Modelling of storm wash-off of suspended solids from impervious surfaces

A mathematical model of suspended solids discharge from impervious surfaces during storm events has been developed. The model continuously simulates two major processes of different time scales; solids build-up at impervious surfaces between two storm events, and solids wash-off from the surfaces during storm events. Buildup is modelled using the Sartor and Boyd equation (21) in which the amount of solids available on the surface is an exponential function of antecedent dry weather period duration, The spatial distribution of solid particles over the street surface is also modelled, which is an innovation. The wash-off process is divided into three subprocesses that are modelled consecutively. A kinematic wave model is used for overland flow modelling. The particle entrainment into suspension is estimated by two methods. In one, the rainfall and overland flow effects are not separated and the total shear stress is used to predict:entrainment. Ln the other, the rainfall and overland flow effects are treated separately and then summed. An original equation was developed for this method. The model is applied on two small experimental catchments, one at Miljakovac-Belgrade, Yugoslavia and the other in Lund, Sweden. The description and verification of the model are presented and discussed in the paper.