[Eric R]

I have never used external methods to resolve this. For my models and purposes, I have always found satisfactory results by decreasing the local grid (as suggested in the FEMA manual itself).
To me, determining the optimal cell size seems to require an iterative process, optimizing computational time with the desired level of result.
In some specific cases, you can perform auxiliary analyzes using a 1D model.
In your case, where it is a large watershed, I think that locally reducing the mesh can partially help, depending on the degree of cupping you are experiencing.

[Eric R]

I’m not sure (I’m not very familiar with unsteady 1D simulations), but it could be an initial conditions issue. My suggestion is that you check what the associated initial conditions are.

[Eric R]

I’ve had similar problems exporting C3D geometry to HEC-RAS. For me, I could only solve them by reinstalling C3D, without adding any updates.
But for me this only applied to a 1D geometry.
Although I solved the problem, I started building one-dimensional geometries (whenever possible) directly in HAS-Mapper, because it is much simpler.

[Eric R]

You need to keep in mind that HEC-RAS 2D computes the hydraulic parameters not only individually on each face (a single point per face), but performs computations inside each face, which allows using cells with larger faces without losing fidelity of the results. This feature of HEC-RAS is called “sub-grid hydraulic model”.

A general idea of this property is presented in this topic: << kleinschmidtgroup.com/ras-post/hec-ras-subgrid-bathymetry-theory-and-application >>

I recommend that you increase the size of your model’s cells, which may eventually eliminate the error you are facing and even improve the calculation time.

Hope this help.

[Eric R]

The option called “calculate” is no longer available in version 6.3.1. We now have the “Update Cross Sections” option, which does exactly the same thing.

[Eric R]

Couldn’t you use a rating curve?

[Eric R]

Problem solved. I was able to post by removing the http://www

• This reply was modified 1 year, 9 months ago by Eric R.

[Eric R]

Thank you, Jillian.
I’m trying to post the description of my problem in that same box available at the foot of the pages of this forum.
I believe that some problem may be occurring because I have added two external links that show images of what I have been experiencing. I don’t know what other problem could be occurring.

[Eric R]

Hi steven crisp.
It’s hard to assess and say what could be going on with your model. There are many possibilities.
Have you ever tried to build a new model from scratch, following all the usual recommendations for one-dimensional models?

[Eric R]

What version of HEC-RAS are you working on?

[Eric R]

Additionally, to crop the terrain you can use the idea put in this video: https://youtube.com/shorts/1GWINC3Txi8?feature=share

[Eric R]

Mikayla. Do you keep the satellite image layer on? This generally slows down the rasmapper. Also, wouldn’t you be able to work with a smaller terrain, limited to the area you will simulate? This can be done, for example, in QGIS. I am not referring to decreasing terrain accuracy, but to cropping the image so that it is limited to just the region of interest. Another aspect: are you working on an SSD or a conventional hard disk? Consider working on an SSD; this greatly speeds up the processing and reading time of data by HEC-RAS.
Hope these starter tips help you.

[Eric R]

This same error was happening for me. I solved it by changing the reference system in C3D from Sirgas 2000 to WGS 84.

• This reply was modified 1 year, 9 months ago by Eric R.

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