It is industry best practice to split up the subcatchments in a model into their pervious and impervious areas when adopting the Laurenson (or RAFTS) runoff routing method ie U = 2 and U = 0. The current workflow to achieve this is to setup the model with 2 subcatchments representing the impervious and pervious surfaces within a subcatchment. Existing Innovyze software (ICM and XPSWMM/XPSTORM) provide the user the ability to split the area of a catchment up into a number of different runoff surfaces. A feature like this would be great to have for InfoDrainage.
Thank you for the suggestion and thanks to those who voted/commented.
This is not under consideration and we will update the status here when we make a decision to implement it.