Reference Document - Stormwater Management Plan - RAL26/0001 (As Published)

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 5 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                         0.018              -0.002

      39.3           0.030                      0.032                         0.023              -0.007

      18.1           0.043                      0.046                         0.042              -0.001

       10            0.051                      0.056                         0.047              -0.004

       5             0.063                      0.066                         0.060              -0.003

       2             0.072                      0.074                         0.071              -0.001

       1             0.082                      0.085                         0.082              0.000
TABLE 5 PRE AND POST COMPARISON OF PEAK DISCHARGE RATES

The effect of the underground tank is effective attenuation of discharge rates to maintain existing rates
or even a reduction of the pre-development rates. Controlled flows from the outlet of this tank will be
discharged to the LPOD via a level spreader device to maintain the pre-development drainage
regime.

Refer to Appendix A Proposed Development Concept Plan for the proposed stormwater drainage layout
plan illustrating the concept described above. Note the specific details of the level spreader pipe inlet
will be determined during the Operational Works phase and this demonstrates the drainage concept.


3.2. Quality

        3.2.1.Construction Phase
To fulfill the General Environmental Duty, a person “…must not carry out any activity that causes or is
likely to cause environmental harm, unless measures to prevent or minimise the harm have been taken…”. It is
necessary to manage and mitigate these impacts through best practise erosion and sediment controls.
Due to the development area being less than 2,500 m2 the construction impacts will be managed
using the principles aligned with the desired outcomes of Appendix 2 of State Planning Policy (SPP).

A site-specific erosion and sediment control plan must be prepared and submitted as part of the
Operational Works approval.


        3.2.2.Operational Phase
This development consists of an additional dwelling as part of the subdivision and is consistent in
character with the existing residential dwelling and environment. As the development proposal is not