[cameron]

You should follow the courant criteria for timestep. You should also think about using the full momentum equation if you are not. Not sure of the grid cell size you are using, but that may also have an impact.

[cameron]

It is a software issue. I think the limitation will persist unless HEC updates the program to handle more data.

The idea behind how HEC-RAS deals with the geometry is supposed to allow for bigger cells that give the same results as smaller. Which should mean that you should not need 2 million elements. Depending on what you are trying to accomplish this can be true, but for very detailed models this does not always workout.

[cameron]

You need to go into Mapper and assign a terrain to the 2D Mesh so it can calculate all of the 2D curves.

[cameron]

It would be considered a Storage Area Connection and you would need to go to View|Stage and Flow Hydrographs|Storage Area Connection and then the rating curve tab.

[cameron]

Have you thought of modeling the spillway in 2D? I have modeled spillway capacity before using different 2D models, but HEC-RAS should be able to do it as well if you make the grid cells small enough.

[cameron]

Yes there is a manual just for sediment transport which was in draft a few years ago when I was using it. I couldn’t find it by a simple google search so you may need to ask HEC directly.

[cameron]

There is a new sediment transport manual for HEC-RAS that explains some of the new features in HEC-RAS 5.0. I misplaced my copy and you would probably need to contact HEC to obtain the manual. You may also want to ask if you can beta test the next version as I believe they have fixed a few things with sediment transport sine the release of 5.0.3.

[cameron]

That would depend if they are using the inline structure feature in HEC-RAS or if they are modeling the inline structure as only cross-sections instead of the inline structure option.

[cameron]

You have two cross-sections that are super close together (reach length of 1), but if you open it in HEC-RAS, the extents are crazy and probably is the issue.

[cameron]

What is your time step and grid cell size? Are you using the full momentum or diffusion wave equation?

[cameron]

Why would there be multiple cross-sections across the inline structure? Do you have cross-section spacing very small?

[cameron]

You would have to delete the reach you don’t want from the geometry or allow a very small amount of water to flow in it so it does not crash.

[cameron]

could be your time step is too high or could be lots of other things hard to say based on just that error.

[cameron]

the cutline is what cross-section looks like in the plan view. If you delete points in an XS, you will want to trim the cutline down. The cutline is used for many things such as helping develop the water surface grids.

[cameron]

Based on the plot you provided, it appears that turning on all 8 at the same time is overkill until about hour 8. It also appears that your starting stage is above 0.4m which is when the pumps turn off. Have you tried a warm up period or a run where the pumps do not start out on? This is possibly why you are getting an error at the beginning of your run. Also it is probably not good for the pumps to be turning on, off, and back on again so quickly. That just tells me that you have too many pumps turned on or you have the wrong size of pumps.

When do the largest errors occur? Does it occur during the highest stages at the pump when all the pumps are running full (hour 8 to 14) or before and after? If it is before or after, it is not going to impact the max wse plot (if that is what you care about). If it is during the peak stage, that may impact the max wse which depending on the error may be ok.

It is very difficult to get a complex unsteady model that has no error and is in some cases impossible.

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