TASS is a software programme that enables the user to predict the spatial development and concentration of turbidity plumes arising from dredging activities by trailer suction hopper dredgers. TASS has been developed because of a recognised need by the dredging industry to improve the quality of predictions of the effects of dredging in Environmental Impact Assessments. This article describes the TASS model and the validation of TASS predictions against validation measurements off the Dutch and German coasts.