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Glen - REC13/0146 Flood Study BSM 30 April 2014. Email 2 Attachment 2
Attached to the e-mail REC13/0146 - Response to Information Request - Email 2.
Brisbane Stormwater Management Pty Ltd
VALKEV PTY LTD
STORMWATER DETENTION AND FLOODING
FOR SUBDIVISION OF LOT2 ON RP173883
AND LOTS 135, 136 AND 137 ON MCH978
AT ELM STREET AND LAKE MACDONALD DRIVE
COOROY
30 APRIL 2014
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Page 2
SUBDIVISION OF LOT 2 ON RP173883 AND LOTS 135, 136 AND 137 ON MCH 978
AT ELM STREET AND LAKE MACDONALD DRIVE, COOROY
STORMWATER DETENTION AND FLOODING REPORT
COMPILED FOR VALKEV P/L BY BRISBANE STORMWATER MANAGEMENT P/L
DOCUMENT CONTROL SHEET
Document Title: Stormwater Detention And Flooding For Subdivision Of Lot 2 On RP173883 And
Lots 135, 136 And 137 On MCH978, At Elm Street & Lake Macdonald Drive, Cooroy
Client: Valkev Pty Ltd
BSM Job No: 2013-08
Project Manager: Denis Ogle
Distribution:
Doc Filename Status Format Issued To Date
ValkevSDF.Doc Draft Pdf Callaghan & Toth P/L 28/4/14
BSM – Office 28/4/14
ValkevSDF.Doc Final Pdf & Callaghan & Toth P/L 30/4/14
Hardcopy BSM – Office Copy 30/4/14
Brisbane Stormwater Management P/L
92 Alkoomie St, PO Box 8119, Wynnum Nth, Q4178
Ph (07)33963383, Email [email protected]
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List Of Contents
1. Summary 3
2. Introduction 4
3. Stormwater Detention Requirement 5
4. Stormwater Discharges To No 2 Pearsons Road 6
5. Runoff Rates To Floodway Model 8
5.1 Catchment Areas And Subdivision 8
5.2 Design Rainfall Data 8
5.3 Model Calibration 10
5.4 Linkage From Catchment Model To Floodway Model 11
6. Floodway Profiles, Pre-Development 13
7. Floodway Profiles, Post-Development 17
7.1 Mitigation Concept For Increased Stormwater Runoff 17
7.2 Model Simulation 17
7.3 Sensitivity Test 18
8. Certification 19
List Of Figures (following text)
1 Locality And Lot Plan
2 Urbs Models Of Stormwater Detention Requirement
3 Proposed Change In Discharge Scenarios To No 2 Pearsons Road
4 Catchment Subdivision For Pre-Development Urbs Model
5 Catchment Subdivision For Post-Development Urbs Model
6 XPStorm Hydraulic Model Network
7 Photographs Of Eastern Floodway On 25 November 2013
8 Photographs Of Western Floodway On 25 November 2013
9 Proposed Floodway Modifications
10 Longitudinal Floodway Profiles
11 Floodway Cross-Section Changes – West Tributary
12 Footbridge And Bio-Basin Schematics
13 Flood Levels And Flood Boundaries
Appendices
A. Design Rainfall Data
B. Rational Method Calculations Of Floodway Inflows, Pre-Development
C. Rational Method Calculations Of Floodway Inflows, Post-Development
D. Floodway Storage Volumes
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1.0 SUMMARY
This analysis has found that the development’s stormwater detention requirement can be achieved by
enlarging the flood storage on the site, by the means shown on Figures 9 to 11 of this report, to augment
the small amount of conventional detention storage that can be gained in two bio-basins on the site (as in
Figure 12). The additional storage volumes generated by these works, after allowing for the small
amounts of flood storage that will be lost to filling of lot margins and active parkland, are compared to
the detention storages that would be required of a fully-conventional detention system, in Table S1:
Table S1: Comparison Of Pre-Development And Post-Development Floodplain Volumes (m3)
To Required Detention Volumes
1Year 2 Year 5 Year 10 Year 20 Year 50 year 100 Year
Pre-Development 5456 6184 8515 9927 11352 12986 14493
Floodway Storage
Post-Development 5781 6591 9349 11121 12976 14807 16240
Floodway Storage
Floodway Gain 325 407 834 1194 1624 1821 1747
Plus Bio-Basins 162 183 252 252 252 252 252
Less Active Park Fill -0 -0 -0 -0 -0 -18 -45
Nett Gain 487 590 1086 1446 1876 2055 1954
Req’d Extra Volume
(From Table 3) 395 525 770 910 1095 1370 1585
The abovementioned works, together with a minor regrading of the invert profile around node 5 (as also
shown on Figure 10) will result in the development having practically nil adverse impact on flood levels
on adjoining properties, as summarised in Tables 16 to 18 of this report. The only exception to this
generality is at node 23, just upstream of the site boundary in the western tributary, where the affluxes
will range from 0.02 metre in a 10 year storm to 0.05 metre in a 100 year storm. The western channel
between node 23 and the site boundary was designed in 2006 to be deliberately revegetated to a
Manning’s n of 0.15, as part of the adjoining Blue Wren Place development. That revegetation was
installed at the time of that development, but has since been removed, thereby reducing the present (“pre-
development”) Manning’s n in this area to about 0.04, consequently decreasing the flood levels at node
23 to about 0.4 metre below the original design levels. The post-development flood levels as a result of
Valkev’s development, while being 0.02 to 0.05 metre above the present levels, will nevertheless be at
least 0.3 metre below the original design levels for this area, and the quoted affluxes are therefore
suggested to be of no consequence. This is illustrated by the levels of the adjoining lot in Blue Wren
Place, which are marked on the longitudinal floodway profiles in Figure 10 of this report.
The works will also result in nil adverse impact on downstream peak flow rates, apart from a slight
increase in flows along the western tributary through the immediately adjoining downstream property
(No2 Pearsons Road). That increase on the adjoining property results in the deliberate diversion of local
runoff away from that adjoining property, and directly to the western floodway upstream of that property.
Downstream of the natural point of inflow to the floodway for that runoff, on the adjoining property, the
flows revert to their pre-development rates.
The consequent flood levels for design of the development are summarised in Tables 16 to 18 and in
Figures 13 of this report. A sensitivity test has identified the impact of uncontrolled floodplain regrowth
on the abovementioned design levels. The consequent 100 year flood levels are summarised in Table 21
and in Figures 13, and appropriate account should be taken of these possible flood levels when
considering appropriate design levels for the development.
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2.0 INTRODUCTION
This report describes Brisbane Stormwater Management P/L’s (BSM’s) stormwater detention and
flooding assessment of a proposed subdivision of Lot 2 on RP173883 and Lots 135, 136 and 137 on
MCH978, at Elm Street and Lake Macdonald Drive, Cooroy. The site locality and the proposed lot layout
are shown in Figure 1 of this report.
The site is traversed by two tributaries of Six Mile Creek, hereafter described as the eastern and western
tributaries. The catchment areas of the two tributaries are shown in Figure 4, and the tributary floodways
can be seen in more detail in Figure 6.
Some of the increased stormwater runoff from the proposed residential areas is proposed to be mitigated
by conventional detention volumes in two bio-retention basins, but most of the increased runoff is
proposed to be attenuated by an increase in the floodway storage on the site. The increased floodway
storage will be achieved by deliberately “roughening” the floodways (by revegetating the riparian zones,
as required by Council) and by constructing a restrictive footbridge across the eastern tributary to back-up
the flood profiles in that tributary floodway.
Hydraulic model analyses of the interaction between increased site runoff and floodway through-flows
can be skewed by “hydrograph separation”, whereby the urbanisation of a particular site is predicted to
hasten the discharge of the increased site runoff down the floodway before the arrival of the major
floodway flows from the upstream catchment – which can lead to a perception that the peak flow-rates
along the floodway will not be significantly increased, which in turn leads to a perception that little or no
attenuation volume is required. This perception may be valid for a site development that is considered in
isolation, but it becomes invalid when the “equal opportunity” development of all such sites in the
catchment is collectively considered.
To overcome the abovementioned modelling difficulty without resorting to a catchment-wide “equal
opportunity” analysis, this assessment has firstly determined the detention volume that would be required
for a fully-conventional system of dedicated basins on the site’s stormwater outlets. The assessment was
thereafter focussed on achieving at least that volume from the proposed combination of bio-basin
detention and increased floodway volume, while also using a floodway model to verify that the proposed
changes to the floodway profiles on the site would not adversely affect the flood profiles upstream and
downstream of the site.
The development proposal is particularly cognisant of the need to not increase local stormwater
discharges (as distinct from tributary channel through-flows) onto an adjoining property to the north –
namely No 2 Pearsons Road (refer Figure 1). This is proposed to be achieved by diverting part of the
runoff from the relevant sub-catchment, directly across to the western tributary floodway within the site.
This diversion proposal had to be accounted in the floodway modelling process.
The assessment process was therefore structured as follows:
- Determination of the required detention volume - as described in Section 3 of this report.
- Devising a diversion mechanism, in liaison with the applicant’s civil consultant (Callaghan & Toth),
to ensure no increase in stormwater discharges to No 2 Pearson Road – as described in Section 3.
- Calculation of the runoff rates to the floodways and running them though floodway models of the pre
and post-development scenarios – as described in Sections 4 to 7.
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3.0 STORMWATER DETENTION REQUIREMENT
As already noted in Section 1, the increased rates of stormwater runoff from the site are proposed to be
mitigated partly by conventional detention storage in two bio-basins and partly by increased floodway
storage on the site, with a requirement that the combined volume of those two storages should be at least
equal to the detention volume that would be required for a fully-conventional system.
The detention volume that would be required for a fully-conventional system has been determined by
compiling hydrologic models of four distinct parts of the proposed development platform, notated as
models A, B, C and D in Figure 2 of this report.
The attenuation objective for each of the four models was set by Rational Method calculations of the pre-
and post-development peak flow rates, as summarised in Tables 1 and 2 hereafter. The contributing areas
shown for Area A in Tables 1 and 2 are slightly less than the actual area of 2.49 hectare, because of
partial-area criticality (refer Figure 2 for partial-area limits).
Table 1: Rational Method Calculations Of Pre-Development Peak Flow Rates
Area C10 Tc I (mm/hr) A Q (m3/s)
(min) 1 / 2 / 5 / 10 / 20 / 50 / 100 (Ha) 1 / 2 / 5 / 10 / 20 / 50 / 100
A 0.72 24 65 / 73 / 98 / 116 / 130 / 152 / 166 2.43 0.25 / 0.30 / 0.45 / 0.56 / 0.66 / 0.85 / 0.97
B 0.70 18 75 / 84 / 112 / 132 / 151 / 172 / 192 0.85 0.10 / 0.12 / 0.18 / 0.22 / 0.26 / 0.33 / 0.38
C 0.70 20 71 / 80 / 106 / 127 / 142 / 165 / 180 1.85 0.20 / 0.24 / 0.36 / 0.46 / 0.54 / 0.68 / 0.78
D 0.70 16 80 / 90 / 120 / 140 / 158 / 183 / 202 1.34 0.17 / 0.20 / 0.30 / 0.37 / 0.43 / 0.55 / 0.63
Table 2: Rational Method Calculations Of Post-Development Peak Flow Rates
Area C10 Tc I (mm/hr) A Q (m3/s)
(min) 1 / 2 / 5 / 10 / 20 / 50 / 100 (Ha) 1 / 2 / 5 / 10 / 20 / 50 / 100
A 0.78 18 75 / 84 / 112 / 132 / 151 / 172 / 192 2.34 0.30 / 0.36 / 0.54 / 0.67 / 0.80 / 1.00 / 1.17
B 0.80 13 89 / 100 / 133 / 155 / 175 / 201 / 221 0.85 0.13 / 0.16 / 0.24 / 0.29 / 0.35 / 0.44 / 0.50
C 0.80 14 86 / 96 / 129 / 150 / 169 / 194 / 214 1.85 0.28 / 0.34 / 0.50 / 0.62 / 0.73 / 0.92 / 1.06
D 0.80 11 93 / 105 / 141 / 163 / 186 / 215 / 235 1.34 0.22 / 0.27 / 0.40 / 0.49 / 0.58 / 0.74 / 0.84
Version 3.5g of the URBS software was used as the basis for the hydrological models of Areas A to D.
Each of those areas was modelled as a sub-area network, using the subdivision lines indicated on Figure
2. Each of the four models was based on post-development conditions and was calibrated to closely
match its peak outflow rates to the Rational Method calculations of the post-development flow rates (as
in Table 2). A hypothetical detention basin was then added to the outlet of each model, with its storage-
discharge characteristics adjusted so as to reduce the peak outflow rates to the Rational Method
calculations of the pre-development flow rates (as in Table 1). The resultant storage requirements are
summarised in Table 3, below:
Table 3: Required Detention Volumes (m3) For Fully-Conventional System
Area 1 Yr 2 Yr 5 yr 10 Yr 20 Yr 50 yr 100 Yr
A 130 170 245 290 355 445 520
B 60 80 110 130 150 195 220
C 130 175 260 300 360 425 495
D 75 100 155 190 230 305 350
Total 395 525 770 910 1095 1370 1585
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4.0 STORMWATER DISCHARGES TO No 2 PEARSONS ROAD
A catchment area of 2.49 hectares presently drains across the northern boundary of the site and onto No 2
Pearsons Road, as shown for the pre-development scenario in Figure 3. Local stormwater discharges onto
the adjoining property will be maintained at or below their existing rates by diverting part of the runoff
from the relevant catchment, directly across to the western tributary floodway within the site, as shown
for the post-development scenario in Figure 3.
The existing discharge rates to the adjoining property, as calculated by the Rational Method for the
partial-area of 2.43 hectares shown in Figure 3, are summarised in Table 4 below:
Table 4: Rational Method Calculations Of Pre-Development Peak Flow Rates To No 2 Pearson Road
C10 Tc I (mm/hr) A Q (m3/s)
(min) 1 / 2 / 5 / 10 / 20 / 50 / 100 (Ha) 1 / 2 / 5 / 10 / 20 / 50 / 100
0.72 24 65 / 73 / 98 / 116 / 130 / 152 / 166 2.43 0.25 / 0.30 / 0.45 / 0.56 / 0.66 / 0.85 / 0.97
In the post-development scenario, runoff from the 2.40 hectare post-development catchment (excluding a
0.018 hectare drainage corridor connecting to the adjoining property) will be collected at the sag in the
proposed road, from which flows up to Q5 will be diverted eastward by piping along the road, to the
western tributary channel. Flows in excess of Q5 at the sag will discharge overland, through the
abovementioned drainage corridor, to the adjoining property.
The Q5 diversion capacity, as calculated by the Rational Method for a partial area of 2.25 hectares, is
summarised in Table 5, below:
Table 5: Rational Method Calculation Of Q5 Diversion Capacity
C10 Tc (min) I5 (mm/hr) A (Ha) Q5 (m3/s)
0.78 18 112 2.25 0.00278 x (0.95 x 0.78) x 112 x 2.25 = 0.52
The post-development discharge rates to the adjoining property up to Q5, being just the runoff from the
surface of the connecting drainage corridor, are calculated by the Rational Method as in Table 6 below.
These flow rates are all practically zero.
Table 6: Rational Method Calculations Of Post-Development Flows Up To Q5 To No 2 Pearson Road
C10 Tc I (mm/hr) A Q (m3/s)
(min) 1 / 2 / 5 (Ha) 1 / 2 / 5
0.90 10 97 / 109 / 147 0.018 0.003 / 0.004 / 0.006
The post-development discharge rates to the adjoining property from Q10 to Q100, as calculated by the
Rational Method for the partial area of 2.30 hectares shown in Figure 3, are summarised in Table 7,
below:
Table 7: Rational Method Calculations Of Post-Development Flows Q10 - Q100 To No 2 Pearson Road
C10 Tc I (mm/hr) A Q (m3/s)
(min) 10 / 20 / 50 / 100 (Ha) 10 / 20 / 50 / 100
0.78 18 132 / 151 / 172 / 192 2.30 0.66 / 0.79 / 1.00 / 1.15
Less 0.52 m3/s Q5, =
0.14 / 0.27 / 0.48 / 0.63
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The consequent changes in local discharges from the site, to No2 Pearsons Road, are collated from Tables 4, 6 and 7 and summarised in Table 8, below. The changes are seen to be non-adverse, from Q1 to Q100. Table 8: Changes To Local Stormwater Discharges (m3/sec) From Site To No 2 Pearsons Road Scenario Q1 Q2 Q5 Q10 Q20 Q50 Q100 Pre-Development 0.25 0.30 0.45 0.56 0.66 0.85 0.97 Post-Development 0.003 0.004 0.006 0.14 0.27 0.48 0.63 Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 7
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5.0 RUNOFF RATES TO FLOODWAY MODEL
5.1 Catchment Areas And Subdivision
Flood profiles along floodways such as the subject tributaries are affected by the hydraulic capacity of the
adjoining downstream reaches and by any waterway structures in those downstream reaches.
Accordingly, the Extran model extends some distance downstream of the site to the convergence of the
two tributaries just downstream of Pearsons Road, as shown in Figure 3. The catchment modelling
therefore includes not just the contributing areas alongside and upstream of the site, but also the areas
downstream of the site to that termination point downstream of Pearsons Road. The extent of the 151.7
hectare overall catchment is shown in Figures 4 and 5. The site occupies 8.0 hectare, or about 5 percent,
of the overall catchment area.
The catchment has been subdivided into 23 subareas for modelling of the pre-development scenario (as in
Figure 3), and 41 subareas for the post-development scenario (as in Figure 4). The subdivision of the
areas external to the site is identical between the two scenarios, whereas the subdivision of those areas
which discharge to the floodways within the site are treated differently between the two scenarios, to
allow for accurate modelling of the increased runoff from the proposed urban development of 65 percent
of the site area. The modelling of the post-development scenario also accounts for the Q5 splits of the
inflows to the bio-basins, which necessitates doubling-up of the relevant six subareas, taking the total
sub-area count to 47 as marked on Figure 5. The impervious fractions applied to each of the modelled
subareas are summarised in Table 9, on the following page of this report.
5.2 Design Rainfall Data
The Bureau of Meteorology has recently updated the rainfall intensity-frequency-duration data that was
previously published in Volume 1 of Australian Rainfall and Runoff (1987). The previous data was based
on rainfalls recorded up to 1985, whereas the latest data is based on rainfalls recorded up to 2010 / 2011.
There has also been a change of nomenclature, whereby the previous description of severity in terms of
“average recurrence interval” has been updated to “annual exceedence probability” for storms from 2-
year to 100 year severity. Rainfall intensities for the 1 year severity are still quoted for an average
recurrence interval of once per year. The updating has increased the rainfall intensities at higher ARI’s
(or lesser exceedence probabilities) by about 4 percent, compared to the previous data. The updated
intensity-frequency-duration data for Cooroy is reproduced in Appendix A of this report.
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Table 9: Impervious Fractions Assigned To Urbs Model Subareas Pre-Development Scenario Post-Development Scenario Subarea Impervious Subarea Impervious (Figure 1) Fraction (Figure 2) Fraction 1 0.10 1 0.10 2 0.15 2 0.15 3 0.15 3 0.15 4 0.35 4 0.35 5 0.15 5 0.15 6 0.50 6 0.50 7 0.20 7 0.30 8 0.06 8 0.60 9 0.10 9 0.00 10 0.30 10 0.60 11 0.30 11 0.50 12 0.58 12 0.50 13 0.65 13 0.50 14 0.28 14 0.50 15 0.45 15 0.50 16 0.45 16 0.50 17 0.00 17 0.50 18 0.04 18 0.50 19 0.08 19 0.60 20 0.31 20 0.00 21 0.35 21/22 0.30 22 0.25 23 0.37 23 0.45 24 0.58 25 0.65 26 0.28 27 0.45 28 0.45 29/39 0.15 30/40 0.15 31/41 0.50 32/42 0.50 33/43 0.55 34 0.55 35 0.55 36 0.45 37 0.08 38 0.60 44 0.39 45 0.35 46 0.25 47 0.45 Brisbane Stormwater Management Pty Ltd Document File: WalkevSDF.Doc Page 9
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5.3 Model Calibration
The catchment runoff processes have been modelled with the “basic” variant of Version 3.5g of the Urbs
software, with the “Rational Method” procedure invoked so as to improve the routing simulation within
individual subareas, and with rainfalls converted to runoff via the initial/continuing loss procedure. The
operating parameters of the model which affect the outcome of the simulation are the storage lag
parameter (alpha), the non-linearity parameter (m), the initial rainfall loss (IL) and the continuing rainfall
loss (CL).
Ideally, the operating parameters should be calibrated to observed rainfall and runoff data in the subject
catchment, using either data from particular storm events or derived statistical data via a frequency curve
of recorded flows. In this instance, there is a streamgauge further downstream in the broader catchment
(at Cooran, where the contributing catchment area is 180 square kilometres, or about 120 times larger
than the subject catchment). This gauge has been recording flood flows for 60 years, but the accuracy of
its height/flow rating curve has been confirmed by current-metering to only just above the 1-in-2 year
flood height, which means that its usefulness for model calibration to flows of 5 year or greater severity
is very questionable.
The calibration has therefore reverted to an alternative process involving three stages:
- Calibration to Rational Method calculations of the peak flow rates from individual subareas and groups
of subareas.
- Comparing the calibrated parameters from the first stage to the corresponding parameters from
previous calibrations to other morphologically similar catchments with more highly rated streamgauge
data.
- Comparing the predicted peak flow rates at particular locations in the modelled area to the
corresponding flow rates in the 2002 L&T floodway model.
The Rational Method calibration has been applied to the peak flow rates entering the floodway model
near the upstream boundaries of the site and to the peak inflow rates from each of the subareas which
discharge to the floodway within the subject site. The relevant calculations are summarised in
Appendices B and C of this report, for the pre- and post-development scenarios respectively. An
acceptably close calibration to these calculated peak flow rates was achieved, as in Table 10 below and in
Table 11 on the following pages of this report, using an alpha parameter of 0.85 an m parameter of 0.8,
an initial rainfall loss of 16 mm, and a continuing rainfall loss of 2 mm/hour. The alpha parameter for
individual small subareas which discharge overland flow mostly as shallow sheet flow was increased by
arbitrarily applying reach factors of up to 3.
Table 10 : URBS / Rational Method Peak Flow Calibration (m3/sec) For Pre-Development Scenario
(Refer Figure 4 For Subarea Locations)
Subareas 1 year 2 year 5 Year 10 Year 20 year 50 year 100 Year
1–5 5.2 / 6.0 6.7 / 7.6 11.2/ 11.5 14.5 / 14.2 17.4 / 16.9 21.4 / 21.5 24.8 / 24.6
7 0.29 / 0.29 0.36/ 0.35 0.54 / 0.52 0.64 / 0.63 0.78 / 0.75 0.96 / 0.95 1.10 / 1.10
8 0.24 /0.25 0.30 /0.30 0.47 / 0.45 0.56 / 0.55 0.68 / 0.65 0.83 / 0.83 0.96 / 0.96
9 0.21 / 0.23 0.26 / 0.27 0.40 / 0.40 0.49 / 0.49 0.60 / 0.59 0.74 / 0.74 0.85 / 0.85
12 – 16 4.8 / 4.8 6.1 / 5.8 9.3 / 8.6 11.2 / 10.8 13.6 / 12.8 16.5 / 16.2 18.8 / 18.7
17 0.19 / 0.22 0.24 / 0.26 0.39 / 0.38 0.48 / 0.48 0.59 / 0.57 0.72 / 0.71 0.82 / 0.83
18 0.20 / 0.21 0.25 / 0.26 0.39 / 0.38 0.47 / 0.47 0.57 / 0.56 0.70 / 0.71 0.81 / 0.81
19 0.19 / 0.21 0.23/ 0.25 0.37 / 0.37 0.46 / 0.46 0.56 / 0.54 0.69 / 0.70 0.79 / 0.79
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Table 11 URBS / Rational Method Peak Flow Calibration (m3/sec) For Post-Development Scenario
(Refer Figure 5 For Subarea Locations)
Subareas 1year 2 year 5 Year 10 Year 20 year 50 year 100 Year
7 0.30 / 0.30 0.37 / 0.36 0.56 / 0.54 0.68 / 0.67 0.81 / 0.79 1.00 / 1.00 1.14 / 1.15
8 0.05 / 0.05 0.06 / 0.06 0.10 / 0.09 0.12 / 0.11 0.14 / 0.13 0.17/ 0.17 0.19 / 0.19
9 0.13 /0.14 0.17 /0.16 0.27 / 0.25 0.33 / 0.30 0.39 / 0.36 0.47 / 0.46 0.53 / 0.53
10-18 0.19 / 0.20 0.24 / 0.24 0.37 / 0.37 ---- /----- ---- / ---- ---- / ---- ---- / ----
19 0.06 / 0.06 0.08 / 0.08 0.12 / 0.11 0.14 / 0.14 0.17 / 0.17 0.20 / 0.21 0.23 / 0.24
20 0.19 / 0.20 0.23 / 0.22 0.39 / 0.34 0.47 / 0.42 0.55 / 0.50 0.66 / 0.64 0.74 / 0.74
25-35 0.37 / 0.39 0.47 / 0.46 0.71 / 0.68 ---- / ---- ---- / ---- ---- / ---- ---- / ----
36 0.21 / 0.21 0.26 / 0.25 0.39 / 0.38 0.48 / 0.43 0.56 / 0.56 0.68 / 0.70 0.77 / 0.80
37 0.10 / 0.11 0.13 / 0.13 0.20 / 0.19 0.24 / 0.24 0.29 / 0.28 0.36 / 0.35 0.41 / 0.41
38 0.06 / 0.06 0.07 / 0.07 0.11 / 0.11 0.14 / 0.13 0.16 / 0.16 0.19 / 0.20 0.22 / 0.23
The calibrated parameters compare favourably with those inferred from other morphologically similar
catchments having more highly rated streamgauge data. In this instance, data have been inferred from
previous model calibrations to streamgauge records in Moggill Creek and Bulimba Creek in the outer
suburbs of Brisbane, with a comparison as in Table 12 below:
Table 12 Comparison Of Adopted Operating Parameters With Other Calibrations
Operating Parameter Adopted Values Moggill, Bulimba Creeks
Alpha 0.85 0.80 – 0.83
m 0.80 0.75 – 0.80
IL (mm) 16 15 – 20
CL (mm/hr) 2 2-3
The predicted peak inflow rates to the upstream end of the floodway model also compare favourably to
the peak flow rates in L&T’s Mike 11 floodway model, as in Table 13, below:
Table 13 : Comparison of BSM / CLT Peak Flows (m3/sec) At Upstream Boundaries Of Site
BSM Subareas CLT Mike XS 10 Year 20 Year 50 Year 100 Year
1–5 T3-789 14.4 / 12.1 17.3 / 16.1 21.3 / 21.8 24.8 / 25.7
12 – 16 T2-457 11.2 / 11.0 13.5 / 13.2 16.5 / 16.5 18.8 / 18.7
5.4 Linkage From Catchment Model To Floodway Model
BSM’s in-house ‘UrbsInt’ and “AsciXP” subroutines were used to convert flow outputs from particular
subareas or groups of subareas within the Urbs model to inflow hydrographs at particular nodes within
the floodway model, as in Table 14, hereafter:
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Table 14: Discharge Points From Urbs Hydrologic Model To XPStorm Hydraulic Model Pre-Development Scenario Post-Development Scenario Urbs Subareas (Location, Figure 4) XPStorm Node (Location, Figure 6) Urbs Subareas (Location, Figure 5) XPStorm Node (Location, Figure 6) 1-5 1 1-5 1 6 3 6 3 7 4 7 4 8 8 8 7 9 13 9 8 10 16 10 - 18 10 11 20 19 11 12-16 23 20 13 17 25 21 16 18 28 22 20 19 - 20 31 24 - 28 23 21 32 29 - 36 27 22 35 37 28 23 38 3823 29 44 31 45 32 46 35 47 38 Brisbane Stormwater Management Pty Ltd Document File: WalkevSDF.Doc Page 12
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6.0 FLOOD PROFILES, PRE-DEVELOPMENT
Version 9.28 of the Extran software, as embedded in the XPStorm modelling suite, has been used to
convert the catchment runoff hydrographs to flood profiles along the floodways. The extent and detail of
the model are shown in Figure 3 of this report. Te model provides approximately three times the detail of
the Mike11 model which L&T used in 2002 to model these floodways. The model network also includes
a number of interconnecting links to provide for simulation of overflows between the two tributaries
where they are aligned in close proximity, downstream of the site.
This version of the Extran software includes a facility to specify different internodal distances for the left
overbank, channel and right overbank segments, which in turn provides for a reasonably accurate
calculation by the software of the internodal flood volumes up to the peak flood level profile. This feature
was vital for checking that the reshaping of the floodway in the post-development scenario achieves the
required stormwater detention volumes, over-and-above the existing floodway volumes. Accordingly,
this facility was invoked for this analysis and separate internodal distances were measured and applied to
each connecting link of the model network.
Field-surveyed spot heights, which can be seen in the background of Figure 6 were used to define the
cross-section shape of each of the links between adjoining nodes of the model. The Manning’s n values
of the channel and overbank sectors of the floodways were perceived by site inspection. The adopted
values ranged from 0.035 for open grassed paddock or park, to 0.150 in densely timbered areas.
Examples of the adopted values are shown in Figures 7and 8 of this report.
The starting point for the simulations was the tailwater level just downstream of the convergence of the
two tributaries. Initial runs of the model, based on a “normal-depth” criterion at node 39 at the
downstream end of the model, simulated a 100 year tailwater level substantially higher than L&T’s
predicted tailwater level at this location. The slope of the outfall reach, between nodes 38 and 39, was
therefore artificially steepened so as to induce a simulated tailwater level much closer to the L&T level.
Initial runs of the model, for ARI’s of 2 year and 100 year, and for storm durations from 20 minutes to 9
hours, revealed that the critical storm durations varied from 1.5 hours to 3 hours along these floodways.
Accordingly, all subsequent simulations included three storm durations: - namely, 1.5, 2 and 3 hours.
The set-up of the model resulted in simulated flood levels near the upstream and boundaries of the site
that, apart from node 23, were generally at or slightly above the co-located levels from L&T’s Mike 11
model, as indicated in Table 15 below. Overall, the consistency between the two models appears to be
quite good, despite the considerable difference in network density between the two models.
Table 15 : Comparison of BSM / CLT Flood Levels (m) In Vicinity Of Site Boundaries
BSM Node CLT X-Sect 10 year 20 Year 50 Year 100 Year
3 T3-811 101.61 / 101.38 101.65 / 101.54 101.72 / 101.69 101.81 / 101.71
16 T3-1199 99.60 / 99.58 99.68 / 99.61 99.74 / 99.68 99.79 / 99.71
23 T2-389 100.98 / 101.33 101.05 / 101.39 101.12 / 101.47 101.17 / 101.51
29 T2-611 99.89 / 99.82 99.95 / 99.89 100.01 / 99.97 100.05 / 100.05
The predicted pre-development peak flood levels at each node of the model, for ARI’s from 1to 100
years, are summarised in Tables 16 to 18 on the following pages of this report, where they are compared
to the corresponding post-development flood levels. The corresponding 100 year pre-development flood
profile is shown on Figure 10, and the pre-development 100 year boundary is mapped on Figures 9 and
13.
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Table 16: NODE Predicted 1 Year To 5 Year Flood Levels (m) And Affluxes (m) (Pre-Development Levels Are Based On Existing Floodplain Condition) (Post-Development Levels Are Based On Proposed Floodplain Condition) (Yellow shading indicates areas within site) PRE-DEV EASTERN TRIBUTARY ON Oak WD = NMNUNAZBBABABaAnnnany, yONsH CO AN DAHKWNM =O WESTERN TRIBUTARY 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 102.259 102.213 101.350 101.327 101.250 100.761 100.755 100.084 100.056 100.061 100.012 99.915 99.644 99.554 99.439 99.128 98.873 98.687 98.620 97.962 97.706 97.604 100.729 100.580 100.111 100.056 99.898 99.785 99.651 99.448 98.923 98.871 98.576 98.529 97.745 97.706 97.623 97.417 96.818 1 YEAR POST-DEV AFFLUX 102.254 102.207 101.162 101.112 100.766 100.763 100.755 100.134 100.119 100.122 100.069 99.964 99.699 99.606 99.434 99.121 98.866 98.680 98.615 97.960 97.703 97.602 100.691 100.492 100.230 100.088 100.005 99.819 99.688 99.452 98.930 98.878 98.581 98.533 97.746 97.703 97.621 97.415 96.815 0.00 -0.01 -0.19 -0.22 -0.48 0.00 0.00 0.05 0.06 0.06 0.06 0.05 0.05 0.05 0.00 -0.01 -0.01 -0.01 -0.01 0.00 0.00 0.00 -0.04 -0.09 0.12 0.03 0.11 0.03 0.04 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 PRE-DEV POST-DEV AFFLUX 102.625 102.614 101.386 101.351 101.287 100.776 100.768 100.145 100.121 100.131 100.079 99.983 99.725 99.647 99.551 99.230 98.971 98.776 98.681 97.993 97.840 97.688 100.791 100.631 100.177 100.114 99.965 99.844 99.706 99.469 99.048 98.996 98.686 98.611 97.881 97.840 97.710 97.521 96.920 2 YEAR 102.635 102.624 101.200 101.134 100.783 100.780 100.769 100.203 100.200 100.205 100.149 100.040 99.777 99.689 99.545 99.224 98.966 98.771 98.678 97.992 97.841 97.689 100.768 100.562 100.297 100.156 100.075 99.891 99.758 99.477 99.053 99.000 98.692 98.614 97.882 97.841 97.710 97.521 96.920 0.01 0.01 -0.19 -0.22 -0.50 0.00 0.00 0.06 0.08 0.07 0.07 0.06 0.05 0.04 -0.01 -0.01 -0.01 0.00 0.00 0.00 0.00 0.00 -0.02 -0.07 0.12 0.04 0.11 0.05 0.05 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 PRE-DEV 102.977 102.969 101.542 101.479 101.395 100.846 100.829 100.295 100.299 100.323 100.270 100.195 99.963 99.887 99.799 99.471 99.192 99.057 98.832 98.088 98.033 97.841 100.923 100.730 100.317 100.233 100.095 99.969 99.833 99.538 99.266 99.223 99.036 98.832 98.084 98.032 97.927 97.721 97.124 5 YEAR POST-DEV AFFLUX 102.978 102.969 101.368 101.213 100.871 100.867 100.849 100.473 100.461 100.457 100.404 100.272 99.992 99.926 99.792 99.461 99.186 99.053 98.830 98.086 98.031 97.839 100.923 100.709 100.433 100.297 100.213 100.032 99.893 99.549 99.265 99.221 99.033 98.830 98.082 98.031 97.924 97.718 97.121 0.00 0.00 -0.17 -0.27 -0.52 0.02 0.02 0.18 0.16 0.13 0.13 0.08 0.03 0.04 -0.01 -0.01 -0.01 0.00 0.00 0.00 0.00 0.00 0.00 -0.02 0.12 0.06 0.12 0.06 0.06 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Brisbane Stormwater Management Pty Ltd Document File: WalkevSDF.Doc Page 14
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Table 17: NODE EASTERN TRIBUTARY OnNoahwhd = NVNUNMAAHABBAAAA AH OG NH COANDAHKRWNH =O WESTERN TRIBUTARY 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Predicted 10 Year To 50 Year Flood Levels (m) And Affluxes (m) (Pre-Development Levels Are Based On Existing Floodplain Condition) (Post-Development Levels Are Based On Proposed Floodplain Condition) (Yellow shading indicates areas within site) PRE-DEV POST-DEV AFFLUX 103.013 103.000 101.605 101.553 101.447 100.920 100.903 100.415 100.404 100.428 100.375 100.305 100.002 99.956 99.877 99.604 99.347 99.180 98.931 98.173 98.111 97.938 100.977 100.777 100.377 100.287 100.147 100.021 99.888 99.604 99.379 99.347 99.153 98.934 98.172 98.111 98.043 97.823 97.224 103.013 103.001 101.509 101.305 100.949 100.946 100.923 100.635 100.616 100.615 100.568 100.386 100.037 99.996 99.875 99.600 99.342 99.176 98.928 98.170 98.108 97.934 100.998 100.777 100.504 100.364 100.277 100.097 100.957 99.614 99.377 99.343 99.151 98.931 98.169 98.108 98.039 97.819 97.221 0.00 0.00 -0.10 -0.25 -0.50 0.03 0.02 0.22 0.21 0.19 0.19 0.08 0.04 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.13 0.08 0.13 0.08 1.07 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 103.045 103.028 101.654 101.611 101.484 100.983 100.963 100.552 100.538 100.532 100.476 100.405 100.031 100.000 99.930 99.678 99.441 99.252 99.022 98.272 98.200 98.066 101.047 100.831 100.438 100.346 100.213 100.079 99.946 99.663 99.494 99.448 99.216 99.025 98.271 98.200 98.163 97.935 97.333 103.044 103.027 101.599 101.366 100.973 100.967 100.938 100.751 100.716 100.723 100.673 100.506 100.151 100.051 99.930 99.678 99.441 99.252 99.021 98.271 98.199 98.065 101.078 100.850 100.577 100.438 100.346 100.170 100.033 99.668 99.494 99.448 99.216 99.025 98.271 98.199 98.162 97.934 97.332 PRE-DEV POST-DEV AFFLUX 0.00 0.00 -0.05 -0.25 -0.51 -0.02 -0.02 0.20 0.18 0.19 0.20 0.10 0.12 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.02 0.14 0.09 0.13 0.09 0.09 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 103.083 103.059 101.723 101.679 101.530 101.009 100.979 100.634 100.604 100.627 100.572 100.518 100.144 100.055 99.999 99.737 99.541 99.318 99.121 98.381 98.299 98.210 101.123 100.890 100.504 100.411 100.282 100.144 100.007 99.730 99.649 99.555 99.273 99.124 98.381 98.299 98.280 98.045 97.445 103.082 103.058 101.702 101.452 100.989 100.982 100.948 100.811 100.778 100.787 100.726 100.580 100.234 100.135 99.998 99.737 99.539 99.317 99.119 98.379 98.297 98.207 101.167 100.930 100.662 100.521 100.426 100.253 100.115 99.735 99.647 99.554 99.272 99.122 98.379 98.297 98.278 98.043 97.443 PRE-DEV POST-DEV AFFLUX 0.00 0.00 -0.02 -0.23 -0.54 -0.03 -0.03 0.18 0.17 0.16 0.15 0.06 0.09 0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.04 0.16 0.11 0.14 0.11 0.11 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Brisbane Stormwater Management Pty Ltd Document File: WalkevSDF.Doc Page 15
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Table 18: Predicted 100 Year Flood Levels (m) And Affluxes (m)
(Pre-Development Levels Are Based On Existing Floodplain Condition)
(Post-Development Levels Are Based On Proposed Floodplain Condition)
(Yellow shading indicates areas within site)
100 YEAR
NODE PRE-DEV POST-DEV AFFLUX
EASTERN
TRIBUTARY
1 103.110 103.110 0.00
2 103.080 103.079 0.00
3 101.805 101.745 -0.06
4 101.731 101.529 -0.20
5 101.561 101.042 -0.52
6 101.025 101.034 0.01
7 100.910 100.986 0.08
8 100.720 100.856 0.14
9 100.667 100.825 0.16
10 100.702 100.838 0.14
1 100.642 100.767 0.13
12 100.594 100.629 0.04
13 100.216 100.293 0.08
14 100.116 100.192 0.08
15 100.051 100.038 -0.01
16 99.791 99.786 0.00
17 99.606 99.600 -0.01
18 99.357 99.354 0.00
19 99.186 99.181 -0.01
20 98.451 98.444 -0.01
24 98.363 98.357 -0.01
22 98.308 98.298 -0.01
WESTERN
TRIBUTARY
23 101.173 101.226 {0105
24 100.932 100.984 0.05
25 100.544 100.716 0.17
26 100.454 100.574 0.12
27 100.325 100.476 0.15
28 100.186 100.297 0.11
29 100.047 100.147 0.10
30 99.817 99.813 0.00
31 99.766 99.758 -0.01
32 99.620 99.615 -0.01
33 99.307 99.304 0.00
34 99.189 99.184 0.00
35 98.451 98.444 -0.01
36 98.363 98.356 -0.01
37 98.350 98.343 -0.01
38 98.110 98.103 -0.01
39 97.509 97.513 0.00
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7.0 FLOOD PROFILES, POST-DEVELOPMENT
7.1 Mitigation Concept For Increased Stormwater Runoff
The impact of the increased site runoff on flood profiles along the floodways is proposed to be mitigated
mostly by increasing the floodway storage on the site, and partly by conventional detention storage in
two of the proposed bio-basins. The increase in the floodway storage will be achieved by deliberately
roughening the floodways (by revegetating the riparian zones, as required by Council) and by
constructing a restrictive footbridge across the eastern tributary to back-up the flood profiles in that
tributary floodway.
A small additional amount of storage is also required to offset the minor intrusions of the development
platform into the pre-development 100 year flood boundary, and for some minor regrading of an artificial
hump in the existing low-flow channel around node 5 of the Extran model (as seen on Figure 10).
The full suite of the proposed modifications to the flood storage system is shown on Figure 9, with
additional detail on Figures 10 to 12.
The revegetation of the riparian zones, by planting of shrubs (typically, Lomandra sp) and trees at
densities of one item per 1.5 to 2 square metres, is presumed to increase the Manning’s n of the presently
grassed areas from 0.03/0.05 to 0.07.
The detention storages in the bio-basins are accounted as only the “live” storages, in the narrow range of
elevation between the riser overflow level and the weir level. The overflow level in the riser will be
controlled by an overflow slot in one side of the riser, with details as in Figure 12.
7.2 Model Simulation
An Extran model of the post-development scenario was compiled by adjusting a copy of the pre-
development model so as to include the reshaped and revegetated floodways and associated increases in
Manning’s n values, together with the inclusion of the proposed footbridge, the minor regrading of the
invert around Node 5, and hypothetical vertical walls at the boundaries of the proposed allotments.
The achievement of the required increase in floodplain volume, to offset the development’s stormwater
detention requirement, is summarised in Table 19, below:
Table 19: Comparison Of Pre-Development And Post-Development Floodplain Volumes (m3)
To Required Detention Volumes
1Year 2 Year 5 Year 10 Year 20 Year 50 year 100 Year
Pre-Development 5456 6184 8515 9927 11352 12986 14493
Floodway Storage
Post-Development 5781 6591 9349 11121 12976 14807 16240
Floodway Storage
Floodway Gain 325 407 834 1194 1624 1821 1747
Plus Bio-Basins 162 183 252 252 252 252 252
Less Active Park Fill -0 -0 -0 -0 -0 -18 -45
Nett Gain 487 590 1086 1446 1876 2055 1954
c.f.
Req’d Extra Volume 395 525 770 910 1095 1370 1585
(From Table 3)
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Page 19
The impact of the proposed development on peak flow rates downstream of the site is summarised in
Table 20, below. Flow rates leaving the site via the eastern tributary (nodes 15 – 16) will be slightly
reduced. Flow rates leaving the site via the western tributary (nodes 29-30) will increase, and this is a
result of the diversion of local stormwater runoff away from No 2 Pearsons Road and directly to the
western floodway. Further downstream along the western floodway, past the junction with the remaining
local runoff from that adjoining property (nodes 31-32), the post-development flows will revert to the
pre-development rates (within +/- 0.01 m3/sec). Further downstream, at the downstream end of the model
(nodes 38-39), where the two tributaries have converged, the flow-rates will be slightly reduced.
Table 20 : Pre / Post-Development Peak Flow Rates (m3/sec) Through Downstream Properties
Between 1 Year 2 Year 5 Year 10 Year 20 Year 50 Year 100 Year
Nodes
15 - 16 6.8 / 6.7 8.4 / 8.3 13.8 / 13.5 17.3 / 17.2 20.4 / 20.4 22.9 / 22.8 26.0 / 25.1
29 - 30 5.1 / 5.7 6.4 / 6.7 9.9 / 10.3 11.9 / 12.8 14.4 / 14.9 17.6 / 18.2 20.0 / 20.6
31 - 32 5.6 / 5.6 6.8 / 6.9 10.2 / 10.3 12.6 / 12.5 18.1 / 18.1 26.5 / 26.6 31.9 / 31.4
38 - 39 12.8/12.6 15.9 / 15.9 24.3 / 24.2 30.2 / 30.0 38.1 / 37.8 47.9 / 47.8 55.0 / 54.1
The flood levels predicted by the post-development model have been compared to those for the pre-
development scenario in Table 16 to 18 on preceding pages of this report, for ARI’s from 1 to 100 years.
Yellow highlighting is used in those two tables to identify nodes that are within the site boundaries. The
flood level affluxes on all external properties as a result of the proposed development are generally seen
to be practically zero (maximum 0.01 metre), when quoted to the nearest centimetre.
The only exception to the abovementioned generality regarding affluxes is at node 23, just upstream of
the site boundary in the western tributary, where the affluxes will range from 0.02 metre in a 10 year
storm to 0.05 metre in a 100 year storm. The western channel between node 23 and the site boundary was
designed in 2006 to be deliberately revegetated to a Manning’s n of 0.15, as part of the adjoining Blue
Wren Place development. That revegetation was installed at the time of that development, but has since
been removed, thereby reducing the present (“pre-development”) Manning’s n in this area to about 0.04,
consequently decreasing the flood levels at node 23 to about 0.4 metre below the original design levels.
The post-development flood levels as a result of Valkev’s development, while being 0.02 to 0.05 metre
above the present levels, will nevertheless be at least 0.3 metre below the original design levels for this
area, and the quoted affluxes are therefore suggested to be of no consequence. This is illustrated by the
levels of the adjoining lot in Blue Wren Place, which are marked on the longitudinal floodway profiles in
Figure 10 of this report.
The corresponding 100 year post-development flood profiles are shown on Figure 10, and the post-
development 100 year boundary is mapped on Figure 13.
7.3 Sensitivity Test
The sensitivity of the development to uncontrolled regrowth along the floodways was examined by
applying a Manning’s n of value of 0.15 to all overbank sectors of all of cross-sections of the model. The
100 year flood levels predicted by this test are summarised in Table 21, on the following page of this
report, and in Figures 10 and 13. The design levels for the development platform should take due account
of these flood levels.
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Table 21: 100 Year Flood Levels (m) With Manning’s n 0.150 On All Overbank Areas XPStorm Node Flood Level 3 101.78 4 101.67 5 101.16 6 101.15 7 101.11 8 101,00 9 100.98 10 100.98 11 100.91 12 100.81 13 100.55 14 100.43 15: 100.16 23 101.53 24 101.27 25 101.00 26 100.83 oF 100.70 28 100.50 29 100.30 30 100.00 8.0 CERTIFICATION I hereby certify that the findings described in this report have been deduced by industry-standard analytical procedures and that the Sunshine Coast Regional Council can rely on those findings in their considerations of the relevant development application. Denis Ogle, RPEQ 2405, 30 April 2014 Rrichane Gtarmwater Manacament Pty T td Dacument File: VallavSNF Dac Page 19
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NORTH
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28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
LOCALITY AND LOT PLAN FIGURE 1
Page 22
NORTH
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PARTIAL-AREA LIMITS, FOR CALCULATION OF
PRE- AND POST-DEVELOPMENT FLOW RATES 16
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0 SCALE 100 m
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
URBS MODELS OF STORMWATER DETENTION REQUIREMENT FIGURE 2
Page 23
AD
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PARTIAL-AREA LIMIT, FOR CALCULATION OF
PRE-DEVELOPMENT FLOW RATES
No 2, PEARSONS ROAD
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28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
PROPOSED CHANGE IN DISCHARGE SCENARIOS TO No 2 PEARSONS ROAD FIGURE 3
Page 24
NORTH
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28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
CATCHMENT SUBDIVISION FOR PRE-DEVELOPMENT URBS MODEL FIGURE 4
Page 25
NORTH
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28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
CATCHMENT SUBDIVISION FOR POST-DEVELOPMENT URBS MODEL FIGURE 5
Page 26
SCALE BSM— 200m 28 Apr 2014 | VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY | XPSTORM HYDRAULIC MODEL NETWORK | [FIGURE 6 |
Page 27
LOOKING DOWNSTREAM FROM NODE 10, THROUGH NODE 11 TO NODE 12
LOOKING DOWNSTREAM FROM NODE 12, THROUGH NODE 13 TO NODE 14
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
PHOTOGRAPHS OF EASTERN FLOODWAY ON 25 NOVEMBER 2013 FIGURE 7
Page 28
LOOKING DOWNSTREAM FROM NODE 25, TO NODE 26
LOOKING UPSTREAM FROM NODE 27, TO NODE 26
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
PHOTOGRAPHS OF WESTERN FLOODWAY ON 25 NOVEMBER 2013 FIGURE 8
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NORTH
0 SCALE 100 m
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
PROPOSED FLOODWAY MODIFICATIONS FIGURE 9
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WESTERN TRIBUTARY
EASTERN TRIBUTARY
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
LONGITUDINAL FLOODWAY PROFILES FIGURE 10
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DETAIL OF CHANNEL RESHAPING
TYPICAL CROSS-SECTION DETAILS
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
FLOODWAY CROSS - SECTION CHANGES, WEST TRIBUTARY FIGURE 11
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DECK LEVEL 100.55 (10 YR FLOOD LEVEL)
0.25 M 0.4 M
APPROACH FILL APPROACH FILL
0.2 M DIA PILE IL 98.63
0.45 M DIA PILE
PROPOSED FOOTBRIDGE, LOOKING DOWNSTREAM
(ONE 8.8 M CLEAR BRIDGE SPAN, PLUS THREE 2.2 M CLEAR BOARDWALK SPANS)
Q5 STORAGE LEVEL
Q1 STORAGE LEVEL
0.3 M BIO-STORAGE 0.7 M 0.4 M 0.1 M
WEIR
N-3
1-O
SAND SURFACE AREA 200 M2
1 M x 1M (INT) RISER BOX
0.7 M WIDE x 0.4 M DEEP NOTCH IN ONE SIDE
OUTLET PIPE, DIA AS REQ'D SAFETY / TRASH RACK AS REQ'D
TO CONVEY Q5 = 0.63 M3/SEC
BIO-BASIN SCHEMATIC, WESTERN TRIBUTARY
Q5 STORAGE LEVEL
0.2 M BIO-STORAGE
0.2 M 0.07 M Q1 STORAGE LEVEL
WEIR
-5
1 - ON
SAND SURFACE AREA 150 M2
1 M x 1M (INT) RISER BOX
1.0 M WIDE x 0.2 M DEEP NOTCH IN ONE SIDE
OUTLET PIPE, DIA AS REQ'D SAFETY / TRASH RACK AS REQ'D
TO CONVEY Q5 = 0.35 M3/SEC
BIO-BASIN SCHEMATIC, EASTERN TRIBUTARY
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
FOOTBRIDGE AND BIO - BASIN SCHEMATICS FIGURE 12
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NORTH
0 SCALE 50 m
28 Apr 2014
VALKEV PTY LTD - ELM STREET AND LAKE MACDONALD DRIVE, COOROY
FLOOD LEVELS AND FLOOD BOUNDARIES FIGURE 13
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Appendices
A. Design Rainfall Data
B. Rational Method Calculations Of Floodway Inflows, Pre-Development
C. Rational Method Calculations Of Floodway Inflows, Post Development
D. Floodplain Storage Volumes
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 20
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Appendix A
Design Rainfall Data
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 21
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Saori k eta cercutag “ Bureau of Meteorology Location Label: Cooroy Latitude: 26° 24' 26" Longitude: 152° 54! 51" $)] (Nearest grid cell: 152.9125 (E)] mm) Rainfall depth for Durations, Exceedance per Year (EY), and Annual Exceedance Probabilities (AEP). EY Duration : 1EY 1 min : ; 27 2 min 4.8 3 min 6.8 4 min 8.5 Simin 10.1 10 min 16.1 15 min - 20.4 30 min 28.9 1 hour 39.3 2 hour 52.3 3 hour — : 61.6 6 hour 81.4 12 hour 106.3 24 hour 134.9 48 hour 164.5 72 hour — 181.6 96 hour 194.2 120 hour 204.9 144 hour 214.8 /168 hour 7 224.5 11.4 18.2 - 23.0 326 44.4 59.4 70.4 93.9 124.0 158.8 194.4 214.5 229.4 241.2 252-3) 263.2 20% 42 7.4 10.4 13.0 15.4, 24.5 30.9 43.9 10% 5% 49 ~— 5.6 88 10.1 aza] 14a] 15.300 17.5 18.0 20.6 28.5 32.4 ; 36.0 40.9 514 58.6 71.2 817, 118.0 137.6 97.8 113.4, 162.8 191.6 222.5 264.1 294.8 353;6 S712 450.7 413.8 505.7 442.8 542.9 465.2 570.8 484.2 593.7, 501.3 613.4 Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc 95.7 134.5 164.3 231.0 321.7, 436.1, 564.9 640.0 690.6 : 106.4 “151.0 185.3 262.3 367.6 502.8 659.8 753.4 816.5 861.7 895.5
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Appendix B
Rational Method Calculations Of Floodway Inflows, Pre-Development
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 23
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Concentration Times
Subareas 1 - 5
Average Stream Velocity: 5-6% catchment slope = hilly; T = 1206 / 0.9 x 60 = 22 mins
Components Of Flow: 40 m sheet flow @ 10% = 9 mins
530 m steep [email protected] m/sec = 7 mins
730 m [email protected] – 1.1 m/sec = 12 mins
Total: 28 mins
Bransby-Williams: T = 58 L / A0.1 Se0.2 = 58 x 1.206 / 66.8 0.1 x 1.04 0.2 = 46 mins
From 22, 28, 46 mins (average 32) : Adopt Tc = 30 mins
Subarea 7
55 m sheet flow @ 4-5% = 12 mins
230 m swale/channel @ 5% = 4 mins
Total: 16 mins
Subarea 8
130 m sheet flow, partly lawn @ 7% = 16 mins
Subarea 9
85 m sheet flow @ 8% = 13 mins
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 24
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Subareas 12 — 16 Std inlet time for 10% grade = 9 mins 150 m pipe/kerb along Tewantin Rd@ 6% = 1.2 min 60 m pipe/kerb along Kauri St@ 4% grade = 0.6 mins 115 m pipe/kerb along Pearl St @ 4% grade = 1.2 mins 115 m pipe flow to sapphire [email protected]% grade = 1.8 mins 260 m open easement [email protected]% grade = 6.0 mins 370 m natural floodway @ hydraulic model 0.8 m/sec = 7.7 mins Total: = 27 mins Subarea 17 130 m sheet flow @ 4% = 19 mins Subarea 18 90 m sheet flow @ 4%, partly lawn = 16 mins Subarea 19 85 m sheet [email protected]%, average grass = 19 mins 85 m natural [email protected] m fall = 5 mins Total: 24 mins Q=0.00278 x FxCxIx A (F = 0.80 / 0.85 / 0.95 / 1.00 / 1.05 / 1.15 / 1.20) Subs Fi | C10 Tc I (mm/hr) A Q (m3/s) (min)| 1/2 / 5 / 10 / 20 / 50 / 100 | (Ha)} 1/2 /5 / 10 / 20 / 50 / 100 1-5 | 0.21 | 0.74 | 28 60/67 / 90 / 107 / 123 / 140 / 155 | 66.8 | 6.0/7.6/11.5/14.2/16.9 /21.5 /24.6 7 0.20 | 0.74 | 16 80/90 /120/ 140 / 158 / 183 / 202 | 2.2 | 0.29/0.35/0.52/0.63 /0.75/ 0.95/ 1.10 8 0.06 | 0.71 16 80/90 /120/ 140 / 158 / 183 / 202 | 2.0 | 0.25/0.30/0.45/0.55 / 0.65 / 0.83/ 0.96 9 0.10 | 0.72 | 13 89 /100/133/ 155 / 175 / 201 / 221 | 1.64 | 0.23/0.27/ 0.40 / 0.49 / 0.59 / 0.74 / 0.85 12-16 | 0.50 | 0.80 | 24 61/73/ 98 / 116 / 130 / 153 / 165 | 44.4 | 4.8/5.8 /8.6 /10.8 /12.8 /16.3/ 18.7 17 0.00 | 0.70 | 19 73: 182/109 / 129 / 148 / 167 / 186 | 1.9 | 0.22/0.26/ 0.38 / 0.48 / 0.57 / 0.71 / 0.83 18 0.04 | 0.71 16 80/90/120/ 140 / 158 / 183 / 202 | 1.7 | 0.21/0.26/0.38/0.47/0.56/0.71/0.81 19 0.09 | 0.72 | 24 65/ 73/ 98/ 116/ 130/ 152 / 166 | 1.99 | 0.21/0.25 / 0.37 / 0.46 / 0.54 / 0.70 /0.79 Brisbane Stormwater Management Pty Ltd Document File: WalkevSDF.Doc Page 25
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Appendix C
Rational Method Calculations Of Floodway Inflows, Post-Development
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 26
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Concentration Times Subarea 7 As per “Pre-Development”, Tc = 16 mins Subarea 8 QUDM std inlet time, 6 – 7% slope = 10 mins Subarea 9 Most of the area is within the 100 yr flood boundary: adopt Tc = 5 mins. Subareas 10 - 18 50 m sheet flow across lawn @ 8% = 13 mins 50 m swale/pipe @ 1% = 1 min Total: = 14 mins Subarea 19 30 m sheet flow across lawn @ 3% = 10 mins 45 m pipe / swale @ 2% = 1 min Total: = 11 mins Subarea 20 Most of the area is within the 100 yr flood boundary: adopt Tc = 5 mins Subarea 29 - 35 70 m sheet flow across lawn @3% = 17 mins 65 m pipe/kerb @ 2 m fall = 1 min 160 m pipe @ 6 m fall = 2 mins Total: = 20 mins Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 27
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Subarea 36 QUDM std inlet time for 8% grade = 10 mins 70 m wq-swale & pipes @ 1% = 2 mins Total : = 12 mins Subarea 37 As per “Pre-Development” : 16 mins Subarea 38 QUDM std inlet time for 1.5% grade = 15 mins 5-10 m pipe = 0 mins Total: = 15 mins Q=0.00278 x FxCxIx A (F = 0.80 / 0.85 / 0.95 / 1.00 / 1.05 / 1.15 / 1.20) Subs Fi C10 Tc I (mm/hr) A Q (m3/s) (min) 1/2/ 5 / 10 / 20/50 / 100 | (Ha) 1/ 2/5/10 / 20/50 / 100 0.30 | 0.76 16 80/90/ 120/140 / 158/ 183/202 | 2.25 | 0.30/ 0.36/ 0.54 / 0.67 / 0.79 / 1.00/ 1.15 0.60 | 0.82 10 97/109 / 147/171 / 194/224/245 | 0.29 | 0.05/0.06/ 0.09 / 0.11 /0.13 /0.17/0.19 9 0.00 | 0.70 5 121/137 /185 / 216 / 247 / 288/318 | 0.72 | 0.14/0.16/ 0.25 /0.30/ 0.36 / 0.46 / 0.53 10-18 | 0.50 | 0.80 14 84/96 / 128 / - / - / -/ - | 1.35 | 0.20/0.24/0.37/ ----/ ---- / ---- / ---- 19 0.60 | 0.82 11 94/106 /143 / 166 / 189 / 218/238 | 0.37 | 0.06/0.08 / 0.11 /0.14/0.17/0.21 /0.24 20 0.00 | 0.70 5 121/137 / 185 / 216 / 247 / 288/318 | 0.99 | 0.20/0.22 / 0.34 / 0.42 /0.50/ 0.64 /0.74 29-35 | 0.46 0.79 20 71/80/106/ --- / --- / --- /--- | 3.09 | 0.39/0.46/0.68/ --- / --- / --- /--- 36 0.45 0.79 12 92 /103 /138/ 160 / 183/211 /231 | 1.32 | 0.21/0.25/0.38/0.48 / 0.56 /0.70/0.80 37 0.08 0.72 16 80 /90/ 120/140 / 158 / 183/202 | 0.84 | 0.11/0.13 / 0.19 / 0.24 / 0.28 / 0.35 /0.41 38 0.60 | 0.82 15 82/92 /124/ 144/ 164/ 188/206 | 0.40 | 0.06/0.07 / 0.11 / 0.13 / 0.16 / 0.20 / 0.23 oo; Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 28
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Appendix D
Floodplain Storage Volumes
Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 29
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PRE-DEVELOPMENT FLOODPLAIN STORAGE VOLUMES (CUBIC METRES) USNODE DSNODE 1YEAR 2YEAR 5SYEAR 10YEAR 20 YEAR 50 YEAR 100 YEAR 3 4 273 286 356 398 438 490 549 4 5 127 136 178 204 225 250 273 5 6 583-612 724 815 900 957 988 6 7 648 669 776 910 1031 1075 1090 7 8 139 178 341 465 535 560 702 8 9 197 227 318 392 499 563 635 9 10 175 200 281 340 422 497 564 10 11 300 345 491 592 712 842 947 11 12 247 = 282 403 480 561 668 750 12 13 314 362 523 590 663 827 960 13 14 470 558 867 988 1071 1262 1462 14 15 310 386 615 718 792 900 1000 23 24 224 256 329 369 425 497 547 24 25 114 136 193 225 262 307 340 25 26 312 352 440 485 535 598 641 26 27 158 192 278 321 379 447 493 27 28 185 221 317 368 428 505 554 28 29 260 311 454 526 611 715 786 29 30 420 475 631 741 863 1026 1212 TOTAL 5456 6184 8515 9927 11352 12986 14493 POST-DEVELOPMENT FLOODPLAIN STORAGE VOLUMES (CUBIC METRES) USNODE DSNODE 1YEAR 2YEAR SYEAR 10YEAR 20 YEAR 50 YEAR 100 YEAR 3 4 208 217 253 293 326 375 420 4 5 85 8691 114 148 168 195 229 5 6 646 667 785 896 929 951 1030 6 7 650 673 812 955 990 1000 1108 7 8 144 187 413 511 760 966 1065 8 9 225 263 436 568 681 756 818 9 10 197 9229 364 492 588 650 699 10 11 339 396 624 830 993 1095 1179 11 12 280 322 473 573 683 764 823 12 13 347 = 397 567 649 819 952 1047 13 14 523 607 941 1074 1268 1520 1697 14 15 323 400 630 736 822 953 1053 23 24 224 261 346 392 446 511 560 24 25 161 191 264 303 352 413 456 25 26 285 331 444 510 590 687 751 26 27 235 280 382 437 502 583 638 27 28 223 275 395 459 534 626 680 28 29 305 373 538 626 735 862 924 29 30 381 9 431 568 669 790 948 1063 TOTAL 5781 6591 9349 11121 12976 14807 16240 Brisbane Stormwater Management Pty Ltd Document File: ValkevSDF.Doc Page 30