Slope stability analysis of earthen levee strengthened by high performance turf reinforcement mat under hurricane overtopping flow conditions. Only 9 percent (approximately 62 miles) of all levee miles were found to be accredited. 2009. Sustainable Floodplains Through Large-Scale Reconnection to Rivers. in many cases they face significant risks. The selection of which measure to use is a function of the location in which it will be employed (topography, expected flood levels, etc. FIGURE 6-12 (A) National Levee Status Map capturing levees inventoried in the MLI. Straightening the river speeds up the water so high volumes can pass through an area quickly. A critical part of the goals of the strategy is to define the relative levels of protection both in front of and behind levees and then to lay out the appropriate combination of mitigation measures (structural, nonstructural, or insurance) to achieve those levels. 2012. (Note that flooding during Hurricane Sandy (2012) exceeded the one percent annual chance flood.) 2009. In addition, 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. FEMA Region 2. 2007. 2010a. Restoring and protecting coastal Louisiana. 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. Risk mapping is discussed further in Chapter 7. The above recommendations reflect the 2006 documents available but need to be adjusted to reflect more recent publications. 1973. FWS. Coastal barriers possess many characteristics that make them attractive building sites. Simply looking at an economic balance sheet tilts decision making toward structural approaches. Rather than allowing accreditation to remain in effect until the FIRM is revised, periodic submission of operation and maintenance records as well as a written assessment of the levee systems performance in any flood events that have occurred to FEMA is needed. This releases methane which is a. WRC. • 44 CFR §65.10, Mapping of Areas Protected by Levee Systems. Draft State Plan of Flood Control Descriptive Document. 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. Accessed February 21, 2013. Available online at: http://www.npr.org/2012/11/06/164362276/norfolk-va-puts-flooding-survival-plan-to-the-test. SOURCE: (A) Modified from FEMA (2011); (B) FEMA (2012b). Upward pointing triangles represent increases in the magnitude; downward pointing triangles, decreases. 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 communication, 2012). FEMA 551. 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. ———Flood Damage Reduction Strategies and Tools——— 7-3 impacts of flood losses on the individual and the co mmunity to an acceptable level. Some risk scenarios are associated with long time horizons, such as flooding associated with climate change, and might be less perceptible to the at-risk community compared with, for example, a design deficiency in a levee discovered during the Map Modernization process. Each mitigation and risk transfer measure reduces the overall risk to some degree, but it is impossible to completely eliminate risk. This new strategy includes, for example, new floodgates, pumping stations, and floodwalls at an estimated cost of $1 billion dollars (NPR, 2012). Flood Risk Management Strategy: Goals at the Local Level. The NFIP was established by Congress with passage of the National Flood Insurance Act in 1968, to help reduce future flood damages through NFIP community floodplain regulation that would control development in flood hazard areas, provide insurance for a premium to property owners, and reduce federal expenditures for disaster assistance. The SFHA is delineated on FEMA's Flood Insurance Rate Maps (FIRM's) using topographic, meteorologic, hydrologic, and hydraulic information. Brody, S. D., W. E. Highfield, and J. E. Kang. 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. Wet floodproofing includes construction of veneers to seal potential water entry into or under a structure, installation 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). 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. Climate change will have a variety of regional impacts, and the geographic location of a community will affect how changing conditions affect risk. DEVELOPING COMMUNITY STRATEGIES FOR AREAS BEHIND LEVEES, Circumstances produce a variety of flood risk scenarios behind levees. FEMA. To successfully develop a flood risk management strategy, a community, in collaboration with those entities that may be called upon to assist in the implementation of the strategy, needs to first establish the goals of the strategy. FEMA. FMA, SRL, and RFC grants are designed to, over time, reduce flood losses to the NFIP by mitigating insured properties with particular attention to repetitive loss and severe repetitive loss properties. Top). 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. Accessed August 8, 2012. 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). Jones, C. P., W. L. Coulbourne, J. Marshall, and S. M. Rogers, Jr. 2006. If water levels continue to rise, the relief channel may also flood. Today, this issue still plagues the Sacramento-San Joaquin Delta area, and a Central Valley Flood Protection Plan was adopted in June 2012. The initial risk is represented by the area’s characteristics without consideration of mitigation and risk transfer measures and the vulnerability of the population. Schropp, M. H. E., and T. W. Soong. USACE is currently. 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. 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). FIGURE 6-13 Overlap between USACE NLD inventory of USACE levees and levees identified in FEMA’s MLI. Collectively, these grant programs become important parts of the risk management portfolio. London, UK: Taylor and Francis Group. As indicated in earlier chapters, there is some level of risk to all locations within the floodplain. Available online at http://chl.erdc.usace.army.mil/dirs/events/319/08%2087th%20CERB%20Crowell.pdf. Midterm Levee Inventory Project Summary Report. Flood risk management begins with goal and policy development, identification of the hazard, analysis that includes assessment of the hazard’s potential impact, and development of flood risk management strategies, representing the amalgamation of the various measures discussed in this chapter and Chapter 7 available to deal with the flood challenge . ASFPM (Association of State Floodplain Managers). Building a disaster-resistant community: Project Impact. Total Miles of Levees in the United States. Report of Flooding and Stormwater in Washington, DC. All values are approximate. Available online at http://www.fema.gov/library/viewRecord.do?id=1424. An example of one such armored levee is shown in Figure 6-4. Washington, DC: The National Academies Press. FEMA defines floodproofing as. A recent special report of the Intergovernmental Panel on Climate Change (IPCC, 2012) indicates a likely increase in many regions of the frequency of heavy precipitation events, and when coupled with increasing vulnerability presents a myriad of challenges for coping with climate-related disastersIPCC. This is known as River Management. Accessed February 18, 2013. 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. Resource for levee data in the NLD and MLI have identified less than 32,000 miles of levees its. 5 ): 330-345 their execution the Lower Mississippi Vision Summit, New Orleans, Louisiana understand these changes... 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