FLOOD04360

• County: Bent
• Community: Las Animas
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Interim Report on Review Survey for Flood Control
• Date: 8/1/1963
• Prepared For: Las Animas
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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13. The principal tributaries of the Arkansas River above Las
Animas are Fountain Creek, which rises on the slopes of Pikes Peak and
flows generally southward to join the Arkansas River at Pueblo, Horse
Creek which enters from the north a few mi les upstream from Las Animas,
and the Huerfano and Apishapa Rivers which enter from the south. The
largest tributary above John Martin Dam is the Purgatoire River which
enters the main stem at the head of the reservoir, about three mi les
downstream from Las Animas.

16. STREAM CHARACTERISTICS.- The Arkansas River ebove Canon City
is a typical mountain torrent which descends over 6,000 feet in eleva-
tion in a distance of less than 130 mi les, at gradients often exceeding
50 feet per mi Ie. From Canon City, elevation 5;300 feet, the river
descends on a diminishing gradient to about 10 feet per rT)ile at Pueblo,
elevation 4,668 feet. From Pueblo to Las Animas the stream slope
decreases to 8 feet per mi Ie and the channel capacity varies from
5,000 to 10,000 c.f.s.( I) The present channel capacity in the vicinity
of Las Animas is 6,500 c.f.s.

14. The Purgatoire River rises in the Sangre de Cristo Range west
of Trinidad, where several peaks exceed 13,000 feet and one exceeds
14,000 feet, and flows eastward for a distance of about 30 mi les before
it reaches Trinidad. The mountainous area above Trinidad cOmprises
about 22 percent of the watershed. From Trinidad the river flows in a
generally northeast direction through an alluvial valley about 35 mi les
long, and then becomes entrenched in a rugged canyon for a distance of
105 mi les. Below the canyon the river flows through a second alluvial
val ley for 17 mi les to its confluence with the Arkansas River.

15. Las Animas is the county seat of Bent County. The Arkansas
River passes through Bent County from west to east with about one-
third of the county on the north side and two-thirds on the south. The
area north of the Arkansas River Val ley is featured by rol ling plains
and benches with outcrops of shale and I imestone along most of the
streams. Rol i ing hi I Is and benches characterize about one-half of the
area south of the valley; however, the southern third of the county is
broken with bluffs, canyons, and sandstone mesas. Most of the soi I is
derived from the shale and limestone of the Benton and Niobrara Groups.
The valley section consists of valley fi II and alluvial fans composed
of silty sand and clays. There is a light c lay loam topsoi I and a
heavy clay loam subsoi I to a depth of 5 feet or more. Outside of the
irrigated areas, vegetation is sparse consisting generally of cedar,
juniper, cacti, and grass. Vegetal cover in the project area is
mostly tamarisk, cottonwoods, wi I lows, and grass.

17. Continuous records of the Arkansas River flows at Las Animas
began in May 1939 when the stream gage was instal led on the left bank

(I) Cubic feet per second.

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