I am working on StormCAD v8i.
The total flow according to the individual 63 sub-catchments is 33.6m3/s and I am getting a flow of 23.5m3/s at the final outfall for this catchment group. Can you please explain?
This is probably due to flow attenuation, which is explained in this wiki article. To understand how flow is calculated in StormCAD using the GVF rational sovler review this wiki article.