The result of all this human activity, a slew of studies suggest, is bigger and more destructive floods. At Davenport, Iowa, the Mississippi exceeded flood levels five times in the first half of the 20th century, and 24 times in the second half. But an amazing thing happened after the Mississippi flood of 1993. They began to create a demilitarized zone in the 150-year war with the Mississippi. It's like moving in the sides of a bathtub.
Levees lock the river into a narrower channel - so the water has nowhere to go but up.
After the flood, the Army Corps did design a few outlets to give the river and its tributaries some room to ramble during floods. The plan called for the Mississippi to enter the floodway at Birds Point, where the Corps would dynamite a hole in the levee during high water, and return to its channel 60 miles away in New Madrid, where the Corps left a 1,500-foot gap in the levee. In 1937, the plan was executed for the first and only time, providing a desperately needed release valve. But the main goal of the Corps was always to control the river, not to accommodate it. The military leaders of the Corps have tended to see fancy engineering as the answer to nearly everything, and Congress has tended to pass pork-barrel projects that have allowed the Corps to indulge its penchant for moving dirt and pouring concrete.