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<br /> <br />PLAN VIEW <br /> <br /> <br />PROFILE VIEW <br />Figure 2. Open,channel flow reach in plan and profile views (modified from Dalrymple and Benson, 1967, fig, 1), <br /> <br />I'1hv = upstream velocity head minus the <br />downstream velocity head, in feet; <br /> <br />k( Mv) = energy loss due to acceleration of <br />velocity in a contracting reach, or <br />deceleration of velocity in an expanding <br />reach, in feet; and <br /> <br />k coefficient assumed to be equal to 0 for <br />contracting reaches, and 0.5 for <br />expanding reaches (Barnes, 1967), <br /> <br />where <br /> <br />a = velocity, head coefficient; and <br />g = acceleration due to gravity, in feet per <br />second per second, <br /> <br />In computing the values of n using this method, <br />the value of IX is always considered to be 1.00, This <br /> <br />requirement limits verification computations to unit <br />channels that do not reqnire segmenting or subdividing <br />(Jarrett and Petsch, 1985), Although IX can be much <br />larger than 1.00 in natural channels (Jarrett, 1985), any <br />resulting error in the computation of n is assumed to be <br />minimal because the effect of IX actually depends on <br />the relative difference between the velocity,head <br />coefficients from upstream and downstream cross <br />sections rather than their actual magnitudes (Coon, <br />1995), <br />The friction slope, Sf' to be used in Manning's <br />equation is defined as: <br /> <br />h <br />Sf = L = <br /> <br />L1h + L1hv - k (L1h) <br />L <br /> <br />(5) <br /> <br />where <br /> <br />6 Verification of Roughness Coefficients for Selected Natural and Constructed Stream Channels in Arizona <br />