Rivers will do what rivers do. Historic flooding of the Mississippi River shows that our approach to flood control hasn’t worked and can have effects far beyond the limited area of a floodplain. The consensus of scientists around the world is that we are in a period of rapid global climate change, which makes working with rivers–instead of against them–increasingly important. Some places will get more intense rainstorms, while others may get less frequent summer rains. Still other areas may get winter storms with less snow and more rain, producing immediate runoff instead of storing water for spring. These and other changes may increase flooding, and, in some cases, may also increase drought.
In many cases, flood management practices are based on dam or levee projects that do not incorporate all we now understand about river processes. They try to control the river. Many years of experience with dam and levee systems have shown their limitations. Though dams and levees may be necessary in some cases, more often a larger suite of tools is available. We suggest instead that a better solution is to work with the natural tendencies of the river: retreat from the floodplain by preventing future development and sometimes even removing existing structures; accommodate the effects of floodwaters with building practices; and protect assets with nonstructural measures if possible, and large structural projects only if absolutely necessary.
To help decide on the best (cheapest, longest lasting, most beneficial, and so on) project choice to control destructive floods or enhance our water resources, we should answer six questions:
1. What values or assets do you want to protect or enhance?
2. What are the apparent risks or opportunities for enhancement?
3. What is the range of risk-reduction or opportunity-enhancement strategies available?
4. How well does each strategy reduce the risk or enhance the resource?
5. What other risks or benefits does each strategy introduce?
6. Are the costs imposed by each strategy too high?
Only after answering all six questions will we find the optimal strategy.
