The software discussed provides a decision support system for drainage engineers involved in the design of stormwater management facilities. Runoff modelling is versatile and involves a variety of methods for storm description, rainfall loss estimation and overland flow routing. In addition to normal pipe and channel sizing, the design options include a number of detention devices for on-site controls such as rooftop and parking lot storage, in-line storage ‘super-pipes’ and exfiltration trenches. In all cases, the program provides suggested design parameter values that the user can modify, test and accept. A special feature allows the output file from one design session to be used as input to automatically test the design for a different storm, test a change in catchment or design parameters or simply to complete a design in two or more sessions.