Mapping the Zone Improving Flood Map Accuracy (2009) / Chapter Skim
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2 Flood Mapping and Flood Insurance
2 Flood Mapping and Flood Insurance
Pages 13-24
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From page 13... ...
. The 1 percent annual chance flood, series of devastating floods, including a 1927 flood of the Mississippi River, which inundated 13 million acres and killed several hundred also known as the base flood or 100-year flood, is the people.
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From page 14... ...
Unshaded Zone X, Zone C: Area of minimal flood hazard, commonly understood to have a lower probability of flooding than the moderate hazard area. The numbers for zones A1 through A30 were determined by computing the difference between the 1 percent annual chance and 10 percent annual chance flood elevation, multiplying by 10, then applying a conversion factor (FEMA, 1983)
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From page 15... ...
Consequently, the resulting from multiple 1 percent annual chance floods accuracy of BFEs on the flood maps is important for in a given year or higher than expected flood waters.
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From page 16... ...
. FLOOD MAP PRODUCTION Data for Digital FIRMs The process for producing flood maps involves Digital Flood Insurance Rate Maps (DFIRMs)
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From page 17... ...
assess the effects of storm surge and wave action and determine base flood elevations (FEMA, 2003, V 1 and Riverine Flooding.
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From page 18... ...
decision about which to use depends on the type of Drainage ditches and stormwater management facili- flood hazard, the resources available, and the risk of flood ties may be overloaded by storms more severe than the damage. Coastal flood mapping is currently done using 10 percent annual chance floods for which they are the equivalent of detailed studies.
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From page 19... ...
The standard is aimed at ensuring that the flood maps match FEMA'S MAP MODERNIZATION PROGRAM the topographic data used, although adherence to the standard does not itself validate the topographic data. The nation has floodplains along approximately The validation guidelines for flood data and engineering 3.5 million miles of rivers and coasts (FEMA, 2006a)
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From page 20... ...
These Ground elevations in the floodplain can change -- for figures illustrate the challenges of increasing flood map example, when fill is placed in the floodplain to accuracy: even if the goals articulated in the midcourse raise building sites or when a new flood control adjustment are achieved, 70 percent of the mapped p roject introduces levees, reservoirs, or stream chanstream miles will not have validated engineering nel modifications -- affecting the spread of floodwater. a nalyses supporting the flood map, and 25 percent will Small projects, such as clearing channels or building not meet the floodplain boundary standard.
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From page 21... ...
population covered by digital flood maps 100 92 Percentage of mapped stream and coastal miles with new, updated, or validated engineering analysis 22 30 Percentage of population covered by maps with new, updated, or validated engineering analysis 15 40 Percentage of mapped stream and coastal miles that meet the 2005 floodplain boundary standard 57 75 Percentage of population covered by maps that meet the 2005 floodplain boundary standard 32 80 SOURCE: FEMA (2006a)
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From page 22... ...
The recent availability of LOMCs and This is especially important, given that FEMA flood Flood Insurance Study reports online has made data data are increasingly being used for land use planning, even more accessible. Yet although more products are emergency response, and risk assessment, in addition to available and distribution has improved, digital updat- the insurance and regulatory purposes for which they ing processes have lagged.
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From page 23... ...
Unless both sets of coordinates are stored merged to delineate the Special Flood Hazard Area on in the archived map and model information, it will be a map panel. The digital information describing a single difficult or impossible at a later date to place a hydraulic flood study is stored in hundreds or even thousands of model cross section at the correct map location along files, which must be compiled for each county mapped the stream.
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