[Scott Miller]

Give it a try by choosing the quick start file where you would set the initial conditions. Choose a start time that makes sense for your computation and output intervals. Restart the model under a new plan, because there will be output only for the remaining period.

I find it preferable to model locally, on a C: drive or peripheral hard drive, in order to reduce bottlenecks that affect computation speed. Doing so also eliminates the potential to lose a server connection.

[Scott Miller]

Those values look reasonable. Changing them has a significant influence on the accuracy of the model, regardless of channel width. The roughness can be adjusted so that the modeled water surface elevations matches observed elevations.

What would happen to the water surface elevation if you brought the levees a bit closer together?

[Scott Miller]

What roughness values are in channel and overbanks of the model?

[Scott Miller]

That is interesting the model ran with a 3000 point lateral structure. The 500 point station-elevation limit for lateral structures (and other alignments) is not new. It ought to have been necessary to break the lateral structure into several pieces to run in 5.0.6. It would be good to know what was going on. Was there an option to filter points that was applied before?

[Scott Miller]

What happens when you vary the minimum flow tolerance? It looks like the water surface is a higher elevation on the 2D side of the interface. Do the water surfaces converge during 1D/2D iterations, or are there 1D/2D flow errors? How large, compared to the minimum flow tolerance?

What do maps of velocity and Courant number reveal? The transition from 2D to 1D should be uniform. How well do the cross section, Manning number, and slope at the interface match upstream 2D channel characteristics?

How persistent is the problem through the duration of the run?

Full momentum can help identify problematic cells. Give it a try and pinpoint those cells. Keep in mind there may be superelevation at the outside of a bend.

[Scott Miller]

I am reading this as a 1D to 1D model. Is that correct? Open the Unsteady Flow Analysis window, where you set up the plan, and open Options>Calculation Options and Tolerances… On the General tab, you can set the 1D theta, the number of iterations, and the Lateral Structure Flow Stability Factor. Make sure theta is 1.0 to start out with, and try a stability factor of 3.0. They both trade off accuracy for stability. See if that helps.

[Scott Miller]

I do not think it is a matter of suitability of the water quality module. If it is a continuous injection of a conservative constituent in a single channel with uniform flow, numbers would look pretty boring downstream. The flow, cross section, and injection rate tell you enough for the calculation.

But if there is complex topography, additional inflows, a reactive constituent, or other complexities, 2D transport can answer interesting questions. For instance, if a flood washes out an open sludge pond, how concentrated is the pollutant at the edge of a flood eddy down river? 2D should be quite useful for the numbers you cannot calculate by hand.

[Scott Miller]

The second figure does show diffusion of the conservative pollutant. Notice that the duration at the peak concentration becomes shorter downstream. There is diffusion in upstream and downstream directions. Notice also that the rates of increase and of decrease in concentration each become lower as the slug moves downstream.

There is a plateau because at any instant, in the middle of the slug, diffusion is occurring away from the point of flow in both directions and to the point of flow from both directions, simultaneously. Concentration does not go down until the clear water at the leading or tail edge of the slug diffuses to that point in the slug.

[Scott Miller]

The canal and gate structure could be isolated from the river. I suggested putting ‘constant’ head on this, but that would be an unsteady model. A stage hydrograph would be the upstream boundary condition.

The upstream boundary condition for the gate and canal could be a steady flow, to verify that this part of the model works. If your clients have a way to know the river stage at this location, this part of the model may be all that is needed.

[Scott Miller]

How about backing up a bit? It could help to simplify. What about modeling the canal and gate with a constant head? And make sure the whole thing works part by part. The model goes from 1D reach to 1D reach after all. Any complex hydraulics due to the river bend and the intake structure configuration are lost. It’s steady. How uniform are the upstream and downstream river channels, not considering meanders? What, ultimately, is the task?

[Scott Miller]

I would expect the pipes to show, like in the screenshot below. (I changed the lateral structure hatch.) The culverts in your model appear to be at the right elevation. Have you got both upstream and downstream elevations in the geometry? Do the culverts run the entire length of the in-line structure? Those are the first things that come to mind.

[Scott Miller]

Shouldn’t the canal in line structure barrels be showing in the profile?

[Scott Miller]

Hi Wesley. Exporting the 2D animation from Mapper is not straight forward, but it can be done. Each water surface can be exported as a raster. Take a look at this blog post for guidance on how to export a series of rasters. From there you’re working with ArcScene, which can display elevation rasters as surfaces.

[Scott Miller]

The 1D approach looks reasonable. Take a closer look at how the headgate culverts are set up. See if there is anything there, or at the lateral structure, that would be limiting flow. Viewing the canal profile may reveal what’s going on. This is steady flow, isn’t it?

When 1D is working like you expect it, give 2D a try. The results ought to be comparable. A detailed terrain model including the channel bottom is needed for 2D. The 2D can capture effects of that sharp bend in the river. The 1D is still a good way to go for the culverts and canal. What velocities are actually going through the culverts?

[Scott Miller]

Jennifer – When you reply, look for something like the tool bar shown below. Choose the ‘insert image’ button. A smaller window should come up. For an image you stored to your computer, select the ‘choose image’ button. Find and select the image. It won’t be loaded yet. Next select the ‘insert image’ button. A short string of code should show up in the text box, like [nabble_img src=”Capture.png” border=”0″/], but with angle brackets instead of square brackets. That’s it. The image should show up when you post the message.

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