The paper is focussed on the concept of defining the “predictability” of sediment transport. Engineers are faced with a number of sediment transport formulas derived from different tests and described as suitable for application in sewers. Bed and suspended load formulas vary in form and performance, generally depending on the data sets that were used to calibrated them. As different sediment types have been tested no single, generally valid formula has been established so far. Formulas are distributed in the scientific literature and are often reported without the information necessary to define their range of potential applicability. Therefore, this paper along with analysing the formulas available, will also comment on the assumptions used in their development as well as the reliability of their underlying data to aid engineers in the selection of the most appropriate sediment transport formulae to correspond with the environment in which they are working.