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Reference Document - Stormwater Management Plan - RAL26/0001 (As Published)
STORMWATER MANAGEMENT REPORT 58 on RP32777 25 Tulip Street, Cooroy July 2026 NOOSA COUNCIL REFERENCE DOCUMENT RAL26/0001
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Contents 1. INTRODUCTION .............................................................................................................. 4 2. SITE DETAILS ................................................................................................................... 4 2.1. Existing Site Description and Drainage Regime ................................................................. 4 2.2. Proposed Development Drainage Regime .......................................................................... 6 2.3. LPOD Assessment ........................................................................................................... 6 3. STORMWATER CHARACTERISTCS ............................................................................... 7 3.1. Comparison of Pre/Post Development and Quantity.......................................................... 7 3.2. Quality ............................................................................................................................ 9 3.2.1. Construction Phase....................................................................................................... 9 3.2.2. Operational Phase ........................................................................................................ 9 4. Conclusion and Recommendations ..................................................................................... 10 Appendix A –Proposed Development Concept Plans ................................................................... 11
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Document Control
Report Title Stormwater Management Report
Client Ashley Trompf
Client Contact Ashley Trompf Client Reference 25 Tulip St, Cooroy
Verifier
Rev Date Revision details/status Author Reviewer Approver
(if required)
0 5 Nov 2025 Initial Version J.Bauleka J.Bauleka J.Bauleka
1 10 Nov 2025 Issued for Use J.Bauleka J.Bauleka
2 29 May 2026 Information Request response J.Bauleka J.Bauleka
3 21 July 2026 Further information response 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
Auxilium Consulting Pty Ltd
ABN 84 639 195 092
9 Ginger Bell Ave
Bli Bli, Qld 4560
Australia
M +61 423 415 419
E [email protected]
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1. INTRODUCTION Auxilium Consulting Pty Ltd (Auxilium) has been engaged to prepare a Stormwater Management Report to accompany a development application for a residential subdivision located at 25 Tulip Street, Cooroy. 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 (Council) requirements for stormwater drainage. Council issued an Information Request (IR) on 7 April 2026 focussing on clarification of stormwater aspects. A further information request and clarification about the stormwater management was issued on the 7 July 2026, which this report has been updated to address. 2. SITE DETAILS 2.1. Existing Site Description and Drainage Regime The existing Site is located at 25 Tulip Street, described as Lot 58 on Plan RP32777, and contains an existing dwelling and shed with an area of 1,529 m2. The Site is a residential setting with a large proportion of permeable areas. FIGURE 1 SITE LOCALITY PLAN (NOOSA COUNCIL INTRAMAPS, 2025) The Site slopes away from the road frontage towards the rear of the property. An unmapped channel conveys flows to the east and eventually into the Lake Macdonald catchment system. This existing, open channel discharges in a concentrated state from the Site.
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Roof run-off from the existing dwelling is discharged to the rear of the Site as overland flows to the existing channel. Road surface flows are excluded from the Site’s catchment with the kerb and channel and crossover. FIGURE 2 SITE FRONTAGE (GOOGLE STREETVIEW, AUG 2023) FIGURE 3 EXISTING ROOF DRAINAGE TO OVERLAND FLOWS TO REAR OF THE SITE (NOV 2025)
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2.2. Proposed Development Drainage Regime
The proposed subdivision results in the creation of one additional rear lot with an increase of
impermeable surfaces through roof areas and driveway. It is expected that stormwater quantities will
increase because of these impermeable areas with attenuation via above ground tanks proposed.
To address Council’s further information request, the stormwater attenuation was amended to
incorporate a single underground detention tank to attenuate flows from the access easement and
future lot.
Existing surface flows from upstream adjacent properties will remain unchanged. The existing
drainage regime of discharging to the Lawful Point of Discharge (LPOD) at the northeastern
boundary (unmapped channel) is maintained in the developed state. Further discussion about the
LPOD is detailed in 2.3.
The roof and allotment drainage system for the proposed site shall be designed to comply with:
1. Noosa Council Planning Scheme SC6.7.6 Stormwater Management and 9.4.8 Water Quality
and Drainage Code
2. The Queensland Urban Drainage Manual (QUDM); and
3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.
2.3. LPOD Assessment
As per QUDM’s criteria for determining the LPOD test, an assessment of the proposed drainage has
been detailed below:
Criteria Development Outcome
Will the proposed development alter the site’s The proposed development must ensure that
stormwater discharge characteristics in a manner that stormwater discharge is maintained as sheet flow to
may substantially damage a third-party property? the discharge point and avoid concentrating flows,
increasing quantities and/or velocities.
Therefore, utilise stormwater attenuation systems
and level spreader devices to ensure the
characteristics do not damage a third-party’s
property.
Is the location of the discharge from the development The location of the discharge is its existing location
site under the lawful control of the local government because of the natural, steep terrain. It is part of the
or other statutory authority from whom permission surrounding terrain and natural flow of the land and
to discharge has been received? eventually flows into a natural watercourse feeding
into the Lake Macdonald system.
This will include a park, watercourse, drainage or
road reserve, stormwater registered drainage Therefore, as the immediate downstream discharge
easement, or land held by local government point from the Site is not under the lawful control of
(including freehold land). the local statutory authority, further consideration of
the next criteria is required.
An authority to discharge over affected properties In the context of obtaining authority to discharge
will be necessary. In descending order of certainty, over the affected property, this would be a matter if
an authority may be in the form of: there was a material change that resulted in damage
to a third-party’s property and/or actionable
Dedication of a drainage reserve or park nuisance occurring.
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A registered easement for stormwater As this is the existing point of discharge and
discharge/works conveyance of flows through the Site, maintaining
Written discharge approval quantities and velocities to a pre-development state
would result in no actionable nuisance occurring.
Therefore, a further assessment is undertaken below.
Common Law: Principles of nuisance If the existing discharge point is maintained, and
discharge quantities and velocities are maintained as
Alterations to the natural flow regime will be lawful per the pre-developed state, then no third-party
if all necessary statutory approvals have been damage is occurring, and this gives no rise to
obtained and complied with, and: actionable nuisance claims.
There is no nuisance or interference to the Therefore, if the development can maintain these
use or enjoyment of affected land; or pre-development attributes when discharging from
The affected land owner has consented to the the Site in the post-developed state, the alterations
change in drainage will be lawful.
TABLE 1 LPOD ASSESSMENT AGAINST PROPOSED DEVELOPMENT
3. STORMWATER CHARACTERISTCS
3.1. Comparison of Pre/Post Development and Quantity
The development proposes to increase the impervious area of the site by using the following
parameters:
Increased impervious area of the access easement to Lot 2
100% impervious area of Lot 2’s building envelope area
50% impervious area of Lot 1’s area in accordance with Table 4.5.1 of QUDM (for Urban
residential – low density).
To summarise the development characteristics throughout the modelling and Council’s IR process, a
table has presented the various changes below.
Report revision Post-Development impervious catchment (%)
1 31
2 45
3 57
TABLE 2 DEVELOPMENT CHARACTERISTICS WITH REPORT REVISION
The developed catchment increases from the 31% to 57% and the modelling has been updated to
account for this change in Table 3.
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Pre-Development Post-Development
Catchment Pre-01 Post-01
Area (Ha) 0.153 0.153
Fraction Imp (%) 20 57
Time of Concentration (mins) 10.13 10.13
TABLE 3 MODELLING PARAMETERS
Pre and post discharge rates have been calculated using DRAINS software to evaluate the effect of
the development. Attenuation of post-development flows have achieved by modelling a single 9kL
underground detention tank servicing all catchments.
Underground tank 9kL
Orifice (@0mm of Storage Depth) Or_100 mm
Orifice overflow (@0.75 of Storage Or_225 mm
Depth)
Max depth 0.84 m
TABLE 4 DETENTION TANK CONFIGURATION
FIGURE 4 POST-DEVELOPMENT DRAINS MODEL LAYOUT
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Utilising the modelling methods of ARR2019, parameters from the ARR Data Hub for the site
location, and rainfall Intensity Frequency Distribution data from the Australian Bureau of
Meteorology have been implemented into the DRAINS model to determine the mean peak discharge
rates from the storm events. This is presented in Table 5 below.
QPROPOSED M³/S (WITH
% AEP EVENT Q EXISTING M³/S QPROPOSED M³/S (NO ATTENUATION) QCHANGE M³/S
ATTENUATION)
63.2 0.020 0.023 0.018 -0.002
39.3 0.030 0.032 0.023 -0.007
18.1 0.043 0.046 0.042 -0.001
10 0.051 0.056 0.047 -0.004
5 0.063 0.066 0.060 -0.003
2 0.072 0.074 0.071 -0.001
1 0.082 0.085 0.082 0.000
TABLE 5 PRE AND POST COMPARISON OF PEAK DISCHARGE RATES
The effect of the underground tank is effective attenuation of discharge rates to maintain existing rates
or even a reduction of the pre-development rates. Controlled flows from the outlet of this tank will be
discharged to the LPOD via a level spreader device to maintain the pre-development drainage
regime.
Refer to Appendix A Proposed Development Concept Plan for the proposed stormwater drainage layout
plan illustrating the concept described above. Note the specific details of the level spreader pipe inlet
will be determined during the Operational Works phase and this demonstrates the drainage concept.
3.2. Quality
3.2.1.Construction Phase
To fulfill the General Environmental Duty, a person “…must not carry out any activity that causes or is
likely to cause environmental harm, unless measures to prevent or minimise the harm have been taken…”. It is
necessary to manage and mitigate these impacts through best practise erosion and sediment controls.
Due to the development area being less than 2,500 m2 the construction impacts will be managed
using the principles aligned with the desired outcomes of Appendix 2 of State Planning Policy (SPP).
A site-specific erosion and sediment control plan must be prepared and submitted as part of the
Operational Works approval.
3.2.2.Operational Phase
This development consists of an additional dwelling as part of the subdivision and is consistent in
character with the existing residential dwelling and environment. As the development proposal is not
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considered to significantly alter the potential for pollutant generation, stormwater quality treatment
processes are not proposed for the development.
4. Conclusion and Recommendations
This Stormwater Management Report demonstrates how the stormwater run-off from the site is to be
managed to comply with the relevant requirements and mitigate adverse impacts to the downstream
catchment. Of note, QUDM assessment has been undertaken against the LPOD criteria demonstrating
no actionable nuisance arising from the proposed development.
The proposed site stormwater run-off maintains the existing drainage regime. The existing
surface runoff from the upstream properties remains unchanged compared to the existing state.
An assessment against the LPOD criteria of QUDM has been detailed in this revised report
with the outcomes incorporated into the concept stormwater layout, demonstrating no
actionable nuisance outcomes because of the development.
Pre and post development modelling of the resultant peak flows has been carried out, with
attenuation using a single 9kL underground tank to mitigate peak flows. Outlet from the tank
discharge via a level spreader device to the LPOD, to maintain the pre-development drainage
regime.
A site-specific erosion and sediment control plan is to be prepared and submitted with the
Operational Works approval to mitigate impacts to the receiving catchments and fulfil the
general environmental duty of care and Appendix 2 of the SPP.
The proposed development is not considered to significantly alter the pollutant generating
potential of the site; therefore, stormwater quality treatment processes are not proposed for the
development.
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Appendix A –Proposed Development Concept Plans [OCR of page images] Appendix A —Proposed Development Concept Plans
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Concrete
STREET
Deck
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EXISTING BUILDING
TULIP
DECK
Slab
[OCR of page images]
NORTH
57
RP32777
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TULIP STREET
LEGEND
ADJACENT BOUNDARY CATCHMENT TABLE
EXISTING ELECTRICAL
EXISTING DRAINAGE CATCHMENT | AREA (ha) | IMPERVIOUS ( % )
EXISTING KERB PRE 01 0.153 20.00
EXISTING MINOR CONTOUR
_ EXISTING MAJOR CONTOUR
=a =o CATCHMENT BOUNDARY
trop C) LEGAL POINT OF DISCHARGE
F [Associated Job Nos] Survey Data Scales CLIENT 25 TULIP STREET, COOROY QLD 4563 COUNCIL
E Horiz. .
0 i mee YJ. & C. TROMPF PRE CATCHMENT NOOSA SHIRE COUNCIL
2 rey Oa Worftos. [WOOD | 9 sgn SEE TANNING DEVELOPMENT LAYOUT PLAN
8 Height T py 66,329 Scale 1150 @Al © ABN 84 639 195 092 NAN PLAN STATUS Job No] =
A [ISSUE FOR REVEW 23.10.25 Datum . PIKKI ST JARO BALLEKA SIGNATURE ISSUE FOR USE Contract_No. -
- Signatory: - RPEQ Full Name, Eng. Area and RPEQ No. or Survey | SURVEYPLAN ] Dimensions shown in metres MAROOCHYDORE BC, QLD 4558 RPEQ #20695 DRAWN DESIGNED DATE i
Revisions/Descriptions = Full Name and Position Title Date Books | __%% __| except where shown otherwise +61 423 415 419 cPEng TN MN 23.10.25 Drawing No.| C900 [A
WHS IT] { [email protected].AU__} DATE:23.10.25 WU. Series Number 1 of 4
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Emt for Access & Services Concrete
STREET
Deck
806m²
725m²
Shed
2
Step
1
EXISTING BUILDING
TULIP
DECK
Slab
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Emt for Access & Services Concrete
STREET
Deck
806m²
725m²
Shed
2
Step
1
EXISTING BUILDING
TULIP
DECK
Slab
LEVEL SPREADER SECTION LEVEL SPREADER PLAN
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WEIR: 1.0m LENGTH AT 0.75m TAMK DEPTH PROPOSED ATLAN VAULT TANK 5.03m x 236m x 0.90m f E€ & g a _ ( ?\ - () : k \ 5.03m 9225 PIPE OUTLET |e 9100 AT 0.0m TANK DEPTH DETENTION TANK DETAIL-9kL F [Associated Job N Survey Dat CLIENT COUNCIL . seeing se To “oe Seales J. & C. TROMPF 25 TULIP STREET, COOROY QLD 4563 _ AHD AUXILIUM . a D Datum cONSUETING TANK DETAIL NOOSA SHIRE COUNCIL C ‘Auxiliary Drg Nos|Horiz. | MGA2020 | 9 02 04 08m ASSOCIATED CONSULTANTS Grid ZONE96 | ju ; ; NAN B | STORMWATER UPDATE 20.07.26 Height Tp 66,329 Scale 10 @A1 © ABN 84 639 195 092 BREN PLANNING STATUS Job No] PO-035 A | ISSUE FOR REVIEW 28.05.26 Datum . PIKKI ST JARO BAULEKA SIGNATURE ISSUE FOR USE Contract_No, - - a Signatory: - RPEQ Full Name, Eng. Area and RPEQ No. or Survey | SURVEYPLAN ] Dimensions shown in metres MAROOCHYDORE BC, QLD 4558 RPEQ #20693 DRAWN DESIGNED DATE ‘ Revisions/Descriptions = Full Name and Poston Tile Date Books | 7% | except where shown otherwise +61 423 415 419 cPEng HN MN 20.07.26 drawing No.| C905 |B ALES TI I [email protected] | DATE:20.07.26 U7. Series Number 4 of 4