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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from 12,000 to 14,000 feet above MSL. The South Arkansas River main stern
flows eastward from the Monarch Pass area to Poncha Springs where it meets
Poncha Creek. Poncha Creek drains the southeastern portion of the basin
from the Marshall Pass and Poncha Pass areas.

The South Arkansas River and Poncha Creek basins comprise the southern
A k River Valley in Chaffee and Lake Counties.
portion of,the Upper r ansas
The valley occupies a narrow and long trough that was formed mainly by fault-
ing. The main topographic features of this valley are the two great parallel
north-south mountain ranges that border the valley, the Sawatch Range on the
west and the Mosquito Range on the east, The Mosquito R~nge merges with a
low range of hills along the southern portion of the valley. The larger
tributaries of the Arkansas River, including the South Arkansas River, origin-
ate in the Sawatch Range.
Vegetation varies considerably according to elevation in the basin, Vege-
tation below the 8000 feet elevation consists of semi-arid growth such as pinon
. ., d e w1th spar"e grass ground cover. Increased precipita-
p1ne, ]Un1per, an sag' "
tion supports dense pine and aspen forests above this elevation to timberline.
Rock outcrops and tundra grasses predominate on the high mountain peaks where
climatic conditions are too severe for forest growth.

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mile upstream from its mouth, recorded flows during the 1912-1917 period.

The remaining two stations were located on the South Arkansas River main

stem; one near Panch a Springs recording flows during the years 1911-1917

and 1971-1973; and one near Salida recording flows during the years 1922-

1923, 1929-1940, and 1971-1976, Streamflow records from gaging stations

in hydrologically similar watersheds north of the study area are available

and were used in the hydrologic analysis portion of this study.

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A basin map depicting the drainage basin and the location of the gaging
stations is presented on Plate-I.

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Characteristics of Different Reaches

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The study reach for the South Arkansas River is shown on the Index Map

(Plate-2). The reach begins at the confluence with the Arkansas River and

extends upstream approximately 5.4 miles.

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The South Arkansas River study reach has a defined channel with channel

banks ranging from flat to steep slopes. The river reach meanders through

the alluvial materials deposited by the streams and suggests a shift of the

river bed in the past in certain areas.

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A number of irrigation ditches; such as the North Fork Ditch, Cameron

Ditch, and the Missouri Park Ditch; convey water across natural drainage

boundaries into adjacent basins, The Larkspur Ditch conveys water from the

headwaters of the Tomichi Creek drainage basin in the Colorado River basin

across the Continental Divide at Marshall Pass and into the Poncha Creek

basin. Othe~ small irrigation ditches which do not divert water from the

basin are labeled on the flooded area plates.

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The area adjacent to both sides of the stream channel is comprised of

alluvial fans formed by the meandering river and is nearly level to gently

sloping. It consists of gravel and sand bars and of wet, stratified, medium

textured to coarse textured soil materials. Next to the alluvial fans and

on both 'sides of the stream, the soils consist primarily of moderately coarse

textured alluvium ranging in slope from 1 to 3 percent. This soil is on

long narrow bottoms along the main river and is used primarily for irrigated

meadows. Further away from the stream, on the north side, the soils consist

of somewhat excessively drained soils on terraces and terrace edges, These

soils are very shallow over cobbles, gravel, and sand. Most of this land is

used for grazing with a small percentage used for irrigated hay. Further

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Except for a water-stage recorder at Marshall Pass which records trans-

mountain diversions via the Larkspur Ditch, no streamflow gaging stations are

currently active in the South Arkansas River drainage basin. The historical

streamflow records show that three stations have recorded flows in the study

area in the past years. The first station, located on Poncha Creek one-quarter

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