Detritus accumulation at, and impact on performance of, siphonic rainwater outlets

This paper presents the findings of an 18-month study of detritus accumulation at two siphonic rainwater drainage systems installed in a building in Edinburgh. Findings are based on an analysis of data recorded from the site, and are positioned within the context of enhancing representation of the outlet loss coefficient used within both steady-state design calculations and finite-difference based unsteady flow modelling techniques. The scope of findings reported herein is extensive but, in the main, shows how detritus accumulation not only builds relatively rapidly, but also that ‘wash-through’ or ‘displacement’ occurs. Further, data suggests that detritus accumulation can, and does, build with only relatively low intensity rainfall but that high-intensity rainfall events do seem to result in a direct and significant increase in detritus. An indication of the impact upon performance, assessed using simulation software, is also presented.