Dealing with EPA SWMMs subcatchment model

[GKCOTTON]

I wanted to get some feed back and opinions on the SWMM subcatchment
model from others that have used this basic component.

The conceptual framework is very different compared to unit hydrograph
based approaches (CUHP, SCS, Sneider, etc). Computation of a lag time
for a unit hydrographic typically breaks the flow path down into an
overland flow segment and a swale or gutter flow segment. For SWMM
all runoff from a subcatchment is sheet flow. There are pervious and
impervious subareas and these can cascade to each other or go directly
to the outlet. The subareas can also have their own n-values.
However, there is only one slope and one width for the entire
subcatchment.

I have recently reviewed a model that used the subcatchment model in
UDSWM. Porting it to EPA SWMM 5.0 resulted in the same subcatchment
hydrographs. So, this routine seems to be very stable but maybe a bit
of a dinosaur.

If anyone has come across guidance or research on how to estimate SWMM
subcatchment parameters, I would be interested in knowing about them.