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Hydraulic Assessment_compressed
CIVIL ENGINEERING PROJECT MANAGEMENT
SEDIMENT AND EROSION CONTROL
HYDRAULIC IMPACT ASSESSMENT
at 332 Eastern Branch Road, KIN KIN
for QRE Constructions
DATE: 22.03.23 REF: 304-001-01
ATT: Development Officer EMAIL: [email protected]
Noosa Council
REV: A
2261 david low way, peregian beach, qld 4573 acn: 626 671 092 [email protected]
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Page 2
CONTENTS PAGE
Topography ............................................................................................................... 11
Hydraulic Roughness Coefficients.............................................................................. 11
Boundary Conditions and 1d infrastructures ............................................................. 11
Base case and Post Development hydraulic model results........................................ 12
Flood Extents ............................................................................................................. 13
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LIST OF FIGURES
Figure 1 - Locality Plan Source: Queensland Globe ............................................................................................. 5
Figure 2 – Existing Waterways Source: Noosa Council ........................................................................................ 6
Figure 3 – Existing Flood Risk Source: Noosa Council .......................................................................................... 7
Figure 4 – Proposed Nature Based Tourism Layout............................................................................................. 8
Figure 5 – Point inspection location................................................................................................................... 12
LIST OF TABLES
Table 1 – Peak Discharge at Culvert Crossing .................................................................................................... 13
Table 2 –Culvert Crossing Capacity .................................................................................................................... 13
Table 3 - General Construction Pollutants ......................................................................................................... 14
LIST OF APPENDICES
Appendix A Development layout
Appendix B WBNM Catchment Plan
Appendix C Tuflow Model Extent
Appendix D Pre-Development Flood Maps
Appendix E Post-Development Flood Maps
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INTRODUCTION
Bax Engineering has been commissioned by QRE Constructions to provide a Hydraulic Impact Assessment for
the Proposed Nature Based Tourism application at 322 Eastern Branch Road , Kin Kin Queensland.
The existing site covers a site area of 0.75ha and is located in 332 Eastern Branch Road , Kin Kin. The proposed
development consists of an access road and four (4) Glamping Tent/Cabin style accommodation units to be
constructed around the property.
This report has been developed to address the hydraulic impact assessment and stormwater management.
The report investigates the flood constraints and details in relation to water levels and flood depths across the
site, the management of stormwater during the operational phase of the project as well as emergency access
requirements during major storm events.
This HIA and SMP has been prepared in accordance with:
• Noosa Council 9.4.8 Water Quality and Drainage Code,
• The Queensland Urban Drainage Manual (QUDM), and
• Australian Rainfall and Runoff (2019)
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THE SITE AND ITS CONTEXT
SITE LOCATION
The site is formally described as Lot 218 on MCH186 and is located at 332 Eastern Branch Road in Kin Kin. The
site covers an area of 19.65ha and is covered by grass with heavy vegetation along the creek and throughout
the site. The site is zoned rural under the Noosa Plan (2020).
Figure 1 presents the site and its surroundings.
Figure 1 - Locality Plan Source: Queensland Globe
SITE CHARACTERISTICS
The total area of the subject lot is 19.65ha with the elevation range between 175m AHD in the south west to
80.0m AHD towards the south east boundary. Based on the provided survey and aerial information, any
stormwater runoff from the site overland flows to the existing creek systems that runs through the property.
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Several existing culvert crossings are noted throughout the property to enable vehicle access across these
waterways.
The defined drainage paths over the property Figure 2 and consist of both ephemeral and constantly running
waterways. It is noted that the waterway crosses the Eastern Branch Road in numerous locations to the north
and south of the property and is prone to flooding during prolonged rain events (Refer Figure 3). During such
times, the risk of temporary isolation to residents living in these surrounds is well recognised.
Twenty-four external upstream catchments to the south east of the site drain to the watercourse as overland
flow. These catchments are identified in Appendix A (Project: BAX22100 Drawing: C01)
Figure 2 – Existing Waterways Source: Noosa Council
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Figure 3 – Existing Flood Risk Source: Noosa Council
EXISTING VEGETATION AND USE
The project site is covered by grass with heavy vegetation along the creek and throughout the site. Several
cleared areas with long grass are scattered throughout the property along with vehicle tracks access to each
of these areas. Cattel yards are present on the property and an existing residential dwelling is located in the
north at an elevation of approximately 98m AHD. A non-habitable shed is located to the south of the dwelling
at approximately 86m AHD. Both structures are connected to the Eastern Branch Road by a gravel access road.
This road traverses the waterway via an existing concrete culvert crossing.
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PROPOSED DEVELOPMENT
The proposed development will consist of 4 glamping style tents/cabins with a driveway connection to each
from the main property entrance. The cabins will be located in the existing cleared areas on the property and
linked via a single access driveway. The existing concrete culvert crossings over the creek will also be utilised
to limit disturbance to the riparian area.
Each cabin will be connected to a rainwater harvesting tank for water re-use and the tanks will discharge via a
level spreader to the surrounding grassed area and discharge as sheet flow to the creek. This system will be
clear of the wastewater effluent disposal system (refer Ground Drill Effluent Disposal Report 22/388 dated
11.11.22).
The proposed layout has been designed to provide privacy for each user while minimising the environmental
footprint by utilising existing cleared areas and vehicle access locations across the waterways. The proposed
layout is shown in Figure 4 and a detailed concept of the access driveways and unit localities are provided in
the civil plans prepared by BAX Engineering (Ref: 304-001) in Appendix B.
Figure 4 – Proposed Nature Based Tourism Layout
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PROPOSED DRAINAGE CONCEPT
It is proposed that the runoff from the cabins be captured for reuse and diverted to a proposed rainwater tank
located adjacent to each cabin. In accordance with Council Planning Scheme Policy for Development Works,
a development type MCU for purposes other than industrial use and for lot sizes greater than 2500m 2 and
with a fraction impervious of less than 25% will require vegetated buffers to waterways and drainage lines.
It is noted on the proposed layout that large open zones allow a natural buffer from each cabin to the creek
line. This buffer along with the proposed rainwater tanks would deem to comply with the stormwater quality
requirements of the Noosa Council.
RAINFALL DATA
Rainfall intensity data has been obtained from the Australian Bureau of Meteorology’s 2016 Design IFD Rainfall
System. The IFD data and average rainfall intensities used in this report are in accordance with the procedures
outlined in Geosciences Australia, Australian Rainfall and Runoff 2019.
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DATA
Data which has been sourced or provided, in order to prepare this report for the site, was gathered from the
following sources:
• Proposed site layout provided by BAX Engineering civil plans, (Ref: 304-001);
• LIDAR data for the subject site sourced from Australian Government Elevation and Depth
Foundation Spatial Data (ELVIS), Date Source: 2015, DEM Data;
• Rainfall and Meteorological 2019 IFD Data by the Australian Bureau of Meteorology;
• Information Extracted from Noosa Council Interactive Mapping;
• Aerial Imagery by Nearmap.
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HYDRAULIC MODELLING
Based on Council’s flood overlay mapping, the project site is affected by flood from the eastern Branch of Kin
Kin Creek which runs through the property. Overland flow modelling, has been undertaken for the site and
surrounding area under the existing conditions to establish the level of inundation immunity for the
development. Overland flow modelling was conducted for the 1%, 10% and the 63% AEP design flood events.
The modelling was completed using the TUFLOW software 2020-10-AD package and LiDAR data sourced from
the Department of Natural Resources and Mines. Details on the development of the model and discussion of
the results are provided herein.
BASE CASE MODEL SETUP
Topography
A Digital Terrain Model (DTM) was created for the study area using 1m resolution LiDAR supplied by the
Department of Natural Resources and Mines in conjunction with detailed site survey.
Hydraulic Roughness Coefficients
Different Manning’s coefficients (n) have been applied to reflect the various land uses within the catchment.
This was achieved by defining polygons for the various land uses and assigning the relevant “n” value. The
study area was delineated based on the following land uses:
• Urban Area (default) n = 0.06;
• Road/Carpark n = 0.02;
• Light Grass n = 0.035;
• Dense Woodlands n = 0.1;
• Buildings and Shed n = 1;
• Creeks/Waterway n = 0.07;
Boundary Conditions and 1d infrastructures
Inflows were undertaken and TUFLOW’s automatic HQ relation was adopted at Downstream boundary and
existing culverts’ details were indicated in the Tuflow model key
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HYDRAULIC MODELLING RESULT
Base case and Post Development hydraulic model results
2D Flood mapping has been conducted for peak flood levels, velocity, depth and flood level impact for the 1%,
10% and 63.2% AEP for the Base Case and Post development scenarios and are presented in the appendices
as follows:
• Appendix C Base Case Flood Maps; and
• Appendix D Post Development Flood Maps;
Inspection locations have been identified at the culvert crossing to assess the flooding characteristics of the
crossings. These inspection points are shown in Figure 5. The peak discharge levels for the simulated design
storm events in the pre-development scenario are presented in Table 4. These include the Q100, Q10 and the
Q2 events whereby vehicle access should be achievable.
Figure 5 – Point inspection location
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Table 1 – Peak Discharge at Culvert Crossing
Location 1% AEP (m³/s) 10% AEP (m³/s) 50% AEP (m³/s)
3 x 600 RCP
60.0 32.1 16.3
(Existing Driveway)
3 x 900x600 RCBC 51.9 32.7 17.3
1500 x 900 RCBC 8.2 2.6 0.2
Table 2 –Culvert Crossing Capacity
Pipe Capacity
Location 1% AEP (m³/s) 10% AEP (m³/s) 50% AEP (m³/s)
(m³/s)
3 x 600 RCP
(Existing
4.119 60.0 32.1 16.3
Driveway)
at 5% grade
3 x 900x600 RCBC
6.882 51.9 32.7 17.3
at 3% grade
1500 x 900 RCBC
9.967 8.2 2.6 0.2
at 5% grade
As demonstrated in Table 2, the existing driveway location to the dwelling (3 x 600 RCP) and the crossing to
the proposed units would be inaccessible during the design storm events. However, the existing culvert (1500
x 900 RCBC) linking the existing dwelling/managers residence to the cabin locations is immune to flooding for
each of the design events. Considering the flooding which would be occurring external to the site - along the
Eastern Branch Road - and would restrict access to the property during rain events, the only consideration
should be for clients who are already at the accommodation and are obliged to seek refuge.
It could therefore be considered the location of the existing dwelling/managers residence at a much higher
elevation would provide suitable protection during such times until water levels resided.
Flood Extents
The flood extents for each storm event have been modelled and shown in Appendix D. The locations of each
of the proposed cabins are immune from flooding for all the design events. Though, it is noted that the most
eastern cabin would likely become isolated – albeit intermittently - during the designed storm events.
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STORMWATER QUALITY MANAGEMENT
In accordance with Council Planning Scheme Policy for Development Works, a development type MCU for
purposes other than industrial use and for lot sizes greater than 2500m2 and with a fraction impervious of less
than 25% will require vegetated buffers to waterways and drainage lines.
CONSTRUCTION PHASE
The design milestones for water quality during the construction phase of the development will be in
accordance with SPP Code: Water Quality. The design objectives will be achieved using approved Sediment
and Erosion Control measures.
General pollutants generated during construction are listed in Table 3 below.
Table 3 - General Construction Pollutants
Pollutant Potential Source Priority
Paper, construction packaging, food packaging, cement bags,
Litter High
off cuts
Unprotected exposed soils and stockpiles during earthworks
Sediment High
and building works
Fuel and oil spills, leaks from construction equipment and
Hydrocarbons High
temporary car park areas
Cement slurry, asphalt primer, solvents, cleaning agents,
Toxic Materials Medium
wash waters (e.g., From tile works)
Alkaline
Cement slurry and wash waters High
Substances
Below are the characteristic treatment measures that will be implemented prior to any construction works.
Detailed Sediment and Erosion control measures and drawings are included as part of an operational works
application.
• Sensible site planning
• Stabilized site entry / exit point
• Minimization of site disturbance and duration of disturbance
• Implementation sediment control along the lower edge of the site
• Appropriate location and protection of stockpiles
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• Early connection of roof water downpipes
• Compaction of backfilled trenches
• Revegetation and stabilization of the site
OPERATIONAL PHASE
As demonstrated on the proposed layout, large open zones allow a natural buffer from each cabin to the creek
line. This buffer along with the proposed rainwater tanks would deem to comply with the stormwater quality
requirements of the Noosa Council.
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CONCLUSION
The pre and post development scenario for the subject and the external catchment hydrology has been
reviewed to ensure safe access can be achieved or refuge sought during flood events. Stormwater quantity
and quality from each of the proposed cabin locations has also been considered.
The following conclusions have been made:
• based on the proposed locations of the cabins, the areas proposed appear to be free of flood during
the modelled storm events.
• Access to the cabins would be restricted during the design storm events modelled. Nonetheless so
would access to the property based on the unpassable creek crossings on Eastern Branch Road.
Therefore, access from the cabins to a point of refuge has been considered and can be achieved. This
point of refuge would be the existing dwelling/managers residence at a higher elevation.
• Stormwater quality treatment can be achieved through rainwater harvesting tanks and buffer areas.
• The environmental footprint for the cabins would be minimal based on the areas already cleared and
the tracks and culverts already in place.
In summary, the proposed cabin locations on the subject site will result in non-actionable nuisance of
stormwater runoff, be free of flooding and have safe refuge opportunities should it be faced with unpredicted
intermittent weather.
Yours Faithfully,
GLENN AINSWORTH
MIEAust CPEng NER RPEQ CPESC
BAX ENGINEERING PTY. LTD.
Ph: 0407 021 300
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REFERENCES
Civil Design
Prepared by Bax Engineering (Document No: 304-001-001 to 800) dated 25.11.22
Noosa Council – Relevant Codes and Standards
Part 9 Development Code
9.4.8 Water Quality and Drainage Code
Noosa Council – Flood Hazard Mapping
Queensland Globe – Site Mapping
https://qldglobe.information.qld.gov.au/
The Queensland Urban Drainage Manual (QUDM),
Australian Rainfall and Runoff (2019)
MUSIC modelling guidelines (Water by Design, 2010).
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APPENDIX A
Development Layout
https://www.dropbox.com/s/g7j0l9rofobnb32/Appendix%20A.pdf?dl=0
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APPENDIX B WBNM Catchment Plan
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Page 21
Legend
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Coordinate System: GDA 94/MGA Zone 56 Figure: Internal Catchment Plan
Page 22
APPENDIX C Tuflow Model Extent
Page 23
3x600x900 RCBC
1500x900 RCBC
3x600 RCP
Legend
Existing Culvert
Existing Track
Project Site
Local inflow
Tuflow Model Extent
Rev. Date Project: Residential Development - 332 Eastern Branch Road, Date
Feb 2023
Kin Kin
Project #
Client: QRE Construction BAX22100
1:7,000 (A3)
Drawing C02
Coordinate System: GDA 94/MGA Zone 56 Figure: Tuflow Model Configuration
A 10.02.23
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APPENDIX D
Pre Development Flood Maps
https://www.dropbox.com/s/g7j0l9rofobnb32/Appendix%20A.pdf?dl=0
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APPENDIX E
Post Development Flood Maps
https://www.dropbox.com/s/g7j0l9rofobnb32/Appendix%20A.pdf?dl=0