"The images are all too familiar: overtopped levees, homes submerged in floodwaters, rescuers motoring down city streets in fishing boats. This summer, before the muck had even been cleared from neighborhoods in the heart of the Midwest, the question resurfaced: What happened? Three years after Hurricane Katrina, and 15 years after disastrous flooding throughout the Midwest, how could the country allow rising waters to kill at least 24 people and cause billions in damage to structures and crops? And the Mississippi Basin isn't the only region at risk. Aging flood walls protect areas from California's Sacramento–San Joaquin River Delta to the shores of Florida's Lake Okeechobee, threatening future devastation. For many, the answer seems clear. Raise levees high enough to ensure that no flood ever wreaks havoc again.
Unfortunately, it's not so simple. For one thing, it's unclear just how high levees should be built. "In Cedar Rapids [Iowa], nobody would have dreamed the river could get that high," says Jeffrey Schott, an instructor of urban and regional planning at the University of Iowa in Iowa City, where 21 buildings were flooded. The flood walls in Cedar Rapids, which had been built to a so-called 100-year standard, were overwhelmed by water that rose to a 500-year level. (The language is misleading: The next "500-year flood" could come next spring.)
'After '93, we could have built the levees in the Midwest 10 ft. higher, for example,' says Robert Holmes, national flood specialist for the United States Geological Survey. 'But the cost far exceeds the benefit.'"