David Kurtz May 13, 2011, 10:54 AM

The 1927 flood is the standard against which all Mississippi River floods, including this year’s, are measured:

The ‘27 flood had enormous often forgotten historical impacts. The secretary of commerce at the time, whose oversight of the flood relief efforts brought him to national prominence, was Herbert Hoover, who went on to win election as President the following year. The flood also set the stage for Huey Long’s election as governor of Louisiana in 1928.

If you’re interested in this period — and the country’s long effort to try to control and harness the river — I highly recommend John Barry’s chronicle of the disaster, Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America.

This weekend the Army Corps of Engineers is set to open to the Morganza Spillway in Louisiana to divert an enormous amount of the river’s floodwaters into the Atchafalaya River basin and save points downriver, including New Orleans.

This will be only the second time the Morganza Spillway has been opened since it was built in the 1950s (construction began two decades earlier after the 1927 flood). The last time was in 1973, when it was used in a desperate and ultimately successful attempt to prevent the Mississippi River from changing course entirely, as it does every millennia or so. Were it not for man’s intervention, the river would have bypassed Baton Rouge and New Orleans by now, taking the steeper, more direct route to the Gulf of Mexico offered by the Atchafalaya River, itself a former main channel of the Mississippi River before the ancient river jumped its banks.

John McPhee devotes an entire section of his splendid book The Control of Nature to the ancient and manmade hydrological forces at work in the Mississippi River delta and the Atchafalaya Basin.

The Atchafalaya River, a distributary of the Mississippi, under normal conditions siphons off about one-third of the volume of the Mississippi and carries it to the Gulf. Opening the Morganza Spillway will flood hundreds of thousands of acres of mostly swamp. But the Atchafalaya Basin also contains farms and small towns, including Morgan City at the mouth of Atchafalaya which is protected by a huge floodwall that may not be up this task.

When I was growing up in Louisiana, there were two natural disasters that you knew were not a matter of if, but when: a direct strike on New Orleans by a major hurricane and a Mississippi River flood that overwhelmed the modern flood control system. Hurricane Katrina contained elements of both disasters: the city survived the direct strike but its shoddy levees were overwhelmed. This may not be the year the Mississippi River gets the upper hand on the Army Corps of Engineers. But it will happen eventually. It’s just a matter of time.