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1 1 (December 7, 2017)

handle is hein.crs/govcgyp0001 and id is 1 raw text is: FF. ' ,iE SE.$.! i , December 7, 2017 Levee Safety and Risk: Status and Considerations Levees can reduce or exacerbate flood risk. Prior to Hurricane Katrina in 2005, there was little public attention to the safety of the nation's levees. The failure of floodwalls (which were designed and constructed by the U.S. Army Corps of Engineers, or USACE) and breaching of levees in and around New Orleans contributed to significant loss of life and economic damage. The events of 2005 led to the enactment of legislation and ongoing efforts to inventory, inspect, and assess U.S. levees. Although these efforts have improved understanding of levee safety, significant data gaps remain for many levees in the United States, and many measures to correct identified safety concerns remain uncompleted. Recent floods and dam safety concerns (e.g., Oroville Dam in California) have increased interest in flood risk among policymakers, including those concerned about federal disaster response and recovery spending. This In Focus covers the evolution of efforts to inventory U.S. levees and assess their risks, and policy considerations for decisionmakers. & ft, Risk, ntrAck nd kcr Levees (i.e., engineered earthen embankments), engineered coastal dunes and berms, and floodwalls (which are constructed of metal or reinforced concrete) are built to reduce flood losses. Herein these structures are collectively referred to as levees. Risk associated with levees is a function of the hazard (e.g., level and duration of floodwaters), the performance of the levee (both prior to overtopping and after being overtopped), and the potential consequences (i.e., what is exposed to loss, damage, and disruption). Some risk, referred to as residual risk, remains behind a levee. Larger flood events can overwhelm levees; also, levees that are poorly designed, constructed, or maintained can fail. Figure 1 illustrates the components of levee risk and some levee performance concerns. Many of the nation's early levees were privately constructed to protect agricultural lands and rural communities. As early as 1917 and regularly thereafter, Congress authorized and funded USACE to construct numerous flood control projects that included levees; the agency continues to own, operate, and maintain some early USACE-constructed levees. Since the late 1980s, USACE- built levees are cost-shared 65% federal and 35% nonfederal during construction, and then transferred to nonfederal entities (e.g., municipalities, water utilities, levee districts) for operation, maintenance, repair, and rehabilitation. Other federal agencies also have constructed levees for their own missions (e.g., International Boundary and Water Commission) or assisted in the construction of levees that are now operated by nonfederal entities (e.g., U.S. Department of Agriculture). Since its establishment in 1968, the National Flood Insurance Program (NFIP) has encouraged levee construction, operation, and maintenance; this encouragement results from the elimination of flood insurance purchase requirements and reduced premiums for structures that are mapped as removed from the 100-year floodplain due to the levee's protection. The Federal Emergency Management Agency (FEMA) is responsible for accrediting levees to appear on NFIP insurance rate maps (for more on NFIP, see CRS Report R44593, Introduction to the National Flood Insurance Program (NFIP), by Diane P. Horn and Jared T. Brown). There may be as many as 100,000 miles of levees in the United States. Nonfederal or private entities are responsible for maintaining most existing levees and often have few if any local or state requirements to satisfy regarding levee design and safety. Federal agencies are responsible for maintaining their own levees in good condition. USACE owns and maintains 4,200 miles of levees, and it also regularly inspects 8,200 miles of levees that participate in its Rehabilitation and Inspection Program (RIP). If the RIP- participating nonfederal levee owner has maintained the levee in good condition, USACE uses RIP to repair levees damaged from a flood or other natural event at a federal cost share of 80% to 100%. In 2005, when Hurricane Katrina focused public attention on levee safety, there was no effort for levees equivalent to the National Inventory on Dams or the National Dam Safety Program. (See CRS In Focus IF10606, Dam Safety: Federal Programs and Authorities, by Charles V. Stern et al.) Through P.L. 110-114, in 2007 Congress charged the USACE with developing a National Levee Database (NLD). The NLD is a partial inventory of U.S. levees; it currently covers 29,000 miles of levees (see Figure 2). Nonfederal levee data are provided voluntarily. Figure I. Illustration of Levee Risk ComDonents and Levee Performance Concerns Source: CRS, adapted from Zina Deretsky, National Science Foundation, and USACE, Risk Assessment for Flood Risk Management Studies, 2017. gognpo 'popmm ggmm g 'S a X

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