FLOOD01901

• County: Larimer
• Community: Larimer County Unincorporated
• Title: Flood Insurance Study - Larimer County Unincorporated Areas, Volume 1 of 3
• Date: 3/23/1999
• Prepared For: Larimer County
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

All elevations are referenced to the National Geodetic Vertical
Datum of 1929 (NGVD). Elevation reference marks in the vicinity of
Estes Park are shown on the maps; other elevation mark data can be
obtained from the Larimer County Planning Commission.

4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS

The National Flood Insurance Program (NFIP) encourages State and local
governments to adopt sound flood plain management programs. Therefore,
each Flood Insurance Study produces maps designed to assist communities
in developing flood plain management measures.

4.1 Flood Boundaries

To provide a national standard without regional discrimination, the
1 percent annual chance (laO-year) flood has been adopted by FEMA
as the base flood for flood plain management purposes. The 0.2
percent annual chance (SOO-year) flood is employed to indicate
additional areas of flood risk in the community. For each stream
studied in detail, the 100- and SOD-year flood plain boundaries
have been delineated using the flood elevations determined at each
cross section. Between cross sections, the boundaries were
interpolated using topographic maps at scales of 1:2,400, 1:1,200,
and 1:6,000, with contour intervals of 2 and 4 feet (References 19,
20, 21, 23, 24, 2S, 26, and 29).

On the Little Thompson River, approximate flood boundaries were
delineated using aerial photographs at a scale of 1:12,000
(Reference 27). Approximate flood boundaries for the Cache La
Poudre River were delineated from two COE Flood Plain Information
reports (References 6 and 28).

Approximate flood boundaries for Boxelder Creek and Cooper Slough
in the vicinity east of the City of Fort Collins were delineated
using topographic maps at a scale of 1:1,200 with a contour
interval of 2 feet (Reference 30).

The 100- and SOD-year flood plain boundaries are shown on the Flood
Boundary and Floodway Map (Exhibit 2). In cases where the 100- and
SOD-year flood plain boundaries are close together, only the 100-
year flood plain boundary has been shown. Small areas within the
flood plain 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.

For the streams studied by approximate methods, only the 100-year
flood plain boundary is shown.

Approximate lOa-year flood plain boundaries in some portions of the
study area were taken directly from the Flood Hazard Boundary Map
(Reference 31).

21