The Army Corps of Engineers is expected to open the Morganza spillway on Saturday, sending a torrent of water into the Atchafalaya River basin but taking the pressure off levees that protect populous Baton Rouge and New Orleans and oil refineries and industries.Maj. Gen. Michael Walsh, president of the Mississippi River Commission, issued the order to open the spillway when river flow reaches 1.5 million cubic feet per second. That mark was expected Saturday.

Flooding is expected to affect thousands of homes as the Atchafalaya River swells.

But the process will be a slow one; the Mississippi's waters first have to flow 20 miles before entering the Atchafalaya. It will be several days before the high water reaches Morgan City in coastal St. Mary Parish.