TSS - Sediment Fraction

The TSS sediment fraction in the sewer system is not modelled for each time step but assumed to be constant during the simulation. It can be defined as a fraction of the total TSS load entering the combined sewer system at the beginning of a rainfall event. The total TSS load is computed as:

 Total TSS load = TSS load from catchment surface/(1.0 - SF)

SF = 0.3 means that 30% of the total TSS load arises from sediments in the sewers and 70% of the TSS are washed off by stormwater from the catchment surface into the sewer system during rainfall.

The sediment fraction is added to the TSS load (from rainwater, wastewater and external inflow) per rainfall event. The TSS load in time step t is computed due to the first flush coefficient b.