FLOOD01776

• County: Pueblo
• Community: Pueblo
• Stream Name: Pueblo Reservoir
• Title: Pueblo Reservoir 1993 Sedimentation Survey
• Date: 5/1/1994
• Prepared For: State of Colorado
• Prepared By: BOR
• Floodplain - Doc Type: Educational/Technical/Reference Information

sediment inflow. The estimated sediment contributing area is the total drainage area minus
the contributing drainage areas above the dams located in the drainage area above Pueblo
Reservoir.

At the beginning of reservoir storage in January 1974, Pueblo Reservoir had a calculated
surface area of 5,671 acres and a capacity of 357,821 acre-feet at spillway crest elevation
4898.7. "

SUMMARY AND CONCLUSIONS

This report presents the results of an investigation to monitor changes caused by sediment
accumulations in Pueblo Reservoir after 19.3 years of reservoir operations. The report also
describes the surveying procedures and equipment used in the 1993 investigation and
provides data for future survey use. The primary purpose of the 1993 survey was the
collection of data to compute the area-capacity relationships for operation of Pueblo Reservoir.

Table 1 contains a summary of reservoir sediment data for the 1993 survey. The 1993 survey
determined that the reservoir has a storage capacity of 349,940 acre-feet and a surface area
of 5,671 acres at spillway crest elevation 4,898.7. Since closure in January 1974, the
reservoir has accumulated a volume of 8,181 acre-feet of sediment below elevation 4,898.7.
This volume represents a 2.28-percent loss in total capacity and an average annual loss of
423.9 acre-feet for the operating period of January 1974 through May 1993.

DESCRIPTION OF BASIN

The Arkansas River originates in central Colorado and flows in a southerly direction to above
Salida, Colorado, and then eastward to Pueblo Reservoir. The mean annual runoff of the
drainage basin above Pueblo Reservoir prior to its construction was 511,800 acre-feet. The
runoff was calculated using the 80-year average flow at the USGS (U.S. Geological Survey)
gauge Arkansas River near Pueblo, Colorado, which was located about 5 miles downstream
from the dam location. The total drainage area above Pueblo Dam is 4,669 square miles, and
the net sediment contributing area is estimated to be 4,170 square miles. The net
contributing area includes removal of areas above the upstream developed reservoirs that are
assumed to trap all sediment inflow. The upper Arkansas River is a steep mountain stream,
and the basin has about 25 mountain peaks above 14,000 feet. The river emerges from the
mountainous area through the Royal Gorge, where the valley gradually gets wider through
the foothills to the plains around Pueblo.

The vegetative cover in the basin above Pueblo is widely diversified because of the wide range
of annual precipitation. The highest mountain peaks are above timberline and are devoid
of cover. In the timber areas, conifers, aspens, brush, and grasses are found. In the
woodland zone, pinon, juniper, scrub oak, sagebrush, and scattered growths of bunch grass
predominate. In the plains region, vegetation consists mainly of grasses, shrubs, and
occasional cactuses. The only trees in the plains region are cottonwood, willow, tamarisk, and
associated deciduous trees that fringe the water courses and irrigation ditches.

Wide variations of climate occur in the Arkansas Basin. In the mountainous regions, the
precipitation varies widely over relatively short distances. Much of the total precipitation
occurs in the form of snow. In the plains, most of the precipitation is from rainfall, which at
times occurs in the form of violent cloudbursts, producing small volumes but causing short-

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