Manning's n under Bridge

[ShwethaP]

In a backwater computation for subcritical conditions in HEC RAS, under a bridge, which of the two section's manning's n values are applied; downstream section or the upstream section?

Please indicate the correct ans, Thanks!

[M_Brooks]

Your mannings coefficients for the internal sections of the bridge are taken from both the upstream and downstream cross sections.

However you can go into your internal bridge sections and alter it if your n value within the bridge do not correlate with those directly upstream and downstream.

[ShwethaP]

Thanks so much, but how can I chage the coeeficients for the internal sections

[M_Brooks]

Go into Geometry

Bridge and Culvert Data

than within the Options pull down bar there is "Internal Bridge Cross Sections" about half way down, click that and you can alter your internal bridge cross section data.

[ShwethaP]

Thanks Brooks!
Appreciate your help.