Three Rivers Confluence

The three rivers confluence is where the Red River, Old River and the Atchafalaya River meet and combine the distributary outflow of the Mississippi River with the Atchafalaya Basin. This complex intersection is the origin of the Atchafalaya River Basin.

The connection between the Mississippi, Red and Atchafalaya rivers began long ago when the Red started flowing toward a large meander of the Mississippi. This meander (later called Turnbull’s Bend) intercepted the Red River, turning it into a tributary. The Atchafalaya River also eventually connected with the meander, becoming a distributary. In the mid-1800s, construction of a cut through the narrow neck of Turnbull’s Bend made navigation on the Mississippi more efficient. While the upper channel of Turnbull’s Bend gradually silted in and separated from the Mississippi, the lower channel, Old River, became an important connection between the three rivers.

After extensive logjams in the Red and Atchafalaya rivers were removed in the 1840s, the Mississippi started showing signs of switching course by sending increasing amounts of water to the Atchafalaya via Old River. Water naturally wants to flow in this direction because the Atchafalaya River is a shorter route to the Gulf of Mexico and its elevation is lower (the Atchafalaya at Old River is 7.9 feet above sea level while the Mississippi is 17.1 feet above sea level). In the early 1950s it became clear that, without more human intervention, the Mississippi would eventually change course to the Atchafalaya. To prevent this from happening and address flooding issues, multiple structures and floodways were built over several decades to create the complex controls that define this area today.

When completed in 1963, the Old River Control Complex contained a Low Sill Structure designed to regulate normal flow and an Overbank Structure used only when the Mississippi exceeds its banks. During the Mississippi River Flood of 1973, the Low Sill Structure was almost destroyed as the river threatened to dig it out of the ground, so the Morganza Floodway was operated to relieve pressure. An Auxiliary Structure was competed in 1986 to provide additional emergency capacity during excessive spring floods.

The other elements of the Old River Control Complex are the privately funded Sidney Murray Jr. Hydroelectric Plant at the north end and the Old River Lock and Dam at the south end. By 1990, all five structures were completed and operational. Today, the outflow at the control structure is limited by law to 30 percent of the volume of the Mississippi River.

Visitors to this region can explore the Richard K. Yancey Wildlife Management Area, located north of Lower Old River (between the Mississippi and Red rivers). Popular activities in the area include hunting, sport and commercial fishing, crawfishing and frogging.

Visit Atchafalaya.org for more information about this site.

This site’s geology/geomorphology: Holocene meander-belt (point bar and overbank) deposits of the Mississippi River.