If recent events in Japan were not enough, the news of the past week has reminded us that nature can make our efforts to control it seem like nothing more than hubris. A historic swath of tornadoes has ripped across the South, and now a potentially major Mississippi River flood is gathering. The tornadoes have done their damage already. The rising waters of the Mississippi are about to test human judgment and engineering anew.

As of Friday, Maj. Gen. Michael Walsh of the U.S. Army Corps of Engineers...