that the Mississippi River could change its course to the Atchafalaya River by 1990 if it were not controlled, since this alternative path 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...
through the Atchafalaya River is much shorter and steeper.
The Corps completed construction on the Old River Control Structure in 1964 to prevent the main channel flow of the Mississippi River from altering its current course to the Gulf of Mexico through the natural geologic process of avulsion
Avulsion
Avulsion in general refers to a tearing away. Specifically, it can refer to:* A type of amputation where the extremity is pulled off rather than cut off* Avulsion fracture* Avulsion injury, the removal of all the layers of skin from abrasion...
. Historically, this natural process has occurred about every 1,000 years, and is overdue. Some researchers believe the likelihood of this event increases each year, despite artificial control efforts.
If the Mississippi diverts its main channel 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....
, it would develop a new delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
south of 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....
in southern Louisiana, greatly reducing water flow to its present channel through Baton Rouge and New Orleans. Integrity of the Old River Control Structure, the nearby Morganza Spillway
Morganza Spillway
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...
, and other levees in the area is essential to prevent such a diversion; see "Mississippi River: Future course changes" for further discussion. Jeff Masters of Weather Underground
Weather Underground (weather service)
Weather Underground is a commercial weather service that provides real-time weather information via the Internet. Weather Underground provides weather reports for most major cities across the world on its Web site, as well as local weather reports for newspapers and Web sites...
noted that failure of that complex "would be a serious blow to the U.S. economy."
Components
The present Old River Control Structure was completed in 1964 and expanded in 1990. The first two floodgates are the Low Sill Control Structure, which regulates routine flow in the waterway, and the Overbank Control Structure, in use only when the Mississippi exceeds its banks. A navigation channel and lock were also part of the original facility design. Subsequent expansion created what is now known as the Old River Control Complex, when the Auxiliary Structure, which became operational in 1986, was added to reduce pressure on the original floodgates after extensive damage caused by the flood of 1973. The Sidney A. Murray, Jr. Hydroelectric StationSidney A. Murray, Jr. Hydroelectric Station
The Sidney A. Murray, Jr. Hydroelectric Station, also known as Louisiana Hydroelectric , opened in response to a need for a non-polluting, less-costly power source for Vidalia, Louisiana. A site approximately 40 miles south of the town was selected for the new facility. The 192 MW plant started...
, completed in 1990, also provides an additional measure of control at the site.
Operation
Water from the Mississippi is normally diverted into the Atchafalaya Basin only at Old River, 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..Water diverted at Old River flows into the Atchafalaya Basin, first entering the Red River, then continuing down the Atchafalaya River to the Gulf of Mexico, bypassing Baton Rouge and New Orleans (see diagram).
The Morganza Floodway, between the Mississippi and the Atchafalaya Basin nearby downstream, is normally closed, but can be opened in an emergency to relieve water levels and water-pressure stress on various levees and other flood-control structures, including the Old River Control Structure. The floodway can reduce stress by diverting additional water from the Mississippi into the Atchafalaya. The Morganza Floodway was never used before the construction of ORCS, and has only been opened twice (as of 2011) for flood control since completion of the ORCS.