Numerical and experimental investigations were undertaken to study sediment transport under steady flow conditions and under flush waves in sewer pipes. Experiments were carried out with sand and gravel of different size distributions under smooth and rough bed conditions. Moreover, different hydraulic boundary conditions were investigated for flush waves. The numerical part of this study was carried out in the computational fluid dynamics (CFD) software ANSYS Fluent, which is two-way coupled to the Discrete Element Method (DEM) software EDEM. The main focus of this study is to determine if the CFD-DEM coupled method could reasonably predict the behaviour of sediments in sewers and thus be used for studying various features of sediment transport that are not easy to determine in laboratory experiments or in-situ measurements. Furthermore, it is important to replace the traditional empirical approaches developed for fluvial conditions with new methodologies, which are able to consider the high number of variables involved in sediment transport in sewers. The numerical model was validated with laboratory experiments and used to study details of sediment transport processes in sewers.