FLOOD08336

• County: Chaffee
• Community: Poncha Springs, Salida
• Stream Name: South Arkansas River
• Basin: Arkansas
• Title: Floodplain Information Report - Lower South Arkansas River
• Date: 4/1/1979
• Prepared For: Chaffee County
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CHAPTER II

STUDY AREA DESCRIPTION

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Location

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The study area is located in the vicinity of the Town of Salida, Colo-

rado. The stream reach of the South Arkansas River which was studied begins

at the confluence with the Arkansas River at Salida and extends upstream to

a point just east of Poncha Springs. The upstream limit adjoins the previous-

ly published floodplain information report entitled, "South Arkansas/Poncha

Creek." This floodplain information report includes approximately 5,4 miles

of the South Arkansas River located in Sections 4, 5, and 6 of Township 49

North, Range 9 East and in Sections 1, 10, 11, and 12 of Township 49 North,

Range 8 East. A map of the study reach and surrounding area is shown on Plate-I.

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Climate

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The climate of the study area is influenced by the westerly winds coming

over the mountains. It is also influenced by less frequent but important mois-

ture bearing winds from the east during the sUmmer months. These climatic

features are typical of a mountain valley on an eastern slope near the central

portion of a large continent. They include low precipitation, low humidity,

abundant sunshine, a wide daily temperature range, and generally low winds.

The surrounding mountains act as a barrier preventing the northern cold air

or eastern storms from penetrating the Upper Arkansas River valley.

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The records at the Salida weather station, elevation 7060 feet, show an

average annual precipitation of 10.87 inches. Precipitation varies at Salida

from less than 8 inches in one year out of six to over 15 inches in one year

out of six. The highest recorded annual precipitation was 17.92 inches in

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1961. This was followed by the lowest annual precipitation on record, 4.91

inches 1n 1962. The monthly distribution of precipitation varies consider-

ably from one year to the next. Dry months (less than one-quarter inch of

precipitation) are rare for April, July and August. Wet months (more than

2 inches precipitation) occur about one in four years in July, one in five

years in April and August. Summer thunderstorms account for almost 59 per-

cent of the annual precipitation, and account for local high flows. Hail

falls occasionally in the study area.

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Summers are cool in the study area with temperatures reaching into the

90's a few times each summer. A maximum temperature of 1000 F was recorded

in August 1902. Temperatures for the sUmmer nights usually drop below 500 F.

Winter temperatures, particularly in the daytime, are usually warmer than those

found at similar or lower elevations. Periods of extreme cold temperatures

are of short duration. The lowest temperature recorded at Salida was 300 F

below zero in January 1919. The average annual temperature is 46.50 F, and

the average summer temperature is 62,60 F. The average frost free period is

approximately 107 days.

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Because of the climatic conditions, the irrigated land in the vicinity

of the study area is in meadows, native hay, and alfalfa. The area is better

adapted to livestock production as compared with farming. Dryland farming is

almost nonexistent in the upper reaches of the Arkansas River basin.

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Drainage Basins

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The South Arkansas River drains approximately 196 square miles at the
upstream study limit. Several small tributaries which enter the river between
Poncha Springs and Salida increase the total drainage area to 210 square miles
at the river mouth.

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The elevation of the South Arkansas River confluence with the Arkansas

River is 6985 feet above mean sea level (MSL). The headwaters of the river

originate at the Continental Divide among mountain peaks ranging in elevation

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