Attachment 6 - Stormwater Management Plan and Engineering Response. · MCU23/0078

BORNHORST + WARD PTY. LTD.

A.B.N. 78 010 151 354



Level 14

133 Mary Street

Brisbane Qld 4000

Australia



                                                                                                                 21 Nov 2023
                                                                                                                Ref. No. 22159

Noosa Shire Council
PO Box 141
Tewantin QLD 4565

ATTENTION:              NADINE GORTON

Dear Nadine,

Re:          28 EENIE CREEK ROAD NOOSAVILLE QLD 4566
             APPLICATION MCU23/0078
             INFORMATION REQUEST

Please find the below responses relating to civil engineering from your RFI dated 17th July 2023.

Issue – Flooding – Item 38:

Provide calculations/modelling for flow within the natural drainage channel within Covenant J on Lot 1 in order to
establish the peak flood levels in the DFE (1% AEP including allowance for climate change at 2100). Provide sections
which show the DFE level relative to the minimum opening elevation in the basement car park and demonstrate that a
minimum freeboard of 300mm is provided.

Civil Response:

A flood assessment of the natural drainage channel within Covenant J on Lot 1 has been undertaken to determine
peak flood levels in the 1% AEP flood event (with allowance for climate change at 2100) under both existing and
developed (with stormwater quantity mitigation) scenarios. Details of this flood assessment, with peak flood
water levels, velocities and water depths can be found in the revised SWMP submitted to Council with this letter.

The 1% AEP flood event water levels within the natural drainage channel can also be found in the revised
earthworks sections found in the revised SWMP and Serviceability Report. It is noted that these levels are slightly
above the minimum basement level, however the minimum opening elevation between the basement and
Covenant J are a minimum of 1.5m higher than the basement floor level based on the architectural drawings. As
such, 300mm freeboard between the openings of the basement wall and the 1% AEP flood levels is achieved.

Issue – Stormwater Quantity – Item 39:

Provide an updated SWMP and stormwater detention analysis which addresses the following:

                    •   Clarify whether rainfall intensities have been increased to account for the effects of climate change at
                        year 2100, and if not provided a revised analysis for the 1%AEP which includes allowance for climate
                        change.
                    •   Consider whether detention for events greater than 63% AEP are required based on the analysis of the
                        capacity of the drainage channel in Covenant J on Lot 1 and the drainage network further downstream.




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