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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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3.3 Rational!Method!Calibration!
The! existing! scenario! WBNM! model! has! been! calibrated! to! the! Rational! Method!
derived!peak!flows!at!the!outlet!of!the!catchment!draining!to!northern!boundary!of!
the!site!(WBNM!catchment!node!‘Outlet’).!!The!adopted!calibration!parameters!are!
detailed!in!the!Section!3.1.!
A!summary!of!the!Rational!Method!calculation!input!parameters!is!provided!below!
in!Table!9!and!additional!details!of!the!Rational!Method!calculation!are!provided!in!
Appendix!1!of!this!report.!
Table!9:!Rational!Method!Calibration!Summary!(Total!Catchment)!
Parameter! Value!
Time!of!Concentration!(tc)! 6!min!
Catchment!Area! 1.1784!ha!
C10!Value! 0.48!
100!year!Rainfall!Intensity! 302.7!mm/hr!
!
A! comparison! of! peak! Rational! Method! flow! rates! compared! with! peak! WBNM!
model!flow!rates!are!provided!in!Table!10!below.!
Table!10:!Rational!Method!Peak!Flows!Versus!WBNM!Peak!Flows!!
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)!
Rational! 0.24! 0.3! 0.33! 0.42! 0.54! 0.62!
WBNM! 0.298! 0.387! 0.437! 0.506! 0.536! 0.598!
%!Difference! 19%! 22%! 24%! 17%! T1%! T4%!
!
The!above!results!show!that!a!reasonable!peak!flow!calibration!has!been!achieved,!
particularly!for!the!larger!events!of!the!WBNM!model!when!compared!to!a!Rational!
Method! calculation.! ! The! WBNM! model! estimates! slightly! lower! peak! flows! in! the!
smaller! events,! however,! this! would! be! considered! acceptable! in! assessing! nonT
worsening!of!flows.!
3.4 Developed!Scenario!
The! proposed! development! has! been! incorporated! into! the! WBNM! model! by!
adjusting! the! site! subTcatchments! and! the! fraction! impervious! values.! ! Fraction!
impervious! values! of! the! existing! and! proposed! scenarios! are! provided! in! Table! 11!
below.!!The!modelled!development!case!adopts!conventional!impervious!fractions!as!
a! conservative! estimate.! The! developed! scenario! WBNM! model! layout! is! shown! in!
Figure!6!of!this!report.!!!
The! developed! catchments! have! been! modified! to! reflect! the! altered! water!
management! strategy! for! the! site.! ! This! modification! was! undertaken! in! order! to!
address! Items! 1! and! 3! of! the! OPW! RFI! (NSC! 5! April! 2016)! and! differs! from! that!
proposed! in! the! original! OPW! application! (AquaIntel,! RevB,! January! 2016).! ! The!
! ! ! 16!
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