Water Always Wins

Building a levee on one bank pushes high waters onto the opposite bank, launching an engineering arms race. People on the other side build levees too, and the water, confined to an unnaturally narrow channel, unable to spread and slow upon its floodplains and wetlands, rises up and flows faster. The longer the length of levees, the greater the constriction, the higher and faster the water, the worse the flooding becomes downstream and at every place where a levee breaks. A narrowed river can even cause flooding upstream by creating a bottleneck. The US General Accounting Office acknowledged these hydrological truths with regard to both the Missouri and Mississippi Rivers in 1995: “That levees increase flood levels is subject to little disagreement.” Studies noted that flood levels near St. Louis had increased up to thirteen feet over the twentieth century. Unfortunately, these effects are generally recognized only in hindsight because proposed levees are evaluated individually without considering the cumulative effects of many projects along the length of a river.