FLOOD10696

• County: Larimer
• Community: Larimer County and Incorporated Areas
• Title: FIS - Larimer County and Incorporated Areas - Vol 1
• Date: 12/19/2006
• Prepared For: Larimer County and Incorporated Areas
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

All flood elevations shown in this FIS report and on the FIRM are referenced to NA VD88.
Elevation Reference Marks (ERMs) shown on the FIRM represent those used during the
preparation of this and previous FIS reports. Users should be aware that these ERM
elevations may have changed since the publication of this FIS report. To obtain up-to-date
elevation information on National Geodetic Survey (NOS) 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-NOS 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 NOVD. This may result in differences in Base Flood Elevations (BFEs)
across the corporate limits between communities.

For this revision, a vertical datum conversion was completed for each studied reach. The
range of conversion factors was prohibitively high; therefore, a standard conversion factor
was not applied for the entire community. The Profile Panel and FDT conversion from
NGVD29 to NA VD88 was carried out in accordance to the procedure outlined in the
FEMA document Map Modernization - Guidelines and Specifications for Flood Hazard
MaDDing Partners Appendix B: Guidance for Converting to the North American Vertical
Datum of 1988.

Using the multiple conversion factor approach, an average conversion factor for each
flooding source was developed by establishing separate conversion factors at the upstream
end, at the downstream end and at an intermediate point of the studied reach. From this
data, the average conversion factors for each reach were developed. In some cases, it was
necessary to divide each reach into multiple sections in order for the maximum offset from
the average conversion factor to be less than or equal to 0.25 feet.

For more information on NA VD88, 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, National Geodetic Survey,
Coast and Geodetic Survey, National Oceanic and Atmospheric Administration, Rockville,
Maryland 20910 (Internet address http://www.ngs.noaa.gov).

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 this data.

Conversion factors for each studied reach are shown in Table 3.

For the Big Thompson River new studies in the areas of the Towns of Johnstown and
Loveland, no datum conversion was needed.

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