Time to drain pipe (profile: extended V-shape)

[qaztor]

Hello!

I have a 36" sewer (under pressure) that holds over 200,000 gallons of sewer when we stop the flow from the Lift Station. In order to repair such section we are required to drain most of it through an 8" valve on the lowest point due to the lenght of the pipe (1000' from one end and over 3000' from the other end).

I know how to calculate the time to drain a tank but I haven't found literature that will guide me on this one. any tips??? thanks

 

[cvg]

Can you use HEC-1 or other hydrology software to "route" the flow as if this was a pond with an outlet? The discharge rating curve would be calculated using the orifice equation, or weir equation for low heads. Then calculate the stage - storage relation for the pipe. Use the software to route the flow and determine the drain time.

Maybe a better (faster) method would be to pump the water out...