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Last modified
1/25/2010 6:45:54 PM
Creation date
10/5/2006 12:32:34 AM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
495
County
Arapahoe
Community
Cherry Hills Village
Basin
South Platte
Title
Flood Insurance Study - Arapahoe County, Colorado and Incorporated Areas, Cherry Hills Village - Volume 1
Date
3/1/1991
Designation Date
5/1/1999
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />floodplain boundary has been shown. <br />floodplain boundaries may lie above the <br />be shown due to limitations of the <br />detailed topographic data. <br /> <br />Small areas within the <br />flood elevations but cannot <br />map scale and/or lack of <br /> <br />Approximate 100-year floodplain boundaries in some portions of the <br />study area were taken directly from the Flood Insurance Rate Map <br />for the Town of Deer Trail, Colorado (Reference 59). <br /> <br />For the streams studied <br />floodplain boundary is <br />(Exhibit 2). <br /> <br />by approximate methods, only the 100-year <br />shown on the Flood Insurance Rate Map <br /> <br />4.2 Floodways <br /> <br />Encroachment on floodplains, such' as structures and fill, reduces <br />flood-carrying capaci ty, increases flood heights and veloci ties, <br />and increases flood hazards in 1 areas beyond the encroachment <br />itself. One aspect of floodplain ~anagement involves balancing the <br />economic gain from floodplain development against the resulting <br />increase in flood hazard. For purposes of the NFIP, a floodway is <br />used as a tool to assist local communities in this aspect of <br />floodplain management. Under this concept, the area of the 100- <br />year floodplain is divided into a, floodway and a floodway fringe. <br />The floodway is the channel of a stream, plus any adjacent <br />floodplain areas, that mus t be kept free of encroachment so that <br />the 100-year flood can be carried ,without substantial increases in <br />flood heights. Minimum Federal standards limit such increases to <br />1.0 foot, provided that hazardous velocities are not produced. The <br />floodways in this study are presented to local agencies as minimum <br />s,tandards that can be adopted directly or that can be used as a <br />basis for additional floodway studies. <br /> <br />The floodways presented in this study were computed for certain <br />stream segments on the basis of 1 equal conveyance reduction from <br />each side of the floodplain. F1loodway widths were computed at <br />cross sections. Between cross s~ctions, the floodway boundaries <br />were interpolated. The results of the floodway computations are <br />tabulated for selected cross sections (Table 2). The computed <br />floodways are shown on the Flood Insurance Rate Map (Exhibit 2). In <br />cases where the floodway and 100-year floodplain boundaries are <br />either close together or collineat, only the floodway boundary is <br />shown. <br /> <br />The area between the floodway and !lOO-year floodplain boundaries is <br />termed the floodway fringe. The! floodway fringe encompasses the <br />portion of the floodplain that could be completely obstructed <br />without increasing the water-surface elevation of the 100-year <br />flood by more than 1.0 foot at any point. Typical relationships <br />between the floodway and the flo04way fringe and their significance <br />to floodplain development are shown in Figure 8. <br /> <br />24 <br />
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