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Stormwater Management Plan
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Log in to see the plans as drawnSITE BASED STORMWATER MANAGEMENT PLAN
For
Elkhorn Investments (QLD) Pty Ltd
Proposed Sub-division at
28 Elkhorn Drive,
Tewantin
Job Ref: SC- 5551
March 2016
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SC5551 - 28 Elkhorn Dr, Tewantin 1
AUTHORSHIP INFORMATION
Site Based Stormwater
REPORT TITLE
Management Plan
Affected
Properties
Street Address 28 Elkhorn Drive, Tewantin
RP Description Lot 70 M37807
Prepared For Elkhorn Investments (QLD) Pty Ltd
Date March 2016
Report Status For DA Approval
Prepared By
Name Matt Johnson
Qualifications BE (Civil)
Company Empire Engineering Pty Ltd
Phone Number 07 5477 6437
Reviewed By
Name Sean Dwyer
Qualifications BE (Civil)
Approved By
Name Troy Paulsen
Qualifications BE (Civil), CPEng, RPEQ 6990
REVISION DATE Reviewed/ Approval
A 21.03.16
Document Qualifying and Ownership Statement:
The contents of this document represent an assessment of the facts and circumstances pertaining to this
matter, as they are known to the writer at the time of preparation. It is possible that upon completion and
distribution of this document further information may come to hand that impact upon the findings,
recommendations or conclusions drawn in this document. This document and its contents remains the
property of Empire Engineering and cannot be reproduced in whole or in part for any reasons that could be
considered to be outside the exact, intended original use of this document.
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TABLE OF CONTENTS
1.0 Introduction ............................................................................................................. 3
1.1 Background ......................................................................................................... 3
1.2 Scope .................................................................................................................. 3
1.3 Existing Topography ............................................................................................ 3
1.4 Proposed Development........................................................................................ 4
2.0 Water Cycle Management ....................................................................................... 5
2.1 Background ......................................................................................................... 5
2.2 Wastewater Minimisation ..................................................................................... 5
2.3 Stormwater Harvesting Tanks .............................................................................. 5
3.0 Water Quality Management .................................................................................... 6
3.1 Background ......................................................................................................... 6
3.2 Construction Phase.............................................................................................. 6
3.3 Operational Phase ............................................................................................... 7
3.3.1 Water Quality Objectives.................................................................................. 7
3.3.2 Pollutant Export Modelling ............................................................................... 7
3.3.2.1 Rainfall Data................................................................................................ 8
3.3.2.2 Treatment Nodes ......................................................................................... 9
3.3.3 Effectiveness in Pollution Reduction................................................................. 9
4.0 Stormwater Quantity Management....................................................................... 10
5.0 Conclusions .......................................................................................................... 11
APPENDIX A – STORMWATER MANAGEMENT PLAN..................................................... 12
APPENDIX B – STORMWATER QUALITY MUSIC MODELLING ....................................... 13
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SC5551 - 28 Elkhorn Dr, Tewantin 3 1.0 Introduction 1.1 Background This report is to accompany and be considered part of an application to Noosa Council for a proposed sub- division at 28 Elkhorn Dr, Tewantin. 1.2 Scope Empire Engineering Pty Ltd was commissioned by Elkhorn Investments (QLD) Pty Ltd to develop a site based Stormwater Management Plan (SWMP) to outline water management strategies for the proposed development that will comply with Council’s relevant planning scheme policies, Queensland Development Code and the Environmental Protection Act (1994) and associated Environmental Protection (Water) Policy 1997. This report presents the results of a SWMP and outlines the proposed measures to be adopted in relation to stormwater quality management and stormwater quantity management for the subject site and the proposed development. 1.3 Existing Topography The subject site is described as Lot 70 M37807 with a combined area of 12,938m2. The site is bounded by Elkhorn Drive and existing residential allotments to the south, existing residential allotments to the west and north, and Noosa River Esplanade to the east. The site is currently occupied by a single residential house with an associated shed. The remainder of the lot is covered in grass and tree/shrubbery. See Figure 1.1.
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Subject Site:
28 Elkhorn Dr,
Tewantin
N
Figure 1.1 Subject Site
The site has a crest approximately 45m off the eastern boundary on the southern end of the site, to
approximately 25m off the eastern boundary at the northern end of the site. This crest is at approximately
RL10.25. The site falls to the west at approximately 2.5% grade to almost RL8.25 in the south-western
corner. The site also falls to the east at approximately 18% to RL2.00 in the south-eastern corner. Under
existing conditions rainfall sheet flows from the site’s crest into either the Noosa River or the adjacent
residential property.
1.4 Proposed Development
Preliminary drawings prepared by KHA Development Managers depict a proposed 11 lot residential sub-
division and associated road.
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2.0 Water Cycle Management
2.1 Background
The purpose of this section of the SWMP is to outline water saving measures that will be implemented in
the design and construction of the proposed development.
2.2 Wastewater Minimisation
To reduce the impact of water demand from the development and to minimise the loading on the existing
sewerage network, it is intended to reduce the wastewater leaving the site through the use of “at source”
measures. This will include:
Water saving shower roses with a AAA rating or better
Dual flush toilet cisterns that do not exceed 6 litres on full flush and 3 litres on half flush
The use of 3 star (or higher) water efficient appliances
2.3 Stormwater Harvesting Tanks
In an effort to reduce the demand on town water supply and to assist with meeting water quality objectives
for this development, it is proposed to incorporate stormwater harvesting tanks on each lot within the
hydraulic design of the proposed development. A total volume of 55,000L is proposed, with a minimum of
50% of the roof area to be connected with first flush diversion capabilities as determined using MUSIC
modelling to achieve water quality objectives, refer section 3.0.
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3.0 Water Quality Management
3.1 Background
A requirement of the proposed development is that Stormwater quality treatment shall be provided to meet
the design objectives set out in Section 2.4 of DERM’s Urban Stormwater Quality Planning guidelines 2010
and the associated with State Planning Policy (SPP) 4/10 Healthy Waters. The scope typically
encompasses the ‘post construction’ phase of the development however ‘construction phase’ water quality
is briefly addressed.
3.2 Construction Phase
Table 3.1 has been adapted from Table C4.1 of Brisbane City Council’s (BCC) Stormwater Best
Management Practices 2000 and details the typical stormwater pollutants which may be generated during
the construction phase of the development.
Pollutant Sources
Litter Paper, construction packaging, food packaging,
cement bags and off-cuts
Sediment Unprotected exposed soils and stockpiles during
earthworks and building
Hydrocarbons Fuel and oil spills, leaks from construction equipment
Toxic Materials Cement slurry, solvents, cleaning agents, wash waters
pH Altering Substances Cement slurry, wash waters
Table 3.1 –Typical Construction Phase Pollutants
The following measures should typically be implemented prior to the commencement of
construction:
Education of all site workers in sediment and erosion procedures
Specified storage areas for construction materials and plant that are bunded to prevent
any spillages from escaping
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During the construction phase of the development, silt fences should be erected downstream of all
disturbed areas. In addition erosion and sediment control devices should be regularly inspected and
maintained following storm events. An Erosion and Sediment Control Plan will be provided as part of the
operational works application.
3.3 Operational Phase
During the operational stage of the development, the following impacts have been identified in relation to
stormwater runoff and water quality of the receiving waterways:
Gross pollutants which include human derived litter, course sediment and vegetation
Sediment and suspended solids
Nutrients such as phosphorous and nitrogen
To target these potential pollutants stormwater quality improvement devices (SQID’s) are proposed to be
incorporated within the design.
3.3.1 Water Quality Objectives
The water quality objectives (WQO’s) for this site were determined in accordance with Appendix 2 of the
State Planning Policy (SPP) Dec 2013.
Table 3.2 indicates the minimum load reduction targets required to be met:
Pollutant Minimum Reduction Targets
Total Suspended Sediments (TSS) 80%
Total Phosphorus (TP) 60%
Total Nitrogen (TN) 45%
Gross Pollutants (>5mm) 90%
Table 3.2 - Water Quality Objectives
3.3.2 Pollutant Export Modelling
The Model for Urban Stormwater Improvement Conceptualisation (MUSIC) has been utilised to calculate
pollutant loads from the proposed development and to predict performance characteristics of the proposed
treatment train. Modelling parameters used were adopted from the Water by Design “Music Modelling
Guidelines for South-East Queensland”, and the updated MUSIC Version 5 recommended parameters for
Bio-retention basin nodes. MUSIC modelling setup and results are attached within Appendix B.
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Under the proposed conditions, the site was ‘split’ into three land use catchment nodes; the roofed area,
driveways and ground level uses. The pollutant export parameters utilised were based on the Urban
Residential pollutant loads, refer Table 3.3 & 3.4.
Parameter Value
Rainfall threshold (mm) 1
Soil storage capacity (mm) 500
Initial storage (% capacity) 10
Field capacity (mm) 200
Infiltration capacity coefficient (a) 211
Infiltration capacity exponent (b) 5.0
Initial depth (mm) 50
Daily recharge rate (%) 28
Daily baseflow rate (%) 27
Daily deep seepage rate (%) 0
Table 3.3 – Rainfall-runoff Parameters Adopted (Urban Residential)
TSS Log TP Log TN Log
Flow Type Surface Type
Mean Std Dev. Mean Std Dev. Mean Std Dev.
Roof N/A N/A N/A N/A N/A N/A
Baseflow
Driveways 1.00 0.34 -0.97 0.31 0.20 0.20
Parameters
Ground Level 1.00 0.39 -0.97 0.31 0.20 0.20
Roof 1.30 0.39 -0.89 0.31 0.26 0.23
Stormflow
Driveways 2.43 0.39 -0.30 0.31 0.26 0.23
Parameters
Ground Level 2.18 0.39 -0.47 0.31 0.26 0.23
Table 3.4 – Pollutant Export Values Adopted (Urban Residential)
3.3.2.1 Rainfall Data
Rainfall data for the site was chosen to give the best representation of actual conditions. A time period of
10 years between 1973 and 1983 was selected from the Cooroy Composite station, using a six minute time
step.
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3.3.2.2 Treatment Nodes
The following devices have been used in the treatment train to reduce these pollutant loads to achieve WQO’s.
Bio-Retention Basin – An area of 95m2 of designated Bio-retention to treat road, landscape, and roof
catchments to achieve the WQO’s was modelled. An extended detention depth of 200mm with a filter
media of 180mm/hr sandy loam hydraulic conductivity has been modelled. The location of these
devices is shown on the attached Appendix A.
Rainwater Tanks – A combined volume of 55,000L rainwater harvesting was modelled to receive 50%
roofwater areas. This volume is to be re-used for irrigation purposes (excluding road reserve areas).
Re-use rates for irrigation were calculated as follows: 5,167m 2 ground areas x 75% (areas to receive
irrigation) x 0.548m annual irrigation, equating to 2,124kL/yr per the MUSIC Modelling Guidelines
3.3.3 Effectiveness in Pollution Reduction
The water quality development model was set up with the incorporation of the above devices to reduce
pollutant export to WQO levels. Table 3.5 indicates the predicted pollutant mean values of stormwater
discharged from the site as calculated by MUSIC:
Pollutant Percentage Load Reduction
Total Suspended Solids (TSS) 83.2%
Total Phosphorus (TP) 60.3%
Total Nitrogen (TN) 56.2%
Gross Pollutants (>5mm) 100%
Table 3.5 - Flow Based Pollutant Load Reduction
The MUSIC modelling results shown above indicate that the treatment train will adequately treat TSS, TP
and TN generated by stormwater runoff in accordance with the targets required under the water quality
objectives stated previously.
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SC5551 - 28 Elkhorn Dr, Tewantin 10 4.0 Stormwater Quantity Management The subject site is located adjacent to the Noosa River Esplanade where a portion of the site currently sheet flows into. This is deemed the lawful point of discharge for the subject site as no other practical stormwater connection exists for the site. The site is directly adjacent to the point of discharge into the Noosa River, resulting in a very small time of concentration for the proposed development compared to that of any upstream catchments. On-site detention would therefore have no beneficial impact to peak flow discharge rates. As such, no detention is proposed within the development.
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5.0 Conclusions
This report has outlined a total water cycle strategy to be adopted in the construction and operational
works phase of the development which satisfies the acceptable solutions set out in Councils planning
scheme policies.
Wastewater minimisation strategies will be adopted to reduce the demand on Council’s existing
infrastructure,
Best practice and practical water quality improvement devices are proposed which include 55,000L
of rainwater harvesting, and a Bio-retention basin area of 95m 2,
Due to the site’s location adjacent to the point of discharge into Noosa River, no detention volume
is proposed.
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APPENDIX A – STORMWATER MANAGEMENT PLAN
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APPENDIX A — STORMWATER MANAGEMENT PLAN
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LEGEND
CONCEPT STORMWATER MANAGEMENT PLAN
EMP RE
Bundaberg Gladstone Sunshine Coast
9 Princess Street Bundaberg Qld 4 Goondoon Street Gladstone Qld 45 Brisbane Road Mooloolaba Qld
PO Box 2052 Bundaberg Qld 4670 PO Box 1743 Gladstone DC Qld 4680 PO Box 102 Mooloolaba Qld 4557
T: 07 4154 4894 F: 07 4154 4274 T: 07 4972 5387 T: 07 5477 6437 F: 07 5444 4216
E N G I N E E R I NG E: [email protected] E: [email protected] E: [email protected]
ACN 112761510 ABN 21112761510
Page 15
INSTALLATION MAINTENANCE 2. REMOVE COLLECTED SEDIMENT AND 4. GRADE THE AREA AND SMOOTH IT OUT
DISPOSE OF IN A SUITABLE MANNER IN PREPARATION FOR STABILISATION.
1. REFER TO APPROVED PLANS FOR 1. INSPECT THE LEVEL SPREADER AFTER THAT WILL NOT CAUSE AN EROSION OR
LOCATION, DIMENSIONS AND EVERY RAINFALL EVENT UNTIL POLLUTION HAZARD. 5. STABILISE THE AREA AS SPECIFIED ON
CONSTRUCTION DETAILS. IF THERE ARE VEGETATION IS ESTABLISHED. THE APPROVED PLAN.
QUESTIONS OR PROBLEMS WITH THE 3. REMOVE AND APPROPRIATELY
LOCATION, DIMENSIONS, OR METHOD OF 2. AFTER ESTABLISHMENT OF DISPOSE OF ANY EXPOSED GEOTEXTILE.
INSTALLATION CONTACT THE ENGINEER VEGETATION OVER THE LEVEL
OR RESPONSIBLE ON-SITE OFFICER FOR SPREADER, INSPECTIONS SHOULD BE
ASSISTANCE. MADE ON A REGULAR BASIS AND AFTER
RUNOFF-PRODUCING RAINFALL.
2. WHEREVER PRACTICAL, LOCATE THE
LEVEL SPREADER ON UNDISTURBED, 3. ENSURE THAT THERE IS NO SOIL
STABLE SOIL. EROSION AND THAT SEDIMENT
DEPOSITION IS NOT CAUSING THE
3. ENSURE FLOW DISCHARGING FROM CONCENTRATION OF FLOW.
THE LEVEL SPREADER WILL DISPERSE
ACROSS A PROPERLY STABILISED SLOPE 4. ENSURE THAT THERE IS NO SOIL
NOT EXCEEDING 10:1 (H:V) AND EROSION OR CHANNEL DAMAGE
SUFFICIENTLY EVEN IN GRADE ACROSS UPSTREAM OF THE LEVEL SPREADER,
THE SLOPE TO AVOID CONCENTRATING OR SOIL EROSION OR VEGETATION
THE OUTFLOW. DAMAGE DOWNSTREAM OF THE LEVEL
SPREADER.
4. THE OUTLET SILL OF THE SPREADER
SHOULD BE PROTECTED WITH EROSION 5. INVESTIGATE THE SOURCE OF ANY
CONTROL MATTING TO PREVENT EXCESSIVE SEDIMENTATION.
EROSION DURING THE ESTABLISHMENT
OF VEGETATION. THE MATTING SHOULD 6. MAINTAIN GRASS IN A HEALTH
(a) Typical layout of level spreader
BE A MINIMUM OF 1200mm WIDE CONDITION WITH NO LESS THAN 90%
EXTENDING AT LEAST 300mm UPSTREAM COVER UNLESS CURRENT WEATHER
OF THE EDGE OF THE OUTLET CREST CONDITIONS REQUIRE OTHERWISE.
AND BURIED AT LEAST 150mm IN A
VERTICAL TRENCH. THE DOWNSTREAM 7. GRASS HEIGHT SHOULD BE
EDGE SHOULD BE SECURELY HELD IN MAINTAINED AT A MINIMUM 50mm BLADE
PLACE WITH CLOSELY SPACED LENGTH WITHIN THE LEVEL SPREADER
HEAVY-DUTY WIRE STAPLES AT LEAST AND DOWNSTREAM DISCHARGE AREA,
150mm LONG. AND A MAXIMUM BLADE LENGTH NO
GREATER THAN ADJACENT GRASSES.
5. ENSURE THAT THE OUTLET SILL
(CREST) IS LEVEL FOR THE SPECIFIED REMOVAL
LENGTH.
1. TEMPORARY LEVEL SPREADERS
6. IMMEDIATELY AFTER CONSTRUCTION, SHOULD BE DECOMMISSIONED ONLY (b) Typical profile of the the outlet weir
TURF, OR SEED AND MULCH WHERE AFTER AN ALTERNATIVE STABLE OUTLET
APPROPRIATE, THE LEVEL SPREADER. IS OPERATIONAL, OR WHEN THE INFLOW
CHANNEL IS DECOMMISSIONED.
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APPENDIX B – STORMWATER QUALITY MUSIC MODELLING
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APPENDIX B —- STORMWATER QUALITY MUSIC MODELLING
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Figure B.1 – MUSIC Model Node Layout
Figure B.2 – MUSIC Model Treatment Train Effectiveness
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Figure B.3 – MUSIC Model ‘Bio-retention’ Node
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Figure B.3 — MUSIC Model ‘Bio-retention’ Node
A : — | |
| Properties of BIO A [= | | Lf (entiom]
Location * Products >>
(Inlet Properties ;— Lining Properties
Low Flow By-pass (cubic metres per sec) 0.000 Is Base Lined? Yes [| No
igh Fi bic metres 100.000
High Flow By-pass (cubic metres per sec) — Vegetation Proper
[oe coats © Vegetated with Effective Nutrient Removal Plants
Extended Detention Depth (metres) 0.30
Surface Area (square metres) 105.00 © Vegetated with Ineffective Nutrient Removal Plants
| Filter and Media Properties © Unvegetated
Filter Area (square metres) 95.00
Unlined Fier Media Perimeter (metres) 38.00 pe eoeates
Overflow Weir Width (metres) 2.40
Saturated Hydraulic Conductivity (mm/hour) 180.00
Fiter Depth (metres) 0.40 Underdrain Present? Yes [F] No
TN Content of Fitter Media (mg/kg) 400 Submerged Zone With Carbon Present? © Yes No
-| Orthophosphate Content of Filter Media (mg/kg) 50.0 a 0.00
| Depth 3,00
\~ Infiltration Properties
Exfitration Rate (mm/h) D0 | Fluxes... | | Notes... | | More |
| %concet || <P Back || WV Bish |
a eer mes seo eons sjmnfemspomy
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Figure B.4 – MUSIC Model ‘Rainwater Harvesting’ Node
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}—-+---->+-+--_—_—_—- ——1—..
Properties of Rainwater Tank [ la a)
Location | 5 Produets >>
;— Inlet Properties
Low Flow By-pass (cubic metres per sec) 0.000000
High Flow By-pass (cubic metres per sec) 100.000000
-— Individual Tank Properties
[=| Number of Tanks 1
‘Total Tank Properties
;~ Storage Properties
i Volume below overflow pipe (kL) 44.00
Depth above overflow (metres) 0.20
Surface Area (square metres) 275
Initial Volume (kL) 44.00
(Outlet Properties
Overflow Pipe Diameter (mm) 298
l [-) Use Custom Outflow and Storage Relationship
i | | Define Custom Outflow and Storage | Noi
| XK cancer || <r Back || A Bish |
SS
Figure B.4 — MUSIC Model ‘Rainwater Harvesting’ Node