Minimising the total cost of renewal and risk of water infrastructure assets by grouping renewal interventions

Planning the renewal of water infrastructure assets involves balancing the costs of renewal with the costs of risk. A considerable proportion of the renewal budget is spent on planning and mobilising resources to the intervention location. One may therefore reap benefits from the economies of scale by grouping the renewal of water mains which are spatially close. If one can express the total cost of renewal, risk and unavailability of a water main as a function of time, one may use this to find an optimal configuration of groups to be renewed together, where the benefits of grouping are balanced with the costs of shifting renewal investments in time. This paper demonstrates a methodology for optimising the grouping of renewals of connected water mains. The methodology is applied both to obtain an optimal set of groups for all mains in the network, as well as considering the contingency of renewing a group of mains in the event of a pipe burst. The methodology has been demonstrated with a case study, where the costs of leakage, and structural and hydraulic reliability are considered. The results show that there can be considerable monetary savings made by grouping the renewal of water mains.