What is the Old River Control Structure designed to prevent?

The Old River Control Structure is designed to prevent the Mississippi River from permanently diverting its flow into the Atchafalaya River.1

Without this system of locks and barrages, the Mississippi would likely capture the Atchafalaya as its primary channel, which would bypass New Orleans, inundate the lower Atchafalaya basin, and render millions of dollars of existing flood-control works and port facilities useless. By maintaining the current distribution of water, the structure ensures the stability of the lower river's path and protects the economic and infrastructure investments along its traditional course.12