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Stormwater Management Report · MCU22/0087.01
REC: waht 37 Bottlebrush Avenue 20220051 Stormwater Management Plan October 2024
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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
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Document control
Report title Stormwater Management Plan
Document code 20220051-SWMP01 Project number 20220051
File path
Client Bottlebrush Property Pty Ltd
Client contact - Client reference -
Rev Date Revision details/status Author Reviewer Verifier Approver
(if required)
0 05/05/2022 Initial Version B. Parry N. Wagstaff
1 28/10/2024 Updated for revised design M. Poynter A. Steele
Current revision 0
Approval
Author signature Approver signature
Name M. Poynter Name A. Steele
Title Director Title Civil Engineer
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Contents
Introduction .................................................................................................................................... 4
Site Details...................................................................................................................................... 5
2.1. Existing Site Description ...................................................................................................................... 5
2.2. Existing Drainage Patterns .................................................................................................................. 5
2.3. Proposed Development Drainage Pattern ......................................................................................... 7
2.4. Flood Considerations ........................................................................................................................... 7
Stormwater Quality Management ..................................................................................................... 8
3.1. Operational Stormwater Management................................................................................................ 8
3.2. Construction Stormwater Management .............................................................................................. 8
Stormwater Quantity Management ..................................................................................................10
3.3. Pre-post comparison ..........................................................................................................................10
Conclusion....................................................................................................................................13
Appendices
Appendix A
DRAINS Modelling Results
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INTRODUCTION
RECOR has been engaged to prepare a Stormwater Management Report to accompany a development application
for development of residential units on a property located at 37 Bottlebrush Avenue.
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 Council requirements
for stormwater drainage.
This document has been prepared with consideration for the following specifications, guidelines and reports:
• Noosa Plan 2020
• State Planning Policy 2017
• Queensland Urban Drainage Manual (QUDM), IPWEA
• International Erosion Control Association (IECA) Best Practice Erosion and Sediment Control
• Water Sensitive Urban Design Technical Design Guidelines for Southeast Queensland, Healthy Waterways
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SITE DETAILS
2.1. Existing Site Description
The existing site is known in real property terms as Lot 133 RP 88934, located at 37 Bottlebrush Avenue, Noosa
Heads. The existing site covers an area of 491m² and contains an existing residential dwelling with vehicular access
from Berrima Row. A locality plan of the proposed site is presented 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
The site is developed, with the internal catchment being made up of the existing dwelling roof area and surrounding
landscaping. An internal network of grated drains and field inlet pits provide for the capture and conveyance of
surface stormwater run-off from within the site.
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The survey of the site has identified two 100mm diameter PVC pipes discharging into the Bottlebrush Avenue
drainage system. The internal stormwater drainage network, as well as the outlets from the roof drainage will be
discharged via this outlet as the lawful point of discharge.
An upstream catchment from the adjacent property to the northeast is expected to drain overland into the subject
site. The upstream catchment, of approximately 380m² is currently undeveloped and is expected to drain as overland
sheet flows across the property boundary. This area is shown in yellow in Figure 2.2 - Site Characteristics (Noosa
Council Intramaps, 2022).
Approx. upstream
catchment 380m²
Discharge via
2x100mm PVC
Kerb Outlet
Figure 2.2 - Site Characteristics (Noosa Council Intramaps, 2022)
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2.3. Proposed Development Drainage Pattern
2.3.1 Stormwater Concept
The existing dwelling will be replaced by the proposed unit building and outdoor areas. As the existing site is
developed, an assessment of the impacts of the proposed change to impervious areas has found that the increase
to stormwater discharge from the site is negligible.
It is proposed that the lawful point of discharge for the development will be maintained as per the existing site, with
stormwater run-off from the property discharging via kerb adaptors into the Bottlebrush Avenue drainage system.
Inlet pits will be provided along the northern boundary to provide for the capture of upstream run-off to ensure it
can be conveyed through the development without impacting upon the open space areas for the proposed
development. The internal drainage network will provide for the collection of run-off from impervious areas as well
as for roof drainage connections. The run-off will be discharged via direct connection to existing pits and kerb
adaptors in the new kerb and gutter to be provided for the site frontage.
With the scale and residential nature of the development being consistent with the existing site usage, it is
considered that the development will not impact upon pollutant generation characteristics of the site in a way that
would cause significant impacts to the water quality being discharged from the development. As a result, no
stormwater quality treatment is proposed for the development.
The roof and internal drainage system for the proposed site shall be designed to comply with:
1. Noosa Council Planning Scheme Policy (PSP) 6 – Engineering Design Standards;
2. The Queensland Urban Drainage Manual (QUDM); and
3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.
2.4. Flood Considerations
Review of the Noosa Council Intramaps flood layers including the Flood Hazards Overlay and Flood Inundation
Extents has identified that the site is not within a flood affected area and that no special consideration for flood
management is required for the site.
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STORMWATER QUALITY MANAGEMENT
3.1. Operational Stormwater Management
The proposed development site will maintain the residential nature of the existing site and the proposed
development area results in only a small increase to the impervious area of the site, being predominately an
increase in roof area. As a small lot residential site with similar characteristics to the existing site, there are not
expected to be any significant water quality impacts during the operational phase of the site that would require
additional stormwater quality management, therefore no water quality treatment is proposed for the future
development.
3.2. Construction Stormwater Management
3.2.1 Erosion and Sediment Control Measures
During construction, it is necessary to manage stormwater run-off to avoid potential contamination to downstream
environments in accordance with the objectives of Appendix 2 of the SPP (DERM, July 2017), which are shown below
in Figure 3.1 SPP 2017 Construction Phase Stormwater Management Design Objectives.
Figure 3.1 SPP 2017 Construction Phase Stormwater Management Design Objectives
As the site area is only 500m² sediment control targets are not imposed upon the proposed development, however
best practice erosion and sediment controls shall be installed to minimise the discharge of potential contaminants
from the site in accordance with the SPP.
A site-specific erosion and sediment control plan has been prepared and is included with Proposed Development
Plans detailing the proposed treatment for erosion and sediment controls however the contractor for the
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development is required to assess based on local site conditions and provide for any additional controls determined
to be necessary. The erosion and sediment controls proposed for the site include:
1. Sediment fencing downstream of the work areas within the site to prevent sediment from leaving the
disturbed construction area.
2. Providing a stabilised construction entry and washdown area to minimise sediment carried by construction
vehicles from the site.
3. Minimising disturbed areas where possible.
4. Diverting clean upstream run-off around disturbed areas within the site.
5. Protecting material and equipment stockpile areas with upstream diversion banks and downstream
sediment fencing to prevent sediment transport.
6. Providing grass filter strips within the downstream verge
7. Ensuring any loose material tracked onto roads by construction vehicles is swept and removed from the
access road before the end of the day.
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STORMWATER QUANTITY MANAGEMENT
3.3. Pre-post comparison
As development of a site may results in increase in peak stormwater discharges, an analysis of the existing conditions
has been carried out as well as a comparison against the proposed development conditions. The proposed
development will result in net increase to the impervious area of only 33m², with most of this increase being through
a larger roof area, therefore the analysis will quantify the impacts of this increase to the downstream receiving
environment.
The site has been modelled using the DRAINS software to assess the peak flow hydrology off the site. In accordance
with ARR2019, an Initial Loss-Continuing Loss (IL-CL) model has been used to assess the proposed development
against the ensemble of storm temporal patterns for the East Coast North region. The models have been run using
the ensemble of storm events for durations from 5 minutes to 6 hours to determine the critical storm duration and
the mean peak flowrate from the storms.
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 for the location. A climate change factor of 1.2 has
been applied to the rainfall data to account for the expected changes in rainfall under 2100 climate conditions. Due
to the small nature of the development, a time of concentration of a minimum 5 minutes has been considered for
the site. Details of these parameters are provided in Appendix A.
The model used for DRAINS for the site is shown below in Figure 0.1 – DRAINS Model Layout. A single catchment is
used to represent the existing site and assumed future site conditions, with comparison of these results used to
establish the impact of the development on the existing flow rates.
Figure 0.1 – DRAINS Model Layout
The configuration of the catchment areas for pre-development and post development areas are shown in Figure 0.2
– DRAINS Pre-development catchments and Figure 0.3 – DRAINS Post-development catchments respectively.
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Figure 0.2 – DRAINS Pre-development catchments
Figure 0.3 – 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 0.1 Existing and proposed site peak discharge rates.
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Table 0.1 Existing and proposed site peak discharge rates (unmitigated)
A.E.P Qy Pre (m3/s) Qy Post (m3/s) Qchange (m3/s) Qchange (%)
63.2% AEP 0.013 0.013 0.000 0%
50% AEP 0.019 0.019 0.000 0%
20% AEP 0.023 0.023 0.000 0%
10% AEP 0.030 0.030 0.000 0%
5% AEP 0.034 0.034 0.000 0%
2% AEP 0.039 0.039 0.000 0%
1% AEP 0.042 0.043 0.001 2%
Based on the modelling, the minor increase to impervious area from the proposed development will only result in
an increase of 1L/s for the 1% storm AEP event, being a change of only 2% The pre-post comparison found that
under all other storm events up to the 1% AEP analysed not resulting in an increase of the peak flows. As such, the
proposed development is considered to not impact the downstream receiving environment in a manner that will
alter the catchment hydrology or result in nuisance run-off that may impact downstream properties.
As peak outflows from the development are typically as per existing conditions, no stormwater attenuation is
required to control outflows from the proposed 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 to minimise any adverse impacts to the downstream environment.
• The lawful point of discharge for the proposed development will be as per existing conditions, with run-off
from the site discharged by kerb adaptors into the Bottlebrush Avenue and/or direct connection to existing
stormwater infrastructure.
• The proposed development will result in an insignificant increase compared to existing conditions and will
retain the residential site usage of the existing lot. The stormwater quantity and quality discharging from the
site is unlikely to change and the net impact on existing infrastructure by the proposed development is
negligible. No operational stormwater quality controls are therefore proposed for the development.
• During construction, erosion and sediment control measures including sediment fencing, stabilising
construction access, grass filter strips and diversion of clean water around disturbed areas will be provided
as best practice management controls during the construction phase of the development.
• Assessment of the existing and proposed site peak flow hydrology has found that the insignificant increase
in impervious areas does not alter the peak flow from the development for all storms up to the 1% AEP. The
1% AEP peak outflow is increased by 1L/s however this is considered a negligible change and unlikely to
result in nuisance impacts to downstream properties. No on-site stormwater detention is therefore
considered necessary for the proposed development.
• Stormwater inlet pits will be provided for provide for drainage from the upstream catchment to ensure the
run-off can be conveyed through proposed development without impacting upon the future usage.
• The proposed development has been assessed as not altering the discharge characteristics for stormwater
quality or quantity from the site to any significant extent, and the proposed stormwater solution is considered
appropriate for the scale and nature of the development to minimise any adverse impacts to the downstream
environment arising from the stormwater run-off in accordance with Noosa Council requirements.
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REC*:R Appendix A DRAINS Modelling Results P 1300 469 707 E [email protected] Page 14 of 14
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Site Catchment Areas for DRAINS Modelling
Project number: 20220051 Calculations: M. Poynter
Street Address: 37 Bottlebrush Ave
Locality: Noosa Heads, NSC Date: 14/10/2024
Existing Site
Existing Site Directly connected (m²) Indirectly connected (m²)
37 Bottlebrush Ave Roof 199.8 199.8 -
Impervious Ground 64.7 - 64.7
Driveway 47.9 47.9 -
Total Imp 312.4
Total Per 179.1
Site Area 491.5 247.7 64.7
% impervious Effective DCIA = 75% DCIA ICIA +25% ineffective DCIA
185.78 126.59
Impervious 63.6% 37.8% 25.8%
Pervious 36.4%
Proposed Site 22.97
Proposed Directly connected (m²) Indirectly connected (m²)
37 Bottlebrush Ave Roof 222.8 222.8 -
Impervious Ground 96.1 63.3 32.8
Driveway 26.1 26.1 -
Total Imp 344.9
Total Per 146.5
Site Area 491.5 312.1 32.8
% impervious Effective DCIA = 75% DCIA ICIA +25% ineffective DCIA
234.1 110.8
Impervious 70.2% 47.6% 22.6%
Pervious 29.8%
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BOM IFDs Frequent and Infrequent Storm Events Project number: 20220051 R E ¢ > ‘2 R Street Address: 37 Bottlebrush Ave aw Locality: Noosa Heads, NSC Date: 14/10/2024 Source http://www bom.gov.au/ water/designRainfalls/revised-ifd/ Location: Latitude -26,397271 ow “AEP Arua! Exceedance Probably Nearest Latitude 26.3875 (5) 3000 - Longitude 153,0921809 vovo |. icone | Nearest Longitude 153.0875 (E) seoe [. ~ i —— 1% Date obtained: 5/04/2022 1000 F- —— x» |] 750 F ~ H Annual Exceedance |—— Probability (AEP) Duration 63.20% SO%H 20% 10% 5% 2% 1% in| 94] 262] 307] 349} 404] aa 146] 166] 229) 272 314) 372| 47) 137] 156] 214) 253} 292] 34a] 384] ii] 148| 202] 238| 274) 320} 355] 125} 141] 192] 226] 258| 300] 332] 102] 115} 155} 180] 205} 235] 258} 865 97.6 ii] 153} 173} 199} 217] 755 85.2 115] 134] 152| 175] 191] 674 76.1 103} 120) 136] 157] 173} @1| 68.9 332 109} 24) 14a} 158] 8.3 547 746 87.8 101] 117] 130] 40.6 46.1 633 749) 86.2 101] 13} 315 36| 50] 59.6 69] 813 316 263 301 22 50.6 58.9 702 7g 20.4 25 333 40.2 47.2 56.6 4 153) 18.4] 26.4 321 37.8 45.6 517 133 155 2A 273 323 39.1 44.4 af | 10.4 12.1 173 21.8 25.8 314 35.8 875 10.2] 15.1 185| 2| 26.8 30.7 osf 4 18 hour 6.82 7.99 119) 146 175] 24 245 24 hour 5.69 6.68 9.94 12.3 143 18.1 209 30 hour 4.93 5.78 8.63 10.7] 123] 159) 1833 02 poi i po 36 hour 437] 5.12 7.66 9.53 115 142 16.4 = 73450 35 = 1 73 es RP 4B 4ST [48 hour 3.58 42 63 7.86 95 118] 133 Times hours aye 7hour 2.67 313 47 5.88 7.15 8.98 105| 96 hour 2.15 251 37 473 5.76 7.21) 8.53 Duration 120 hour 18 2.11 3.16 3.96 4.83 61 7.16 144 hour 156] 1.82] 272 341 4.16 5.24 6.15 168 hour 138! Tell 24 3 365 459 5,37 ©Copyright Commonwealth of Australia 2016, Bureau af Meteorology (ABN 92 637 533 532)
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ARR Datahub Parameters Project number: 20220051 Street Address: 37 Bottlebrush Ave Locality: Noosa Heads, NSC Date: 14/10/2024
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Median Preburst Depths and Ratios Values are of the format depth (ratio) with depth in mm min (h)\AEP(%) 50 60 (1.0) 34 (0.073) 90 (1.5) 76 (0.140) 120 (2.0) 19.1 (0.316) 180 (3.0) 219 (0.311) 360 (6.0) 216 (0.233) 720 (12.0) 20.4 (0.166) 1080 (18.0) 13.3 (0.092) 1440 (24.0) 39 (0.024) 2160 (36.0) 24 (0.012) 2820 (48.0) 00 (0.000) 4320 (72.0) 00 (0.000) Interim Climate Change Factors 2030 2050 g 3 3 RCP 4.5 0.869 (4.3%) 1.057 (5.3%) 1.272 (6.4%) 1.488 (7.5%) 1.8676 (8.5%) 1.810 (9.2%) 1.862 (9.5%) 20 10 68 o4 (0.108) (0.122) 18 147 (0.158) (0.164) 21.5 234 (0255) (0.228) 25.4 278 (0.254) (0.230) 47.4 644 (0.353) (0.393) 41.2 54.9 (0.228) (0.247) 377 53.9 (0.177) (0.204) 224 34.2 (0.093) (0.116) 165 26.0 (0.060) (0.076) 02 152 (0.031) (0.041) 37 62 (0.011) (0.015) RCPS 0.783 (3.9%) 1.014 (5.1%) 1.236 (6.2%) 1.458 (7.4%) 1.691 (8.6%) 1.944 (9.9%) 2.227 (11.5%) 13 (0.131) 174 (0.168) 247 (0.209) 30.0 (0.212) 808 (0.417) 68.1 (0.258) 69.4 (0.220) 459 (0.129) 35.2 (0.085) 212 (0.046) 86 (0.017) 132 (0.130) 193 (0.157) 23.2 (0.165) 735 (0.433) 114.0 (0.486) 991 (0.308) 102.0 (0.265) 95.4 (0.219) 656 (0.128) 428 (0.086) 137 (0.021) RCP 8.5 0.983 (4.9%) 1.348 (6.8%) 1.773 (9.0%) 2.237 (11.5%) 2.722 (14.2%) 3.209 (16.9%) 3.679 (19.7%) 146 (0.129) 207 (0.151) 220 (0.140) 1062 (0.553) 138.8 (0.521) 1223 (0.332) 126.5 (0.286) 1326 (0.265) 883 (0.149) 605 (0.105) 176 (0.023)
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DRAINS Modelling Results
Project number: 20220051 Calculations: M. Poynter
Street Address: 37 Bottlebrush Ave
Locality: Noosa Heads, NSC Date: 14/10/2024
Pre / Post Comparison
A.E.P Qy Pre (m3/s) Qy Post (m3/s) Qchange (m3/s) Qchange (%)
63.2% AEP 0.013 0.013 0.000 0%
50% AEP 0.019 0.019 0.000 0%
20% AEP 0.023 0.023 0.000 0%
10% AEP 0.030 0.030 0.000 0%
5% AEP 0.034 0.034 0.000 0%
2% AEP 0.039 0.039 0.000 0%
1% AEP 0.042 0.043 0.001 2%
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