Long-Term Cost-Effective Trunk Main Discolouration Risk Management Strategy

Material responsible for discolouration risk has been shown to accumulate on pipe walls even after cleaning intervention, suggesting that risk cannot be eliminated with a single applied intervention and hence the long-term water quality benefits are uncertain. This recurring cleaning requirement can substantially increase total expenditure on interventions. Although different interventions exist to manage accumulated material, flow conditioning is considered to be a long-term intervention due to the use of only system hydraulic (shear stress) with minimal resources. The water quality performance of the selected intervention was tested in multiple operational trunk mains including a control main with similar physical, chemical and microbiological conditions and their discolouration risk and chlorine wall decay were measured as a water quality performance indicator. The periodic trunk main flow conditioning improved the long-term chronic material loading and chlorine wall decay of trunk mains compared to the control. Although transport of occasional acute loading to the downstream network from the flow conditioning trial was recorded, the improved downstream accumulation return period found for the flow conditioned main evidenced that chronic loading has a significant influence on discolouration risk than acute loading. Using the field observed material accumulation processes for large diameter main and long-term measured data, the Variable Condition Discolouration (VCD) model was used successfully to simulate long-term discolouration behaviour with high accuracy and the model’s accumulation functionality was validated. This fundamental way of capturing accumulation behaviour in the VCD model was used to develop a novel whole life costing (WLC) model for designing flow conditioning intervention cycle cost trading against hydraulic resilience. The WLC modelling framework derived exponential Pareto front solutions that can select best solutions between intervention expenditure and level of resilience achieved. This research enlightens for the first time how the trunk main and downstream network discolouration risk behaves in response to periodically controlled interventions and how risk can be managed proactively and strategically from treatment works to trunk main and downstream distribution zone.