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Stormwater Mgmt Plan
SITE BASED STORMWATER MANAGEMENT PLAN For Dr. Drew McMenamin Proposed Medical Centre Development at 45 Maple Street, Cooroy Job Ref: SC- 8407 March 2020
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SC-8407 – 45 Maple Street, Cooroy ii
AUTHORSHIP INFORMATION
REPORT TITLE Site Based Stormwater Management Plan
Affected
Properties
Street Address 45 Maple Street, Cooroy
RP Description Lot 15 C5605
Prepared For Dr. Drew McMenamin
Report Status For DA Approval
Prepared By
Name Aaron Petersen
Qualifications Undergraduate Civil Engineer
Phone Number 07 5477 6437
Reviewed By
Name Sean Dwyer
Qualifications BE (Civil), CPEng, RPEQ 17012
Phone Number 07 5477 6437
Approved By
Name Troy Paulsen
Qualifications BE (Civil), CPEng, RPEQ 6990
Phone Number 07 5477 6437
REVISION DATE Reviewed/ Approval
A 19.03.20
B 24.03.20
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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SC-8407 – 45 Maple Street, Cooroy iii
TABLE OF CONTENTS
1.0 Introduction ................................................................................................................. 1
1.1 Background ...............................................................................................................1
1.2 Scope ........................................................................................................................1
1.3 Existing Topography .................................................................................................1
1.4 Proposed Development ............................................................................................1
2.0 Existing Drainage Regime .......................................................................................... 3
2.1 Subject Site ...............................................................................................................3
3.0 Stormwater Quality Management .............................................................................. 4
3.1 Background ...............................................................................................................4
3.2 Construction Phase ..................................................................................................4
3.3 Operational Phase ....................................................................................................6
3.3.1 Water Quality Objectives ......................................................................................6
4.0 Stormwater Quantity Management ............................................................................ 7
4.1 Background ..........................................................................................................7
4.2 Methodology .........................................................................................................7
4.3.2 Catchment Areas ..................................................................................................8
4.3.3 Roughness Coefficients .......................................................................................8
4.3.4 Storm Events ........................................................................................................8
4.3.5 Outlet Condition ....................................................................................................9
4.3.6 On-Site Detention .................................................................................................9
4.4 Modelling Results ...................................................................................................10
5.0 Flood Hazard Overlay and External Catchment ..................................................... 11
6.0 Conclusions ............................................................................................................... 11
APPENDIX A – CONCEPT STORMWATER MANAGEMENT PLAN AND ........................... 12
DETAIL & CONTOUR SURVEY ............................................................................................. 12
APPENDIX B – XP STORM MODELLING RESULTS ............................................................ 13
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SC-8407 – 45 Maple Street, Cooroy 1
1.0 Introduction
1.1 Background
This report is to accompany and be considered part of an application to Noosa Shire Council to gain approvals
for a proposed medical centre development at 45 Maple Street, Cooroy.
1.2 Scope
Empire Engineering Pty Ltd was commissioned by Dr. Drew McMenamin to develop a Site Based Stormwater
Management Plan (SBSWMP) 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 engineering design and outlines the proposed measures to be adopted in
relation to stormwater quality and quantity management for the subject site and the proposed development.
1.3 Existing Topography
2
The subject site has a total area of 2,252m , is fronting Maple Street to the west and bounded by existing
commercial lots to the north-east and existing residential allotments to the remaining boundaries. The subject
site is currently occupied by a large residential dwelling, refer Figure 1.1.
The average site elevations vary from RL122.50 on the Western boundary, to RL115.00 on the Eastern
boundary with an average slope of approximately 8%.
1.4 Proposed Development
Schematic architectural drawings prepared by Blackburne Jackson depict the proposed medical centre.
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SC-8407 – 45 Maple Street, Cooroy 2
Subject Site:
N
Figure 1.1 - Subject Site
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SC-8407 — 45 Maple Street, Cooroy 2
Figure 1.1 - Subject Site
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Engineering
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SC-8407 – 45 Maple Street, Cooroy 3
2.0 Existing Drainage Regime
2.1 Subject Site
Stormwater currently sheet flows across the subject site and the ‘Balance Lot’ towards Myall Street road
reserve to the east. Then travel’s south via kerb and channel towards two kerb inlets ‘KI 1 & 2’ (Refer
Figure 2.1). The existing underground drainage network conveys south along the western side of Myall
Street. Kerb inlets (KI 1 & 2) drain to an existing 450mm dia network which outlets to an existing drainage
easement (DEMT) on the eastern side of Myall Street.
Subject Site
N
Balance Lot
KI 1 & 2
DEMT
Figure 2.1 - Existing Drainage Regime
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SC-8407 – 45 Maple Street, Cooroy 4
3.0 Stormwater Quality Management
3.1 Background
A requirement of the subject site 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 ESC 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.
Table 3.2 illustrates the State Planning Policy objectives for construction phase stormwater quality
that the erosion and sediment control plan to be submitted with the operational works approval is
required to achieve.
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SC-8407 – 45 Maple Street, Cooroy 5
Issue Design objectives
Drainage Temporary drainage 1. Design life and design storm for temporary drainage works:
control works Disturbed area open for <12 months—1 in 2-year ARI event
Disturbed area open for 12–24 months—1 in 5-year ARI event
Disturbed area open for > 24 months—1 in 10-year ARI event
2. Design capacity excludes minimum 150 mm freeboard
3. Temporary culvert crossing—minimum 1 in 1-year ARI hydraulic
capacity
Erosion Erosion control 1. Minimise exposure of disturbed soils at any time
control measures 2. Divert water run-off from undisturbed areas around disturbed
areas
3. Determine the erosion risk rating using local rainfall erosivity,
rainfall depth, soil-loss rate or other acceptable methods
4. Implement erosion control methods corresponding to identified
erosion risk rating
Sediment Sediment control 1. Determine appropriate sediment control measures using:
control measures Potential soil loss rate, or
Monthly erosivity, or
Average monthly rainfall
Design storm for 2. Collect and drain stormwater from disturbed soils to sediment
sediment control basin for design storm event:
basins Design storm for sediment basin sizing is 80th% five-day event
or similar
3. Site discharge during sediment basin dewatering:
Sediment basin TSS < 50 mg/L TSS, and
dewatering Turbidity not >10% receiving waters turbidity, and
pH 6.5–8.5
Water Litter and other 1. Avoid wind-blown litter; remove gross pollutants
quality waste, hydrocarbons 2. Ensure there is no visible oil or grease sheen on released waters
and other 3. Dispose of waste containing contaminants at authorised facilities
contaminants
Waterway Changes to the For peak flow for the 1-year and 100-year ARI event, use constructed
stability and natural waterway sediment basins to attenuate the discharge rate of stormwater from the
flood flow hydraulics and site
management hydrology
Table 3.2 - Construction Phase Stormwater Quality Objectives
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SC-8407 – 45 Maple Street, Cooroy 6
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 and vegetation
Coarse sediment
To target these potential pollutants coarse sediment traps or GPT baskets are proposed to be incorporated
within the drainage within trafficable pavement areas.
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) Jul 2017. As the development proposal involves a material change of use for
urban purpose that involves premises of less than 2500 square metres, the development is exempt from
demonstrating WSUD load reductions.
Noosa Councils Planning Scheme Policy, ‘Division 20’ Water Sensitive Design Code requires the capture
and utilising of run-off from appropriate areas on-site. Accordingly, 60kL of harvesting and reuse is
proposed to be available for all external uses including gardening, irrigation, ponds and outdoor cleaning,
to satisfy specific outcome O2, Table 14-61 to this code.
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SC-8407 – 45 Maple Street, Cooroy 7 4.0 Stormwater Quantity Management 4.1 Background The subject site has an existing fraction impervious of 30%. The proposed works will increase this fraction impervious to approximately 80%. The proposed Medical Centre will subsequently require on-site detention to ensure non-worsening to the downstream drainage infrastructure. In preventing nuisance to the downstream Balance Lot, a formal inter-allotment drainage system is proposed in accordance with QUDM. The software package XP-STORM was used to model the site and calculate an on-site detention volume as described in the following sections. 4.2 Methodology XP-STORM V2017.2.2 has been used to model the site in its current and post-developed state. The modelling has been undertaken to determine detail design parameters of on-site detention to replicate pre- development peak flow rates. As the development falls within the ‘Commercial’ development category (QUDM), the (10% AEP) storm event was adopted for sizing the minor design drainage system. Events ranging up to and including the 1% AEP storm event were analysed to compare pre/post development discharges ensuring ‘non-worsening’. The development modelling and analysis undertaken was based on the information provided by the detailed site survey and preliminary architectural layouts.
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SC-8407 – 45 Maple Street, Cooroy 8
4.3.2 Catchment Areas
The subject site has been modelled in its existing pre-development and proposed post-development states
with the catchment areas illustrated in Tables 4.1 & 4.2. In its pre-development state the subject
catchments were each modelled as one hydrologic node to replicate the existing drainage situation for the
lot. XP-STORM model layouts and outputs are included in Appendix B of this report.
Catchment Description % Impervious Area (Ha)
Roof 100 0.068
‘A’
Landscape 0 0.244
Table 4.1 - Pre Development Node Sub-Catchment Areas
Catchment Description % Impervious Area (Ha)
Roof 100 0.106
‘B’ Carpark/hardstand areas 100 0.180
Landscape 0 0.045
Roof 100 0.016
‘C’
Landscape 0 0.034
Roof 100 0.022
‘D’
Landscape 0 0.077
Table 4.2 - Post Development Sub–Catchment Areas
4.3.3 Roughness Coefficients
The conduits and links used within the model are based on the ultimate design scenario for the internal
roadways and overland flow paths. Mannings “n” roughness coefficient values are specified as 0.014 for
RCP pipes and 0.011 for uPVC pipes.
For overland flow within the sub-catchment areas a Mannings “n” value of 0.014 for concrete areas and
0.025 for vegetated areas was adopted.
4.3.4 Storm Events
Storm patterns were setup using Australian Rainfall and Runoff (ARR 2016) storm patterns with intensity
frequency duration data taken for the local area. Storm durations of 10, 15, 20, 25, 30, 45, 60, 90, 120 and
180 minutes were investigated for the pre and post developed scenarios.
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SC-8407 – 45 Maple Street, Cooroy 9
4.3.5 Outlet Condition
The subject site is not impacted by regional flooding or tidal backwater.
4.3.6 On-Site Detention
It is calculated from the development site plan that the proposed development will increase impervious
areas on the site. The proposed increase in impervious areas has the potential to increase peak flow rates
to the existing drainage system. To mitigate potential increases in flow rates it is planned to detain
stormwater flows on-site and discharge at a mitigated rate to the existing stormwater infrastructure system.
Mitigation of flow is provided by the following volumes:
Catchment A – Minimum 60kL of on-site detention volume.
A concept drainage layout plan has been included as Appendix A of this report.
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SC-8407 – 45 Maple Street, Cooroy 10
4.4 Modelling Results
A node layout plan is included in Appendix B of this report and the resultant peak flow rates are displayed
in Table 4.3 & 4.4.
3
Peak Flow (m /s)
AEP (%)
Pre Development
50 (Q2yr) 0.093 (30min_1)
20 (Q5yr) 0.137 (20min_10)
10 (Q10yr) 0.166 (30min_3)
5 (Q20yr) 0.194 (30min_3)
2 (Q50yr) 0.222 (15min_8)
1 (Q100yr) 0.245 (15min_8)
Table 4.3 – Pre-Development Peak Flow Rate Results
3
Peak Flow (m /s)
AEP (%)
Post Development
50 (Q2yr) 0.082 (20min_10)
20 (Q5yr) 0.120 (10min_5)
10 (Q10yr) 0.132 (30min_3)
5 (Q20yr) 0.151 (30min_3)
2 (Q50yr) 0.161 (15min_8)
1 (Q100yr) 0.175 (15min_8)
Table 4.4 – Post-Development (mitigated) Peak Flow Rate Results
As can be seen in Tables 4.3 & 4.4 the post-development peak flow rates to the existing drainage system
compare well to that of the existing pre-development site discharges. This is due to the large volumes of
on-site detention proposed to be included as part of the development.
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SC-8407 – 45 Maple Street, Cooroy 11
5.0 Flood Hazard Overlay and External Catchment
The subject site is not affected by regional flooding impacts.
6.0 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 State and Council planning scheme policies.
Rainwater harvesting and re-use is adopted to reduce the demand on Council’s existing
infrastructure;
Best practice and practical water quality improvement methods;
60kL of peak flow mitigation volume is required of the development; and
Formalisation of drainage regimes in accordance with QUDM including inter-allotment drainage
and dedicated drainage easements.
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SC-8407 – 45 Maple Street, Cooroy 12
APPENDIX A – CONCEPT STORMWATER MANAGEMENT PLAN
AND
DETAIL & CONTOUR SURVEY
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LEGEND
MC
MC
MC
MC
MC
MC
Project North:
N
Scales:
0 2 4 6 8 10m 1:200 at A1
A
1:400 at A3
CONCEPT STORMWATER MANAGEMENT PLAN Status:
NOTES Client: GRAEME JONES Designed: SFD Drawn: TAK Title: Date: MARCH 2020 Scale: AS NOTED
Issue Amendment Date Dft 1. This is the property of the engineer, and may not be Sunshine Coast Office Bundaberg Office
A
B
FOR APPROVAL
FOR APPROVAL
19.03.20
24.03.20
TAK
TAK
used, copied, or reproduced wholly, or in part without the
express permission of the engineer. Infringement in any
L2, 13 Norval Court Maroochydore Q 4558
PO Box 102 Mooloolaba Q 4557
66A Barolin Street Bundaberg Q 4670
PO Box 2052 Bundaberg Q 4670
Project: PROPOSED MEDICAL CENTRE Approved: CONCEPT STORMWATER Job Ref No: Drawing No: Issue:
way may result in legal action. 45 MAPLE STREET, COOROY
2. Figured dimensions take precedence over scaled.
3. Verify all dimensions on site. ACN 112761510 ABN 21112761510
Engineering P: 07 5477 6437
E: [email protected]
P: 07 4154 4894
E: [email protected] MANAGEMENT PLAN SC-8407 C001 B
GAVIN EVANS / RPEQ: 8054
Page 17
PROPERTY DESCRIPTION NOTES NOTES
LOTS 15 & 18 on C5605 & (1) This plan was prepared for the purpose and exclusive use of (5) Spot heights and contours are representative of the
Dr DREW McMENAMIN and his other professional advisers and is topographical terrain at time of survey, 22/10/2019.
LOT 1 on RP99323 not to be used for any other purpose or by any other person or
LOCALITY of COOROY corporation. (6) Spot heights are not shown on this plan. Refer to the AutoCAD
JFP URBAN CONSULTANTS PTY LTD accepts no responsibility for drawing for all spot heights and codes in frozen layers: X-RL-T,
LOCAL GOVERNMENT: any loss or damage arising to any person or corporation who may X-CODE-T & X-NOTES-T.
NOOSA SHIRE COUNCIL use or rely on this plan in contravention of these terms.
(7) These notes form an integral part of this plan. If others use this
TOTAL AREA 2868m² (Deed) (2) The title boundaries shown on this plan were not marked at information, they should be advised of its purpose and limitations.
the time of survey and have been determined from recent
adjoining surveys. While the boundaries shown are a better (8) This plan may not be reproduced unless these notes are
approximation than the subject survey plans (dated 1909 & 1962), included.
an Identification Survey is required to accurately determine
boundary dimensions. 12d Project: S:\M2815\McMenamin - Cooroy\12D\contour survey
LM 221019\contour_survey_LM_221019.project
(3) " Dial Before You Dig " search has not been carried out, and
Position of Underground services and utilities not obtained. Contour Interval: 0.5m
(4) Prior to any demolition, excavation or construction on the site,
the relevant authority should be contacted for detailed locations
of all services.
LEGEND
BLOCK RETAINING WALL
TOP of BANK
BOTTOM of BANK/CHANGE GRADE
APPROXIMATE BUILDING
LOCATION FROM AERIAL PHOTOS
NORTH: SCALE: ISSUES: TITLE: DETAILS:
PROJECT: PLAN: ISSUE:
N SCALE: @ A3 1:300
BRISBANE - SUNSHINE COAST - CENTRAL QLD PLANNERS 0 2.5 5 7.5 10 12.5 15 17.5 20
CONTOUR SURVEY M2815 01 A
SCALE 1:300 at (A3) size SHEET:
URBAN DESIGNERS
SUNSHINE COAST
Tower 1, Level 2, 55 Plaza Parade,
Maroochydore, Qld 4558
SURVEYORS
THIS SCALE SHOWN IS ORIGINAL DRAWING SCALE - (A3 SIZE)
DO NOT SCALE FROM THIS DRAWING - USE ONLY DIMENSIONS PROVIDED - IF IN DOUBT PLEASE ENQUIRE
Dr DREW McMENAMIN 1 OF 1
FILE:
P 07 5450 3900 W www.jfp.com.au ENGINEERS
LANDSCAPE ARCHITECTS
SURVEYED LM CHECKED MC
HORIZONTAL DATUM:
RP867327 A ORIGINAL ISSUE 24-10-2019 SCP
9 MYALL STREET & 45 MAPLE STREET M2815-01A Contour.dwg
DATE:
C O N S U L T A N T S JFP URBAN CONSULTANTS PTY LTD ACN 050 414 045
INIT: COOROY
VERTICAL DATUM:
DRAWN SCP APPROVED MC PM54011_RL 114.880 AHD ISSUE: DETAILS: DATE: 24th October 2019
COPYRIGHT © 2018 JFP URBAN CONSULTANTS PTY LTD. THIS DOCUMENT MAY NOT BE COPIED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS IN PART OR IN WHOLE WITHOUT THE WRITTEN CONSENT OF JFP URBAN CONSULTANTS PTY LTD.
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APPENDIX B – XP STORM MODELLING RESULTS
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SC-8407 — 45 Maple Street, Cooroy 13
APPENDIX B — XP STORM MODELLING RESULTS
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Catchment A
Figure B.1 – XP-STORM Pre-Development Catchment Plan
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Figure B.2 – XP-STORM Pre-Development Peak Flow Hydrographs
Figure B.3 – XP-STORM Pre-Development Peak Flow Hydrograph (50% AEP)
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Figure B.4 – XP-STORM Pre-Development Peak Flow Hydrograph (20% AEP)
Figure B.5 – XP-STORM Pre-Development Peak Flow Hydrograph (10% AEP)
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Figure B.6 – XP-STORM Pre-Development Peak Flow Hydrograph (5% AEP)
Figure B.7 – XP-STORM Pre-Development Peak Flow Hydrograph (2% AEP)
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Figure B.8 – XP-STORM Pre-Development Peak Flow Hydrograph (1% AEP)
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Catchment C
Catchment D
Catchment B
Figure B.9 – XP-STORM Post-Development Catchment Plan
Figure B.10 – XP-STORM Post-Development Hydrograph Outlet
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Figure B.11 – XP-STORM Post-Development Peak Flow Hydrograph (50% AEP)
Figure B.12 – XP-STORM Post-Development Peak Flow Hydrograph (20% AEP)
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Figure B.13 – XP-STORM Post-Development Peak Flow Hydrograph (10% AEP)
Figure B.14 – XP-STORM Post-Development Peak Flow Hydrograph (5% AEP)
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Figure B.15 – XP-STORM Post-Development Peak Flow Hydrograph (2% AEP)
Figure B.16 – XP-STORM Post-Development Peak Flow Hydrograph (1% AEP)