Old River: The General Problem

The Atchafalaya River, which is joined to the Mississippi River by the-Old River, is the farthest upstream distributary of the Mississippi River. It provides a route to the sea that is only one-half as long as the Mississippi River's present course past Baton Rouge, La., and New Orleans, La. In recent years the Atchafalaya River has diverted increasingly larger percentages of Mississippi River flow, and in 1956 approximately 23.5% of the latter was diverted. Studies, which have been conducted by the Mississippi River Commission, Corps of Engineers (United States Department of the Army), in recent years, and observations that have been made on these streams since 1885 lead to the conclusion that the diversion of flow through the Old River and the Atchafalaya River approaches and will reach the “critical” stage (approximately 40% of the major river's flow), at which time the course of the parent stream will be uncertain. Additional exhaustive studies of past major diversions show that the present development is similar to those leading to earlier diversions, and the studies support the conclusion that diversion through the Atchafalaya River will reach the critical stage by 1975 unless preventive measures are used.

Should this diversion occur, it would be necessary to discard the present flood-control plan in the lower reaches of the Mississippi River and in the Atchafalaya River Basin; navigation would be seriously disrupted; utilities would be relocated; fresh-water supplies for New Orleans would be seriously affected; and the impact on the economy of the region would be disastrous. In order to prevent diversion, the Mississippi River Commission has recommended the construction of two control structures on the west bank of the Mississippi River approximately ten miles upstream from the Old River; a navigation lock connecting the Mississippi River and the Old River; an earth-fill dam in the Old River; approach channels for the lock; inlet and outlet channels for the control structures; and an enlargement and extension of the main-line Mississippi River levee at that site.