[maputnam]

Momentum and Energy Balance

[maputnam]

Michael,

Thanks for all your help. The inline structure works for modeling the culverts with flap gates save for 1 of the 5 culverts under this roadway in which the flap gate broke off. Since the software will only allow a blanket application of flap gates on culverts I modeled the 5th culvert with the broken flap gate with a sluice gate. Also, I figured out what was going on with the storage area and the elevation not fluctuating. Turns out I had the wrong units for the storage volume. I had thought that I set my spreadsheet to output in Ac-ft but it was set to cubic feet instead. This made the available storage in the reservoir extremely large and as such its elevation was not changed very much with tidal influence.

One further question, Is it possible to place a storage area in-line along a reach instead of just at the top of the reach or bottom of the reach?

Thanks,

[maputnam]

Michael,

Thank you for your response. I do have a couple of questions regarding the boundary conditions. At first this model is intended to be “dry weather” with rainfall added in during subsequent analysis. If I add inflow as a boundary conditions during dry weather, would I be specifying the inflow from the downstream culverts, and not letting the program calculate the inflow to the storage basin based on the culvert hydraulics? (See Image Below)

Also, when I specify the initial elevation for the storage node the water surface elevation of the storage node does not change while the model is running. If I do not specify an initial elevation the model will not run. (See Image below)

My approach thus far has been to use inline storage. However, after thinking about this would it better to use offline storage and a lateral structure for use in analyzing this reach? (See Image Below)

Finally, I still have the need model flap gates on the downstream culverts. Is there a way to do this in RAS?

Thanks in advance!

Mike

[maputnam]

For unsteady simulations ensure you have meet the samuel’s equation for section spacing {0.15(depth)/Slope}. This will help with some stability issues. Also this does apply to near your junctions. Often when issues appear near them you may need sections closer in each direction to it to assist with resolving inherent instabilities. Also adjust your timestep by Courant condition {Spacing/V+c} but not less than 5secs or you can take the time of the flood rise / 20.

I have checked the cross section spacing vs. Samuel’s equation and find that Samuel’s equation species a maximum cross section spacing of 1113 lf. I have examined the data and found that cross sections are spaced, on average, about 422′ apart with a maximum of 1450 (only two cross sections in the entire model exceed the length recommended by Samuels equation). I have reduced the computation time step to 1 second; if a greater time step is used the model will crash.

There is a pretty significant difference in the inverts of these two reaches. However, the tributary has a pilot channel to account for this.

I have also managed to get the model to run with the tributary however the lateral structures included in the original model will not allow the model to run. Additionally, any change I seem to make in the geometry or the Htab parameters seems to cause the model to go unstable.

[maputnam]

how did you set up the junction for the model? did you try the different options in the junction editor?

I have tried both the “Force Equal WS Elevations” and the “Energy Balance Method” using the junction. The error I am getting is not contained to one cross section and seems to “Jump” all over the place. However the same cross sections, when the junction and parallel reach was removed, work just fine with no issue.

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