FLOOD10000

• County: Bent
• Community: Las Animas
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Las Animas Local Protection Project Design Memo Number 1 Hydrology
• Date: 9/1/1967
• Prepared For: Las Animas
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

The combined hydrograph produced a peak and volume of 200,800 c.f.s.
and 451,800 acre-feet, respectively. The volume amounts to 0.91 inch
of rainfall excess from the 9,306 square miles of contributing area
between Pueblo damsite and Las Animas. Listed in table 12 are perti-
nent data by subareas for the standard project flood. Standard project
flood data are shown on plate 12.

5-07. Fiood frequeneies.- Peak frequency curves were computed
for seyen locations along the Arkansas River below the authorized Pueblo
damsite during studies conducted for the forthcoming survey report on
Arkansas River above John Martin Dam. The curves were computed for
conditions with and without the authorized Pueblo Dam in operation.
The flow data were subjected to analysis using the methods presented
in "Statistical Methods in Hydrology," dated January 1962. The. curves
were based on data for various periods of record through 1965 and were
regionalized. After a review of these studies it was concluded that
the curves of peak frequency for Arkansas River at Las Animas that
evolved as a segment of a regionalized series of curves would consti-
tute a better representation than curves developed using only data for
one specific location. Data used in the development of the curves at
Las Animas are shown in table 13. The recommended curves, with and
without the authorized Pueblo Reservoir in operation, are based on the
flow data for the period 1921-65. The project document curves were
based on the period 1921-60. The recommended curves for the Arkansas
River at Las Animas for conditions with and without the authorized
Pueblo Dam in operation are shown on plates 13 and 14. A comparison
of the recommended curves and the project document curves is given be-
low.

Recurrence
Interval
(Years)

2
5
10
20
SO
100
200
500

Recommended
Existing W/Pueblo
(c.f.s.) (c.f.s.)

4,600
14,500
27,000
45,000
82,000
125,000
183,000
300,000

4,000
12,600
23,600
40,000
74,000
113,000
170,000
285,000

Project
Existing
(c.f.s.)

Document
W/Pueblo
(c.f.s. )

5,000
25,000
40,000
53,000
67,000
105,000
144,000
216,000

4,000
17,000
26,000
38,000
59,000
81,500
110,000
161,000

The change in the discharge-frequency relationships indicates an in-
crease in the benefit-cost ratio of the project. Details of the in-
crease will be presented in the forthcoming general design memorandum.

5-08. Peak frequency curves were developed for the Purgatoire
River at Las Animas for conditions With and without the authorized
Trinidad Reservoir in operation. Peak flow records are available for
Purgatoire River at Las Animas for the years 1922-31 and 1949-65.

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