Prioritising sewerage maintenance using serviceability criteria

In the UK and elsewhere, there has been a concerted move away from primarily assessing sewer system capacity to focus on ‘serviceability’ as a key performance indicator in sewerage provision. Increasingly, water regulators are recognising that a prime concern of customers is avoiding flooding of their property, as environmental improvements can often be intangible. However, regulators insist that environmental factors are also given strenuous attention. Based on these considerations, it is evident that sewerage providers will increasingly consider undertaking proactive maintenance on sub-critical and non-critical sewers in order to reduce the risk of customers experiencing reduced levels of serviceability. This paper documents the development of a methodology to manage capital maintenance expenditure within the context of ‘serviceability’ to customers, the public and the environment. The methodology has been applied alongside Infoworks-CS software to determine critical points in a small coastal catchment in Edinburgh, Scotland. The paper also discusses how these results are linked to customer complaints held in a geographic information system (GIS) database, and how the approach developed was able to recommend which assets should be proactively maintained to minimise the risk of serviceability loss. For the catchment considered, key serviceability performance indicators were found to be combined sewer overflow (CSO) spills, flooding in residential areas, flooding in commercial zones and disruption to traffic.