Levees and the National Flood Insurance Program Improving Policies and Practices (2013) / Chapter Skim
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6 Implementing Flood Risk Management Strategies
6 Implementing Flood Risk Management Strategies
Pages 97-126
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From page 97... ...
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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From page 98... ...
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.
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From page 99... ...
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.
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. 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.
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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.
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. 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)
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From page 103... ...
SOURCE: USACE Management Measures Digital Library. Available online at http://www.iwr.usace.army.mil/docs/MMDL/ FLD/Feature.cfm?
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From page 104... ...
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.
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From page 105... ...
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, 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)
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From page 106... ...
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.
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From page 107... ...
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)
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Commercial flood insurance is available and is issued by numerous major insurers and is issued by a worldwide network of reinsurance organizations, providing coverage for property value in excess of the NFIP maximum of $250,000 for residential property and $500,000 for businesses. However, unlike the NFIP, commercial insurance rates and rates for homeowner coverage in excess of the NFIP cap are based on more detailed analysis of properties as they apply for coverage and may reflect more sophisticated risk analysis and requirements for mitigation measures (Chapter 5)
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From page 109... ...
This includes recognition that the one percent annual chance flood standard of the NFIP might not serve as an appropriate life safety or property protection standard. Also critical to evaluating flood risk management strategies at the local level is the ability to acquire the resources it will need to carry out the floodplain management strategy.
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From page 110... ...
Today, this issue still plagues the Sacramento–San Joaquin Delta area, and a Central Valley Flood Protection Plan was adopted in June 2012. This plan promotes integrated, systemwide wise flood management, a key implication of which is that flood management investments (e.g., levees)
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IMPLEMENTING FLOOD RISK MANAGEMENT STRATEGIES 111 FIGURE 6-8 Average sea level trend at Seawells Point, Virginia, recording a 4.44-mm/year rise with a 95 percent confidence interval of ±0.27 mm/year based on data from 1927 through 2006. This is equivalent to 1.46 feet in 100 years.
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From page 112... ...
With sea-level rise, a far larger area would be flooded in the event of a one percent annual chance flood event. (Note that flooding during Hurricane Sandy (2012)
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The Biggert-Waters Act further charges the Administrator to review and update NFIP rate maps and to incorporate any future risk assessment submitted by the Technical Mapping Advisory Council in any such revision or update. 7 Implementing Flood Risk Management 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 (Figure 3-3)
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From page 114... ...
Successful flood risk management strategies are developed through a bottom-up process that is supported from the top down. Development of flood risk strategies by the community is critical, as is support from and collaboration with FEMA (Box 6-3)
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EFFECTIVE FLOOD RISK MANAGEMENT: ADMINISTRATION OF LEVEES Development and maintenance of appropriate supporting policies and data affecting the portfolio of mitigation measures are both critical effective floodplain management strategies. For example, managing the inclusion of levees in the NFIP is an important mission of the Federal Insurance and Mitigation Administration and requires the development of policies and procedures as well as regulatory instruments.
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From page 116... ...
Establishing a unique zone designation for areas behind levees would more clearly distinguish 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)
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From page 117... ...
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.
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From page 118... ...
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)
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From page 119... ...
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, commissioned and conducted the Statewide Levee Inventory and Flood Protection Study to better understand the current status of accredited levees within its borders.
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B FIGURE 6-12 (A) National Levee Status Map capturing levees inventoried in the MLI.
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2012. National Committee on Levee Safety (NCLS)
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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.
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2006. Evaluation of the National Flood Insurance Program's Building Standards.
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From page 125... ...
Washington, DC: WRC. WRDA (Water Resources Development Act)
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