 The book begins by describing how the Atchafalaya River drains 30 percent of the Mississippi River at its source 300 miles upriver from New Orleans.Thanks to its steeper gradient and more direct route, the Atchafalaya seeks to change the course of the Mississippi as has happened in its long geological history.Due to the Mississippi's vital importance to industry, the Army Corps of Engineers constructed a control structure at the Atchafalaya's source to prevent this from occurring and to maintain the 30 percent drainage.