Question about U.S.F.example in HEC-RAS 4 Beta

[chicopee]

I am still learning this program eventhough I had to put it on the side for a while. The Unsteady State example: Multiple Reach Data Set incorporates a table of the Manning's n/k values under Geometric Data. Why is it that some stations have only one set of values and other stations have multiple sets?

 

[SMIAH]

This is specified in Geometric Data/Cross Section Data/Option Horizontal Variation in n Values or Vertical.

Might be wrong but this is often done to "fit" with measured data.

 

[SMIAH]

BTW you should download HEC RAS 4.0 (not Beta).
I had some issues with the Beta version with Unsteady flow.

 

[froude]

SMIAH,

You're quite correct in your reasoning. Horizontal Variation in N Values is used to more accurately represent the change in Manning's roughness along a cross-section; particularly in longer cross-sections where the land cover abruptly changes.

 

[chicopee]

I agree with the reasoning that the "n/k" represent variations along a cross section and these values are properly presented when developing these cross sections but the table mentioned above does not jive with the info. presented in the X-S's.