OPW16/0021- Operational Works Application 2 of 4

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2 Stormwater!Quality!
2.1 Design!Objectives!
This! report! identifies! the! stormwater! quality! management! objectives! for! the!
operational! phase! (postZconstruction! phase)! of! the! proposed! development.!!
Construction! based! stormwater! quality! management! objectives! will! need! to! be!
addressed!as!part!of!operational!works!documentation.!
Water! quality! objectives! or! performance! criteria! for! the! proposed! urban!
development! in! this! location! are! those! stipulated! in! the! State! Planning! Policy! July!
2014! for! the! South! East! Queensland! region.! ! The! applicable! water! quality! design!
objectives!for!this!location!are!shown!in!Table!1!below.!!!
However,!the!applicability!of!these!objectives!for!this!development!are!questionable.!!
The!SPP4/2010!–!Healthy!Waters!states!that!“the!making!a!material!change!of!use!or!
carrying! out! operational! work! for! the! purposes! of,! or! associated! with,! a! single!
detached! dwelling”! is! outside! the! scope! of! the! policy.! ! However,! the! policy! does!
apply! where! a! MCU! or! ROL! for! urban! purposes! includes! a! land! area! greater! than!
2500! m2.! ! In! order! to! demonstrate! a! high! level! of! protection! of! the! environmental!
values! of! the! receiving! waters! within! the! receiving! catchment! the! water! quality!
objectives!provided!in!Table!1!are!adopted!for!use!in!this!investigation.!
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Table!1:!Site!stormwater!quality!objectives!(operational!phase)!

       Minimum!reductions!in!mean!annual!loads!from!unmitigated!development!(%)!
       Total!Suspended!           Total!              Total!Nitrogen!!   Gross!pollutants!!
         Solids!(TSS)!       Phosphorous!(TP)!             (TN)!             >5!mm!
               80!                   60!                    45!                  90!
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2.2 Stormwater!Quality!Treatment!
2.2.1 Strategy!
The!proposed!development!is!unique!with!respect!to!water!quality!as!the!majority!of!
the! structure! is! proposed! to! be! covered! in! a! living! ‘green’! roof.! ! Detail! of! the!
proposed!living!’green’!roof!is!contained!within!the!site!landscape!plan!(James!Birrell!
Design! Lab,! 2015).! ! The! green! roof! is! proposed! to! consist! of! cells! of! planted! soil!
media!of!a!total!depth!of!200!mm.!!These!cells!will!be!drained!via!an!under!drainage!
network! and! gravel! drainage! channels! to! the! edges! of! the! structure! prior! to!
discharge!from!the!roof.!
While!the!living!‘green’!roof!will!in!effect!act!to!reduce!impervious!area!and!provide!
a!level!of!water!quality!treatment,!for!the!purpose!of!quantification!of!stormwater!
quality! the! roof! area! has! been! included! in! the! quality! treatment! strategy! as!
catchment!area!and!not!as!a!treatment!device.!!
The! original! treatment! train! for! the! proposed! development! was! that! runoff! from!
roads/hardstand!and!roofed!areas!will!be!collected!in!a!stormwater!drainage!system!


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