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The Atchafalaya Basin is a large marsh in Louisiana, managed as a National Heritage Area and important flood control area for South Louisiana. It has diverse wildlife and is home to valley floor hardwood forest, cypress swamp, and coastal marsh grasslands. The Morganza Canal diverts additional flow from the Mississippi to the Atchafalaya to prevent flooding further south.
The Atchafalaya Basin is a 595,000-acre (240,788 ha) marsh located along the Atchafalaya River in the US state of Louisiana. It is the largest basin swamp in North America. Atchafalaya, pronounced ah-CHA-fa-LIE-ah, is a Choctaw word translated as “long river”. The Atchafalaya Basin is an important flood control area for South Louisiana and the city of New Orleans and is also home to a diverse array of wildlife. At the same time, it is managed as a National Heritage Area and has several towns within its borders.
In the mid-20th century the Atchafalaya Basin was developed as an important flood diversion area for the Mississippi River north of New Orleans. The Atchafalaya River leaves the Mississippi near Simmesport, Louisiana, carrying 30 to 50 percent of the total water present at the split. From there it travels 130 miles (about 209 km) south to the Gulf of Mexico. In the 1950s, retaining levees were built parallel to the river on both sides. The levees, which are a minimum of 15 miles (about 24 km) down the course of the river, are the boundaries of the Atchafalaya Basin.
Water levels in the reservoir vary up to 15 feet (about 4.5m) in a normal year due to the varying volume of water carried by the Atchafalaya River. The central channel of the river, which runs through the heart of the reservoir, can have waves up to 3 feet (about 1 m) high if there is enough wind. All of the smaller streams in the Atchafalaya Basin are bayous, meaning that the water flow changes direction depending on rainfall and the current height of the river itself.
Spanning the northern portion of the Atchafalaya Basin is the largest remaining reserve of valley floor hardwood forest in the United States. Across the center of the basin is a swath of cypress swamp. Along the Gulf Coast, there are coastal marsh grasslands.
The Morganza Canal is the primary flow control structure for the Atchafalaya Basin. It is designed to divert additional flow from the Mississippi into the Atchafalaya, causing the Atchafalaya to flood into the basin. This spares levees and communities further south on the Mississippi. Army Engineers, who operate the spillway, consider opening it whenever flow in the Mississippi reaches record highs, but it has only been used twice. In 1973 it was partially opened and in May of 2011 a record flood forced the Corps to use the entire spillway for the first time.
