As almost everyone knows about SWMM runoff surfaces there are three (non snowmelt) related surfaces in SWMM 1 to SWMM 5:
1. Impervious with depression storage, evaporation and no infiltration
2. Pervious with depression storage, evaporation, infiltration, with infiltration connecting to groundwater,
3. Impervious without depression storage, no infiltration, evaporation. This was used to simulate fast runoff from gutters and roofs in the original SWMM 1.
SWMM4 and SWMM5 added pervious to impervious routing, impervious to pervious and Subcatchment to Subcatchment routing. SWMM5 has further enhanced this feature by adding Low Impact Development (LID) for both pervious and impervious surfaces.
Newer versions of SWMM should expand the number of runoff surfaces from 3 to 10 and make each Surface have a flag for depression storage, flag for evaporation, flag for infiltration, a flag for groundwater, a flag for RDII, a flag fo…