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PA2906-Coastal Hazard Assessment-R3 · MCU21/0212
REPORT 66 Seaview Terrace, Sunshine Beach Coastal Hazards Assessment Client: Gavin & Catherine Deane (c\- Pivitol Planning) Reference: PA2906-RHD-ZZ-XX-RP-Z-0001 Status: S0/P01.01 Date: 03 June 2022
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HASKONINGDHV NEDERLAND B.V.
,
Industry & Buildings
Trade register number: 56515154
email E
royalhaskoningdhv.com W
Document title: 66 Seaview Terrace, Sunshine Beach
Document short title: 66 Seaview Terrace, Sunshine Beach
Reference: PA2906-RHD-ZZ-XX-RP-Z-0001
Status: P01.01/S0
Date: 03 June 2022
Project name: 66 Seaview Terrace, Sunshine Beach
Project number: PA2906
Classification
Internal use only
Unless otherwise agreed with the Client, no part of this document may be reproduced or made public or used for any
purpose other than that for which the document was produced. HaskoningDHV Nederland B.V. accepts no
responsibility or liability whatsoever for this document other than towards the Client.
Please note: this document contains personal data of employees of HaskoningDHV Nederland B.V.. Before
publication or any other way of disclosing, this report needs to be anonymized.
03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 i
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Internal use only Revision history Revision Date Description Prepared Checked Approved D1 15/10/2021 Final Draft P Prenzler D Messiter R1 28/10/2021 Final P Prenzler D Messiter N Lewis R2 12/04/2022 Final P Prenzler D Messiter N Lewis R3 3/06/2022 Final (minor correction Fig 19) P Prenzler D Messiter N Lewis 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 2
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Internal use only Contents 1 Introduction 5 2 Site Description 6 2.1 Development Proposal 6 2.2 Site Inspection 7 2.3 Geotechnical Investigations 7 2.4 Survey 7 3 Historical Aerial Photograph Analysis 8 3.1 Satellite Imagery 12 4 Queensland Planning Framework 16 4.1 Planning Act 2016 16 4.2 Coastal Management Mapping 16 5 Coastal Processes 19 5.1 Tides and Storm Tide 19 5.1.1 Astronomical Tides 19 5.1.2 Sea Level Rise 19 5.1.3 Storm Tide 20 5.2 Wave Climate 20 5.3 Sediment Transport 22 6 Erosion Prone Area 23 6.1 Erosion Prone Area Reassessment 23 6.1.1 Long-term Erosion (N x R) 24 6.1.2 Short-term Erosion (C) 24 6.1.3 Recession due to Sea Level Rise 29 6.1.4 Dune Scarp Component 30 6.1.5 Summary of the Erosion Prone Area Reassessment 30 7 Coastal Building Line 32 8 Conclusion 33 9 References 34 Table of Tables Table 1 Noosa Head Tidal Planes (Maritime Safety Queensland, 2021) 19 Table 2 Adopted Storm Tide Levels (excluding wave setup) for Sunshine Beach (Aurecon, 2013) 20 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 iii
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Internal use only Table 3 Summary of Long-Term Recession Results from BMT (2018) 24 Table 4 Design Storm Events for Short-term Beach Erosion Assessment 26 Table 5 Predicted Short-term Erosion - Sunshine Beach 28 Table 6 Summary of Shoreline Recession due to Sea Level Rise 29 Table 7 Reassessed Erosion Prone Area for 66 Seaview Terrace, Sunshine Beach 30 Table of Figures Figure 1 Site Location 6 Figure 2 1972 Aerial Photograph (qimagery.information.qld.gov.au) 8 Figure 3 1974 Aerial Photograph (qimagery.information.qld.gov.au) 9 Figure 4 1981 Aerial Photograph (qimagery.information.qld.gov.au) 9 Figure 5 1988 Aerial Photograph (qimagery.information.qld.gov.au) 10 Figure 6 1994 Aerial Photograph (qimagery.information.qld.gov.au) 10 Figure 7 1999 Aerial Photograph (qimagery.information.qld.gov.au) 11 Figure 8 2004 Aerial Photograph (qimagery.information.qld.gov.au) 11 Figure 9: DEA recession analysis near the site. 13 Figure 10 DEA Annual Coastlines near the site. 14 Figure 11: CoastSat shoreline position timeseries approximately 60m north of the site. 15 Figure 12 Coastal Management District (source: SARA DA Mapping System) 17 Figure 13 Erosion Prone Area (source: SARA DA Mapping System) 17 Figure 14 Coastal Building Line (source: SARA DA Mapping System) 18 Figure 15 Wave Rose for Sunshine Beach (BMT, 2013) 21 Figure 16 Offshore Significant Wave Height Design Curves (BMT, 2013) 21 Figure 17 Sketch of pre-storm and predicted post-storm profiles based on Vellinga (1983) 25 Figure 18 100-year ARI storm profile (Vellinga, 1983) at 66 Seaview Terrace for current climate 27 Figure 19 Extreme storm event profile (Vellinga, 1983) at 66 Seaview Terrace for current climate 28 Figure 20 Conceptualisation of recession due to sea level rise due to Bruun Rule (Bruun, 1962) 29 Figure 21 Extent of the reassessed erosion prone area 31 Appendices Appendix A: Development Proposal Appendix B: Erosion Prone Area Plans Appendix C: Site Survey by Minstaff Survey Pty Ltd 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 iv
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Internal use only 1 Introduction Royal HaskoningDHV (RHDHV) has been engaged by Gavin and Catherine Deane, the owners of 66 Seaview Terrace (Lot 69 on RP81810), Sunshine Beach to undertake a coastal hazards assessment in relation to the subject property. The subject site is currently vacant, and the owners intend to construct a three-level house. The site is subject to coastal planning constraints layers and this coastal hazard risk assessment is required to address the assessment requirements of Noosa Shire Council and the State Assessment Referral Agency. The assessment reported herein provides a site-specific assessment of erosion hazard risk, including a reassessment of the erosion prone area width and an assessment of the beach erosion likely to occur with an extreme storm event. Accordingly, it provides an estimate of erosion vulnerability along this section of beach and will be used to address the assessment criteria considered by Noosa Shire Council and the Queensland Government. It should be noted that that the erosion prone area reported is an estimate of erosion vulnerability and does not consider the likely planning response to beach erosion for previously developed coastal areas. Previous development applications for other properties in Seaview Terrace, Sunshine Beach had considered the extent of erosion likely to occur with an extreme storm event. These previous development applications were decided through a Planning and Environment Court ordered mediation processes between the applicants and Noosa Shire Council. For these previous development applications an extreme event consisting of a 500 year ARI storm tide level, sea level rise of 0.8 metres and a 100 year ARI significant wave height was agreed through mediation and adopted as the criteria for the design of the building foundations. The assessment in this report has adopted the same criteria as the assessments for the previous developments within Seaview Terrace, Sunshine Beach. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 5
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Internal use only 2 Site Description The site is a 574 square metre residential property located at 66 Seaview Terrace (Lot 69 on RP81810), Sunshine Beach, see Figure 1. The site slopes away from Seaview Terrace towards the dunes that adjoin Sunshine Beach with a change in elevation from Seaview Terrace to the rear property boundary of approximately 7 metres. The rear property boundary that adjoins the dune is elevated at approximately 28 metres above Australian Height Datum (AHD). Sunshine Beach is located south of Noosa Head and has an east-south-easterly aspect with exposure to waves from the north-east, east, and south-easterly sectors. The site is approximately 210 metres south of Noosa Headland which has a significant influence on coastal processes and sand transport along this section of coastline. A small ephemeral creek crosses the beach to the north of the site. This creek is observed in aerial photography to meander across the beach. Figure 1 Site Location 2.1 Development Proposal The subject property is currently vacant. It is proposed to construct a three-level house and a pool on the property. The lower level and pool are to be setback on the landward side of the coastal building line. The ground floor is proposed to be cantilevered seaward of the coastal building line such that the building’s foundations would be setback landward of the coastal building line. The architectural drawings of the proposed house and pool are presented in Appendix A. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 6
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Internal use only 2.2 Site Inspection A site inspection was undertaken by Paul Prenzler and Andrew Fielding on 23 September 2021 to observe the site conditions and undertake field measurements of the beach. The ‘seaward toe of the frontal dune’ was mapped using a handheld GPS to assist with determining the erosion prone area width at the site. The ‘seaward toe of the frontal dune’ was determined based on the guidance provided in the ‘Coastal Hazards Technical Guide’ (Department of Environment and Heritage Protection, 2013) and the notes of NOS3A dated 8 July 2015 prepared by the Department of Environment and Science (refer Appendix B). Figure 1 shows the ‘seaward toe of the frontal dune’ on Sunshine Beach near the subject site in 2019 and 2021. The distance from the rear property boundary of the site to the toe of the frontal dune approximately 90 metres. 2.3 Geotechnical Investigations The geotechnical conditions at the site have been investigated by Tectonic Geotechnical Pty Ltd. The scope of the geotechnical investigation includes the design of the house foundations to mitigate impacts on the structure from potential beach erosion. 2.4 Survey Survey of the site and adjoining beach system was undertaken by Minstaff Survey Pty Ltd on the 6th October 2021. The survey is presented in Appendix C. The survey has been supplemented with survey information from ETA 602 to describe the beach profile through the surf zone to the depth of closure. This is consistent with the approach adopted by BMT (2018). 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 7
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Internal use only 3 Historical Aerial Photograph Analysis Aerial photography has been reviewed to understand the historical extents of beach movement at the site. Figures 2 to 8 show the aerial photographs for 1972, 1974, 1981, 1988, 1994, 1999 and 2004 together with the toe of the frontal dune captured by hand-held GPS in 2019 and 2021. The beach was in an eroded state in 1971 and 1974, which was due to a high number of tropical cyclones impacting the south-east Queensland coastline during the late 1960’s and early 1970’s. The 1974 photograph shows the beach in its most eroded state in the photographic record and outcrops of indurated sand (i.e., coffee rock) can be seen adjacent to the dune vegetation. From the 1981 photograph onwards the beach is seen to be recovering and accreting to its current position show in Figure 1 (based on satellite imagery from 2021). There were 18 tropical cyclones within 200 kilometres of the site between 1960 and 1979, seven tropical cyclones between 1980 and 1999, and three tropical cyclones since 2000. The reduced number of tropical cyclones affecting the southeast Queensland region since 1980 is reflected in the beach recovery observed during this period. Figure 2 1972 Aerial Photograph (qimagery.information.qld.gov.au) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 8
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Internal use only Figure 3 1974 Aerial Photograph (qimagery.information.qld.gov.au) Figure 4 1981 Aerial Photograph (qimagery.information.qld.gov.au) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 9
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Internal use only Figure 5 1988 Aerial Photograph (qimagery.information.qld.gov.au) Figure 6 1994 Aerial Photograph (qimagery.information.qld.gov.au) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 10
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Internal use only Figure 7 1999 Aerial Photograph (qimagery.information.qld.gov.au) Figure 8 2004 Aerial Photograph (qimagery.information.qld.gov.au) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 11
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3.1 Satellite Imagery
Satellite imagery can be used to determine shoreline position and behaviour from 30+ years of satellite
imagery. Satellite platforms include Landsat 5 (1984 - 2013), 7 (1999 - present), 8 (2013 - present) and
Sentinel-2 (2015 - present), with pixel resolution ranging between 10m and 15m and image capture
varying from 5 to 16 days.
Two independent tools have been developed to analyse the satellite imagery, which are:
1. CoastSat a Python tool that enables extraction of shoreline position from individual satellite
images at any coastline worldwide using sub-pixel extraction methods (Vos et al., 2019a, 2019b).
While the horizontal errors for detected shoreline range have been reported to be between 7.3m
and 12.7m Root Mean Square Error (RMSE) considering individual images, the bias of the data is
much lower (Vos et al., 2019a). As such, the temporal resolution of the data means that signals
can be discerned at seasonal and greater timescales.
2. Digital Earth Australia (DEA) is a tool to accurately map the boundary between land and water
(the ‘waterline’) (Bishop-Taylor et al, 2019). The tool uses the same sub-pixel extraction method
as CoastSat. However, DEA combines aerials to provide a single, annualised shoreline position
and is therefore suited to determining long-term trends.
Outputs from both CoastSat and DEA are available online, with key outputs for the coastline adjacent to
the site are provided in Figure 9 to Figure 11.
Figure 9 from DEA indicates that the position of the shoreline in the immediate vicinity of the site has
prograded by approximately 0.5 metres annually (±0.3 metres at 95% confidence interval). However,
minimal progradation (less than ±0.1m/yr) is reported at transects nearby to the north and south. Further,
the location/s where accretion is reported (i.e. blue dots in Figure 9) generally coincides with the location
of drainage channels across the beach. The shoreline position from the DEA dataset in Figure 10
indicates that the beach has generally been stable from 1990 to present. At locations where progradation
has been reported in Figure 9, the shoreline was generally further landward in 1988 with rapid
progradation from 1988 to 1989. Given the progradation during this time was localised, it is inferred that
freshwater flows and/or rip heads caused localised erosion of the beach around 1988, which is otherwise
stable. The localised erosion at commencement of the reporting interval has resulted in the reported
accretion.
The CoastSat time series in Figure 11 indicates that the shoreline at this location was relative stable.
Figure 11 indicates the shoreline fluctuated by approximately ±30m from the mean shoreline position
annually, some of which may be due to the RSME of the dataset. However, it is likely that episodic
recession and progradation would occur due to annual beach rotation and storm events.
Care should be taken when analysing shoreline recession to ensure the data captures long term trends
rather than annual or interdecadal variability. Long-term shoreline recession is adopted as 0m/yr.
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Internal use only Figure 9: DEA recession analysis near the site. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 13
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Internal use only Figure 10 DEA Annual Coastlines near the site. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 14
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Internal use only Figure 11: CoastSat shoreline position timeseries approximately 60m north of the site. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 15
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4 Queensland Planning Framework
The planning framework in Queensland is supported by the Planning Act 2016 which outlines the plan-
making system that guides strategic planning and development assessment. In relation to coastal
development there are specific requirements that are discussed in the following sections.
4.1 Planning Act 2016
The Planning Act 2016 details the planning and development approval framework for Queensland. In
relation to this application, the proposed house footprint is a trigger to consider building works seaward of
a coastal building line.
The Planning Act 2016 includes provision for the State Development Assessment Provisions (SDAP) to
form the assessment criteria for development assessed by the Queensland Government. Performance
Outcome 6 of SDAP State Code 8 states, “In areas where a coastal building line is present, building work
is located landward of the coastal building line unless coastal protection work has been constructed to
protect the development”. This is the only performance outcome that relates to a Coastal Building Line.
4.2 Coastal Management Mapping
The Coastal Protection and Management Act 1995 provides for the declaration of erosion prone areas,
coastal management districts and coastal building lines, which are used as triggers for development
approvals under the Planning Act 2016.
The site is located within three coastal management mapping layers prepared by the Queensland
Government Department of Environment and Science. These mapping layers are:
• Coastal management district (see Figure 12);
• Coastal area - erosion prone area (see Figure 13); and
• Coastal building line (see Figure 14).
The State Planning Policy (dsdmipprd.blob.core.windows.net/general/spp-july-2017.pdf) requires local
governments, including Noosa Shire Council, to base their planning scheme mapping on the above
mapping. The specific details of the erosion prone area and coastal building line for this site will be further
discussed in Sections 6 and 7.
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Internal use only Figure 12 Coastal Management District (source: SARA DA Mapping System) Figure 13 Erosion Prone Area (source: SARA DA Mapping System) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 17
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Internal use only Figure 14 Coastal Building Line (source: SARA DA Mapping System) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 18
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5 Coastal Processes
The coastal processes of interest to this investigation are water levels (including sea level rise
predictions), wave conditions, and sediment transport processes.
5.1 Tides and Storm Tide
The water levels of interest for a reassessment of the erosion prone area include the astronomical tide,
storm tide and the predicted rise in mean sea level associated with climate change. The following
sections describe the water levels adopted for the assessment.
5.1.1 Astronomical Tides
Sunshine Beach adjacent to the site experiences semi-diurnal tides with a tidal range of 1.4 metres at
spring tides. Table 1 presents the published tidal planes for Noosa Head (Maritime Safety Queensland,
2021) which are considered consistent with conditions at Sunshine Beach due to the proximity.
Table 1 Noosa Head Tidal Planes (Maritime Safety Queensland, 2021)
Water Level Water Level
Tidal Plane
(m above LAT) (m AHD)
Highest Astronomical Tide 2.28 1.157
Mean High Water Spring 1.78 0.657
Mean High Water Neap 1.45 0.327
Mean Sea Level 1.06 -0.063
Mean Low Water Neap 0.71 -0.413
Mean Low Water Spring 0.38 -0.743
Lowest Astronomical Tide - -1.123
5.1.2 Sea Level Rise
The effects of climate change associated with emission of greenhouse gases has caused a rise in mean
sea level above pre-industrial levels, and sea levels are predicted to continue to rise into the future. The
Queensland Government has adopted a predicted sea level rise of 0.8 metres by the year 2100 above
present day mean sea level. It is noted that BMT (2018) adopted the following sea level rise allowances
(above present day mean sea level) as part of phase 3 of the Coastal Hazard Adaptation Strategy
(CHAS):
• 0.2 metres by 2040,
• 0.5 metres by 2070, and
• 0.8 metres by 2100.
The adopted sea level rise allowances are consistent with industry practice and will be used for this
assessment.
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5.1.3 Storm Tide
Storm tide is the total water level associated with the combination of the normal astronomical tide and the
tidal surge from a storm event (e.g., tropical cyclone). There have been several previous storm tide
studies undertaken for the Sunshine Coast with the most recent being the ‘Sunshine Coast Storm Tide
Study’ (Aurecon, 2013). The design storm tide levels determined by Aurecon (2013) for the 100, 500 and
1000-year ARI events are presented in Table 2.
Noosa Shire Council has undertaken a broad-scale reassessment of coastal hazards from Peregian
Beach to Teewah Beach as part of the ‘Noosa Shire Council Coastal Hazards Risk, Vulnerability and
Adaptation Assessment’ (BMT, 2018). The 100-year ARI storm tide level of 1.74m AHD was adopted by
BMT (2018) for the reassessment of the erosion prone area width at Sunshine Beach.
To address the SDAP (Performance Outcome 6 of State Code 8) outlined in Section 4.1 the vulnerability
of the proposed property and house to an extreme storm events has been considered and assessed. As
discussed in the introduction, a 500-year ARI storm tide level has been adopted for the extreme analysis
with an allowance for climate change induced sea level rise of 0.8 metres. The extreme event
assessment is discussed further in Section 6.1.2.
Table 2 Adopted Storm Tide Levels (excluding wave setup) for Sunshine Beach (Aurecon, 2013)
Current Climate
Return Period
Storm Tide Level
(years ARI)
(m AHD)
100 1.74
500 1.84
1000 1.89
5.2 Wave Climate
The wave climate at Sunshine Beach is influenced by both locally wind-generated sea and ocean swell.
Sea describes wind generated waves where wind energy is still being transferred to the ocean. Swell
describes wind generated waves that have travelled out of their generating area. Swell characteristically
exhibits smoother, more regular, and uniform crests and a longer period than wind waves. In open coastal
areas sea waves generated by local winds are often superimposed on swell waves.
The wave climate for Sunshine Beach has been previously reported by BMT (2013), ‘Coastal Processes
Study for the Sunshine Coast’ prepared for the Sunshine Coast Regional Council. BMT WBM (2013) has
shown the wave climate for Sunshine Beach is dominated by waves from the east-southeast direction
(refer Figure 15).
The design offshore significant wave heights for the Sunshine Coast have been previously published by
BMT (2013), refer Figure 16. For this assessment a 100-year ARI offshore significant wave height of 6.2
metres has been adopted to be consistent with the BMT (2013) assessment.
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Internal use only Figure 15 Wave Rose for Sunshine Beach (BMT, 2013) Figure 16 Offshore Significant Wave Height Design Curves (BMT, 2013) 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 21
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Internal use only 5.3 Sediment Transport Sand is transported over time in a net northerly direction along the Sunshine Coast driven by the prevailing south-easterly wave climate in a process known as littoral drift. The average longshore littoral transport rate at Sunshine Beach has previously been estimated at 23,300 cubic metres annually (BMT, 2013). Noosa Head at the northern end of Sunshine Beach is a control feature that influences sand transport processes. The net northerly littoral transport of sand along Sunshine Beach is interrupted by the headland which traps sand on the southern side (i.e., Sunshine Beach) until such time that the beach to the south is effectively “full” at which point some sediment bypassing of the headland will occur. Noosa Head also provides protection to Sunshine Beach from waves from the northeast quadrant that will be more prevalent during the summer cyclone season. It is also likely that Noosa Head would assist with post-storm event beach recovery of Sunshine Beach through the trapping of long-term net northerly littoral transport of sand and associated rebuilding of the beach system towards a beach full state. The location of the site relative to Noosa Heads and ongoing littoral transport process ensure that (in the absence of sea level rise) the foreshore at the site will fluctuate within a steady state envelope of positions; subject to short term storm erosion events, but long term always accretes towards a beach full state controlled by the headland. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 22
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6 Erosion Prone Area
The erosion prone area identifies land that may be vulnerable to coastal erosion or tidal inundation over a
100-year planning period and are declared under section 70 of the Coastal Protection and Management
Act 1995.
The ‘Coastal Hazards Technical Guide’ (Department of Environment and Heritage Protection, 2013)
provides guidance on the calculation of an erosion prone area. The erosion prone area width is based on
the following:
• short-term erosion from extreme storm events (e.g., a tropical cyclone);
• a dune scarp component to accommodate slumping of the erosion scarp following short-term
erosion;
• long-term erosion associated with a deficit in sediment supply;
• shoreline recession due to sea level rise; and
• a 40% safety factor.
The Erosion prone area is calculated using the following equation:
𝐸𝐸 = {(𝑁𝑁 × 𝑅𝑅) + 𝐶𝐶 + 𝑆𝑆} × (1 + 𝐹𝐹) + 𝐷𝐷 Equation 1
Where:
E= Erosion Prone Area (metres)
N= planning period (years)
R= rate of long-term erosion (metres/year)
C= short-term erosion from the design storm event (metres)
S= recession due to sea level rise (metres)
F= factor of safety (0.4)
D= Dune scarp component to allow for slumping of the erosion scarp (metres)
The calculation of the erosion prone area assumes:
• the beach and dune consist of unconsolidated loose sand with uniform physical characteristics;
• physical features (e.g., headland) do not influence sand movement;
• the duration of storm events is sufficient to allow for an equilibrium storm beach profile to develop;
and
• the long-term erosion trend is independent of recession due to sea level rise.
6.1 Erosion Prone Area Reassessment
The declared erosion prone area for the Noosa Shire Council area is provided on Department of
Environment and Science Plan Number NOS3A dated 8 July 2015 (refer Appendix B). This shows an
erosion prone area width for Sunshine Beach of 175 metres measured inland from the seaward toe of the
frontal dune.
Noosa Shire Council has completed a Coastal Hazard Adaptation Study (CHAS) through the QCoast2100
program. Phase 3 of the CHAS involved refining coastal hazard mapping, including reassessment of the
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erosion prone area undertaken by BMT (2018). It should be noted that the reassessment by BMT (2018)
was at a beach compartment scale and did not provide site-specific estimation of erosion vulnerability.
The following sections will review each component of the Erosion prone area based on site specific
conditions.
6.1.1 Long-term Erosion (N x R)
The long-term erosion component is based on the selected planning period (N) and the average annual
rate of long-term erosion (R).
In relation to the planning period, the Department of Environment and Heritage Protection (2013) states,
“The long-term erosion component (excluding sea level rise) of the calculation is often cyclical in nature
and typically of a decadal scale. For this reason, it is considered the estimated annual rate of long-term
erosion is only applied for a 50-year period”. Where there is no clear evidence of long-term erosion
trends, the Department recommends a nominal provision of 10 metres.
The annual rate of long-term erosion (R) reflects changes to sediment supply to a beach and where there
is a long-term deficit in sediment supply this results in a longer-term recession of the shoreline. BMT
(2018) has calculated the long-term erosion rate for Sunshine Coast at beach profile line ETA 602. Table
3 provides a summary of BMT (2018) estimated long-term erosion for 2040, 2070 and 2100.
Table 3 Summary of Long-Term Recession Results from BMT (2018)
Annual Recession Long-Term Recession (m)
Beach Survey Profile
Rate (m/year) 2040 (N=23) 2070 (N=53) 2100 (N=3)
Sunshine Beach ETA 602.0 0.03 0.7 1.6 2.5
BMT (2018) calculated an annual long-term erosion rate of 0.03 metres/year for Sunshine Beach.
However, the subject site is located approximately 210m south of Noosa Headland which will influence the
sediment transport processes along this section of coast by trapping the long-term net northerly littoral
transport of sand (discussed in Section 5.3). This is supported by the assessment of aerial photography
presented in Section 4 which has shown recovery and progradation of the beach adjacent to the site
since severe storm event related erosion in the early 1970’s.
It is noted that BMT (2018) had adopted a nominal 10m value for long-term erosion for erosion prone area
calculation over a 100-year planning period and this is in accordance with the Department of Environment
and Heritage Protection (2013) methodology. This is consistent with the Department of Environment and
Heritage Protection (2013) methodology. However, it does not consider the effect of the site’s proximity to
Noosa Headland which will reduce long-term erosion.
Long-term erosion of 0 metres is considered more realistic given the influence of Noosa Headland which
would act in a similar fashion to a groyne by trapping sand moving north along the coast with the
prevailing south-easterly wave climate.
6.1.2 Short-term Erosion (C)
The Department of Environment and Heritage Protection (2013) recommends the calculation of the short-
term erosion based on a 100-year ARI storm event using the method developed by Vellinga (1983).
Figure 17 shows a conceptual representation of the erosion and accretion zones associated with storm
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induced erosion predicted by Vellinga (1983). The Department provides the following recommendation in
relation to defining a storm event:
“For a tide-dominated coast where storm tide levels can be large, the parameters
adopted for the minimum design storm are:
storm tide level corresponding to an average recurrence interval of 1-in-
100 years
wave height for a moderate storm using the 1-in-20-year significant wave
height (Hs).
However, for wave-dominated coastlines where extreme storm tide levels can be
relatively minor, such as the Gold Coast, the significant wave height and duration
of the storm event are major factors influencing short term erosion, rather than
storm tide. Hence it may be necessary to consider a larger wave event (for
example, a storm event with a 1-in-100 ARI) and a moderate storm tide level.
Decisions on appropriate parameters to be used must be based on local
conditions and the experience of the coastal engineer undertaking the
assessment.”
Figure 17 Sketch of pre-storm and predicted post-storm profiles based on Vellinga (1983)
In relation to the probability of such an event occurring the Department of Environment and Heritage
protection (2013) states:
“Although the abovementioned probability of occurrence may appear to be fairly
high, it is considered that this choice is reasonable when considered in
conjunction with the method used to determine erosion prone area widths. This
method implies that the erosion prone area has sufficient width to accommodate
the design storm erosion in 100 years’ time, when all of the estimated long-term
erosion has occurred. Therefore, it also follows that for much of the 100-year
planning period, the erosion prone area is sufficient to accommodate a larger
storm than the one selected for design purposes. In fact, in the most critical last
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10 years of such a planning period, there is only a 10% probability of occurrence
of the design storm. Thus, the risk of a storm breaching the entire erosion prone
area at some time during the 100-year period will be significantly less than 63%.”
BMT (2018) adopted a combination of a 100-year ARI Storm Tide level and 100-year ARI significant wave
height as the design storm event for the reassessment of erosion prone areas with Noosa Shire Council.
It should be noted that the joint probability of a combined 100-year ARI storm tide and 100-year ARI
significant wave height is likely to greater than a 100-year ARI storm event. This combination of design
storm tide level and wave height will be adopted for the site-specific reassessment of the erosion prone
area reported herein.
An additional assessment of short-term erosion will be undertaken for a more extreme event to assess the
vulnerability of the proposed house and pool to assist with foundation design. The design parameters for
the assessment of the short-term beach erosion and scenarios are presented in Table 4.
Table 4 Design Storm Events for Short-term Beach Erosion Assessment
Storm Event
Storm Component
100-year ARI Extreme Event
Significant Wave Height 6.2m 6.2m
Storm Tide 1.74m AHD 1.84m AHD
Sea Level Rise - 0.8m
Figure 18 and Table 5 present the results of the modelled storm erosion associated with the above 100-
year ARI design storm event. This shows storm erosion of 51 metres measured from HAT position on the
current beach profile (pre-storm profile) to the toe of the erosion scarp.
The extreme event scenario adopted in Table 4 incorporates the impact associated with a 0.8m increase
in mean sea level in addition to a 500 year ARI storm tide event (i.e. 1.84m AHD). This provides for a total
water level of 2.64m AHD for this assessment and therefore incorporates additional erosion associated
with the adopted sea level rise projection. This allowance for sea level rise is consistent with the
Queensland Government policy for the planning period to 2100.
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Internal use only Figure 18 100-year ARI storm profile (Vellinga, 1983) at 66 Seaview Terrace for current climate Figure 19 and Table 5 present the results of the modelled storm erosion associated with the extreme design event (refer Table 2). This shows a storm erosion cut of 73 metres is predicted to occur and will be used to inform slope stability assessment and foundation design by the geotechnical engineering consultants, Tectonic Geotechnical Pty Ltd. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 27
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Figure 19 Extreme storm event profile (Vellinga, 1983) at 66 Seaview Terrace
Table 5 Predicted Short-term Erosion - Sunshine Beach
Predicted Short-term
Design Water Level Significant Wave Height
Design Event Erosion
(m AHD) (m)
(m)
100-year ARI Event 1.74 6.2 58
Extreme Event 2.64 6.2 82
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6.1.3 Recession due to Sea Level Rise
As discussed in Section 5.1.2, sea levels are predicted to rise in response to climate change and the
Queensland Government have adopted a sea level rise of 0.8 metres above present day mean sea level
by the year 2100. The Department of Environment and Heritage Protection (2013) requires the shoreline
response to sea level rise be considered when assessing erosion prone area widths. An industry
standard practice for the assessment of shoreline recession due to sea level rise is to apply the ‘Bruun
Rule’ (Bruun, 1962), see Figure 20.
Figure 20 Conceptualisation of recession due to sea level rise due to Bruun Rule (Bruun, 1962)
The Bruun Rule assumes an equilibrium beach profile is maintained with rising sea level resulting in an
elevation and landward movement of the profile, as shown in Figure 20. The Bruun Rule is given by:
𝐵𝐵𝐵𝐵
𝑟𝑟 = Equation 2
𝐷𝐷
Where:
r= shoreline recession due to sea level rise (m)
B= horizontal distance of the active beach profile (m)
a= rise in mean sea level (m)
D= vertical height of the active beach profile (m)
The Bruun Rule assumes that the beach and dune consist of a uniform loose sand material. It is also
applicable to long straight sections of beach. The geotechnical assessment which is supported by aerial
photography from 1974 has shown the underlying soil profile includes indurated sand layers (i.e., coffee
rock) which may slow recession rates.
The assessment of recession due to sea level rise is presented in Table 6. The profile adopted has been
based on site survey supplemented with Sunshine Beach profile survey for ETA 602.0. Based on the
information available an active beach height of 40 metres has been adopted from the depth of closure of -
12m AHD to the dune height at the rear of the subject property of 28m AHD. This provides an active
beach profile width of 550 metres.
Table 6 Summary of Shoreline Recession due to Sea Level Rise
Profile Width Dune Height Depth of Closure 2100 Shoreline Recession
Beach
(m) (m AHD) (m AHD) (m)
Sunshine Beach 550 28 -12 11
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6.1.4 Dune Scarp Component
The methodology for calculating the erosion prone area includes an allowance for slumping of the frontal
dune following a short-term erosion event.
The angle of repose for dry sand is 35o and this has been used to determine the dune scarp component of
the erosion prone area. The short-term erosion calculations shown in Figure 18 and Table 5 indicate a
dune scarp of approximately 2 metre and this would result in erosion due to slumping of approximately 4
metres.
6.1.5 Summary of the Erosion Prone Area Reassessment
The erosion prone area reassessment for this appeal has been undertaken in accordance with the
Department of Environment and Heritage Protection (2013) requirements with a planning period of 100
years to accommodate the asset lifespan of the proposed house. We have also considered the effect of
shoreline recession due to 0.8 metres of sea level rise, short-term erosion associated with a 100-year ARI
storm event and dune scarp recession.
The site-specific erosion prone area calculated for the site is 91 metres measured from the seaward toe of
the frontal dune. The components of the erosion prone area for 66 Seaview Terrace, Sunshine Beach are
presented in Table 7 and the spatial extents are shown in Figure 21.
Table 7 Reassessed Erosion Prone Area for 66 Seaview Terrace, Sunshine Beach
Erosion Prone Area Component Value
Long-term Erosion (m) 0
Short-term Erosion (m) 58
Recession due to 0.8m SLR (m) 11
Safety Factor 1.4
Dune scarp slumping (m) 4
Erosion prone area Width (m) 101
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Internal use only Figure 21 Extent of the reassessed erosion prone area 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 31
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Internal use only 7 Coastal Building Line Coastal building lines were introduced as a planning control by the former Beach Protection Authority under the provisions of the Beach Protection Act 1968 (repealed) and have been continued through transitional provisions in the Coastal Protection and Management Act 1995. The Coastal Building Line is an arbitrary line placed over properties with the intention to accommodate natural erosion and accretion processes associated with storm events (i.e., the short-term erosion component of the erosion prone area). Coastal Building Lines are declared under section 66 of the Coastal Protection and Management Act 1995. The Coastal Building Line at 66 Seaview Terrace is located 10 metres measured from the seaward property boundary. It is used as a development trigger under the Planning Act 2016 for assessment of building works within a Coastal Management District against the provisions of the State Development Assessment Provisions (SDAP). Performance Outcome PO6 of SDAP State Code 8 states, “In areas where a coastal building line is present, building work is located landward of the coastal building line unless coastal protection work has been constructed to protect the development”. The proposed building has been designed to cantilever seaward of the coastal building line, with the foundations of the building located landward of the coastal building line. This approach is considered to comply with this performance outcome as it achieves the protection required for the building from the storm events considered in Section 6.1.2. Figure 19 shows the extent of short-term erosion and dune scarp recession for an extreme storm event consisting of a 500-year ARI storm tide level, climate change induced sea level rise and a 100-year ARI significant wave height. The site is located outside of the zone that may be vulnerable to short-term erosion and as such it is unlikely that the coastal building line would have been applied to the site by the former Beach Protection Authority with the information currently available. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 32
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Internal use only 8 Conclusion A detailed coastal engineering assessment has been undertaken to assess the vulnerability to erosion of the beach adjacent to 66 Seaview Terrace, Sunshine Beach, Noosa Shire. The methodology adopted for this report is based on best practice and is appropriate for risk assessment in relation to the proposed development and the coastal hazard associated with beach erosion for the section of beach in the vicinity of 66 Seaview Terrace, Sunshine Beach. This assessment has found that the proposed house and pool are unlikely to be subject to erosion from the sea during the expected asset lifespan (i.e., 60 years for a residential house). The assessment also found that the proposed development will not impact on the future coastal management option for this section of Sunshine Beach. To accommodate future climate conditions, it is recommended that a site-specific slope stability assessment be undertaken to inform the design of foundations of the house to mitigate impacts from beach erosion associated with future climate conditions as presented in Figure 19. Construction of the proposed house at 66 Seaview Terrace, Sunshine Beach as shown in Appendix A, with appropriate foundation design, would not adversely impact coastal processes and would not affect the future coastal management options for this section of Sunshine Beach. 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 33
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9 References
Allen, M., & Callaghan, J. (2001). Extreme Wave Conditions for the South Queensland Coastal Region -
Environmental Technical Report No. 32. Brisbane: Queensland Environmental Protection Agency.
Aurecon. (2013). Sunshine Coast Storm Tide Study - Storm Tide Definition. Brisbane: Aurecon.
Beach Protection Authority. (1984). Hervey Bay Beaches. Brisbane: Queensland Goverment.
BMT. (2013). Coastal Processes Study for the Sunshine Coast. Brisbane: BMT.
BMT. (2018). Noosa Shire Council Coastal Hazards Risk, Vulnerability and Adaptation Assessment -
Coastal Hazard Mapping Refinement. Brisbane: BMT.
Bruun, P. (1962). Sea Level Rise as a cause of shoreline recession. ASCE Journal, Waters and Harbours
Division, Vol. 188, 117-130.
Department of Environment and Heritage Protection. (2013). Coastal Hazards Technical Guide -
Determining Coastal Hazard Areas. Brisbane: Department of Environment and Heritage
Protection.
Maritime Safety Queensland. (2021). Queensland Tidal Planes. Retrieved from
https://www.msq.qld.gov.au/Tides/Tidal-planes
Patterson, C. (1986). Storm Tide Statistics. Beach Protection Authority - Beach Conservation, Issue 62.
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Internal use only Appendix A: Development Proposal 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 35
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Internal use only Appendix B: Erosion Prone Area Plans 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 36
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Internal use only Appendix C: Site Survey by Minstaff Survey Pty Ltd 03 June 2022 66 SEAVIEW TERRACE, SUNSHINE BEACH PA2906-RHD-ZZ-XX-RP-Z-0001 39
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