Investigation of factors contributing to dirty water events in reticulation systems and evaluation of flushing methods to remove deposited particles

This investigation was to evaluate the factors contributing to dirty water customer complaints within the area supplied by South East Water Limited, a wholesale water company in Melbourne, Australia. It also evaluated the potential to derive a predictive method to facilitate proactive mains flushing. The study focused on a single reticulation network, within the suburb of Wantirna. A desktop and field study were undertaken. The desktop study evaluated a range of parameters and their association with dirty water customer complaints over an 8-year period. Parameters evaluated included distance from the water source, street topography, population distribution, and variations in water velocity. The field investigation focused on evaluating the quantity of turbid material deposited in key locations, identified from the desktop investigations. Several factors appeared to influence the likelihood of a dirty water complaint. These were: population density and the associated complexity of the reticulation network; the presence of an undulating topography in the street of concern; and the presence of a dead end. Evaluation of hydrant flushing indicated there might be potential to reduce water usage and improve flushing efficiency by flushing at a reduced flow rate of 5L.s -1 , down from the typical 10L.s -1 or higher currently used. Time to clear at a hydrant appeared to be the most effective measure of settled material in a water main, however more work is required to confirm a threshold value that could be used as a predictive measure for proactive mains cleaning.