Inverted syphons

[Binod]

I have been using HEC-RAS to simulate flows through a canal system in around 5500 ha of lands in Nepal. There are numerous inverted syphons along the main canal, in addition to other canal structures like bridges, drops, head and cross regulators etc. All features of a culvert could be used to simulate the siphon if the pipe of the culvert could be simulated as having two bends in vertical plane. However, I am not able to do this in HEC -RAS. Next week I am going to install RIVER CAD. Please suggest me how can I accomplish the task using any of the simulation tools.

[Debajit Basu Ray]

Hi,

You could model the siphons by treating them as an "Alternate Equivalent Canals Using Energy Grade Line Elevations". The steps you could follow are as follows:

1. Replace the inverted siphon with an alternate equivalent canal
(open channel)

2. Assume a Manning’s coefficient for the alternate equivalent
canal

3. Analyze the flow in the canals

4. Compare the computed and observed energy grade
elevations across the cross sections. If the difference between
the elevations is within an acceptable range, then stop.
Otherwise, go to next step

5. Adjust the Manning’s coefficient in the equivalent canal in order
to try to get a more accurate computed energy grade
elevation. Then, return to Step 3 and repeat the process

Thanks,

Debajit Basu Ray