The Effect of the LID Percent Impervious Treated in SWMM5
If you use the option percent impervious treated for LID's on a Subcatchment then a percent of the impervious flow is routed to the LID. For example, 50 percent of roof runoff to a LID Swale. It has the impact of reducing the peak and total runoff fro the whole Subcatchment but increases the LID only flow. From the SWMM 5 help file "The percent of the impervious portion of the subcatchment's non-LID area whose runoff is treated by the LID practice. (E.g., if rain barrels are used to capture roof runoff and roofs represent 60% of the impervious area, then the impervious area treated is 60%). If the LID unit treats only direct rainfall, such as with a green roof, then this value should be 0. If the LID takes up the entire subcatchment then this field is ignored"