OPW16/0021- Operational Works Application 2 of 4

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this!catchment!will!be!significantly!reduced!in!events!up!to!and!including!the!100!yr!
ARI! event.! ! As! such,! no! further! consideration! of! the! developed! impacts! in! this!
catchment!are!reported!in!this!plan!and!all!previous!requirements!for!detention!in!
this!catchment!are!deleted.!
!
Table!11:!!WBNM!SubbCatchment!Fraction!Impervious!Values!–!Developed!Scenario!
                                                              Developed!
                                                              Scenario!b!         Existing!Scenario!
      WBNM!SubbCatchment!                  Area!(ha)!
                                                             Conventional!         Impervious!(%)!
                                                            Impervious!(%)!
External!                                   0.286!               75!                     75!
D1c!                                        0.155!                0!                      0!
D1a_Driveway!                               0.026!               100!                     0!
OPW_Green_Roof!                             0.067!               100!                     0!
OPW_Lower_A!                                0.024!                0!                      0!
OPW_Lower_B!                                0.057!                48!                     0!
OPW_Roof!                                   0.022!               100!                     0!
C3!                                         0.317!                0!                      0!
                 Total!                     1.175!                 !                      !
!
Peak! flows! tabulated! in! this! report! represent! the! peak! values! extracted! from! the!
modelled!range!of!storm!events.!!
Table!12:!!Developed!Scenario!WBNM!Outlet!Peak!Flows!–!Outlet!2!

                                              Developed!
                          Existing!Peak!     Conventional!      Change!in!Peak!      %!increase!in!
!!                         Flow!(m3/s)!       Peak!Flow!         Flow!(m3/s)!         Peak!Flow!
                                                (m3/s)!
      2!year!                 0.11!              0.13!                  0.02!             14%!
      5!year!                 0.15!              0.16!                  0.02!             12%!
     10!year!                 0.17!              0.19!                  0.02!             11%!
     20!year!                 0.20!              0.21!                  0.02!             9%!
     50!year!                 0.21!              0.23!                  0.02!             8%!
     100!year!                0.23!              0.25!                  0.02!             8%!
!
It!can!be!seen!that!the!peak!flows!have!increased!at!the!outlet!of!Catchment!2!(C2).!!
This!is!a!result!of!the!realignment!of!catchment!boundaries!with!most!of!the!flows!
directed!through!Catchment!2.!!Hence,!for!Catchment!1!mitigation!is!not!required.!!
Mitigation!within!Catchment!2!will!be!required!due!to!worsening!of!flows.!!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.!


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this catchment will be significantly reduced in events up to and including the 100 yr
ARI event. As such, no further consideration of the developed impacts in this
catchment are reported in this plan and all previous requirements for detention in
this catchment are deleted.

Table 11: WBNM Sub-Catchment Fraction Impervious Values — Developed Scenario

 

 

 

 

 

 

 

 

 

 

 

Developed
WBNM Sub-Catchment Area (ha) Consational ms serious ()
Impervious (%)
External 0.286 a5 75
Dic 0.155 0 0
D1a_Driveway 0.026 100 0
OPW_Green_Roof 0.067 100 0
OPW_Lower_A 0.024 0 0
OPW_Lower_B 0.057 48 0
OPW_Roof 0.022 100 )
C3 0.317 0 0
Total 1.175

 

 

 

 

 

Peak flows tabulated in this report represent the peak values extracted from the
modelled range of storm events.

Table 12: Developed Scenario WBNM Outlet Peak Flows — Outlet 2

 

 

 

 

 

 

 

 

Developed
Existing Peak Conventional Change in Peak % increase in
Flow (m?/s) Peak Flow Flow (m?/s) Peak Flow
(m?/s)
2 year 0.11 0.13 0.02 14%
5 year 0.15 0.16 0.02 12%
10 year 0.17 0.19 0.02 11%
20 year 0.20 0.21 0.02 9%
50 year 0.21 0.23 0.02 8%
100 year 0.23 0.25 0.02 8%

 

 

 

 

 

 

It can be seen that the peak flows have increased at the outlet of Catchment 2 (C2).
This is a result of the realignment of catchment boundaries with most of the flows
directed through Catchment 2. Hence, for Catchment 1 mitigation is not required.
Mitigation within Catchment 2 will be required due to worsening of flows. 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.

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