Environment. One step forward, two steps back on U.S. floodplains.

T he great Midwestern flood of 1993 broke flow records along 1600 km of the Mississippi and Missouri rivers and caused up to $16 billion in damages (1, 2). Formal reviews of U.S. flood-control policy, both before and after the 1993 flood, concluded that the optimum strategy for reducing flood losses is to limit or even reduce infrastructure on floodplains. New emphases on flood-damage prevention included widely publicized Federal Emergency Management Agency (FEMA) buyouts of floodplain properties. In Illinois and Missouri, the two most heavily impacted states, 7700 properties were acquired at a cost of $56.3 million, including the relocation of the town of Valmeyer, Illinois (3). Unfortunately, these buyouts are now being massively counterbalanced by new construction on the floodplains. The center of this recent rush onto the flood-plain is the St. Louis metropolitan region (see figure, right). This paper explores the impacts of such encroachment, including raising future flood levels, and outlines alternatives that have been proposed and implemented worldwide. It has been asserted that flood-control structures prevented $19 billion in damages during the 1993 flood; however, most infrastructure on the floodplain would not be there were it not for the historic reliance on levees [e.g. (4–7)]. Since 1993, the amount of such infrastructure has increased dramatically: 28,000 new homes were built, population increased 23%, and 26.8 km 2 (6630 acres) of commercial and industrial development were added on land that was inundated during the 1993 flood (8). In all, $2.2 billion in new development has occurred in the St. Louis area alone on land that was under water in 1993 (3). The majority of this floodplain development has occurred in the state of Missouri, and around St. Louis in particular. Of the total new commercial and industrial development in the 1993 inundation area, 76% was located in Missouri, and 60% in St. Louis and St. Charles counties alone (8). Since 1993, projects now complete, under way, and in planning have put or will put 72.8 km 2 (18,000 acres) of the Mississippi and Missouri floodplains near St. Louis behind new levees, enlarged enlarged lev-ees, or floodplain land raised above the 100-year to 500-year protection level (see figure, above). Most of these projects have been financed or heavily subsidized by local governments in each area. The U.S. Army Corps of Engineers also has spent $197 million working on nine local levees in its St. Louis District since 1993 …