The Atchafalaya River is a distributary of the Mississippi and Red rivers, approximately 170 mi (270 km) long, in south central Louisiana in the United States. It is navigable and provides a significant industrial shipping channel for the state of Louisiana, as well as the cultural heart of the Cajun Country. The maintenance of the river as a navigable channel of the Mississippi has been a significant project of the U.S. Army Corps of Engineers for over a century. The river is known locally as the "Tchafalya".

It is formed near Simmesport at the confluence of the Red River with the Mississippi, where the Mississippi connects to the Red by the 7 mi (11 km) canalized Old River . It receives the water of the Red as well as part of the water of the Mississippi, which itself continues in its main channel to the southeast. It meanders south as a channel of the Mississippi, through extensive levees and floodways, past Morgan City, and empties into the Gulf of Mexico in Atchafalaya Bay approximately 15 mi (25 km) south of Morgan City.

The Atchafalaya Basin, the surrounding plain of the river, is filled in bayous, baldcypress swamps, and marshes, that give way to more brackish conditions and end in the Spartina grass marshes. The basin is susceptible to heavy flooding and is sparsely inhabited. The few roads that cross it follow the tops of levees. Interstate 10, which crosses the Basin on elevated pillars south of Baton Rouge, is essentially a continuous bridge.

Geologically, the Atchafalaya has served periodically as the main channel of the Mississippi through the process of delta switching, which has built the extensive delta plain of the river. Since the early 20th century, because of manmade alterations in the channel, the Mississippi has sought to change its main channel to Atchafalaya. By law a regulated proportion of the water from the Mississippi is diverted into the Atchafalaya at the Old River Control Structure .

Degradation of the buffer marshes

The control of the river's floods, along with those of the Mississippi, has become a controversial issue in recent decades. It is now widely suspected that the channeling of the river and subsequent lowering of siltation rates has resulted in severe degradation of the surrounding saltmarsh wetlands as well as widespread submerging of populated and agricultural lands of the bayou country. The US Geological Survey (USGS) reports that over 75 kilometers are lost to the sea each year (see link). The coastal salt marshes form a buffer zone protecting the entire coast of Louisiana from the effects of hurricanes in the Gulf of Mexico and dissipating their accompanying storm surges. The marshes depend on replenishment from deposited silt, which is now being deposited over the edge of the continental shelf, due to the artificially canalized flow of the Mississippi. From the 1950s through 1970s, the oil industry dredged deep channels into the marsh so that they could move barges in as work platforms. The edges continued to degrade, until wide shallow channels in the saltmarsh have resulted.

The disappearance of the delta country is considered by many environmentalists, as well as by the State of Louisiana, to be one of the most significant ecological threats in the United States. The loss of the delta lands was discussed by author Mike Tidwell in his 2003 book Bayou Farewell: The Rich Life and Tragic Death of Louisiana's Cajun Coast.

See also

• List of Louisiana rivers

Mississippi delta

External links

• The Atchafalaya Trace Heritage Area
• National Weather Service: Atchafalaya Basin
• Atchafalaya River Coalition: industry coalition seeking to maintain open channel
• U.S. Army Corps of Engineers
• USGS Infobank: Atchafalya River
• Delta Switching: Early Responses to Atchafalya Diversion
• Bayou Farewell: The Rich Life and Tragic Death of Louisiana's Cajun Coast
• USGS Fact Sheet: Louisiana Coastal Wetlands: A Resource At Risk
• B. E. Fleury, "The Louisiana Environment: The Salt Marsh"
• Loss of wetlands from the perspective of Wildfowl Magazine