2014022_71_SeaviewTce_SWMP-revC_full · OPW16/0021

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treat!runoff!from!the!site!to!a!quality!which!achieves!the!objectives!of!the!SPP!but!
which!will!also!maintain!the!natural!hydrological!regime!as!far!as!is!practical.!!!
The!external!catchment!will!not!contribute!runoff!to!any!bioretention!or!detention!
system!on!site!and!will!be!diverted!around!the!site!to!the!north.!!The!driveway!will!
be! directed! to! a! bioretention! basin! of! 5m2,! to! be! coTlocated! with! the! detention!
basin,! at! the! northern! end! of! the! driveway.! ! Discharge! from! this! basin! will! be!
returned!to!sheet!flow!prior!to!being!discharged!to!natural!areas!within!the!site!but!
below!the!development!footprint.!!The!grassed!area!only!the!southern!boundary!of!
the!site!and!the!pool!deck!and!lawn!are!to!be!collected!and!treated!in!a!bioretention!
basin!of!12m2!surface!area,!outleting!into!the!receiving!environment!via!a!pipe!and!
level! spreader! at! a! location! on! site! below! the! elevation! stipulated! by! the!
development! MCU! approval! conditions.! ! The! hard! surface! roof! will! be! collected!
within!a!25!kL!tank!and!reused!on!the!site!at!an!assumed!rate!of!500!L/day.!!Green!
Roof!(North!and!South)!and!the!lawn!areas!below!the!building!are!not!proposed!to!
be!treated!but!instead!the!runoff!from!the!green!roof!is!to!be!spread!and!returned!to!
sheet!flow!prior!to!reaching!the!natural!vegetation.!!While!it!is!proposed!that!part!of!
the!site!will!not!pass!directly!through!a!water!quality!improvement!device!it!will!be!
demonstrated! that! this! overall! treatment! train! is! sufficient! to! meet! the! entire!
treatment!needs!of!the!site.!
During! the! detailed! building! design! FLOTH! Sustainable! Building! Consultants! have!
undertaken! the! hydraulic! design! of! the! internal! stormwater! management!
infrastructure.! ! The! internal! hydraulic! design! has! been! modified! from! that! initially!
proposed!with!the!OPW!application!in!order!to!address!the!issues!raised!in!the!RFI!
(April!2016).!!As!noted!above!it!is!proposed!that!runoff!from!the!‘hard’!roof!area!be!
collected!within!a!‘Rainwater!Tank’!and!will!now!be!used!for!limited!internal!use!and!
external! water! demands.! ! Water! will! no! longer! be! harvested! from! the! green! roof!
areas!for!reuse!on!the!site!and!instead!will!be!either!discharged!to!the!lawn!areas!in!
order!to!return!flows!to!sheet!flow!prior!to!entering!existing!drainage!paths!or!will!
be!collected!in!a!detention!tank!in!order!to!mitigate!any!increases!in!peak!flows!from!
the! site.! ! Discharges! from! the! site! will,! as! far! as! practical,! be! directed! to! the!
predevelopment!drainage!paths!below!the!proposed!development!footprint.!
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