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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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!
3.2 Existing!Scenario!
SubTcatchment! fraction! impervious! values! have! been! calculated! based! on! aerial!
imagery! data.! ! The! existing! scenario! subTcatchment! areas! and! fraction! impervious!
values!for!each!subTcatchment!are!tabulated!below!in!Table!7.!
!
Table!7:!!WBNM!SubbCatchment!Fraction!Impervious!Values!–!Existing!Scenario!
Existing!Scenario!!
WBNM!SubbCatchment! Area!(ha)!
Impervious!(%)!
External! 0.2856! 75!
C1! 0.2265! 0!
C2! 0.3490! 0!
C3! 0.3173! 0!
TOTAL! 1.1784! !
!
The!WBNM!model!has!been!calibrated!to!Rational!Method!derived!peak!flows!at!the!
catchment!outlet.!!Details!of!the!Rational!Method!calibration!are!provided!in!Section!
3.3.!
The! WBNM! model! has! been! calibrated! by! adjusting! the! WBNM! catchment! lag!
parameter.!!The!value!of!the!catchment!lag!parameter!adopted!for!the!investigation!
is!1.49,!which!is!within!the!accepted!range!of!values!provided!in!the!WBNM!technical!
reference!manual.!The!rainfall!loss!rates!adopted!for!this!investigation!are!initial!and!
continuing!losses!of!0!mm!and!2.5!mm!for!pervious!areas,!and!0!mm!and!0!mm!for!
impervious!areas,!respectively.!
WBNM!modelling!has!been!carried!out!for!the!range!of!standard!design!ARI!events!
ranging!from!2!year!up!to!100!years.!!Modelling!has!also!been!carried!out!for!the!full!
range! of! standard! design! event! storm! durations! ranging! from! 15! minutes! up! to! 3!
hours.!!Peak!flows!tabulated!in!this!report!represent!the!peak!values!extracted!from!
this!range!of!storm!events.!!
Table!8:!!Existing!Scenario!WBNM!Outlet!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)!
External! 0.124! 0.153! 0.17! 0.193! 0.201! 0.222!
C1! 0.188! 0.24! 0.27! 0.311! 0.329! 0.365!
C2! 0.111! 0.147! 0.167! 0.195! 0.208! 0.233!
C3! 0.102! 0.135! 0.154! 0.18! 0.191! 0.214!
Outlet! 0.298! 0.387! 0.437! 0.506! 0.536! 0.598!
!
! ! ! 15!
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