Growing Deltas in Atchafalaya Bay

The delta plain of the Mississippi River is disappearing. The lobe-shaped arc of coastal land from the Chandeleur Islands in eastern Louisiana to the Sabine River loses a football field’s worth of land every hour.
Put another way, the delta has shrunk by nearly 5,000 square kilometers (2,000 square miles) over the past 80 years. That’s as if most of Delaware had sunk into the sea. Though land losses are widely distributed across the 300 kilometer (200 mile) wide coastal plain of Louisiana, Atchafalaya Bay stands as a notable exception.

In a swampy area south of Morgan City, new land is forming at the mouths of the Wax Lake Outlet and the Atchafalaya River. Wax Lake Outlet is an artificial channel that diverts some of the river’s flow into the bay about 16 kilometers (10 miles) west of where the main river empties. Both deltas are being built by sediment carried by the Atchafalaya River.

The Atchafalaya is a distributary of the Mississippi River, connecting to the “Big Muddy” in south central Louisiana near Simmesport. Studies of the geologic history of the meandering Mississippi have shown thatif left to naturemost of the river’s water would eventually flow down the Atchafalaya. But the Old River Control Structure, built in the 1960s by the U.S. Army Corps of Engineers, ensures that only 30 percent of the Mississippi flows into the Atchafalaya River, while the rest of the keeps moving toward Baton Rouge and New Orleans.

Larger image Image Credit: NASA/Earth Observatory