The physical and biochemical nature of the material transported near the bed (‘bed-load’) in combined sewers is established. The merits of the recent evolution of the terminology used in this field are discussed. The physical characteristics of material found in transport at three separate combined sewer field sites are described. The importance of this mode of transport, in terms of the mass transported and pollutant potential, is demonstrated based on data collected from Dundee combined sewerage system sites. The development of a novel near bed solids transport prediction equation is described. Comparisons are made between measured near bed solids transport rates obtained in the field, at sites with and without deposited beds, with predictions obtained using the new methodology. The need for future research in this subject area is emphasised.

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