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{{Short description|Floodgate system in Louisiana, USA}}
[[File:Old River Control Structure Complex.jpg|right|thumb|The Old River Control Structure complex. View is to the [[east-southeast]], looking downriver on the [[Mississippi River|Mississippi]], with the three [[dam]]s across channels leading to the [[Atchafalaya River]] to the right of the Mississippi. [[Concordia Parish, Louisiana]] is in the foreground, on the right, and [[Wilkinson County, Mississippi]], is in the background, across the Mississippi on the left.]]
[[File:Old River Control Structure Complex.jpg|right|thumb|The Old River Control Structure complex. View is to the [[east-southeast]], looking downriver on the [[Mississippi River|Mississippi]], with the three [[dam]]s across channels leading to the [[Atchafalaya River]] to the right of the Mississippi. [[Concordia Parish, Louisiana]] is in the foreground, on the right, and [[Wilkinson County, Mississippi]], is in the background, across the Mississippi on the left.]]
[[File:Old River Control discharge.jpg|right|thumb|Old River Control Structure discharging water into the Atchafalaya, May 2011]]
[[File:Old River Control discharge.jpg|right|thumb|Old River low-sill control structure discharging water into the Atchafalaya, May 2011]]


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 leaving the Mississippi into the [[Atchafalaya 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]], a former channel of the Mississippi.<ref>{{cite magazine |last=McPhee |first=John |title=The Control of Nature: Atchafalaya |magazine=The New Yorker |date=February 23, 1987 |url=http://www.newyorker.com/archive/1987/02/23/1987_02_23_039_TNY_CARDS_000347146 |accessdate=May 12, 2011}} Republished in {{cite book |last=McPhee |first=John |title=The Control of Nature |publisher=Farrar, Straus and Giroux |year=1989 |isbn=978-0-374-12890-6}}</ref><ref>{{cite web | title=Old River Control | work=The Mighty Mississippi River | author=Angert, Joe and Isaac | url=http://users.stlcc.edu/jangert/oldriver/oldriver.html |archiveurl=https://web.archive.org/web/20090515010700/http://users.stlcc.edu/jangert/oldriver/oldriver.html |archivedate=May 15, 2009 |accessdate=2011-05-12}}. Includes map and pictures.</ref><ref name="AmericasWetlands"/><ref name="InteractiveMap" /><ref name="kemp">{{cite web |url=http://www.tulane.edu/~bfleury/envirobio/enviroweb/FloodControl.htm |title=The Mississippi Levee System and the Old River Control Structure |first=Katherine |last=Kemp |date=January 6, 2000}}</ref> The Old River Control Structure is actually a complex containing the original low-sill<ref>{{Cite web | url=http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/lowsillstructure.html | title=Low Sill Structure}}</ref> and overbank<ref>{{cite web|url=https://www.johnweeks.com/river_mississippi/pages/lmiss23.html|title=Old River Control Structure, Point Breeze, LA|website=www.johnweeks.com}}</ref> structures, as well as the auxiliary structure that was constructed after the low-sill structure was damaged during the [[Mississippi flood of 1973|Mississippi River Flood of 1973]]. The complex also contains a navigation lock and the Sidney A. Murray Jr. Hydroelectric Station.<ref name=Piazza2014>{{cite book |last=Piazza |first=Bryan P. |title=The Atchafalaya River Basin: History and Ecology of an American Wetland |year=2014 |publisher=Texas A&M University Press |isbn=978-1-62349-039-3}}</ref>
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 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]], a former channel of the Mississippi.<ref>{{cite magazine |last=McPhee |first=John |title=The Control of Nature: Atchafalaya |magazine=The New Yorker |date=February 23, 1987 |url=http://www.newyorker.com/archive/1987/02/23/1987_02_23_039_TNY_CARDS_000347146 |access-date=May 12, 2011}} Republished in {{cite book |last=McPhee |first=John |title=The Control of Nature |publisher=Farrar, Straus and Giroux |year=1989 |isbn=978-0-374-12890-6}}</ref><ref>{{cite web | title=Old River Control | work=The Mighty Mississippi River | author=Angert, Joe and Isaac | url=http://users.stlcc.edu/jangert/oldriver/oldriver.html |archive-url=https://web.archive.org/web/20090515010700/http://users.stlcc.edu/jangert/oldriver/oldriver.html |archive-date=May 15, 2009 |access-date=2011-05-12}}. Includes map and pictures.</ref><ref name="AmericasWetlands"/><ref name="InteractiveMap" /><ref name="kemp">{{cite web |url=http://www.tulane.edu/~bfleury/envirobio/enviroweb/FloodControl.htm |title=The Mississippi Levee System and the Old River Control Structure |first=Katherine |last=Kemp |date=January 6, 2000}}</ref>
The Old River Control Structure is a complex containing the original low-sill<ref>{{Cite web | url=http://www.uoguelph.ca/geology/geol2250/glossary/HTML%20files/lowsillstructure.html | title=Low Sill Structure}}</ref> and overbank<ref>{{cite web|url=https://www.johnweeks.com/river_mississippi/pages/lmiss23.html|title=Old River Control Structure, Point Breeze, LA|website=www.johnweeks.com}}</ref> structures, as well as the auxiliary structure that was constructed after the low-sill structure was damaged during the [[Mississippi flood of 1973|Mississippi River Flood of 1973]]. The complex also contains a navigation lock and the Sidney A. Murray Jr. Hydroelectric Station.<ref name=Piazza2014>{{cite book |last=Piazza |first=Bryan P. |title=The Atchafalaya River Basin: History and Ecology of an American Wetland |year=2014 |publisher=Texas A&M University Press |isbn=978-1-62349-039-3}}</ref>


== Old River ==
== Old River ==
[[File:Geomorphology of Old River.jpg|thumb|left|300 px|Formation of the Atchafalaya River and construction of the Old River Control Structure.]]
[[File:Geomorphology of Old River.jpg|thumb|left|300 px|Formation of the Atchafalaya River and construction of the Old River Control Structure.]]


Before the 15th century, the [[Red River of the South|Red River]] and Mississippi River were entirely separate and more or less parallel to one another.<ref name="AmericasWetlands">{{cite web |title=Louisiana Old River Control Structure and Mississippi river flood protection |url=http://www.americaswetlandresources.com/background_facts/detailedstory/LouisianaRiverControl.html |work=America's Wetland Resource Center |publisher=Loyola University's Center for Environmental Communication}}</ref> Beginning in the 15th century, the Mississippi River created a small, westward, [[meander|oxbow loop]], later called Turnbull's Bend, near present-day [[Angola, Louisiana]]. This loop eventually intersected the Red River, making the downstream part of the Red River a distributary of the Mississippi; this distributary came to be called the [[Atchafalaya River]].<ref name="AmericasWetlands" />
Before the 15th century, the [[Red River of the South|Red River]] and Mississippi River were entirely separate and flowed more or less parallel to one another.<ref name="AmericasWetlands">{{cite web |title=Louisiana Old River Control Structure and Mississippi river flood protection |url=http://www.americaswetlandresources.com/background_facts/detailedstory/LouisianaRiverControl.html |work=America's Wetland Resource Center |publisher=Loyola University's Center for Environmental Communication |access-date=2007-04-01 |archive-date=2016-03-10 |archive-url=https://web.archive.org/web/20160310124727/http://www.americaswetlandresources.com/background_facts/detailedstory/LouisianaRiverControl.html |url-status=dead }}</ref> Beginning in the 15th century, the Mississippi River created a small, westward, [[meander|oxbow loop]], later called Turnbull's Bend, near present-day [[Angola, Louisiana]]. This loop eventually intersected the Red River, making the downstream part of the Red River a distributary of the Mississippi; this distributary came to be called the [[Atchafalaya River]].<ref name="AmericasWetlands" />


In the heyday of [[steamboat]]s along the Mississippi River, it would take a boat several hours to travel the {{convert|20|mi|km}} of Turnbull's Bend, after which it would have progressed only about {{convert|1|mi|km}} from the entrance to the bend. To reduce travel time, [[Henry Miller Shreve|Captain Henry M. Shreve]], a river engineer and namesake of [[Shreveport, Louisiana|Shreveport]], Louisiana, dug a canal in 1831 through the neck of Turnbull's Bend; this canal became known as Shreve's Cut. At the next high water, the Mississippi roared through this channel.<ref name="nytimes">{{cite news |url=https://www.nytimes.com/1987/05/03/us/612487.html |title=$500 Million (and Rising) to Contain a River |date=May 3, 1987 |newspaper=The New York Times |agency=Associated Press}}</ref> The upper portion of Turnbull's Bend became the smaller ''Upper Old River'' while the lower portion became the larger ''Lower Old River''. At first, the Lower Old River would flow eastward, to the Mississippi, until 1839, when locals began removing the [[Great Raft]], a natural log jam that was obstructing the Atchafalaya River. The project was finished in 1840. After that, the Lower Old River would flow eastward to the Mississippi when the Red River was high and the Mississippi was low, and westward to the Atchafalaya when the Mississippi was high and the Red River was low. Over time, the number of days when the river flowed east to the Mississippi decreased and the number of days when the river flowed west increased, until eventually the Lower Old River flowed west over half the time. By 1880, it rarely flowed eastward and was now rapidly capturing more and more of the flow of the Mississippi. With this extra intake of water, the channel of the Atchafalaya River was worn deeper and wider throughout the 1800s and early 1900s.<ref name="nytimes" /> Between 1850 and 1950, the flow increased from less than 10% of the Mississippi to 30%, and the U.S. Army Corps of Engineers began work on the Old River Control Structure to prevent the Atchafalaya becoming the main channel of the Mississippi. The project was completed in 1963, and it completely sealed off the Old river. However, a lock, a diversion channel, and flood spillway were installed to allow barges to pass between the Atchafalaya and Mississippi.
In the heyday of [[steamboat]]s along the Mississippi River, such a vessel would need several hours to travel the {{convert|20|mi|km}} of Turnbull's Bend, after which it would have progressed only about {{convert|1|mi|km}} from the entrance to the bend. To reduce travel time, Captain [[Henry Miller Shreve|Henry M. Shreve]], a river engineer and namesake of [[Shreveport, Louisiana|Shreveport]], Louisiana, dug a canal in 1831 through the neck of Turnbull's Bend; this canal became known as Shreve's Cut. At the next high water, the Mississippi roared through this channel.<ref name="nytimes">{{cite news |url=https://www.nytimes.com/1987/05/03/us/612487.html |title=$500 Million (and Rising) to Contain a River |date=May 3, 1987 |newspaper=The New York Times |agency=Associated Press}}</ref> The upper portion of Turnbull's Bend was referred to as ''Upper Old River,'' while the larger, lower portion became known as the ''Lower Old River''.
At first, the Lower Old River would flow eastward, to the Mississippi, until 1839, when locals began removing the [[Great Raft]], a natural log jam that was obstructing the Atchafalaya River. The project was finished in 1840. After that, the Lower Old River would flow eastward to the Mississippi when the Red River was high and the Mississippi was low, and westward to the Atchafalaya when the Mississippi was high and the Red River was low. Over time, the number of days when the river flowed east to the Mississippi decreased and the number of days when the river flowed west increased, until eventually the Lower Old River flowed west over half the time. By 1880, it rarely flowed eastward and was rapidly capturing more and more of the flow of the Mississippi. With this increased water flow, the channel of the Atchafalaya River was worn deeper and wider throughout the 1800s and early 1900s.<ref name="nytimes" />


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, Louisiana|Red River Landing]], located {{convert|5|mi|km|spell=in}} 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.<ref name="AmericasWetlands" />
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, Louisiana|Red River Landing]], located {{convert|5|mi|km|spell=in}} 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.<ref name="AmericasWetlands" />


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]] through the Atchafalaya River is much shorter and steeper.<ref name="AmericasWetlands" />
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]] through the Atchafalaya River is much shorter and steeper.


The Corps completed construction on the Old River Control Structure in 1963 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 (river)|avulsion]].<ref name="AmericasWetlands" /><ref name="DailyImpact">{{cite web |title=Mississippi Rising: Apocalypse Now? |date=April 28, 2011 |url=http://www.dailyimpact.net/2011/04/28/mississippi-rising-apocalypse-now/ |publisher=Daily Impact |accessdate=May 10, 2011}}</ref> 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.<ref>{{cite book |last=Daniels |first=Ronald Joel |title=On Risk and Disaster: Lessons from Hurricane Katrina |year=2006 |publisher=University of Pennsylvania Press |page=45}}</ref>
The Corps completed construction on the Old River Control Structure in 1963 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 (river)|avulsion]].<ref name="AmericasWetlands" /><ref name="DailyImpact">{{cite web |title=Mississippi Rising: Apocalypse Now? |date=April 28, 2011 |url=http://www.dailyimpact.net/2011/04/28/mississippi-rising-apocalypse-now/ |publisher=Daily Impact |access-date=May 10, 2011}}</ref> Historically, this natural process of course change has occurred about every 1,000 years, and is overdue. Some researchers believe the likelihood of this event increases each year, despite manmade artificial control efforts.<ref>{{cite book |last=Daniels |first=Ronald Joel |title=On Risk and Disaster: Lessons from Hurricane Katrina |year=2006 |publisher=University of Pennsylvania Press |page=45}}</ref>


If the Mississippi diverts its main channel to the [[Atchafalaya Basin]] and the [[Atchafalaya River]], it would develop a new [[river delta|delta]] south of [[Morgan City, Louisiana|Morgan City]] in southern Louisiana, greatly reducing water flow to its present channel through [[Baton Rouge]] and [[New Orleans]].<ref name="InteractiveMap">{{cite web |url=http://www.mappingsupport.com/p/gmap4.php?q=https://sites.google.com/site/gmap4files/p/news/mississippi_course_change.txt&ll=30.417887,-91.201416&t=h&z=9&label=on |title=Will the Mississippi River change its course in 2011 to the red line? |accessdate=May 8, 2011 |publisher=Mappingsupport}}</ref> The [[Mississippi Flood of 1973]] almost caused the control structure to fail. Integrity of the Old River Control Structure, the nearby [[Morganza Spillway]], and other levees in the area is essential to prevent such a diversion. Jeff Masters of ''[[Weather Underground (weather service)|Weather Underground]]'' noted that failure of that complex "would be a serious blow to the U.S. economy."<ref>{{cite web |url=https://www.wunderground.com/blog/JeffMasters/mississippi-river-sets-alltime-flood-records-2nd-major-spillway-open.html |title=Mississippi River sets all-time flood records; 2nd major spillway opens |first=Jeff |last=Masters |publisher=Weather Underground |date=May 9, 2011 |accessdate=November 11, 2017}}</ref>
If the Mississippi diverts its main channel to the [[Atchafalaya Basin]] and the [[Atchafalaya River]], it would develop a new [[river delta|delta]] south of [[Morgan City, Louisiana|Morgan City]] in southern Louisiana, greatly reducing water flow to its present channel through [[Baton Rouge]] and [[New Orleans]], with adverse economic effects on both port cities.<ref name="InteractiveMap">{{cite web |url=http://www.mappingsupport.com/p/gmap4.php?q=https://sites.google.com/site/gmap4files/p/news/mississippi_course_change.txt&ll=30.417887,-91.201416&t=h&z=9&label=on |title=Will the Mississippi River change its course in 2011 to the red line? |access-date=May 8, 2011 |publisher=Mappingsupport}}</ref> The [[Mississippi flood of 1973]] almost caused the control structure to fail. Maintenance of the integrity of the Old River Control Structure, the nearby [[Morganza Spillway]], and other levees in the area is essential to prevent such a diversion. Jeff Masters of ''[[Weather Underground (weather service)|Weather Underground]]'' noted that failure of that complex "would be a serious blow to the U.S. economy."<ref>{{cite web |url=https://www.wunderground.com/blog/JeffMasters/mississippi-river-sets-alltime-flood-records-2nd-major-spillway-open.html |title=Mississippi River sets all-time flood records; 2nd major spillway opens |first=Jeff |last=Masters |publisher=Weather Underground |date=May 9, 2011 |access-date=November 11, 2017}}</ref>


== Components ==
== Components ==
[[File:Mississippi Project Design Flood.tif|thumb|right|upright=2.0|alt=diagram of river flows during Project Design Flood|A diagram that depicts river flows associated with [[Project Design Flood]].]]
[[File:Mississippi Project Design Flood.tif|thumb|right|upright=2.0|alt=diagram of river flows during Project Design Flood|A diagram that depicts river flows associated with [[Project Design Flood]].]]
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 Station]], completed in 1990, also provides an additional measure of control at the site.<ref name="AmericasWetlands"/>
The Old River Control Structure (ORCS) and Overbank Control Structure became operational in 1964 and expanded in 1986 with the addition of the Old River Control Auxiliary Structure (ORCAS). The primary one that regulates routine flow in the waterway is the Low Sill Control Structure. The Overbank Structure is only used when the Mississippi exceeds its banks. The ORCAS is used during floods to assist the ORCS and prevent it from being damaged due to high flow rates. ORCAS was added to reduce pressure on the original floodgates after extensive damage caused by the flood of 1973. The northernmost and newest structure is the [[Sidney A. Murray Jr. Hydroelectric Station]], completed in 1990. It provides an additional measure of control at the site.<ref name="AmericasWetlands"/> These four structures are located approximately where the Upper Old River used to be before Shreve's Cut.

A navigation channel and lock are also part of the facility design, but they are situated well south of the other structures on the Lower Old River at the Old River Lock. This makes the Lower Old River navigable, allowing ship and barge traffic between the Mississippi River and the Atchafalaya River/[[Red River of the South]].

All five structures in the complex carry [[Louisiana Highway 15]], starting at the power plant, then the Overbank Structure, then the Low Sill ORCS, followed by ORCAS, the island created between the rivers, and finally the Old River Lock.


== Operation ==
== 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.<ref>{{cite web |title=Mississippi River at Red River Landing (01120) |url=http://www2.mvr.usace.army.mil/WaterControl/stationinfo2.cfm?sid=01120&fid=BTRL1&dt=S |date=May 7, 2011 |publisher=United States Army Corps of Engineers |accessdate=May 10, 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20110927153416/http://www2.mvr.usace.army.mil/WaterControl/stationinfo2.cfm?sid=01120&fid=BTRL1&dt=S |archivedate=September 27, 2011 |df= }}</ref><ref>{{cite web |title=Daily State and Discharge Data - Water Control - New Orleans District |url=http://www.mvn.usace.army.mil/eng/edhd/dailystagedisplay.asp |publisher=U.S. Army Corps of Engineers |accessdate=May 10, 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20040514060639/http://www.mvn.usace.army.mil/eng/edhd/dailystagedisplay.asp |archivedate=May 14, 2004 |df= }}</ref> This flow split was not based on science, but rather was based on the approximate flow allocation between the two rivers that existed at the time of construction.<ref name="Piazza2014"/>
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.<ref>{{cite web |title=Mississippi River at Red River Landing (01120) |url=http://www2.mvr.usace.army.mil/WaterControl/stationinfo2.cfm?sid=01120&fid=BTRL1&dt=S |date=May 7, 2011 |publisher=United States Army Corps of Engineers |access-date=May 10, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110927153416/http://www2.mvr.usace.army.mil/WaterControl/stationinfo2.cfm?sid=01120&fid=BTRL1&dt=S |archive-date=September 27, 2011 }}</ref><ref>{{cite web |title=Daily State and Discharge Data - Water Control - New Orleans District |url=http://www.mvn.usace.army.mil/eng/edhd/dailystagedisplay.asp |publisher=U.S. Army Corps of Engineers |access-date=May 10, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20040514060639/http://www.mvn.usace.army.mil/eng/edhd/dailystagedisplay.asp |archive-date=May 14, 2004 }}</ref> This flow split was not based on science, but rather was based on the approximate flow allocation between the two rivers that existed at the time of construction.<ref name="Piazza2014"/>


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).
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.<ref>{{cite news |url=http://www.nola.com/environment/index.ssf/2011/05/morganza_floodway_opens_to_div.html |title=Morganza Floodway opens to divert Mississippi River away from Baton Rouge, New Orleans |newspaper=NOLA.com |first=Paul |last=Rioux |date=May 14, 2011}}</ref> The Morganza Floodway was never used before the construction of Old River Control Structure, and as of 2016 has been opened only twice <ref>{{cite web|url=http://www.nola.com/weather/index.ssf/2016/01/morganza_floodway_will_not_be.html|title=Morganza Floodway will not be opened, Corps of Engineers decides|publisher=}}</ref> for flood control since completion of the Old River Control Structure.
The [[Morganza Floodway]], between the Mississippi and the Atchafalaya Basin nearby downstream, is normally closed. It 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.<ref>{{cite news |url=http://www.nola.com/environment/index.ssf/2011/05/morganza_floodway_opens_to_div.html |title=Morganza Floodway opens to divert Mississippi River away from Baton Rouge, New Orleans |newspaper=NOLA.com |first=Paul |last=Rioux |date=May 14, 2011}}</ref> The Morganza Floodway was never used before the construction of Old River Control Structure, and as of 2016 has been opened only twice<ref>{{cite web|url=http://www.nola.com/weather/index.ssf/2016/01/morganza_floodway_will_not_be.html|title=Morganza Floodway will not be opened, Corps of Engineers decides|date=27 September 2023 }}</ref> for flood control since completion of the Old River Control Structure.


== See also ==
== See also ==
Line 38: Line 47:
== External sources ==
== External sources ==
{{Commons category}}
{{Commons category}}
*{{cite web |url=http://www.johnweeks.com/river_mississippi/pages/lmiss23.html |title=Old River Control Structure |last=Weeks |first=John |accessdate=2014-09-20 }}
*{{cite web |url=http://www.johnweeks.com/river_mississippi/pages/lmiss23.html |title=Old River Control Structure |last=Weeks |first=John |access-date=2014-09-20 }}


{{Coord|31.0768|-91.5979 |format=dms |region:US-LA_type:landmark |display=title}}
{{Coord|31.0768|-91.5979 |format=dms |region:US-LA_type:landmark |display=title}}


{{authority control}}
[[Category:Rivers of Louisiana]]

[[Category:Atchafalaya River]]
[[Category:Buildings and structures in Concordia Parish, Louisiana]]
[[Category:Buildings and structures in Concordia Parish, Louisiana]]
[[Category:Dikes in the United States]]
[[Category:Dikes in the United States]]

Latest revision as of 15:14, 28 August 2024

The Old River Control Structure complex. View is to the east-southeast, looking downriver on the Mississippi, with the three dams across channels leading to the Atchafalaya River to the right of the Mississippi. Concordia Parish, Louisiana is in the foreground, on the right, and Wilkinson County, Mississippi, is in the background, across the Mississippi on the left.
Old River low-sill control structure discharging water into the Atchafalaya, May 2011

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 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, a former channel of the Mississippi.[1][2][3][4][5]

The Old River Control Structure is a complex containing the original low-sill[6] and overbank[7] structures, as well as the auxiliary structure that was constructed after the low-sill structure was damaged during the Mississippi River Flood of 1973. The complex also contains a navigation lock and the Sidney A. Murray Jr. Hydroelectric Station.[8]

Old River

[edit]
Formation of the Atchafalaya River and construction of the Old River Control Structure.

Before the 15th century, the Red River and Mississippi River were entirely separate and flowed more or less parallel to one another.[3] Beginning in the 15th century, the Mississippi River created a small, westward, oxbow loop, later called Turnbull's Bend, near present-day Angola, Louisiana. This loop eventually intersected the Red River, making the downstream part of the Red River a distributary of the Mississippi; this distributary came to be called the Atchafalaya River.[3]

In the heyday of steamboats along the Mississippi River, such a vessel would need several hours to travel the 20 miles (32 km) of Turnbull's Bend, after which it would have progressed only about 1 mile (1.6 km) from the entrance to the bend. To reduce travel time, Captain Henry M. Shreve, a river engineer and namesake of Shreveport, Louisiana, dug a canal in 1831 through the neck of Turnbull's Bend; this canal became known as Shreve's Cut. At the next high water, the Mississippi roared through this channel.[9] The upper portion of Turnbull's Bend was referred to as Upper Old River, while the larger, lower portion became known as the Lower Old River.

At first, the Lower Old River would flow eastward, to the Mississippi, until 1839, when locals began removing the Great Raft, a natural log jam that was obstructing the Atchafalaya River. The project was finished in 1840. After that, the Lower Old River would flow eastward to the Mississippi when the Red River was high and the Mississippi was low, and westward to the Atchafalaya when the Mississippi was high and the Red River was low. Over time, the number of days when the river flowed east to the Mississippi decreased and the number of days when the river flowed west increased, until eventually the Lower Old River flowed west over half the time. By 1880, it rarely flowed eastward and was rapidly capturing more and more of the flow of the Mississippi. With this increased water flow, the channel of the Atchafalaya River was worn deeper and wider throughout the 1800s and early 1900s.[9]

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, located five miles (8.0 km) 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.[3]

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 through the Atchafalaya River is much shorter and steeper.

The Corps completed construction on the Old River Control Structure in 1963 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.[3][10] Historically, this natural process of course change has occurred about every 1,000 years, and is overdue. Some researchers believe the likelihood of this event increases each year, despite manmade artificial control efforts.[11]

If the Mississippi diverts its main channel to the Atchafalaya Basin and the Atchafalaya River, it would develop a new delta south of Morgan City in southern Louisiana, greatly reducing water flow to its present channel through Baton Rouge and New Orleans, with adverse economic effects on both port cities.[4] The Mississippi flood of 1973 almost caused the control structure to fail. Maintenance of the integrity of the Old River Control Structure, the nearby Morganza Spillway, and other levees in the area is essential to prevent such a diversion. Jeff Masters of Weather Underground noted that failure of that complex "would be a serious blow to the U.S. economy."[12]

Components

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diagram of river flows during Project Design Flood
A diagram that depicts river flows associated with Project Design Flood.

The Old River Control Structure (ORCS) and Overbank Control Structure became operational in 1964 and expanded in 1986 with the addition of the Old River Control Auxiliary Structure (ORCAS). The primary one that regulates routine flow in the waterway is the Low Sill Control Structure. The Overbank Structure is only used when the Mississippi exceeds its banks. The ORCAS is used during floods to assist the ORCS and prevent it from being damaged due to high flow rates. ORCAS was added to reduce pressure on the original floodgates after extensive damage caused by the flood of 1973. The northernmost and newest structure is the Sidney A. Murray Jr. Hydroelectric Station, completed in 1990. It provides an additional measure of control at the site.[3] These four structures are located approximately where the Upper Old River used to be before Shreve's Cut.

A navigation channel and lock are also part of the facility design, but they are situated well south of the other structures on the Lower Old River at the Old River Lock. This makes the Lower Old River navigable, allowing ship and barge traffic between the Mississippi River and the Atchafalaya River/Red River of the South.

All five structures in the complex carry Louisiana Highway 15, starting at the power plant, then the Overbank Structure, then the Low Sill ORCS, followed by ORCAS, the island created between the rivers, and finally the Old River Lock.

Operation

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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.[13][14] This flow split was not based on science, but rather was based on the approximate flow allocation between the two rivers that existed at the time of construction.[8]

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. It 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.[15] The Morganza Floodway was never used before the construction of Old River Control Structure, and as of 2016 has been opened only twice[16] for flood control since completion of the Old River Control Structure.

See also

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References

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  1. ^ McPhee, John (February 23, 1987). "The Control of Nature: Atchafalaya". The New Yorker. Retrieved May 12, 2011. Republished in McPhee, John (1989). The Control of Nature. Farrar, Straus and Giroux. ISBN 978-0-374-12890-6.
  2. ^ Angert, Joe and Isaac. "Old River Control". The Mighty Mississippi River. Archived from the original on May 15, 2009. Retrieved 2011-05-12.. Includes map and pictures.
  3. ^ a b c d e f "Louisiana Old River Control Structure and Mississippi river flood protection". America's Wetland Resource Center. Loyola University's Center for Environmental Communication. Archived from the original on 2016-03-10. Retrieved 2007-04-01.
  4. ^ a b "Will the Mississippi River change its course in 2011 to the red line?". Mappingsupport. Retrieved May 8, 2011.
  5. ^ Kemp, Katherine (January 6, 2000). "The Mississippi Levee System and the Old River Control Structure".
  6. ^ "Low Sill Structure".
  7. ^ "Old River Control Structure, Point Breeze, LA". www.johnweeks.com.
  8. ^ a b Piazza, Bryan P. (2014). The Atchafalaya River Basin: History and Ecology of an American Wetland. Texas A&M University Press. ISBN 978-1-62349-039-3.
  9. ^ a b "$500 Million (and Rising) to Contain a River". The New York Times. Associated Press. May 3, 1987.
  10. ^ "Mississippi Rising: Apocalypse Now?". Daily Impact. April 28, 2011. Retrieved May 10, 2011.
  11. ^ Daniels, Ronald Joel (2006). On Risk and Disaster: Lessons from Hurricane Katrina. University of Pennsylvania Press. p. 45.
  12. ^ Masters, Jeff (May 9, 2011). "Mississippi River sets all-time flood records; 2nd major spillway opens". Weather Underground. Retrieved November 11, 2017.
  13. ^ "Mississippi River at Red River Landing (01120)". United States Army Corps of Engineers. May 7, 2011. Archived from the original on September 27, 2011. Retrieved May 10, 2011.
  14. ^ "Daily State and Discharge Data - Water Control - New Orleans District". U.S. Army Corps of Engineers. Archived from the original on May 14, 2004. Retrieved May 10, 2011.
  15. ^ Rioux, Paul (May 14, 2011). "Morganza Floodway opens to divert Mississippi River away from Baton Rouge, New Orleans". NOLA.com.
  16. ^ "Morganza Floodway will not be opened, Corps of Engineers decides". 27 September 2023.

External sources

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Wikimedia Commons has media related to Old River Control Structure.

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