Levees: The Double-edged Sword
It has long been recognized that flood protection provided by levees is a double-edged sword. On one hand, flood protection has been afforded by levee systems. On the other hand, given enough time levees either will be overtopped or will fail—leading to severe flood impacts on an unsuspecting population. Unlike a natural flood, levee failure flooding is often rapid, forceful, extremely damaging, and occurs with little or no warning.
New Orleans is only one example of a community that has felt both edges of the “sword.” Many floods were repelled by the levees around the city over the years, but catastrophic flood damage occurred in 2005 as a result of levee failures and overtopping. Subsequent efforts to properly reflect the location of and true protection provided by levees on flood maps in the nation has heightened the awareness of policy makers and citizens about the enormous risk the nation faces in levee-protected areas. An additional concern is that levees are often placed so that they excessively encroach on river systems. This creates adverse impacts both on flood frequency and severity as well as on the natural functions of the river system.
Because of the nature of levee failure flooding, the ASFPM believes that levees are not a wise community choice and should never be used to protect undeveloped land so development can occur in the flood risk area behind the levee. However, many levees already exist in the nation, especially in communities that were built right on the river or coast, usually at a time when the nation was convinced it could engineer its way out of flooding. Where levees already exist, or where a levee appears to be the best option after careful analysis of all mitigation options to reduce the incidence of flooding to existing development, the ASFPM advocates that levees (1) must be designed to a high standard; (2) must be frequently and adequately inspected, with all needed maintenance funded and performed, or else treated as nonexistent; (3) should be used only as a method of last resort for providing a LIMITED means of flood risk reduction for existing development; and (4) are inappropriate as a means of protecting undeveloped land for proposed development.
It is apparent that over time, the nation has gradually and imprudently modified its various policies that affect levees and levee failure. The outcome is an unacceptably high risk of catastrophic levee failure and the resultant damage and costs at numerous sites across the United States.
Correcting this problem will require an evaluation of
• The definition of a “levee”;
• Existing and future levee inventory;
• Levee design standards;
• Levee operation and maintenance, including inspection and certification;
• Managing for residual risk including (1) identification of all areas at risk of flooding from levee overtopping or failure and from internal drainage; (2) community and citizen emergency action plans (EAP) that address flood warning and response actions; (3) flood insurance, floodplain management measures, and effective risk communication about the residual risk areas for which levees provide “some level of protection”; and
• Mitigating for adverse flooding impacts of levees on others.