Normal Depth o Rating Cuve?

[Anonymous]

Hi all,
in HEC-RAS 2D with only 2D Area when suggest to use in output of 2D Flow Area the boundary condition Normal Depth and when Rating Curve? What are the “strenghts” of one condition and other?
Thank you

[ldguethle]

I have not had the opportunity/need to use a rating curve. However, generally you would use a downstream rating curve if:

– you have a control structure that either can not be modeled or you don’t want to model it
– normal depth is not matching up with a known, trusted rating curve at a cross-section (i.e., a USGS rating curve at a gage)

[Anonymous]

Thank you for answer.
But the downstream boundary conditions, have effect for all model or for the last part of it? In a model of 24 km with only 2D Area, what effect a bad choose to downstream boundary conditions?
Best Regards

[Anonymous]

If you have a rating curve, from a gage for instance, then it would generally be preferable to Normal Depth.

Normal Depth is what you use when you don’t have any other information.

You can check the sensitivity of the downstream boundary condition.

Use your best estimate of Normal Depth and run the model.

Increase the slope (maybe double it), run the model.

Decrease the slope (maybe by half), run the model.

Then look to see how much the results changed. Are the results different in the particular areas you are interested in? If they are, you may need to extend your model further downstream.

[Author]

Posts