FLOOD05002

• Designation Number: 209
• County: Prowers
• Community: Lamar
• Basin: Arkansas
• Title: Flood Insurance Study - Lamar, Prowers County, Colorado
• Date: 5/1/1982
• Designation Date: 1/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

5.1 Reach Determinations

Reaches are defined as lengths of watercourses having relatively the
same flood hazard, based on the average weighted difference in water-
surface el evati ons between the 10- and 100-year floods. Thi s dif-
ference does 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 100-Year Floods

Variation

Less than 2 feet
2 to 7 feet

0.5 foot

1.0 foot

One reach meeting the above criteria was required for the Arkansas
River and four reaches were required for Willow Creek at the City of
Lamar. The location of each reach is shown on the Flood Profiles
(Exhibit 1) and summarized in Table 3.

5.2 Flood Hazard Factors

The FHF is used to correlate flood information with insurance rate
tables. Correlations between property damage fran floods and their
assigned FHFs are used to set actuarial insurance premium rate tables
based on FHFs from 005 to 200.

The FHF for a reach is the average wei ghted difference between the
10- and 100-year flood water-surface elevations expressed to the
nearest one-half foot, and shown as a three-digit code. For example,
if the difference between water-surface elevations of the 10- and
100-year floods is 0.7 foot, the FHF is 005; if the difference is 1.4
feet, the FHF is 015; if the difference is 5.0 feet, the FHF is 050.
When the difference between the 10- and 100-year water-surface eleva-
tions is greater than 10.0 feet, accuracy for the FHF is to the near-
est foot.

5.3 Flood Insurance Zones

After the determination of reaches and their respective Flood Hazard
Factors, the entire incorporated area of the City of Lamar was
divided into zones, each having a speCific flood potential or hazard.
Each zone was assigned one of the following flood insurance zone
designations:

Zones A7, A8, A12,
and A15:

Special Flood Hazard Areas inundated by
the 100-year flood, detenni ned by de-
tail ed methods; base fl ood el evati ons
shown, and zones subdivided according
to Flood Haza rd Factors.

13