CCWI2017: F86 'DISCOLOURATION RISK MANAGEMENT AND CHLORINE WALL DECAY'

This paper explores the concept that periodic imposed excess shear stress events to manage discolouration risk in trunk mains can also impact on the chlorine wall decay by changing the properties of the accumulated pipe wall material. By implementing a series of varying magnitude shear stress events in multiple trunk main demonstrated that significant material was mobilised, thereby cleaning the mains and reducing discolouration risk. Measured chlorine data also suggests that repeated shear stress intervention also reduced the chlorine wall decay relative to a control network and the larger the intervention greater the benefit. Calibrated first order chlorine decay simulations in EPANET supported this finding. The modelling results further show that the wall decay has a dominant influence on this change even for these large diameter pipes. The significance of these findings is to evidence the additional value of regular hydraulics based cleaning interventions for large diameter mains delivering service improvement in terms of both discolouration risk and persistence of chlorine residual.