In this paper we propose an empirical approach to quantify the hydrographs' attenuation in sewers. The purpose is to evaluate attenuation's consequences for the scale-transfer between the parcel and the catchment in urban settings, and in particular for stormwater source control (SC) regulation. In fact, SC regulation practices often consider this scale-transfer by a linear approach. We draw a formulation for the attenuation of peaks in partially full pipes, and we assess, by a sensitivity analysis, the respective weights of the different pipes' and hydrographs' characteristics on attenuation. We found that the driving factors of the peak attenuation vary according to the distance from the outlet, and we draw possible guidelines for SC regulation.