Compare the existing and proposed scenarios, in order to clearly demonstrate the betterment

We currently have an existing building which is due to be refurbished. As part of the proposed works, we are introducing an attenuation structure with a restricted discharge flow of 1 l/s. In the existing condition, surface water freely discharges into the drainage system without attenuation.

It would be very helpfull that we can set up the model in Flow (Causeway Flow) to compare the existing and proposed scenarios, in order to clearly demonstrate the betterment.