6

Implementing Flood Risk Management Strategies

Flood risk management seeks to reduce the risk from flood events to the people who are located in floodprone areas. As indicated in earlier chapters, there is some level of risk to all locations within the floodplain. The magnitude of that risk is a function of the flood hazard, the characteristics of a particular location (its elevation, proximity to the river or coast, and susceptibility to fast-moving flows and surges, etc.), measures that have been taken to mitigate the potential impact of flooding, the vulnerability of people and property, and the consequences that result from a particular flood event. The initial risk is represented by the area’s characteristics without consideration of mitigation and risk transfer measures and the vulnerability of the population. Each mitigation and risk transfer measure reduces the overall risk to some degree, but it is impossible to completely eliminate risk. A flood risk management strategy identifies and implements measures that reduce the overall risk and what remains is the residual risk (Figure 6-1). In developing the strategy, those responsible judge the costs and benefits of each measure taken and their overall impact in reducing the risk. This chapter describes measures that can be used to reduce the risk behind levees.

Levees represent one method of reducing the impacts of flooding on a community or a region. Levees keep the floodwaters away from the area behind the levee until the point at which the levee is overtopped or fails and the area behind the levees is inundated and the people and property are affected. The risk to those behind levees is a function of the characteristics of the levee (height, strength), their location, and the mitigation and risk transfer measures and vulnerability reduction actions that they have taken or have been taken on their behalf. As has been previously discussed, every location within a floodplain, regardless of the presence or absence of a levee and whether or not the levee is accredited, is subject to some level of risk.

It is important for those located in the floodplain and those responsible for activity in the floodplain (public officials, investors, and those relying on activities in the floodplain, etc.) to ensure that those in the floodplain understand the nature of the risks they face and the steps that may be taken to reduce this risk. In communities that are part of the National Flood Insurance Program (NFIP), those portions of the community located in the Special Flood Hazard Area (SFHA) are subject to mandatory insurance purchase and special land-use requirements including minimum first-floor elevations for new construction. FEMA’s Community Rating System (CRS) identifies actions that can be taken by the community to reduce their risk and gives insurance premium reductions for communities that take appropriate mitigation actions.

Structure owners and occupants in NFIP communities who are not location in the SFHA, either outside of the one percent annual chance floodplain or behind an accredited levee, have no such federal restrictions even though



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6 Implementing Flood Risk Management Strategies Flood risk management seeks to reduce the risk from flood events to the people who are located in flood- prone areas. As indicated in earlier chapters, there is some level of risk to all locations within the floodplain. The magnitude of that risk is a function of the flood hazard, the characteristics of a particular location (its elevation, proximity to the river or coast, and susceptibility to fast-moving flows and surges, etc.), measures that have been taken to mitigate the potential impact of flooding, the vulnerability of people and property, and the consequences that result from a particular flood event. The initial risk is represented by the area’s characteristics without con- sideration of mitigation and risk transfer measures and the vulnerability of the population. Each mitigation and risk transfer measure reduces the overall risk to some degree, but it is impossible to completely eliminate risk. A flood risk management strategy identifies and implements measures that reduce the overall risk and what remains is the residual risk (Figure 6-1). In developing the strategy, those responsible judge the costs and benefits of each measure taken and their overall impact in reducing the risk. This chapter describes measures that can be used to reduce the risk behind levees. Levees represent one method of reducing the impacts of flooding on a community or a region. Levees keep the floodwaters away from the area behind the levee until the point at which the levee is overtopped or fails and the area behind the levees is inundated and the people and property are affected. The risk to those behind levees is a function of the characteristics of the levee (height, strength), their location, and the mitigation and risk transfer measures and vulnerability reduction actions that they have taken or have been taken on their behalf. As has been previously discussed, every location within a floodplain, regardless of the presence or absence of a levee and whether or not the levee is accredited, is subject to some level of risk. It is important for those located in the floodplain and those responsible for activity in the floodplain (public officials, investors, and those relying on activities in the floodplain, etc.) to ensure that those in the floodplain understand the nature of the risks they face and the steps that may be taken to reduce this risk. In communities that are part of the National Flood Insurance Program (NFIP), those portions of the community located in the Special Flood Hazard Area (SFHA) are subject to mandatory insurance purchase and special land-use require- ments including minimum first-floor elevations for new construction. FEMA’s Community Rating System (CRS) identifies actions that can be taken by the community to reduce their risk and gives insurance premium reductions for communities that take appropriate mitigation actions. Structure owners and occupants in NFIP communities who are not location in the SFHA, either outside of the one percent annual chance floodplain or behind an accredited levee, have no such federal restrictions even though 97

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98 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM Federal, State, Local High Individual Homeowner Level of Risk or Business Low FIGURE 6-1 Examples of tools and measures to reduce and transfer flood risk in flood-prone areas. The remaining risk after these techniques are employed is the residual risk. The bar on the far left indicates the initial, unmitigated risk that is faced by a community. Actions taken through the methods indicated in the subsequent bars, which are illustrative, reduce the unmitigated risk. Some of these actions are taken at the federal, state, and local levels, whereas others are taken by the homeowners and businesses at risk. The risk that remains after these actions are taken (bar on the far right) is the residual risk. SOURCE: Modified from USACE (2006). in many cases they face significant risks. As Figure 6-2 illustrates, a structure whose first-floor elevation is at the one percent annual chance level, might suffer only minor consequences should a greater than one percent annual chance flood occur, whereas those behind a one percent annual chance levee might suffer significant consequences. Because there are no federal requirements for land-use restrictions or mitigation in the non-SFHA area, many owners and public officials erroneously assume that the absence of requirements for action can be equated with absence of risk, when in reality, the risk may actually be greater in some areas of the SFHA. All NFIP communities, because of the land-use regulation provisions for the SFHA, have given some attention to the development of risk management strategies. However, once a levee is accredited, the area behind that levee is considered by most communities to be outside the floodplain and not subject to land-use regulation or require- ment for communities to consider the consequences of failure or overtopping. Depending on the topography of the area behind the levee, these strategies consider interior drainage systems to ensure that water “trapped” behind the levee during a storm will not create internal flooding and a SFHA. 1 One measure of the potential risk behind levees is measured by the number of structures protected by levees. FEMA currently estimates that 8.6 million housing units (6.5 percent of units in the United States) are located in SFHAs (FEMA, 2012a). The U.S. Army Corps of Engineers (USACE) estimates that there are 14 million struc- tures behind the 14,000 miles of levees for which it has oversight; many of these levees are also accredited under the NFIP (Chapter 8) (Bryan Baker, USACE, personal communication, January 10, 2013). USACE is currently 1  See 44 CFR §65.10 (b)(6).

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 99 FIGURE 6-2 Scenarios of residual risk. In scenario (A), the levee protects the home up to the one percent annual chance flood. In scenario (B) the water is higher and the one percent annual chance flood overtops the levee. The consequences to Home 1 are more significant than to Home 2: Home 1 is submerged; Home 2 is flooded. SOURCE: FEMA (2006). developing a Levee Safety Action Classification (LSAC) for use in screening the results of its inspection of levees under its oversight. Information from the LSAC will be provided to levee owners (USACE, 2012a). MITIGATION AND RISK TRANSFER MEASURES Mitigation is defined by the Federal Emergency Management Administration (FEMA) as “sustained action taken to reduce or eliminate long-term risks to people and property from hazards” (FEMA, 2010b). Traditionally, mitigation is divided into structural and nonstructural options. USACE, n.d.a defines structural and nonstructural mitigation measures as follows: Structural measures such as dams, levees, and floodwalls alter the characteristics of the flood and reduce the prob- ability of flooding in the location of interest. Nonstructural measures alter the impact or consequences of flooding and have little to no impact on the characteristics of the flood. A portfolio of structural and nonstructural mitigation measures can reduce the likelihood and/or impact of flooding (Table 6-1). For nearly two centuries, the nation relied principally on structural measures to control floods. TABLE 6-1 Examples of Structural and Nonstructural Flood Mitigation and Risk Transfer Measures Structural Nonstructural Levees Structure elevation Floodwalls Natural systems Seawalls Risk mapping Dams Hazard forecasting, early warning systems, and emergency plans Floodways and spillways Dry and wet floodproofing Channels Land-use planning and zoning Controlled overtopping Construction standards and building codes Levee armoring Acquisition and relocation Seepage control Insurance

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100 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM In the mid-20th century, in recognition that even with significant use of structural approaches, flood damages were still on the rise, governments initiated multifaceted floodplain management and expanded use of nonstructural means and risk transfer (flood insurance) mechanisms (Sayers et al., in press). Structural Mitigation Measures A brief description of the structural measures most often used in flood control follows, along with discussion about how each of these measures relates to levees. This discussion was adapted, in part, from NRC (2012b). Levees, Floodwalls, Seawalls, and Other Appurtenant Structures These structures are designed to prevent floodwaters and storm surges from reaching areas that are at risk. Consequences of failure can be catastrophic because those behind the structure can be subject to rapid inundation and flooding conditions more severe than if the floodwaters had risen gradually. Dams Barriers that impound hydrologic flows, dams retain floodwaters before they reach areas at risk. For example, during high-precipitation periods, dams hold upstream floodwaters that are released gradually to minimize the likelihood of damage to downstream communities. However, during exceptionally large events, the storage capac- ity of a dam can be exceeded and uncontrolled flood flows are passed downstream. Under these circumstances, downstream levees may not be able to contain floodwaters and will fail. This condition occurred in 2011 during spring floods on the Missouri River (USACE, 2012b). Under exceptional circumstances, dams can fail and send significant quantities of water downstream, resulting in damage or destruction of levees and communities below the dams. Floodways, Spillways, and Channels Floodways, spillways, and channels are constructed to carry floodwaters around a community or region where the capacity of a river to pass a large volume of floodwaters past a critical location is limited. Under some circumstances, river channels can be modified to increase their flood carrying capacity. During the 2011 flooding of the Mississippi River, USACE opened floodways near New Madrid Missouri to take the pressure off upstream and downstream levees in Illinois, Kentucky, and other locations in Missouri, and three floodways in Louisiana to relieve pressure on structures in the New Orleans area. A similar floodway provides relief when needed to relieve pressure on levees surrounding Sacramento, California. Structural Mitigation Through Improved Levee Design or Modification During a flood, levees are under continuous stress that threatens their integrity. The most serious challenges result from wave action against a levee face, the erosion of the land side of a levee as the levee is overtopped or subject to waves breaking over its top, and seepage under the levee that destroys the levee from within. Forms of these occurred during Hurricane Katrina and caused the failure of levees in the New Orleans region in 2005. Use of controlled overtopping, armoring, and underseepage control can greatly reduce the potential for catastrophic failure. Controlled Overtopping and Breaching of Levees During a flood event, the risk of a levee overtopping can be significant and the consequences can be cata- strophic. Controlled overtopping of levees or engineered overtopping involves designing a levee to force overtop- ping in the least hazardous location (USACE, 1986). This can be done by using different levee heights, known as superiority, or notches or openings in a desired location (Figure 6-3).

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 101 FIGURE 6-3 A gated overflow spillway that would control flows into a desired area. SOURCE: Courtesy of Jae-won Chung. The advantages of controlled overtopping in a designated area are (1) reducing the impact of overtopping failure in the selected area and in other parts of the levee system, (2) reducing the likelihood of overtopping in less desirable areas (i.e., areas with more development), and (3) reducing levee maintenance and repair costs after the flood event. Controlled breaching of levees is occasionally carried out during sustained high flow events (floods), when the benefit of the intentional diversion is deemed to be justified, economically, to mitigate more extensive damage that would likely otherwise occur. Controlled breaches are relatively rare, but have been used in most major flood events since 1927 as a last ditch means to lower flood stages threatening high-value areas, such as New Orleans (in 1927), Cairo, Illinois, and the St. Francis Basin in Missouri and Arkansas 1937 and 2011 along the Missis- sippi River, or historic towns such as Prairie du Rocher, Illinois, during the 1993 Missouri–Middle Mississippi River flood. These are not to be confused with so-called “forced breaches,” which are routinely employed during floods, usually to help drain flooded tracts of urban or agricultural land. Forced breaches are necessary if there is no other ready means of draining flooded lands that are ringed by intact levees about their lower, or “downstream” perimeters. Forced breaches are usually made using tracked backhoe excavators and are commonly employed whenever a diked tract of land is compromised by flooding. The natural breaches and forced breaches must then be repaired before the succeeding flood season. Since records began being tabulated within the NFIP in 1969, forced breaches have historically accounted for 40 to 50 percent of the post-flooding repair costs sustained by local agencies (Storesund et al., 2009). Levee Armoring Armoring a levee involves making a levee less susceptible to erosion induced by floodwaters and overtopping. It involves the use of a variety of materials, from concrete to vegetation. Three key factors in determining levee survival in a significant flood event and overtopping are depth and duration of flow, flow velocity (a function of slope inclination, height of the drop, and flow friction), and the erosive resistance of the vegetation mat and underlying soils (Briaud et al., 2008; Storesund et al., 2009). The earliest methods of armoring employed in the 1800s, involved timbers reinforcing the submerged wall of the levee. Today, particularly after levees failed in Hurricanes Katrina and Rita in 2005, considerable attention is being given to new methods and technologies that might make earthen levees more survivable during short-term overtopping, as occurs during hurricane-whipped storm surges. These concepts include the use of embedded soil reinforcement (high-density polyethylene mesh and fiber reinforcement), turf reinforcement, and paving land-side slopes with soil admixtures, such as clay, soil cement, and other forms of tensile reinforcement (Rogers, 2009; Xu et al., 2012). An example of one such armored levee is shown in Figure 6-4. Seepage Berms and Cutoff Walls Depending on the nature of the material used in the construction of the levee and the foundation of the levee, water may flow through or under a levee creating the potential for collapse of the levee or its foundation (Figure

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102 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM FIGURE 6-4 Example of an armored levee in Japan. SOURCE: Courtesy of Gerald E. Galloway. 6-5, Top). Cutoff walls and trenches can be used to stop the flow through and below a levee (Figure 6-5, Lower Left). Construction of land-side seepage berms can add sufficient weight to counteract the upward seepage forces (Figure 6-5, Lower Right). Pressure relief wells can be placed on the land side of the levee to deal with seepage and are part of the levee repair effort for the East St. Louis, Illinois levees mentioned in Chapter 5 . Nonstructural Mitigation Measures Nonstructural measures vary in cost and effectiveness and the physical and political effort required to imple- ment them. The selection of which measure to use is a function of the location in which it will be employed (topography, expected flood levels, etc.), the availability of funds, and public acceptance of use. Structure Elevation By raising a structure above the expected flood level, flood damages can be prevented (Figure 6-6). Behind an accredited levee, if a flood greater than the one percent annual chance flood occurs, there could be some damage to such elevated properties but considerably less than if the structures had been at the base flood elevation (BFE). In the SFHA, buildings are elevated to the BFE in the case of new construction, substantial improvements are made to existing buildings, and repairs are made to substantially damaged buildings to comply with the NFIP (FEMA, 2000). NFIP insurance rates for structures in the SFHA are discounted for elevations above the BFE, providing that supporting documentation (i.e. an elevation certificate) is provided. Elevation includes moving key or essential equipment from low-lying elevations within a structure to areas that would not be subject to flooding. Having building support systems such as computers, heating and air-con- ditioning units, and electrical stations located in the basement areas puts the functionality of the entire building

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 103 FIGURE 6-5 Levee seepage and control methods. (Top ) Seepage paths under and through a levee. (Lower Left) Use of cutoff walls and trenches to block seepage. (Lower Right) construction of a land-side seepage berm to provide additional weight and length to counteract upward seepage forces. SOURCE: USACE Management Measures Digital Library. Available online at http://www.iwr.usace.army.mil/docs/MMDL/ FLD/Feature.cfm?ID=5, accessed January 25, 2013. at risk during a flood event. In 2006, a heavy storm in downtown Washington, D.C. flooded much of the federal triangle including the National Archives, the Federal Bureau of Investigation Headquarters, and the basement of the Internal Revenue Service (IRS), damaging essential mechanical and electrical equipment. The IRS was closed for 6 months to allow for repairs (GAO, 2007; National Capital Planning Commission, 2008). When building a structure on the floodplain, the cost of incorporating freeboard in a pile or a masonry pier foundation averages approximately 1 to 2 percent of the at-BFE building cost for 4 feet of added freeboard. For a masonry wall with interior pier (crawlspace) foundation, the cost averages 3 to 6 percent of the at-BFE building cost (Jones et al., 2006). Jones and colleagues (2006) concluded that it is financially reasonable to spend between 103 to 106 percent of the at-BFE building cost to elevate a structure, depending on local circumstances. Challenges in elevating structures do exist. For example, properties that service people with disabilities may require either an elevator or a long ramp, the cost of which could make elevation economically infeasible. In addi- tion, there is growing concern that having an entire community elevated creates the potential for small islands (houses) in a flood sea that cannot be accessed during the flood event. In the case of fire or a medical emergency, first responders would find it very difficult to reach many of these homes. If flooding were to last for an extended period, the elevated homes would rapidly become uninhabitable.

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104 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM FIGURE 6-6 Elevated homes behind levees in New Orleans, Louisiana. SOURCE: Courtesy of Gerald E. Galloway. Natural Systems Naturally existing, restored, or developed wetlands, as well as land in periodic cultivation, can store overflow waters from riverine flooding and help reduce downstream impacts. Wetlands also provide a natural barrier to storm surge inundation. Coastal sand dunes protect structures built behind them and help slow down coastal erosion and also the immediate impact of rising storm surge. Floodways built to relieve flood pressure can also provide ecosystem benefits. These natural systems can be effective in reducing flooding behind levees with interior drain- age problems (Galloway et al., 2009; Opperman et al., 2009). Use of natural systems typically requires some form of real estate acquisition (fee simple, easement, payment for use, etc.) because the benefits from such measures normally do not accrue to the individual who may own the property required. In some cases, there will be a need for construction of appropriate inlet and outlet works to permit the entry and exit of stored waters. Risk Mapping Accurate mapping of risks provides those living or working in flood-prone areas, in front of or behind levees, with the information necessary to make rational decisions in developing their personal or corporate flood risk management strategies. Risk mapping is discussed further in Chapter 7. Combining the natural hazard risk assessment with quantitative consideration of mitigation measures yields expected outcomes that can be graphically portrayed in a manner that facilitates public understanding of the risk and its implications for them. NRC (2012b)

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 105 Hazard Forecasting, Early Warning Systems, and Emergency Plans Detailed weather forecasts of the path and severity of a tropical storm, and accurate predictions of stages (heights) of flooding rivers enable government officials and the public to make decisions to evacuate or move valuable property from high-hazard areas. Advance information about potential failures of levees or dams can significantly reduce the consequences should failures occur. Preparation of emergency action and evacuation plans can similarly reduce or eliminate casualties and property losses. Dry and Wet Floodproofing Damage to structures in the SFHA and behind levees can be greatly reduced through effective dry and wet floodproofing. Dry floodproofing seals structures to prevent floodwaters from entering; wet floodproofing makes uninhabited portions of a structure resistant to floods by allowing water to enter and flow through the structure during a flood. FEMA defines floodproofing as a combination of adjustments and/or additions of features to buildings that eliminate or reduce the potential for flood damage. Examples of such adjustments and additions include anchoring of the building to resist flotation, collapse, and lateral movement; installation of watertight closures for doors and windows; reinforcement of walls to withstand floodwater pressures and impact forces generated by floating debris; use of membranes and other sealants to reduce seepage of floodwater through walls and wall penetrations; installation of pumps to control interior water levels; installation of check valves to prevent the entrance of floodwater or sewage flows through utilities; and the location of electrical, mechanical, utility, and other valuable damageable equipment and contents above the expected flood level (FEMA, n.d.a). The Federal Alliance for Safe Homes (FLASH) indicates that dry floodproofing can be accomplished by measures such as • Applying a waterproof coating or membrane to the exterior walls of the building; • Installing watertight shields over doors, windows and other openings; • Anchoring the building as necessary so that it can resist floatation; • Installing backflow valves in sanitary and storm sewer lines; • Raising utility system components, machinery and other pieces of equipment above the flood level; • Anchoring fuel tanks and other storage tanks to prevent flotation; • Installing a sump pump and foundation drain system; • Strengthening walls so that they can withstand the pressures of floodwaters and the impacts of flood borne debris; • Construct nonsupporting, break-a-way walls designed to collapse under the force of water without causing damage to the house or its foundation.2 Wet floodproofing includes construction of veneers to seal potential water entry into or under a structure, installa- tion of vents to allow water to move through crawl spaces under homes (avoiding different water levels outside and under a home).3 Floodproofing can also include permanent or temporary installation of barriers such as modular dams and small levees designed to keep floodwaters away from one or more structures for limited periods of time (Figure 6-7). There is an increasing demand for products and techniques that can be used in existing properties to reduce the potential damage when flooding occurs. To ensure that floodproofing products are well designed and manufac- 2  See http://www.flash.org/peril_inside.php?id=59. 3  See http://www.flash.org/peril_inside.php?id=60.

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106 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM FIGURE 6-7 Barriers and small levees floodproof a home from low-level flooding. SOURCE: FEMA (2007). tured to perform the task for which they are being developed, both the Association of State Floodplain Managers (ASFPM) and FM Global have developed certification standards to support this need (FM Global, 2006, n.d.). 4 Land-Use Planning and Zoning Wise land use is at the center of nonstructural flood mitigation activity and is an effective tool for reducing risk at the community level. Land-use planning implements public policy to direct how land in a given area is used. It is executed through zoning ordinances and takes place on multiple levels of government, from national policy to local policy where there may be designation of parcels for a specific use at the local level. When appropriate, wise land use may mean a lack of investment in a particular area (Box 6-1). Few issues have gained attention and controversy like land-use planning. The tension between promoting development in order to foster growth in the community and the potential long-term liabilities (i.e., flood risk) is significant. Unfortunately, when individuals or businesses develop an area that may be subject to flooding and are unaware of the potential risk, these individuals suffer when a flood event occurs. Although the NFIP requires regulation of the land within the SFHA, it does not require flood-prone communities to regulate areas beyond the one percent annual chance flood level or areas behind levees even though both areas face flood risks. When a community’s land-use plans treat all areas behind a levee the same way even though some areas are substantially below the BFE and would be fully inundated in the event of a major levee failure, these land-use plans ignore the risk in placing occupants of the lower areas at an economic and safety disadvantage. Construction Standards and Building Codes Construction standards and building codes can be developed at any level of government but they are enforced at the local level. While codes provide for public safety, they also prescribe practices and measures that directly address known causes of disaster damages. Damages can be significantly reduced by attention to modern construc- tion standards and building codes. Kunreuther (1996) found that one-third of the damages associated with the 1992 Hurricane Andrew could have been avoided had Florida enforced its building codes. 4  See http://www.floods.org/index.asp?menuid=421&firstlevelmenuid=183&siteid=1.

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 107 BOX 6-1 The Coastal Barriers Resources Act Coastal barriers possess many characteristics that make them attractive building sites. These include their rich biological diversity, their status as popular vacation destinations, and their role as large drivers to local economies. However, these areas pose substantial risks to both developers and homeowners. They are often the location of first landfall by tropical storms, bearing the full force of storm surges and hurricane winds, and are the victim of a constantly fluctuating landscape due to chronic coastal erosion (FWS, 2002). The federal government historically subsidized and encouraged development in these coastal areas until the late 1970s and early 1980s, when it was realized that this subsidization and encouragement had been resulting in the loss of natural resources; presented a threat to human life, health, and property; and cost American taxpayers millions of dollars each year (FWS, 2012). In an effort to remove any federal incentive to develop on coastal barriers, Congress passed the Coastal Barrier Resources Act (CBRA) in 1982. Reauthorized in 1990, the CBRA designated relatively undeveloped coastal barriers along the Atlantic and Gulf coasts, the Florida Keys, the Great Lakes, Puerto Rico, and the U.S. Virgin Islands as part of the newly created John H. Chafee Coastal Barrier Resources System. This designation renders these coastal barriers ineligible for most new federal expenditures and financial assistance, including, most significantly, access to federal flood insurance through the NFIP (FWS, 2012). Although no longer encouraged by the federal government, development in these hazard- prone areas is not prohibited, provided any work and investment is made by private developers and other nonfederal parties. In return for a lack of restrictions on development, any individual or developer choosing to live and invest in these areas agrees that they will bear the full cost of development and rebuilding (in the case of a flooding event or other natural disaster) instead of relying upon federal funding for roads, wastewater systems, potable water supply, and disaster relief (FWS, 2012). This approach has saved over $1 billion in federal dollars between 1982 and 2010 and is expected to continue saving federal dollars in the future (FWS, 2012). Acquisition and Relocation Acquisition or relocation of properties that are repetitively flooded, substantially damaged, or need flood- related project construction have been supported by FEMA and USACE, allowing many communities to deal with the challenges of these frequent flood losses. When land is not suitable or only marginally suitable for development or agricultural activity, that land can be acquired and placed into public use for either environmental or recreational purposes to enhance the overall quality of life in the community. Buyouts of properties that are repetitively flooded have been supported by FEMA and have allowed many communities to deal with frequent flood losses. Although a few sections of communities have been relocated, more relocations or removals usually take place where specific parcels are identified as being at risk. When property is acquired for environmental purposes. this land can frequently be used during flood periods for off-river storage of floodwaters. This flood storage reduces the downstream impact of the flood and the area is restored after the flood to its previous condition. During the 2011 Mississippi River floods, over 500,000 acres of land in the lower Mississippi Valley was used for flood stor- age, which dramatically reduced river stages that otherwise would have affected large communities such as New Orleans and smaller ones such as Cairo, Illinois. Insurance Through the purchase of insurance, some of the financial risk of living on a floodplain in or outside the SFHA or behind a levee is transferred, for a premium, from the individual to the entities that provide insurance. Floodplain managers tend to consider this a mitigation technique, when in fact unlike physical measures that reduce damages,

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116 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM 44 CFR §59.1, Definitions In the past, existing roads and railroads, that is, embankments, were assumed to be included in the definition of a levee system and its accreditation even though the information concerning the integrity of the structures was unknown. As defined in 44 CFR §59.1, a levee system is: “a flood protection system which consists of a levee, or levees, and associated structures, such as closure and drainage devices, which are constructed and operated in accordance with sound engineering practices” (emphasis added). Although such embankments can provide a degree of flood protection, they can also be the source of catastrophic failures. If embankments are to be included in a levee system, they need to be subject to the same examination as levees designed specifically for flood protection purposes or the definition modified to exclude them because they were not designed to provide risk reduction from flood damages (ILPRC, 2006). 44 CFR §64.3 Flood Insurance Maps Under current procedures, areas behind accredited levees are normally shown as Zone X or a shaded Zone X with the latter frequently indicating the presence of a levee. Section 64.3 identifies Zone X as either an area “of moderate flood hazards or areas of future-conditions flood hazard” or an area “of minimal hazards.” FEMA’s Map Service Center indicates that a shaded Zone X is an “Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floods. Are also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100-year flood, or shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile” (Appendix E). Neither of these definitions adequately identifies areas behind accredited levees. Establishing a unique zone designation for areas behind levees would more clearly dis- tinguish areas behind accredited levees from the 0.2 percent annual chance floodplain and the one percent annual chance floodplain and would provide clarity and assist in risk communication (ILPRC, 2006). 44 CFR §65.10, Mapping of Areas Protected by Levee Systems If the definition of a levee system in 44 CFR §59.1 is modified to specifically exclude embankments, such as roads and railroads that were not engineered to provide risk reduction from flooding, similar modification of 44 CFR §65.10 is necessary (ILPRC, 2006). This would ensure that nonengineered levee systems are not certified as providing protection from the base flood. As part of periodic update of FRIMs (map modernization), all levees are being subjected to analysis as they are mapped. Even though the map modernization program has a high priority, at current resource levels, the period between updates may be lengthy. It is important that, independent of the mapping of levees, FEMA maintain some degree of surveillance over the integrity of levees in the NFIP (ILPRC, 2006). At present, once accredited, a levee maintains this status until the next update. Rather than allowing accreditation to remain in effect until the FIRM is revised, periodic submission of operation and maintenance records as well as a writ- ten assessment of the levee systems performance in any flood events that have occurred to FEMA is needed. Furthermore, periodic recertification of the engineering and geotechnical aspects of the levee is critical. These continued actions verifying to FEMA that an accredited levee maintains its integrity would require modifica- tion of 44 CFR §65.10. The design of levee systems is based on conditions at the time of the design including the flow and channel carrying capacity. As a result of upstream activity or normal geomorphic processes, the flow can be increased and the carrying capacity of these channels can be significantly reduced, thereby increasing the elevation of the base flood and reducing or eliminating the capability of an accredited levee to pass the base flood. Attention to the maintenance of these channels is an important part of maintaining the integrity of the levee system. Assurance that the flood carrying capacity of the main river channel is maintained is critical. Channel maintenance preserves the required level of protection, ensures that encroachments are controlled, and that an increased flow does not affect the integrity of the levee or the ability of the levee sponsor to maintain the levee and fight floods, when necessary (ILPRC, 2006).

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 117 To ensure that levees are designed to meet widely recognized standards, FEMA, in the past, has included references to the appropriate USACE manuals.9 During the establishment of the NFIP and the inclusion of levees in the program, FEMA worked in close coordination with USACE to determine the appropriate design guidance to be used in construction of levees and in their evaluation and ceded to USACE the lead in several areas. The above recommendations reflect the 2006 documents available but need to be adjusted to reflect more recent publications. An Inventory of the Nation’s Levees The first step in properly dealing with levee risk and developing flood risk management strategies is to identify the location, condition, and ownership of levees, as well as the extent of the areas protected by the levee and the consequence of failure or overtopping (i.e., assets and lives), if it should occur. Compiling this information and making it readily available is fundamental to ensuring public safety and reducing flood losses. Because levees can alter natural hydrologic flows, knowledge of their location, properties, and conditions is essential to understand- ing, quantifying, and mitigating flood hazards, including working to increase public awareness of vulnerability during a flood event. Although some responsibilities have been assigned by Congress to FEMA and USACE for developing and maintaining levee information, several states and communities also are working to develop and maintain this information. The U.S. Army Corps of Engineer’s National Levee Database The biggest single resource for levee data in the United States is the National Levee Database (NLD). Admin- istered and populated by the USACE, the NLD was authorized by Congress in the 2007 Water Resources Develop- ment Act. Congress directed the Secretary of the Army to establish and maintain a database with an inventory of the nation’s levees; the database was to include: (A) location information of all Federal levees in the Nation (including global information system information) and, for non-Federal levees, such information on levee location as is provided to the Secretary by State and local governmental agencies; (B) utilizing such information as is available, the general condition of each levee; and (C) an estimate of the number of structures and population at risk and protected by each levee that would be adversely impacted if the levee fails or water levels exceed the height of the levee. (WRDA, 2007) Appropriations for the database since 2007 have been insufficient to carry out the charge (Eric Halpin, USACE, personal communication, November 7, 2011). The NLD currently includes the more than 2,500 levees and asso- ciated structures (together known as “levee systems”) that total more than 14,500 miles in length, cataloged in digital format. This includes levees that were built by USACE and are still operated and maintained by USACE (2,800 miles), built by USACE and turned over to local sponsors to operate and maintain (9,500 miles), or are under USACE oversight under Public Law 84-9910 program that permits USACE to provide pre-and post-disaster assistance to nonfederal levees that meet certain standards of performance (2,200 miles) (Bryan Baker, USACE, personal communication, January 13, 2013; USACE, n.d.b). All data except information that could be considered to affect national security are accessible to both official data users and partners such as federal, state, and local governments, sponsors, and the general public (USACE, 2012c).11 It should be emphasized that levee data are 9  Reference USACE Engineer Manual EM 1110-2-1413, Engineering and Design, Hydrologic Analysis of Interior Areas as the acceptable/ preferred methodology for interior drainage analysis. [65.10(b) (6]. Reference the USACE Levee Owners Manual for Non-Federal Flood Control Works as required for operation, maintenance, and inspection guidance and procedures for non-Federal levees and floodwalls [65.10(c) and 65.10(d)]. 10  Under Public Law 84-99, Flood Control and Coastal Emergency Act, USACE is authorized to undertake activities including disaster preparedness, advance measures, emergency operations (flood response and post-flood response), rehabilitation of flood control works threat- ened or destroyed by flood, protection or repair of federally authorized shore protective works threatened or damaged by coastal storm, and provisions of emergency water due to drought or contaminated source. 11  See http://nld.usace.army.mil/egis/f?p=471:1:0::NO for additional information.

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118 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM currently being collected from a variety of sources. Based on discussions with FEMA and USACE staff, the com- mittee expects that the accuracy of the NLD and FEMA levee data will improve over time. Currently, any data provided to USACE for inclusion in the NLD on levees that do not fall under the auspices of USACE and its national portfolio are collected on a voluntary basis. Efforts are under way to integrate the levee data collected on the communities that participate in the NFIP into the NLD, which will improve the information in the levee database (NRC, 2012b). Though USACE is working closely with other federal agencies and nonfed- eral levee owners to incorporate their data into the NLD on a voluntary basis, this current effort is not likely to yield the desired results (e.g., the building of a comprehensive national levee inventory) because of its voluntary nature (Eric Halpin, USACE, personal communication, 2011). Additionally, information collected and information voluntarily supplied are not likely to be in a format consistent across states, tribes, and local and regional entities, challenging the development of a comprehensive understanding. FEMA Mid-Term Levee Inventory FEMA has long maintained an inventory of NFIP-accredited levees; however, in 2006 the ILPRC reported that “various levee databases have been developed, but for the most part they are not geospatially referenced, are incomplete, and lack usable information concerning the condition of the levees and attendant supporting structures” (ILPRC, 2006). As a result, in FY 2007, FEMA funded and developed the FEMA Mid-Term Levee Inventory (MLI) database, which was designed to complement the NLD and uses a data model extracted from the NLD’s database. Whereas the NLD inventories levees of all protection levels, the MLI gathered levee data for structures designed to provide protection from a base (one percent annual chance) flood, to better to support the production of countywide flood insurance studies and Flood Insurance Rate Maps (FIRMs) and any other levees that were located in the area covered by FIRMs (FEMA, 2012b; Figure 6-12). Maintenance of the MLI data is performed at FEMA’s regional level and additional levee data is added as it becomes available (FEMA, 2012b). As of November 2012, the inventory identified approximately 29,800 miles of levees. Of those, approximately 5,100 miles have been or are accredited or in Provisionally Accredited Levee (PAL) status (i.e., NFIP levees) and 22,000 miles are not part of the NFIP but are located on FIRMs and could affect hydraulics in those areas or provide protection at less than the one percent annual chance flood level (FEMA, 2012b). These latter levees were identified by FEMA’s Production and Technical Services contractors in counties covered by FIRMs. Overlaps There is currently no method for determining whether a levee in the NLD is also in the FEMA MLI except through a one-by-one comparison of certain levee characteristics. Because some data elements in the two invento- ries are different, USACE and FEMA have been attempting to manually look for overlaps, but have yet to complete the effort. A preliminary analysis by both agencies indicates that approximately 3,400 miles of accredited or PAL levees (66 percent of NFIP levee miles) may be operating under oversight of both agencies (Figure 6-13). Because the 2012 Flood Insurance Reform and Modernization Act requires the two agencies to synchronize their analyti- cal methodologies where both agencies inspect the same levee, FEMA and USACE have accelerated their efforts to define overlaps (David Bascom, FEMA, personal communication, November 1, 2012; Bryan Baker, USACE, personal communication, December 9, 2012). Total Miles of Levees in the United States The National Committee on Levee Safety (NCLS), a group of federal, state, local, and private-sector members with expertise in representing national interests in levee safety, was convened in 2008 to prepare recommendations and a strategic implementation plan on a National Levee Safety Program with direction from Congress under the Water Resources Development Act of 2007 (NCLS, 2009). The draft NCLS report was issued in 2009 (ASFPM, 2012).

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 119 Acknowledging the fact that little was currently known about the specific size of the national levee portfolio outside efforts at the federal level, the NCLS formulated an estimate of the number of privately owned and state levees by extrapolating data entered by the state of California into their levee inventory database and then apply- ing that ratio of USACE program and other federal levees to private and nonfederally owned levees across the nation. The NCLS estimated that there may be 100,000 or more miles of levees (including thousands of miles of irrigation and water-supply canal embankments) that were built by federal, public, or private entities and operated by nonfederal, public, or private organizations. The current inventories in the NLD and MLI have identified less than 32,000 miles of levees. Mapping under the NFIP covers areas containing 92 percent of the U.S. population and more than 21,000 communities with flood-prone areas, logically the areas in need of levees. Analysis, discus- sions with members of the NCLS, and site visits by this committee indicate that levees not contained in the NLD and MLI probably represent small individually owned levees, private levees used to protect industrial assets, and roads and railroads that act as levees. It is also likely that the NCLS estimate, based on the California inventory, overestimated the number of levees, given that the California levee population is one of the densest in the nation and is not reflective of the nation as a whole (Figure 6-10). Based on the judgment of the committee, the total mileage of significant levees in the United States, excluding embankments, is estimated to be under 50,000 if not under 40,000 miles. The NCLS report recommended that Congress grant USACE the authority and appropriation to expand and maintain the National Levee Database by conducting a one-time inventory and assessment of all nonfederal levees and canal embankments12 in the United States (NCLS, 2009). Such an action would allow for baseline informa- tion on levee performance to be collected for the entirety of the nation’s levee systems, resulting in an accurate, cost-effective, and efficient decision-making process when it comes to managing the nation’s levee portfolio. Upon completion of this one-time inventory, the responsibility for periodic inventory and inspection updates to the NLD would fall to the states where these levees are located. Congressional action has yet to be taken on this recommendation. State Levee Inventory Efforts As of 2006, only Wisconsin and North Dakota had geospatial inventories of levees; Illinois, Mississippi, North Dakota, Ohio, and California had some levee database efforts under way (ILPRC, 2006). Today, the majority of states still do not have levee inventories (Larry Larson, ASFPM, personal communication, September 2012). As an example of what can be accomplished, the California Department of Water Resources (CA DWR) has created the California Levee Database (CLD), a “statewide central repository for levee and flood control structures for use by public agencies for flood risk assessments and emergency response” (Rod Mayer, CA DWR, personal com- munication, 2012). Using data from sources such as the NLD, FEMA’s Mid-Term Levee Inventory, CA DWR, and the California Emergency Management Agency, as well as local agencies and publicly available maps, the CLD includes more than 13,725 miles of levees and levee-like structures within the state. Currently, the inventory includes 92 percent of all state–federal State Plan of Flood Control (SPFC) levees 13 in the state, 85 percent of all non-SPFC levees, and 71 percent of all local levees. Washington State has also taken steps to create a levee inventory. In the absence of a comprehensive national levee inventory, the state, well aware of its status as being one of the more flood-prone states in the nation, com- missioned and conducted the Statewide Levee Inventory and Flood Protection Study to better understand the current status of accredited levees within its borders. This study was divided into two parts: the Washington State Final Report on Levee Certification and Accreditation, which summarized current levee policies and practices, and the development of a statewide inventory that includes the location, level of protection, and certification/ 12  Canal embankments, although not designed to protect areas from flooding, can pose threats to some communities. When embankment walls are aboveground, the water they contain can break through and flood nearby areas. In 2008, over 300 homes in Fernley, Nevada, flooded when the walls of an irrigation canal collapsed. In 2012, the first court settlement of numerous lawsuits awarded $10 million to 600 local residents for damages. 13  SPFC levees are federally authorized levees located in California’s Central Valley for which the state has provided assurances of coopera- tion with the federal government (CA DWR, 2010).

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120 A

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B FIGURE 6-12 (A) National Levee Status Map capturing levees inventoried in the MLI. Roman numerals denote the 10 individual FEMA regions. (B) Counties across the nation containing levees captured in the MLI. SOURCE: (A) Modified from FEMA (2011); (B) FEMA (2012b). 121

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122 LEVEES AND THE NATIONAL FLOOD INSURANCE PROGRAM FIGURE 6-13 Overlap between USACE NLD inventory of USACE levees and levees identified in FEMA’s MLI. FEMA’s MLI includes 29,800 miles of levees, and USACE’s NLD identifies 14,500 miles of levees; 17,100 miles of levees in FEMA’s MLI are not included in USACE’s NLD, approximately 1,700 of which are accredited; 12,700 miles of levees in FEMA’s MLI are included in the USACE’s NLD, approximately 3,400 of which are accredited or PAL. This represents a 66 percent overlap. All values are approximate. accreditation status of all currently known levees14 at the statewide level (Resilience Institute, 2010). Of the 697 miles of identified levees found within the state, 18 percent (approximately 125 miles) were found to currently be accredited, provisionally accredited, or de-accredited. Only 9 percent (approximately 62 miles) of all levee miles were found to be accredited. The long-term goal is that the Washington inventory will be strengthened to the point where it will be a useful tool in developing a prioritized list of levees needing site-specific attention (such as repair, certification and accreditation, and/or removal) and in the prioritization of state support for such levees (Resilience Institute, 2010). REFERENCES ASFPM (Association of State Floodplain Managers). 2012. National Committee on Levee Safety (NCLS). Available online at http://www.floods.org/index.asp?menuID=338. Accessed August 7, 2012. Boon, J. D., J. M. Brubaker, and D. R. Forrest. 2010. Chesapeake Bay Land Subsidence and Sea Level Change: An Evalua- tion of Past and Present Trends and Future Outlook. Available online at http://web.vims.edu/GreyLit/VIMS/sramsoe425. pdf?svr=www. Accessed February 21, 2013. Briaud, J. L., H. C. Chen, A. V. Govindasamy, and R. Storesund. 2008. Levee erosion by overtopping in New Orleans during the Katrina hurricane. Journal of Geotechnical and Geoenvironmental Engineering 134(5): 618-632. Brody, S. D., S. Zahran, P. Maghelal, H. Grover, and W. E. Highfield. 2007. The rising costs of floods: Examining the impact of planning and development decisions on property damage in Florida. Journal of the American Planning Association 73(5): 330-345. 14  The State of Washington defines a levee as a “fabricated barrier along rivers, streams, channels, sloughs, and other water courses” (Re- silience Institute, 2010).

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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 123 Brody, S. D., W. E. Highfield, and J. E. Kang. 2011. Rising Waters: Causes and Consequences of Flooding in the United States. Cambridge, UK: Cambridge University Press. Burby, R. J., and L. C. Dalton.1994. Plans can matter: The role of land use plans and state planning mandates in limiting the development of hazardous areas. Public Administration Review 54(3): 229-238. CA DWR (California Department of Water Resources). 2010. Draft State Plan of Flood Control Descriptive Document. Available online at: http://www.water.ca.gov/cvfmp/docs/DRAFT_SPFC_Descriptive_Doc_20100115.pdf. Accessed July 31, 2012. Crowell, M. 2010. Impact of Climate Change on the NFIP. Presentation to the Coastal Engineering Research Board Meeting, June 22. Vicksburg, MS: USACE. Available online at http://chl.erdc.usace.army.mil/dirs/events/319/08%2087th%20 CERB%20Crowell.pdf. Accessed March 3, 2013. CVFPP (Central Valley Flood Protection Plan). 2012. 2012 Central Valley Flood Protection Plan, a Path for Improving Public Safety, Environmental Stewardship, and Long-Term Economic Stability. Available online at http://www.cvfpb.ca.gov/ CVFPP/index.cfm. Accessed January 28, 2013. FEMA (Federal Emergency Management Agency). 1997. Building a disaster-resistant community: Project Impact. The Project Impact Guidebook. Washington, DC: FEMA. FEMA. 2000. Above the Flood: Elevating Your Floodprone House. Available online at http://www.fema.gov/library/viewRecord. do?id=1424. Accessed November 28, 2012. FEMA. 2006. The National Levee Challenge: Levees and the FEMA Flood Map Modernization Initiative. Washington, DC: FEMA. FEMA. 2007. Selecting Appropriate Mitigation Measures for Floodprone Structures. FEMA 551. Available online at http:// www.fema.gov/library/viewRecord.do?id=2737. Accessed January 22, 2013. FEMA. 2010a. Hazard Mitigation Assistance Unified Guidance on the Hazard Mitigation Program, Pre-Disaster Mitigation Program, Flood Mitigation Assistance Program, Repetitive Flood Claims Program, and Severe Repetitive Loss Program. Available online at http://www.fema.gov/library/viewRecord.do?id=4225. Accessed January 29, 2013. FEMA. 2010b. Mitigation Planning Fact Sheet on Risk MAP. Available online at http://www.fema.gov/library/viewRecord. do?id=2066. Accessed November 14, 2012. FEMA. 2011. Midterm Levee Inventory Project Summary Report. Available online at: http://www.r3levees.org/wiki/images/0/03/ MLI_Summary_Report_20111130_Final.pdf. Accessed August 8, 2012. FEMA. 2012a. Analysis and Update of National Flood Hazard Layer Demographics and NFIP Policy and Claims Data. Prepared by Risk Assessment, Mapping, and Planning Partners, project report for task order #HSFEHQ-11-J-002. Washington, DC: FEMA. FEMA. 2012b. Midterm Levee Inventory Project Summary Report: Standard Operations Task Order 4, November. Washington, DC: FEMA. FEMA. n.d.a. Non-residential Floodproofing Requirements and Certification for Buildings Located in the Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. Technical Bulletin 3-93. Available online at http:// www.fema.gov/library/viewRecord.do?id=1716. Accessed February 15, 2013. FEMA. n.d.b. The Unified Hazard Mitigation Assistance Grant Programs Factsheet. Available online at http://www.fema.gov/ library/viewRecord.do?id=3648. Accessed January 29, 2013. FEMA. 2013. Hurricane Sandy Advisory Base Flood Elevations (ABFEs) in New Jersey and New York. FEMA Region 2. Available online at http://www.region2coastal.com/sandy/abfe, accessed February 27, 2013. FM Global. 2006. Approval Standard for Flood Abatement Equipment, Class Number 2510. Available online at http://www. fmglobal.com/assets/pdf/fmapprovals/2510.pdf. Accessed December 6, 2012. FM Global. n.d. Understanding the Benefit, FM Approved Flood Abatement. Available online at http://www.fmglobal.com/ assets/pdf/P11204.pdf. Accessed December 6, 2012. FWS (U.S. Fish and Wildlife Service). 2002. The Coastal Barrier Resources Act: Harnessing the Power of Market Forces to Conserve America’s Coasts and Save Taxpayers Money. Available online at http://www.fws.gov/CBRA/Docs/Taxpayer- SavingsfromCBRA.pdf. Accessed November 28, 2012. FWS. 2012. Background information on the Coastal Barrier Resource Act. Available online at http://www.fws.gov/CBRA/Act/ index.html. Accessed November 28, 2012. Galloway, G. 2009. Reacting to Climate Change, Floods, and Uncertainty. Available online at http://www.colorado.edu/hazards/. Accessed October 31, 2012. Galloway, G. E, D. F. Boesch, and R. R. Twilley. 2009. Restoring and protecting coastal Louisiana. Issues in Science and Technology 25(2): 29-38. GAO (Government Accountability Office). 2007. IRS Emergency Planning, Headquarters Plans Supported Response to 2006 Flooding, but Additional Guidance Could Improve All Hazard Preparedness. GAO-07-579. Washington, DC: GAO.

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