Floodplain Roughness
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I was wondering if you could clear up some confusion for me. I have been under the impression for some time that the floodplain roughness cannot be reduced below 0.1 for shallow flow conditions, regardless of the AMANN setting. But some new info circulating in our office suggests that setting AMANN to -0.99 and SHALLOWN to 0.00 will cause the model to use ONLY the roughness values in FPLAIN.DAT (i.e., no adjustment at all). Can you confirm? Thanks!
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Yes, if you don't want the n-values to adjust at all then set AMANN = -99 and SHALLOWN = 0.00. That will turn off any n-value adjustment and depth variable roughness due to shallow flow. It doesn't matter if SHALLOWN is set to 0.00. That's just what we do. You have to set AMANN = -99.
If you want to globally adjust the n-values use AMANN with the following conditions.
AMANN = - 0.4 to +0.4; These values cause the n-values in fplain.dat to increase or decrease by subtracting or adding the AMANN value to each n-value.
AMANN is greater than 1.0; These values cause the n-values in fplain.dat to increase by multiplying each n-value by AMANN.
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