FLOOD09224

• County: Statewide
• Basin: Statewide
• Title: Steep Channel Water Surface Profiles
• Date: 7/1/1971
• Prepared By: CSU
• Floodplain - Doc Type: Educational/Technical/Reference Information

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The form of this equation is analogous to the wier equation,

Q = CLH1.5. Conditions of application are also similar, as flow is
in a rapidly varying state. Equation (3-1) is proposed to be used
for finding the water surface elevation at any section where an energy
balance with the previous section could not be attained within
tolerable limits. This control section computation mechanism will
thus account for problems of shifts of control sections with changing

discharges. The equation should provide a fairly accurate solution

of water surface elevation at any control section in a natural channel,

if the section coefficient and hydraulic exponent can be adequately

defined. A long reach of stream with a sustained supercritical flow

could cause significant error. Such a condition is not covered by

the present scheme because, as mentioned previously, long sustained

reaches of rapid flow are hypothesized as not occurring in natural

stream flow. Such a condition can be solved by calculating downstream

from a section of critical flow. The photographs in Appendix E, and
earlier efforts at computation of water surface profiles assuming
sustained rapid flow in mountain streams, tend to support this hypothesis.

The main problem in application is to properly assign values of

the section coefficient C and hydraulic exponent m. In construction
s
of this program, it is assumed that these values remain relatively

constant throughout the length of the channel. The assumption should

be valid where all cross-sections are formed in the same type of

material and are subjected to the same set of constraints. This is

equivalent to stating that, given similar conditions of formation,
stream cross-sections will develop similar hydraulic characteristics.

Should the stream traverse areas where a different set of stream