A Data-Tiered Lifecycle Cost Framework for Risk-Based Renewal of Water Distribution Networks

Abstract

Most North American drinking water mains were installed in the 1940s–1960s and are now past their design service life, especially cast-iron mains. Most existing lifecycle costing frameworks work with specific levels of data that smaller utilities rarely hold. Many also omit discounting, which obscures the net present value (NPV) of future expenditure. This paper introduces a data-tiered lifecycle cost framework that integrates power-law non-homogeneous Poisson process break-rate modelling, risk-based prioritization, tiered cost-assessment modules and NPV discounting to determine if proactive renewal is cheaper than a fix-upon-break approach and under what conditions. When applied to Kitchener (936 km) and Calgary (5391 km) with an adopted break growth of 3%/yr, lining-intensive strategies result in up to 12% and 20% lower undiscounted lifecycle expenditures, respectively, but the ranking reverses at discount rates close to 2% and 3%. Sweeping the break growth rate from 0%/yr to 6.5%/yr shifts the break-even discount rate from no crossover to 6.6 in Kitchener and 7.5% in Calgary; thus, the economic case for renewal is set jointly by the break growth rate and discounting. Utilities can deploy the framework on their datasets and situate their own network in that space.