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Re: Calculation of overbank losses
The n values are used at a cross section to compute an "instantaneous" friction slope. While doing backwater (or forewater) computations for subcritical (or supercritical) flow, the instantaneous friction slope is averaged (using one of the friction slope methods) with the friction slope of the upstream (or downstream) cross section to compute a friction loss.
So one way of thinking of it is that the n-values at a cross section extend halfway to the next downstream cross section and halfway to the next one upstream.
If you haven't already, browse through the hydraulic user's manual available under Help (or download from HEC's web site if the manual wasn't installed).
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