roches beach coastal hazard lines reassessment · table 2-1: 100 year ari swell and wind-waves...

Roches Beach Coastal Hazard Lines Reassessment

WRL Technical Report 2011/05 September 2011

by T D Shand, J T Carley and C D Wasko

Water Research Laboratory University of New South Wales

School of Civil and Environmental Engineering

Roches Beach Coastal Hazard Lines Reassessment

WRL Technical Report 2011/05 September 2011

by Tom D Shand, James T Carley and Conrad D Wasko

Project Details

Report Title Roches Beach Coastal Hazard Lines Reassessment

Report Author(s) Tom D Shand, James T Carley and Conrad D Wasko

Report No. 2011/05

Report Status Final

Date of Issue September 2011

WRL Project No. 10086

Project Manager T D Shand

Client Name Clarence City Council

Client Address 38 Bligh Street Rosny Park TAS 7018

Client Contact Phil Watson

Client Reference 70370

Document Status

Version Reviewed By Approved By Date Issued

Final JTC BMM September 2011

Water Research Laboratory 110 King Street, Manly Vale, NSW, 2093, Australia

Tel: +61 (2) 8071 9800 Fax: +61 (2) 9949 4188 ABN: 57 195 873 179 www.wrl.unsw.edu.au

Quality System certified to AS/NZS ISO 9001:2008

Expertise, research and training for industry and government since 1959

This report was produced by the Water Research Laboratory, School of Civil and Environmental Engineering,

University of New South Wales for use by the client in accordance with the terms of the contract.

Information published in this report is available for release only with the permission of the Director, Water Research Laboratory and the client. It is the responsibility of the reader to verify the currency of the

version number of this report. All subsequent releases will be made directly to the client.

The Water Research Laboratory shall not assume any responsibility or liability whatsoever to any third party arising out of any use or reliance on the content of this report.

- i -

Executive Summary

This study provides updated and more detailed Inundation Hazard and Design Floor Levels and Erosion Hazard and Setback Distances form those calculated during the Coastal Processes, Coastal Hazards, Climate Change and Adaptive Responses Study undertaken by WRL for Clarence City Council in 2007-2008. Roches Beach was identified as being particularly vulnerable to coastal hazards within the original study, however, the hazard risk zones were derived and applicable on an embayment scale within the region without consideration of gradients within the embayments. The shape, orientation and variation in exposure along Roches Beach means that hazard risk is likely to vary along the shoreline and necessitates a more detailed assessment. This study updates the inundation and erosion hazard and resultant risk zones along the beach at a resolution of approximately 300 m. This study has revised the extreme wave climate using updated data and wave modelling, undertaken more detailed setup and runup calculations taking into account the alongshore variation in wave exposure and offshore bathymetry, updated erosion potential taking into account the same alongshore variations in wave climate and bathymetry and assessed medium to long-term changes using photogrammetry data. Resultant still-water (exclusive of wave run-up) inundation levels are similar to those derived within the original Clarence-wide study. Wave run-up levels are around 1 m lower at the southern end of the beach and around 1 m higher at the northern end of the beach than the original study reflecting the alongshore variation in wave climate and bathymetric slope. It should be noted that while run-up is a dynamic process, contributing only intermittent quantities of water, wave set-up constitutes a more sustained period of elevated water, capable of significant flooding. It is therefore usual that the wave setup elevation is considered when assessing coastal inundation levels rather than the higher run-up level. However, wave run-up may erode dunes, reducing sand levels below the wave setup level. While revetments and seawalls do not increase protection against coastal inundation if they are below still water levels, their rough and highly permeable nature can reduce run-up elevation. Setback distances and hazard lines at the northern end of Roches Beach are generally identical to those derived by the previous study. An exception occurs for the present case hazard line which is located 5 m further landward than the previous study north of Bambra Reef. This is attributed to apparent medium term fluctuations and the low dune height and therefore available volumes compared to that assumed in the previous study. Setback distances and hazard lines at the southern end of Roches Beach are 20 to 25 m less than at the northern end due to the lower wave climate and storm demand volumes. Detailed assessment for individual properties may generate slightly different hazard line locations. Buildings may still be permitted seaward of the hazard lines shown in this report in the following circumstances:

Detailed assessment for an individual property by a qualified coastal practitioner varies the hazard line location;

Rock is present beneath a veneer of sand, with the location and level of rock mapped and considered by a coastal engineer and/or geotechnical engineer;

Buildings are constructed on piles, with design input from a coastal engineer, together with a structural and/or geotechnical engineer;

A protection scheme is implemented (e.g. sand nourishment or a seawall).

- ii -

Contents

1. Introduction 1 2. Assessment of Coastal Inundation 3

2.1 Introduction 3 2.2 Extreme Wind 3

2.2.1 Wind setup 3 2.3 Extreme Wave Analysis 3

2.3.1 Extreme Offshore Wave Climate 3 2.3.2 Wave modelling 4 2.3.3 Extreme local waves 5

2.4 Wave Setup and Run-up 6 2.5 Climate Change 7

2.5.1 Sea level rise 7 2.5.2 Changes to Wind and Wave Climate 8

2.6 Extreme Water Level 8 2.7 Risk Areas for Coastal Inundation 9

3. Assessment of Coastal Erosion Risk and Recession Hazard 15 3.1 Analysis of Photogrammetry 15 3.2 Analysis of Council Topographic Survey and LIDAR 17 3.3 Erosion Hazard 17 3.4 Recession Hazard 19 3.5 Beach Rotation and Medium Term Trends 22 3.6 Sea-level Rise Effects 23 3.7 Risk Areas for Coastal Erosion and Recession 24

4. Conclusions and Recommendations 31 5. References and Bibliography 33 Appendix A Roches Beach 1 m Contour and Beach Volume above 0 m AHD for Photogrammetry and Council Surveys 36

- iii -

List of Tables

Table 2-1: 100 year ARI Swell and Wind-waves along Roches Beach 6 Table 2-2: 100 yr ARI Swell and Wind-Wave Setup and Run-up along Roches Beach 7 Table 2-3: Simplified Engineering Estimates of Global Sea Level Rise (by WRL) based on IPCC (2001, 2007) and NCCOE (2004) 8 Table 2-4: Design Water Levels using Mid and High Range Sea Level Rise (SLR) Scenarios 8 Table 2-5: Present Day 100 year ARI (1% AEP) Wave Setup and Run-up Levels 9 Table 2-6: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2050 Mid Range Sea Level Rise (0.2 m) 10 Table 2-7: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2050 High Range Sea Level Rise (0.3 m) 10 Table 2-8: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2100 Mid Range Sea Level Rise (0.5 m) 11 Table 2-9: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2100 High Range Sea Level Rise (0.9 m) 11 Table 3-1: Photogrammetry Details 15 Table 3-2: Indicative houses/buildings at risk 25 Table 3-3: Allowances for Erosion and Recession 26 Table 4-1: Design floor level for still water (SWL) and including wave run-up (R2%)1 32 Table 4-2: Idealised erosion setback distances and houses/buildings at risk 32

List of Figures

Figure 1-2: Roches Beach, Clarence City 1 Figure 1-1: Components of coastal inundation 2 Figure 2-1: Extreme Wave Analysis for Cape Sorell compared to Directional Analysis of NWW3 data 4 Figure 2-2: Extreme swell waves from the south and wind-waves generated by easterly winds 5 Figure 2-3: Potential Inundation Areas for Roches Beach 12 Figure 2-4: Potential Inundation Areas for Roches Beach (North) 13 Figure 2-5: Potential Inundation Areas for Roches Beach (South) 14 Figure 3-1: Photogrammetry and Topographic survey Line Locations 16 Figure 3-2: Synthetic design swell (A) and wind-wave (B) time series at each profile (P) location along Roches Beach 18 Figure 3-3: Profile response to Swell and Wind-wave design events at Profile 10, Roches Beach 19 Figure 3-4: Erosion predicted by SBEACH above 0 m AHD during design swell and wind-wave events 19 Figure 3-5: Example change in 1m (□) and 2m (o) AHD contour locations (A) and beach volume above 0 m AHD (B) based on photogrammetry (□), LIDAR (□) and topographic survey (□) data at northern end of Roches Beach. Trend lines show best linear fit to photogrammetry data. 20 Figure 3-6: Long-term change in contour location and beach volume above 0 m AHD along Roches Beach determined using Photogrammetry. Council topographic survey locations marked. 21 Figure 3-7: Relative Change in Chainage Position of 1 m Contour for Regions of Roches Beach 23 Figure 3-8: Erosion and Recession Hazard Lines for Roches Beach 27

- iv -

Figure 3-9: Erosion and Recession Hazard Lines for Roches Beach (North) 28 Figure 3-10: Erosion and Recession Hazard Lines for Roches Beach (Central) 29 Figure 3-11: Erosion and Recession Hazard Lines for Roches Beach (South) 30

WRL Technical Report 2011/05 FINAL September 2011 1

1. Introduction

The Water Research Laboratory (WRL) was commissioned by Clarence City Council (CCC) to revise coastal hazard lines at Roches Beach, Tasmania. The main Roches Beach is approximately 3500 m long and Roches Beach north, between Bambra Reef and the sailing club is approximately 800 m long (Figure 1-1). These lines were first derived during the Coastal Processes, Coastal Hazards, Climate Change and Adaptive Responses Study undertaken by WRL for Clarence City Council in 2007-2008 (Carley et al. 2008). This earlier study assessed the vulnerability of 15 locations around Clarence City to coastal hazards, both at present, and due to sea level rise and climate change into the future and provided maps showing present and future coastal hazard risk areas.

Figure 1-1: Roches Beach, Clarence City

Coastal inundation includes components of astronomical tide, tidal anomalies through wind and barometric setup and coastally trapped waves and extreme wave set-up and run-up (Figure 1-2). The erosion hazard may include erosion by an individual design storm event, underlying long-term recession, allowance for beach rotation or medium term fluctuations in sediment supply, stable foundation zones following erosive episodes and recession due to sea level rise.

Roches Beach

Frederick Henry Bay

Storm Bay and Southern Ocean


While inundation from the seaward side of the isthmus is possible, Carley et al. (2008) noted that inundation may also occur from the landward (Ralphs Bay) side of the isthmus. While Roches Beach was identified as being particularly vulnerable to coastal hazards, the hazard risk zones were derived and applicable as an embayment-wide average only. The shape, orientation and variation in exposure along Roches Beach means that hazard risk is likely to vary along the shoreline and necessitates a more detailed assessment. This study updates the inundation and erosion hazard and resultant risk zones along the beach at a resolution of approximately 300 m with assessment locations coinciding with Clarence City Council topographic survey profile lines. Even more local, site-specific factors such as seawalls, site-specific topography, underlying rock or offshore bathymetry and reefs could therefore further influence hazard and risk presented in this report. Such site-specific assessments should be undertaken by a qualified coastal engineer.

Figure 1-2 Components of coastal inundation

1.1 Project Datums All topographic coordinates are provided in terms of Australian Map Grid 1984 (AMG84), which is based on a Universal Transverse Mercator (UTM) projection. Site reduced levels (RL) are in terms of Australian Height Datum 1984 (AHD84), which is approximately mean sea level at Hobart. For convenience, a chainage system has been implemented along Roches Beach with a datum located at the southern end the beaches at 540900m E, 5248245m N. This is approximately equal to the high tide mark at Clarence City Council topographic survey Profile 1.


2. Assessment of Coastal Inundation

2.1 Introduction

Coastal inundation generally occurs with a combination of elevated ocean levels and extreme wind and wave conditions. Large waves at Roches Beach may occur when large offshore swell waves propagate into Frederick Henry Bay and into Roches Beach, or, when a strong wind from the easterly quarter blows across Frederick Henry Bay generating local wind-sea at Roches Beach. This study assesses both wind and swell scenarios and determines extreme inundation and erosion hazard for both possibilities, selecting the worse-case scenario on a section-by-section basis along Roches Beach.

2.2 Extreme Wind

Australian Standard AS/NZS 1170.2:2002 Structural Design Actions Part 2: Wind Actions gives design wind velocities for Australia excluding tornadoes. Design wind velocities (3 second gust, 10 m elevation, Terrain Category 2) applicable to coastal engineering assessments are given for average recurrence intervals (ARI) of 1 to 1000 years. Directional multipliers for Hobart vary from 0.80 for four directions from north-east to south, to 1.0 for the north-west octant. Waves generated by winds blowing across Fredrick Henry Bay are the result of sustained winds rather than extreme gusts. Equivalent sustained one hour wind speeds are therefore calculated according to the methods of the Shore Protection Manual (CERC, 1984) and described in Carley et al. (2008). The 100 year ARI (1% AEP), 1 hour wind speed for north-east, east and south-east directions is 21.5 ms-1 (~ 42 knots).

2.2.1 Wind setup

During times of high wind, surface water is transported downwind through surface drag. In an enclosed bay, this water may “pile up” at the downwind end of the bay. While Frederick Henry Bay is open to Storm Bay on the southern side, some wind setup would be expected along Roches Beach during onshore wind conditions. Consistent with the methodology presented in Carley et al. (2008), wind setup was assessed based on the equations given in Dean and Dalrymple (1991) and implemented within the software package CRESS (V4.0.2). Resultant local wind setup of 0.15 m was found along the beach under extreme onshore wind conditions. Larger, regional scale storm surge resulting from regional scale wind and barometric setup would be measured on the Hobart tide gauge which is considered separately in Section 7.6.

2.3 Extreme Wave Analysis

2.3.1 Extreme Offshore Wave Climate

Carley et al. (2008) undertook an assessment of extreme offshore wave conditions based on an analysis of data from the Cape Sorell, Storm Bay and Eden wave buoys. They concluded that while the largest waves arrived from the south-west, the most effective wave direction for propagation into Storm Bay was from the south to south-east direction. As none of the afore-mentioned buoys provided directional data, a full directional analysis was precluded. Extreme waves from the south to south-east were assumed equivalent to those found for the Eden, NSW buoy, with a 100 year ARI wave height estimated at 8.5 m and from the west to south-west, equivalent to the Cape Sorell estimates of 13.0 m. A more recent and comprehensive study of extreme wave climate around Australia by Shand et al. (2011) refined these estimates to 8.7 m at Eden and 12.9 m at Cape Sorell. Data from


NOAA’s global Wavewatch III (NWW3) model was obtained immediately south of Storm Bay for the period 1997 to 2010. This data contains directional information and was analysed consistent with the methodologies presented in Shand et al. (2011). Estimates of extreme waves from the west, south-west and south to south-east are compared with those from the Cape Sorell Buoy (Figure 2-1). Results show NWW3 estimates from the south-west to be largest, waves from the west to be around 10% smaller and waves from the south around 35% smaller. Resultant directional wave multipliers derived from the NWW3 model were adjusted in magnitude based on the Cape Sorell Buoy estimate and used for further analysis.

1 5 10 20 50 1004

5

6

7

8

9

10

11

12

13

14

15

Average Recurrence Interval (Years)

Sto

rm P

ea

k S

ign

ific

an

t W

av

e H

eig

ht

(m)

NOAA NWW3 - All DirNOAA NWW3 - 180 (157.5 to 202.5) deg

NOAA NWW3 - 225 (202.5 to 247.5) degNOAA NWW3 - 270 (247.5 to 292.5) degCape Sorrell Wave Buoy - All Directions

Cape Sorrell Wave Buoy +90% CICape Sorrell Wave Buoy -90% CI

Figure 2-1: Extreme Wave Analysis for Cape Sorell compared to Directional Analysis of NWW3

data

2.3.2 Wave modelling

Offshore swell waves reaching the Clarence coast may be modified by the processes of refraction, diffraction, wave-wave interaction and dissipation by bed friction and wave breaking. Waves generated locally within Fredrick Henry Bay undergo generation processes as well as the aforementioned propagation and dissipation processes. The model SWAN (Simulating WAves Nearshore) version 40.51 was used to quantify the change in wave conditions from a deepwater boundary into Roches Beach and to model the generation of local wind-waves within Fredrick Henry Bay. Details of SWAN can be found in Booij et al. (1999a, 1999b). Three nested models were constructed to represent different scales of the spatial domain:


The first model extended from the NWW3 output location some 40 km south of the Tasmanian mainland, into Storm Bay at a grid resolution of 500 m and used the deepwater waves at the NWW3 output location as a boundary condition.

The second model included all of Frederick Henry Bay at a resolution of 100 m and used either a swell wave boundary condition supplied by the 500 m grid or generated local wind-waves within Frederick Henry Bay using a constant wind field. Figure 2-2 shows an example of swell waves propagating from the south into Frederick Henry Bay and Roches Beach and local wind waves generated within the bay by strong easterly winds.

The third model included Roches Beach at high resolution of 20 m and modelled detailed wave refraction processes as swell and wind waves approached the shore.

Extreme swell waves were modelled from the west to south-east directions and extreme wind waves assessed for winds from south-east to north-east. Output locations provided wave conditions just prior to breaking at positions along Roches Beach.

Figure 2-2: Extreme swell waves from the south and wind-waves generated by easterly winds

2.3.3 Extreme local waves

Characteristics of the maximum 100 year ARI swell and wind-waves immediately offshore of the break point at 12 locations along Roches Beach are provided in Table 2-1. While no nearshore calibration data was available, resultant extreme waves appear in general agreement with anecdotal evidence and photos of large waves breaking offshore of the Roches Beach Canal. It should be noted that waves up to twice as large as the reported significant wave height (average of the largest one third of waves) may occur. Overall, wave height increases from south to north as the sheltering effect afforded by the southern headland reduces, although this is less notable for wind waves than swell waves. For 100 year ARI design conditions, both swell and wind wave significant height are comparable at just under 1.5 m at the northern end of Roches Beach, although extreme swell wave height is around half the extreme wind-wave height at the southern end. The peak period of extreme swell waves is much longer than extreme wind-waves and the direction of extreme wind-waves slightly more easterly. Extreme swell waves found during this study are slightly smaller than found by Carley et al. (2008) using a similar SWAN model, and extreme wind waves are substantially smaller than those previously found using simple 1D wave hindcasting techniques (CERC, 1984; USACE, 2003).


Table 2-1: 100 year ARI Swell and Wind-waves along Roches Beach

Profile

Approximate Chainage

(m)1

100yr ARI Wave Height (m)

Swell Waves Wind Waves

Hs (m)

Tp (s)

Dp (°)

Hs (m)

Tp (s)

Dp (°)

1 0 0.69 15.0 76 1.22 5.2 64

2 300 0.55 15.0 66 1.08 5.2 57

3 380 0.58 15.0 73 1.12 5.2 61

4 900 0.69 15.0 89 1.28 5.2 75

5 1250 0.90 15.0 103 1.35 5.2 82

6 1550 1.02 15.0 106 1.39 5.2 86

7 1800 1.08 15.0 114 1.33 5.2 92

8 2100 1.17 15.0 115 1.38 5.2 93

9 2450 1.30 15.0 120 1.32 5.2 100

10 2730 1.39 15.0 129 1.28 5.2 108

11 3150 1.49 15.0 115 1.49 5.2 93

12 3360 1.47 15.0 123 1.42 5.2 101

Roches Beach for Carley et al. (2008) study

1.6 15.0 - 2.2 5.4 -

1 Chainage from southern end of Roches Beach at approximately Clarence City Council topographic survey Profile 1

2.4 Wave Setup and Run-up

Wave setup occurs as a release in radiation stress by breaking waves is balanced by a gradient in the water surface, thus elevating the water level through the surf zone to reach a maximum at the top of the beach and minimum at the breakpoint. While the increase is often assumed linear across the surf zone in first-order assessments, in reality, the majority of set-up induced water elevation occurs within the very shallow regions of the surf zone. Run-up occurs after a wave breaks, travels across the surf zone and then is carried by momentum above the still water level until momentum forces are exceeded by gravity. The wave run-up calculations implicitly include wave setup. Mase (1989) presented predictive equations for run-up of irregular waves on plane, impermeable beaches (slopes 1:5 to 1:30) based on laboratory data. Unpublished work by WRL has successfully verified the Mase equations against recorded run-up at numerous beaches (Higgs and Nittim, 1988) if the entire surf zone slope is used. This approach has also been used within the SBEACH erosion model which has successfully predicted the upper limit of profile change at numerous Australian beaches (Carley and Cox, 2003). Wave run-up is generally defined as a percentage exceedance elevation, i.e. the elevation exceeded by 10% of waves is referred to as R10%. For design wave run-up on beaches, the R2% value is the most commonly used, which is the run-up exceeded by two run-up waves out of 100. Wave setup has been calculated according to the surf-zone model presented Dally, Dean and Dalrymple (1984) and implemented within the numerical model SBEACH (version 4.03). Results are shown for both the swell and wind-wave case in Table 2-2. Wind setup (as described within Section 2.2.1) may also contribute to elevated water level in the case of strong onshore winds


and is shown combined with wave setup. Results show that swell wave-induced setup general increases to the north with swell wave climate. Wind wave set-up is smaller due to the lower period and more consistent along the beach but when combined with wind setup is roughly equivalent to swell wave setup in the north and exceeds swell wave setup in the south. The maximum combined wind and wave setup level is therefore relatively constant along the beach at 0.3 to 0.4 m. Run-up exceeded by 2% of swell waves and wind waves (R2%) according to Mase, 1989 (USACE, 2003) is similarly shown within Table 2-2. Wave run-up increases from south to north as a function of increased wave height and steeper offshore bed slopes, particularly for the swell case where maximum R2% levels of almost 2.5 m AHD are reached along the northern sections of beach.

Table 2-2: 100 yr ARI Swell and Wind-Wave Setup and Run-up along Roches Beach

Profile


(m)

Swell Waves Wind Waves

Wave Setup (m)

Local Wind Setup (m)1

Comb. Setup (m)

2% Run-up level (m)3

Wave Setup (m)

Local Wind Setup (m)2

Comb. Setup (m)

2% Run-up level (m)3

1 0 0.18 - 0.18 0.32 0.15 0.15 0.30 0.40

2 300 0.10 - 0.10 0.46 0.12 0.15 0.27 0.54

3 380 0.10 - 0.10 0.50 0.12 0.15 0.27 0.52

4 900 0.15 - 0.15 0.59 0.12 0.15 0.27 0.58

5 1250 0.18 - 0.18 0.68 0.12 0.15 0.27 0.56

6 1550 0.18 - 0.18 0.98 0.12 0.15 0.27 0.68

7 1800 0.21 - 0.21 1.19 0.12 0.15 0.27 0.77

8 2100 0.36 - 0.36 1.31 0.15 0.15 0.30 0.80

9 2450 0.30 - 0.30 2.11 0.15 0.15 0.30 1.02

10 2730 0.33 - 0.33 2.29 0.15 0.15 0.30 1.00

11 3150 0.40 - 0.40 1.71 0.15 0.15 0.30 0.86

12 3360 0.36 - 0.36 2.47 0.16 0.15 0.31 1.10


0.24 1.93 0.48 1.32

(1) Regional scale storm surge including wind and barometric setup is included in measurements on the Hobart tide gauge

(2) Local wind setup beyond the regional scale process (3) Relative to still water level

2.5 Climate Change

2.5.1 Sea level rise

The Intergovernmental Panel on Climate Change (IPCC) have produced major reports in 1990, 1996, 2001 and 2007. Hence the 2007 report is known as the Fourth Assessment Report (AR4) and the 2001 report the Third Assessment Report (TAR). The latest IPCC Summary for Policymakers Report (IPCC SPM, 2007a) and Working Group 1 Report (IPCC, 2007b) provide numerous sea level rise scenarios for 2090 to 2100. Values for 2050 are not available in the Summary Report or Working Group 1 2007 reports. Simplified “mid” and “high” sea level rise scenarios developed by WRL for engineering application are shown in Table 2-3. Similar engineering scenarios were developed in NCCOE (2004) based on the IPCC (2001) scenarios and are almost identical when ice melt is included and the end


date is extended to 2100. As such, the NCCOE (2004) values for 2050 have been used. Further detail is provided within Carley et al. (2008). No reliable information is yet available for local sea level rise for Clarence which differs substantially from the global projections. Hunter et al. (2003) estimated that the land at Port Arthur (approximately 50 km east of Hobart) is rising at 0.2 ±0.2 mm/year upwards. There is no documented evidence of substantial subsidence of coastal land around Clarence, which could justify higher levels of relative sea level rise, than the global average values reported in IPCC.

Table 2-3: Simplified Engineering Estimates of Global Sea Level Rise (by WRL)

based on IPCC (2001, 2007) and NCCOE (2004)

Sea Level Scenario Year

2050 2100

Adopted “Mid” scenario

0.2 0.5

Adopted “High” scenario

0.3 0.9

2.5.2 Changes to Wind and Wave Climate

As discussed within Carley et al. (2008), future climate change effects may result in increased wind and wave climates around Tasmania. Based on studies by CSIRO (2007) and, following the recommendations of DEFRA, UK (2006), an allowance for a +5% increase in extreme wave height and wind speed by 2050 and +10% by 2100 has been incorporated into future hazard assessment.

2.6 Extreme Water Level

Water levels consist of (predictable) tides which are forced by the sun, moon and planets (astronomical tides), and a tidal anomaly. Tidal anomalies result from factors such as wind setup or setdown, barometric effects, seasonal changes and coastally trapped waves. Based on analysis of the Hobart tide gauge data was undertaken by Hunter (2007). Carley et al. (2008) determined extreme values for the Clarence City coastline as shown within Table 2-4 including mid- and high-range sea-level rise components at 2050 and 2100. No new information has arisen which indicates a need to revise these values and a present day design value of 1.44 m AHD has been adopted. This value does not incorporate local wind and wave setup and run-up components which are added in the following section.

Table 2-4: Design Water Levels using Mid and High Range Sea Level Rise (SLR) Scenarios

ARI (years)

AEP

Water level (m AHD)

Mid range SLR High range SLR

2000 2050 2100 2050 2100

Sea level rise (m) 0.0 0.2 0.5 0.3 0.9

1 63% 0.97 1.17 1.47 1.27 1.87

50 2% 1.37 1.57 1.87 1.67 2.27

100 1% 1.44 1.64 1.94 1.74 2.34

*excludes local effects such as local wind setup, wave setup and wave run-up


2.7 Risk Areas for Coastal Inundation

For the case where the calculated (“designated”) flood level is known, the current Tasmanian Building Act 2000, Section 159 prescribes a freeboard of 0.3 m above the calculated (“designated”) flood level. This 0.3 m freeboard value is within the range adopted in other jurisdictions and has been adopted for this study. Design floor levels for the present day case and 2050 and 2100 mid- and high-range sea-level rise scenarios are presented within Table 2-5 to Table 2-9 below and in Figure 2-3 to Figure 2-5. In general, extreme still water level and design floor levels are consistent along the beach with less than 0.1 m variation shown and consistent with those found during the previous Roches Beach hazard study (Carley et al. 2008). Previous inundation maps remain appropriate for coastal inundation on the seaward side of Roches Beach isthmus. It should be noted that while run-up is a dynamic process, contributing only intermittent quantities of water, wave set-up constitutes a more sustained period of elevated water, capable of significant flooding. However, run-up may erode dunes, reducing sand levels below the wave setup level. While revetments and seawalls do not increase protection against coastal inundation if they are below still water levels, their rough and highly permeable nature can reduce runup elevation. The revetment at the southern end of Roches Beach could provide some protection against run-up due to its roughness and high permeability. However, as the revetment crest level and its design and stability are unknown, and the structure’s future lifespan uncertain, any possible benefits have not been assessed within this study.

Table 2-5: Present Day 100 year ARI (1% AEP) Wave Setup and Run-up Levels

Profile


(m)1

Tide gauge water level

Still water level (incl wave and wind setup)

Design floor level (excl wave runup)

R2% Wave runup

Design floor level on frontal dune (incl wave runup)2

(m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD)

1 0 1.44 1.7 2.0 1.8 2.1

2 300 1.44 1.7 2.0 2.0 2.3

3 380 1.44 1.7 2.0 2.0 2.3

4 900 1.44 1.7 2.0 2.0 2.3

5 1250 1.44 1.7 2.0 2.1 2.4

6 1550 1.44 1.7 2.0 2.4 2.7

7 1800 1.44 1.7 2.0 2.6 2.9

8 2100 1.44 1.8 2.1 2.7 3.0

9 2450 1.44 1.7 2.0 3.5 3.8

10 2730 1.44 1.8 2.1 3.7 4.0

11 3150 1.44 1.8 2.1 3.1 3.4

12 3360 1.44 1.8 2.1 3.9 4.2


1.44 1.8 2.1 2.8 3.1

1 Chainage from southern end of Roches Beach at approximately CCC topographic survey Profile 1 2 Includes 0.3 m freeboard


Table 2-6: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2050 Mid Range Sea Level

Rise (0.2 m)

Profile


(m)1




R2% Wave runup



1 0 1.64 1.9 2.2 2.0 2.3

2 300 1.64 1.9 2.2 2.2 2.5

3 380 1.64 1.9 2.2 2.2 2.5

4 900 1.64 1.9 2.2 2.2 2.5

5 1250 1.64 1.9 2.2 2.3 2.6

6 1550 1.64 1.9 2.2 2.7 3.0

7 1800 1.64 1.9 2.2 2.9 3.2

8 2100 1.64 2.0 2.3 3.0 3.3

9 2450 1.64 2.0 2.3 3.8 4.1

10 2730 1.64 2.0 2.3 4.0 4.3

11 3150 1.64 2.1 2.3 3.4 3.7

12 3360 1.64 2.0 2.3 4.2 4.5


1.64 2.0 2.3 3.0 3.3


Table 2-7: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2050 High Range Sea Level

Rise (0.3 m)

Profile


(m)1




R2% Wave runup



1 0 1.74 2.0 2.3 2.1 2.4

2 300 1.74 2.0 2.3 2.3 2.6

3 380 1.74 2.0 2.3 2.3 2.6

4 900 1.74 2.0 2.3 2.3 2.6

5 1250 1.74 2.0 2.3 2.4 2.7

6 1550 1.74 2.0 2.3 2.8 3.1

7 1800 1.74 2.0 2.3 3.0 3.3

8 2100 1.74 2.1 2.4 3.1 3.4

9 2450 1.74 2.1 2.4 3.9 4.2

10 2730 1.74 2.1 2.4 4.1 4.4

11 3150 1.74 2.2 2.4 3.5 3.8

12 3360 1.74 2.1 2.4 4.3 4.6


1.74 2.1 2.4 3.1 3.4



Table 2-8: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2100 Mid Range Sea Level

Rise (0.5 m)

Profile


(m)1




R2% Wave runup



1 0 1.94 2.3 2.6 2.4 2.7

2 300 1.94 2.2 2.5 2.5 2.8

3 380 1.94 2.2 2.5 2.5 2.8

4 900 1.94 2.2 2.5 2.6 2.9

5 1250 1.94 2.2 2.5 2.7 3.0

6 1550 1.94 2.2 2.5 3.0 3.3

7 1800 1.94 2.2 2.5 3.2 3.5

8 2100 1.94 2.3 2.6 3.3 3.6

9 2450 1.94 2.3 2.6 4.2 4.5

10 2730 1.94 2.3 2.6 4.4 4.7

11 3150 1.94 2.4 2.6 3.8 4.1

12 3360 1.94 2.3 2.6 4.6 4.9


1.94 2.3 2.6 3.3 3.6


Table 2-9: 100 year ARI (1% AEP) Wave Setup and Run-up Levels for 2100 High Range Sea Level

Rise (0.9 m)

Profile


(m)1




R2% Wave runup



1 0 2.34 2.7 3.0 2.8 3.1

2 300 2.34 2.6 2.9 2.9 3.2

3 380 2.34 2.6 2.9 2.9 3.2

4 900 2.34 2.6 2.9 3.0 3.3

5 1250 2.34 2.6 2.9 3.1 3.4

6 1550 2.34 2.6 2.9 3.4 3.7

7 1800 2.34 2.6 2.9 3.6 3.9

8 2100 2.34 2.7 3.0 3.7 4.0

9 2450 2.34 2.7 3.0 4.6 4.9

10 2730 2.34 2.7 3.0 4.8 5.1

11 3150 2.34 2.8 3.0 4.2 4.5

12 3360 2.34 2.7 3.0 5.0 5.3


2.34 2.7 3.0 3.7 4.0


WRLReport No. 2011/05

POTENTIAL INNUNDATION AREAS - ROCHES BEACH, LAUDERDALE Figure2.3

2011_05_FIG2_3.mxt

539500

539500

540000

540000

540500

540500

541000

541000

541500

541500

542000

542000

542500

542500

52

46

50

0

52

46

50

0

52

47

00

0

52

47

00

0

52

47

50

0

52

47

50

0

52

48

00

0

52

48

00

0

52

48

50

0

52

48

50

0

52

49

00

0

52

49

00

0

52

49

50

0

52

49

50

0

52

50

00

0

52

50

00

0

52

50

50

0

52

50

50

0

52

51

00

0

52

51

00

0

Potential inundation areas for 1% AEP event

Present Day Depth > 300 mm (Land < 1.5 m AHD)

Present Day Depth < 300 mm (Land 1.5 m - 1.8 m AHD)

2050 Mid SLR (Land 1.8 m - 2.0 m AHD)



2100 High SLR (Land 2.3 m - 2.7 m AHD)

No Inundation

Nominal Coastline

GDA 1994 MGA Zone 55


POTENTIAL INNUNDATION AREAS - ROCHES BEACH, LAUDERDALE (NORTH)

Figure

2.42008_04_FIG21_5.mxt

539500

539500

540000

540000

540500

540500

541000

541000

52

49

00

0

52

49

00

0

52

49

50

0

52

49

50

0

52

50

00

0

52

50

00

0

52

50

50

0

52

50

50

0

52

51

00

0

52

51

00

0

Potential inundation areas for 1% AEP event







No Inundation

Nominal Coastline



POTENTIAL INNUNDATION AREAS - ROCHES BEACH, LAUDERDALE (SOUTH)

Figure

2.52011_05_FIG2_5.mxt

539500

539500

540000

540000

540500

540500

541000

541000

52

46

50

0

52

46

50

0

52

47

00

0

52

47

00

0

52

47

50

0

52

47

50

0

52

48

00

0

52

48

00

0

52

48

50

0

52

48

50

0Potential inundation areas for 1% AEP event







No Inundation

Nominal Coastline



3. Assessment of Coastal Erosion Risk and Recession Hazard

3.1 Analysis of Photogrammetry

Photogrammetry allows spatially extensive elevation data to be derived from aerial photograph stereo pairs. Sequential photogrammetry records provide extremely valuable information on temporal and spatial changes in shoreline position and beach volumes. Such data may be used to derive long-term shoreline recession, beach rotation and, if records are of sufficient temporal resolution (i.e. closely spaced in time), to derive individual storm or seasonal erosion volumes. Photogrammetry data was supplied by the Information & Land Services (I&LS) Division of the Department of Primary Industries Parks, Water & Environment, Tasmania. Profiles were extracted from each photographic record for up to 42 cross sections between Long View Crescent at the southern end of Roches Beach and the reef outcrop in front of no. 9 Kirra Road (Figure 3-1). Photographic dates, scale and photogrammetry accuracies are presented within Table 3-1. This metadata shows that the maximum elevation error in the 1957, 1969 and 1981 data is greater than 1.5 m. Such an error may translate to large errors when calculating contour position or total beach volume and resultant values must therefore be treated with appropriate caution.

Table 3-1: Photogrammetry Details

Aerial photography date Photo Scale Maximum elevation error (m)

Spatial accuracy (± m) (horizontal)

12/02/1957 1:14000 2.4 1.5

17/02/1969 1:14600 1.6 3

22/12/1975 1:5000 0.2 0.5

1/11/1981 1:6000 2.0 1.5

13/01/1984 1:5000 0.2 0.5

26/02/1986 1:12500 0.5 0.6

4/02/1988 1:12500 0.25 0.6

19/02/1992 1:12500 0.5 0.6

15/02/1997 1:12500 0.5 0.6

14/12/2002 1:10000 0.2 0.5

4/01/2007 1:10000 0.2 0.5

Software written at WRL enables specific contours and beach volume to be extracted from each photogrammetry record including allowances for spatial and elevation errors in photogrammetry. Assessing changes in contour position and beach volumes both over time and along the shoreline allows quantifications of long-term trends but also of alongshore changes associated with beach rotation, fluctuations in sediment supply and effects of anthropogenic modification such as seawall construction and beach nourishment. Due to the time period between photogrammetry data (typically 2 to 5 years), photogrammetry is less accurate for determining individual storm demand due to the beach recovery which may occur after storm events. For this component, pre- and post-storm topographic surveys or numerical beach response modelling remains best-practice. Full processed datasets for each profile position are presented within Appendix A, with the 1 m contour and beach volume above 0 m AHD presented.

Southern Revetment

Northern Revetment

Bambra Reef

Profile 9

Profile 11

Profile 7

Profile 8

Profile 12

Profile 6

Profile 10

Pro

file

1

Profile 5

Profile 3

Profile 4

Profile

2

9

4

8

6

3

7

5

42

11

12

16

14

15

25

28

20

29

19

18

31

26

35

33

22

21

32

24

34

27

38

540000

540000

540500

540500

541000

541000

541500

541500

542000

542000

524

8500

524

8500

524

9000

524

9000

524

9500

524

9500

525

0000

525

0000

525

0500

525

0500

525

1000

525

1000

Figure 3.1WRL Technical Report 2011/05

Roches Beach with Council Topographic Survey Lines Indicated

Photogrammetry Lines

Roches Beach Topographic Survey Lines


3.2 Analysis of Council Topographic Survey and LIDAR

Between December 2006 and January 2011, six sets of profile surveys were undertaken at Roches Beach by registered surveyors Noel Leary & Associates for Clarence City Council. Each survey collected beach profile data along 10 shore-normal survey lines extending from behind the foredune crest to the water line at time of survey. These survey lines correspond to the individual sections being evaluated for the present coastal hazard reassessment. An additional LIDAR (Light Detection and Ranging) survey was undertaken between the 4th and 9th March, 2008 by Digital Mapping Australia. The LIDAR has been thinned to 1 m horizontal intervals and has a quoted spatial accuracy of 0.1 m. A previous assessment (Shand and Carley, 2009) found that while the LIDAR data agrees reasonably with the corresponding council survey on the beach face, both the dune face slopes and maximum dune crest elevation obtained by LIDAR measurement are typically lower than the topographic survey. The cause of these differences in the front dune slope and dune crest elevation remain unknown but could be attributed to spatial averaging which occurs during the LIDAR data acquisition (due to the laser sensor area) and subsequent post-processing (data thinning and DTM generation) and/or the effect of trees and vegetation on obtained values.

3.3 Erosion Hazard

Using idealised, deepwater synthetic design storms derived in Shand et al. 2011, synthetic design storms comprising wave height and period time series were constructed for extreme swell and wind-wave events at 12 locations along Roches Beach (Figure 3-2). Consistent with Carley et al. (2007), design event time series comprised two sequential design storms and a water level record inclusive of the 100 year ARI level of 1.44 m AHD. While these combinations remain conservative, further refinement requiring a full statistical joint-probability analysis is beyond the scope of this present re-assessment. Both the swell and wind events at Roches Beach were slightly smaller and the wave height time series more peaked than those used in the previous Clarence City Coastal Hazard Assessment (Carley et al. 2008). Profile response to the design events was assessed at 12 locations along Roches Beach using the numerical cross-shore sediment transport and profile change model SBEACH (Larson and Kraus, 1989). SBEACH considers sand grain size, the pre-storm beach profile and dune height, plus time series of wave height, wave period, water level in calculating a post-storm beach profile. Model development involved extensive calibration against both large scale wave tank laboratory data and field data and SBEACH has been verified for measured storm erosion on the Australian east coast, including at Warilla, Narrabeen and Wamberal (Carley, 1992), and at the Gold Coast (Carley et al. 1998). Model results showed swell events to be generally more erosive than wind-wave events (Figure 3-3) and erosion volumes to generally increase from south to north (Figure 3-4). Erosion volumes were slightly lower than the 100 m3/m found during the previous coastal hazard assessment (Carley et al. 2007), due to the slightly reduced design wave heights found during this study. Erosion between successive photogrammetry and topographic survey records of up to 60 m3/m was found, but was generally between 10 and 30 m3/m. This provides support to the SBEACH model results as some post-storm recovery before a successive photogrammetry and topographic surveys is likely. Additionally, a design storm event such as that shown in Figure


3-2 combining extreme waves and water level has not occurred during the observation period. Such a design event will result in larger erosion volumes than observed to date.

Figure 3-2: Synthetic design swell (A) and wind-wave (B) time series at each profile (P) location

along Roches Beach


Figure 3-3: Profile response to Swell and Wind-wave design events at Profile 10, Roches Beach

Figure 3-4: Erosion predicted by SBEACH above 0 m AHD during design swell and wind-wave

events

3.4 Recession Hazard

Photogrammetry for 42 profiles between 1959 and 2007 was processed to extract the 0, 1 and 2 m AHD contour locations and the beach volume above 0 m. Large vertical errors in the 1959, 1967 and 1981 photogrammetry data precluded their use. Long-term changes in horizontal contour positions and in beach volume were assessed using a linear regression analysis (Figure 3-5) with resultant trends plotted in Figure 3-6 with a best-fit parabolic curve fitted. While this linear analysis is acknowledged as a relatively simplistic treatment of a dynamically fluctuating system, with sufficient data, general trends become apparent. Figure 3-6 shows a long-term trend of slight accretion (0 to 0.2 m/year) north of Bambra Reef (> Profile 10) and south of the southern revetment (< Profile 2), and recession of 0.1 to 0.3 m/year between the southern revetment and Bambra Reef. Results are consistent with expected recession patterns in a zeta-


curve planform bay such as Roches Beach where sediment input is less than output. They are also consistent with the 0.1 to 0.25 m/year found by Sharples (2007) in his examination of ongoing change at Roches Beach using aerial photographs from 1957, 1977, 1987, 2001 and 2005. This work is discussed in more detail within Carley et al. (2008). While long-term shoreline movement along the southern section of beach backed by revetment (chainage 50 to 530 m) is shown as zero, this is due to the presence of the seawall with the adjacent shoreline continuing to recede (i.e. Photograph A). However, unless a structure has been adequately engineered to withstand design conditions and future sea level rise, it will at some point fail and the backing land will likely rapidly erode/recede to a position consummate with the adjacent shoreline. Long-term recession at the seawall is therefore calculated as equivalent to that immediately adjacent to it of between 0.1 and 0.2 m/year.

1970 1980 1990 2000 201010

20

30

40

50

Date

Cha

inag

e (m

)

Chainage 2450m Contour Position

1970 1980 1990 2000 20100

50

100

150

200

Date

Vol

ume

(m3/

m)

Chainage 2450 Volume

Figure 3-5: Example change in 1m (□) and 2m (o) AHD contour locations (A) and beach volume

above 0 m AHD (B) based on photogrammetry (□), LIDAR (□) and topographic survey (□) data at

northern end of Roches Beach. Trend lines show best linear fit to photogrammetry data.

Trend ≈ -0.15 m/yr

Trend ≈ -0.5 m3/m/yr


Figure 3-6: Long-term change in contour location and beach volume above 0 m AHD along Roches

Beach determined using Photogrammetry. Council topographic survey locations marked.

Revetment 1998-present)

Revetment 1998-present)


3.5 Beach Rotation and Medium Term Trends

Beach rotation involves either a cyclic or one way change in the alignment of a beach’s planform due to changes in the wave direction over medium (weeks to months) to long (decades) term time scales. It is a well known seasonal phenomenon in Perth WA, where the beach planform alignment is influenced by north-west storms in winter and south-west seabreezes in summer. Fluctuations in sediment supply are also known to occur at headland bounded crescentic beaches (PWD, 1978) with sediment slugs often being driven around a headland by large wave events or series of wave events. Such fluctuations in sediment supply result in temporal and spatial variation in erosion patterns and beach volume. Figure 3-7 shows the average, relative movement of the 1 m AHD contour for different Roches Beach sections. Chainage 0 to 1000 m represents the southern part of Roches Beach extending from the southern end of the beach to just north of the canal. In this section, small but sustained recession was observed from 1975 to 1986, followed by a rapid progradation coinciding with the construction of the revetment and beach nourishment. Between 1988 and 1992 this section receded slightly, presumably as the nourishment material was lost from the system, before stabilising until 2007. Between 2007 and present, a series of large storm events are known to have occurred and the section appears to have receded around 7 m on average. The mid-section of Roches Beach extends from 1000 to 2000 m chainage or between Profile 4 and Profile 8. In this section shows a relatively stable shoreline until 1983 when the shoreline receded rapidly. The sections accreted slightly until 1991, presumably following updrift nourishment, then began to recede with a large erosion event occurring in 2007. The northern section of Roches Beach between Profiles 8 and 10 (Bambra Reef) shows a relatively stable shoreline with erosive events in 1988 to 1991 and from 2007 until 2010. This section of shoreline receded, on average, 4 m during each of these erosive periods and did not recover significantly between. The far northern section north of Bambra Reef shows a pattern of relative stability with fluctuating erosion in the mid and late 1980s and since 2003, and accretion in between. Overall, beach rotation is not evident but rather the southern and northern sections of Roches Beach show relative stability punctuated by episodic erosive events. The mid section of Roches Beach shows less stability, continuing to slowly recede between intense erosion events. The far northern section (north of Bambra reef) shows a shoreline in dynamic equilibrium, generally recovering between erosive events. Overall, based on the present available data, the identified (natural) medium-term fluctuations south of Bambra reef are small and generally implicitly accounted for within the higher recession rate (Section 3.4) and storm demand (Section 3.3). North of Bambra reef, the recession rate is lower but medium term fluctuations are more pronounced. Along this section of coastline, an allowance of 5 m has been made for medium term fluctuations, associated with fluctuations in sediment supply due to accretion and erosion of the salient at Bambra Reef..


Figure 3-7: Relative Change in Chainage Position of 1 m Contour for Regions of Roches Beach

3.6 Sea-level Rise Effects

As discussed within Section 2.5.1, future climate change is expected to result in accelerated sea level rise (IPCC SPM, 2007a). Response models such as that of Bruun (1962, 1988) propose that as sea level rises, open coast beaches will recede. A recession rate can be estimated using the Bruun Rule (Bruun, 1962, 1988) as the rate of sea level rise divided by the average slope of

Ave

rage

Ch

ain

age

- M

ean

Ch

ain

age

of 1

m C

onto

ur

(m)

Likely Nourishment Effect


the active beach profile. This rule is based on the concept that the existing beach profile is in equilibrium with the incident wave climate and existing average water level. It is a simple concept, which assumes that the beach system is two-dimensional and that there is no interference with the equilibrium profile by headlands and offshore reefs. The Bruun Rule is typically expressed as

cdh

Xr R

(3-1)

where R is horizontal recession (m) r is sea level rise (m) X is the horizontal distance between h and dc h is active dune/berm height (m) dc is profile closure depth (m, expressed as a positive number) The Bruun Rule provides an order of magnitude of long term recession due to sea level rise, that is only applicable to wave dominated beaches. A Bruun Rule factor, which incorporates profile slope at a particular site and thus gives horizontal distance as a function of sea level rise has been assessed for each profile using Hallermeier’s expression for closure depth and at the seaward limit of profile change based on SBEACH results. Results are in general agreement with the value of 50 derived by Carley et al. (2008) using a range of similar methods. This value is consistent with NSW and southern Queensland ‘rule-of-thumb’ values and indicates that for every 0.1 m of sea level rise, 5 m of shoreline retreat can be expected. While there is considerable controversy regarding the Bruun Rule, there are no accepted alternatives.

3.7 Risk Areas for Coastal Erosion and Recession

Allowances for setbacks for erosion and recession are shown in Table 3-3. Setback distances comprise the following factors: S1: Allowance for storm erosion S2: Allowance for long term (underlying) recession S3: Allowance for beach rotation and/or medium term fluctuations in sediment supply S4: Allowance for reduced foundation capacity (to Stable Foundation Zone) S5: Allowance for future recession (Bruun Rule). The design setback (DS) is defined as:

DS = S1 + N*S2 + S3 + S4 + S5 (3-2) Where N is the project life in years (usually 0 for present day hazard, 50 or 100 years). Storm erosion hazard lines have been developed in accordance with the scheme of Nielsen et al (1992) using the shoreline position assumed by Carley et al. (2008) and adjusted for long-term recession since that time, based on average rates. Revised hazard lines are presented in Table 3-3 and in Figure 3-8 to Figure 3-11 for a 100 year ARI (1% AEP) erosion event with present-day conditions and for 2050 and 2100. Detailed assessment for individual properties may generate slightly different hazard line locations.


At the northern end of Roches Beach setback distances and hazard lines are generally identical to those derived by the previous study. An exception occurs for the present day hazard line which is located 5 m further landward than the previous study. This is attributed to the low dune height and therefore available volumes in the northern part of Roches Beach compared with that assumed in the previous study. At the southern end of Roches Beach setback distances and hazard lines are 20 to 25 m less than at the northern end due to the lower wave climate and storm demand volumes. An estimate of the number of buildings affected by the erosion and recession hazard lines is shown in Table 3-2. This has only been applied to buildings on sandy areas fronting the coast. This is an approximate estimate only, and does not consider the building type or any specific protection works. These buildings would only be lost if adaptation was not undertaken, emergency action was not taken and if the sea level rise and coastal change projections in this report eventuate. Roads and other infrastructure would also be affected. The presence of rock and/or a seawall may protect properties from short to medium term erosion and recession. However, unless the structures have been adequately engineered to withstand design conditions and future sea level rise, they will at some point fail and the backing land will likely rapidly erode to a position consummate with the adjacent shoreline. While this study has not assessed the structural or geotechnical integrity of the structures presently located along Roches Beach, they do not appear to have been designed or maintained to contemporary engineering standards. Hazard lines are therefore presented discounting any possible beneficial effects of the protective works.

Table 3-2: Indicative houses/buildings at risk

Scenario Number of houses/ buildings seaward of hazard line1

Present day (m) 15

2050 mid SLR (m) 114

2050 high SLR (m) 119

2100 mid SLR (m) 147

2100 high SLR (m) 217 1Number of buildings assessed based on 2007 OrthoMosaic provided by Clarence City Council, 2010.


Table 3-3: Allowances for Erosion and Recession

Profile


(m)

S1 S2 S3 S4 S5 Design Setbacks (DS)

Horizo

nta

l st

orm

er

osi

on

(m)

Under

lyin

g r

eces

sion

(m/y

ear)

Allo

wan

ce f

or

rota

tion

or

med

ium

ter

m

fluct

uat

ions

(m)

Sta

ble

Foundat

ion

zone

(m)

Des

ign B

ruun r

ule

fa

ctor

Bru

un r

eces

sion 2

050

mid

SLR

(m

)

Bru

un r

eces

sion 2

050

hig

h (

m)

Bru

un r

eces

sion 2

100

mid

SLR

(m

)

Bru

un r

eces

sion 2

100

hig

h S

LR (

m)

Tota

l pre

sent

(m)

2050 m

id S

LR (

m)

2050 h

igh S

LR (

m)

2100 m

id S

LR (

m)

2100 h

igh S

LR (

m)

1 0 10 0.1 0 2 50 10 15 25 45 15 30 35 50 70

2 300 10 0.1 0 2 50 10 15 25 45 15 30 35 50 70

3 380 10 0.1 0 2 50 10 15 25 45 15 30 35 50 70

4 900 15 0.2 0 2 50 10 15 25 45 20 40 45 65 85

5 1250 15 0.2 0 3 50 10 15 25 45 20 40 45 65 85

6 1550 15 0.2 0 3 50 10 15 25 45 20 40 45 65 85

7 1800 20 0.2 0 4 50 10 15 25 45 25 45 50 70 90

8 2100 20 0.2 0 4 50 10 15 25 45 25 45 50 70 90

9 2450 25 0.2 0 3 50 10 15 25 45 30 50 55 75 95

10 2730 25 0.2 0 4 50 10 15 25 45 30 50 55 75 95

11 3150 30 0.1 5 1 50 10 15 25 45 35 50 55 75 95

12 3360 30 0.1 5 2 50 10 15 25 45 35 50 55 75 95


25 0.2 ? 5 50 10 15 25 45 30 50 55 75 95


EROSION AND RECESSION HAZARD LINES- ROCHES BEACH, LAUDERDALE

Figure

3.82011_05_FIG3_8.mxt

540000

540000

540500

540500

541000

541000

541500

541500

542000

542000

52

48

50

0

52

48

50

0

52

49

00

0

52

49

00

0

52

49

50

0

52

49

50

0

52

50

00

0

52

50

00

0

52

50

50

0

52

50

50

0

52

51

00

0

52

51

00

0

52

51

50

0

52

51

50

0

2100 High Range SLR

2100 Mid Range SLR

2050 High Range SLR

2050 Mid Range SLR

Present Day

Current Shoreline


Presence of rock or seawall may limit erosion, but this protection has not been quantified.


EROSION AND RECESSION HAZARD LINES- ROCHES BEACH, LAUDERDALE (NORTH)

Figure3.9

2011_05_FIG3_9.mxd

540500

540500

541000

541000

52

50

50

0

52

50

50

0

52

51

00

0

52

51

00

0

52

51

50

0

52

51

50

0

2100 High Range SLR

2100 Mid Range SLR

2050 High Range SLR

2050 Mid Range SLR

Present Day

Current Shoreline



Erosion may also exceed estimatesin this area due to loss of controlfrom Bambra Reef


EROSION AND RECESSION HAZARD LINES- ROCHES BEACH, LAUDERDALE (CENTRAL)

Figure

3.102011_05_FIG3_10.mxt

540000

540000

540500

540500

541000

541000

52

49

00

0

52

49

00

0

52

49

50

0

52

49

50

0

52

50

00

0

52

50

00

0

2100 High Range SLR

2100 Mid Range SLR

2050 High Range SLR

2050 Mid Range SLR

Present Day

Current Shoreline



EROSION AND RECESSION HAZARD LINES- ROCHES BEACH, LAUDERDALE (SOUTH)

Figure

3.112011_05_FIG3_11.mxt

540500

540500

541000

541000

52

48

00

0

52

48

00

0

52

48

50

0

52

48

50

0

52

49

00

0

52

49

00

0

2100 High Range SLR

2100 Mid Range SLR

2050 High Range SLR

2050 Mid Range SLR

Present Day

Current Shoreline




4. Conclusions and Recommendations

This study provides updated and more detailed Inundation Hazard and Design Floor Levels and Erosion Hazard and Setback Distances form those calculated during the Coastal Processes, Coastal Hazards, Climate Change and Adaptive Responses Study undertaken by WRL for Clarence City Council in 2007-2008 (Carley et al. 2008). The 2008 study was undertaken on an embayment wide basis. This study has revised the extreme wave climate using updated data and wave modelling, undertaken more detailed setup and runup calculations taking into account the alongshore variation in wave exposure and offshore bathymetry, updated erosion potential taking into account the same alongshore variations in wave climate and bathymetry and assessed medium to long-term changes using photogrammetry data. Resultant still-water (exclusive of wave run-up) inundation levels (Table 4-1) are similar to those derived during the previous study. Wave run-up levels are around 1 m lower at the southern end of the beach and around 1 m higher at the northern end of the beach reflecting the alongshore variation in wave climate and bathymetric slope. It should be noted that while run-up is a dynamic process, contributing only intermittent quantities of water, wave set-up constitutes a more sustained period of elevated water, capable of significant flooding. However, run-up may erode dunes, reducing sand levels below the wave setup level. While revetments and seawalls do not increase protection against coastal inundation if they are below still water levels, their rough and highly permeable nature can reduce run-up elevation. At the northern end of Roches Beach setback distances and hazard lines (Table 4-2) are generally identical to those derived by the previous study. An exception occurs for the present case hazard line which is located 5 m further landward than the previous study north of Bambra Reef. This is attributed to apparent medium term fluctuations and the low dune height and therefore available volumes compared to that assumed in the previous study. At the southern end of Roches Beach setback distances and hazard lines are 20 to 25 m less than at the northern end due to the lower wave climate and storm demand volumes. Detailed assessment for individual properties may generate slightly different hazard line locations. Buildings may still be permitted seaward of the hazard lines shown in this report in the following circumstances:

Detailed assessment for an individual property by a qualified coastal practitioner varies the hazard line location;

Rock is present beneath a veneer of sand, with the location and level of rock mapped and considered by a coastal engineer and/or geotechnical engineer;

Buildings are constructed on piles, with design input from a coastal engineer, together with a structural and/or geotechnical engineer;

A protection scheme is implemented (e.g. sand nourishment or a seawall).


Table 4-1: Design floor level for still water (SWL) and including wave run-up (R2%)1

Profile

Approx. Chainage (m)

100yr ARI - Present

100yr ARI - 2050 Mid Range SLR

100yr ARI - 2050 High Range SLR

100yr ARI - 2100 Mid Range SLR

100yr ARI - 2100 High Range SLR

SWL2 Inc.

R2%3

SWL2 Inc.

R2%3

SWL2 Inc.

R2%3

SWL2 Inc.

R2%3

SWL2 Inc.

R2%3

1 0 2.0 2.1 2.2 2.3 2.3 2.4 2.6 2.7 3.0 3.1

2 300 2.0 2.3 2.2 2.5 2.3 2.6 2.5 2.8 2.9 3.2

3 380 2.0 2.3 2.2 2.5 2.3 2.6 2.5 2.8 2.9 3.2

4 900 2.0 2.3 2.2 2.5 2.3 2.6 2.5 2.9 2.9 3.3

5 1250 2.0 2.4 2.2 2.6 2.3 2.7 2.5 3.0 2.9 3.4

6 1550 2.0 2.7 2.2 3.0 2.3 3.1 2.5 3.3 2.9 3.7

7 1800 2.0 2.9 2.2 3.2 2.3 3.3 2.5 3.5 2.9 3.9

8 2100 2.1 3.0 2.3 3.3 2.4 3.4 2.6 3.6 3.0 4.0

9 2450 2.0 3.8 2.3 4.1 2.4 4.2 2.6 4.5 3.0 4.9

10 2730 2.1 4.0 2.3 4.3 2.4 4.4 2.6 4.7 3.0 5.1

11 3150 2.1 3.4 2.3 3.7 2.4 3.8 2.6 4.1 3.0 4.5

12 3360 2.1 4.2 2.3 4.5 2.4 4.6 2.6 4.9 3.0 5.3 1 Includes 0.3 m freeboard as per the Tasmanian Building Act 2000, Section 159 2 Design still water includes astronomical tide, barometric, wind and wave setup but excludes wave run-up 3 Only applies to frontal dune directly impacted by wave run-up – not for setting general floor levels

Table 4-2: Idealised erosion setback distances and houses/buildings at risk

Profile

Approx. Chainage (m)

Total present (m)

2050 mid SLR (m)

2050 high SLR (m)

2100 mid SLR (m)

2100 high SLR (m)

1 0 15 30 35 50 70

2 300 15 30 35 50 70

3 380 15 30 35 50 70

4 900 20 40 45 65 85

5 1250 20 40 45 65 85

6 1550 20 40 45 65 85

7 1800 30 45 50 70 90

8 2100 30 45 50 70 90

9 2450 35 50 55 75 95

10 2730 35 50 55 75 95

11 3150 35 50 55 75 95

12 3360 35 50 55 75 95

Indicative houses/buildings at risk *

* likely presence of rock and/or a seawall may preclude protect properties from erosion and recession, however, this has not been quantified. Such properties may also be vulnerable to wave impacts.


5. References and Bibliography

AS/NZS 1170.2:2002, Structural Design Actions – Wind Actions, Standards Australia. Booij, N, Ris, R C and Holthuijsen, L H (1999a), “A third-generation wave model for coastal regions, Part I, Model description and validation”, Journal of Geophysical Research C4, 104, 7649-7666. Ris, R C, Booij, N and Holthuijsen, L H (1999b), “A third-generation wave model for coastal regions, Part II, Verification”, Journal of Geophysical Research C4, 104, 7667-7681. Bruun, P (1962), "Sea Level Rise as a Cause of Beach Erosion", Proceedings ASCE Journal of the Waterways and Harbours Division, Volume 88, WW1, pp 117-130, American Society of Civil Engineers. Bruun P (1988), "The Bruun Rule of Erosion by Sea-Level Rise: A Discussion on Large-Scale Two- and Three-Dimensional Usages", Journal of Coastal Research, 4(4), 627-648. Carley J T (1992), "Analysis of SBEACH Numerical Beach Erosion Model", MEngSc Thesis, University of New South Wales. Carley, J T and Cox, R J (2003), “A Methodology for Utilising Time-Dependent Beach Erosion Models for Design Events”, Proceedings of Australasian Coasts and Ports Conference, Auckland, The Institution of Engineers Australia. Carley, J T, Blacka, M J, Timms, W A, Andersen, M S, Mariani, A, Rayner, D S, McArthur, J and Cox, R J (2008), Coastal Processes, Coastal Hazards, Climate Change And Adaptive Responses For Preparation Of A Coastal Management Strategy For Clarence City, Tasmania. WRL-TR 2009/04. 138p. Church, J A, Hunter, J R, McInnes, K L and White, N J (2006), “Sea-level rise around the Australian coastline and the changing frequency of extreme sea-level events”, Australian Meteorological magazine, 55, 253-260. CSIRO (2007), Climate Change in Australia. ISBN 9781921232947 (PDF), CSIRO, Australia. Dean, R G and Dalrymple, R A (1991), Water Wave Mechanics for Engineers and Scientists, World Scientific, Singapore. DEFRA UK (2006), Department for Environment, Food and Rural Affairs, Flood and Coastal Defence Appraisal GuidanceFCDPAG3 Economic Appraisal Supplementary Note to Operating Authorities – Climate Change Impacts October 2006 http://www.defra.gov.uk/environ/fcd/pubs/pagn/default.htm October 2006 Hanslow D J and Nielsen P (1995), “Field Measurements of Runup on Natural Beaches”, Proceedings 12th Australian Conference on Coastal Engineering, pp 189 – 193. Hallermeier R J (1983), “Sand Transport Limits in Coastal Structure Design”. Proceedings, Coastal Structures ’83. American Society of Civil Engineers, pp 703-716.


Hemer, M A, Church, J A and Hunter, J R, “Waves and Climate Change on the Australian Coast”, Journal of Coastal Research SI 50 432 - 437 ICS2007 (Proceedings) Australia ISSN 0749.0208. Holman, R A (1986), “Extreme Value Statistics for Wave Run-up on a Natural Beach,” Coastal Engineering, Vol 9, No. 6, pp 527-544. Hunter, J R (2007), “Historical and Projected Sea-Level Extremes for Hobart and Burnie, Tasmania”, Commissioned by the Department of Primary Industries and Water, Tasmania Antarctic Climate & Ecosystems, Cooperative Research Centre, Private Bag 80, Hobart, Tasmania 7001.

IPCC (2007a), Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

IPCC (2007b), Climate Change 2007 - The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, (ISBN 978 0521 88009-1 Hardback; 978 0521 70596-7 Paperback), [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

Larson, M and Kraus, N C (1989), “SBEACH: Numerical Model for Simulating Storm-Induced Beach Change, Report 1: Theory and Model Foundation”. Technical Report CERC-89-9, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg USA.

Larson, M, Kraus, N C and Byrnes, M R (1990), “SBEACH: Numerical Model for Simulating Storm-Induced Beach Change, Report 2: Numerical Formulation and Model Tests”. Technical Report CERC-89-9, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg USA.

Mase, H (1989), “Random Wave Runup Height on Gentle Slopes”, Journal of the Waterway, Port, Coastal and Ocean Engineering Division, American Society of Civil Engineers, pp 593-609.

Nielsen, A F, Lord, D B and Poulos, H G (1992), “Dune Stability Considerations for Building Foundations”, Engineers Australia, Vol CE34 No 2, June.

PWD (1978) - also Gordon, A D, Lord, D B and Nolan, M W (1978). “Byron Bay – Hastings Point Erosion Study”, PWD 78026, NSW Public Works Department, Coastal Engineering Branch Report.

Sharples, C (2007), “Shoreline Change at Roches Beach 1957 – 2006, South-Eastern Tasmania” A Report to the Antarctic Climate and Ecosystems Co-operative Research Centre, Tasmania, October 2007.

Shand, T D, Mole, M A, Carley, J T, Peirson, W L and Cox, R J (2011), Coastal Storm Data Analysis: Provision of Extreme Wave Data for Adaptation Planning. WRL Research Report 242. 53p + Appendices. US Army Corps of Engineers (2003), EM 1110 Coastal Engineering Manual.

WRL Technical Report 2011/05 FINAL September 2011

Appendix A Roches Beach 1 m Contour and Beach Volume above 0 m AHD for Photogrammetry and Council Surveys

□ = Photogrammetry □ = LIDAR □ = Topographic Survey

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)

Chainage -100m Contour Position

1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage -100 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 0 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 120 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 210 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 300 Volume

Profile 1

Profile 2

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 380 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 480 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 580 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 680 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 780 Volume

Profile 3

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 850 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 900 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)

Chainage 970 Volume

1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 4

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 5

Profile 6

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 7

Profile 8

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 9

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 10

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


Profile 12

Profile 11

□ = 1 m contour

O = 2 m contour


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


1970 1980 1990 2000 201010

20

30

40

50

Date

Chain

age (

m)


1970 1980 1990 2000 20100

50

100

150

200

Date

Volu

me (

m3/m

)


□ = 1 m contour

O = 2 m contour

roches beach coastal hazard lines reassessment · table 2-1: 100 year ari swell and wind-waves...

Documents