Is it possible to enter catchment data like the C value, area, and time of concentration directly to a catch basin, rather than including the catchment element itself?
Sometimes the catchment elements are not readily available to include in a drawing, but the data itself, such as C value, area, and Tc, is available. In such a case, it is possible to add the data directly to the catch basin element. In the catch basin properties, you will see property fields for "External Tc" and "External CA".
This data can be added directly to the catch basin properties or flextables. You can also import the data through ModelBuilder. Note that the C value and area are not entered separately, but as a single property. If the data you have is separate, you will need to multiply the C and area first, such as in Excel.
Also, the flow generated by the External CA/Tc enters subsurface (does not approach the inlet opening) so this may only be appropriate for full-capture or in-sag inlets.
If you have the flow expected from the catchment available, you could also enter that flow as "Flow (Addition Carryover)". This flow would be captured by the catch basin or possibly passed to a downstream gutter.
Catchment polygon visualization after importing from non-spatial data source
Understanding Flow (Additional Subsurface) and Flow (Additional Carryover)
Understanding Known Flows
Types of flows that can be applied at a catch basin for the GVF-Rational solver