Catchments are used to capture rainfall events and route the runoff that doesn't infiltrate into the ground, into the stormwater system. The first step is to ensure that the CAD layer is "St_Catchment_Tables" is visible(check-box ticked) in the GIS layer explorer on the left . The following step is to delineate the catchment using the 'Add Catchment' tool 
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Click on the icon and then click on each of the catchment vertices in succession to form the catchment polygon. Once the last vertex has been selected, right click to terminate the draw process. Repeat this process for the remaining catchments. The catchments should all be a light blue-grey once complete. The catchment labelled 'Large Catchment' is to be left out for this section of the tutorial.
For each catchment, first select the junction that will be drained to, then select Model Data -> Model Topology -> Modify Catchment "Drain To", and select the relevant catchment. Once complete a drainage link will be drawn.