drainage design & calculations for a building in the UK to cope with the 30 year storm

we are architects and already have a full drainage design for this 4 storey building in the UK
However the local council has asked for more information as below


* Floatation calculations where applicable
* Calculations to demonstrate that the proposed drainage system can contain up
to the 1:30 year storm event without flooding. Any onsite flooding between the
1:30 and the 1:100 climate change storm event should be safely contained on
site
* Clarification regarding the ARWH tank size and intended use of the system
*Updated active rainwater harvesting calculations in accordance with BS EN
16941-1:2018
*Updated drainage layout
* Details of the proposed overland flood flow routes in the event of system
exceedance
* Updated construction drawings for all SuDS and drainage components
* Updated maintenance plan

the freelancer has to study our drawings and report, and work on it comprehensibly to produce the above and satisfy the local council