Residual Life of Wastewater Pipes

University of Auckland

Auckland, , NZ


Wastewater networks provide an essential service to society, whithout which modern cities would not be able to exist. Municipalities in New Zealand have invested billions of dollars to construct tens of thousands of kilometer of wastewater pipes. Like all infrastructure, wastewater pipes have a limited service life after which they need to be replaced. To properly plan for and manage wastewater systems, it is important that the remaining life of wastewater pipes can be estimated as accurately as possible. 

The aims of this project will be to develop a model to predict the remaining useful life of wastewater pipes, determining the most critical pipes in the network based on risk and whole-life cost analyses and use these models to assist municipalities to make better investment decisions. The work will be done in collaboration with industry.

To accomplish the above objectives requires the interdisciplinary integration of two fundamental components outlined below. The Models Framework component must inform the Data Framework Analysis component and vice versa.

Models Framework

The models used by the three waters industry to assess useful life, risk/criticality and whole‐of‐life costs of different pipe classes is largely based on professional judgement and limited data sets. These models have a very large impact of long‐term plans for pipe renewals and other investment decisions. Improving these models can reduce uncertainty and risk from both the financial and engineering perspectives.

Subsequent physical models will be based on the Data Framework.

Data Framework Analysis

Data requirements, sensitivity and data criticality analysis.

  • Establishing the Data Framework is difficult due to the complex nature and inter‐relationships between different performance measures.
  • Councils collect and use a variety of criteria related to pipes (e.g., criticality, risk, vulnerability, repair and operational costs) when evaluating renewal decisions (e.g., replacement, resilience upgrades, preventative maintenance).
  • The marginal benefit of adding criteria needs to be weighed against cost and complexity.
  • Large datasets are now available to evaluate the value‐added of various criteria.
  • It is not clear to what extent the choice of criteria matters in terms of changes in decisions.
  • An opportunity exists to better understand the value of adding criteria through analysis of a variety of actual data sets.
What we are looking for in a successful applicant

A self-driven and enthusiastic student with a background in civil engineering and an excellent academic record. 


1) Models Framework – Whole‐Of‐Life Models

In the first instance a literature search is required to collate national and international perspectives on the problem. From that a series of workshops will be carried out with academic and industry representatives to: 

  • Define current methodologies required to create the appropriate whole‐of‐life models.
  • Define new areas to create innovation with regards to whole‐of‐ life models.
  • Prioritise the pipe classes and conditions for initial study.
  • Create and enable virtual teams to carry out the required research.
  • The highest priority study/studies will be identified and undertaken.

2) Data Framework Analysis

This will be complemented by a Data Framework Analysis that will:

  • Review wastewater renewal criteria used now by councils and the decisions they relate to.
  • Review decision schema used for other NZ infrastructure systems and internationally as well in other industries (e.g., petrochemical).
  • Partner with one council and use their database as a case study.
  • Analyse data to identify the inter‐correlation of existing criteria and degree of gaps and overlaps in sets of criteria.
  • Develop representative decisions that rely on pipe ratings in order to analyse effectiveness of criteria sets.
  • Develop a series of criteria sets for evaluation; explore the potential for alignment with existing metrics and KPIs of organisations (such as councils, treasury; consider small and large sets; expensive and inexpensive criteria.
  • Conduct sensitivity analysis on the effect of criteria sets on decisions.
  • Liaise with stakeholders on implications of results for pipe rating systems.
  • Develop guidelines on use of pipe rating criteria (e.g., scope, limits of applicability).
  • Generalise results from wastewater case study to other NZ wastewater systems, and to other asset management systems (potable water, stormwater, buildings).