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17 Bottlebrush Avenue, · MCU26/0001
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Stormwater Management Plan Multiple Residential Dwelling 17 Bottlebrush Avenue, Noosa Heads Prepared for Made Capital PTY LTD Reference No. P0433-25-001 7 January 2026
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Page 2
Document Control
Document Stormwater Management Plan
Synergy12d://remote.recorconsulting.com/RECOR/Clients/0433 Made Capital/P0433-
File Location
25-001 17 Bottlebrush Avenue, Noosa Heads/03 Engineering/01 Civil/Reports/SWMP
Project Name 17 Bottlebrush Avenue, Noosa Heads QLD
Project Number P0433-25-001
Revision Number 1
Revision History
Revision No. Date Prepared By Reviewed By Approved for Issue By
1 07/01/2026 John McLaughlan Eoin Whitmore Eoin Whitmore
Issue Register
Distribution List Date Issued Number of Copies
RECOR Company Details
Approved by Eoin Whitmore
Address Level 11
269 Wickham Street
Fortitude Valley QLD 4006
Telephone 0451453640 Website www.recor.au
Email [email protected]
Signature RPEQ 34231
The information within this document is and shall remain the property of RECOR.
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Important Notice
This document is confidential and has been prepared exclusively to support the town planning application for the
proposed development. It is issued in accordance with the Consultancy Agreement between RECOR and Made
Capital, under which RECOR was engaged to perform a specific and limited scope of work for Made Capital.
The contents of this report are strictly confined to the matters outlined within and are subject to various
assumptions, qualifications, and limitations. No implicit applicability to other matters should be inferred. RECOR
makes no representation that the scope, assumptions, qualifications, or exclusions within this report will be
appropriate for any other purpose, nor does it assert that the report comprehensively addresses all matters of
potential relevance to the reader.
This report must be read in its entirety, as the executive summary does not serve as a replacement. Any
subsequent reports must be considered in conjunction with this document.
This report supersedes all prior drafts or interim versions, whether written or verbally presented, preceding its
issue date. It has not been and will not be updated to reflect events, transactions, or material changes occurring
after its issuance. RECOR assumes no obligation to notify the recipient of any such developments or to revise the
report accordingly.
Unless expressly agreed otherwise in writing, RECOR disclaims any duty of care or legal responsibility in relation
to this report, its associated inquiries, advice, or related work. Furthermore, RECOR does not extend any
representation regarding this report to any party other than Made Capital. Any third party who obtains a copy of
this report, whether in whole or in part, or engages in discussions regarding its content with RECOR, acknowledges
and accepts that they may not rely on this report or any associated information or advice for any purpose.
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List of Tables and Figures
Table of Contents
Executive Summary ............................................................................................................................. 3
1 Introduction ................................................................................................................................ 4
1.1 Background and Scope .............................................................................................................................. 4
1.2 Stormwater Management Objectives and Design Approach .................................................................. 4
1.3 Supporting Documentation and Reports ................................................................................................... 5
2 Existing Site ................................................................................................................................ 6
2.1 Site Overview .............................................................................................................................................. 6
2.2 Flow calculation using the Rational Method ............................................................................................. 6
2.3 DRAINS model and comparison to Rational Method ................................................................................ 8
3 Proposed Development Works ................................................................................................. 11
3.1 Proposed Site Description......................................................................................................................... 11
3.2 Time of Concentration Inputs into DRAINS .............................................................................................. 11
3.3 Hydrological Modelling Results ................................................................................................................ 12
3.4 Stormwater Detention and Mitigation Strategy ...................................................................................... 14
4 Stormwater Quality .................................................................................................................. 16
4.1 Erosion and Sediment Control ................................................................................................................. 16
5 Conclusion ................................................................................................................................ 17
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List of Tables and Figures
List of Tables
Table 1-1 Property Details ................................................................................................................................................ 4
Table 2-1: Rational Method key inputs ............................................................................................................................ 8
Table 2-2: Rational Method flow calculations ................................................................................................................. 8
Table 2-3: DRAINS results for existing catchment ......................................................................................................... 9
Table 2-4: Comparison between DRAINS and the Rational Method ........................................................................... 10
Table 3-1: Comparison of Pre-Development vs. Unmitigated Post-Development Peak Flows ................................ 13
Table 3-2: Detention tank parameters .......................................................................................................................... 14
Table 3-3: Mitigated Flow comparison to existing ....................................................................................................... 15
List of Figures
Figure 2-1: Subject Site Location (QLD Globe, 2025)..................................................................................................... 6
Figure 2-2 Max overland flow path .................................................................................................................................. 7
Figure 2-3: Overland sheet flow times (QUDM, 2025) ................................................................................................... 7
Figure 2-4: DRAINS model for existing catchment ......................................................................................................... 9
Figure 2-5: DRAINS catchment inputs ............................................................................................................................. 9
Figure 3-1 Proposed Stormwater Layout ....................................................................................................................... 11
Appendices
Appendix A – DRAINS Results
Appendix B – Rational Method Results
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Executive Summary
RECOR Consulting Engineers have been engaged by Made Capital to prepare a Stormwater Management Plan
(SWMP) to support a Development Approval Application for a proposed Material Change of Use (MCU), from a
single dwelling into a multiple dwelling residence at 17 Bottlebrush Avenue, Noosa Heads.
This SWMP outlines the stormwater management strategy for the proposed development and demonstrates
compliance with the Noosa Shire Council (NSC) Planning Scheme Policies, the Queensland Urban Drainage Manual
(QUDM), and Water by Design guidance material. The report establishes that the development can be constructed
and operated in accordance with acceptable stormwater quantity and quality performance objectives.
Lawful Point of Discharge
All stormwater runoff from the development will be directed to a single lawful point of discharge into Council’s
existing stormwater system in Bottlebrush Avenue. The onsite drainage system consolidates flows and integrates
with downstream infrastructure. The discharge arrangement has been verified through hydraulic modelling and is
consistent with Council’s lawful discharge requirements.
Stormwater Quantity
The hydrological assessment was undertaken using both the Rational Method and DRAINS modelling to establish
pre-development baseline conditions and to assess post-development impacts.
Results confirmed an increase in peak flow rates from underdeveloped conditions due to added impervious
surfaces. To mitigate these effects, the use of a detention tank is proposed within the southwestern portion of the
site.
Hydrological modelling confirms that post-development discharges remain equal to or below pre-development
flows across all assessed Annual Exceedance Probability (AEP) storm events, refer to section 3.3.
Stormwater Quality
The site does not exceed the thresholds of the SPP Part E – Water Quality and therefore does not require MUSIC
modelling or formal stormwater quality treatment. The proposed works are less than 2,500 m² and involves fewer
than six lots.
The proposed management approach aligns with the Urban Stormwater Quality Planning Guidelines (2010) and
ensures that stormwater discharges do not adversely impact downstream waterways.
Erosion and Sediment Control
During the construction phase, ESC measures must be implemented in accordance with the applicable
requirements.
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1 Introduction
1.1 Background and Scope
RECOR has been engaged by Made Capital to prepare a Stormwater Management Plan (SWMP) for the proposed
MCU from a single dwelling residence to a multiple residential dwelling, located at 17 Bottlebrush Avenue, Noosa
Heads.
This report has been prepared to support the Development Approval Application submission to Noosa Shire
Council and any nominated referral agencies. The proposed development’s property details have been summarised
in Table 1-1.
The SWMP addresses potential stormwater impacts resulting from the proposed development and outlines the
necessary mitigation measures to meet both quantity and quality requirements of Noosa Shire Council.
This report presents the hydrological assessment of the proposed development, including any external catchments
that may directly influence peak flows exiting the site. The purpose of the assessment is to ensure that post-
development stormwater discharge does not adversely impact existing flooding or stormwater conveyance
conditions on surrounding properties and that the stormwater management objectives of the QUDM and Noosa
Shire Council requirements are achieved.
Additionally, the assessment evaluates the development requirements for stormwater treatment to ensure
compliance with Water by Design guidelines, the SPP, and council water quality requirements.
Table 1-1 Property Details
Site Details Parameters
Site Location 17 Bottlebrush Avenue, Noosa Heads QLD
Lot Number 143 RP88934
Intended Land Use Material Change of Use for a Multiple Residential Dwelling
Development Area 505 m2
1.2 Stormwater Management Objectives and Design Approach
The intent of this report is to document the design considerations and outcomes that satisfy the stormwater
management objectives for the proposed development. The strategy has been developed to address the following
key aspects and performance objectives:
• Catchment Definition: Identification of all catchments and sub-catchments discharging through or into the
site.
• Hydrological Assessment: Determination of existing flow conditions for multiple storm events and
assessment of development impacts on surrounding properties.
• Flow Management: Ensuring post-development peak flows do not exceed pre-development flows across
all relevant storm events, up to and including the 1% AEP.
• Lawful Point of Discharge: Identification and utilisation of a lawful point of discharge in accordance with
QUDM, ensuring no actionable nuisance to downstream properties or infrastructure.
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• Site Drainage and Conveyance: Development of a preliminary site drainage layout that ensures safe
conveyance of stormwater through the site without adverse impacts on adjacent areas.
• Erosion and Sediment Control: Adoption of construction-phase measures consistent with the International
Erosion Control Association (ICEA) – Best Practice Erosion and Sediment Control (2008) guidelines.
Stormwater management for the proposed development has been designed in accordance with the following
documents:
• Noosa Shire Council Planning Scheme Policy – Stormwater Management
• State Planning Policy (SPP), 2017
• Environmental Protection (Water) Policy, 2009
• Environmental Protection Act 1994
• Queensland Urban Drainage Manual (QUDM) Fourth Edition, 2016
• Australian Rainfall and Runoff Guideline (ARR)
1.3 Supporting Documentation and Reports
The SWMP is supported by technical documentation and reports which provide the basis for the engineering
recommendations and support the DA and OPW application, including:
• Civil Design Drawings prepared by RECOR, File No: P0433-25-001_17_Bottlebrush_Avenue_REVA
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2 Existing Site
2.1 Site Overview
The site, located at 17 Bottlebrush Avenue, Noosa Heads, is bounded by residential properties to the northwest,
southeast and northeast, and is bound by Bottlebrush Avenue in the southwest and has a single site access
driveway along this boundary. Properties to the northeast are zoned low residential, properties to the northwest
and southeast are zoned as high density residential, and the properties to the southwest are zoned as a major
centre, as per the Noosa plan 2020 – Amendment 2.
Topography generally falls to the southwest with observed ground levels ranging from approximately RL 37 m AHD
in the northeast to approximately RL 31 m AHD in the southwest.
Drainage across the site occurs in one primary direction to the southwest into Bottlebrush Avenue, which is picked
up by the local stormwater infrastructure via kerb and channel before entering the drainage network.
Stormwater infrastructure is located in the site conveying flows from the northeastern lots into the stormwater
network located in Bottlebrush Avenue.
Figure 2-1: Subject Site Location (QLD Globe, 2025)
2.2 Flow calculation using the Rational Method
The Rational Method was initially applied as a verification tool to cross-check outputs from the DRAINS
hydrological model, which was subsequently developed to assess both pre- and post-development flows.
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The time of concentration (Tc) of 7 minutes was determined using figure 4.4 – Overland sheet flow times (refer to
Figure 2-3) in accordance with Table 4.6.6 of QUDM. This approach provides a reliable estimate of the travel time
for runoff from the hydraulically most distant point in the catchment to the outlet.
A maximum flow path length of 34.0 m was adopted, based on survey data collected by Eagle Survey Pty Ltd in
2025 (refer to Figure 2-2).
To refine the analysis, the following factors were incorporated to ensure accuracy and representativeness of the
stormwater design:
• Surface roughness and vegetation cover, which influence flow resistance and travel time
• Topographic gradients, confirming alignment between flow velocities and assumed conditions
• Site hydraulic connectivity, including potential depressions or ponding areas, verifying the
appropriateness of the adopted Tc.
Figure 2-2 Max overland flow path
Figure 2-3: Overland sheet flow times (QUDM, 2025)
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The fraction impervious for the existing site was determined to be 38%, based on a manual measurement of the
exact impervious area to accurately represent existing site conditions in accordance with QUDM methodology.
This measured impervious area was input directly into the model to ensure realistic simulation of runoff generation.
Using QUDM Table 4.5.2, the C₁₀ was determined based on the 1-hour, 10 % AEP rainfall intensity of 74.9 mm/hr.
Applying this methodology, a C₁₀ value of 0.75 was derived, as summarised in Table 2-1.
Table 2-1: Rational Method key inputs
Catchment Area (ha) Tc (min) Actual Tc (min) fy C10
Pre-Development 0.051 7 7 0.38 0.75
To quantify the peak flow rates for various Annual Exceedance Probability (AEP), the Rational Method formula
was applied:
where:
• Q = Peak discharge (m³/s)
• C = Runoff coefficient
• I = Rainfall intensity (mm/hr)
• A = Catchment area (hectares)
The following Table 2-2 presents the calculated pre-development flow rates for each of the assessed storm
events:
Table 2-2: Rational Method flow calculations
AEP % 63.2% 50% 20% 10% 5% 2% 1%
Pre-Development Flow (m³/s) 0.010 0.012 0.018 0.022 0.026 0.033 0.037
These calculations establish the hydrological baseline for the site and form the foundation for further stormwater
management analysis. The results will be used to assess post-development runoff characteristics and determine
the necessary mitigation measures to ensure compliance with the QUDM and Noosa Shire Council stormwater
management requirements.
2.3 DRAINS model and comparison to Rational Method
The DRAINS model was configured using the appropriate Australian Rainfall and Runoff (ARR) parameters specific
to the site conditions. Inputs for each catchment were derived from the parameters discussed in previous sections,
ensuring consistency with site-specific hydrology and QUDM low residential density development criteria. The
general configuration of the DRAINS model is shown in Table 2-4.
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Figure 2-4: DRAINS model for existing catchment
This assumption is considered appropriate as the existing site is currently developed with a single dwelling and
associated impervious area consistent with low density residential conditions. The relevant DRAINS catchment
inputs are detailed in Figure 2-5.
Figure 2-5: DRAINS catchment inputs
The pre-development flow rates for various AEP were calculated using DRAINS. The results are summarized in
Table 2-3.
Table 2-3: DRAINS results for existing catchment
AEP % 63.2% 50% 20% 10% 5% 2% 1%
Pre-Development Flow (m³/s) 0.011 0.013 0.020 0.024 0.028 0.034 0.038
A comparative assessment was conducted to evaluate the variance between DRAINS results and the Rational
Method calculations. The differences between the two methodologies are presented in Table 2-4.
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Table 2-4: Comparison between DRAINS and the Rational Method
AEP % Rational Method (m³/s) DRAINS (m³/s) Difference %
63.2% 0.010 0.011 -6%
50% 0.012 0.013 -6%
20% 0.018 0.020 -6%
10% 0.022 0.024 -5%
5% 0.026 0.028 -4%
2% 0.033 0.034 -2%
1% 0.037 0.038 -1%
The results obtained from the Rational Method and the DRAINS model show differences that are within acceptable
engineering tolerances and align with expectations given the inherent methodological differences between the
two approaches.
• The Rational Method is a simplified empirical approach that assumes uniform rainfall intensity across the
entire catchment for the duration of the storm event. It does not account for hydraulic routing, storage
effects, or time-variant rainfall intensities, which can lead to either under- or over-estimations of peak
flows depending on local site characteristics.
• DRAINS, in contrast, is a hydrologic and hydraulic modelling tool that provides a more detailed, event-
based assessment incorporating:
o Rainfall losses (initial and continuing losses)
o Time-dependent storm profiles.
o Pipe and channel storage effects and
o Flow routing dynamics.
• The Rational Method remains a valid tool for preliminary estimation and cross-checking of peak flows;
however, the DRAINS model, utilising the ILSAX method, provides a more detailed and accurate
assessment of catchment behaviour. Therefore, DRAINS model results have been adopted for final design.
• Minor discrepancies, particularly for higher AEP events (20-year and above), indicate that the Rational
Method provides a reasonable approximation for design verification.
• The largest discrepancies are typically observed in low-frequency events (1 to 5 year), where DRAINS
captures additional hydrological complexities such as temporal rainfall variation and surface storage,
which are not represented in the Rational Method.
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3 Proposed Development Works
3.1 Proposed Site Description
The proposed development will comprise a multi residential dwelling, accessed via a single driveway and
supported by a dedicated on-site stormwater management system.
A key feature of the stormwater management strategy is the inclusion of a detention tank located in the
southwestern portion of the site. This detention tank has been designed to capture and attenuate stormwater
runoff from the developed catchment prior to discharging via the lawful point of discharge into the Council’s
stormwater network to the southwest of the site located within Bottlebrush Avenue ensuring seamless integration
with the downstream network.
In addition to mitigating potential downstream impacts, the proposed system has been designed to achieve
compliance with the Noosa Shire Council Planning Scheme Policy – Stormwater Management, by:
• Consolidating site runoff into a single lawful discharge point
• Attenuating post-development peak flow rates to pre-development levels or better
This integrated approach delivers a sustainable stormwater solution that not only mitigates the hydrological
impacts of the proposed development but also assists in alleviating existing overland flow from the site into the
properties located to the southwest. The stormwater layout of the proposed development is illustrated in Figure
3-1.
Figure 3-1 Proposed Stormwater Layout
3.2 Time of Concentration Inputs into DRAINS
The time of concentration (Tc) for each catchment has been determined using a combination of:
1. Roof inlet time (time for runoff to travel from impervious surfaces to the drainage system)
2. Pipe flow time (travel time through the underground drainage system)
Each component is broken down below for the catchment, as shown in the provided screenshot.
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Catchment
• Total area: 505 m² (0.051 ha)
• Tc components:
1. Roof inlet time Q 5 minutes
Assigned based on standard inlet times from QUDM Table 4.6.2 for urban residential
areas.
2. Time in pipe flow → 2 minutes
Pipe length: 10 m
Slope: 0.5%
Manning's n: 0.012
Using Manning’s equation, the travel time is calculated based on hydraulic parameters.
3. Total Time of Concentration (Tc): 7 minutes
Calculation Methodology
• Roof inlet travel times were estimated using QUDM guidelines and empirical flow path analysis.
• Pipe flow times were determined using Manning’s equation for open channel and pipe flow, referencing
the chart provided in the screenshot for additional validation.
• Catchment delineation and flow paths were confirmed using the development layout and area tool
measurements.
Final Considerations
• One catchment has been adopted for the entire development, the development site flows will be conveyed
to the proposed detention tank.
• These times of concentration will be used in hydrological modelling to determine peak flow rates and
ensure adequate stormwater infrastructure design.
3.3 Hydrological Modelling Results
Analysis of Unmitigated DRAINS Model Results and Required Mitigation Measures
A review of the unmitigated DRAINS model results indicates a significant increase in peak flows across various
AEP storm events due to the transition from an existing low-density residential condition to a more intensive urban
condition.
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Key Observations
1. Increase in Flow Depths and Velocities
• The developed scenario shows higher water levels across all storm events, particularly at
constricted sections of the drainage network.
• Flow velocities have increased, indicating a higher runoff volume due to reduced permeability.
2. Peak Discharge Variations
• Peak discharge rates in the developed scenario have increased substantially, particularly for
higher return period storms (e.g., 1% AEP).
• The most significant changes occur at sections with concentrated overland flow paths,
suggesting increased runoff from new impervious surfaces.
3. Impact of Increased Impervious Area
• The development introduces more impervious surfaces (e.g., roads, driveways, rooftops),
reducing infiltration and increasing direct runoff.
• The loss of natural detention and permeability results in quicker times of concentration and higher
peak flows.
Table 3-1: Comparison of Pre-Development vs. Unmitigated Post-Development Peak Flows
Storm Event (AEP) Pre-Development Peak Flow Post-Development Peak Increase %
(m³/s) Flow (m³/s)
63.2% 0.011 0.013 8%
50% 0.013 0.015 7%
20% 0.020 0.022 5%
10% 0.024 0.027 6%
5% 0.028 0.031 5%
2% 0.034 0.037 4%
1% 0.038 0.042 5%
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Required Mitigation – Installation of a Detention tank
Due to the projected increase in post-development peak flows, mitigation measures are required to ensure
compliance with Noosa Shire Council stormwater management requirements and to prevent potential downstream
impacts. The most suitable solution is the use of the existing detention tank; modelling will ensure the designed
tank will achieve the following outcomes:
• Attenuate peak discharge by temporarily storing excess runoff and releasing it at controlled, pre-
development rates
• Control flow velocities, thereby reducing the risk of downstream erosion and infrastructure overloading
and
The detention tank will be designed to ensure that post-development peak flows do not exceed pre-development
flow conditions for all relevant design storm events. Further hydrological modelling will be undertaken to
appropriately size the tank and confirm its effectiveness in mitigating increased flow volumes and velocities.
3.4 Stormwater Detention and Mitigation Strategy
A detention tank is proposed to be utilised for stormwater attenuation and will be sized to detain all site-generated
flows. The proposed tank is to be located on the southwestern portion of the development, as shown on the Civil
Set of Plans (Drawing P0433-25-001_17_Bottlebrush_Avenue_REVA), for Council’s consideration.
The tank has been designed to detain and control stormwater flows for all assessed events, including the 1% AEP,
such that post-development peak discharges do not exceed pre-development levels. Attenuation is provided
across all assessed AEP storm events in accordance with the Queensland Urban Drainage Manual (QUDM). Refer
to Table 3-2 for tank design parameters.
As outlined in the preceding sections, the site naturally drains toward the southwest. Earthworks and site drainage
are proposed to direct all stormwater runoff to the proposed detention tank to ensure appropriate drainage
outcomes for the site. This enables controlled discharge to Council’s existing stormwater network within
Bottlebrush Avenue.
Stormwater modelling assumes the entire site will be conveyed into the detention tank. This provides a consistent
comparison between pre- and post-development conditions and demonstrates improved local drainage outcomes
Table 3-2: Detention tank parameters
Parameter Value
Storage Volume 8.0 m³
1% AEP Storage Volume 7.6 m³
1% AEP Water Depth 0.95 m
Lower Discharge Control 75 mm orifice at 28.50 m AHD
Secondary Discharge Control 90 mm orifice at 28.65 m AHD
Outlet Pipe Size 375 mm pipe RFC Class 3
Outlet Pipe Invert Level 28.50 m AHD
The tank outlet will discharge via a new stormwater pipe connection into Council’s existing stormwater network
located within Bottlebrush Avenue.
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Stormwater Mitigation Results
A detailed analysis of the mitigated peak flows, as summarised in Table 3-3, confirms that the use of the proposed
detention tank successfully reduces post-development discharges across all assessed storm events, ensuring
compliance with QUDM requirements and mitigating potential downstream impacts.
Table 3-3: Mitigated Flow comparison to existing
Storm Event Pre-Development Peak Flow Post-Mitigation Peak Flow Reduction %
(m³/s) (m³/s)
63% (1-Year AEP) 0.011 0.011 0%
50% (2-Year AEP) 0.013 0.013 0%
20% (5-Year AEP) 0.020 0.017 -8%
10% (10-Year AEP) 0.024 0.019 -12%
5% (20-Year AEP) 0.028 0.022 -12%
2% (50-Year AEP) 0.034 0.024 -17%
1% (100-Year AEP) 0.038 0.026 -19%
Key Observations
The results of the hydrological modelling demonstrate that the proposed detention tank provides effective
attenuation of post-development peak flows, particularly for the more frequent rainfall events.
As summarised in Table 3-3, the following peak flow reductions were achieved:
• 1 – Year AEP approximately 0% reduction
• 2 - Year AEP – approximately 0% reduction
• 5 - Year AEP – approximately 8% reduction
• 10 - Year AEP – approximately 12% reduction
• 20 - Year AEP – approximately 12% reduction
• 50 - Year AEP – approximately 17% reduction.
• 100 - Year AEP – approximately 19% reduction.
These results indicate that the tank has been optimised to effectively manage frequent, smaller storm events,
which are most critical for protecting downstream properties and infrastructure, while allowing major flood events
to pass through the system without increased risk.
This outcome reflects the intent of the stormwater management strategy:
• To provide a reduction in nuisance flooding and frequent storm impacts
• To ensure safe conveyance of major flows consistent with pre-development drainage conditions and
• To maintain compliance with both QUDM and Noosa Shire Council stormwater management objectives.
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4 Stormwater Quality
Under State Planning Policy Part E – Water Quality (July 2017), developments are required to achieve prescribed
stormwater quality objectives where they exceed the defined thresholds for reconfiguring a lot or operational
works. The proposed MCU comprises a multiple dwelling development with works less than 2,500 m² and fewer
than six lots; therefore, formal post-construction stormwater quality treatment to meet SPP Part E pollutant
reduction targets are not required.
Although the development is not required to demonstrate compliance with the SPP post-construction water quality
objectives, the SPP emphasises the importance of protecting environmental values, applying water sensitive urban
design principles, and managing stormwater in a manner consistent with total water-cycle management. In keeping
with these principles, the development will adopt best-practice stormwater management measures to improve
water quality outcomes during the operational phase.
These measures include:
• Implementing a stormwater drainage layout that provides effective conveyance and attenuation of runoff,
ensuring flows are safely and appropriately managed before discharge from the site.
• Provision of rainwater tanks to provide additional storage and enable reuse within the development.
The proposed stormwater strategy ensures that runoff is managed in accordance with best practice, supports the
environmental values of downstream receiving waters, and aligns with both the intent of the SPP and Council’s
stormwater management requirements.
4.1 Erosion and Sediment Control
An Erosion and Sediment Control Plan (ESCP) will be submitted as part of this application. The ESCP will outline
the specific measures to be implemented during the construction phase to minimise erosion and prevent sediment-
laden runoff from leaving the site or impacting downstream water quality.
The ESCP will be prepared in accordance with the IECA – Best Practice Erosion and Sediment Control Manual
(2008) and the requirements of the Environmental Protection Act 1994.
Typical ESC measures to be adopted during construction may include:
• Installation of sediment fences along downstream boundaries and around stockpile areas.
• Stabilised construction entry/exit points incorporating shakedown grids.
• Temporary diversion drains and bunds to direct runoff away from exposed areas.
• Sediment barriers at stormwater inlet pits.
• Dust suppression measures, including watering and covering of stockpiles.
• Progressive stabilisation and rehabilitation of batters and disturbed areas.
The principal contractor will be responsible for implementing and maintaining ESC measures in accordance with
the approved ESCP, including routine inspections and necessary maintenance throughout the construction period.
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5 Conclusion
The Stormwater Management Plan for the proposed multi residential dwelling at 17 Bottlebrush Avenue, Noosa
Heads has been prepared to demonstrate compliance with the stormwater management requirements of Noosa
Shire Council, QUDM and relevant State Planning Policy provisions. The assessment incorporates detailed
hydrological modelling, comparison against existing conditions, and the development of an effective stormwater
management strategy that mitigates potential impacts arising from the proposed works.
Hydrological and Hydraulic Considerations
Assessment of the existing site confirmed that stormwater runoff naturally flows towards the southwest following
the existing topography, discharging into downstream Bottlebrush Avenue. Pre-development peak flows were
calculated using both the Rational Method and DRAINS modelling, providing a reliable baseline for comparison with
post-development scenarios.
The comparative assessment demonstrated that while the Rational Method provides reasonable estimates, the
DRAINS model more accurately captures hydrologic and hydraulic behaviour, including rainfall losses, temporal
storm patterns, storage and flow routing. This model was therefore used for the final design.
Stormwater Quantity Management
Post-development conditions introduce increased impervious areas, resulting in higher runoff volumes and
elevated peak flow rates. To ensure no worsening of drainage conditions downstream, a detention tank has been
incorporated into the proposed stormwater management strategy.
Modelling of the proposed detention tank demonstrates that post-development peak flows are attenuated to at or
below pre-development levels for all assessed storm events, up to and including the 1% AEP event. This satisfies
the intent of QUDM and Council stormwater objectives for lawful, non-worsening discharge.
The detention tank has been designed to provide adequate flood storage and controlled discharge via an orifice
and overflow system. Key design parameters include:
• Storage volume: 8.0 m³
• 1% AEP event Storage volume: 7.6 m³
• Maximum water depth: 0.95 m
• Lower outlet: 75 mm orifice
• Secondary outlet: 90 mm orifice
• Outlet pipe: 375 mm diameter discharging to Council’s lawful point of discharge in the stormwater network
located in Bottlebrush Avenue
These design elements ensure safe and effective management of stormwater flows generated by the
development.
Stormwater Quality Management
Although the development does not trigger the State Planning Policy (SPP) thresholds requiring formal post-
construction stormwater quality treatment, best-practice measures have been incorporated to support good water
quality outcomes.
These include:
• Providing an effective stormwater drainage layout that conveys and attenuates runoff before discharge
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• Ensuring construction-phase erosion and sediment control in accordance with IECA Best Practice
guidelines
These measures align with the intent of the SPP to protect environmental values and apply water-sensitive urban
design principles where practicable.
Regulatory Compliance and Sustainable Outcomes
The proposed stormwater management measures comply with the requirements of Noosa Shire Council, QUDM
and State Planning Policy guidance, ensuring:
• No adverse impact on surrounding properties or downstream drainage systems
• Effective attenuation of peak flows through the proposed detention tank
• Improved stormwater quality outcomes through best-practice measures
• A hydraulically neutral post-development condition
Overall, the stormwater management strategy demonstrates that the development can proceed without adverse
stormwater impacts and with appropriate safeguards for downstream water quality and flood behaviour. The
SWMP supports the development application by confirming that stormwater has been appropriately assessed and
managed in accordance with recognised engineering and environmental standards.
Final Recommendations
To support the effective implementation and long-term operation of the proposed stormwater management
system, the following recommendations are made:
• Final detailed engineering design should verify the detention tank, outlet structure and internal pipe
network to ensure compliance with QUDM and Council requirements for all relevant design storm events.
• Routine inspection and maintenance of the detention tank, including removal of sediment build-up, and
inspection of the outlet structure, should be undertaken to maintain system performance over time.
• Post-construction review of the stormwater infrastructure should be completed to confirm that as-
constructed conditions match the approved design and that the system is performing in accordance with
Council standards.
By implementing these recommendations, the development will maintain effective stormwater performance, and
ensure protection of downstream properties, infrastructure and receiving waterways.
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Appendix A – DRAINS Results
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Pre-development Post-development No Mitigation Post-development Mitigated Pre-development Post-development No Mitigation Post-development Mitigated Pre-development Post-development No Mitigation Post-development Mitigated
Page 24
Pre-development Post-development No Mitigation Post-development Mitigated Pre-development Post-development No Mitigation Post-development Mitigated Pre-development Post-development No Mitigation Post-development Mitigated
Page 25
Pre-development
Post-development
No Mitigation
Post-development
Mitigated
Pre-development
Post-development
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Appendix B – Rational Method Results
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REC:-R Ration Method Results Catchment Area (m2) Actual Tc 505.71 7 505.71 7 AEP % 63.20% 50% 20% 10% 5% 2% 1% Pre Development 0.010 0.012 0.018 0.022 0.026 0.033 0.037] Post Dev1 0.013 0.015 0.020 0.024) 0.027 0.031 0.035 Annual Exceedance Probability (AEP) Duration 63.20% 50%# 20%* 10% 5% 2% 1% 1 min 172 194 262 307 349 404 444 2 min 146 166 229 272 314 372 417 3 min 137 156 214 253 292 344 384 4 min 131 148 202 238 274 320 355 5 min 125 141 192 226 258 300 332 7 min 114 129 175 205 233 269 295 9 min 106 119 161 188 213 245 269 10 min 102 115 155 180 205 235 258 15 min 86.5 97.6 131 153 173 199 217 20 min PAD EE 85.2 115 134 152 175 191 25 min 67.4 76.1 103 120 136 157 173 30 min 61 68.9 93.2 109 124 144 158 45 min 48.3 54.7 74.6 87.8 101 117 130 1 hour 40.6 46.1 63.3 74.9 86.2 101 113 1.5 hour 31.5 36 50 59.6 69 81.8 91.6 2 hour 26.3 30.1 42.2 50.6 58.9 70.2 79 3 hour 20.4 23.5 33.3 40.2 47.2 56.6 64 4.5 hour rns) 18.4 26.4 32.1 37.8 45.6 51.7 6 hour 13.3 15.5 22.4 27.3 32.3 39.1 44.4 9 hour 10.4 12.1 17.8 21.8 25.8 31.4 35.8 12 hour 8.75 10.2 15.1 18.5 22 26.8 30.7 18 hour 6.82 7.99 11.9 14.6 17.5 21.4 24.5 24 hour 5.69 6.68 9.94 12.3 14.8 18.1 20.9 30 hour 4.93 5.78 8.63 10.7 12.9 rns) 18.3 36 hour 4.37 5.12 7.66 9.53 11.5 14.2 16.4 48 hour 3.58 4.2 6.3 7.86 9.5 11.8 13.8 72 hour 2.67 3.13 4.7 5.88 7.15 8.98 10.5 96 hour Les 2.51 3.77 4.73 5.76 7.27 8.53 120 hour 1.8 2.11 3.16 3.96 4.83 6.1 7.16 144 hour 1.56 1.82 2.72 3.41 4.16 5.24 6.15 168 hour 1.38 1.61 2.4 3 3.65 4.59 5.37
Page 28
www.RECOR.au
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Client Reference: P0433-25-001
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