Attachment C - Stormwater Management Plan - 30-32 Doonella Street_SMP-revA_full (00016826)

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3 Stormwater!Quantity!
The!objective!of!this!component!of!the!study!is!to!investigate!the!potential!impact!
that!the!proposed!development!will!have!on!peak!flows!discharging!downstream!of!
the!site.!!Where!any!increases!of!peak!flows!are!found,!potential!mitigation!options!
will!be!investigated!in!the!form!of!a!detention!system.!!!
Hydrologic!modelling!of!the!catchment!has!been!carried!out!using!WBNM!software!
developed! jointly! by! the! University! of! Wollongong,! Rienco! Consulting! and! Balance!
R&D.! ! The! 2012! version! has! been! used! for! this! investigation.! ! A! peak! flow! rational!
method!calibration!has!also!been!carried!out.!
Modelling! has! been! carried! out! for! the! 1,! 2,! 5,! 10,! 20,! 50! and! 100! year! ARI! storm!
events.!!The!following!scenarios!have!been!investigated:!
          1.!    Existing!Scenario!
          2.!    Developed!Scenario!
          3.!    Mitigated!Scenario!

3.1       Existing!Scenario!
Sub"catchment! fraction! impervious! values! have! been! calculated! based! on! aerial!
imagery! data.! ! The! existing! scenario! sub"catchment! areas! and! fraction! impervious!
values!were!calculated!to!be!0.2527ha!and!20%.!!The!existing!catchment!is!confined!
to!the!site!boundary!itself.!
The!WBNM!model!has!been!calibrated!to!Rational!Method!derived!peak!flows!at!the!
catchment! outlet.! ! Details! of! the! Rational! Method! calibration! are! provided! in!
Section3.2.!
The! WBNM! catchment! lag! parameter! adopted! for! the! investigation! is! 1.8,! which! is!
within! the! accepted! range! of! values! provided! in! the! WBNM! technical! reference!
manual.!!Rainfall!loss!rates!adopted!for!this!investigation!are!an!initial!and!continuing!
loss!of!0mm!and!2.5mm!for!pervious,!and!0mm!and!0mm!for!impervious.!!
WBNM!modelling!has!been!carried!out!for!the!range!of!standard!design!ARI!events!
ranging!from!1!year!up!to!100!years.!!Peak!flows!tabulated!in!this!report!represent!
the!peak!values!extracted!from!this!range!of!storm!events.!!
Table!8:!!Existing!Scenario!WBNM!Outlet!Peak!Flows!

                 1yr!ARI!    2yr!ARI!    5yr!ARI!       10yr!ARI! 20yr!ARI! 50yr!ARI! 100yr!ARI!
    Catchment!                           (m3/s)!                                       (m3/s)!
                 (m3/s)!     (m3/s)!                     (m3/s)!   (m3/s)!   (m3/s)!
      Outlet!      0.08!       0.10!      0.12!          0.14!      0.16!     0.16!       0.18!
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