TABLE 1-1 National Special Flood Hazard Area (SFHA) Population, Housing Units, and Square Miles Distribution
|Total in SFHA||Total
|Population within SFHA (million)||6.9||11.3||18.2||294.2|
|National percentage population in SFHA||2.2||3.6||5.8||94.2||312.4|
|Housing units within SFHA (million)||3.8||4.9||8.6||124.7|
|National percentage housing units within SFHA||2.8||3.7||6.5||93.5||133.3|
|Area within SFHA (square miles)||42,677||222,621||265,299||3,375,949|
|National percentage area in SFHA||1.2||6.1||7.3||92.7||3,641,247|
SOURCE: RAMPP (2012).
Use of the Word “Protection”
In the literature, the word “protection” is often used to describe a levee that “protects” against a one percent annual chance flood. For example, from 44 CFR §65.10 when describing levee design criteria, “For levees to be recognized by FEMA, evidence that adequate design and operation and maintenance systems are in place to provide reasonable assurance that protection from the base flood exists must be provided.” This type of language leads to the inaccurate conclusion that levees are “safe” and protect, without fail, to the one percent annual chance flood. However, all levees, even accredited levees, can fail or be overtopped—that is, achieving zero risk is not a possibility. Thus, in trying to make areas safer, in reality, the potential for catastrophic losses is increased (Burby, 2006).
The use of the word protection is unavoidable in discussion of levee-related flood risk. However, it is important to keep in mind that although levees do offer “protection” from floodwaters, they only separate the area behind a levee from floodwaters until the point where the levee fails or is overtopped.
within a participating community may be exempted from the mandatory purchase requirement and land-use regulations when located behind a levee system that has been recognized by FEMA as providing protection against the one percent annual chance flood event, that is, accredited.
For a levee system to gain accreditation status, a community or other party must submit an accreditation package to FEMA (Figure 1-2). This package includes certification by a registered Professional Engineer (P.E.) or federal agency with responsibility for levee design that the levee system has been adequately designed and constructed to provide protection against the base flood according to the structural requirements of the FEMA criteria as found in Title 44, Section 65.10 of the Code of Federal Regulations (44 CFR §65.10; see Appendix A of this report for the full text of this regulation). Accreditation also requires an operation plan and a maintenance plan for the levee system, the details of which are also found in 44 CFR §65.10. FEMA’s Procedure Memorandum 63, Guidance for Reviewing Levee Accreditation Submittals, discusses the process of review for compliance with 44 CFR §65.10 and accreditation (FEMA, 2010).
Levees can provide some flood control benefits that range from minor to substantial. For example, during record-setting floods in 2011, the levee system on the Lower Mississippi River was credited with preventing over $110 billion dollars in damages to the lands behind them (MRC, 2011). At the same time, no levee can provide absolute protection against all floods and failures of levee systems, such as those that occurred during Hurricane Katrina, which can cause billions of dollars worth of damages and threaten lives. All levees are subject to struc-