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