RFI - Stormwater Management Plan

              5.1.1 Piped Flows (< 10 Year ARI)

              Minor event flows would be conveyed by underground pipework
              through the development site to Serenity Close and down the existing
              pathway to discharge to existing informal wetlands.

              It is proposed to upgrade existing pipework and headwalls within the
              road reserve and pathway in order to cater for the increased catchment
              area but maintain existing alignments and discharge point.
              Notably the nett effect would be to combine the two (2) existing
              stormwater discharge points into one with flows from the additional
              catchment area at the eastern end of Serenity Close effectively moved
              around 120m westward.

              Refer to Engineering Drawings at Appendix A for details.



              5.1.2 Major Event Overland Flows (100 Year ARI)

              Emergency overflow, for events (>Q10) which cannot be wholly
              conveyed by underground pipework would be conveyed overland
              through the development site via a landscaped swale.

              Simple manning calculations (Appendix E) have been carried out at three
              (3) nodes along the proposed route through the development site and
              confirm that 100 Year ARI flows may be conveyed safely in respect to
              maximum velocity x depth products (maximum 0.4m2/se3c – QUDM
              7.0.4.2) and minimum freeboard (minimum 0.3m – QUDM 7.0.3.5).

              Calculations have been performed for both gap flows (Q100-Q10) and
              Q100 + 100% blockage conditions.
              Calculations have applied a Manning roughness coefficient of 0.035
              (short-long grass) reflecting proposed landscape outcomes for the area
              as depicted on Architectural drawings at Appendix B.
              The proposed swale would ‘daylight’ at the western end of the
              development site with emergency flows spreading out into sheet flow
              onto Serenity Close.

              Existing flush kerbing and grated pit at the end of Serenity Close and
              the concrete footpath down to the informal wetland would be reformed
              as part of the pipe upsizing works and convey overland flows to the
              existing informal wetland.




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A6769/22/SWMP/RevB – June 2023                                              Page 8 of 9
SH/PL
                       Brah101 Pty Ltd t/as ALTA PROJECTS