Can I analyze surface inlet and gutter capture without having to lay out the sub-surface network? (conduits)
Yes. Starting with the V8i SELECTseries 4 release (and greater), inlet-only hydraulics can be performed. You can simply lay out the Catchments (with Storm Data), Catchbasins (with inlets) and gutters and the program will calculate the inlet capture efficiency, bypass flow, etc.
This can be useful for analyzing road drainage design before designing the subsurface piping. In earlier versions of the software, in order to calculate the inlet capacities, conduits needed to be connected to the catchbasins to direct captured subsurface flow.
NOTE: This applies only to the GVF-Rational (StormCAD) solver, which requires the use of the Rational Method for runoff (utilizing IDF curves for rainfall). If you are using the Implicit or Explicit (SWMM) solver in SewerGEMS or CivilStorm and need to route a runoff hydrograph such as the SCS Unit Hydrograph Method or Modified Rational Method, conduits would need to be connected to carry the subsurface captured flow. You could simply approximate with a short, large diameter conduit connected to an outfall at an elevation low enough so as not to have an impact on the surface hydraulics (so as not to cause overflow).
An example model with surface gutter hydraulics only can be downloaded from the below link. Note that you will need to have version 10.01.00.70 or greater to open this model. This model is intended as a supplemental example, to illustrate a surface gutter network.
Surface system example 2 - 2019-Jun-18.zip
What's New in StormCAD SELECTseries 4
What's New in SewerGEMS and CivilStorm V8i SELECTSeries 4