Experimental Study of Multiple Outlets in a Siphonic Roof Drainage System

Recent trends in the development of our urban landscape have seen the introduction of larger buildings with vast roof areas especially in localised business and industry parks. It is anticipated that the onset of climate change will see increased intensities and volumes of rainfall which will place significant pressures on the roof drainage systems for these buildings, potentially leading to failure and major flooding. There is an urgent need to examine alternative forms of roof drainage and a potential future solution is the adoption of siphonic roof drainage systems. However, it has been identified that there is a universal lack of understanding of the hydraulic performance of siphonic systems, particularly with regard to multi-outlet systems.

The work presented in this thesis describes a comprehensive experimental programme of research using novel and sophisticated measurement techniques including flourometry and particle image velocimetry, to increase the understanding of the hydraulic performance of multi-outlet siphonic roof drainage systems. The overall aim was to deliver a step change and better understanding of the performance of such systems and how they may be better designed. A total of 63 steady flow tests were completed using the siphonic roof drainage test facility at the University of Sheffield.

The results from this study support key findings that within a multi-outlet siphonic system the flow rate through each individual outlet is contrary to existing design practice and significantly different flow regimes occurred within the horizontal carrier pipe. Hence, current approaches applied in conventional siphonic roof drainage practice and design software should be reviewed.

The outputs from this study have highlighted the need for further research to better understand the performance of multi-outlet siphonic roof drainage systems. These topics may be addressed with the technology and methodologies developed within the experimental programme of research reported in this thesis.