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Stormwater Management Plan -OPW (A) · OPW25/0042
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STORMWATER MANAGEMENT
PLAN- Operational Works
Proposed Hotel Development
at
Lots 10 and 11 Serenity Close,
Noosa Heads
for Calile Malouf Developments Pty Ltd
A6769/25/SWMP/Rev OpW(A)
Feb 2025
SH/PL
Prepared by Brah101 Pty Ltd Trading As Alta Projects ABN 91 611 354 511
Civil and Structural Engineering
Project Management
26 Memorial Avenue
P. O. Box 559
Cotton Tree, Queensland, 4558
Telephone: (07) 5475 4125
Facsimile: (07) 5479 1607
e-mail: [email protected]
The content of this document is provided in strict commercial confidence. The content of this
document shall not be disclosed to any third party, without the express written authority of Brah101
Pty Ltd t/as Alta Projects..
Document Control
Revision A6769/25/SWMP/Rev OpW(A)
Author Signature
No. Date Reviewer Signature Document Status
A Oct 2022 Steven Harrison Steven Harrison A
B Jun 2023 Steven Harrison Steven Harrison A
C Jul 2023 Steven Harrison Steven Harrison A
OpW Feb 2025 Steven Harrison Steven Harrison A
(A)
R - Revision F - Final A - Approval P - Preliminary
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Section 2
- Contents -
1.0 INTRODUCTION ......................................................................................................................... 1
2.0 EXISTING SITE CONDITIONS ………………………………………………………………..1
3.0 PROPOSED DEVELOPMENT…………………………………………………………………..2
4.0 COUNCIL CONDITIONS……………………………………………………………………….2
5.0 RAINWATER HARVESTING AND RE-USE…………………………………………………4
6.0 STORMWATER TREATMENT AND INFILTRATION…………………………………….5
6.1 RAPID INFILTRATION PITS/RAPID INFILTRATION CULVERT (RIP/RIC) ..7
6.2 RIP/RIC INFILTRATION CAPACITIES……………………………………………..7
6.2.1 PROTOTYPE RIP TEST RESULTS 2003……………………………………………8
6.2.2 PROTOTYPE RIC TEST RESULTS 2025……………………………………………9
6.2.3 PROTOTYPE RIP/RIC TEST RESULT COMPARISON & APPLICATION…...9
7.0 RIP/RIC DESIGN AND MODELLING………………………………………………………..9
7.1 RIP/RIC CAPACITY MODELLING – EXCEL SPREADSHEET…………………………..10
7.2 OVERALL DEVELOPMENT SITE INFILTRATION – QUANTITY MUSIC MODEL...12
7.2.1 DETERMINATION OF INFILTRATION RATES FOR QUANTITY MUSIC
MODELLING
………………………………………………………………………………….............................……12
7.2.2 DETERMINATION OF EXTENDED DETENTION DEPTHS FOR QUANTITY
MUSIC MODELLING ………………………………………………………………………….…..12
7.2.3 DETERMINATION OF OTHER PARAMETERS FOR QUANTITY MUSIC
MODELLING ……………………………………………………………………………..…………13
7.2.3(A) DEPTH OF INFILTRATION MEDIA………………………………………….………..13
7.2.3(B)UNLINED FILTER MEDIA PERIMETER……………………………………………….13
7.2.3(C)FILTER AREA……………………………………………………………………………….13
7.3 QUANTITY MUSIC MODEL RESULTS……………………………………………………..14
8.0 STORWMATER QUALITY…………………………………………………………………….15
Section 3
8.1 QUALITY MUSIC MODEL………………………………………...…………………………..15
8.2 QUALITY MUSIC MODEL RESULTS……………………………………………………….18
- Contents -
9.0 SYSTEM MAINTENANCE………………………………….…………………………………18
10.0 EXTERNAL CATCHMENTS DRAINAGE ROUTE……………………………………….19
10.1 PIPED FLOWS (< 10 YEAR ARI)……………………………………………………………..19
10.2 MAJOR EVENT OVERLAND FLOWS (>10 YEAR ARI)…………………………………20
APPENDICES
APPENDIX A – Engineering Drawings
APPENDIX B – Engeny Flood Analysis Report
APPENDIX C – Architectural Drawings
APPENDIX D – Prototype RIP/RIC Test Results
APPENDIX E – Detail Survey
APPENDIX F –Stormwater Management Device Maintenance Plan
APPENDIX G – Excel Spreadsheet Water Balance Model (Electronic Only)
APPENDIX H – Excel Spreadsheet RIP/RIC Models (Electronic Only)
APPENDIX J – Quantity MUSIC Model & Quality MUSIC Model (Electronic Only)
APPENDIX K – Prototype Test Videos (4 December 2024)
Section 4
1.0 INTRODUCTION
This report is lodged in support of an Operational Works (OpW) application to Noosa Council on
behalf of Calile Malouf Investments seeking to develop a luxury hotel at Lots 10 and 11 SP195871,
Serenity Close, Noosa Heads.
This Revision C represents refinement of previous versions lodged and addresses conditions 46,
47 and 48 of Council’s Decision Notice-Other Change 132008.176.05 dated 17th October 2024
The proposed development follows seven stages of residential unit buildings developed by Cape
Bouvard over the greater Settlers Cove site with Alta Projects’ Engineers having completed
stormwater design, inspection and certification for all previous stages.
Design solutions presented in this report are consistent with those previously adopted with
minor refinements borne of experience.
2.0 EXISTING CONDITIONS
The subject site is currently undeveloped and supports vegetation subject to assessment and
recommendations by the Ecological Consultant.
The site falls at moderate grades away from Serenity Close towards an existing concrete
pedestrian path with informal natural wetlands areas of Noosa Inlet to the south.
The entire site consists of loose to dense, poorly graded dune sand and as such contains no
defined overland drainage paths since rainwater infiltrates directly through the permeable
surface, although a number of gentle natural gullies and swales are present over the site
particularly toward the southern boundary.
Stormwater and sewer lines within Easements R, S and F roughly bisect the site adjacent the
existing boundary between lots 10 and 11.
In order to make way for the proposed building footprint, the existing sewer and stormwater
infrastructure will need to be relocated through the site.
Previous reports proposed relocation of the sewer to Serenity Close but technical and budgetary
challenges now sees the sewer relocation proposed alongside stormwater pipework through the
site.
Lots 10 and 11 are proposed to be amalgamated as part of the development.
Refer detail survey at Appendix E.
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Section 5
3.0 PROPOSED DEVELOPMENT
The proposed development consists of multi storey hotel buildings with basement carparking
and all buildings to be surrounded by extensive landscape areas, both hard and soft. The
northern face of the development provides for two (2) swimming pools; one at the eastern end of
the site surrounded by hardstand and landscaping and a second ‘quiet pool’ at the western end
of the site with predominantly soft-landscaped surrounds.
An ephemeral stream will provide a suitable route for conveyance of external catchment flows
through the site with minor events piped and emergency major event flows conveyed as
overland flow.
Guests’ vehicular entry to basements will be from Banksia Avenue while service vehicles will
access back of house areas via the cul-de-sac bowl at the end of Serenity Close.
Refer architectural drawings at Appendix C.
4.0 COUNCIL CONDITIONS
46. Stormwater Drainage
1. Prior to the lodging of a development application for Operational Works, provide and
have endorsed by Council updated architectural plans, preliminary engineering plans,
and Stormwater Management Plan, which addresses the following:
a. Acceptance of all external catchments
b. Provide sizing and nominate the locations of roofwater harvesting tanks. The tanks
are to be sized to provide 80% reliability to supply water for landscape irrigation
and flushing of toilets in public/communal areas of the resort
c. Provide a method of removal of gross pollutants from all surface runoff (eg litter
baskets)
d. Provide treatment of internal site runoff such that the pollutant removal
requirements of AO6.1 and AO6.2 of the Water Quality and Drainage Code are
achieved prior to discharge to surface waters or infiltration to groundwater. Provide
MUSIC modelling to demonstrate this will be achieved by the proposed stormwater
treatment train
e. Provide in-situ hydraulic conductivity testing at the locations and depths nominated
for Rapid Infiltration Pits and demonstrate that the assumptions regarding
infiltration rates will be achieved. If not achievable, provide a revised design.
f. Ensure the proposed method of stormwater management achieves no net
reduction of rainwater infiltrating the sand dunes beneath the site. This may be
achieved either by infiltrating all flows up to the 10%AEP or by alternative
measures designed and managed in accordance with a groundwater recharge and
discharge management plan prepared by a suitably experienced and qualified
groundwater hydrologist. The groundwater recharge or discharge must
demonstrate that the development does not affect groundwater balances beyond
the property boundaries.
g. Updated the maintenance and management plan of the Stormwater Management
Plan to reflect any changes.
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Section 6
47. The site must be provided with a stormwater drainage system connecting to a lawful
point of discharge. The works must be undertaken in accordance with an Operational
Works approval the Queensland Urban Drainage Manual, and must include in particular:
a. the works as generally described in the updated Stormwater Management Plan
required by this permit
b. collection and discharge of stormwater from the external catchment through the
development site, including provision of an overland flowpath which accounts for
severe storms or severe blockage of the underground network
c. provision of drainage easements over all flowpaths conveying catchments external
to the site, in accordance with QUDM. Easement dimensions and locations are to
be shown on the plans submitted with the development application for Operational
Works.
d. the use of gravity stormwater drainage and not surcharge pits
48. Stormwater Quality Management
A stormwater quality treatment system must be provided for the development in
accordance with the updated Stormwater Management Plan required by this permit. The
works must be undertaken in accordance with an Operational Works approval.
53. An easement for stormwater drainage purposes must be registered in favour of Council
against the title of the subject site. The easement must:
h. Extend through the site from the northern Serenity Close frontage to the south-
western Serenity Close frontage,
i. Be of sufficient width to fully contain the 1%AEP flows (year 2100) from the local
catchment encompassing the development,
j. Be clearly shown on any plans submitted for Operational Works approval, and
k. Be registered prior to the commencement of the use.
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Section 7
5.0 RAINWATER HARVESTING AND RE-USE
Runoff from approximately 7,532m2 (80%) of roofed areas will be directed to
a rainwater harvesting tank to be located beneath back-of-house areas at the
south-western corner of the site.
Captured rainwater will be utilised for landscape irrigation and swimming
pool top up.
Alta Projects have developed a water balance model in eXcel format which
models tank inflow and outflow over a ten (10) year period of historical
rainfall data from 2013 to 2024 at Tewantin RSL Weather Station.
Tank performance was modelled utilising the following reuse parameters: -
• Landscape irrigation = 1.5mm/m2/day
o No irrigation for one day after 1.5mm of rain or more
• Daily Pool top-up = Evapotranspiration – Rainfall
Results appear below in table 5.1
Table 5.1 Water Balance Model Results
By inspection approximately 80% reliability on rainwater reuse for pool top
up and landscape irrigation may be expected with a tank of 300m3 total
volume installed.
Refer Appendix G for full model.
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Section 8
6.0 STORMWATER TREATMENT & INFILTRATION
Treatment and disposal of runoff from the subject site will be carried out in
accordance with the approved document Settlers Cove Noosa Residential High
Density (RHD) Environmental Management Plan (EMP 1) by WBM Oceanics
Australia and above Conditions 46-48 & 53 of Council’s decision notice.
Alta Projects Engineers (formally TATE) were involved in formulation of the
overarching development approval document and EMP1 produced by WBM
Oceanics.
EMP1 recognises in particular the regimes of stormwater runoff and
infiltration which existed over the broader RHD site pre-development.
Essentially it was recognised that the RHD site lies atop a dune of poorly
graded sand with particularly high rainfall infiltration rates. As such the
natural state sees rainfall infiltrate the dune close to where it lands and
replenish the water table below with little or no runoff.
The standing water table forms a profile similar to the shape of the dune,
albeit at a depressed scale and emerges as seepage flows adjacent Noosa inlet
at or about RL 5.0m.
The zone between RL 5.0m and the inlet was recognised as having
particularly high ecological values, supporting numerous stands of swamp
mahogany and various species of fauna.
Critically it was recognised that these ecological values were dependant on
maintenance of the natural hydrogeological regime and no nett reduction in
rainwater infiltration post-development.
Section 3.1 of the EMP is reproduced below:-
Strategy: To ensure no net reduction of rainwater infiltrating the sand dunes
beneath the site. To ensure adequate treatment of runoff from landscaped and
hardstand areas prior to infiltration.
Responsibility: Consulting Engineer and Landscape Architect.
Management Actions: All design within the Residential High Density areas to comply
with the following guidelines:
1. All runoff from storms up to 10 year average recurrence interval (ARI) to
be infiltrated into the sand subgrade without runoff.
2. Infiltration to be achieved via swales and ephemeral streams and rapid
infiltration pits (RIP’s)
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3. All infiltration devices to be located within the “residential high density
building envelope” as shown on Ken Hicks and Associates drawing 1128
Master.
4. Surcharge runoff from storms greater than the capacity of infiltration
devices to be directed toward ecological restoration areas and roadways as
dispersed sheet flow rather than concentrated flows.
5. Stormwater runoff from landscaped and hardstand areas to be pretreated
prior to infiltration.
6. Runoff from roadways and landscaped areas to be directed to landscaped
swales or ephemeral streams for biological treatment including vegetative
plantings in accordance with the Landscape Master Plan.
7. Areas of swales and ephemeral streams shall be lined with a soil layer to
retard infiltration and allow biological treatment of runoff. Soils will be
remediated by mixing with loams to achieve a hydraulic conductivity of
100mm/hr.
8. Swales and ephemeral streams to be planted in accordance with approved
Landscape Master Plan in order to promote biological treatment of runoff.
Consequently, and in order to counteract the effect of significant impervious
areas being constructed, the design approach will see stormwater runoff from
the proposed development’s roofs, hardstand and landscaped areas
infiltrated into the natural sands via a series of Rapid Infiltration Pits (RIPs)
and a consolidated Rapid Infiltration Culvert (RIC) in order to achieve no net
reduction in rainwater infiltration.
Discrete RIPs are to be located along the northern and eastern edges of the site
accepting runoff from relatively minor nearby impervious and landscaped
areas.
Treatment of runoff prior to infiltration by RIPs will be via small bioretention
basins adjacent individual RIPs with low flows (< 3 month ARI) directed to
the bioretention surface.
Major event surcharge of RIPs would be directed to adjacent roadways (legal
point of discharge) as dispersed overland flow.
Runoff from approximately 7,532m2 (80%) of roofed areas will be piped to the
abovementioned rainwater harvesting tank at the south-western corner of the
site with tank overflow discharging to an adjacent Bioretention Basin and
Rapid Infiltration Culvert (RIC).
A weir and splitter pit arrangement will be employed within the tank such
that flows of 3 month ARI or lower will be directed to the bioretention basin
surface for formal treatment with larger event flows piped directly into the
RIC.
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Section 10
Major event flows surcharging from the RIPs in the unlikely event of RIC
failure would be directed eastward via a stone pitched weir toward existing
vegetated swale areas and ultimately Noosa Inlet (legal point of discharge) as
dispersed sheet flow.
The rough nature of the stone pitching will also provide an “energy
dissipation” effect.
All grated stormwater pits around the site will be fitted with litter baskets to
intercept gross pollutants.
6.1RAPID INFILTRATION PITS/RAPID INFILTRATION CULVERTS
(RIP/RICS)
RIPs/RICs consist of a bottomless stormwater pit/culvert which promotes
infiltration through its base.
Crushed rock and multiple layers of geofabric and “sacrificial sand” are
installed at the base of the RIP to protect against clogging of dune sands
below.
Refer engineering drawings at Appendix A for RIP/RIC details.
6.2 RIP/RIC INFILTRATION CAPACITIES
6.2.1 PROTOTYPE RIP TESTING 2003
Alta Projects Engineers (formally TATE) were involved in formulation of the
over-arching development approval document and EMP1.
Such involvement included construction of a prototype RIP on the Settlers
Cove site consisting of a 225mm diameter pipe buried vertically in clean
white sand and with a geofabric filter across the base.
A test site was chosen near the end of Serenity Close at the time (circa 2003)
roughly coinciding with the existing stormwater/sewer easement through the
site.
By inspection it is inferred that 2003 prototype testing would likely to have
been carried out at an approximate level of RL18-20m AHD, with a
corresponding estimated base RL of 15-17m AHD for a 3m length of pipe.
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Section 11
Field testing was carried out consisting of filling the pipe with water from a
nearby fire hydrant and timing the rate of fall as water infiltrated sands
below.
Results were consistent indicating a linear relationship between driving head
and infiltration rate such that:
Infiltration Rate (mm/s) = 4mm/sec + 13.6 x head (m)
Refer to Appendix D for 2003 prototype test results.
6.2.2 PROTOTYPE RIP TESTING 2024
On 4th December 2024 further on-site prototype testing was carried out in
similar fashion to that completed in 2003 at a location approximating the
proposed RIC/Bioretention basin location on site (refer RIP/RIC site layout
drawing at Appendix A).
The 2024 prototype differed from the 2003 version in that a shorter 2.2m long
pipe was utilised with a rock spalls wrapped in geofabric as a base rather than
a simple geofabric filter over the end of the pipe.
Levels taken on site indicated a prototype base level of approximately RL8.8m
AHD.
Once again field testing was carried out consisting of filling the pipe with
water from a nearby fire hydrant and timing the rate of fall as water
infiltrated sands below.
Notably, at the commencement of testing, the 50mm diameter fire hose being
used to fill the pipe with water could not keep up and water levels remained
at or near the base.
After approximately 20 minutes with the fire hose on maximum flow the pipe
began to fill to the top allowing timing of the rate of water level fall to be
taken.
Results once again were consistent but this time indicating a significantly
higher liner relationship between driving head and infiltration rate such that:
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Section 12
Infiltration Rate (mm/s) = 13mm/sec + 33 x head (m)
Refer to Appendix D for 2024 prototype test results.
Video of prototype testing being carried out are included at Appendix K.
6.2.3 PROTOTYPE RIP TEST RESULT COMPARISON AND
APPLICATION
It is not entirely clear as to the factors contributing to differing infiltration
rates observed in 2003 and 2024.
2003 testing was carried out at a relatively elevated northern area of the site
compared to 2024 rates observed at a lower southern area of the site.
Both locations saw the prototype founded on clean white sands although
possibly insitu sand density may have differed between the two locations.
Inclusion of a rock base may have contributed to higher infiltration rates
observed in 2024 although the arrangement better replicates actual RIP/RIC
construction.
Regardless of contributing factors both 2003 and 2024 prototype test results
returned very high infiltration rates.
7.0 RIP/RIC DESIGN AND MODELLING
In order to ensure a conservative approach is adopted for infiltration of
stormwater and to minimise risk of RIP/RIC surcharge the following
approach has been adopted: -
• Size proposed RIPs/RICs to infiltrate associated catchment flows based
on the Excel model mentioned in Section 5.1
• Conservatively adopt the lower 2003 algorithm for all RIP and RIC
infiltration rates modelled in eXcel.
• Apply a Factor of Safety of 2.0 to infiltration rates modelled.
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Section 13
• Size RIPs/RICs and surrounding bio basins such that all flows up to
100-year ARI are infiltrated on site
• Test RIP/RIC sizes derived above via a Quantitative MUSIC model to
predict performance of RIPs/RIC and quantify percentage of incident
rainfall infiltrated on site.
This approach satisfies both performance criteria of Council Condition 46 (f).
Infiltration of 100-year ARI catchment flows is a higher standard than the 10
year ARI required by EMP 1 or Council Condition 46 (f) and is consistent with
the approach taken on previous Settlers Cove projects.
Quantitative MUSIC modelling employs infiltration rates of 3,600mm/hour
(1mm/second) as recommended in the MUSICX1.0 modelling guidelines for
coarse sands.
7.1 RIP/RIC CAPACITY MODELLING- EXCEL SPREADSHEET
In order to model the operation of the RIP’s, a spreadsheet has been
developed and utilised for all previous stages of Settlers Cove.
Temporal patterns for Zone 3 from the Australian Rainfall and Runoff,
Volume 2 were applied. These temporal patterns were used in conjunction
with the average rainfall intensities for the Noosa region to create a series of
design storms of varying durations and for a range of different average return
intervals (ARI). Notably existing observed and documented rainfall intensities
from AR&R were increased by 20% as per Council ‘Climate Change’
requirements.
Temporal patterns were converted to flow rates by breaking each storm event
into a series of short duration storms. A triangular flow verses time
approximation was used for each sub storm with sub storm flows then added
to produce flow Vs time for RIP inflow.
Outflow and water depth were then calculated through iterations for the
duration of the storm based on the infiltration rate / head relationship
discussed above. A factor of safety of 2.0 was applied to the observed
prototype infiltration rate. Each RIP/RIC was then sized to prevent
overtopping in a 10-year ARI storm event of any duration, with 100-year ARI
storms contained within the RIP/RIC and adjacent bioretention basin.
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Section 14
Individual sub-catchments are applied to corresponding RIPs/RICs.
Existing vegetated areas where no significant works are proposed are
excluded from modelling on the basis that they will continue to infiltrate
incident rainfall as per the existing pre-development case.
Largely soft landscaped catchments 4/1, 4A/1 and 4B/1 are to be directed to
RIPs constructed along the external catchment drainage line discussed in
Section 6. This arrangement is consistent with the existing stormwater line.
The above RIPs are not modelled via spreadsheet in recognition of the fact
that they will accept commingled runoff from both internal and external
catchments. They are however addressed in the overall development site
Quantitative MUSIC model.
Spreadsheet model results for all proposed RIPs and the RIC appear below in
Table 5.1.1
Table 7.1.1 Summary of Excel Spreadsheet Modelling
By inspection criteria of infiltrating all flows up to the 10% AEP over the
developed site has been demonstrated.
Excel model files are attached at Appendix H with catchment drawings
appearing at Appendix A.
Emergency Overland Flow Weir calculations model the unlikely case of
complete RIC failure with full 100 Year ARI flows conveyed toward existing
vegetated swale areas and appear on engineering drawings at Appendix A.
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Section 15
7.2 OVERALL DEVELOPMENT SITE CATCHMENT INFILTRATION –
QUANTITY MUSIC MODEL
The above Quantity MUSIC model is utilised to predict quantity of rainfall
infiltrated over the site for a 10-year horizon and using the Cooroy Rainfall
Station as a meteorological base.
For simplicity the model conservatively ignores bioretention, swales,
rainwater harvesting and reuse.
A separate Quality MUSIC model discussed in Section 6 is utilised to predict
quality of stormwater achieved prior to infiltration.
7.2.1 DETERMINATION OF INFILTRATION RATES FOR QUANTITY
MUSIC MODELLING
MUSIC model infiltration parameters do not consider varying infiltration
rates with increasing driving head whilst observations during prototype tests
in both 2003 and 2024 indicated a generally linear relationship.
For MUSIC Modelling purposes a decision was made to adopt infiltration
rates of 3,600mm/hour (1mm/second) as recommended for coarse sands in the
MUSICX1.0 modelling guidelines.
This rate is considered to be extremely conservative being 18 to 46 times
lower than those observed on site for 1m of driving head.
7.2.2 DETERMINATION OF EXTENDED DETENTION DEPTHS FOR
QUANTITY MUSIC MODELLING
Extended detention depth parameters were generally set to design RIP/RIC
depths.
For RIPs incorporated into the external catchment drainage line extended
detention depth parameters were set to the depth of RIP over-run below the
stormwater pipe.
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7.2.3 DETERMINATION OF OTHER PARAMETERS FOR QUANTITY
MUSIC MODELLING
7.2.3(A) DEPTH OF INFILTRATION MEDIA
Set at 0.3m for all RIPs/RIC reflecting depth of rock spalls below.
7.2.3(B)UNLINED FILTER MEDIA PERIMETER
Set at sum of perimeter of RIPs/RIC (conservative-ignores rock spall
overspread)
7.2.3(C)FILTER AREA
Set at area of base of RIPs/RIC (conservative-ignores rock spall overspread).
A conceptual layout of the treatment train as input to the Quantity MUSIC
Model is shown in Figure 7.2 below.
Figure 7.2 : Quantity MUSIC Model Layout
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Section 17
7.3 QUANTITY MUSIC MODEL RESULTS
Quantity MUSIC Modelling returned the following results:-
• Average Annual Incident Rainfall 19.32 ML/Year
• Average Annual Infiltration to Water Table 19.32 ML/Year
• Average Annual Overflow Off site 0 ML/Year
• Average Annual Percentage Infiltration to Water Table 100%
• Average Annual Percentage Overflow Off Site 0%
By inspection criteria of no nett reduction in infiltration over the developed
site has been demonstrated.
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Section 18
8.0 STORMWATER QUALITY
Stormwater runoff from roofed and hardstand areas is to be treated prior to
infiltration via small bioretention basins surrounding discrete RIPs and a
large consolidated bioretention basins adjacent the RIC .
Piped low flows (<3 month ARI) from catchments to be treated will generally
discharge to bioretention surfaces while larger flows will discharge directly to
RIPs/RIC.
Rainwater harvesting and re-use will be employed as discussed in Section 5.0.
Largely soft-landscaped catchments 4/1, 4A/1 and 4B/1 are to be directed to
the ephemeral stream (vegetated swale) constructed along the external
catchment drainage line discussed in Section 5.
Existing vegetated areas where no significant works are proposed are
excluded from modelling on the basis that they will continue to infiltrate
incident rainfall as per the existing pre-development case.
Infiltration via RIPs/RIC is conservatively ignored in the Quality MUSIC
Model.
8.1 QUALITY MUSIC MODEL
The efficiency of the proposed treatment train has been identified by the
Model for Urban Stormwater Improvement Conceptualisation
(MUSICXV1.1.0) developed by Monash University.
A conceptual layout of the treatment train as input to the Quality MUSIC
Model is shown in Figure 8.1
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Figure 8.1 : Quality MUSIC Model Layout
The locations and details of the water quality treatment devices are shown on
engineering drawings at Appendix A.
Water Quality analysis has been developed in accordance with Noosa
Council, State Planning Policy July 2017 (SPP) and the Queensland Water
Quality Objectives (2009).
Queensland Water Quality Objectives (2009) have been adopted which
recommend the following minimum reductions in mean annual pollutant
loads leaving a development site compared to the developed unmitigated
case:
• 80% reduction in Total Suspended Solid Load;
• 65% reduction in Total Phosphorous Load;
• 45% reduction in Total Nitrogen Load;
• 90% reduction in Gross Pollutant Load.
Quality MUSIC modelling of the proposed treatment train has been
undertaken generally in accordance with Water by Design’s - MUSIC Modelling
Guidelines, Version 1.0-2010.
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A6769/25/SWMP/Rev OpW(A) – Feb 2025
Page 16 of 9
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Brah101 Pty Ltd t/as ALTA PROJECTS
Section 20
Quality Modelling has been undertaken using the ‘split catchment’ method.
The Rainfall Runoff Parameters for the source catchments have been taken
from table 3.7 of Water By Design’s – MUSIC Modelling Guidelines, Version 1.0
2010 and are shown in Table 8.1 below.
Pervious Area Properties
Soil Storage Capacity (mm) 18
Initial Storage (% of Capacity) 10
Field Capacity (mm) 80
Infiltration Capacity Coefficient ‘a’ 243
Infiltration Capacity Exponent ‘b’ 0.6
Groundwater Properties
Initial Depth (mm) 50
Daily Recharge Rate (%) 0
Daily Baseflow Rate (%) 31
Daily Deep Seepage Rate (%) 0
Rainfall Threshold (mm) 1
Table 8.1: Rainfall Runoff Parameters & Pervious Area Properties
The pollutant load concentrations for each source catchment have been taken
from Table 3.8 of the Water by Design MUSIC Modelling Guidelines Version 1.0,
2010 using the concentrations recommended for Urban Residential areas.
The model was run for an average rainfall recorded at Cooroy Rainfall Station
using a 6 minute time step.
Please refer to the electronic MUSIC model attached at Appendix J.
__________________________________________________________________________
A6769/25/SWMP/Rev OpW(A) – Feb 2025
Page 17 of 9
SH/PL
Brah101 Pty Ltd t/as ALTA PROJECTS
Section 21
8.2 QUALITY MUSIC MODEL RESULTS
The results of the Quality MUSIC model are shown in Table 8.2 below.
Flow TSS TP TN Gross
ML/y Kg/y Kg/y Kg/y Pollutant
Kg/y
Source Load 19.32 1035 3.825 40.27 414.6
Residual Load 14.86 181.2 1.239 19.48 0
% Reduction 23.06 82.48 67.6 51.62 100
%Target Reduction - 85 60 45 90
Table 8.2 Treatment Train Effectiveness
Inspection of Table 8.2 shows that the target pollutant load reductions will be
achieved for the developed site.
9.0 SYSTEM MAINTENANCE
RIPs/RICs, bioretention basins and the rainwater harvesting tank will be
subject to routine inspection and maintenance by the hotel’s maintenance
team and such maintenance is critical to their ongoing function.
Failure to carry out such maintenance could result in system failures,
environmental harm and surcharge of infiltration pits and culverts.
A recommended maintenance schedule for elements of the water quality
treatment and train and infiltration devices appears at Appendix F.
__________________________________________________________________________
A6769/25/SWMP/Rev OpW(A) – Feb 2025
Page 18 of 9
SH/PL
Brah101 Pty Ltd t/as ALTA PROJECTS
Section 22
10.0 EXTERNAL CATCHMENTS DRAINAGE ROUTE
The eastern end of the Serenity Close roadway and the existing residential building at
the north-eastern corner of the Settlers Cove site; Macquarie Lodge and Petrie Mansions
were all constructed by RF Thompson Developments during the 1990’s and early 2000’s
predating the Settlers Cove Noosa Residential High Density Environmental Management
Plan (EMP 1) produced by WBM Oceanics Australia.
Current best practice of rainwater infiltration was not adopted for those early
developments and instead stormwater was collected and conveyed to Noosa Inlet via
traditional methods including the existing stormwater line mentioned in Section 2.0.
In accordance with the existing change approval and the previous version of this
report it is proposed that flows from external catchments be re-routed through the
development site on a revised alignment and in a traditional fashion consisting of
minor event flows conveyed underground via piped drainage with a landscaped
major event overland flow path above.
10.1 PIPED FLOWS (< 10 YEAR ARI)
The proposed route for minor event pipework and major event overland flow will be
generally westward from the existing sag point on Serenity Close following the
northern face of the proposed building and the southern extent of ‘quiet pool’
landscaped areas to the Serenity Close cul-de-sac head consistent with approved
architectural drawings.
It is proposed to upgrade existing pipework and headwalls within the road reserve
and pathway in order to cater for the increased catchment area but generally
maintain existing alignments and discharge point.
Notably the nett effect would be to combine the two (2) existing stormwater
discharge points into one with flows from the additional catchment area at the
eastern end of Serenity Close effectively moved around 120m westward.
A proposed sewer diversion will follow a similar route generally parallel to the
stormwater line.
Realigned pipework will be contained within an easement in favour of Council and ,
where sewer is adjacent a shared easement in favour of Council and Unity Water.
Notably the stormwater line passes under elevated structure in two areas, one in the
form of a footbridge and the other hotel units.
It is proposed that volumetric easements will be registered in these areas.
Refer to Engineering Drawings at Appendix A for details.
________________________________________________________________________________________
A6769/25/SWMP/Rev OpW(A) – Feb 2025 Page 19 of 21
SH/PL
Brah101 Pty Ltd t/as ALTA PROJECTS
Section 23
10.2 MAJOR EVENT OVERLAND FLOWS (>10 YEAR ARI)
Emergency overflow, for events (>Q10) which cannot be wholly conveyed by
underground pipework would be conveyed overland through the development site
via a landscaped ephemeral stream.
Previous versions of this report relied on simple manning calculations carried out at
three (3) nodes along the proposed route through the development site in order to
estimate 100 Year ARI flow characteristics and check that such flows could be
conveyed safely with the following criteria adopted:-
-Maximum velocity x depth product = 0.4m2/sec (QUDM 7.0.4.2)
-Minimum channel freeboard = 0.3m (QUDM 9.03.1)
-Minimum freeboard to any structural floor=500mm (Council Standards SC6.7).
For increased accuracy and certainty and to ensure no impacts to adjacent properties
or non-compliant flows through roadways and footpaths performance of the
ephemeral stream has now been more accurately modelled by Engeny using specialist
software.
The Engeny report is included at Appendix B and drew the following conclusions: -
Engeny Australia Pty Ltd (Engeny) have been engaged by Calile Malouf Investments Pty Ltd
to prepare a Local Overland Flow Assessment for a proposed Operational Works (OPW)
development for application resort complex and shop at 3 & 7 Serenity Close Noosa Heads
QLD 4567.
Detailed overland flow modelling has been completed at a level of detail appropriate for
Operational Works approval to confirm Alta Project’s proposed realigned drainage and
overland flow design through the site is appropriate in achieving the design requirements for
the project.
The assessment has found that flows can be appropriately managed through the site via an
overland flow path which connects into the Serenity Close cul-de-sac footpath, without
impacting adjoining properties or resulting in non-compliant flows with the road and
footpath.
The assessment found that the finished floor levels of each building achieve a minimum 0.5m
freeboard and is able to contain the severe storm event (i.e. 1% (2100) AEP fully blocked
stormwater network).
Reinforced turf is recommended for the last 20m of channel upstream of Serenity Close
(velocity up to 2.30 m/s) and rock protection be placed to manage the outlet velocities (rock
size D50 = 200mm and extend 3.6m past the outlet).
________________________________________________________________________________________
A6769/25/SWMP/Rev OpW(A) – Feb 2025 Page 20 of 21
SH/PL
Brah101 Pty Ltd t/as ALTA PROJECTS
Section 24
Engineering Drawings
Section 25
21
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The text continues on section 27.
Used in these records
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