The origins of sediments and associated pollutants found in sewers are clear, and demonstrable temporal and spatial variations have been found. It is likely that these variations are such that it is not possible to formulate general rules for the rates and nature of surface wash-in to sewers. Sanitary sources, however, are more amenable to deterministic assessment. The rates of build-up of sediments in sewers vary widely, and whilst it is possible to estimate the build-up in small-sized collector sewers, no general rules are yet available to predict the rate of deposition in larger sewers. There are broad similarities in the nature of sediments found in sewers in terms of particle size and pollutant characteristics. It is possible to formulate a pragmatic taxonomy for distinct classes of these sediments in order to facilitate understanding of sediment effects and to assist engineers with developing control strategies.

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