Use of a full-scale test facility to examine sewer sediment mobility

The mobility of granular in-sewer sediments was measured in a study which was carried out at the National Combined Sewer Overflow Test Facility, Wigan. It is thought that these measurements are unique in that the facility permits tests using crude sewage and real in-sewer sediments to be conducted under full-scale controlled hydraulic conditions. Tests were carried out in which the bedload transport rates, resulting from different steady-flow discharges and flow depths, were measured. The results were compared with transport-rate predictions made using relationships which are recommended by the Construction Industry Research and Information Association. These comparisons indicated that, for the sewer sediments, the existing prediction methods are likely to significantly under-predict the mobility of in-sewer sediments - particularly if a range of grain sizes is present. This might have important implications both for the design of sewerage systems and for sewer flow quality modelling.