Tailwater in a pipe network

[rallen]

I am trying to size the pipes in a drainage network. Here is my question:

At a junction where 3 pipes come together, can i figure my tailwater depth for each of the 2 contributing pipes separetely and simply add them together for a total tailwater depth to apply to the main pipe, or is there another method I should use to apply the 2 tailwater depths?
Thanks

 

[dicksewerrat]

I would use the sum of the flows in the two pipes and Manning's eq. to size the next one.

 

[gbam]

First, is the system under pressure? If it is then you will need to establish the hydraulic grade at the downstream end of the structure and apply losses through the structure. FHWA's HEC22 describes the procedure for both free surface flow and pressure flow. Sorry that I do not have the link rt now.