FLOOD00051

• County: Pueblo
• Title: The Arkansas River Flood of June 3-5, 1921
• Date: 2/5/1996
• Prepared For: Pueblo County
• Floodplain - Doc Type: Flood Documentation Report

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THE FLOOD AT PV~BLO.

29

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This caused the peak flows from the near-by tributaries to reach
Pueblo at the same time as the peak' flows from the more distant
streams, producing the most favorable conditions possible for a flood
of great height. '.
It is impossible to dete1;'lIline accurately the total discharge at
Pueblo during the flood, owing to the great size of the area over':
flowed, the breaks in the levee, and the scour in the main channel
caused by the flood. The discharge up to the time the levees ,vere
overtopped and broke, about 9 p. m. June 3, can be determined satis-
factorily, as a fair rating curve for the State gage is ayailable. For
the remainder of the period only a rough estimate can be made. The
peak flow at the maximum stage of 24.66 feet was 103,000 second-
feet. (See p. 20.) To determine the discharge at the time the levees'
were overtopped it was assumed that of the total Scour of 1.4 feet
noted after the flood, about.0.5 foot had occurred at that time, and
the flow through the breaks in the levees was estimated to be 10,000
second-feet. Although this estimate may be as much as 100 per cent
in error the effect of such an error on the entire discharge would be
very small. '
As eXplained on page 24, the levees were built to protect the city
against a flood flow of 40,000 second-feet, ,vhich would reach a gage
height of 18.1 feet. The additional flow permitted by the scour of
0.5 foot, however, would give a discharge of 40,000 second-feet at
gage height 17.6 feet. Adding the 10,000 feet that escaped through
the breaks would give a flow of 50,000 second-feet at gage height
17.6 feet. From this figure and the maximum discharge at 24.66 feet
(103,000 second-feet) an approximate rating curve was plotted for
use between 9 p. m. and midnight. .
As the river fell the scouring action continued until at the time the,'
river was once more within its channel the gage height was 0.9 foot
lower for the same discharge than it was when the break had just:
occurred.
The lower part of the rating CUrve was defined by a measure-,
ment made by the State engineer's office at a stage of 5.6 feet, showing
a discharge of 6,270 second-feet. By app{ying the above-described
rating curve to the hydrograph the total discharge from 8 a. m. June
2, at the time the river first started to rise, until midnight of June 5,
after the flood had passed, was found to be 145,000 acre-feet. Of this
amount 90,000 acre-feet was the total flow from noon of June 3 to
midnight of June 4.
It was impossible to determine the total dischnrO'P of t,},,, hihntn,..".

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