The application of technical performance evaluation to urban sewer systems

Abstract

The assessment of performance in public utilities infrastructure is an important, yet still embryonic field of knowledge, especially as regards urban sewer systems. Performance has traditionally been expressed in terms that relate to local design practices. This has resulted in a variety of ways of assessing performance in different countries without a consensus on how it should be expressed. While performance indicators are a suitable tool for addressing the utility s performance in all its sectors of activity, the efficient technical management of the systems deserves a specific approach, better suited to the type of methodologies regularly employed while planning, designing, constructing, operating, maintaining and rehabilitating the systems. At this engineering level, decisions are made based on operational, physical and natural resources data, and on the results of analyses deploying common engineering tools such as simulation models and information systems. However, such tools tend themselves to produce vast amounts of insufficiently aggregated information, which is scarcely performance-oriented. This paper presents the application of a performance assessment system, designed as a technical analysis tool, in order to shift the focus of technical management of urban drainage systems to a wider, more rigorous, performance-oriented view. The system draws from the experience gathered in performance assessment in water supply, and is based on the decisional concept of utility (performance) functions, in order to accommodate individual sensitivities and interpretations. The system is implemented as a post-processor to sewer modelling, showing significant potential in the performance evaluation of sewer systems, and provides a decision support basis for sewer system design, diagnosis, operation and rehabilitation. A comparative study involving several subsystems of the Estoril Coast interceptor system (Portugal) is presented in order to illustrate the method.