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5179Flood Report_REV_3
FLOOD ASSESSMENT REPORT
REVISION 3
16 Lot Reconfiguration at Pearsons Road, Cooroy
FOR
VANTRALIA PTY LTD
APRIL 2021
Pathway
H
16
RP881300
15
RP881300 14
RP881300
13
RP881300 RP881300
12
S
RP881300
RP881300
10
RP881300
AD
BM: Pin
RP881300
H
RL: 109.315
WM
S
99
RP881300
RO
BM: Pin
RL: 107.32
Park
S
11
4 00
12
21
938m² S
13
AR
766m² ex access
99.9
606m²
15
YE
836m²
WM
600m² 14 100 YR
99.85
NOW
624m²
S
.95
ON
99
10
S
RP113733
686m²
AR
PE
9 AY
86
RW
.26
100
E
66
AT
19
W
WM
656m²
SP
Shed
.29
D
PE
Single Storey
Brick House
8 M
AP
100 100
16 1165m²
3524m²
H
681m² 931m² ex Emt Park 100.19
ay
100 YR
7
BM: PM24974
RL: 110.614
NOW
6
210 4
0
Pathw
YE 100.3
781m² 600m² 5 4
AR
600m²
600m² 3
Emt AS
2
STREET
Em ck
tA
600m²
a
44
Tr
600m²
ELM
SP305293
43
Timber Retain
ing Wall
Timber Retaini
1
ng Wall
600m²
SP305293 42
SP305293 41
SP305293 40 39 38 Timber Reta
ining Wall
SP305293 SP305293 SP305293
Emt AT
101
SP291337
45 37 WM H
Park
SP305293
SP305293 36
SP305293 35 33
Emt AQ
SP305293 SP305293
34
Emt AR
SP305293
SPOTT
ED GUM
T
COURT
REN C
BLUE W
Callaghan & Toth
Civil, Environmental &
Hydraulic Engineers
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Callaghan & Toth
DOCUMENT HISTORY
Document Reference: No: 2035_Flood_Revision 3.doc
Project Manager: Max Watterson
Author: Denis Ogle BE (CIVIL)
Reviewer: Lex Toth RPEQ (ENV) (CIVIL) RPEQ 6069 CPESC
Client: Vantralia Pty Ltd
Contact Person: Darren Matthews
DISTRIBUTION LIST
POSITION ON
NAME ORGANIZATION REVISION REVISION REVISION
MANAGEMENT TEAM
1 2 3
Darren Matthews Vantralia Pty Ltd Client 1 1 1
Environmental / Civil
Lex Toth Callaghan & Toth 1 1 1
Engineers
Noosa Council Assessment Officer 1 1 1
Max Watterson Max Watterson & Assoc Surveyor 1 1 1
REVISION LIST
REVISION DATE DISTRIBUTED ISSUED BY CHECKED BY
0 8th Sept 2020 DO LT
1 30th November 2020 DO LT
2 5th February 2021 DO LT
3 22nd April 2021 DO LT
The information contained in this report is confidential and proprietary to Callaghan and Toth. It may only be used by the
person to whom it is provided, for the stated purpose for which it is provided, and must not be imparted to any third person
without the prior written approval of Callaghan and Toth. Callaghan and Toth reserve all legal rights and remedies in relation
to infringement of its rights in respect of its confidential information.
©
Callaghan & Toth
2021
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
CONTENTS
1.0 INTRODUCTION .................................................................................................................... 4
Figure 1.2 Existing Site Topography And Relevant Catchment Boundaries ............................. 5
Figure 1.3 Proposed Development Layout And Relevant Catchment Boundaries ..................... 5
2.0 FLOOD IMMUNITY ................................................................................................................. 6
3.0 STORMWATER DETENTION REQUIREMENT ............................................................ 7
3.1 Broad-Brush Estimate Of Required Detention Volume ....................................................... 7
3.2 Hydrologic Model Set Up .................................................................................................... 7
Table 1 Predicted Peak Outflow Rates (m3/sec) – Sanity Check................................................ 8
3.3 Model Determination Of The Required Detention Volume ................................................. 9
Table 2: Required Detention Volumes ....................................................................................... 9
3.4 Provision of Required Detention Volume ............................................................................ 9
Table 3 Required Detention Water Levels.......................................................................... 9
4.0 SUMMARY ........................................................................................................................... 11
APPENDIX 1 - Reconfiguration of a Lot Layout plans .................................................................... A
APPENDIX 2 - FLOOD CALCULATIONS ..................................................................................... D
LIST OF FIGURES
Figure 1.1 Site Location Plan……………………………………………………………..........4
Figure 3.1 URBS Model of the Pre-Development Catchment Condition……….………….7
Figure 3.2 URBS Model Of the Post-Development Catchment Condition……….……......8
Figure 3.3 Proposed Stormwater Detention Facilities………………………………..…......10
LIST OF TABLES
Table 1 Predicted Peak Outflow Rates……………………..……………. …………………………8
Table 2 Required Detention Volumes …………………….……………. …………………………..9
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
1.0 INTRODUCTION
This Flood Study has been prepared as part of a Reconfiguration of a Lot (RAL) application to Noosa Council.
The lot contributing to the overall development and subject to this report is shown in the Site Location Plan, Figure
1.1, below, and is described as Lot 3 on RP113733, located at 2 Pearsons Road, Cooroy. The existing topography of
the site and the relevant catchment areas are shown in Figure 1.2 on the following page of this report, together with
the proposed development layout on Figure 1.3.
The north-east corner of the site is traversed by the floodway of a tributary of Six Mile Creek, and a minor waterway
flows in a north-easterly direction across the middle of the lot.
The increased stormwater runoff from the proposed residential areas will be mitigated by an off-line detention basin
linked to a flow profile control in the minor waterway, as shown in Figure 1.3. The development proposal is
particularly cognisant of the need to not adversely affect the storage-routing capacity of the adjoining floodway and to
not increase local stormwater peak discharge rates to that floodway.
The assessment process was therefore structured as follows:
• Abstraction of the Year2100 1%AEP flood levels from a 2014 flood model of the adjoining floodway
compiled by Brisbane Stormwater Management Pty Ltd, so as to define the floodway boundaries, and then ensuring
that the new lots are flood-immune and the stormwater detention facilities to not intrude into that floodway - as
described in Section 2.0 of this report.
• Determination of the required detention volume so as to match the post-development peak discharges to
the pre-development peak discharges, from 1 year ARI to 100 year ARI, and proposing a detention arrangement that
will achieve that volume – as described in Section 3.0 of this report
Site location
Figure 1.1: Site Location
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
Page 5
_ Callaghan & Toth DASHED PART OF +. CATCHMENT BDY J+ ALIGNED ALONG '6) EXTENT OF WORKS (SEE FIGURE 1.3) ATCHMENT BDY 0 SCALE 50m jr ae Figure 1.2 Existing Site Topography And Relevant Catchment Boundaries Figure 1.3 Proposed Development Layout And Relevant Catchment Boundaries 2035 2 Pearsons Road — Flood Study — Revision 3 April 2021
Page 6
Callaghan & Toth
2.0 FLOOD IMMUNITY
The Year 2100 1%AEP flood levels across the north-east corner of the site have been abstracted from a
flood study undertaken by Brisbane Stormwater Management Pty Ltd for the adjoining Erindale
Development in 2014. The relevant flood levels are 100.34 m AHD across the eastern (upstream)
boundary of the site and 99.94 m AHD across the northern (downstream) boundary of the site. Those
Year 2100 1%AEP flood levels are marked on the preceding Figure 1.3 and on Figures 3.2 and 3.3
hereafter, together with the inferred Year 2100 1%AEP flood boundary between those two levels.
The proposed lots are seen, in comparison to the 0.5 metre contours on Figure 3.3, to be at least a metre
above the flood profile and will therefore be immune to 100-year flooding, even with a 20% impost on the
design rainfalls for future climate change.
The proposed stormwater detention facilities are also seen on Figures 1.3 and 3.3 to be outside the Year
2100 1% AEP flood boundary and will therefore have no impact on the storage-routing capacity of the
floodway.
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
3.0 STORMWATER DETENTION REQUIREMENT
3.1 Broad-Brush Estimate Of Required Detention Volume
The proposed reconfiguration of the site, seen in Figure 3.2, will comprise 16 lots and an internal road
and a park. Lot 16 will retain its existing structures and other paved areas, thereby having no impact on
the site’s stormwater runoff. The remaining lots 1 to 15 and the internal road, will have a combined area
of 1.34 hectares. The required 100-year detention volume is expected to be in the order of 250 to 300
cubic metres for each hectare of a development platform of this lot density. For the abovementioned 1.34
hectare platform, this equates to a 100 year detention volume in the order of 335 to 402 cubic metres.
3.2 Hydrologic Model Set Up
For the sake of simplicity at this RAL stage of the development application, the required 100-year
detention volume has been determined by URBS modelling of the pre-development and post-
development catchment conditions, using the ARR87 design storm rainfall data with a simple
initial/continuing loss model. A more complex modelling procedure at the Operational Works stage, using
the Bureau of Meteorology’s 2016 design rainfall data, could result in a slightly smaller detention volume.
The pre-development catchment condition and the relevant catchment area and model subareas are
shown in Figure 3.1. The modelled catchment includes the existing development to the south, which
features a 525 mm diameter bypass pipe with a full-flow bypass capacity of 0.46 m3/sec (or slightly more
than Q5) to conduct lower flows away from the proposed development site. The total catchment area in
the model is 3.27 hectares, including 1.47 hectares in the adjoining development to the south. The
modelled catchment includes the site of the proposed open detention basin but excludes the area of a
proposed park in the north-east corner of the site, which will not be noticeably impacted by the proposed
development.
2
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ACITY
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REN
BLUE W
#2
CATCHMENT BDY 0 SCALE 50 m
Figure 3.1 URBS Model of the Pre-Development Catchment Condition
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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The Urbs model of the post-development catchment condition, covering the same overall catchment
area as the Urbs model of the pre-development condition, is shown in Figure 3.2. The model’s subarea
network for the external catchment in the adjoining development to the south is identical to that used for
the pre-development model.
28
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0 SCALE 50 m
Figure 3.2 URBS Model of The Post-Development Catchment Condition
The models’ operating parameters comprised the commonly-used default value of 1.2 for the alpha
parameter and an m (non-linearity) exponent of 0.8. The initial rainfall loss was set at 20 mm and the
continuing loss rate was set at 2 mm/hr, for all of the modelled ARI’s from 1 year to 100 year.
The models’ predictions of the peak outflow rates from the system, at the location of the outflow from the
proposed detention basin, are summarised in Table 1 hereafter. That tabulation also includes Rational
Method calculations of the peak outflow rates, to provide a sanity check on the models’ performance.
Table 1 Predicted Peak Outflow Rates (m3/sec) – Sanity Check
ARI Pre-Development Post-Development, Without Detention
(years) URBS Rational Method URBS Rational Method
100 0.89 1.07 1.00 1.25
20 0.60 0.58 0.67 0.72
5 0.41 0.39 0.48 0.48
1 0.15 0.20 0.24 0.25
8
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
3.3 Model Determination Of The Required Detention Volume
The hydrologic modelling process at this RAL stage has determined only the required detention volumes
at various ARI’s from 1 to 100 years and has not calculated the exact dimensions of the outlet control
works that would accompany those volumes.
The required detention volumes were determined by adding a tabulation of storage-discharge pairs to the
model of the post-development condition and then successively adjusting the storage values in that
tabulation until the. model indicated that the adjusted storage on each data line produced the adjusted
basin outflow on that line and matched the pre-development discharges from the total catchment after
adding the unmitigated discharges from subarea #14. The resultant basin storages and total catchment
outflows for each ARI are summarised in Table2, below. The required 100-year storage requirement is
predicted to be 334 cubic metres, or almost exactly equal to the 335 cubic metre lower limit of the broad-
brush assessment in Section 3.1 of this report. The 334 cubic metres includes 128 cubic metres for no-
worsening of the 1 Year peak discharges to the downstream waterway, as required for downstream
waterway stability.
Table 2: Required Detention Volumes
ARI Pre-Dev. Outflow Post-Dev. Outflow (m3/sec) Storage Volume
(years) (m3/sec) Required (m3)
No Basin With Basin
100 0.93 1.06 0.93 334
20 0.62 0.74 0.62 285
5 0.43 0.53 0.43 216
1 0.16 0.21 0.16 128
3.4 Provision of Required Detention Volume
The required 100-year detention volume of 334 cubic metres is proposed to be provided partly in an open
offline detention basin and partly by backwatering the minor waterway upstream of the proposed footpath
crossing, as shown in Figure 3.3 on the following page of this report.
The detention volumes in Table 2 require the following detention water levels in Table 3 below, as
calculated in Item 8 of the calculations appended hereto. Those calculations allow for the detention
requirement being achieved over-and-above the normal (un-backwatered) flow volumes in the swale.
Table 3 Required Detention Water Levels
ARI (years) Req’d Volume (m3) Req’d Water Level (m)
100 334 101.26
20 243 101.09
5 190 100.98
1 128 100.84
The required water levels can be controlled by a low-flow culvert of approximately 375 mm diameter at
the footpath crossing of the swale together with a weir outlet box in the basin for mid- to high-flows. A sag
in the footpath crossing can provide further high-flow control while also providing for emergency release
in higher flows or during debris blockage of the other outlets. These facilities have not been designed in
detail at this RAL stage of the application. A freeboard of at least 0.2 metre to the footpath will provide for
a greenhouse-induced 20 percent increase in storm rainfall intensities.
9
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
LOW-FLOW OUTLET PIPE, APPROX 375 DIA TH
EMERGENCY / HIGH FLOW WEIR OVER FOOTPA
94 00
CONFINEMENT BUND
SWALE
99E. AR 21
0.8
10
xIL 100.10
4
Y
1.
0 0.
10 10
BACKWATERED SWALE 0.6 100 YR
2
10
1.
4
5m WIDE x 0.5m DEEP VEE
1.
10
10
x FL 100.45 99.85
375 DIA
1 ON 4 BATTERS ABOVE 2 x APPROX
102
x NOW
100.6
0.8
.0
10
101
x .95
99
2
100
100.8
L TW 101.10
.
101
WAL
MID/HIGH FLOW OUTLET BOX
101.2
101.4
OFFLINE BASIN
x TW 101.35
101.4
100 YR WL 101.26
1
FOOTPA
10
BIO FL 100.55
x
100.6
FL 100.55
x
TH
101.4 101.2 101.0 100.8
FOOTPATH
.26
100
0 SCALE 25m
Figure 3.3 Proposed Stormwater Detention Facilities
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
4.0 SUMMARY
The proposed residential lots fronting the creek’s floodway will have at least a metre of a freeboard to the
Year2100 1%AEP flood level in the adjoining floodway and the proposed development will therefore be
adequately flood-immune, even with a 20% impost on the design rainfalls for future climate change.
The proposed stormwater detention facilities will be located outside the Year 2100 1% AEP flood
boundary and will therefore have no impact on the storage-routing capacity of the floodway.
The required 100-year stormwater detention volume is 334 cubic metres. This can be achieved by an
open offline basin linked to an elevated backwater profile in the minor waterway swale, with the required
volume being achieved over-and-above the normal (un-backwatered) flow volume in the swale. Lateral
flows from the swale to the basin will commence when the water depth in the swale reaches 0.3 metres.
A more complex modelling procedure at the Operational Works stage, using the Bureau of Meteorology’s
2016 design rainfall data, could result in a slightly smaller detention volume.
The 334 cubic metre volume includes 128 cubic metres for no-worsening of the 1-year peak discharge to
the downstream waterway, as required for downstream waterway stability.
The 100-year water depth is expected to be 1.15 metres above the invert of the low-flow outlet pipe and
0.8 metres above the floor of the open basin. A freeboard of 0.25 metres to the basin’s embankment
crest will be sufficient to contain the inflows from a greenhouse-induced 20 percent increase in storm
rainfall intensities.
11
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
APPENDIX 1 - Reconfiguration of a Lot Layout plans
A
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
Page 13
RP881300
99 Callaghan & Toth
RP881300
Park Civil, Environmental &
S
Hydraulic Engineers
+
94 0
+
99.AR 210
+
+
+
+ S
13 15
+
YE
836m²
600m² 14 100 YR
99.85
NOW
624m²
.95
99
EJ
10
0W
100W
100W
100WEJ
SC
100W
100W AY
SC
86
.26
W
ER 100W
SC
100
66
AT 100W
19
SC
W
100W
SC
SP
.29
D
PE
100
AP
100
SC
EJ M
100W
SC
SC
SC
3524m²
EJ
SC
Park 100.19
100 YR
10
0W NOW
R 2 .34
100
4
0
5
10
E A
600m² 600m²
3
100W
Y
2 EJ
ac
k
tA
600m² T r
600m²
Em
1
100W
600m²
38 Timber R
etaining
Wall
SP305293
100W
101
SP291337
37 WM H
Park
SP305293
36
SP305293 35 33
Emt AQ
SP305293 SP305293
SC SC
100W
SC SC
34
Emt AR
WM
EJ
SP305293
+
Gum
SPOTT
ED GUM
CT
COURT
Page 14
Callaghan & Toth
E
Civil, Environmental &
H
E
Hydraulic Engineers
E
16
E
RP881300
15
E
RP881300 14
RP881300
E
13
E
RP881300
12
S
RP881300
E
AD BM: Pin
RL: 109.315
H
S
E
WM
RO
BM: Pin
RL: 107.32
E
11
938m² 12
766m² ex access
13
E
606m²
WM
600m²
S E
WM WM
0W
N
10
10
10
0 W
SO
EJ EJ
E
100W
RP113733 10
0W
686m²
E
AR
WM
100W
WM
WM
PE
+
SC
WM
SC
9
0W
+ +
E
10
+ SC
SC
+ EJ
+
+ + SC
E
SC
WM
+ Shed 656m² +
SC
SC
E
Single Storey + SC WM WM
8
+
E
Brick House EJ
WM
16
SC E
+ +
SC
E
1165m² + SC
H
+
681m² 931m² ex Emt SC
E
ay
E
7
BM: PM24974
RL: 110.614 E
6
Pathw
781m² 600m² 5
600m²
Emt AS
STREET
44
ELM
E
Timber Re
SP305293 taining W
all
43 Timber Re
taining W
all
SP305293 42
SP305293 41
E
SP305293 40 39 38
SP305293 SP305293 SP305293
Emt A
Page 15
way
7 6
10
0W
Callaghan & Toth
100
781m²
5 4 Civil, Environmental &
2
Path
600m²
AR
Hydraulic Engineers
YE
600m² 600m²
3
100W
2 EJ
ac
k
tA
600m² Tr
600m²
Em
Timber Re
tainin g Wall
1
100W
Timber Re
taining W
all
600m²
40 39 38 Timber R
etaining
Wall
SP305293 SP305293 SP305293
100W
37 WM H
SP305293
36
SP305293 35 33
Emt AQ
SP305293 SP305293
34
Emt AR
SP305293
SPOTT
E D GUM
T
COURT
REN C
BLUE W
Page 16
Callaghan & Toth
APPENDIX 2 - FLOOD CALCULATIONS
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
APPENDIX – RELEVANT CALCULATIONS
1. Bypass Capacity
2. Design Rainfall Intensities
3. Rational Method Flows – Pre Development
4. Urbs Catchment File – Post Development
5. Rational Method Flows – Pre Developed
6. Urbs Catchment File – Post Development
7. Required Storage
8. Storage Provision
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2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
1. BYPASS CAPACITY
The bypass facility is a 525 mm pipe along Spotted Gum Court in the adjoining development to the
south.
That bypass pipe was originally intended to have a Q5 capacity.
Callaghan & Toth’s 2018 Council-approved HGL tabulation for the bypass pipe indicates a design flow
rate of 0.434 m3/sec at a HWL of 104.602 (c.f. surface level of 105.359) and a TWL of 102.185.
Qcap = [ (105.359 – 102.185) / (104.602 – 101.805) ]0.5 x 0.434 = 0.46 m3/sec.
2. DESIGN RAINFALL INTENSITIES
Based on ARR 1987
F
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
Page 19
ail Callaghan & Toth 3. RATIONAL METHOD FLOWS — PRE DEVELOPMENT ATCHMENT BDY 50m Catchment Area = 1.80 (Pearsons Rd) + 1.47 (Elm St) = 3.27 Ha C10 Runoff Coefficients: 0.69 (Pearsons Rd) and 0.79 (Elm St) Concentration Times: From Elm St: 8m sheet flow @ 1% = 8.0 mins 60 m swale flow @ 1% = 4.0 mins 80 m pipe/path @ 4% @1m/s_ =1.3 mins 57 m pipe/road @ [email protected]/s = 0.7 mins 175 m swale/gully@ 1m/s = 3.0 mins Total: 17 mins From Pearsons Rd: 190 m sheet flow @6% = 18mins Adopt: 18 mins. Q100 = (0.00278 x 1.20 x 0.69 x 190 x 1.80) + [(0.00278 x 1.20 x 0.79 x 190 x 1.47) — 0.46] = 1.07 m/sec Q20 = (0.00278 x 1.05 x 0.69 x 148 x 1.80) + [(0.00278 x 1.05 x 0.79 x 148 x 1.47) — 0.46] = 0.58 m°/sec Q5 = (0.00278 x 0.95 x 0.69 x 120 x 1.80) + [(0.00278 x 0.95 x 0.79 x 120 x 1.47) — 0.46] = 0.39 m/sec Q1 = 0.00278 x 0.80 x 0.69 x 74 x 1.83 = 0.20 m/sec 2035 2 Pearsons Road — Flood Study — Revision 3 April 2021
Page 20
Callaghan & Toth
4. URBS CATCHMENT FILE – PRE DEVELOPMENT
2 Pearson Rd Cooroy - Existing.cat
Model: Basic
Uses: L U I
Default Parameters: alpha=1.20 m=0.8
13 Subareas of Area:
0.0011 0.0010 0.0036 0.0032 0.0032 0.0026 0.0041
0.0022 0.0041 0.0025 0.0031 0.0016 0.0004
Factor=1.50
Rain # 1 L=0.030 U=0.00
Route L=0.030 U=0.25
Store.
Rain # 2 L=0.015 U=0.00
Get.
Route L=0.030 U=0.25
Store.
Rain # 3 L=0.020 U=0.20 I=0.55
Get.
Route L=0.045 U=0.20
Store.
Rain # 4 L=0.020 U=0.20 I=0.55
Route L=0.056 U=0.20
Get.
Route L=0.036 U=0.50
Store.
Rain # 5 L=0.030 U=0.25 I=0.55
Store.
Rain # 6 L=0.030 U=0.25 I=0.55
Get.
Get.
Print. TMR1
Loss C=0.46
{Throws away everything up to 0.46 m3/s}
Print.TMR2
Route L=0.060 U=0.00
Store.
Factor=1.00
Rain # 7 L=0.051 U=0.00 I=0.20
Add Rain # 8 L=0.027 U=0.00 I=0.00
Get.
Route L=0.093 U=0.00
Store.
Rain # 9 L=0.033 U=0.00 I=0.00
Get.
Route L=0.039 U=0.00
Store.
Rain # 10 L=0.075 U=0.00 I=0.02
Add Rain # 11 L=0.066 U=0.00 I=0.00
Get.
Store.
Rain # 12 L=0.022 U=0.00 I=0.00
Store.
Rain # 13 L=0.018 U=0.00 I=0.00
Get.
Get.
Print. OUT
End of Catchment Definition.
H
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
Page 21
ail Callaghan & Toth 1 Pluviographs: Location. ARR_TEMPORAL_DATA 13 Subareas: 1234567 8 9 10 11 12 13 End of Pluviograph Data. End of Gauging Station Data. 5. RATIONAL METHOD FLOWS —- POST DEVELOPMENT ae Catchment Area = 1.80 (Pearsons Rd) + 1.47 (Elm St) = 3.27 Ha C10 Runoff Coefficients: 0.78 (Pearsons Rd) and 0.79 (Elm St) Concentration Times: From Pearsons Rd: 60m sheet flow @ 4% = 13.0 mins 45m driveway @ [email protected] m/sec = 1.5 mins 60m pipe/road @ [email protected] m/sec = 0.4 mins 60 m swale @ 3% = 0.8 mins Total: 15.7 mins From Elm St: 8m sheet flow @ 1% = 8.0 mins 60 m swale flow @ 1% = 4.0 mins 80 m pipe/path @ 4% @ 1m/s = 1.3 mins 57 m pipe/road @ [email protected]/s = 0.7 mins 78 m swale/path @ 1m/s = 1.6 mins 60m pipe/road @ [email protected] m/sec = 0.4 mins 60 m swale @ 3% = 0.8 mins 2035 2 Pearsons Road — Flood Study — Revision 3 April 2021
Page 22
Callaghan & Toth
Total: 16.4 mins
Adopt: 16 mins.
Q100 = (0.00278 x 1.20 x 0.78 x 200 x 1.80) + [(0.00278 x 1.20 x 0.79 x 200 x 1.47) – 0.46] = 1.25
m3/sec
Q20 = (0.00278 x 1.05 x 0.78 x 158 x 1.80) + [(0.00278 x 1.05 x 0.79 x 158 x 1.47) – 0.46] = 0.72
m3/sec
Q5 = (0.00278 x 0.95 x 0.78 x 128 x 1.80) + [(0.00278 x 0.95 x 0.79 x 128 x 1.47) – 0.46] = 0.48
m3/sec
Q1 = 0.00278 x 0.80 x 0.78 x 79 x 1.83 = 0.25 m3/sec
6. URBS CATCHMENT FILE – POST DEVELOPMENT
2 Pearson Rd Cooroy - Develop.cat
Model: Basic
Uses: L U I
Default Parameters: alpha=1.20 m=0.8
14 Subareas of Area:
0.0011 0.0010 0.0036 0.0032 0.0032 0.0026 0.0024
0.0023 0.0019 0.0015 0.0054 0.0018 0.0016 0.0011
Factor=1.50
Rain # 1 L=0.030 U=0.00
Route L=0.030 U=0.25
Store.
Rain # 2 L=0.015 U=0.00
Get.
Route L=0.030 U=0.25
Store.
Rain # 3 L=0.020 U=0.20 I=0.55
Get.
Route L=0.045 U=0.20
Store.
Rain # 4 L=0.020 U=0.20 I=0.55
Route L=0.056 U=0.20
Get.
Route L=0.036 U=0.50
Store.
Rain # 5 L=0.030 U=0.25 I=0.55
Store.
Rain # 6 L=0.030 U=0.25 I=0.55
Get.
Get.
Print. TMR1
Loss C=0.46
{Throws away everything up to 0.46 m3/s}
Print.TMR2
Route L=0.078 U=0.00
Store.
Factor=1.0
Rain # 7 L=0.072 U=0.00 I=0.45
Factor=1.5
Add Rain # 8 L=0.036 U=0.20 I=0.55
Store.
Factor=1.0
Rain # 9 L=0.045 U=0.00 I=0.17
Factor=1.5
J
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
Add Rain # 10 L=0.030 U=0.20 I=0.55
Get.
Get.
Route L=0.030 U=0.50
Store.
Rain # 11 L=0.020 U=0.25 I=0.55
Get.
Route L=0.027 U=0.50
Store.
Rain # 12 L=0.020 U=0.25 I=0.60
Route L=0.020 U=0.50
Get.
Route L=0.062 U=0.00
Add Rain # 13 L=0.020 U=0.70 I=0.15
Store.
Rain # 14 L=0.015 U=0.25 I=0.55
Route L=0.020 U=0.50
Get.
Print. OUT
End of Catchment Definition.
1 Pluviographs:
Location. ARR_TEMPORAL_DATA
14 Subareas:
1 2 3 4 5 6 7
8 9 10 11 12 13 14
End of Pluviograph Data.
End of Gauging Station Data.
7. REQUIRED STORAGE
An S-Q detention table is added to URBS catchment file Develop.Cat immediately after
subarea #13 to create catchment file Mitigate.Cat, hereafter. The S-Q data in that table is
successively adjusted until the model indicates that the adjusted storage on each line
matches the adjusted basin outflow on that line, and mimics the pre-development discharges
from the total catchment after adding the discharges from subarea #14. The resultant basin
storages, basin outflows and total outflows for each ARI are tabulated below.
ARI (yrs) Req’d Storage (m3) Basin Outflow Total Catchment Outflow
(m3/sec) (m3/sec)
100 334 0.87 0.89
20 243 0.58 0.60
5 190 0.39 0.41
1 128 0.14 0.15
2 Pearson Rd Cooroy - Mitigate.cat
Model: Basic
Uses: L U I
Default Parameters: alpha=1.20 m=0.8
14 Subareas of Area:
0.0011 0.0010 0.0036 0.0032 0.0032 0.0026 0.0024
0.0023 0.0019 0.0015 0.0054 0.0018 0.0016 0.0011
Factor=1.50
K
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
Rain # 1 L=0.030 U=0.00
Route L=0.030 U=0.25
Store.
Rain # 2 L=0.015 U=0.00
Get.
Route L=0.030 U=0.25
Store.
Rain # 3 L=0.020 U=0.20 I=0.55
Get.
Route L=0.045 U=0.20
Store.
Rain # 4 L=0.020 U=0.20 I=0.55
Route L=0.056 U=0.20
Get.
Route L=0.036 U=0.50
Store.
Rain # 5 L=0.030 U=0.25 I=0.55
Store.
Rain # 6 L=0.030 U=0.25 I=0.55
Get.
Get.
Print. TMR1
Loss C=0.46
{Throws away everything up to 0.46 m3/s}
Print.TMR2
Route L=0.078 U=0.00
Store.
Factor=1.0
Rain # 7 L=0.072 U=0.00 I=0.45
Factor=1.5
Add Rain # 8 L=0.036 U=0.20 I=0.55
Store.
Factor=1.0
Rain # 9 L=0.045 U=0.00 I=0.17
Factor=1.5
Add Rain # 10 L=0.030 U=0.20 I=0.55
Get.
Get.
Route L=0.030 U=0.50
Store.
Rain # 11 L=0.020 U=0.25 I=0.55
Get.
Route L=0.027 U=0.50
Store.
Rain # 12 L=0.020 U=0.25 I=0.60
Route L=0.020 U=0.50
Get.
Route L=0.062 U=0.00
Add Rain # 13 L=0.020 U=0.70 I=0.15
Print. BASIN
Dam Route VBF=0.0 Number=6
{THOU M3 CUMEC}
0.000 0.00
L
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
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Callaghan & Toth
0.070 0.11
0.128 0.14
0.190 0.39
0.243 0.58
0.334 0.87
Print. BASOUT
Store.
Rain # 14 L=0.015 U=0.25 I=0.55
Route L=0.020 U=0.50
Get.
Print. OUT
End of Catchment Definition.
1 Pluviographs:
Location. ARR_TEMPORAL_DATA
14 Subareas:
1 2 3 4 5 6 7
8 9 10 11 12 13 14
End of Pluviograph Data.
End of Gauging Station Data.
8. STORAGE PROVISION
TH
FOOTPA
99.AR 2100
0.8
10
94
xIL 100.10
YE
4
1.
0 0.
10 10
SWALE 0.6 100 YR
2
10
1.
4
5m WIDE x 0.5m DEEP VEE
1.
10
10
x FL 100.45 99.85
102
x NOW
100.6
0.8
FOOTPA
.0
10
101
x .95
99
.2
100.8
L TW 101.10
101
100
AL
TH
W
101.2
101.4
x TW 101.35
101.4
BIO
1
IL 101.80 FL 100.55
10
x x
100.6
FL 100.55
101.4 101.2 101.0 100.8 x
FOOTPATH
.26
100
0 SCALE 25m
.
M
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021
Page 26
ail Callaghan & Toth Gross storage, including normal (un-backwatered) flow profile in swale: EL(m) A(m2) a(m2) AEL(m) AS (m3) _=S (m3) 101.40 768 448 704 0.20 141 101.20 640 327 583 0.20 117 101.00 526 210 473 0.20 94 100.80 420 116 386 0.20 77 100.60 352 39 344 0.05 17 100.55 336 22 187 0.10 19 100.45 38 3 29 0.05 1 100.40 20 2 12 0.20 2 100.20 3 0 Normal (Un-backwatered) flow volume (“Vol”) in swale: ARI (rs) Nett S Req’d (m3) Approx EL(m) Affected L (m) _ Q (m3/s) A(m2) @ 1m/s Vol (m3) 100 334 101.25 34 0.9 0.9 31 20 243 101.10 29 0.6 0.6 17 5 190 100.95 26 0.4 0.4 10 1 128 100.85 23 0.15 0.15 3 2035 2 Pearsons Road — Flood Study — Revision 3 April 2021
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Callaghan & Toth
EL (m)
101.4
100YR VOL 334 m3 REQUIRES WL 101.26
x
101.2
NETT DETENTION VOL
x
20YR VOL 243 m3 REQUIRES WL 101.09 NORMAL (UN-BACKWATERED)
VOLUME IN SWALE
101.0 x
5YR VOL 190 m3 REQUIRES WL 100.98
1YR VOL 128 m3 REQUIRES WL 100.84
x TOTAL VOL IN BASIN + SWALE
100.8
100.6
100.4
100.2
0 50 100 150 200 250 300 350 400 450 500
VOLUME (m3)
O
2035 2 Pearsons Road – Flood Study – Revision 3 April 2021