FLOOD06515

• County: Las Animas
• Community: Las Animas County and Unincorporated Areas
• Basin: Arkansas
• Title: FIS - Las Animas County and Unincorporated Areas
• Date: 9/1/1977
• Prepared For: Las Animas County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

3.0 ENGINEERING METHODS

For the streams studied in detail In Las Animas County,
standard hydrologic and hydraulic study methods were used
to determine the flood hazard data required for this study.
Floods having recurrence intervals of 10-, 50-, 100-, and
SOD-years have been selected as having special significance
for flood plain management and flood insurance premium
rates. The analyses reported here reflect both current
and planned conditions in the watersheds of the stream.

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish
the peak discharge-frequency relationships for floods
of the selected recurrence intervals for each stream
studied in the county. Recorded flood information
for the majority of the streams studied in detail
within Las Animas County is non-existent. Good runoff
records do exist for the Purgatoire River. Due to
the construction of Trinidad Reservoir, however, the
recorded information on the Purgatoire River is not
applicable. As a result, peak discharges for the
Purgatoire and other streams studied were computed
using the 10-, 50-, 100-, and 500-year floods of the
Plains Region equations given in Reference 6.

Discharges for the 500-year floods of all streams
were checked by straight line extrapolation of frequen-
cies previously determined using the procedure of
the U. S. Geological Survey (Reference 7), and compared
to the U. S. Army Corps of Engineers' Standard Project
Flood data when available.

Frequency-discharge, drainage area curves for the areas
studied are shown in Figures 14 and 15.

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of streams
in the community were carried out to provide estimates
of elevations of floods of the selected recurrence
intervals along each stream studied in detail. The
elevations for the portions of streams studied by
approximate methods were determined by using historic
flood information and engineering judgment.

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