FLOOD10358

• County: Eagle
• Stream Name: Eagle River, Colorado River
• Basin: Colorado Mainstem
• Title: Correspondence presenting Revised Copies of FIRMS for Incorporated Eagle County
• Date: 12/16/2005
• Prepared For: Arn Menconi, Chairman, Eagle County Board of Commissioners
• Prepared By: Kevin Long
• Floodplain - Doc Type: Correspondence

All elevations are referenced to the NA YD. To obtain up-to~te elevation information
on National Geodetic Survey (NGS) Elevation Reference Marks (ERMs) shown on this
map, please contact the Information Services Branch of the NGS at [phone], or
visit their website at www.nl!s.noaa.gov. Map users should seek verification of
non-NGS ERM monument elevations when using these elevations for construction or
'floodplain management purposes. It is important to note that adjacent communities may
be referenced to NGYD. This may result in differences in BFEs across the corporate
limits between the communities.

For more information on NA VD, see the FEMA publication entitled Converting the
National Flood Insurance Program to the North American Vertical Datum of 1988
(FEMA, June 1992), or contact the Vertical Network Branch, NGS, Coast and Geodetic
Survey, National Oceanic and Atmospheric Administration, Rockville, Maryland 20910.

Temporary vertical monuments are often established during the preparation of a flood
hazard analysis for the purpose of establishing local vertical control. Although these
monuments are not shown on the FIRM, they may be found in the Technical Support
Data Notebook associated with the FIS report and FIRM for this community. Interested
individuals may contact FEMA to access these data.

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 100-year floodplain data, which may
include a combination of the following: 10-, 50-,100-, and 500-year flood elevations;
delineations of the 100-year and 500-year floodplains; and 100-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 may 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
l-percent-annual-chance (100-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: 1 ,200,
with a contour interval of 2 feet (References 20, 27, and 28); 1:2,400, with contour
intervals of 2, 5, 10, and 20 feet (References 29, 30, and 31); and I :2,400, with contour
intervals 20 feet and 40 feet (References 32 and 33).

The Brush Creek LOMR used the aerial topographic mapping provided by Alpine
Engineering Inc. dated August 2003 (Reference 34). Flood boundaries for Brush Creek
were delineated using topographic base maps with a scale of 1"=100', with a contour
interval of 2 feet (Reference 35).

The base topographic mapping for the Matrix study of the Eagle River was provided by
Analytical Surveys, Inc. Aerial imagery and mapping was completed October 1998. This
mapping was available at scales of 1" = 200' and has a contour interval of 2 feet

27