Unsteady Model Stabilization using Royghness-Flow Factors

[thod]

I have a model with very steep slopes that gets dry at low flows. Is it ok to use flow-roughness factors for low flows?

[Anonymous]

Yes. Definitely. Other techniques include more base flow and pilot channels. But I think you are right to do flow roughness factors. You might check Jarretts equation to see what n vales to use.

[thod]

Thanks! I found your post about Jarrett’s equation
http://hecrasmodel.blogspot.gr/2009/12/n-values-in-steep-streams.html
The 0.47 coefficient is a little bit different in https://www.fhwa.dot.gov/engineering/hydraulics/pubs/07033/6.cfm
Equation 6.3

N= K*Sf^(0.38)R^(-0.16)

where:

K = 0.32 for SI and 0.39 for CU units, respectively
Sf = the friction slope of the channel
R = hydraulic radius of the channel, m (ft)

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