May 24, 2024
Multiple Opening Analysis
Did you know that if you have a bridge opening and one or more culverts at a single river crossing a Multiple Opening Analysis is required?
Another Reason for Interpolated Cross Sections
Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.
Here’s a classic case for interpolation of cross sections in a RAS model.
Copyright © RASModel.com. 2010. All rights reserved.
Here’s a classic case for interpolation of cross sections in a RAS model.
Notice the drop in water surface to near critical depth at the grade break. Then, at the next cross section upstream of the break, RAS seems to overestimate the head loss. Sometimes this phenomenon can be much more dramatic, occasionally initiating oscillations upstream of the break that can lead to instabilities.
When scanning the results of your model run, or when trying to diagnose sources of instability, keep an eye out for this phenomenon. Interpolation of cross sections around this point will provide a much more accurate and stable answer. Notice in the figure below, that further interpolation upstream of the newly interpolated reach is probably warranted.
Comments
Taylor K
on October 28, 2020Chris,
I have been dealing with an almost identical scenario. I am doing 1D steady flows. The problem I now have is my WSE. I am mapping flood events, my cross sections upstream of the drop flood extensively, but the downstream cross sections do not flood at all. When in reality the water should flow across all of the cross sections to accurately show the extent of flooding. What do I need to adjust so the flood will be accurate both upstream and downstream of a steep drop?
Chris Goodell
on October 28, 2020If it’s a very steep drop and it’s not working with cross sections, you might consider modeling the drop with an inline structure instead. Also, if you’re having trouble seeing results from 1D cross sections in RAS Mapper, make sure your terrain is good in those areas not showing flow.
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