A historical examination of the Corps of Engineers and natural valley storage protection: the economics and politics of ‘green’ flood control

Abstract

Between 1972 and 1994, the US Army Corps of Engineers undertook five studies in New England evaluating the benefits and costs of protecting natural valley storage (NVS) areas—natural reservoirs—for flood mitigation. Only along the Charles River did benefits outweigh costs. Analysis of the studies finds that the costs of large-scale land acquisition will often exceed the sole benefits of avoided flood damages. To generate net benefits, there must be significant amounts of NVS lands still undeveloped, development pressure on those lands, and downstream areas that would sustain large damages. The NVS studies also raised questions of whether the Corps should be involved in land acquisition, and whether regulating land use could substitute for purchasing land. Note, these findings do not apply to other forms of natural flood-risk reduction, such as levee setbacks, green infrastructure for stormwater management, and multi-purpose projects, which have different economic and institutional contexts.

Keywords:

• floodplain conservation
• flood mitigation
• Corps of Engineers
• natural valley storage
• benefit–cost analysis

Acknowledgement

I would like to thank, without implicating, Leonard Shabman and Margaret Walls for helpful discussions and comments on earlier drafts of this paper. I would like to thank the National Academies Keck Futures Initiative for funding this work.

Notes

1. In addition, interest has been growing in so-called green infrastructure, a term that largely refers to land use changes designed to increase infiltration of stormwater. This paper focuses on managing large riverine flood events, not managing stormwater, although there could be overlaps in the policies and approaches.

2. Personal communication with the chief of the Planning Branch of the New England Division of the Corps of Engineers indicates that no natural storage projects have been undertaken since the Charles River case. However, the Corps has used other nonstructural approaches to flood-risk reduction.

3. A report for the Charles River case highlighted three related, but slightly different, criteria for NVS preservation to be recommended as the preferred alternative: (1) extensive NVS still in existence, (2) currently only minor flood damage, and (3) an imminent threat to the loss of NVS (New England Division of the Corps of Engineers, 1976a).

4. Or for restoration projects, which would similarly be adding new protection.

5. Also of note, if a much lower discount rate had been used, this also would make the benefits greater than costs in the Spicket case, again highlighting the important role of the choice of a discount rate in long-lived projects.

6. The report presented details on the assumptions for each river reach.

7. For example, in 2013, FEMA issued mitigation policy FP-108-024-01, which allowed for inclusion of environmental benefits in benefit-cost analysis of property acquisition projects (buyouts).

8. An economic analysis of a greenway along a river in St. Louis County, Missouri found that avoided flood damages alone did not exceed the opportunity costs of land acquisition, but when other benefits were included, the total benefits exceeded costs (Kousky & Walls, 2014).

9. For more information on these projects see: http://www.countyofnapa.org/Pages/DepartmentContent.aspx?id=4294971816; http://www.truckeeflood.us/; and http://www.trinityrivercorridor.com/flood-control/dallas-floodway-project.html.