FLOOD03643

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Hydraulics of Steep Gradient Streams
• Date: 6/8/1982
• Prepared For: State of Colorado
• Prepared By: Colorado Geological Survey
• Floodplain - Doc Type: Educational/Technical/Reference Information

Title (all caps) HYDRAULICS OF STEEP-GRADIENT STREAMS

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Centra I Reg ion
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pages ~
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5.

9

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8.

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35

Authors

Robert D. Jarrett

Descriptors Channels,

regime, Natural
Velocity head

Critical flow, Flow, Flow resistance,
streams, Open-channel flow, Roughness

Hydraulics, HydrolOQical ,
coefficient, Velocity distribution, I
,
,
,
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I

I dent i f iers

Colorado, Steep-gradient streams

Type or publ icaticn

Journal article - Journal of Hydraulics Division, ASCE

Al::stl"ac::

Existing guidelines for the evaluation of the channel roughness
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. 00
of steep-gradient streams (slope greater than 0.2 ~ere~l,t) have been
A

based on insufficient data. Many of these steep-gradient streams also

require additional hydraulic analysis. Onsite surveys and 75 measurements

of discharge were made on 21 steep-gradient streams for the purpose of

computing the Manning roughness coefficient, n, and to provide data on

the hydraulics of these streams. These data show that: (1) n varies

inversely with depth, (2) n varies directly with slope, (3) the vertical-
/
velocity distribution does not fit a logarithmic curve, and (4) streams

thought to be in the supercritical flow range were actually in the

subcritical range.

A simple and objective method was employed to develop an equation

for predicting the n of steep-gradient streams by ~sing multiple-regression

techniques and measurements of the slope and hydraulic radius. The

average standard error of estimate of the prediction equation was 28 percent

when tested with Colorado data. The equation was veriJied using other

data available for steep-gradient streams. Regime-flOW equations for

velocity and discharge also were developed.

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