The Economics and Politics of “Green” Flood Control: A Historical Examination of Natural Valley Storage Protection by the Corps of Engineers

Between 1972 and 1994, the New England Division of the US Army Corps of Engineers undertook five studies evaluating the benefits and costs of protecting natural valley storage (NVS) areas as a flood mitigation strategy in various watersheds. NVS lands function as natural reservoirs, temporarily storing floodwaters. In only one case—along the Charles River in Massachusetts—were the benefits found to outweigh the costs. Along the Charles, the Corps acquired approximately 8,500 acres of floodplain land to keep as open space in perpetuity. This paper reviews the five studies in detail to inform ongoing interest in green approaches to flood control. The analysis finds that large-scale land acquisition to contain major riverine flood events is difficult to justify by avoided flood damages alone. For such a project to generate net benefits, there must be significant amounts of NVS lands still undeveloped, substantial development pressure on those lands, and downstream areas that would sustain high levels of damage in the event of a flood. Perhaps more importantly, however, these studies raise two fundamental institutional questions: (1) Should the Corps, or the federal government more broadly, be involved in land acquisition? (2) Should regulating land use be preferred over purchasing NVS land? The economic and political issues uncovered in the historic examination of these five studies suggest an explanation for the current focus on other approaches to green flood control, such as multipurpose projects, levee setbacks, and green infrastructure to manage stormwater.