Roughness Type

Question

Hi 
 How manning's n can change over flow or depth (according to Roughness Type). Does Roughness-Flow Curve mean changing Material over depth?

Sushma Choure · Answer

Hello Hoshi, 
 Which software are you using? What you are you modeling here? Please provide some details, so that we can help you with your query. 
 Please see related post from Flowmaster, which might help you, if not please elaborate. 
 Flowmaster: Varying Manning's n with flow depth

Yashodhan Joshi · Answer

Hello Hoshi, 
 Manning's n also known as Manning's roughness coefficient corresponds to the roughness coefficient of any material. This roughness coefficient depends on the type of material. Hence different materials have different roughness coefficients. The roughness coefficient is not dependent on flow or depth. Thus when a Roughness vs Flow curve is plotted the change in roughness is due to material only.

Jesse Dringoli · Answer

I assume you're referring to SewerGEMS or CivilStorm. 
 The "Roughness-Flow" Roughness Type is useful when describing a conduit or channel whose roughness changes with flow. This could occur for example in a natural channel, in which higher flows reach sections of the channel that have a different roughness (grassy vs. sandy/rocky, etc) and thus the overall effective roughness coefficient changes. If you instead know how the overall Mannings n changes with flow depth, use the "Roughness Depth" Roughness Type instead. 
 When modeling an Irregular Channel, you also have the option to define changes in roughness using the Bank Channel Roughness Type . With this selected, the Irregular Channel section editor allows you to enter the separate Mannings n beyond the bank stations. You would also choose the Channel Weighting Method (default is Pavlovski) which is used to determine the overall Mannings n as water flows beyond the banks. 
 I have updated the following wiki article with these details: 
 Defining conduit or channel roughness varying with depth or flow