[cameron]

You would need to have data to georeference it to. This means you may have to digitize lines in GIS and then import them into the HEC-RAS model. If you have the x and y coordinates then you could just enter them in a table.

[cameron]

The arrow is just pointing to which way the cell face cross-section stationing goes and is similar to a 1D cross-section. Flow is positive in one direction across the face and negative in the other direction. In 1D modeling you draw your cross-sections left to right looking downstream. 2D uses the same concept left to right. for cell face 54868 if flow is going from the east to west, it would be a negative flow. For cell face 54276, flow going east to west would be positive.

You can plot the discharge of each cell face to see what I mean.

[cameron]

Each cell is a mini storage area with a volume elevation curve generated by the terrain under the cell. HEC-RAS solves the water surface for each cell (only 1 wse per cell) and the velocities are computed at each node of a cell.

Each cell face is a cross-section and has currently 1 roughness value per cell face (will change if future versions) and is what is used to determine which way the flow goes.

If your cell face cross-section cuts through a levee or high ground as in your picture, the model does not see and water appears on the other side just as would happen in a 1D cross-section model. This is called leaking and is why it is important to use breaklines to force the cell faces to go along high ground or levees so the entire cell face cross-section picks up the high ground.

Previous versions of 2D HEC-RAS used a lot of points in the volume curve which slowed the model down and took up a lot more space. There is now a filter that is applied to limit how many points are in the volume curve.

If you are asking what the max height is used for the volume elevation curve, that is calculated internally by HEC-RAS.

[cameron]

Is this with the full momentum solver or diffusion wave solver?

[cameron]

Is the geometry data exactly the same for the steady hydrologic routing model and the hydraulic model?

[cameron]

My guess is that those velocities are occurring either at the beginning of the simulation or when water reaches the downstream end and causing the model to freak out and give volume errors.

[cameron]

Have you adjusted the HTAB parameters for the 1D cross-sections?

[cameron]

What is your initial condition for the 2D area? What is your timestep and are you using the full momentum equation? You need to follow the Courant Criteria for time step. My guess is you have a large timestep and using the diffusion wave equation which never crashes and with large timesteps causes bad results.

[cameron]

do you get really high velocities at the boundary with the low stage?

[cameron]

Not sure for question 1, but question 2 the arrows should represent which way the flow is positive and direction the cross-section stationing are taken from.

[cameron]

You could use the hdf files and some python to automate some of the process, but there is not a way to do it in RAS

[cameron]

Is there water flowing into the model from the stage boundary condition?

What is your time step?

What are your initial conditions?

[cameron]

I would just take the depth or velocity raster and create the inundation boundary in GIS. There is not an option to do this directly in HEC-RAS.

[cameron]

It depends on the dam, how much water is in the reservoir, how much water is anticipated to come to the reservoir, impacts of release downstream, and other things. Most dams have operating guidelines specific to that dam.

[cameron]

The model stopped because the minimum error tolerance was exceeded. This could be caused by a number of things, incorrect time step, need for additional cross-sections, more ineffective flow areas.

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