During the 20th century, the once common practice of trapping sewer sediments at key locations within sewerage systems has lost favour with UK sewerage designers and, to a lesser extent, operators. The reasons for this include the perception of a priori unquantifiable maintenance, and the difficulties of sewer sediment extraction in town centres in an environmentally acceptable fashion. In order to assess the need for and requirements of such trapping systems, a survey of UK sewerage operators was carried out. The results of this survey have been used as a starting point to initiate the development of a design and operational methodology for the utilisation of traps. The survey highlighted the lack of guidance available and the importance of trap monitoring to enhance performance. A fill rate model is proposed for the design and operational aspects of cleaning and monitoring traps, using two of the most recently developed “near bed solids” transport equations. The model has been applied to a trap situated on a trunk sewer in the city centre area of Dundee. The pollution potential of trap and in-pipe sediments has also been assessed by considering the biodegradability of the sediment fractions likely to be released into the flow column during storm events.

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