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<br />The friction loss Hf' is the energy required to overcome the rough- <br />ness of the cu1.vert barrel.. Hf' can be expressed in several. ways. Since <br />most highway engineers are familiar with Manning's n the fo1.10wing ex- <br />pression is used: <br /> <br />[29n2 LJ <br />lit = If.33 <br /> <br />y2 <br />2g <br /> <br />where <br /> <br />n = Manning's friction factor (see nomographs and page 5-30 <br />for vaJ.ues) <br />L = length of' cu1.vert barrel (f't.) <br />y = mean ve1.ocity of' flow in cu1.vert barrel (n./sec.) <br />g = acceleration of gravity, 32.2 (f't./sec.2) <br />R = hydrau1.ic radius or !:.... (ft.) <br />WP <br /> <br />where <br /> <br />A = area of' flow f'or fU1.1. cross-section (sq. ft.) <br />WP = wetted perimeter (ft.) <br /> <br />Substi tuting in equation 1. and simplifying, we get for full flow <br /> <br />H = [1 + ke + :~~3L] ~ <br /> <br />(2) <br /> <br /> <br />- - - - ~ttf:!iG.r. !J!::K <br />- ..1fr.DRAU~GRADE...llNC <br /> <br />He1t <br />, <br />Hf H <br />- -= - -'tHd "LYLS. <br />12 DATUM <br /> <br />~ <br /> <br />LSo <br /> <br />Figure 3 <br /> <br />5-6 <br /> <br />e <br /> <br />;; <br /> <br />e <br /> <br />. <br /> <br />e <br />