The first foul flush in combined sewers: an investigation of the causes

A previously developed numerical model, able to simulate the erosion from an organic in-pipe deposit, was used to investigate the physical parameters that control the first foul flush in combined sewers. Systematic adjustment of physical parameters indicated that the accurate characterisation of bed properties, i.e. the surface erosional strength and its variation with depth, was more important than the accurate description of the imposed hydraulic conditions.