A conceptual model for solid production and transfer in sewer systems is proposed. It has been established for small urban catchments of less than 100 ha, which can be considered from a global point of view. Hydrological and hydraulic phenomena are simply represented with a cascade of two linear reservoirs. The first part of the solid transfer model has been established to reproduce daily and hourly suspended solids loads during dry weather periods. The second part of the model deals with solid transfer during storm events, including sediment build-up over the catchment, washoff, erosion, deposition and transport. Two classes of particles are introduced to distinguish between deposits in pipes and solids transported in suspension. The objectives are the calculation of suspended and bed loads and the evolution of the deposits. Preliminary results are satisfactory but further research is needed in order to test and verify the model for other catchments and rainfalls.