Appendix B - Stormwater Management Report

2.2. Proposed Development Drainage Regime
The proposed subdivision results in the creation of one additional rear lot with an increase of
impermeable surfaces through roof areas and driveway. It is expected that stormwater quantities will
increase as a result of these impermeable areas with attenuation via rainwater tanks proposed.

Existing surface flows from upstream adjacent properties will remain unchanged. The existing
drainage regime of discharging to the Lawful Point of Discharge (LPOD) at the northeastern
boundary (unmapped channel) is maintained in the developed state.

The roof and allotment drainage system for the proposed site shall be designed to comply with:

    1. Noosa Council Planning Scheme SC6.7.6 Stormwater Management and 9.4.8 Water Quality
       and Drainage Code
    2. The Queensland Urban Drainage Manual (QUDM); and
    3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.

Refer to Appendix A Proposed Development Concept Plan for the proposed stormwater drainage layout
plan illustrating the concept described above.


3. STORMWATER CHARACTERISTCS

3.1. Comparison of Pre/Post Development and Quantity
The development proposes to increase the impervious area of the site by 229m2 for the additional
dwelling and allowance for the driveway surface – note this is an approximation to provide allowance
for siting the actual driveway layout.

Pre and post discharge rates have been calculated using DRAINS software to evaluate the effect of
the development. Attenuation of post-development flows have achieved by modelling each dwelling
having a 3kL rainwater tank.

Utilising the modelling methods of ARR2019, parameters from the ARR Data Hub for the site
location, and rainfall Intensity Frequency Distribution data from the Australian Bureau of
Meteorology have been implemented into the DRAINS model to determine the mean peak discharge
rates from the storm events. This is presented in Table 1 below.

                                                                 QPROPOSED M³/S (WITH
% AEP EVENT Q EXISTING M³/S QPROPOSED M³/S (NO ATTENUATION)                           QCHANGE M³/S
                                                                   ATTENUATION)

     63.2           0.020                   0.023                       0.020             0.000

     39.3           0.030                   0.032                       0.027             -0.003

     18.1           0.043                   0.046                       0.041             -0.002

      10            0.051                   0.056                       0.049             -0.002

       5            0.063                   0.066                       0.059             -0.004

       2            0.072                   0.074                       0.067             -0.005

       1            0.082                   0.085                       0.077             -0.005