If we set the Boundary condition type in the Outfall to free outfall or we gives elevation for the user defined tail-water how it affects the Outfall flow in Civil Storm and Storm CAD.Please specify on the Outfall Flow which will be less or which will be more.
Hello Vikas,
Free outfall is used when water is discharged into the water body freely. For a free outfall control, it is assumed that the downstream discharge conditions do not directly affect the hydraulic response of the structure.
And tailwater elevation is generally is used when you have constraint of elevation at the outfall like you are discharging water in a sump, here StormCAD / CivilStorm does backwater calculations to find out water fluctuations in pipe upstream of outfall based on tailwater elevation.
To understand outfall flow will be greater in which case, you could setup two scenarios, one in which outfall is free outfall and another in which outfall is set to user defined tailwater condition.
Backwater Analysis vs Capacity Analysis flow profile methods
Regards,
Sushma Choure
Bentley Technical Suppport