FLOOD04921

• Designation Number: 252
• County: Adams
• Community: Federal Heights
• Basin: South Platte
• Title: Flood Insurance Study - Federal Heights, Adams County, Colorado
• Date: 4/1/1986
• Designation Date: 3/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

Approximate 100-year flood plain boundaries were delineated using
topographic maps at a scale of 1:1,200, with a contour interval of
2 feet (Reference 10).

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

4.2 Floodways

The floodway is the channel of a stream, plus any adjacent flood
plain areas, that must be kept free of encroachment so that the
100-year flood can be carried without substantial increases in
flood heights.

Floodways were not computed because they were not within the scope
of this study.

Regulatory elevations computed at selected cross sections used in
the hydraulic analyses (Section 3.2) are shown in Table 2.

5.0 INSURANCE APPLICATION

To establish actuarial insurance rates, data from the engineering study
must be transformed into flood insurance criteria. This process includes
the determination of reaches, Flood Hazard Factors, and flood insurance
zone designations for each flooding source studied in detail affecting
the City of Federal Heights. '

5.1 Reach Determinations

Reaches are defined as sections of flood plain that have relatively
the same flood hazard, based on the average weighted diffe~ence ,in
water-surface elevations between the 10- and 100-year floods. This
difference may not have a variation greater than that indicated in
the following table for more than 20 percent of the reach:

Average Difference Between
10- and 1007-Year Floods

Variation

LeSS than 2 feet
2 to 7 feet
7.1 to 12 feet
More than 12 feet

0.5 foot
1.0 foot
2.0 feet
3.0 feet

The locations of the reaches determined for the flooding sources
of the City of Federal Heights are shown on the Flood Profiles
(Exhibit 1) and summarized in Table 3.

9