The attached one Subcatchment SWMM 5 model and associated Rainfall was created using the Random function in Excel on a measured NCD station in Boston.    There is a dry weather flow component of 0.5 cfs with an hourly pattern.  The rainfall averages 54 inches over the 1000 years and the runoff is 20 inches on average over the 1000 years.

Figure 1. Combined Flow at the Outfall for the 1000 year Simulation.