Mannings n-value Vertical Variation and Interpolated Sections

[STAndrzejewski]

I’ve been tasked to convert an old 1994 DAMBRK dam breach model to an unsteady-state HEC-RAS analysis. This necessitates I use several HEC-RAS capabilities I don’t typically utilize which are causing me some issues. I can use work-arounds for these issues but still would like to know what is causing these problems.

The DAMBRK model uses a vertical variation in n-values and incorporates interpolated cross sections. For the various elevations, the n-values are constant for the entire width of the section. When I try to interpolate sections in HEC-RAS I get the following error:

I can’t find any documentation of such but wondering if HEC-RAS can’t handle interpolated cross sections with a vertical variation in n-values??? When I run a state-state model without the interpolated sections, the analysis runs successfully and the resulting n-values appear to be correct.

Thanks

[Lonnie A]

Its probably a problem with the conversion. If you open the interpolated xs editor and look under options you can edit (or add) vertical n values.

[Anonymous]

Thank you for your response. However, I’m not seeing any “options” tab within the XS interpolation screen so I think the “options” tab you are referring to is under the cross section editor screen. The problem with that is that I can’t get RAS to interpolate any sections as long as there is a vertical variation in n-values. The interpolation seems to work as long as I utilize the conventional LOB/Ch/ROB definition of n-values or a horizontal variation.

[Author]

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