FLOOD03617

• County: Summit
• Community: Silverthorne
• Basin: Colorado Mainstem
• Title: FIS - Silverthorne
• Date: 8/9/2001
• Prepared For: Silverthorne
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

All elevations are referenced to the North American Vertical Datum of 1988 (NAVD).
Elevation Reference Marks (ERMs) and their descriptions are shown on the maps. ERMs
shown on the FIRM represent those used during the preparation of this and previous Flood
Insurance Studies. The elevations associated with each ERM were obtained and/or
developed during FIS production to establish vertical control for determination of flood
elevations and floodplain boundaries shown on the FIRM. Users should be aware that
these ERM elevations may have changed since the publication of this FIS. To obtain
up-to-date elevation information on National Geodetic Survey (NGS) ERMs shown on this
map, please contact the Information Services Branch of the NGS at [phone], or
visit their website at www.ngs.noaa.gov. Map users should seek verification of non-NGS
ERM monument elevations when using these elevations for construction or floodplain
management purposes.

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

The NFIP encourages State and local governments to adopt sound floodplain management
programs. To assist in this endeavor, each FIS provides IOO-year floodplain data, which may
include a combination of the following: 10-,50-, 100-, and 500-year flood elevations; delineations
of the lOO-year and 500-year floodplains; and lOO-year floodway. This information is presented
on the FIRM and in many components of the FIS, including Flood ProfIles, Floodway Data tables
and Summary of Stillwater Elevation tables. Users should reference the data presented in the FIS
as well as additional information that my be available at the local community map repository before
making flood elevation and/or floodplain boundary determinations.

4.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the I-percent annual
chance (IOO-year) flood has been adopted by FEMA as the base flood for floodplain
management purposes. The 0.2-percent annual chance (500-year) flood is employed to
indicate additional areas of flood risk in the community. For each stream studied by
detailed methods, the 100- and 500-year floodplain boundaries have been delineated using
the flood elevations determined at each cross section. Between cross sections, the
boundaries were interpolated using topographic maps at a scale of 1 :24,000, with a
contour interval of 2 feet (Reference 15).

The 100- and 500-year floodplain boundaries are shown on the Flood Insnrance Rate Map
(Exhibit 2). On this map, the lOO-year floodplain boundary corresponds to the boundary
of the areas of special flood hazards (Zone AE), and the 500-year floodplain boundary
corresponds to the boundary of areas of moderate flood hazards. In cases where the
100- and 500-year floodplain boundaries are close together, only the lOO-year floodplain
bowxlary has been shown. Small areas within the floodplain boundaries may lie above the
flood elevations but cannot be shown due to limitations of the map scale and/or lack of
detailed topographic data.

4.2 Floodways

Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity,
increases flood heights and velocities, and increases flood hazards in areas beyond the
encroachment itself. One aspect of floodplain management involves balancing the

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