Development of design methodology for self-cleansing sewers

New guidelines for the design of self-cleansing sewers have been developed in a recently completed CIRIA research project. Laboratory and field studies were reviewed and compared, and appropriate equations were selected for predicting sediment movement in pipes. Self-cleansing performance was defined in terms of three design criteria covering the transport of fine-grained materials in suspension, the transport of coarser sediments as bed load, and the erosion of cohesive deposits. Information on typical sediment characteristics in UK sewers was reviewed and used to produce guidelines on values of minimum flow velocity and pipe gradient for different types and sizes of sewer.