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Time lapsed animation of basin from 1956 to 1993.

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 Atchafalaya is unique among basins because it has a growing delta system (see illustration) with nearly stable wetlands.[1]

Contents

Geographical features

A swamp in the Atchafalaya Basin

The Atchafalaya Basin, the surrounding plain of the river, is filled with bayous, bald cypress swamps, and marshes that give way to more brackish conditions and end in the Spartina grass marshes, near and at where it meets the Gulf of Mexico. It includes the Lower Atchafalaya River, Wax Lake Outlet, Atchafalaya Bay, and the Atchafalaya River and Bayous Chene, Boeuf, and Black navigation channel. See maps and photo views of the Atchafalaya Deltas centered on 29°26′30″N 91°25′00″W / 29.44167°N 91.4166667°W / 29.44167; -91.4166667.

The basin, which is susceptible to heavy 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.[2] With 595,000 acres (2,410 km2), it is the nation’s largest swamp wilderness, containing nationally significant expanses of bottomland hardwoods, swamplands, bayous and back-water lakes.[3]

The few roads that cross it follow the tops of levees. Interstate 10, which crosses the basin on elevated pillars from Maringouin, Louisiana to Henderson, Louisiana, is a continuous 18.2 mile (29,290 m) bridge. Maps and views of this crossing near at the Whiskey River Pilot Channel at 30°21′50″N 91°38′00″W / 30.36389°N 91.6333333°W / 30.36389; -91.6333333

The Atchafalaya National Wildlife Refuge was established in 1984 to improve plant communities for endangered and declining species of wildlife, waterfowl and migratory birds.[4]

Basin geology

Geologically, the Atchafalaya has served periodically as the main channel of the Mississippi River 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.

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Degradation of the buffer marshes

Aerial view of the Big Island Mining Project restoration site on Atchafalaya Bay.
View of the south side of the I-10 bridge crossing the basin.

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 29 square miles (75 square kilometers) of land is lost to the sea each year.[5]

The decreasing of the siltation rates and a decrease in water movement has been caused due to damming of the bayous, and the laying of sluices by the US Army Corps of Engineers. Also, the placing of a levee along the Atchafalaya Basin has contributed to cutting off the swamp from the river (thus halting it to function as a buffer). This decreasing has caused reduced aeration of the water, causing it to change color. Where the water used to be brown, it is now black. [6]

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.[7]

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.[8]

See also

Footnotes

External links


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