The effect of weather and climate on siphonic rainwater drainage system operation

Abstract

This thesis establishes important siphonic rainwater outlet loss coefficients which may be incorporated into a mathematical model capable of accurately simulating such networks.

The siphonic rainwater drainage system principally operates under sub-atmospheric pressures based upon the potential energy of the disposable head, resulting in depressurization and full-bore flow. These abilities generate many beneficial characteristics, but when in operation the system will be influenced by physical and external conditions, in particular, those introduced when flow pathways are compromised by detritus accumulation at outlets.

Appropriate siphonic outlet loss coefficients have been established from changes in pressure in the discharge pipe and gutter depths as a product of partial blockages at the outlet due to either detritus or percentage coverage barriers. These coefficients were derived from analysis of laboratory data informed by photographic and weather station data established from two major site investigations. Utilising these new loss coefficients allows accurate consequences of particular rainfall events to be predicted using a version of ROOFNET- a Method of Characteristics based simulation model. From this, a rainfall intensity simulated with outlet blockage has produced results similar to those recorded from site.