The Three Rivers Confluence is where the Red River, Old River, and the Atchafalaya River meet, combining the distributary outflow of the Mississippi River with the Atchafalaya Basin and forming the origin of the Atchafalaya River Basin. This connection developed when the Red River began flowing toward a large Mississippi meander later called Turnbull’s Bend, which intercepted the Red and turned it into a tributary, while the Atchafalaya River also eventually connected with the meander and became a distributary. In the mid-1800s, a cut through the narrow neck of Turnbull’s Bend improved navigation on the Mississippi; as the upper channel gradually silted in and separated from the Mississippi, the lower channel, Old River, became an important link between the three rivers. After extensive logjams in the Red and Atchafalaya rivers were removed in the 1840s, the Mississippi showed signs of changing course by sending increasing amounts of water to the Atchafalaya through Old River, a direction favored by the Atchafalaya’s shorter route to the Gulf of Mexico and lower elevation. By the early 1950s, it had become clear that without further human intervention the Mississippi would eventually shift course to the Atchafalaya, so multiple structures and floodways were built over several decades to prevent that change and address flooding. Completed in 1963, the Old River Control Complex included a Low Sill Structure to regulate normal flow and an Overbank Structure for times when the Mississippi exceeded its banks; during the Mississippi River Flood of 1973, the Low Sill Structure was nearly destroyed, and the Morganza Floodway was operated to relieve pressure. An Auxiliary Structure was completed in 1986 to add emergency capacity during excessive spring floods, and by 1990 all five structures of the Old River Control Complex, including the Sidney Murray Jr. Hydroelectric Plant and the Old River Lock and Dam, were completed and operational. Today, by law, outflow at the control structure is limited to 30 percent of the volume of the Mississippi River.
