Constant flow in SSA

[BrianHailey]

I have a client that wants to put in a constant flow into an inlet and have SSA calculate the HGL downstream of that (as well as add additional flows at additional inlets). Is there a way to do this? I tried adding an "Initial flow" to a pipe but after running the analysis, that flow wasn't the peak of the pipe (I used 1cfs for the initial flow and the peak was 0.77 cfs).

This is obviously not what I wanted. How do I go about getting this?

[Hidden_Brain]

you can add the 1cfs as a "External Inflow" to the inlet, within the Inlet properties window under "Initial Water Surface Elevation" field. if the ponded area of the inlet is set to 100, the results should show a straight line at 1 cfs.

[BrianHailey]

Thanks for the reply but that doesn't seem to be working. If I add 2cfs as an external flow to an inlet (only inlet in a 2 pipe system), the pipes each have a peak flow of almost twice that.

[BrianHailey]

I think I got it figured out. I can add an external flow to a junction as well as an inlet. If I set them to junctions and add the external flow, it all goes into the pipe. I have no idea why this didn't work for the inlet.

[BrianHailey]

Thinking back on this problem, the peak flow in the pipe absolutely should not be higher then the peak flow to the inlet. Is it possible this is a bug?

[Hidden_Brain]

I have seen flows not adding up when the inlet "Ponded Area" parameter is set to 10 (default) or something. usually setting it to 100 has worked for me in the past. do not ask me what the rationale is, I have never understood the importance of this parameter myself. there are quite a few threads on the DBs on this topic. seems to affect the inlets only, especially when running SCS method.

[fcernst]

I have a client that wants to put in a constant flow into an inlet and have SSA calculate

Your client is asking you to use the wrong tool for static peak flow analysis.

The correct tool is Hydraflow Storm Sewers for peak flow analysis ( or another HEC 22 methdology standard step software).

[dolvin.buchanan]

Change your initial upstream node into a storage with a external inflow. The model will then work correctly for simple hydraulics. All the downstream nodes can remain inlets/junctions with external Q's you just need the initial upstream node to be a storage node.

Regards,

Dolvin Buchanan