NSW Coastal, Ocean & Port Engineering Panel (COPEP) Half Day Seminar (August 2012)
SYDNEY HARBOUR Sea Level Rise Vulnerability Studies
Phil Watson Principal Coastal Specialist Office of Environment and Heritage NSW Department of Premier and Cabinet Acknowledgements…
Doug Lord, Manager Coastal DECCW *
Cath Snelgrove, Cultural Heritage Manager, Sydney, Parks and Wildlife Division DECCW *
* (as at November 2009) Outline of Presentation
Background
Guided tour and brief history lesson
Vulnerability assessment
Management considerations
Conclusions Background…
Plan of Management being prepared for Sydney Harbour National Park (SHNP)
SHNP contains some of the key and iconic national heritage assets at obvious threat from projected sea level rise
Significant investment of public funds foreshadowed to preserve heritage assets
Vulnerability studies would provide fundamental strategic advice to inform the above-mentioned Background…
Separate pilot studies for Fort Denison and Goat Island
Fort Denison completed November 2008
Goat Island completed January 2009
Both studies available on the internet Outline of Presentation
Background
Guided tour and brief history lesson
Vulnerability assessment
Management considerations
Conclusions Guided tour..… Fort Denison
SYDNEY HARBOUR
Courtesy Google Maps Courtesy Tourism NSW Courtesy Tourism NSW Historic Context…… Once a rocky outcrop some 25m high known to Aboriginal people as “Mat-te-wan-ye”
In 1839 two American sloops entered the harbour undetected raising fears about the apparent inadequacies of Sydney's defences
In response, the island was quarried to create a level gun battery which was completed in 1842 Further concerns about defence capacity arose due to the outbreak of the Crimean War (1850s)
Courtesy Tourism NSW Historic Context…… Plans were drawn up for a fortification with barracks and the characteristic Martello Tower
Work involved quarrying some 8000 tonnes of stone from the Island itself and from nearby Kurraba Point, Neutral Bay
In 1857 the facility was named Fort Denison after Governor Denison and was declared ready for battle with 10, 8 and 12 inch 32 pounder cannons
Courtesy Tourism NSW Historic Context…… Guns were never needed outside of practice and no shots ever fired in anger
The Fort was abandoned as a military facility in the 1870s. At this time the development of iron clad ships and improved weapons made the facility obsolete
Harbour defences moved to the outer harbour from this point onwards
Courtesy Tourism NSW Historic Context……
The first measurements in the State Tide Register were recorded at Fort Denison in 1866
Continuous reliable tide measurements have been recoded at Fort Denison since 1914
Fort Denison is one of the 2 longest ocean water level records in the southern hemisphere
Courtesy Tourism NSW
Goat Island
Fort Denison
SYDNEY HARBOUR
Courtesy Google Maps Courtesy DECCW Historic Context……
Bennelong and his wife Barangaroo, were often seen here claiming a special relationship with the Island
During the early 1830s sandstone quarries were established on the Island until it was reserved for future defence needs
In 1832 Governor Bourke chose the Island as a gunpowder magazine complex with work commencing using convict iron gangs Courtesy DECCW Historic Context……
By 1839 the complex was complete with cooperage, large magazine, sentry compound wall, barracks, kitchen and stone wharf
During the late 1830s Colonial Government identified the eastern tip of the Island as suitable for a Water Police Station
In 1853 additional gunpowder magazines were added and by 1861 the Island housed over 700,000 pounds of gunpowder Courtesy DECCW Historic Context……
By the 1860s the Water Police Station had been appropriated for storing additional explosives such as guncotton and nitro-glycerine
By the 1880s explosives were also being stored at Spectacle Island and the Newington Armoury
By the turn of the century Goat Island was only housing low grade commercial explosives and small arms cartridges
Courtesy DECCW Historic Context……
With the outbreak of the Bubonic Plague in 1900, the Sydney Harbour Trust was established on Goat Island with a dredging and fire-fighting depot and a grand residence for the Harbour Master The MSB was established in 1936 incorporating the functions of the Trust
The MSB constructed wharfage around the Island and developed the shipyard facility
Courtesy DECCW Historic Context……
By the 1990s the role of the MSB had changed significantly and Goat Island was determined surplus to needs Goat Island was transferred to NPWS in 1994 and added to the SHNP in 1995
From 1995, the Island was the production home of the long running Australian drama series “Water Rats”
Courtesy DECCW Outline of Presentation
Background
Guided tour and brief history lesson
Vulnerability assessment
Management considerations
Conclusions Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current)
Up-to-date advice on sea level rise
Design water levels for future planning horizons (incorporating sea level rise)
Correlating design water levels with assets levels of interest (decks, floor levels, crest of seawalls, etc) Management considerations Vulnerability Assessment…… Survey data (bathymetry and assets) Survey Data
DECCW Fort Denison Survey Coverage Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current) Design Water Levels (Fort Denison)
2.60
2.40 2.36
2.20
2.16 2.00
1.80
1.60
1.40 Calculated
Extreme Maximum Tide Level Extreme Maximum( Level m ISLW) Tide Data (Max Levels) 1.20
1.00 0.001 0.01 0.1 1 10 100 Return Period (Year)
Gumbel distribution, co-efficient of correlation = 0.9997 Design Still Water Levels (Fort Denison)
ARI Maximum Level
(years) ISLW (m) AHD (m) 0.02 1.89 0.965 0.05 1.97 1.045 0.10 2.02 1.095 1 2.16 1.235 2 2.20 1.275 5 2.24 1.315 10 2.27 1.345 20 2.30 1.375 50 2.34 1.415 100 2.36 1.435 200 2.38 1.455 Design Wave Climate (3 Types of Waves)
Ocean swell waves (large well defined wave fields, generated remotely with periods generally >6-7 seconds)
Local seas (wind generated wave fields, governed by the wind strength and duration and length of water over which waves can build, periods generally <5-6 seconds)
Boat waves (highly variable with wave heights commonly <1-2m with periods ranging up to 10 seconds) Design Wave Climate (3 Types of Waves)
Ocean swell waves (large well defined wave fields, generated remotely with periods generally >6-7 seconds)
Local seas (wind generated wave fields, governed by the wind strength and duration and length of water over which waves can build, periods generally <5-6 seconds)
Boat waves (highly variable with wave heights commonly <1-2m with periods ranging up to 10 seconds)
These studies combined wind and boat waves into an “equivalent design wave” field based on wave power and applied them in the form of a sensitivity analysis to determine design wave runup levels
Courtesy DECCW Boat Waves in Sydney Harbour
Location Craft Class Averages Maxima Distance Power From Sail (W/m) (5) Hmax T Hmax T Line (m) (m) (sec) (m) (sec)
Hydrofoil 0.45 2.3 0.72 2.0 50-100 1017 Lady Ferry 0.25 2.2 0.44 2.2 418 Sydney Cove Water Taxi 0.38 2.2 0.44 1.8 342
Manly Cove Hydrofoil 0.56 2.4 0.87 2.6 50-100 1931
River Cat 0.32 8.4 0.40 10.0 100-200 1570 First Fleet Ferry 0.45 4.0 0.54 4.3 1230 Drummoyne Cruiser 0.2 2.6 0.25 3.0 184
River Cat 0.45 4.0 0.60 5.2 25-150 1837 Pulpit Point First Fleet Ferry 0.2 2.3 0.25 2.5 153
25m Cat Ferry 0.62 2.0 90 754 Sydney Harbour Lady Ferry 0.39 2.8 418
Source: Edwards and Lord (1995) Wind Waves around Fort Denison
Dir. Max Wind Speed Des. Fetch Fetch Hmo Period Power (1) F* Wind (m) eff Limit. (m) (s) (W/m) Speed F* (Y/N)
km/h m/s U10 (m/s)
N 70 19.4 17.9 1130 34.5 153.2 Y 0.33 1.5 166
NE 70 19.4 19.9 1330 32.9 130.8 Y 0.41 1.7 276
E 80 22.2 22.8 2950 55.8 107.1 Y 0.71 2.3 1160
SE 100 27.8 28.5 1190 14.4 76.6 Y 0.59 1.9 654
S 110 30.6 31.3 1000 10.0 66.4 Y 0.61 1.9 683
SW 90 25.0 23.1 910 16.8 105.1 Y 0.40 1.6 250
W 90 25.0 23.1 1650 30.5 105.1 Y 0.54 1.9 553
NW 80 22.2 20.5 780 18.2 125.4 Y 0.32 1.4 146 Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current)
Up-to-date advice on sea level rise Global Average MSL Rise Predictions
IPCC (2007) Global Average MSL Rise Predictions
91cm 79cm Regional Variations Ice Sheet Uncertainty 59cm
Model Outputs (IPCC 2007)
18cm
IPCC (2001) Advised SLR Estimates for Vulnerability Assessment
Sea Level Rise Scenario YEAR 2050 YEAR 2100
Lower Bound Estimate (LOW) 4 cm (1) 16 cm (3)
Medium Estimate (MED) (5) 21 cm 53 cm
Upper Bound Estimate (HIGH) 38 cm (2) 89 cm (4)
Note: Prior to NSW Government SLR Policy Statement (2009) Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current)
Up-to-date advice on sea level rise
Design water levels for future planning horizons (incorporating sea level rise) Design Water Levels (incorporating sea level rise)
ARI 2008 Design Still SLR Scenario 2050 Design 2100 Design (Years) Water Levels (L, M, H) Still Water Still Water (m AHD) Levels Levels (m AHD) (m AHD) 0.02 0.965 L 1.005 1.125 M 1.175 1.495 H 1.345 1.855 0.05 1.045 L 1.085 1.205 M 1.255 1.575 H 1.425 1.935 0.10 1.095 L 1.135 1.255 M 1.305 1.625 H 1.475 1.985 1 1.235 L 1.275 1.395 M 1.445 1.765 H 1.615 2.125 20 1.375 L 1.415 1.535 M 1.585 1.905 H 1.755 2.265 50 1.415 L 1.455 1.575 M 1.625 1.945 H 1.795 2.305 100 1.435 L 1.475 1.595 M 1.645 1.965 Note: Prior to NSW Government H 1.815 2.325 SLR Policy Statement (2009) Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current)
Up-to-date advice on sea level rise
Design water levels for future planning horizons (incorporating sea level rise)
Correlating design water levels with assets levels of interest (decks, floor levels, crest of seawalls, etc) Goat Island – Survey Summary of Relevant Features
Feature RL (m AHD) Top of concrete wharf superstructure along the western flank 2.07 – 2.35 within the Shipyard Precinct
Top timber decking around Small Boat Enclosure 1.50 – 1.65
Top timber decking along Ferry Wharf 1.49 – 1.62
Natural surface/paved areas along the waters edge due north of 1.35 – 1.80 the Fire Fighting Building, Gear Shed and Dredge Office
Natural surface/paved areas along the waters edge due east of 1.36 – 1.72 the Dredge Office
Top of erosion escarpment along waters edge south-east of the 1.40 – 2.64 Dredge Office, Water Police Station, Cottage and Port Emergency Services Building
Top of concrete wharf superstructure seaward of Port 2.13 – 2.79 Emergency Services Building
Paved forecourt in front of Port Emergency Services Building 1.61 – 1.64
Rock surface in front of Boat Shed 0.60 – 0.87 Floor level 1.78m AHD
Top step level 1.68m AHD
1.63m AHD
1.61m AHD
1.64m AHD Top of concrete superstructure along Eastern Wharf varies in height from 2.13 to 2.29m AHD
Examples of key Vulnerabilities Identified Fort Denison – Present Day
The entry from the wharf to the Western Terrace is the lowest surveyed point (1.41m AHD) This entry point is currently vulnerable to tidal inundation with a recurrence interval of 50 years (excluding wave action) The current 100 year ARI design water level would be sufficient to cover the forecourt area by up to 95mm of seawater for around 30-60 minutes (excluding wave action) This level would not be sufficient to overtop doorway sills entering the barracks Examples of key Vulnerabilities Identified Fort Denison – 2050
Under a “high” SLR scenario, the entry point would be vulnerable to tidal seawater penetration for more than 20 hours per year
The projected 100 year ARI design water level would be sufficient to cover the forecourt area by between 13 and 49 cm of seawater depending on SLR scenario (excluding wave action) Examples of key Vulnerabilities Identified Fort Denison – 2100
Under a “medium” SLR scenario, the entry point would be vulnerable to tidal seawater penetration for more than 50 hours per year
The projected 100 year ARI design water level would be sufficient to cover the forecourt area by between 25 and 99 cm of seawater depending on SLR scenario (excluding wave action) Approximate sea level which could be anticipated to occur as often as 50 times per year under a “high” sea level rise scenario (1.855m AHD) Approximate sea level which could be anticipated to occur as often as 50 times per year under a “high” sea level rise scenario (1.855m AHD) Vulnerability Assessment…… Survey data (bathymetry and assets) Water level & wave data (current)
Up-to-date advice on sea level rise
Design water levels for future planning horizons (incorporating sea level rise)
Correlating design water levels with assets levels of interest (decks, floor levels, crest of seawalls, etc) Management considerations Management Considerations… Both sites could be managed effectively (with minor modifications) to accommodate a modest SLR of 10-20cm
Significant alterations and expensive capital works would be required to manage both sites for “high” projected SLR this century At Fort Denison…… Close the existing entry point and replace with a continuous western seawall
Increase height of external seawall structures and incorporate provision for wave deflector capping to reduce wave overtopping threat
Seal existing rock foundations and external blockwork from seepage and direct ingress of seawater 1.9m tide, 26 November 2007 (Courtesy Rebecca Wise) Conclusions… Projected SLR over the course of the century will have a profound impact on these heritage listed sites
Capital works required to enable continued public access to these sites over the course of the century to protect the heritage assets will be expensive and extensive
All future planning at both sites should be informed by the most up to date advice on SLR projections at the time Conclusions… Engineering measures will only prove practical at both sites for a limited amount of SLR (possibly 50-100cm)
Public access to these sites into the future will be governed by the rate and amount of SLR. At some stage well into the future we must acknowledge that SLR will render these assets submerged artefacts Thank You….
For more information: E-mail: [email protected] Ph: 4904-2590 Mobile: 0413-278-651 Courtesy Tourism NSW