Response to RFI 30-03-22

                                                                    Suite 14, Clayfield Courtyard
                                                          699A Sandgate Road, Clayfield Qld 4011
                                                              Ph: 07 3862 1886 Fx: 07 3862 1397
                                                                   E: [email protected]




March 30, 2022

Our Ref: 20-004

Noosa Council
P O box 141
TWEANTIN 4565

                             Re: OPW21/0272 MCU20/0128
                        Information Requested dated 11/01/2022

Further Advice

Water Quality & Stormwater

Item 1.
We have reviewed Council’s requirements for providing severe storms to 1:2000 year ARI as
well as 1% AEP at year 2100 including sever blockage. We feel this is unreasonable,
however, to satisfy Council’s request we have undertaken the following:

   -   Analysis has been undertaken for the 1:2000 year ARI storm. This is greater than the
       1% AEP (at year 2100) and, therefore, should satisfy Council’s requirements.
   -   With respect to blockage we have incorporated 100% blockage on pits collecting
       stormwater from surface landscaping and gardens. We have also provide for a major
       blockage of the orifice which has been upgraded to 200mm diameter. We note that
       QUDM specifies that blockages only need to be considered where suitable blockage
       materials exist within the drainage catchment. This we consider as unlikely in this
       development.
   -   The analysis was undertaken using Watercom’s latest design software “Drains”. We
       have included the model for year 2100 stormwater event. The checking module, we
       understand, is available to Council for checking purposes. Results of the requirement
       for the much larger storm has resulted in the following modifications to our original
       model.
       a) Upgrade to a number of internal stormwater pipe sizes
       b) Slightly modified unit floor levels
       c) An overland flow path has been provided around apartment 1.
       d) Raising of the bioretention basin wall height to 74.6m in lieu of 74.4m
       e) Provision of a weir overflow in the retention tank as well as an increase in size.




 Neil McKenzie& Associates | 20004 RFI OPW21/0272                                      1