RFI - Att 4 - Stwtr Mngmt Plan

                                                                                                                     ingeniir

      •   IECA Principles of Construction Site ESC – available here
      •   Water by Design ESC Factsheet Suite – available here

Detailed Erosion and Sediment Control design and plans should be documented by a suitably experienced
professional in conjunction with any application, or prior to commencing with the Building Works associated
with the proposed development on site.


5.2       Operational Phase

The site has a lot area of 607 and as such does not trigger local or state requirements for operational
treatment objectives for stormwater quality.

With reference to Acceptable outcome AO2.1 of the Sustainable Building Design Code - a minimum 3,000
litres of rain water storage is to provided per dwelling and reused for non-potable purposes, an example
product is shown in Appendix 3 | Duraplas Lattice Tank Details.


6.        STORMWATER QUANTITY
The Bureau of Meteorology 2016 IFD service has been used for all analysis in this report.

A Rational Method estimation of the stormwater discharge has been used to estimate the pre-developed and
developed runoff performance of the site.

                                  RATIONAL METHOD SITE DISCHARGE SUMMARY
                                    Pre-Development      Post-Development
                      AEP                           Duration                        Duration       Performance
                                    Q (m3/s)                        Q (m3/s)
                                                     (min)                           (min)
                    63.20%              0.013                  5        0.014                  5              7.7%
                    39.35%              0.018                  5        0.019                  5              5.6%
                    18.14%              0.025                  5        0.026                  5              4.0%
                      10%                0.03                  5        0.031                  5              3.3%
                      5%                0.036                  5        0.038                  5              5.6%
                      2%                0.046                  5        0.048                  5              4.3%
                      1%                0.053                  5        0.055                  5              3.8%
                       Table 1: Comparison of pre and post development site discharges to Coral Tree Avenue

As demonstrated in Table 1, the proposed development does not produce a material worsening of flows and
is discharging to a controlled discharge point being Coral Tree Avenue so is deemed unable to cause a
downstream nuisance as the peak increase in discharge is a maximum of only 2L/s. It is considered that the
redirection of existing flows exiting the Northern boundary of the site directly to Coral Tree Avenue is a
beneficial outcome.

The site is also noted as receiving some flows from 28 Banksia Avenue to the West. The proposed
development is designed to convey these flows around the proposed building by providing a cut-off drain
behind the Western retaining wall that directs flows to the driveway to discharge through to Coral Tree
Avenue in a sheet flow manner.

Currently there is no discernable drainage path for the flows from 28 Banksia Avenue, so the provision of a
drainage path for these flows is considered an improvement to the current scenario. Appendix 2 | Rational
                                                Ingeniir Pty Ltd | 221304-SMP-01
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