Movement of Total Suspended Solids in Combined Sewers

Two alternative modeling approaches have been developed to simulate suspended sediment concentrations in storm flows associated with the erosion and transport of the cohesive-like sediment deposits which occur in sewers. One model predicts the first flush pollutograph based on a statistical approach using regressional relationships established from a large number of recorded storm events in a number of different catchments. The outputs from this model are contrasted with those from a deterministic model based on the simulation of the erosion of an in-pipe sediment bed that is assumed to have an increase in the resistance to erosion with depth of erosion. Both methodologies have been applied to field data and have been shown to predict the shape and form of observed pollutographs. The limitations of both approaches have been identified but it is concluded that, with further refinement, the models have the potential to be widely applicable.