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Christmas Island

Coastal Engineering Investigation

Technical Report Report No. DOT R 482 September 2009

Christmas Island – Coastal Engineering Review – September 2009

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Cover photos: Top – Flying Fish Cove during Cyclone Rosie, 2008 (courtesy Darren Bird). Bottom - Flying Fish Cove 21st May 2009

Version Description Author Date Submitted E Draft for internal review KI 8/09/2009

0 Draft for AGD review KI 23/09/2009

1 Final KI 20/05/2010


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Contents Summary of recommendations ................................................................................................3 Introduction...............................................................................................................................4 Available information and recommendations for future monitoring ..........................................5

Water Level Records ............................................................................................................5 Historical data ...................................................................................................................5 Present data collection......................................................................................................5 Recommendations ............................................................................................................5

Wave information..................................................................................................................6 Historical data ...................................................................................................................6 Present data collection......................................................................................................6 Recommendations ............................................................................................................6

Beach and hydrographic survey ...........................................................................................6 Historical data ...................................................................................................................6 Present data collection......................................................................................................7 Recommendations ............................................................................................................7

Aerial photography................................................................................................................7 Historical data ...................................................................................................................7 Present data collection......................................................................................................7 Recommendations ............................................................................................................7

Field photography .................................................................................................................8 Historical data ...................................................................................................................8 Present data collection......................................................................................................8 Recommendations ............................................................................................................9

Kampong seawall .....................................................................................................................9 Available information ..........................................................................................................10 Condition inspection ...........................................................................................................11 Recommendations..............................................................................................................13 Future re-design of seawall ................................................................................................13 Seawall conclusion .............................................................................................................14

Isabel beach...........................................................................................................................14 Recommendation:...............................................................................................................15

Coastal limestone undercutting ..............................................................................................15 Recommendation:...............................................................................................................16

Climate change ......................................................................................................................16 Available information ..........................................................................................................16 Sea level rise ......................................................................................................................17 Recommendations:.............................................................................................................19

References .............................................................................................................................20 Appendix A - Recent hydrographic survey .............................................................................21 Appendix B - Historical field photographs ..............................................................................23 Appendix C - Photographic Monitoring Plan ..........................................................................27 Appendix D - Perched Beaches summary .............................................................................31 Appendix E - Quarry material laboratory analyses.................................................................34 Appendix F – Particle size distributions..................................................................................40 Appendix G – Kampong seawall condition inspection............................................................45


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Summary of recommendations High priority recommendations contained in this report have been summarised here. High priority has been given to those actions which are considered very important and/or urgent. High priority actions for 2010/2011 are:

• Water levels should continue to be monitored in Flying Fish Cove. • Further attempts be made to locate the non-directional wave data from 1988/1989,

and the directional wave data from 2001/2002. • Directional wave data to be collected in Flying Fish Cove using a waverider buoy

offshore for at least 18 months. • A detailed geotechnical investigation is carried out by an engineering geologist or

geotechnical engineer for the Settlement coast. • Reach One of the seawall to be maintained prior to the next swell season of summer

2010/2011. Extensive repointing is required. • Reach Two of the seawall be maintained within the next year. Repointing is required. • Field photographs are collected monthly of the Kampong foreshore, seawall and

Isabel Beach. • Further coastal engineering advice be obtained if a significant section of the wall fails

or is damaged. High priority actions to 2014 are:

• A hydrographic survey is conducted to encompass the waters between Rocky Point and Smith Point between the high water mark and approximately 100m depth.

• Beach survey be conducted from the Kampong seawall to join the hydrographic survey.

• The height of the crest of the seawall be accurately surveyed (+/- 0.1m accuracy). • Aerial photography is collected for the entire island every five to ten years, and

archived by the Attorney-General’s Department. • The AGD consider longer term planning in the Kampong, with respect to climate

change and sea level rise.


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Introduction In autumn 2009 the federal Attorney-General’s Department (AGD) requested preliminary coastal engineering advice for Christmas Island (Figure 1) from the Department of Transport (DoT). Advice was requested regarding:

1) The condition and functionality of the seawall at Kampong in Flying Fish Cove; 2) An initial inspection of the undercutting and honeycombing of the limestone cliff

around the Settlement area; 3) The amenity of Isabel Beach and erosion stabilisation; 4) Future coastal monitoring for locations of interest, and; 5) The likely impacts of projected sea level rise due to climate change.

A DoT coastal engineer visited Christmas Island between the 18th and 25th May 2009. This report summarises the result of onsite inspections and makes recommendations regarding coastal engineering issues on the Island.

Figure 1: Christmas Island location (Google 2009). Christmas Island is located in the northern Indian Ocean approximately 300kms south of the Indonesian Island of Java. The Island experiences a typical tropical equatorial climate with a wet and dry season. The wet season occurs between November and May and is characterised by northwest monsoonal winds and tropical cyclones. The dry season falls between June and November and is characterised by low rainfall and steady southeast tradewinds (ABC, 2009).


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Available information and recommendations for future monitoring Although there is some historical and modern data available, data collection is on an ad hoc basis and not sufficient for detailed coastal engineering design at present, or in the near future.

Water Level Records

Historical data Typical tidal ranges (Table 1) are approximately 1m (MLLW to MHHW). Seven years of historical water level recordings are available for Flying Fish Cove from 29th September 1986 to 19th November 1993. The data were collected by the oceanography division of CSIRO and are available from http://ilikai.soest.hawaii.edu/uhslc/htmld/0170A.html Bureau of Meteorology National Tide Centre records indicate that the sounding datum for this data is 6.966m below local benchmark “CHS 1”. Table 1: Tidal planes for Christmas Island. Taken from DPI Chart 680.

Present data collection The Bureau of Meteorology (BOM) is currently operating a tsunami monitoring gauge on the Marine Jetty in Flying Fish Cove. The gauge was installed in December 2005 as a test site and upgraded to an operational site in December 2006. Correspondence with BOM has revealed that the gauge has not yet been surveyed for vertical position in relation to local benchmarks. The gauge is due to be upgraded later this year, during which it will be surveyed.

Recommendations • The tsunami monitoring gauge should be appropriately surveyed when it is upgraded

so that the water level data collected can be referenced to Chart Datum and used for coastal engineering purposes.

• Water levels should continue to be monitored in Flying Fish Cove into the future.

Tidal Plane Level Relative to Chart Datum (m)

Highest Astronomical Tide (HAT) 1.84

Mean Higher High Water (MHHW) 1.43

Mean Lower High Water (MLHW) 1.08

Mean Sea Level (MSL) 0.86

Mean Higher Low Water (MHLW) 0.57

Mean Lower Low Water (MLLW) 0.36

Lowest Astronomical Tide (LAT) 0.0


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Wave information

Historical data The wet season is commonly referred to as the swell season, as during this northwest monsoon period tropical cyclones can pass close to the Island and bring large northwest swell and seas due to gale force winds. During the dry season, southeast sea and swell dominates due to the persistent southeast trade winds (ABC 2009). It is understood that approximately 18 months of non-directional wave data was collected in 1988/89 with a moored floating waverider buoy. The data was collected by the organisation responsible for running the Christmas Island port at the time. Further, records indicate that directional wave data was collected in 2001/2002. External consultant WNI Oceanographers and Meteorologists (now RPS Metocean – job number J2293) have a record of supplying a directional waverider buoy, and ancillary equipment to CI. Records note the buoy was deployed in August 2001. Unfortunately neither set of wave data appears to have been archived off-island and it is unknown if a copy of either still exists. At the time of writing, historical computer archives were being searched in an attempt to locate a copy of the data sets. A wave buoy is currently stored in the port sheds on CI. It is likely that this is the directional buoy deployed in 2001.

Present data collection No wave data is currently collected at Christmas Island.

Recommendations • Further attempts be made to locate the non-directional wave data from 1988/1989,

and the directional wave data from 2001/2002. • Directional wave data is collected in Flying Fish Cove using a waverider buoy

offshore for at least 18 months (covering two November to March “swell seasons”), but ideally two years or more.

• DoT’s Tides and Waves branch may be able to provide some advice regarding the re-deployment of the wave buoy on CI (or a new one).

• Any wave data collected historically or into the future should be made available to, and be archived by, DoT.

Beach and hydrographic survey

Historical data The following nautical charts are available for Christmas Island:

1) W.A. Department for Planning and Infrastructure Chart # 680; 2) Royal Australian Navy Chart # 400; 3) Royal Australian Navy Chart # 608, and; 4) Royal Australian Navy Chart # 920.

These charts use various depth soundings from different hydrographic surveys. The survey data has been collected historically by various methods and combined to give coverage of the island’s coastal waters.


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Present data collection A hydrographic survey was conducted by Don Shepherd Surveys Pty. Ltd. In March 2008. This survey covered a small area of seabed adjacent to the Port. See Appendix A. There does not appear to be any recent, beach or hydrographic survey which encompasses all of Flying Fish Cove and the near-shore coastal zone to the north and west.

Recommendations • Historical hydrographic survey data be reviewed and summarised by survey extent,

method and date of collection etc. • Historical hydrographic survey data be archived with by the DoT’s Spatial Information

branch; • A hydrographic survey is conducted to encompass the waters between Rocky Point

and Smith Point between the High Water Mark and approximately 100m depth. • Beach survey be conducted from the Kampong seawall to join the hydrographic

survey. The survey shall consist of accurately surveyed cross-shore beach profiles.

Aerial photography

Historical data There are five years of aerial photography available for Christmas Island (Table 2). The photography has been collected primarily by aerial flights, but satellite photography was collected in 2006. Aerial photography is understood to have a higher resolution (~0.3m pixel size) than satellite photography (~1m pixel size). Aerial photography is, however significantly more expensive to collect than satellite photography. Table 2: Summary of known aerial photography for Christmas Island. Year Method of Collection Coverage 1965 Unknown – assumed aerial flight unknown 1976 Aerial flight – black and white Whole island 1981/2 Aerial flight – black and white Whole island 1987 Aerial flight – colour Whole island 1997 Aerial flight – colour Flying Fish Cove area 2006 Satellite - colour Flying Fish Cove area It is understood that Geoscience Australia are the custodians of this photography and that the 1976 and 1981/2 photography is being digitised at the time of writing.

Present data collection Correspondence with Geoscience Australia indicates that there is no aerial photography collection program for Christmas Island into the future.

Recommendations • Aerial photography is archived by the Attorney-General’s Department and Landgate

(W.A.) for ease of future access. • Photography is collected for the entire island every five to ten years by either an

aerial flight or satellite photography.


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Field photography

Historical data Some field photographs of Flying Fish Cove are available from the twentieth century and have been included in Appendix B. Figure 2 is a photograph of the Kampong foreshore in the 1950’s before the current apartment blocks, and seawall were constructed. Note the relatively flat white sandy beach which existed along much of the foreshore.

Figure 2: Kampong foreshore circa 1950’s (Unknown, 2003).

Present data collection Field photographs are collected by various people on an ad hoc basis in Flying Fish Cove. During the site visit to Christmas Island photographs of the April 2008 significant storm event, and repair works to the seawall were kindly donated by the following island residents:

• Darren Bird – Acker Trading (Figure 3); • Dave Robertson – Christmas Island Port (Figure 4), and; • Kevin Walton – AGD (Figure 5).

Figure 3: Field photographs of high wave conditions associated with Cyclone Rosie on 23rd April 2008, courtesy of Darren Bird.


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Figure 4: Field photographs of high wave conditions associated with Cyclone Rosie on 22nd April 2008, courtesy of Dave Robertson.

Figure 5: Field photographs of seawall damage from Cyclone Rosie and subsequent repairs in mid-2008, courtesy of Kevin Walton.

Recommendations • Field photographs are collected monthly of the Kampong foreshore, seawall and

Isabel Beach in accordance with the Christmas Island Photographic Monitoring Plan (Appendix C).

• Arrangements be made for the archiving of field photography in either the Canberra, Perth and Christmas Island office (or all three) of the AGD.

Kampong seawall Flying Fish Cove is the only accessible beach close to the Kampong and Settlement. It is a pocket beach contained by near-continuous limestone cliffs along the coast on either side. The beach is currently constrained horizontally to the rear (landward) by a near-vertical seawall. There is a small section of grassed foreshore behind the seawall (approximately 9m on average) then the foreshore road. Directly behind the road are three residential apartment blocks and other associated buildings. Behind these apartment blocks is a very steep and high limestone cliff. The beach is horizontally constrained to seaward by the ‘drop-off’ into deep water (several hundred metres deep) approximately 500m from the shoreline. A majority of the seabed in the nearshore zone consists of hard coral reef. There is only a narrow section of beach between the nearshore environment and the seawall. The beach varies in nature, but generally consists of a mix of white sand, coral gravel/shingle and coral rubble. The beach in Flying Fish Cove is a perched beach. A perched beach is one characterised by a layer of sand over a rock platform. They can change very quickly as the thin layer of sand of which they comprise can easily be transported to and from the beach face. The presence of a white sandy beach, on this type of coast, is largely controlled by


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local sediment transport and the underlying rock structure. The rock platforms are predominantly located in the inter-tidal zone (Figure 6). For further information about the behaviour of perched beaches refer to Appendix D.

Figure 6: Perched beaches comprise a thin layer of sand on top of a rock platform, often in the inter-tidal zone.

Available information The Kampong seawall was built in the late 1970 or early 1980’s. Construction of the seawall appears to have been haphazard and it’s condition varies greatly along its length. In general it is a near-vertical revetment style seawall constructed from locally quarried limestone rocks (see Appendix E) of approximately 5-20 kgs cemented together. There is no known design information available for a majority of the seawall. An approximately 21m long section of seawall west of the car park was repaired in Winter 2008 after collapsing during a significant storm event in April 2008. Repairs to this section were well documented by the AGD on Christmas Island. A report, design sketches and field photographs during construction are available. Cyclone Rosie in April 2008 provides evidence that the current wall is overtopped during periods of high water level and/or high energy waves. There is no comprehensive accurate survey (+/- 0.1m accuracy) detailing the height of the seawall. This survey information is important for any future coastal structure design in Flying Fish Cove and should be collected. GHD (2001) presents some limited survey data, but no metadata is provided. Sediment samples at the Flying Fish Cove beach, and other CI beaches were collected during the site visit. The results of particle size distribution analyses conducted show that the median diameter (‘D50’) of the samples varies between 0.4 and 1mm (Appendix F). The AGD advised during April 2010 that a sink hole appeared ~1m behind the seawall, near the steps south of the boat ramp (Figure 7). The hole was ~1m in diameter and ~1.5m deep. Site observations (by the AGD) indicated that the soil was likely to have been lost underneath the seawall structure rather than through it. This type of event highlights the importance of having a well-founded structure with appropriate filter layers.


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Figure 7: Sink hole which developed near southern steps in Flying Fish Cove in April 2010, courtesy Stephen Elliot.

Condition inspection A condition inspection of the seawall was conducted on the 20th May 2009 (Appendix G). This condition involved a visual inspection of the seawall, beach and foreshore. For practical purposes the seawall was split into three sections or “reaches”. The first reach extended from the north/east end of the wall for approximately 260m to the foreshore car park. The second reach extended from the car park for approximately 190m to the jetty. The third reach extended from the jetty approximately 210m to the end of the seawall at the western end of Flying Fish Cove (Figure 8).


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Figure 8: Flying Fish Cove from Territory Park lookout, 21st May 2009. The three “reaches” of the Kampong seawall are shown. The condition inspection assessed the structural integrity of the seawall as good, fair or poor (Table 3):

1) Good – The seawall is effective at performing its current designated function, is well maintained and is not subject to damage from active processes.

2) Fair – The structure is largely effective at performing its current designated function, but has experience some damage due to active processes. In general damage is minor and necessary repairs are considered routine maintenance.

3) Poor – Damage has occurred to the structure that reduces its effectiveness for performing its current designated function. Replacement of the structure, possibly with design modifications to cater for active processes may be required to address this problem.

The condition inspection also assessed the functionality of the seawall (Table 3). The purpose of the seawall is shore protection of assets including: foreshore and its amenities, road and car parks; apartment blocks and other buildings. The functionality of the seawall was assessed as good, fair or poor:

1) Good - No evidence of sediment loss behind the structure, indicating that it performs adequately under the full range of conditions experienced since construction or the last major maintenance.

2) Fair - Minor loss of sediment, affecting less than 25% of the area immediately behind the structure. This suggests good retention occurs under moderate conditions, with some material loss during extreme events.

3) Poor - Significant sediment loss, affecting more than 25% of the area immediately behind the structure. Structure is performing unsatisfactorily as a foreshore protection structure.

Reach Three

Reach Two

Reach One


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Table 3: Condition inspection summary for the three “reaches” of the Kampong seawall. Reach Structural Rating Function Rating One Poor Fair Two Fair Fair Three Good Fair

Recommendations • The height of the crest of the seawall be accurately surveyed (+/- 0.1m accuracy) • Reach One be maintained prior to the next swell season of summer 2010/2011.

Extensive repointing is required. Where undermining has occurred (Figure 9) the extent of the foundation should be determined. If absent a foundation should be installed.

• Reach Two be maintained within the next year. Repointing is required. Where undermining has occurred the extent of the foundation should be determined. If absent a foundation should be installed.

• Photographic monitoring of the entire seawall be conducted twice per year during September and March.

• Further coastal engineering advice be obtained if a significant section of the wall fails or is damaged.

• Further coastal engineering advice be obtained when approximately two - three years of water level and wave data has been obtained to allow a long term coastal protection solution to be designed.

Figure 9: Field photographs of undermining of Reach One of the Kampong seawall, 20th May 2009.

Future re-design of seawall Any re-design of the seawall, or sections of it, in the future must include (but is not limited to) the following:

1) Allowance for localised erosion scour at the base of the seawall during high energy wave events.

2) Consideration of the foundation depth, or ensure its placement on bedrock. 3) Consider the crest elevation in accordance with wave overtopping likely from storm

events, both now and in the future. Potential sea level rise from climate change must be considered.

4) Suitable drainage must be incorporated in the design for when overtopping does occur, to prevent “pooling” of seawater behind the wall. This drainage may be provided by permeable rock fill behind the wall and/or one way drainage outlets along the wall.


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The DoT would generally recommend the construction of a sloping rubble-mound rock revetment seawall. This is due to the flexibility of the rubble-mound revetment, and the availability of quarry-blasted rock on the Island. The space constraints in the Kampong, however, must be considered. Due to the sloping nature of a rubble-mound revetment, (approximately 1V:2H) the structure would take up a significant amount of horizontal space. GHD (2001) recommends construction of a concrete hollow block seawall – similar to the structure near Qantas Close on West Island of the Cocos Keeling Islands. Although this structure may be a suitable option, we recommend wave and water level be collected to allow a more informed design decision. The use of locally quarried rock, rather than cast concrete units, is also likely to offer a cost saving. There is a significant risk that the dry beach will be lost in the future due to scour induced by wave reflection off any seawall. Such erosion would limit swimming opportunities along the Kampong. A management decision will be required to prioritise the benefits of protecting coastal assets/infrastructure and the aesthetics/amenity of this section of coast.

Seawall conclusion Although the current seawall is currently in poor to fair structural condition overall, it is still performing its function of protecting the foreshore reserve and landward assets (e.g. roads and buildings). Repairs should be carried out on sections of the seawall as described above.

Isabel beach On the 19th May 2009 Isabel Beach, located immediately north of the Port, was a rock/rubble pocket beach without any sand, contained between two significant rock cliff headlands. Liaison with the AGD and other local residents indicated that the beach used to be largely made up of sand and used for recreation. The missing lower staircase (Figure 10) indicates that the beach may have suffered severe storm damage. It is likely that sand has been eroded during a significant storm event. The nature of this type of beach erosion on a pocket beach is such that the recovery (i.e. transport of sand back onto the beach) is not predictable. As there is limited beach sand available on Christmas Island, artificial sand nourishment of Isabel Beach is not considered viable. Photographic monitoring will provide information on the recovery, or otherwise, of Isabel Beach.


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Figure 10: Isabel Beach, 19th May 2009. Note the missing lower stair case in the top right photograph.

Recommendation: • Field photographs are collected monthly of Isabel Beach in accordance with the

Christmas Island Photographic Monitoring Plan (Appendix C).

Coastal limestone undercutting On the 21st and 22nd May 2009 a brief visual inspection was undertaken of undercutting and honeycombing of coastal limestone cliffs around the Settlement area (Figure 11). The coastal cliff terrace varies in width between approximately 20m and 40m, and height approximately 5m to 10m above mean sea level along this section of coast. The limestone the cliffs are made of is a marine limestone. Uplift of the island has preserved the terrace as an elevated shoreline platform (R Gozzard 2009, pers. Comm., 20 July). A majority of the coastal cliffs had some degree of undercutting evident (less than 5m overhang) at a height between approximate mean sea level and the high tide mark. This undercutting has likely been caused by coastal erosion due to wave action. Various active blowholes were observed along the Settlement coast. It would seem that this section of coast may have an extensive system of honeycombs. The following blowholes and their locations were observed:

1) Behind the fishing tackle shop (at approximately 10° 25.070 S, 105° 40.413 E) there are blowholes approximately 20m from cliff edge and 20m from unsealed road.

2) Rocky Point Rd. foreshore (at approximately 10° 24.867 S, 105° 40.552 E) there are between five and ten blowholes within 8m of the road (Figure 11).

There is concern about the stability of the coastal terrace in general with the potential for collapse of the naturally occurring honeycombs. The coastal erosion due to wave action (evident as undercutting) is unlikely to be of the same importance as the potential collapse from honeycombs (R Gozzard 2009, pers. Comm., 20 July).


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Figure 11: Settlement coast, 21st and 22nd May 2009. Clockwise from top left: typical limestone cliff terrace with fuel tanks close to cliff edge; typical coastal cliff with some undercutting; Blowhole less than one metre from Rocky Point Rd. near bus stop, and; Rocky Point Rd. foreshore.

Recommendation: • A detailed geotechnical investigation is carried out by an engineering geologist or

geotechnical engineer for the Settlement coast. The investigation should determine the extent of honeycombing, and the potential risk of damage to coastal infrastructure, particularly that sited within ~150m of the coastal cliffs.

Climate change There are several key environmental variables that may be affected by climate change, including:

• sea level rise; • ocean currents and temperature; • wind climate; • wave climate; • rainfall / runoff; and • air temperature.

The combined coastal impact of these variables will vary and requires consideration on a local scale and case by case basis. The rise in sea level, however, is currently considered to be the most significant of these.

Available information Maunsell (2009) conducted a risk assessment for both Christmas Island (CI) and the Cocos (Keeling) Islands (CKI). Key comments of the report include:

• CI is less vulnerable to the potential impacts of climate change and sea level rise, compared to the CKI.

• The Kampong and Settlement areas are potentially exposed to sea level rise and increases to storm and cyclonic water level surges. Overtopping events due to high water levels and large waves will become more frequent with rising sea levels.

• Likely to more permanently lose beach in front of Kampong Seawall as sea level rises.

• Undercutting of cliffs is likely to increase with sea level rise and possible increases in wave energy, particularly along sections of coast where there is no protective beach or sub-tidal rock/reef platform.


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• Kampong area is at “definite risk” of sea level rise, and the Port infrastructure is at risk from sea level rise and storm surge associated with a potential increase in extreme events.

The report suggests staged retreat from the Kampong and Settlement is required in the long term to move away from these low-lying areas.

Sea level rise Historic global sea level variation can be estimated from the analysis of tide gauge recordings around the world. Church & White (2006) used monthly mean sea level recordings to reconstruct the global sea level from 1870 to 2004 (Figure 12). Sea level has risen over the past century by approximately 1-2 mm/yr. Observations from satellite altimetry since late 1992 have improved estimation of sea level rise and indicate that the rate of rise over the past two decades has been significantly greater than the rate over the 20th century, approximately 3 - 4 mm/yr.

Figure 12: Reconstruction of global mean sea level from tide gauge recordings 1870 to 2004 (CSIRO 2008). The Intergovernmental Panel on Climate Change’s (IPCC) most recent projections for global sea level rise are contained within the fourth assessment report (IPCC, 2007). The report provides projections based on 40 future greenhouse gas emission scenarios. The IPCC fourth assessment report (IPCC, 2007) provides maximum and minimum projections of sea level rise at the end of the 21st century for the six illustrative scenarios. The projected global sea level rise by 2100 is between 0.2 m to 0.8 m. The upper bound includes a factor of 0.1 m to 0.2 m, depending on scenario, to account for the potential scaled-up ice sheet discharge of the Greenland and Antarctic Ice Sheets. Thermal expansion is responsible for 70 - 75% of the global sea level rise projections and is relatively well understood process. The remainder comprises melt waters from glaciers and ice caps such as Greenland and Antarctica. The


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level of understanding about the magnitude and timing of contributions to sea level rise from ice melt is low (Garnaut, 2008). For all scenarios the projected rate of sea level rise is greater than the average rates recorded over the 20th century and accelerates over the 21st century. The projections only significantly diverge for the second half of the 21st century, with little variation in the average of each scenario up until 2050.

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Figure 13: IPCC AR4 sea level rise projections through the 21st century including scaled-up ice sheet discharge as incorporated by CSIRO (2009). Dashed lines for 5% and solid lines for 95% ranges of confidence limits. Observations from satellite altimetry indicate that the rate of rise of global mean sea level since 1990 has been at the top of the sea level rise projections. There is undisputable evidence that sea level will continue to rise over the 21st century as a result of climate change. However, over the short term (until the middle of the century) it is likely that the changes in mean sea level due to inter-annual variability will be greater than those of climate change. The El-Nino Southern Oscillation is the dominant process driving short term fluctuations in sea level change for Western Australia, with a maximum amplitude of 0.3 m. Future sea level change will not be uniform across the globe. Work has also been undertaken by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to determine local variations around the Australian coastline of one of the IPCC scenarios to 2030 and 2070 (CSIRO, 2009). For Christmas Island, the mean sea level rise estimated by the multi-model mean of the scenario does not significantly differ (less than ± 0.05 m) from the global averaged mean at 2070 (Figure 14). Localised effects of land movement at Christmas Island must also be considered. Should the land be subsiding or emerging the relative rate of sea level rise with respect to the Island will be different to the rate of mean sea level rise. It is not known if there is local land movement at Christmas Island.


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Figure 14: Multi-model mean IPCC SERS scenario A1B projected sea level departure from the global mean for 2070 (CSIRO 2009).

Recommendations: • The AGD consider longer term planning in the Kampong. Managed retreat is likely to

be the most appropriate planning strategy for the Kampong area. When the present apartment blocks reach the end of their useful life they should not be rebuilt in the Kampong. As structurally significant, but not coastally dependant, assets are decommissioned they should be relocated to sections of the island above projected future sea levels.

• The design of new coastal protection structures should be such that they can be adapted for sea level rise in the future, e.g. a seawall could be built with an over-engineered foundation such that the super structure can be upgraded in the future.

• Geological investigation, initially by literature review be undertaken to determine if there is any vertical movement of the Island, and how this may effect the relative rate of sea level rise.


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References ABC, (23rd September 2009). Christmas Island, [Online], ABC, Available from:

<http://www.abc.net.au/nature/island/ep2/about1.htm> Brander, R.W., Kench, P.S., Hart, D. 2004, ‘Spacial and temporal variations on wave

characteristics across a reef platform, Warraber Island, Torres Strait, Australia’, Marine Geology, vol. 207, pp. 169-184.

Church, J.A., & White, N.J., 2006, “A 20th century acceleration in global sea-level rise”,

Geophysical Research Letters, vol. 33, L01602 CSIRO. (21st April 2009), Sea Level Rise, [Online], CSIRO, Available from:

<http://www.cmar.csiro.au/sealevel/index.html> [10th September 2009] Garnaut, R., 2008, The Garnaut Climate Change Review, Australian National University,

Canberra. GHD (2001), ‘Flying Fish Cove Seawall – Report on wave study and design for hollow block seawall’, prepared for Commonwealth Department of Transport and Regional Services Google Maps, (23rd September 2009). Christmas Island, [Online], Google, Available from:

<http://maps.google.com.au/maps> Kench, P.S., & Brander, R.W. 2006, ‘Wave processes on Coral Reef Flats: Implications

for Reef Geomorphology Using Australian Case Studies’, Journal of Coastal Research, vol. 22, no. 1, pp.209-223.

Maunsell-AECOM, 2009, ‘Climate change risk assessment for the Australian Indian

Ocean Territories – Cocos (Keeling) Islands and Christmas Island’, prepared for Commonwealth Attorney-General’s Department

Stul, T. Pattiaratchi, C., Eliot, I. 2007, Physical Characteristics of Perth Beaches,

Western Australia, [Online], Available from http://www.wapc.wa.gov.au/Initiatives/Coast/Perth+coastal+planning+strategy/310.aspx

[11 June 2008]. Unknown. 2003, Historical photograph archive Christmas Island [CD-ROM], Unknown,

Christmas Island.


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Appendix A - Recent hydrographic survey


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Appendix B - Historical field photographs Flying Fish Cove (Unknown, 2003).


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c. 1950’s

c. 1955


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Date unknown

c. 1950’s


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Date unknown


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Appendix C - Photographic Monitoring Plan Christmas Island photographic monitoring plan


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Flying Fish Cove – Kampong Monitoring Photograph No. 1


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Flying Fish Cove – Kampong Monitoring Photograph No. 2


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Isabel Beach Monitoring Photograph


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Appendix D - Perched Beaches summary


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Beaches characterised by a layer of sand over a rock platform are referred to as 'Perched Beaches'. They can change very quickly as the thin layer of sand of which they comprise can easily be transported to and from the beach face. The presence of a white sandy beach, on this type of coast, is largely controlled by local sediment transport and the underlying rock structure. Flying Fish Cove is a perched beach. The rock platforms are predominantly located in the inter-tidal zone (Figure 6).

Figure 15: Perched beaches comprise a thin layer of sand on top of a rock platform, often in the inter-tidal zone. Stul, Pattiaratchi and Eliot (2007 p.3) gave an insight into the nature of perched beaches: "...over 25% of the beaches surveyed on the Perth Metropolitan Coast are perched beaches located on or immediately landward of outcropping rock. These beaches exhibit most variability in width and elevation and hence should be viewed as least stable from a management perspective. Further research is required to establish an adequate conceptual model of their profile form and behaviour in response to changing meteorologic and oceanographic conditions." The "most variability" the authors refer to implies perched beaches can be highly variable in time, compared to simple sandy and rocky coasts. Figure 16 and Figure 17 depict the mechanism for this dynamic variability. Changes in water level create the potential for waves to access different sections of the beach. During low water levels incident waves act primarily on the rock/reef platform, but when/if they do overtop the platform's crest, the waves transport suspended sediment onto the perched beach platform (Figure 16). During times of high water levels, incident waves act on the sandy perched beach, and can suspend sediment and carry it offshore (Figure 17). Brander, Kench and Hart (2004) concluded that little opportunity exists for sediment transport to occur during normal conditions, but that significant changes were likely during extreme events, such as storms. By extension, the stability of perched beaches, such as those in Flying Fish Cove, are largely influenced by changing water levels over the rock platform on which they exist (Kench and Brander 2006).

Figure 16: Perched beach deposition occurs at low water levels when incident waves can suspend sediment in front of the rock platform, then wash it up and over onto the beach.


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Figure 17: Perched beach erosion occurs during times of high water level when waves do not suspend nearshore sediments, but can access beach sediments, which are then carried offshore.


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Appendix E - Quarry material laboratory analyses Historic laboratory analyses of Christmas Island quarry – courtesy Darren Bird


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The quarry currently operating on Christmas Island is located at 10°25.297’S 105°41.694’E. The quarry is likely to be capable of yielding limestone armour rock of several tonnes. At present, rock for retaining walls is sourced by an excavator mechanically chipping away material from the quarry walls. There is currently no shot firer present on the Island to blast rock. Historical analysis of material from the quarry indicates:

1) The density of the limestone is 1.91 tonne/m3; 2) The flakiness of the limestone is between 12% and 16%, and; 3) It can be crushed to produce a sand, granule and pebble mix with D50 = 3mm.

Quarry operated by Acker Trading – 20th May 2009.


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Appendix F – Particle size distributions


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Location table, please note all GPS coordinates were taken using a hand-held GPS.

Site # Site Name

Latitude (S)

Longitude (E)

I Quarry aggregate 10° 25.297 105° 41.694 II Flying Fish Cove - 30m north of jetty 10° 25.770 105° 40.208 III Flying Fish Cove - north end 10° 25.636 105° 40.312 IV Flying Fish Cove - south steps 10° 25.806 105° 40.091 V Ethyl Beach 10° 27.817 105° 42.451 VI Waterfall Bay Beach 10° 27.565 105° 42.308 VII Dolly Beach n/a n/a

Site I - Quarry aggregrate

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Site II - Flying Fish Cove - 30m North of jetty

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Site III - Flying Fish Cove - North end

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Site IV - Flying Fish Cove - South steps

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Site V - Ethel Beach

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Site VI - Waterfall Bay Beach

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Site VII - Dolly Beach

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Appendix G – Kampong seawall condition inspection

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