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RFI - 075-028 SWMP Report
CIVIL ENGINEERING PROJECT MANAGEMENT
SEDIMENT AND EROSION CONTROL
SITE BASED STORMWATER MANAGEMENT PLAN
at 11 Ventura Street, SUNSHINE BEACH
for Sasha Dettori
DATE: 31.10.22 REF: 075-028-01
ATT: Development Officer EMAIL: [email protected]
Noosa Council
REV: A
2261 david low way, peregian beach, qld 4573 acn: 626 671 092 [email protected]
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Page 2
CONTENTS PAGE
Peak Flows ................................................................................................................... 9
Peak Flow Management ............................................................................................ 11
Storage calculation .................................................................................................... 11
Peak Flow at Outlet ................................................................................................... 12
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LIST OF FIGURES
Figure 1 - Locality Plan ......................................................................................................................................... 5
Figure 2 – Pre-Development Catchment Plan...................................................................................................... 6
Figure 3 – Post-Development Catchment Plan .................................................................................................... 7
Figure 4 – Lawful Point of Discharge.................................................................................................................... 8
Figure 6 – Proposed Slimline Detention Tank .................................................................................................... 12
Figure 8 – Site Flooding ...................................................................................................................................... 14
LIST OF TABLES
Table A -Rational method calculation parameters (Pre Development)............................................................... 9
Table B -Rational method calculation parameters (Post Development) ............................................................. 9
Table C -Rational method calculations (Pre Development) ............................................................................... 10
Table D -Rational method calculations (Post Development) ............................................................................. 10
Table E - Rational Method vs XPSWMM Peak discharge (1%AEP) .................................................................... 11
Table F –Peak Flows at Outlet (Pre and Post Development) ............................................................................. 13
LIST OF APPENDICES
Appendix A Engineering Plans
Prepared by Bax Engineering dated October 2022
This report was commissioned by Ms Sasha Dettori and specifically investigates the subject site. Bax Engineering Pty
Ltd accept no responsibility for the accuracy of the information supplied to use by second and third parties.
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INTRODUCTION
Bax Engineering has been commissioned by Ms Sasha Dettori to provide a site-based stormwater management
plan for the proposed residential development at 11 Ventura Street in Sunshine Beach, Queensland.
The existing site covers a site area of 740m2 and the proposed development consists of the renovations and
increase in roof area of one of the two residential townhouses.
This report has been developed to address the stormwater management (both quality and quantity
requirements). The report investigates the requirements to mitigate stormwater runoff for the development
and outlines water quality treatment designed to meet the load-based reduction objectives in Council Planning
Scheme.
The stormwater runoff for the proposed development site has been assessed using the Queensland Urban
Drainage Manual (QUDM) with Rational Method calculations to determine the potential stormwater flows on
the development.
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THE SITE AND ITS CONTEXT
LOCALITY
The site is described as lot 1 on BUP13368 at 11 Ventura Street and is within the Noosa Council local
government boundaries. The development is identified in Figure 1.
The property has an existing 2-unit townhouse on the property. The extent of works is focused on the
renovations proposed for the northern unit known as lot 1. The site has a gradual fall to the eastern frontage
and has residential property to the west, south and north.
The total catchment area of the subject lot is 740m2 with half of this area being the lot 1 development. The
elevation range between approximately 37.25m AHD in the west to 36.75m AHD towards the flow path in the
northeast front boundary.
Figure 1 - Locality Plan
Source: Queensland Globe
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The site experiences no overland flow from other catchments. The catchment draining towards Ventura Street
is 0.074ha in area and is channelled towards the kerb and channel. Roofwater and hardstand areas from both
lot 1 and 2 are connected to an existing field inlet in the property frontage. This pit is the connected directly
to the kerb via kerb adaptors. The pre-development catchment is shown in Figure 2 (and Bax Engineering plan
075-028-SK01 as part of Appendix A).
Figure 2 – Pre-Development Catchment Plan
As part of the proposed renovations, the existing dwelling will increase in impervious area, however the
catchment will not increase. This increase in impervious area will continue to the same outlet point via a
detention tank located in the common property (lot 0 BUP13368). The post-development catchment is
shown in Figure 3 (and Bax Engineering plan 075-028-SK02 as part of Appendix A).
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Figure 3 – Post-Development Catchment Plan
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STORMWATER QUANTITY MANAGEMENT
The site is an existing 2 lot multi-unit development totaling 740m2 with the existing dwellings, grassed surface
and some vegetation.
The site will increase hardstand area and all runoff from the allotments will ultimately flow east towards the
existing overland flow path.
LAWFUL POINT OF DISCHARGE
The post-development ‘Lawful Points of Discharge’ is nominated for the subject property as the Ventura Street
frontage. This is the same location as the pre-development and is shown on Figure 4Error! Reference source
not found. as ‘LPD01’.
Figure 4 – Lawful Point of Discharge
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DESIGN REQUIREMENTS – HYDROLOGY
To demonstrate that no increase in peak flows is occurring to the east (LPD1), the predevelopment catchment
was compared against the pre-development for flow contribution.
Peak Flows
Flows from each catchment for the pre and post development were calculated using the Rational
Method and compared against the XPSWMM estimates for the 63 % to 1 % Annual Exceedance
Probability (AEP) storm event for standard duration storm events.
The Rational Method calculation parameters are provided in Table A and Table B for the pre and post
conditions respectively.
Calculations of the storm events using the Rational Method are provided in Table C and Table D.
Table A -Rational method calculation parameters (Pre Development)
Catchment C01
Area (ha) 0.074
Fraction Imp. (%) 53
1
I10 75
Time of
11.1
Concentration (mins)
Table B -Rational method calculation parameters (Post Development)
Catchment P01
Area (ha) 0.074
Fraction Imp. (%) 71
1
I10 75
Time of
11.1
Concentration (mins)
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Table C -Rational method calculations (Pre Development)
1% 2% 5% 10% 18% 39% 63%
Area tc I100 C100 I50 C50 I20 C20 I10 C10 I5 C5 I2 C2 I1 C1
Catchment AEP AEP AEP AEP AEP AEP AEP
(ha) (min) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s)
C01 0.074 11.14 248 0.96 0.049 226 0.92 0.043 197 0.84 0.034 173 0.80 0.029 152 0.76 0.024 99 0.68 0.014 80 0.64 0.011
Table D -Rational method calculations (Post Development)
1% 2% 5% 10% 18% 39% 63%
Area tc I100 C100 I50 C50 I20 C20 I10 C10 I5 C5 I2 C2 I1 C1
Catchment AEP AEP AEP AEP AEP AEP AEP
(ha) (min) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s) (mm/hr) (m³/s)
P01 0.074 11.14 248 1.00 0.051 226 0.97 0.045 197 0.88 0.036 173 0.84 0.030 152 0.80 0.025 99 0.71 0.015 80 0.67 0.011
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Table C -Rational method calculations (Pre Development)
1% 2% 5% 10% 18% 39% 63%
Area te loo C100 Iso Cso ho C20 ho Cio Is Cs l Q h CG.
Catchment. AEP AEP AEP AEP AEP AEP AEP
(ha) | (min) | (mm/hr) (m?/s) | (mm/hr) (m3/s) | (mm/hr) (m?/s) | (mm/hr) (m3/s) | (mm/hr) (m3/s) | (mm/hr) (m3/s) | (mm/hr) (m3/s)
co1 0.074 | 11.14 248 0.96 | 0.049 226 0.92 | 0.043 197 0.84 | 0.034 173 0.80 | 0.029 152 0.76 | 0.024 99 0.68 | 0.014 80 0.64 | 0.011
Table D -Rational method calculations (Post Development)
1% 2% 5% 10% 18% 39% 63%
Area t loo C100 Is0 Cso lo Cro lio Cio Is Cs Ip Q hh GQ
Catchment AEP AEP AEP AEP AEP AEP AEP
(ha) | (min) | (mm/hr) (m3/s) | (mm/hr) (m?/s) | (mm/hr) (m3/s) | (mm/hr) (m3/s) | (mm/hr) (m3/s) | (mm/hr) (m/s) | (mm/hr) (m/s)
Pol 0.074 | 11.14 248 1.00 | 0.051 226 0.97 | 0.045 197 0.88 | 0.036 173 0.84 | 0.030 152 0.80 | 0.025 99 0.71 0.015 80 0.67 | 0.011
&
&
Pace 10 oF 18
ACN: 626 671 092
2261 DAVID LOW WAY, PEREGIAN BEACH, QLD 4573
[email protected]
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The calculated flows using the Rational Method were compared against the XPSWMM estimates for
the catchment for 1%AEP pre and post development conditions. These are provided in Table E and
show a reasonable calibration.
Table E - Rational Method vs XPSWMM Peak discharge (1%AEP)
Rational
XPSWMM Difference
Catchment Method
(m3/s) (%)
(m3/s)
C01 Pre Development 0.049 0.043 -12.3
C01 Post Development 0.051 0.050 -2.1
Peak Flow Management
In order to ensure that the peak flow mitigation meets the requirements of Council’s Planning scheme policy
for development works. It is proposed to alleviate the increase of fraction impervious by installing a detention
tank connected to the roof and hardstand areas of the proposed development. XPSWMM Modelling was used
to design the detention and minor and major flow pipes from the detention system. The comparison of each
of the storm events is provided in and demonstrates that the installation of a detention tank will allow
mitigation of all events.
Storage calculation
The proposed design has resulted in a reduction in post development flows to the Ventura Street frontage
(LPD1). XPSWMM was used to model the storage requirements to ensure the post development flows were
not higher than the predevelopment flows at this location.
The peak flow management objectives have been addressed using detention storage. It is proposed to alleviate
the increase of fraction impervious by installing a detention tank connected to the roof and hardstand areas
of the proposed development. These detention tank will be sized to control the peak discharge and has been
calculated to total 4.6m3 based on the peak discharge temporal pattern. A slimline aboveground tank with 7m3
of capacity is suggested. This would allow 2.4m3 which could be used for site reuse.
The proposed design of the detention tank will consist of a single slimline tank with dimensions shown in Figure
5 (or similar approved). The tank has been designed with low flow discharges via a 20mm diameter orifice at
the base of the re-use and a second orifice (25mm diameter) 606mm above the base. The tank would also
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have a high flow discharge via a 100mm diameter orifice at a height 1.444m from the reuse base. This would
allow a total storage of 5KL which exceeds the 4.6KL volume requirement.
This tank is shown in Figure 5 (and detailed in Bax Engineering plan 075-028-SK03 as part of Appendix A).
Figure 5 – Proposed Slimline Detention Tank
Peak Flow at Outlet
However, the catchment flowing to the eastern outlet (LPD1) has increased and peak volume will need to be
maintained. With the inclusion of the detention system, post development flows have been analysed for the
outlet location. Modelling of the system was undertaken using XPSWMM for the pre and post development
to ensure no increase. The peak duration and rainfall temporal pattern was nominated as the 15min and Storm
02 for the 1%AEP event. The pre development and post development (unmitigated and mitigated) are
provided in Table F. This demonstrates that the incorporation of the detention system will show no increase
in peak flows.
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Table F –Peak Flows at Outlet (Pre and Post Development)
Post Development
Pre- Development
AEP % Unmitigated Mitigated
Q Peak (m³/s) Q Peak (m³/s) Q Peak (m³/s)
1 0.043 0.050 0.043
2 0.038 0.045 0.038
5 0.033 0.039 0.032
10 0.027 0.034 0.026
20 0.022 0.030 0.022
50 0.017 0.022 0.016
63.2 0.015 0.020 0.014
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STORMWATER QUALITY MANAGEMENT
The reconfiguring of a lot that does not include a new road and has less than 6 new lots it is exempt from
WSUD load reduction targets. Therefore, the water quality objectives are not required for this development.
Nonetheless flows from hardstand areas will be directed towards landscaped areas and vegetated buffers.
FLOODING
Noosa Council mapping of the development site shows that the proposed site is not affected by flooding. The
mapping shown in Figure 6 highlights the extents of Extreme (0.05% AEP) flood events.
Figure 6 – Site Flooding
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CONCLUSION
The pre and post development scenario for the subject has been reviewed to ensure non-actionable nuisance
of flows.
The following conclusions have been made:
• based on the design and proposed detention system, the construction of the development on the
subject site will have negligible impact to the downstream overland flow path.
• the development on the subject site will result in non-actionable nuisance of stormwater runoff
quantities with all runoff to outlet to lawful points of discharge.
It is anticipated the report, when reviewed in conjunction with the planning report and the development plans;
will assist in supporting the application seeking development approval.
Yours Faithfully,
GLENN AINSWORTH
MIEAust CPEng NER RPEQ CPESC
BAX ENGINEERING PTY. LTD.
Ph: 0407 021 300
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REFERENCES
Civil Design
Prepared by Bax Engineering (Document No: 075-028-SK01 to SK03) dated 17.10.22
Noosa Council – Relevant Codes and Standards
Noosa Plan 2020 | interactivemaps
Noosa Council – Flood Hazard Mapping
https://www.mapping.noosa.qld.gov.au/disaster-management
Queensland Globe – Site Mapping
https://qldglobe.information.qld.gov.au/
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APPENDIX A
Engineering Plans
Prepared by Bax Engineering dated October, 2022
[OCR of page images]
APPENDIX A
Engineering Plans
Prepared by Bax Engineering dated October, 2022
Page 18
TP
//
V
V
V
TP
LEGEND:
BAX
SCALE: SURVEYED: CLIENT: NORTH POINT TITLE:
SASHA DETTORI & TONY CARUSO PRE DEVELOPMENT CATCHMENT
DATUM: AHD
A 17.10.22 ISSUED FOR APPROVAL QT GWA
PROJECT NO:
075-025
LOCAL AUTHORITY APPROVAL NO:
DATE
CHECKED
DRAWN
17.10.22
GWA
QT
APPROVED:
GLENN AINSWORTH
CPESC No: 7678
RPEQ No: 19204
Engineering PTY. LTD.
PROJECT:
11 VENTURA ST SINRISE BEACH
No. DATE REVISIONS BY CKD --- DESIGNED QT FOR AND ON BEHALF OF BAX ENGINEERING PTY. LTD.
2261 DAVID LOW WAY, PEREGIAN BEACH, QLD 4573
[email protected] QLD 4576 PLAN No 075-028-SK01 REVISION A A1
Page 19
DN
LEGEND:
BAX
SCALE: SURVEYED: CLIENT: NORTH POINT TITLE:
SASHA DETTORI & TONY CARUSO POST DEVELOPMENT CATCHMENT
DATUM: AHD
A 17.10.22 ISSUED FOR APPROVAL QT
PROJECT NO:
075-025
GWA LOCAL AUTHORITY APPROVAL NO:
DATE
CHECKED
DRAWN
17.10.22
GWA
QT
APPROVED:
GLENN AINSWORTH
CPESC No: 7678
RPEQ No: 19204
Engineering PTY. LTD.
PROJECT:
11 VENTURA ST SINRISE BEACH
No. DATE REVISIONS BY CKD --- DESIGNED QT FOR AND ON BEHALF OF BAX ENGINEERING PTY. LTD.
2261 DAVID LOW WAY, PEREGIAN BEACH, QLD 4573
[email protected] QLD 4576 PLAN No 075-028-SK02 REVISION A A1
Page 20
TP
//
DN
TP
LEGEND:
BAX
SCALE: SURVEYED: CLIENT: NORTH POINT TITLE:
SASHA DETTORI & TONY CARUSO OPERATIONAL CONTROL PLAN
DATUM: AHD
A 17.10.22 ISSUED FOR APPROVAL QT
PROJECT NO:
075-025
GWA LOCAL AUTHORITY APPROVAL NO:
DATE
CHECKED
DRAWN
17.10.22
GWA
QT
APPROVED:
GLENN AINSWORTH
CPESC No: 7678
RPEQ No: 19204
Engineering PTY. LTD.
PROJECT:
11 VENTURA ST SINRISE BEACH
No. DATE REVISIONS BY CKD --- DESIGNED QT FOR AND ON BEHALF OF BAX ENGINEERING PTY. LTD.
2261 DAVID LOW WAY, PEREGIAN BEACH, QLD 4573
[email protected] QLD 4576 PLAN No 075-028-SK03 REVISION A A1