Over the past decade, considerable investment has been made in acquiring knowledge about in-sewer processes, with the objective of developing new analytical tools to predict the performance of these systems. A wide variety of these tools have emerged, from simple aggregated conceptual models of entire systems, to very detailed physically based relationships for particular processes such as suspended transport. The major investors in this research have been determined to produce commercial models which will form part of integrated system analysis suites of software for use in the formulation of holistic and optimum managerial methods for wastewater systems. Unfortunately, sewer processes are extremely complex, and the very limited investment, when compared proportionately with that made in hydrological and hydraulic analysis over previous decades, has produced apparently gaps in underlying knowledge which are not generally acknowledged. This paper reviews the current position with regard to sewer process modelling, highlighting areas where knowledge is still deficient, and where new opportunities and limitations are emerging.
