FLOOD05613

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Rainfall-Runoff Data from Small Watersheds in Colorado June 1968 - September 1971
• Date: 1/1/1972
• Prepared For: State of Colorado
• Prepared By: CWCB
• Floodplain - Doc Type: Data ‎(general)‎

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A typical rain gage used in the study has a 5\-foot length of
3-inch standard galvanized iron pipe that is installed vertically.
A metal shelter is mounted on the top to house the recorder. A
rainfall collector is an integral part of the shelter lid. The
recorder is float driven and provides a record of the precipitation
in hundredths of an inch as reflected by changes of water levels in
the vertical pipe. Sufficient water is maintained in the pipe at all
times to assure that the float does not rest on the bottom of the pipe.

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A stage gage and rain gage are located at the outfall of each
study basin. The gages are inspected and serviced by personnel of the
U.S. Geological Survey at about 4-week intervals during the runoff
season.

Acknowledgments

Installation of rainfall-runoff stations throughout Colorado was
facilitated by the cooperation of municipal and county governments,
the Colorado Department of Highways, and numerous private individuals.

STAGE-DISCHARGE RELATIONS

The theoretical methods used to define stage-discharge relations
at stations operated for these investigations are the step-backwater
method, the culvert method, and formulas for standard and modified
flumes. Indirect determinations of actual peak discharges by the
slope-area method have also been used to supplement theoretical
procedures in defining stage-discharge relations. Runoff data
published herein represent the best theoretical evaluation of stage
versus discharge available at this time. As additional slope-area
and current-meter measurements are made, it may be necessary to
revise the stage-discharge relations and update the affected runoff
data.

Step-Backwater Method

The step-backwater method is used when the stage-discharge relation
is controlled by the resistance to flow in a reach of channel downstream
from the gage. The method, outlined by Anderson and Anderson (1964),
requires an analysis of the geometry of several cross sections downstream
from the gage, and estimates of the channel roughness within each reach
between the cross sections. Analysis of these factors and application
of the principle of conservation of energy results in a theoretical
stage-discharge relation at the gage.

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