[Eric R]

Information like this really helps.
I understand that other users with particular problems, especially those not covered by the manual, should be encouraged to post their experiences in this forum. It would be very beneficial for everyone.

Chris, we’re all waiting for the forum search bar to work properly again, so that information like this doesn’t get lost!

[Eric R]

Maybe it’s possible to do it in Raster Calculator (I’m not sure), but you’ll need to do some code.

[Eric R]

I don’t know if this can help, but in RAS Mapper, in the 2D Flow Area Editor there is a “Spatially Varied Mannin’s on Faces”, which produces variation in the Manning coefficient according to different depths.

[Eric R]

Excellent question, Atkinson.

I understand that the normal depth is calculated considering the cross section covered by the boundary condition line.
Therefore, I understand that for this boundary condition the magnitude of the line has an impact on the local water depth results (at least local, since far enough upstream this may have little or no impact). Also note that the size of the cells embedded in the boundary condition line impacts the accuracy of the calculation.

On the other hand, if you had a discharge curve instead of the normal depth as a boundary condition, the local levels should not be impacted, but the flow approach conditions should be, since not incorporating the flood area can cause unrealistic contractions in flow, although water levels may be adequate.

It is also important to keep in mind the distance between the downstream boundary condition and the areas under study. If this distance is quite large, the boundary conditions may not significantly impact your analysis.

Finally, I would say that the downstream boundary condition can impact your study area more or less depending on the simulated hydrograph, the bottom slope etc., since all this impact in the general flow conditions. Abrupt hydrographs may suffer greater distortion than gradual hydrographs, e.g.

After all this, one might ask: why not make the boundary condition line a little larger than is really necessary? Assuming that there are no local obstructions near the flow exit, this may be an aspect to be considered.

Hope this helps.

[Eric R]

Try a newer or older version of HR.

[Eric R]

Do you mean that each cell in your model has an average dimension of 10397 ft?

• This reply was modified 11 months ago by Eric R.

[Eric R]

What is the average cell size of your model?

[Eric R]

Bill, Have you tried creating this geometry first in RAS Mapper and then populating it in the geometry editor?

[Eric R]

Is there a HEC-RAS group on reddit? Can you put the link here?

[Eric R]

I noticed that the links embedded in my text have lost their validity.
Updated links are available below:
Image 1: 1drv.ms/i/s!AvUqFufoHL4N9VnW3DVAxi82IOdQ?e=37Qxwj
Image 2: 1drv.ms/i/s!AvUqFufoHL4N9Vj-n-vKV6puEoEi?e=lWiHqH

[Eric R]

Perhaps an error occurred while importing the land cover. The program simply doesn’t seem to have found the file.
Alternatively, you can try to import it again in a newer version of Hec-Ras.
Another aspect to note: the sub-areas of your land cover cannot have the same names (at least in my experience, this usually returns an error). But I don’t know if it applies to your case.

• This reply was modified 1 year ago by Eric R.

[Eric R]

Have you checked if this problem occurs equally in newer versions?

[Eric R]

Sometimes, reducing the mesh excessively makes the solution even more unstable. Try increasing the dimensions of local cells.

[Eric R]

This error, it seems to me, may be associated with different coverages between the land cover and the polygonal mesh. Make sure the land cover is not smaller than the 2D polygonal one (sometimes, a small area causes this error). I’m not sure, but check this initially.

Also, check the “Manage geometry associations” tab in ras-mapper.

[Eric R]

I’m not sure, but have you seen this video?

youtube.com/watch?v=fnJrZVRwCks&ab_channel=StanfordGibson

Maybe it can help.

[Author]

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