2D model – variation in manning’s n across cell face in v6.2

[Alison Lackie]

Has anyone worked with a model utilizing this feature? I am updating/revising an existing 2D model that was previously using V6.1. We are now using V6.2; but I noticed that the mannings n vs elevation property tables still shows a constant value for each cell face, even when it crosses a boundary of ‘n’ values.

I dug into the manual a bit and I found a note indicating that horizontal variation in ‘n’ can only be utilized if a model has a land cover data set. In this case there were land cover ‘classification polygons that were used to assign mannings n values, so I am assuming that is the reason this feature is not functioning in my model. I am somewhat of a newbie Hec Ras 2D user, so if anyone is more familiar and can confirm (or correct) my understanding I’d be very interested!

Thanks

[Lonnie A]

Alison, You have to select the option to use horizontal 2D n-value for it to apply. There is a check box is in the geometry editor’s 2D editor, lower left corner. It took me a fair amount of time to locate it as the manual doesn’t give any real insight on it….to their defense it’s still called a “beta”. I have yet to be able to back calculate how they are applying it as the cell face resulting n-value isn’t exactly as I’d of expected it to appear. It looks more vertically varied based on how they present the results.

[alister.hood]

Does anybody have any tips for getting this option to actually work?
I’ve tried to use it on a couple of models and it causes this error:

Writing Geometry…
Computing 2D Flow Area ‘Perimeter 1’ tables: Property tables do not exist.
Error completing geometry for computations:
Index was outside the bounds of the array.
Geometry Writer Failed
Error Processing Geometry

• This reply was modified 2 years, 7 months ago by alister.hood.

[Lonnie A]

Alister, do you have a land classification file associated with the geometry. I’ve not had the error when I’ve ran it.

[alister.hood]

Sorry, I was thinking I would get notified of a reply.
Yes, I had a land classification associated.
I have subsequently been able to run a model with this option, so I’m not sure what was previously causing my problem. I do wonder if I needed to manually run “compute property tables”.

• This reply was modified 2 years, 6 months ago by alister.hood.

[Author]

Posts