Preliminary study of the prospect of reinstating the Nepean Bay Bar barrier to protect Melbourne and Geelong from sea level rise. Flattened version of presentation to Melbourne Emergence Meetup on 9 February 2017, brought forward so it can be cited in response to draft Port Phillip Bay Environmental Management Plan.

1. Tony Smith
Melbourne Emergence Meetup
9 February 2017
Nepean Bay Bar
Can reinstatement and enhancement of
this natural barrier save Melbourne?
Mud Island is
at the centre of
the Great Sand.
Its southern
beachfront
dominates the
view north from
the Queenscliff-
Sorrento ferry.

2. Draft Port Phillip Bay
Environmental Management Plan
2017–2027
Public
consultation
on the draft
Plan will be
open until 10
February
2017.

3. • “(P)opulation growth and climate change pose significant
challenges” (ten mentions)
• “Sea levels will rise and storm surges will become more
frequent” (one mention)
• Our culture is predicated on an exceptional 7,000 year period
of sea level stability
• Average rate of sea level change across 140,000 years is one
metre per 140 years
• Peak rate is much higher
• Several indicators of approaching critical instabilities
• Question is when, not whether, sea level rise really takes off
• Like most coastal cities, Marvellous Melbourne very vulnerable
Draft Port Phillip Bay Environmental Management Plan 2017–2027
Ignores the Elephant in the Room

4. 1000 B.P. Lake Phillip very different
This and more from G. R. Holdgate, B. Wagstaff & S. J. Gallagher 2011
From 2800 B.P.
Nepean Bay Bar
joined the
Bellarine and
Mornington
Peninsulas,
leaving shrinking
Lake Phillip
isolated from
Bass Strait and
evaporating away
faster than rain &
run off refilled,
until some little
aboriginal boys
threw a toy spear
…

5. Where to tonight?
• Geology of river deltas forming crescent beaches
• Comparisons to Zuiderzee in The Netherlands
• Public romanticisation of recent Bay environment
• RAMSAR wetlands serving bird migration tracks
• Aboriginal land occupancy and cultural knowledge
• Staged reinstatement of the Nepean Bay Bar seal
• Port capacity maintained with locks then Bay South
• Predeployment of rail and road capacity both ends
• Returning Barwon to Corio Bay to save Geelong
• Narrowing on peak rate and timing of sea level rise

6. River deltas forming crescent beaches
in rift which failed when Australia was breaking away from Antarctica
Murray Mouth
& the Coorong
Gippsland Lakes
& 90 Mile Beach
Yarra &
Barwon

7. Local variability of
sandhill positioning,
consequent aeolianite
formation, and shoreline
erosion obscure larger scale
structural dynamics of river
delta–based crescent beaches.
}Fragment of
Peninsula
Back Beach.
Many local and wider
considerations should
influence final alignment of
Mornington Peninsula access
to restored Nepean Bay Bar.

8. Aside:
Much of the pain over the Murray Basin scheme
may be traced to a failure to account for the
diversion of natural flows from the wet southeast
of South Australia away from the south end of
the Coorong in an effort to drain the swamp.

9. The Latrobe,
Thompson, Mcallister
and more Gippsland
rivers similarly form
terminal lakes behind
a crescent of sandhills.

10. We have a more permanent terminal salt lake
comparable to Lake Phillip: Lake Corangamite
and more crescent beaches
with more rugged sandhills

11. isolation
watermovement
time
evaporation ∝ lake surface area
run off ∝ 10% catchment minus lake area
rainfall ∝ lake surface area
total inflow into terminal lake
balance
Simplified* hydrological history of terminal lake
*ignoring ground water flows, non-linear compounding effects, etc.

12. Lower Aire River, also just west of Cape Otway, refilled more by
waves at high tide than by freshwater flowing from its catchment.

13. ?
Reinstated Nepean Bay Bar and associated barriers don’t need to start at
20 metres above sea level, but do need foundations to support that later.
Barrier position originally suggested
in 2014 presentation re separation of
planning for Geelong and Melbourne
Dandenong Creek
delta underpins
bayside crescent
beach between
Mordialloc and
Frankston

14. Various grades of mud, silt, sand and gravel are
sorted by wave and wind action
These become sedimentary rock given sufficient
accumulation and pressure
Ground cover, grassy and scrub vegetation
provide surface binding of dunes, flats and
shallows
Lime (calcium oxide) from mollusc shells binds
sand like concrete under water and pressure
Crescent beaches indicate relatively uniform
and gentle sedimentary bottom sloping seaward
Plate tectonics rearranges the pieces, compres-
sing folds, spreading rifts and inserting magma
Shorelines are defined by competing
processes of deposition and erosion
Shorelines are defined by competing
processes of deposition and erosion

15. Zuiderzee in The Netherlands
after sea invading for millennium, much of last century restoring lost land
Zuiderzee in The Netherlands
after sea invading for millennium, much of last century restoring lost land
There was a body of water called
Lacus Flevo by Roman authors
that was much smaller than its
later forms and its connection to
the main sea much narrower.
It may have been a complex of
lakes and marshes and channels,
rather than one lake. Over time
these lakes gradually eroded their
soft peat shores and spread.
During the early Middle Ages rising sea levels and storms started to eat away at
the coastal areas. In this period the inlet was referred to as the Almere, indicating
it was still more of a lake, but the mouth and size of the inlet were much widened
in the 12th century and especially after a disastrous flood in 1282 broke through
the barrier dunes.
The even more massive St. Lucia's flood occurred 14 December 1287, when the
seawalls broke during a storm, killing approximately 50,000 to 80,000 people,
the fifth largest flood toll in recorded history.
Port Phillip Zuiderzee
Area (sq km) 1930 5000
Coastline (km) 264 300
Year/s of flood
breakthrough
c.1000 1282, 1287

16. 1658 map of The Netherlands1658 map of The Netherlands

17. Six decades of proposed plans
Six more decades of construction
Project Dike Length Start Closure Size Drained
Connection of the
island of Wieringen to
continental Holland
Amsteldiep
dijk
2.5 km
June 29,
1920
July 31,
1924
— —
Closure of the
Zuyderzee
Afsluitdijk 32 km
January
1927
May 23,
1932
— —
Pilot Polder Andijk - 1.9 km 1926 Early 1927 40 ha
August 27,
1927
Wieringermeer
Polder
- 18 km 1927
July 27,
1929
20,000 ha
August 31,
1930
Noordoostpolder - 55 km 1936
December
13, 1940
48,000 ha
September
9, 1942
Eastern Flevoland
Polder
- 90 km
Early
1950
September
13, 1956
54,000 ha
June 29,
1957
Southern Flevoland
Polder
- 70 km
Early
1959
October
25, 1967
43,000 ha
May 29,
1968
Markerwaard Polder Houtribdijk 28 km 1963
September
4, 1975
(41,000 ha)
never
done

18. Continuing to paraphrase Wikipedia
Plans were developed during the second half of the nineteenth century to protect areas
from the force of the open sea and create new agricultural land. Cornelis Lely was an
ardent supporter, an engineer and later government minister. His 1891 plan was the
basis for the development of what were to become the Zuiderzee Works.
This consisted of a large dam connecting the northern tip of North Holland with the
western coast of Friesland and the creation of initially four polders in the northwest,
the northeast, southeast, and southwest of what would be renamed the IJsselmeer.
When Lely became Minister of Transport and Public Works in 1913, he used his
position to promote the Zuiderzee Works and gained support. The government started
developing official plans to enclose the Zuiderzee.
On January 13 and 14, 1916 the dikes at several places along the Zuiderzee broke under
the stress of a winter storm, and the land behind them flooded, as had often happened
in previous centuries. This flooding provided the decisive impetus to implement the
existing plans to tame the Zuiderzee.
After small pilot projects, a new study concerned about the financial feasibility of the
project recommended that work should continue and be accelerated. The Zuiderzee
Works Department initiated the next two major projects at the same time, in 1927.
The most important of these was the main dam, which was to be 32 km long and 90
meters wide, rising to 7.25 meters above sea-level, with an incline of 25% on each side.

19. Experience showed that glacial till, rather than just sand or clay, was the best primary
material for a structure like the Afsluitdijk. An added benefit was that it was easily
available; it could be retrieved in large quantities by dredging it from the bottom of the
Zuiderzee. Work started at four points: on both sides of the mainland and on two
construction islands along the line of the future dam.
Construction progressed better than expected. At three points along the line of the dam
were underwater gullies, where the tidal current was much stronger than elsewhere.
These had been considered major obstacles to completing the dam, but proved not to
be so. On May 28, 1932, two years earlier than forecast, the Zuiderzee was closed and
the IJsselmeer was born.
An area designated for heavy industries not immediately required was left alone
initially. After only a couple of years this landscape of shallow pools, islets and swamps
became a popular resting and foraging area for many species of waterfowl, to the extent
that it rapidly turned into a nature reserve of national significance. Although accidental
in origin, the Oostvaardersplassen became by the 1970s the definitive destination for
this section of the polder.
The need for new agricultural land and space for housing dried up and the existing
ecological and recreational value of the final polder was considered by many to be
equal or superior to any other value the Markerwaard might offer. Doubts began to
surface about the cost-effectiveness of the final polder. Although post war governments
had intended to proceed with the Markerwaard, it was decided to indefinitely postpone
the project in September 1986, retaining Markermeer.

20. Romantic view of Bay environment
memories from a human lifetime miss context of longer term evolution
We have no records with respect
to the erosion of Nepean Bay Bar
between when aboriginal boys
threw a toy spear and “discovery”
and charting of Port Phillip by
Murray and Flinders in 1802,
so it might be sensible to assume
some parallels to the fits and starts
erosion of the neck of Zuiderzee
across roughly the same period,
a process which is clearly ongoing
here and will only be exacerbated
by the first metres of sea level rise
as it drowns the surviving natural
remnant land: Mud Island.

22. “Figure 4. 3: Bathymetry and channels of the study area.” Interpretation of maritime chart data by B G
Duncan in his PhD thesis:The Maritime Archaeology and Maritime Cultural Landscapes of Queenscliffe

23. Looking even more closely at Mud Islands
Port Phillip Heads Marine National Park — Mud Islands
Environment Conservation Council
Sites listed under the Ramsar Convention for their importance for
migratory wading birds.
Distinctive bird dominated nutrient rich island ecosystem.
Parks Victoria Management Plan
Dense seagrass beds provide habitat for invertebrate assemblages and
nursery areas for juvenile fish.
Internationally significant shorebird habitat for resident and migratory
species.
Isolated salt marsh communities largely protected from pest species and
human interference.
Complete coverage of intertidal and surrounding subtidal sediment and
seagrass habitats of Mud Islands.
Issues
None: stated objectives and values met by present boundaries and level of
protection
—Edmunds M, Mustoe S, Stewart K, Sheedy E and Ong J (2009)
VNPA Nature Conservation Review:
Marine Conservation Priorities and Issues for Victoria.
Report to Victorian National Parks Association.
Australian Marine Ecology Report 405, Melbourne

24. Wider Port Phillip more disrupted
post-invasion than Nepean Bay Bar
Before 1850 oysters formed vast solid reef structures just like a coral reef in
Port Phillip Bay.
The living reefs were made up of oysters, algae, sponges, urchins and fish.
More than 100 years ago, Port Phillip Bay was filled with oyster reefs and
mussel beds but, after many years of commercial dredging, pollution,
introduced species and disease, the shellfish reefs have almost disappeared.
There were big dredge fisheries in all the bays and estuaries across southern
Australia in the mid to late 1800s. And by the early 1900s most of the
fisheries had collapsed
Oysters were dredged for two reasons. One was to eat and the other was to
burn the shell for lime to be used in concrete and plaster
—Article on recovery project of The Nature Conservancy
by Julia Millard, The Weekly Review, 17 December 2015
Commercial scallop dredging was banned in the bay in 1997.
The bay’s commercial scallop dive fishery was established in 2013 with a
harvest limit of 12 tonnes.
—Scallop diving back on the menu in Port Phillip Bay
by Chris McLennan, The Weekly Times, October 14, 2015

25. Nature operates on many timescales
While all see and act on daily and annual cycles, neither a
human lifetime nor imperial record keeping provides an
instinctive feel for processes on longer timescales.
Forests and large trees renew over hundreds of years and
eventually provide nesting hollows for dependent birds.
7,000 years of stable sea level is an aberration in the full
Pleistocene context of ice ages and brief interglacials.
And that is just the latest moment in the tectonic dance of
continents, opening and closing oceans and weather systems,
speciation and system rebooting mass extinctions.
Many environmental activists are captivated by particular
experiences and images of the natural world at a personally
significant moment which they seek to preserve.
But even that view of an activist lifetime can be more helpful
than the span of PhD research let alone quarterly prophets.

26. Wetlands serving bird migration
birds need reliable availability, can choose any serving migration route
Australasian
Gannets and
Pied Cormorants
happy with
whatever
accomodation
they can find.

27. Carefully manicured Sanctuary Lakes
attracts silver gulls, Eurasian coots,
black swans, pelicans and little else.

28. The adjacent, seemingly
derelict, old salt works,
now Cheetham Wetlands,
suggests transitory birds
have a strong preference
for its seeming inacces-
sibility, sans wings.

29. Main road from Drysdale drops
sharply from Bellarine plateau
Sweeping panorama from here
across Swan Bay and The Rip
20 metre elevation ridge at back
of town forms updrafts for birds
First two hour visit September
demanded return week October
While silver gull is rightly the
town mascot, the east coast of
the Bellarine is flyway for more
How can we put high capacity
rail and road thru edge of town?
Views from around St. Leonards
are as close as it gets to mid bay

31. You didn’t really notice Mud Island?

32. You didn’t really notice Mud Island?

33. First morning of October
visit climbed well-grassed
dredge spoil heap in
St. Leonards Lake Reserve
adjacent to caravan park
and took third pic on high
zoom thru gap in trees …

34. A few of the ascending layers of birds utilising updraft
above the 20 metre ridge at the back of St. Leonards, a
significant resource on the flyway in the right conditions.
https://www.facebook.com/ynotds/videos/vb.
725067880/10154088437682881/?type=2&theater

35. Melbourne vulnerable to rising sea level
Salt marsh wetlands adjacent Swan Bay

36. Now newly
familiar with
Ruddy
Turnstones

40. After Arthurs Seat’s dominance of the
horizon from and beyond the Bellarine,
grabbed opportunity to visit the newly
opened replacement Eagle gondola lift,
but at worst time of day for pictures
toward The Rip and Mud Island.

41. Always was, always will be …
aboriginal land management of area only flooded in peak interglacials
Port Phillip was once dry
land where kangaroos
and emus were hunted.
One day some small boys
were throwing toy spears
near some wooden
troughs full of water when
one spear upset a trough.
This was a magic trough
and held a lot of water,
which came rolling down
engulfing all the land and
threatening to drown all
the people.
Bunjil felt sorry for them
and placed a rock where
Mornington now is, and
told the water not to go
any further.
Then with two other rocks
he made the heads, and
told the water to run out
between them and meet
the ocean.
—Presland 1998 via
Holdgate et al 2011

42. Staged reseal of Nepean Bay Bar
build up platform on shallow banks, progressively close minor channels
Zuiderzee Works’s key 32 km Afsluitdijk
separates the IJsselmeer (right) from the
Wadden Sea (left), protecting thousands
of km² of land.
Pic: C messier - Own work, CC BY-SA 4.0

43. Maintaining port capacity
initially locks on main channel(s), new Bay South port opposite Portsea
Many believe the recent channel deepening increased foreshore erosion
in Port Phillip, downplaying coincident sea level rise.
Is it possible that early closure of all but a couple of the tidal/shipping
channels cutting Nepean Bay Bar might reduce erosion further north?
What water level target north of the closed barrier would best facilitate
lock access to port infrastructure with buffering to what outer sea level?
Salinity management will be a challenge, especially if avoiding over
dependence on pumping. May revive industrial salt production.
The much reduced tidal bay needed to maintain a floating port across
South Channel from Portsea will follow Bass Strait tides with reduced
flow speeds through The Rip and potential silting of the deep channel.
As data on actual rates and sources of sea level change is matched to
models, safe target design allowances should narrow considerably.
Despite better access to transport infrastructure, development of a new
Bay West port is unlikely to be a long term proposition.

44. Predeploy transport capacity
freight & passenger road & rail via Drysdale & Mornington Peninsula
Originally found Holdgate et al 2011 paper searching for a way to
link Mornington and Bellarine peninsulas without compromising
tidally-scoured deep gutter through The Rip
Restored Nepean Bay Bar will not just be a barrier against rising
sea level
It must carry vital transport links connecting logical growth areas
It must be planned to also transport Bay South port freight
Suggestions are around about SkyRail to restore the Queenscliff
line as far as Drysdale which is central to the Bellarine
Robert Whitehill has developed plans for long overdue return of
rail to the Mornington Peninsula as far as Rye
Each end demands planning reservations for sufficient capacity
through and beyond both Geelong and Frankston-Dandenong
Essential first steps at each end need to be prioritised

45. Bonus Save:
Geelong
Divert Barwon from
Reedy Lake between
Moolap and Leopold
into Outer Harbour
Close strait between Lake
Connewarre and Hospital
Swamp, consolidating 10-20
metre ridge from Mt Duneed
Drysdale route to
Nepean Bay Bar via
St Leonards ridge

46. Geologically recent history of Barwon into Corio Bay
Lava from Mount Duneed extended east across a lowland filling the valley of the
ancestral Barwon River.
The Barwon River was diverted and initially flowed north across the Moolap Lowland.
As sea level rose during the late Pleistocene and early Holocene (12,000 to 5,000
years ago), the seaway across the Moolap Lowland was probably briefly reestablished
and the Barwon flowed into Stingaree Bay.
The Moolap Lowland seaway closed and the Barwon estuary was established to the
southeast. This would be within the last 5,000 years.
The Barwon River debouches into a shallow embayment that may have been part of a
larger Reedy Lake west of the ridge of basalt that forms Taits Point and Fishermans
Point.
Rapid sedimentation of the main lagoon of Lake Connewarre and the smaller
embayment west of Fishermans Point has been recorded over the past 150 years.
There is reasonable evidence that the Barwon River delta has extended into this
embayment by about 1500 metres over that time.
Extracted from: Murtnaghurt Lagoon, Bellarine Peninsula & Related Landforms:
Nature, Origin & Geoscience Significance
by Neville Rosengren, La Trobe University & Environmental GeoSurveys Pty Ltd
Prepared for: Save Barwon Heads Alliance, November 2009

47. Ridge of basalt at Fishermans
Point viewed from Taits Point
Northern end of Reedy
Lake in Moolap Lowland
Smaller embayment west
of Fishermans Point
Main lagoon of
Lake Connewarre

48. How soon must we start?
timing uncertainties: sea level change, planning, commitment, construction
Sea Level
(metres)
current
-30
-60
-90
-120
-150
0 20 40 60 80 100 120 140 Years ago
(thousands)
Late Pleistocene to Holocene sea-level record from Huon Peninsula
(after Aharon & Chappell 1986) and pre-120,000 years ago record
from Barbados (after Labeyrie et al 1987) via Holdgate et al 2001.

49. –David Spratt, 23-25 January 2017, (link to complete article)
Breaking news:
An updated NOAA sea-level rise report just released recommends a
revised worst-case sea-level rise rise scenario of 2.5 metres by 2100,
5.5 metres by 2150 and 9.7 metres by 2200.
It says sea level science has “advanced significantly over the last few
years, especially (for) land-based ice sheets in Greenland and
Antarctica under global warming”, and hence the “correspondingly
larger range of possible 21st century rise in sea level than previously
thought”.
It points to “continued and growing evidence that both Antarctica
and Greenland are losing mass at an accelerated rate”, which
“strengthens an argument for considering worst-case
scenarios in coastal risk management”.
Antarctic tipping points for a multi-metre sea level rise

50. Estimates of polar ice sheet contribution to sea level rise have focused on
West Antarctic and Greenland, but mechanisms similar to those causing
deglaciation in West Antarctica are now also found in East Antarctica.
Partial deglaciation of the East Antarctic ice sheet is likely for the current
level of atmospheric carbon dioxide, contributing to 10 metres of more of
sea level rise in the longer run, and 5 metres in the first 200 years.
Recent studies suggest that West Antarctica passed a tipping point for
large-scale deglaciation decades ago.
The research here surveys evidence from the previous warm Eemian
interglacial period around 120,000 years ago. At that time there were
rapid fluctuations in sea level, and the study identifies a mechanism in
the Earth’s climate system not previously understood, which points to a
much more rapid rise in sea levels than currently being allowed for.
The projected cooling pattern of waters around Antarctica and the north
Atlantic waters from the injection of fresh ice-melt water is already
visible in the observed data, and is already contributing to a circulation
decline of Atlantic Meridional Overturning Circulation.

51. During the Eemian interglacial period, the global mean sea level was
6–9 metres higher than it is today, at a time when atmospheric carbon
dioxide concentrations were below 280 parts per million and global
mean temperatures were at worst 2°C warmer.
Antarctic ice mass loss during the end of the last ice age 14,600–
12,700 yrs ago contributed several metres to sea levels which from
various sources rose by tens of metres.
At that time, changes in atmospheric-oceanic circulation led to a
stratification in the ocean with a cold layer at the surface and a warm
layer below. Under such conditions, ice sheets melt more strongly
than when the surrounding ocean is thoroughly mixed.
This is exactly what is happening around the Antarctic now. Research
team member Michael E. Weber says, "The changes that are currently
taking place in a disturbing manner resemble those 14,700 years ago."
The reality of multi-metre sea level rise is not if, but how soon. “The
natural state of the Earth with present CO2 levels is one with sea
levels about 70 feet (21 metres) higher than now.”

52. Questions?
E.g: When you take the
Queenscliff-Sorrento
ferry are you preoccupied
with looking enviously
south towards Portsea?