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2014022_71_SeaviewTce_SWMP-revC_full · OPW16/0021
From the archive OPW16/0021- Response - Civil Plans. File date in the archive: 2016-05-16 04:05.
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Table!13:!!Developed!Scenario!WBNM!Outlet!Peak!Flows!–!Outlet!2!
Developed!
Existing!Peak! Change!in!Peak! %!increase!in!Peak!
!! Flow!(m3/s)!
Conventional!Peak!
Flow!(m3/s)! Flow!
Flow!(m3/s)!
2!year! 0.11! 0.13! 0.02! 15%!
5!year! 0.15! 0.17! 0.02! 12%!
10!year! 0.17! 0.19! 0.02! 10%!
20!year! 0.20! 0.22! 0.02! 9%!
50!year! 0.21! 0.23! 0.02! 9%!
100!year! 0.23! 0.26! 0.02! 8%!
!
It!can!be!seen!that!the!peak!flows!have!increased!to!the!catchment!outlets.!!This!is!a!
result! of! the! development! increasing! the! impervious! area.! ! Mitigation! within! the!
catchment! will! be! required.! ! In! order! to! achieve! a! conservative! outcome! and!
recognizing! that! the! ‘green’! roof! will! not! act! entirely! as! a! catchment! with! a! 0%!
impervious!fraction!sizing!of!detention!infrastructure!was!undertaken!based!on!the!
developed!scenarios!with!the!conventional!roof!structure.!
3.5 Mitigated!Scenario!
When!comparing!the!peak!flows!in!the!existing!and!developed!scenarios,!increases!
in!the!peak!discharge!occur!at!the!catchment!outlets.!!As!a!result!a!realignment!of!
discharge! locations! has! been! undertaken,! as! described! previously.! ! Detention! will!
occur!from!the!driveway!via!the!combined!detention!and!bioTretention!basin,!flows!
from! the! hard! roof! will! be! captured! initially! in! the! 25! kL! Rainwater! Tank,! with!
overflows!to!the!25!kL!Stormwater!Tank,!with!low!flow!outlet!pipes!reducing!volume!
release!and!velocity!rates.!!The!Rainwater!Tank!will!not!serve!as!detention!storage.!!
Runoff!from!the!northern!half!of!the!green!roof!will!be!directed!primarily!onto!lawns!
to! create! sheet! flow! prior! to! exiting! into! the! natural! bushland.! ! Runoff! from! the!
southern!half!of!the!green!roof!will!be!directed!to!the!25!kL!Stormwater!Tank.!!The!
mitigated!scenario!is!detailed!in!Figure!7.!
Table!14:!Storage!and!Outlet!Details!of!Detention!System!
Peak!100!yr!
Storage! Storage!Height!
Catchment! Outlet!Dimensions! Water!Depth!
Volume!(m3)! (m)!
(m)!
1!x!50mm!at!the!
base!of!the!tank!plus!
SW!Tank!! 25! 2.0! 1.97!
1!x!100mm!IL!0.9m!
above!base!
2!x!225!mm!at!1.775!
Rainwater!
25! 2.0! from!the!base!of!the! 2.0!
Tank!
tank!
Driveway!
5m!weir!plus!50mm!
Detention! 7! 0.7!#! 0.704!
outlet!
Basin!
! ! ! 18!
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