[cameron]

first off, the error you have for that cell is small and I would not worry about it. depending on what the study is for, it may be ok to have values up to 1. Lowering the timestep is one of the easiest ways to help with convergence otherwise you would need to adjust iterations or adjust grid cells. A restart file/initial conditions may be helpful depending on when the error occurs in the simulation (at the beginning or when flow first enters a cell).

[cameron]

You cannot have edit flow inside of a 2D model currently. Bank layers are something that HEC-RAS generates based on your bank station in a 1D model. If you are not modeling the tributary in 1D, there is no reason to have this layer. If you are referring to flowpath lines, than you would only need them if you had a 1D model as the flowpath lines determine the reach lengths.

[cameron]

Page 4-9 of the 2D manual discusses.

Bascially 1 and 4 values are converging and 2 and 3 are diverging solutions.

[cameron]

The meshing options in HEC-RAS 2D do need some new tools to make it easier to refine in certain areas. The SMS software is adding HEC-RAS 2D mesh generation and should help create some better refined meshes until HEC is able to add better tools.

As you point out, there are some things that happen near boundary conditions and is why best practice is to move the boundaries far away from areas that you care about for either 1D or 2D models. It is important to note that the boundary is treated as a 1D cross-section as it is determining what water surface elevation it calculates based on the discharge and energy slope you use at the boundary. You can select the boundary condition line and see what cross-section shape it is using. If the cross-section it is using is not able to get a 1D solution easily, then you will get odd results. If the cross-section would give bad results in a 1D model, then it may not give the best answer for the 2D model.

Just remember that each grid cell gets one water surface elevation and treats each grid cell as a small storage area. This causes problems for mapping floodplains in very steep areas which require a lot of refinement.

[cameron]

The file name looked like it had two periods in it.

[cameron]

Unsteady is totally different than Steady modeling. Did you set the Htab parameters correctly, choose the correct computational interval, are the ineffectives correct for low flows? From the figure, it looks like the culvert length is far longer than the width of the road, is this correct?

[cameron]

This can be done. I have done this many times in HEC-RAS. The document below has some information on dam breach modeling in HEC-RAS.

http://www.hec.usace.army.mil/publications/TrainingDocuments/TD-39.pdf

[cameron]

does the terrain file have two decimals in it?

[cameron]

I don’t see why the rules boundary condition would not work inside of 2D unless it is not enabled yet. Is this a model you could share to see if it is set up correctly? You could try a simple test case to see if breaking it up into two different 2D areas fixes it or two 2D areas connected to 1D areas.

[cameron]

This is not possible inside of HEC-RAS. You could do some raster calcs in GIS to come up with the Courant or Froude based on the output rasters or if you could take the output from the hdf file directly.

[cameron]

Yes you can export the depth to a raster (tif format) and display it in GIS. The user’s manual explains how to do this.

What type of web imagery are you trying to open? Are you using a standard projection file or something else?

[cameron]

Did you look at the table outputs? My guess is the depth is very shallow. Since each cell face is a cross-section, any low spots will allow water to flow into the next cell.

You are correct that the best way to fix the issue for item 2 is to reduce the cell size in this area. You could add some breaklines or do it manually by adding points. There is also other software (SMS as one) that help generate the mesh. The render options don’t change the results and is only for display inside of HEC-RAS.

[cameron]

Three boundary conditions should not be a problem. How are the overbanks modeled? Is this a 1D, 2D or 1D/2D model?

[cameron]

This is not possible with the current version of HEC-RAS. This will be added in a future version.

[cameron]

It is not appropriate to extend a lateral structure passed a bridge crossing. The lateral structure should be broken up into two, one for upstream and one for downstream.

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