A year ago, much of America’s heartland was inundated by Missouri River flood waters. At least 1 million acres of U.S. farmland in nine major grain-producing states were under water. More than 14 million people were impacted. Damage exceeded $1 billion.

With 11 dams on the Missouri, why was the flooding so severe? Why didn’t the dams absorb the excess waters?

Its dams are above the flooded...