Sediment transport in sewers has different aspects to be analysed and the present paper describes primarily the transport at "limit deposition" and transport over small mobile (loose) beds. A new model for the transport at "limit deposition" criterion was developed based on physical concepts for extrapolation for large sewers. This model leads to more economical solutions than previously developed best-fit models. The transport phenomenon over mobile beds is modelled based upon the classical dimensionless parameters of bed shear stress and transport using Meyer-Peter Muller method normally used in the studies of alluvial channels. These studies were conducted using uniform sediment materials in order to understand the effect sediment size and then the effect of sediment gradation was focused upon.