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Equivalent Manning Constant

Equivalent Manning Constant. in which subscript refers to values of wetted perimeter and Manning constant for the th sub area [Horton, 1933]. Compound Channel Cross Section.

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Equivalent Manning Constant

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  1. Equivalent Manning Constant • in which subscript refers to values of wetted perimeter and Manning constant for the th sub area [Horton, 1933]

  2. Compound Channel Cross Section • A compound cross section may be defined as a section in which various sub areas have different flow properties (surface roughness). • Roughness of the overbanks is usually higher than that of the main channel (natural streams), therefore the flow velocity in the main channel is higher than that in the overbank flow. • We drive expressions for the energy coefficient, , and for in terms of the conveyance factor, , of the sub areas. (Chaudhry, 2008)

  3. Compound Channel Cross Section (2) • The conveyance of a channel section is: , where . When Manning formula is used

  4. Example • For a depth of 5 m in the symmetrical compound section shown in Figure 4.10, determine: • Equivalent • Velocity-head coefficient, • Slope of the energy grade line, Assume the floodplains and the main channel have the same bottom slope of 0.001, and Manning for the main channel and for the floodplain are 0.021 and 0.039 respectively.

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