this principle in its report. Again, from the IPET report: “…No matter how well designed an HPS may be, some level of residual risk always remains: risk is never reduced to zero. Therefore, even with the construction and strengthening of the New Orleans HPS, some residual risk will always remain (IPET, 2008, VIII-12).
Similarly, in a 2006 report from the Interagency Levee Policy Review Committee, that group noted that, “Levees only reduce the risk to individuals and structures behind them; they do not eliminate the risk. In fact, in many cases, they can create significant and potentially catastrophic residual risk that may increase if conditions in the region change, if levees are affected by natural events, or if the levees are not properly maintained” (Interagency Levee Policy Review Committee, 2006; italics in original).
In 2007, the Association of State Floodplain Managers issued a position paper entitled “Levees: The Double-edged Sword” (ASFPM, 2007). This paper discusses many of the pros and cons of relying too heavily upon levees for flood protection. Several conclusions and recommendations from the ASFPM are relevant to hurricane protection in New Orleans and are consistent with this NAE/NRC committee’s views on lessons learned in the Hurricane Katrina experience. Key points from the ASFPM report thus are presented in Box 3-1.
Views from the Association of State Floodplain Managers on Flood Protection Provided by Levees
The Association of State Floodplain Managers (ASFPM) 2007 report, “Levees: The Double-edged Sword” is a thoughtful and succinct exposition of the pros and cons of relying on levees to provide flood protection. Many of the report’s recommendations overlap and are consistent with the lessons learned section in this NAE/NRC committee report. This box does not list all of the ASFMP report findings and recommendations; rather it presents those that are most relevant to this committee’s report. Elected officials, business owners, and citizens in the New Orleans region interested in another perspective on some of the limitations of relying too heavily upon levee systems will find the ASFPM document of interest.
Several key points from the ASFPM paper—and that are especially relevant to this committee’s report—are contained in a paragraph in the paper’s Introduction:
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 alternatives to mitigate the incidence of flooding to existing development, the ASFPM advocates that levees (1)