The supply of water from source to customer relies on a pipe network system graduated from large pipes at sources, down to small pipes servicing houses. The larger pipes in this system termed Trunk Mains, represent the prime assets of water systems. Failure of trunk mains can cause loss of service to large populations for extensive periods and significant damage to property and social fabric.
A mechanism to identify the riskiest parts of the trunk network offers the potential to focus interventions to achieve capital efficiencies to improve service resilience on a justifiable basis. The approach outlined here has been operated in Scotland for 3 years, being recently upgraded to take on board the learning points from that experience and fits well within a PAS 55 approach to asset management.
Strategic water planners in Scotland were faced in 2006 with a trunk main programme largely defined by Operators based on failures of trunk mains at particular locations. The introduction of OPA interruption service levels sharpened the issue. An insight to the relative risks of service failure from trunk mains would enable limited investigation resources to be focussed for best return.
Farrer Consulting Ltd developed a risk based approach F_Risk for Scotland s SR06 trunk main investigation programme (TMIP) to define the focus of interventions across a risk based selection of 1198km of trunk mains. From lessons learnt during the 3 year programme and pilot trials of the UKWIR Large Diameter Mains Failure Model (LDMFM), the approach has been refined for definition of the investigation programme 2010 to 2015.