Simulating long term discolouration behaviour in large diameter trunk mains

Simulating the long term discolouration behaviour of large diameter trunk mains can aid water utilities to understand and pro-actively manage these critical assets and mitigate a key source of customer dissatisfaction. Validation of such modelling capability is presented for the Variable Condition Discolouration Model (VCDM). This is based on over a year’s field data from three similar physical and hydraulically operated trunk mains supplied from the same source that undergo different planned hydraulic maintenance regimes. In single long-term simulations, measured turbidity responses are reproduced with a general accuracy of ±0.25 NTU with comparable model parameters empirically calibrated for the range of managed and unplanned hydraulic events. Validation of long-term capability supports the concepts of continuous material mobilisation and accumulation processes and that accumulation can be modelled as occurring simultaneously for all wall-bound material shear strengths, critical for quantifying how discolouration potential changes. Benefits from understanding and having the tools to track this behaviour include informing operational risk assessment, evidencing hydraulic management strategies, resilience and scenario planning and optimising network maintenance.