Attachment 7 - Stormwater Management Plan

                                      STORMWATER MANAGEMENT PLAN
Client: Devcon Capital 9                                                   Location: 11 Leo Alley Road, Noosaville


For your information, the peak stormwater discharge from the site for both the existing case and
developed case was estimated based on the Rational Method (as defined in the Queensland Urban
Drainage Manual 2017), aerial images and council mapping. The parameters used and calculations
are shown in Appendix C.

In summary the peak stormwater discharges are shown in Table 6.

                                 Table 6 – Total Site Peak Stormwater Discharge

                                         Peak Stormwater Discharge
                           AEP (%)                 (L/s)                     Difference
                                       Existing Case    Developed Case
                       10 (minor)           209                210                +0.5%
                      100 (major)           358                361                +0.8%

The results show that there is an increase in peak stormwater discharge from the site in the
developed case when compared to the existing case. However, as the increase in stormwater
discharge is minor (less than 1% in the major storm event) the effect on downstream and
neighbouring properties is considered to be insignificant and negligible.

The peak major storm event discharge to the stormwater main to the east in the easement is
estimated to be 144 L/s via a 225mm RPC pipe. The downstream pipe from development connection
point is a 300mm RCP stormwater main at approximately 2.5% grade. The capacity of the
stormwater main has been approximated to be 180 L/s. Therefore, the stormwater main has the
capacity to cater for the piped stormwater flow from the proposed development.

Further, all stormwater discharging from the site in the developed case will discharge to a
bioretention basin which will have an extended detention depth of 300mm. This equates to
approximately 11 kL of total stormwater detention storage for the site. The stormwater detention
volume was not considered in the calculation of peak stormwater discharge from the developed site.
The peak stormwater discharge values are therefore considered to be conservative and the peak
stormwater discharge from the proposed development is likely to be less than the existing case
scenario. Therefore, the proposed development will have a non-worsening effect on surrounding and
adjacent properties with regards to stormwater discharge.

At the pre-lodgement meeting held for the proposed development, council did not have any
objections with regards to using stormwater treatment devices to provide stormwater
detention/mitigation as shown in Appendix D.




Covey Associates Pty Ltd                                 6                                  Project No: 192297
Consulting Engineers                                                                          26719Rpt, Issue D