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RECOR Preliminary Stormwater Management Report - 20220130
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22 Delorme Street
20220130
Santiago Nominees P/L TTE
Stormwater Management Plan
November 2022
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Document prepared by:
RECOR Pty Ltd
ABN 89 647 469 707
37 Mary Street
Noosaville, QLD 4566
Australia
T +61 7 5211 1003
E [email protected]
W recorconsulting.com
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Document control
Report title Stormwater Management Plan
Document code 20220130-SWMP01 Project number 20220130
File path C:\12dS\data\RecorSYN\20220130 22 Delorme St_545\03 Engineering\02 CIV\02
Reports\RECOR Preliminary Stormwater Management Report - 20220130.docx
Client Santiago Nominees P/L TTE
Client contact - Client reference -
Rev Date Revision details/status Author Reviewer Verifier Approver
(if required)
0 19/05/2021 Initial Version B. Parry N. Wagstaff N. Wagstaff
1 08/06/2022 Revised Arch layout B. Parry N. Wagstaff N. Wagstaff
2 30/09/2022 RFI update B. Parry B. Parry
3 8/11/2022 Further Advice update J.Bauleka J.Bauleka
Current revision 3
Approval
Author signature Approver signature
Name J.Bauleka Name J.Bauleka
RPEQ: 20693
Title Civil Engineer Title Civil Engineer
recorconsulting.com
A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected]
P +61 7 5211 1003
Page 3
Contents
Introduction ....................................................................................................................................4
Site Details......................................................................................................................................5
2.1. Existing Site Description & Drainage .................................................................................................. 5
2.2. Existing Drainage Patterns .................................................................................................................. 5
2.3. Proposed Development Drainage Pattern ......................................................................................... 6
2.4. Flood Considerations ........................................................................................................................... 7
Stormwater Quantity .......................................................................................................................8
3.1. Pre-Post Comparison........................................................................................................................... 8
Stormwater Quality........................................................................................................................10
4.1. Construction Phase............................................................................................................................10
4.2. Operational Phase .............................................................................................................................11
Conclusion....................................................................................................................................12
Appendices
Appendix A
Proposed Development Concept Plans
Appendix B
DRAINS Modelling Parameters and Results
Project number 20220130
File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08
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INTRODUCTION RECOR has been engaged to prepare a Stormwater Management Report to accompany a development application for a residential duplex development located on the corner of Safari Street and Delorme Street, Noosa Heads. This report investigates the stormwater management considerations for the existing and proposed development site and assesses how the run-off from the site is to be managed in accordance with Noosa Shire Council requirements for stormwater drainage. Project number 20220130 File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08 Page 4 of 15 Revision 3 P +61 7 5211 1003 A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected] recorconsulting.com
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SITE DETAILS
2.1. Existing Site Description & Drainage
The existing site, known in real property terms as Lot 136 RP 160425, is located at 22 Delorme Street having frontage
to both Delorme Street and Safari Street. The existing site contains a residential dwelling with a site area of 528m².
A locality map of the site is presented below in Figure 2.1 - Site Locality Plan (Noosa Council Intramaps, 2022)
Figure 2.1 - Site Locality Plan (Noosa Council Intramaps, 2022)
2.2. Existing Drainage Patterns
Based on site contours shown in Figure 2.2 - Site Contours (Noosa Council Intramaps, 2022) below, and survey of
the site which did not identify any internal stormwater infrastructure, the run-off from the site is expected to discharge
as overland surface flows towards the south and to the west. With sandy soils typical of the locality, a portion of the
surface run-off is likely to be reduced due to infiltration into the ground. Remaining surface flows are captured
downstream within the drainage network present at the corner of Wyandra Street and Safari Street.
Roof run-off is conveyed by downpipes below ground to a kerb adaptor outlet observed in the Safari Street frontage.
Upstream surface run-off enters the property across the northern boundary of the site from an adjacent residential
dwelling, however infiltration of this run-off into the sandy soils is also considered to reduce the impact of these
overland flows.
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Figure 2.2 - Site Contours (Noosa Council Intramaps, 2022)
2.3. Proposed Development Drainage Pattern
2.3.1 Stormwater Concept
The internal stormwater drainage network will be provided to ensure collection of surface run-off as well as allowing
for capture of upstream run-off at the boundary and discharge from subsoil drainage of retaining walls.
Roof run-off from the new building will be drained via downpipes into a stormwater re-use and attenuation tank for
each unit. The tank is sized to reduce the overall developed site flows to pre-development levels, ensuring discharge
from the site minimises any impact to the downstream environment. Tanks of a suitable size will be provided to each
unit to comply with the relevant code and mitigate developed peak flows from the site. The tank overflows will be
connected into the internal stormwater drainage pits throughout the development.
The internal surface and roof drainage will be conveyed and discharged via kerb adaptors replacing the existing
within Safari Street, being the lawful point of discharge from the development consistent with the existing drainage
characteristics.
The roof and allotment drainage system for the proposed site shall be designed to comply with:
1. Noosa Shire Council Planning Scheme Policy (PSP) - Engineering Design Standards – Roads, drainage and
earthworks;
2. The Queensland Urban Drainage Manual (QUDM); and
3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.
Refer to Appendix A Proposed Development Concept Plan for the proposed stormwater drainage layout plan
illustrating the concept described above.
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2.4. Flood Considerations Review of the Noosa Shire Council Intramaps flood layers including the Flood Hazards Overlay has identified that the site is located outside of any flood or inundation areas within the locality. It is not expected that that the proposed development will be subject to flooding. Project number 20220130 File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08 Page 7 of 15 Revision 3 P +61 7 5211 1003 A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected] recorconsulting.com
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STORMWATER QUANTITY
3.1. Pre-Post Comparison
As the development proposes to increase the impervious area of the site by approximately 119m² (from 247m² to
366m²), there is likely to be a minor increase in peak flows from the site. The site has therefore been modelled using
the DRAINS software to assess the impact on peak flows, comparing the existing site conditions to the proposed
development.
In accordance with ARR2019, an Initial Loss-Continuing Loss (IL-CL) model has been used to assess the site against
the ensemble of storm temporal patterns for the East Coast North region. The loss parameters and temporal patterns
have been imported from the ARR Datahub, and rainfall intensities have been imported from the Bureau of
Meteorology IFD rainfall data allowing for a 20% increase to rainfall depths to account for future climate change
patterns.
The parameters obtained from the Australian Rainfall and Runoff (ARR) Data Hub for the location and the rainfall
IFD data obtained from the Bureau of Meteorology have been imported into Drains to generate the storm events.
The models have been run using the ensemble of storm events for 1EY, 50%, 0.2EY, 10%, 5%, 2% and 1% Annual
Exceedance Probability (AEP) for durations from 1 minutes to 6 hours to determine the critical storm duration and
the mean peak flowrate from the storms. Refer to Appendix B DRAINS Modelling Parameters and Results for details
of the parameters used and summary of the results from the modelling.
The configuration of the catchment areas for pre-development and post-development are shown in Figure 3.1 –
DRAINS Pre-development catchment and Figure 3.2 – DRAINS Post-development catchments respectively.
Figure 3.1 – DRAINS Pre-development catchment
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Figure 3.2 – DRAINS Post-development catchments
The results of the modelling against the range of design storms for the development under the existing and
proposed development conditions are shown in Table 3.1 Existing and proposed unmitigated site peak discharge
rates.
Table 3.1 Existing and proposed unmitigated site peak discharge rates
Delorme Street
Qchange
A.E.P Qexisting Qproposed Qchange (%)
(m³/s) (m³/s) (m³/s)
1EY 0.014 0.016 0.002 14%
50% 0.016 0.018 0.002 13%
0.2 EY 0.025 0.027 0.002 8%
10% 0.032 0.032 0 0%
5% 0.036 0.036 0 0%
2% 0.041 0.042 0.001 2%
1% 0.045 0.046 0.001 2%
The proposed development will result in a maximum of 2L/s increase across all storm events under the increased
2100 climate rainfall conditions, which is considered an insignificant increase beyond the present levels. As the
locality is not prone to flooding and no drainage issues have been identified, this small increase is not expected to
result in any significant impacts or risks to downstream infrastructure, therefore no attenuation is proposed for the
development.
In accordance with the Sustainable Building Design code, a 3,000L rainwater tank per dwelling is to be provided. A
low flow outlet consisting of a 43mm orifice plate in each tank is to be provided at the base of each tank, and a
100mm high flow outlet at the head of the tank will provide discharge for larger storm events. The high flow outlet
will be plumbed into the site’s internal drainage network.
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STORMWATER QUALITY
The following sections discuss the stormwater quality considerations for the construction and operational phase of
the development.
4.1. Construction Phase
4.1.1 Erosion and Sediment Control Measures
During construction, it is necessary to manage stormwater run-off to avoid potential contamination of downstream
waterways from sediments and other pollutants from the site. A range of best practice sediment and erosion controls
should be implemented on the development to ensure negative impacts to the downstream receiving environment
are mitigated.
As the area being developed is below 2,500m², the development’s construction will be managed using best practice
erosion and sediment control principles in line with the desired outcomes of Appendix 2 of the SPP (DERM, July
2017), which are shown below in Figure 4.1.
Figure 4.1 SPP 2017 Construction Phase Stormwater Management Design Objectives
A site-specific erosion and sediment control plan shall be prepared as part of a future submission for Operational
Works approval. Suitable erosion and sediment controls for the site may include:
1. Sediment fencing along downstream of the work areas within the site to prevent sediment from leaving the
construction area.
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2. A shakedown area is to be installed at the construction entry/exit to the proposed development area to
minimise sediment being transported to and from the site.
3. Diversion of upstream catchments around any exposed areas using diversion drains around the site.
4. Ensuring any loose material tracked from the construction site onto the road is swept and removed prior to
the end of the day.
4.2. Operational Phase
The development consists of a small lot duplex consistent in character with the existing residential dwelling. The
proposed development is not considered to significantly alter the pollutant generation potential of the site, and
therefore no additional stormwater quality treatment is proposed for the development.
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CONCLUSION
This Stormwater Management Report has outlined how the stormwater run-off from the site is to be managed to
comply with the relevant requirements and minimise any adverse impacts to the downstream catchments.
The proposed site stormwater run-off is captured internally and discharge by kerb adaptors into Safari Street
as the lawful point of discharge. Field inlet pits are provided within the development to capture upstream
run-off and subsoil drainage from retaining walls to convey it to the point of discharge.
Provision of 3kL tank per dwelling complies with the Sustainable Building Design code for reuse.
The existing and proposed development site have been modelled for the critical design storm events for the
site, which found there would be only a minor increase to peak flows that is unlikely to impact downstream
properties or infrastructure. No attenuation is therefore proposed for the development.
During construction, erosion and sediment control measures are to be implemented to minimise potential
contaminants impacting the downstream receiving environment in line with the objectives of Appendix 2 of
the SPP. An erosion and sediment control plan shall be developed as part of a submission for Operational
Works approvals.
As the development is a small residential site that does not significantly alter the pollutant generating
characteristics of the site, stormwater quality treatment is not proposed for the development.
The proposed stormwater solution is considered to minimise any adverse impacts to the downstream
environment arising from the stormwater run-off while also meeting the stormwater quantity targets required
for the development.
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Appendix A Proposed Development Concept Plans Project number 20220130 File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08 Page 13 of 15 Revision 3 P +61 7 5211 1003 A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected] recorconsulting.com
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Appendix B DRAINS Modelling Parameters and Results Project number 20220130 File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08 Page 14 of 15 Revision 3 P +61 7 5211 1003 A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected] recorconsulting.com
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Document prepared by RECOR Pty Ltd ABN 89 647 469 707 37 Mary Street Noosaville, QLD 4566 Australia T +61 7 5211 1003 E [email protected] Wrecorconsulting.com Project number 20220130 File RECOR Preliminary Stormwater Management Report - 20220130, 2022-11-08 Page 15 of 15 Revision 3 P +61 7 5211 1003 A 75 Noosa Drive, Noosa Heads Qld 4567 E [email protected] recorconsulting.com