The importance of solids in sewer systems as a primary source of pollutants is widely acknowledged. The re-suspension of bed deposits and bed-load material in accelerating flows is believed to be the primary source of foul flushes of pollutants. As yet only inferential data are available linking bed deposits to foul flushes of suspended pollutants.
Studies are described which have investigated the movement of material transported near the bed in combined sewers. The similarities with bed-load and fluid mud in river and estuarine flows are examined and the relationship between this material and foul flushes is considered.