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Atchafalaya Basin
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Atchafalaya Basin
The Atchafalaya Basin, or Atchafalaya Swamp (/əˌtʃæfəˈlaɪə/; Louisiana French: Atchafalaya, [atʃafalaˈja]), is the largest swampy wetland 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 through parts of eight parishes to Morgan City in the south.
The Atchafalaya is different among Louisiana basins because it has a growing delta system (see illustration) with wetlands that are almost stable. The basin contains about 70% forest habitat and about 30% marsh and open water. It contains the largest contiguous block of forested wetlands remaining (about 35%) in the lower Mississippi River valley and the largest block of floodplain forest in the United States. Best known for its iconic cypress–tupelo swamps, at 260,000 acres (110,000 ha), this block of forest represents the largest remaining contiguous tract of coastal cypress in the United States.
The Atchafalaya Basin and the surrounding plain of the Atchafalaya River is filled with bayous, baldcypress swamps, and marshes, which give way to brackish estuarine conditions and end in the Spartina grass marshes where the Atchafalaya River meets the Gulf of Mexico. It includes the Lower Atchafalaya River, the Wax Lake outlet, Atchafalaya Bay, and the Atchafalaya River and bayous Chêne, Boeuf, and Black navigation channel.
The basin, which is susceptible to long periods of deep flooding, is sparsely inhabited. The basin is about 20 miles (32 km) in width from east to west and 150 miles (240 km) in length. The basin is the largest existing wetland in the United States with an area of 1,400,000 acres (5,700 km2), including the surrounding swamps outside of the levees that historically were connected to the basin. The basin contains nationally significant expanses of bottomland hardwoods, swamplands, bayous, and back-water lakes. The thousands of acres of forest and farmland are home to the Louisiana black bear (Ursus americanus luteolus), which has been on the United States Fish and Wildlife Service threatened list since 1992.
The few roads that cross the basin follow the tops of levees. Interstate 10 crosses on elevated pillars on the continuous 18.2-mile (29.3 km) Atchafalaya Basin Bridge from Grosse Tête to Henderson. The Atchafalaya National Wildlife Refuge was established in 1984 to improve plant communities for endangered and declining species of wildlife, waterfowl, migratory birds and alligators.
The basin has a long relationship with the Mississippi River throughout the Holocene epoch, and the geology of the modern basin is a direct manifestation of that relationship. The basin has been part of three historic depositional lobes (Sale-Cypremort, Teche, and Lafourche lobes) of the Mississippi River Delta that formed southern Louisiana, and active delta lobe development is currently occurring at the mouth of the Atchafalaya River and Wax Lake outlet. The geology of the current basin has been driven by flows of Atchafalaya River water and sediment that flowed into open water areas through relict Mississippi River distributary channels.
The basin contains lacustrine and coastal delta landscapes. Natural filling of the basin with sediment was accentuated with the building of the flood control levees that were completed in the 1940s. After the levees, sediment was directed into an area about one-third the size of the original basin. An example of the lacustrine delta development can be seen at Lake Fausse Pointe State Park, where levees severed the connection between the Grand Bayou distributary and the lake, and delta development was frozen in time.
Geologically, the Atchafalaya River has been a backswamp, low area between the paths of the Mississippi River through the process of delta switching, which has built the extensive delta plain of Louisiana. The natural levees of the Mississippi River (on the east) and the levees along its previous course (now Bayou Teche) on the west define the Atchafalaya Basin. The central basin is further bordered by man-made levees designed to contain and funnel floodwaters released from the Mississippi at the Old River Control Structure and the Morganza Spillway south toward Morgan City and eventually to the Gulf of Mexico. Historically there were small and few channel connections to the Mississippi River. The historic lack of significant channel connection indicates that the Atchafalaya Basin did not receive significant sediment from the Mississippi except during large floods.
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Atchafalaya Basin
The Atchafalaya Basin, or Atchafalaya Swamp (/əˌtʃæfəˈlaɪə/; Louisiana French: Atchafalaya, [atʃafalaˈja]), is the largest swampy wetland 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 through parts of eight parishes to Morgan City in the south.
The Atchafalaya is different among Louisiana basins because it has a growing delta system (see illustration) with wetlands that are almost stable. The basin contains about 70% forest habitat and about 30% marsh and open water. It contains the largest contiguous block of forested wetlands remaining (about 35%) in the lower Mississippi River valley and the largest block of floodplain forest in the United States. Best known for its iconic cypress–tupelo swamps, at 260,000 acres (110,000 ha), this block of forest represents the largest remaining contiguous tract of coastal cypress in the United States.
The Atchafalaya Basin and the surrounding plain of the Atchafalaya River is filled with bayous, baldcypress swamps, and marshes, which give way to brackish estuarine conditions and end in the Spartina grass marshes where the Atchafalaya River meets the Gulf of Mexico. It includes the Lower Atchafalaya River, the Wax Lake outlet, Atchafalaya Bay, and the Atchafalaya River and bayous Chêne, Boeuf, and Black navigation channel.
The basin, which is susceptible to long periods of deep flooding, is sparsely inhabited. The basin is about 20 miles (32 km) in width from east to west and 150 miles (240 km) in length. The basin is the largest existing wetland in the United States with an area of 1,400,000 acres (5,700 km2), including the surrounding swamps outside of the levees that historically were connected to the basin. The basin contains nationally significant expanses of bottomland hardwoods, swamplands, bayous, and back-water lakes. The thousands of acres of forest and farmland are home to the Louisiana black bear (Ursus americanus luteolus), which has been on the United States Fish and Wildlife Service threatened list since 1992.
The few roads that cross the basin follow the tops of levees. Interstate 10 crosses on elevated pillars on the continuous 18.2-mile (29.3 km) Atchafalaya Basin Bridge from Grosse Tête to Henderson. The Atchafalaya National Wildlife Refuge was established in 1984 to improve plant communities for endangered and declining species of wildlife, waterfowl, migratory birds and alligators.
The basin has a long relationship with the Mississippi River throughout the Holocene epoch, and the geology of the modern basin is a direct manifestation of that relationship. The basin has been part of three historic depositional lobes (Sale-Cypremort, Teche, and Lafourche lobes) of the Mississippi River Delta that formed southern Louisiana, and active delta lobe development is currently occurring at the mouth of the Atchafalaya River and Wax Lake outlet. The geology of the current basin has been driven by flows of Atchafalaya River water and sediment that flowed into open water areas through relict Mississippi River distributary channels.
The basin contains lacustrine and coastal delta landscapes. Natural filling of the basin with sediment was accentuated with the building of the flood control levees that were completed in the 1940s. After the levees, sediment was directed into an area about one-third the size of the original basin. An example of the lacustrine delta development can be seen at Lake Fausse Pointe State Park, where levees severed the connection between the Grand Bayou distributary and the lake, and delta development was frozen in time.
Geologically, the Atchafalaya River has been a backswamp, low area between the paths of the Mississippi River through the process of delta switching, which has built the extensive delta plain of Louisiana. The natural levees of the Mississippi River (on the east) and the levees along its previous course (now Bayou Teche) on the west define the Atchafalaya Basin. The central basin is further bordered by man-made levees designed to contain and funnel floodwaters released from the Mississippi at the Old River Control Structure and the Morganza Spillway south toward Morgan City and eventually to the Gulf of Mexico. Historically there were small and few channel connections to the Mississippi River. The historic lack of significant channel connection indicates that the Atchafalaya Basin did not receive significant sediment from the Mississippi except during large floods.
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