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

4. The equations should not be used for reaches of stream affected
by backwater from downstream obstructions.

5. The hydraul ic radius does not include the wetted perimeter of

the bed particles.
6. These equations are applicable to streams having relatively

clear water and low suspended sediment.

n = 0.39(0.02)0.38 (7)-0.16 = 0.065

APPLICATION OF THE PREDICTION AND REGIME EQUATIONS

An example of the appl ication of equations 10, 11, and 12 to a
single depth of flow in a steep-gradient stream is as follows: The
reach under study has the following hydraulic properties at one repre-
sentative c~oss section obtained from a transit-stadia survey. The

-channel is straight, high-banked, and trapezoidal in shape, and contains

boulder-size bed material. Cross-section subdivision is not required.

No additional factors affect roughness, so that nT is equal to n. The

cross-sectional area is 1 ,000 ~quare ft (92.9 square meters), the slope

of the water surface for the reach at the time of the survey was 0.02,

and the hydraulic radius was computed to be 7 ft (2.1 1m). Assuming

uniform flow at the section and using equation 10 to solve for Manning's

n, the value obtained is:

The solution is also shown graphically in figure 5.

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