FLOOD11751

• County: Statewide
• Basin: Statewide
• Title: Floods in Colorado
• Date: 1/1/1948
• Floodplain - Doc Type: Educational/Technical/Reference Information

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In the southwestern part of the State the severest floods, and the
only ones of record, have resulted from the storms of September 1909
and October 1911. Precipitation during melting snow in June has
been insufficient to cause floods as severe, except during June 1927
when the resulting flood on the Animas River was more severe than
that during September 1909.
In the North Platte River Basin the slight precipitation is not suffi.
cient to cause floods. This basin includes North Park, a high, level
area surrounded by mountain ranges, except lit the lower end where
rolling hills dis.place the mountains.
The Green Ri\Ter Basin in Colorado, in the northwestern part of the
State, lies on the western slope of the Continental Divide, and is made
up of rolling hills and some comparatively level country. The Yampa
and White Rivers are the principal tributaries of the Green River.
Here, as in the North Platte Ri vel' Basin, the precipitation is insuffi-
cient to cause floods. The greatest flood of record in this part of
Colorado was that of 1884, which was caused by rain at the time the
very heavy snow cover was melting.

9

OF MEASURING FLOODS

METHODS

.

MEASURIXG FLOODS

For most of the earlier floods it has not been possible to estimate
the actual discharge; the facilities and technique for making such
estimates either had not been developed at the time these floods
occurred or were not available for application.
Most of the later floods described have either been of such short
duration as to make measurement of them impossible, or if of longer
duration, as on the larger streams, they ha\-e destroyed the approaches
to bridges and other means whereby they might have been measured.
Few dams exist suitable for use as weirs in computing flood discharges,
and the same is true Of bridges suitable for use in computing the dis-
charge by the contracted-opening method. Discharges for the major
floods of longer duration that have occurred since the establishment
of gaging sta.tions have usually been estimated from the extension of
the rating curves. However, some of these floods reached stages so
far abo.ve stages of current-meter measurements that it \vas necessary
to obtain slope-area measurements of the peak discharges in order to
extend the rating curves. This was particularly true of the Arkansas
River flood of June 1921, which overflowed large areas.
The only means by which most peak discharges could be measured
for most of the floods described in this paper was by the slope-area.
method, which has been in use in Colorado since the early nineties.
The procedure generally followed is to visit the stream soon after the
flood, while the high-water marks are still, visible; and select a straight,
uniform reach as long as possible, up ~o 1,000 fect on the larger streams:

METHODS OF

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