Wastewater velocities required to eliminate deposits in large sewers are greater than typically recognized. Work in recent years has centered on shear stress needed to move certain types of cohesive and non-cohesive materials in both sanitary sewers and combined (wastewater and stormwater) sewers. Research work in Europe on combined sewer deposits is recognizing the unique aspects of these sediments and their water pollution impact from sewer system overflows. Deposits in large sewers are particularly troublesome due to the difficulty in cleaning the sewers and dangers of placing personnel within these potentially toxic atmospheres. It appears that more effort is needed by designers and system managers to evaluate these deposition problems and to better assess cost-effective solutions.