Save Ocean Beach

Erosion and accretion is a natural process, the Otago coastline has been in constant fluctuation for millions of years. Merely 7 thousand years ago the sea level was much higher than now and the peninsular arm was an offshore island. Even back in the 1800's the peninsular arm was only joined to South Dunedin by a sandy isthmus.

Tens of thousands of years ago you had to travel 33 kilometres out to sea to find the shore.
What we are faced with now is the issue of maintaining some kind of equilibrium to protect the man made assets that were placed along and inshore of our coastline in the last 160 years from this natural process.

Where did it all go wrong?
I am no expert at all, but following my natural curiosity I have my theories based upon stacks of research.

1/ Before the white man came to Dunedin, the now almost straight stretch of beach from the salt water pool to lawyers head (Ocean Beach) was an indented sandy bay which reached about 800metres further inland, this was created by the natural offshore morphology in conjunction with the landforms at shore along the coast.

2/ .. white man settles in Dunedin.. and after a few decades decides that he needs more land for settlement and begins the process of land reclamation through the draining of the swamps from South Dunedin to St Kilda, the sand mining of the dunes for harbour land reclamation and subsequent development over the previously sandy bay. This occured over 90 years from 1860 to 1950 when most of the 'reclamation' was completed.

3/ During this time, ongoing and prior, a cyclic natural weather phenomena occurs in 7 to 13 year cycles where natural storm events cause heightened erosion along Ocean Beach. Some storm surge events thrust seawater inland as far as Hillside Road (2ks inland) inundating homes and businesses. Two prior hard rock sea walls were destroyed and the esplanade was washed away completely during one storm event. So began mans battle with the ongoing issue/need for coastal protection, and the implementation of various engineering solutions.

4/ The extensive land reclamation within the previous sandy bay area caused a complete destruction of the natural dune system, which had previously found equilibrium as a self healing system over thousands of years. (actually when Dunedin was first settled, there was only a sandy isthmus joining the peninsula to the mainland, and the flat area of south Dunedin and St Kilda and parts of St Clair was swampy uninhabitable land which was laboriously drained by the market gardening Chinese immigrants).
4a/ After the 1950's periods of effective 'soft engineering' sand stabilisation methods such as sand trap fences gave a reprieve from erosion issues for many decades. After the Ocean Beach Management was handed over to the Dunedin City Council in the late 1980's these methods were disbanded and the erosion issues resurged.

5/ Bring on in 2002 the redesign of the new sea wall at the St Clair end of Ocean Beach. Due to adjustments in its positioning the solid structure created seemingly subtle but critically ongoing changes in currents causing deep erosion of the sandy beach along its base and drastically lowering the beach profile. This placed stress through exposure of the toe of the reconstructed dunes at the end of the sea wall [with whats called an 'end wall effect'] stripping sand and exposing the sand sausages from beneath the dunes.. these sausages (placed as a means to protect the dunes from erosion) then became hard/end wall themselves. and forced the erosion further up the beach as an end wall effect into middles beach to soft dune.
5a/ there is also the possibility that the construction of the bridge/pipe for the sewer outfall placement has been causing disturbances on the nearshore currents which have amplified the erosion.

6/ Then bring on another natural cycle of a series of strong south east swells/storms during June and July this year which caused the lowering of the beach level/profile even more allowing the storm surges to attack the toe of the soft dunes.. causing 8-10 metres of dune depth to be washed away over this 6 week period.

The beach is now in a 'self heal mode', where banks have been naturally created offshore which act as a buffer to incoming swells so the wave energy is dissipated and does not effect too much the eroded dunes. In the past this process allows the beach profile to slowly raise allowing recovery of the dunes by creating a higher dry sand beach again, this dry sand blows onshore to reform fore-dunes, the eroded dunes naturally re-profile and re-grassing occurs, the dunes and beach heal.. Unfortunately it is not at all possible for a self heal to occur here as would have been the case pre-settlement, as the natural profile and function of the dunes has been destroyed.
So its up the the city council to research the best possible way to allow the beach to recover and the dunes to heal ( with help from hundreds of hours of digger work to remove hard fill used in the 50's for reclamation).
I just cross my fingers that they do their homework and take a look at the more natural processes that they have been alerted to [such as Holmberg] that will allow a process to be installed where nature is worked with in conjunction with human intervention.. it is very possible, and is proven overseas.
the dunes must also be allowed to encroach back landward into the reclaimed parks areas so at least some degree of self healing is possible.

we face the truth that the problem is 'man made, aided by nature', so the solution should be 'natural, aided by man'.

Web links to further scientific documentation:

The city of Dunedin is located on the remains of a Miocene volcanic eruptive centre, which is underlain by Tertiary marine sediments and Late Cretaceous quartz gravel, sand and clay with some coal seams. These in turn rest on a basement of Jurassic schist. The geology and topography pose a number of geological hazards that must be considered in urban development. These include landslide, mine subsidence, ground shaking amplification and liquefaction, coastal erosion and tsunami.

A number of research, policy and planning initiatives have been undertaken to assess and mitigate the effects of these hazards. A GIS-based Hazard Information System (for a part of the city) was developed to assist in identifying and mitigating hazards. Under legislation the Dunedin City Council (DCC) is obliged to keep a register of known hazards. In addition, a Lifelines project has been undertaken to identify hazards and related risks to emergency and utility services. These studies may be used by asset managers to prioritise mitigation measures for critical facilities as well as to avoid hazards. The DCC district plan includes policies to gather and maintain hazard information, encourage research into hazards, and control activities in areas that might be affected by hazards.

(cited from: The geology of Dunedin, New Zealand, and the management of geological hazards, Phil Glassey, David Barrel, Jane Forsyt and Rod Macleod )

Below are just a few Articles that have appeared in the Otago Daily Times over the years regarding public concerns and council actions with regards to Erosion issues at Ocean Beach, Sea Wall safety and Construction issues.
from 1937 - 2005

Title: Ocean Beach Domain/Meeting of Board/Erosion at St. Clair.
Date: 29 JAN 1937
Page: 11

Title: Erosion at St Clair.
Date: 20 JUL 1939
Page: 6

Title: Erosion continues at St Clair.
Date: 21 JUL 1939
Page number: 4

Title: Rough seas/St Clair beach pounded.
Date: 15 AUG 1939
Page: 4

Title: Erosion at St Clair/Protective measures required.
Date: 22 AUG 1939
Page: 9

Title: Erosion at St Clair/Domain Board watching position.
Date: 23 AUG 1939

Title: Where will it end?/The foreshore erosion/Inroads in fifty years/A serious position.
Date: 30 AUG 1937

Title: Beach erosion/Position at St Clair.
Date: 19 SEP 1939
Page: 4

Title: Urgent anti-erosion measures needed.
Date: 13 OCT 1993
Page: 5

Title: Erosion at St Clair 'worst in 30 years'.
Date: 10 FEB 1995
Page: 16

Title: Stabilising work begins on sand dunes.
Date: 21 SEP 1996

Title: Erosion management at St Clair Beach.
Publication: Dunedin Star Midweek
Date: 25 SEP 1996
Page: 3

Title: Shifting sands.
Date: 09 MAR 1998
Page: 1

Title: High seas destroy reclamation along St Clair Esplanade.
Date: 02 MAR 1999
Page: 5

Title: Urban sprawl aids beach erosion/Study finds natural dunes replenish themselves.
Date: 04 MAR 1999
Page: 5

Title: Dune erosion concern.
Date: 30 MAR 1999
Pag: 5

Title: Erosion of sea walls a big concern/Future funding "mistake".
Date: 23 APR 1999
Page: 5

Title: St Clair residents to lobby council over erosion.
Date: 22 JUL 1999
Page: 2

Title: Coastal route erosion stuns expert.
Date: 22 AUG 2000
Page: 2

Title: Council assesses coastal erosion.
Date: 02 OCT 2001
Page: 3

Title: Beach users look to help save eroding sand dunes.
Date: 29 OCT 2001
Page: 4

Title: Money the answer to beach blues - expert.
Date: 31 OCT 2001
Page 3

Title: Council to seek funding for coastal erosion study.
Date: 05 AUG 2003
Page: 134

Title: Sand hill erosion preventive measures/Effective steps taken.
Date: 07 JUN 2004
Page: 3

Title: No link between erosion and Waitaki River dam-building.
Date: 21 OCT 2004
Page: 16

Title: Removing rocks foolish, geologist says.
Date: 22 DEC 2004
Page: 2

Title: Ocean waves two, concrete ramp nil.
Date: 10 MAR 2005
Page: 1

Goring, D. G. 2005: Waves and sea levels at St Clair on 14-Dec-2004 and 28-Feb-2005 Mulgor Report No. 2005/2.

Our Ocean Beach, in its natural state before settlement, has been vastly altered from a sandy bay by the destruction of its natural dune system with major land reclamation and the construction of man made dune structures to protect the developing city from the action and inundation of the sea.

Since then Ocean Beach has been subjected to a continual process of erosion since the 1860’s. You can’t conserve the coastline, its dynamic and changing all the time, this beach emergency is man made and has dished up a raw need to implement a totally substantial, practicable and financially sustainable long-term solution.
Hard engineering techniques such as sea walls, sand sausages, groins and gambion baskets have consistently proven to exacerbate erosion, and require ongoing funding and maintenance. Sand replenishment is both unsustainable and unproven as a long term solution, increased storm events mean it’s less likely that sand replenishment will work.

We need to implement something substantial for an artificial beach profile to get a dune system functioning again to rehabilitate the coastline to reduce council and public risk.
This is not only an issue for the DCC, the Otago Regional Council needs to be part of the solution. Any group that is formed to decide on a long term solution needs the co-operation of both these councils working together, as each has jurisdiction over different parts of the affected areas.

The importance of public consultation and information gathering has repeatedly been called for in public arenas. What does the DCC think it will achieve?

What information are the DCC and their consultants missing that the past coastal studies and hazard reports have missed?

Does this mean that current consultants are not fully informed? Hasn’t the consultant got access to scientific info?

Don’t want consideration for a multitude of unsubstantiated ideas no matter how well intentioned from the public.. We need action now, proven solutions now, not a wading through scores of unproven solutions.

Lets agree on some performance criteria to assess and measure against, as a process of public consultation.
.{{ call for a set of perfomance criteria, if public consulted on anything, public not agree on specific solutions.}}
Do we want to comply with the RMA & NZ coastal policy? Is it cost effective? A one off cost or ongoing?
How much are we prepared to pay?
do we want temporary or a permanent soultion?
A review in 10 years? Do we save the dunes, or extend?
Or let the sea take over in a controlled manner?
Do we want the world renowned surf breaks at St Clair and St Kilda to be preserved?


Coastal engineering is a very imprecise science.

What about Holmberg Technologies' Undercurrent Stabilisers?

Nobody in nz that’s doing soft shore protection like this.. the mechanism is soft shore as it stabilises erosive currents in principle [operation] opposed to wall reflected energy and hard armouring,,
It works moree effectively in a high energy situation... workign to raise the profile of the beach.
In a storm the system works better, the more energy, the more sand in system.. more bought on to shore.
Sand sausages work on totally different principle, by reflection & undermining.
Holmberg does have a shore parallel aspect, which is graduated so the sea has to climb it.

We need an open transparent investigation of soft shore methods including this one.

Review of the New Zealand
Coastal Policy Statement
Issues and Options
AUGUST 2006

climate change coastal margins
source

Public demand for coastal protection works is often high when coastal processes
affect private property,public infrastructure or reserves. While protection works such
as seawalls can in some cases shield property if properly designed and constructed,
they can also have significant adverse effects on coastal processes and natural features
(e.g.increasing erosion further along the coast) and on natural character,amenity values
and public access to and along the coastal marine area.

Specific criticisms of RCA criteria,particularly from local government,include:
The criteria on parallel structures (usually seawalls) does not manage cumulative
effects well (i.e.a 00 metre seawall built 00 metres at a time will have the same
adverse effects but not the same consideration as a single 00m project) and does
not provide guidance on structures crossing the line of mean high water springs.


Climate change and sea level rise are expected to lead to more severe erosion
and flooding. While the effects of climate change will vary in different areas,and sea
level rise is expected to occur over a long time-frame, it is likely that current erosion
trends, flooding and storm damage will be more severe.
Public demand for coastal protection works is often high when coastal processes
affect private property, public infrastructure or reserves. While protection works such
as seawalls can in some cases shield property if properly designed and constructed,
they can also have significant adverse effects on coastal processes and natural features
(e.g.increasing erosion further along the coast) and on natural character,amenity values
and public access to and along the coastal marine area.

3.6.3 NZCPS policies
Principle 7 of the existing NZCPS states that:
The coastal environment is particularly susceptible to the effects of natural
hazards.
Policies on natural hazards are in Chapter ,“Activities Involving the Subdivision,use
or Development of Areas of the Coastal Environment”:
3.4 Recognition of Natural Hazards and Provision for Avoiding or
Mitigating Their Effects
Policy 3.4.1
Local authority policy statements and plans should identify areas in the coastal
environment where natural hazards exist.
Policy 3.4.2
Policy statements and plans should recognise the possibility of a rise in sea level,
and should identify areas which would as a consequence be subject to erosion
or inundation. Natural systems which are a natural defence to erosion and/or
inundation should be identified and their integrity protected.
Policy 3.4.3
The ability of natural features such as beaches, sand dunes, mangroves, wetlands
and barrier islands, to protect subdivision, use, or development should be
recognised and maintained, and where appropriate, steps should be required to
enhance that ability.
Policy 3.4.4
In relation to future subdivision, use and development, policy statements and
plans should recognise that some natural features may migrate inland as the
result of dynamic coastal processes (including sea level rise).
Policy 3.4.5
New subdivision, use and development should be so located and designed that
the need for hazard protection works is avoided.
Policy 3.4.6
Where existing subdivision, use or development is threatened by a coastal
hazard, coastal protection works should be permitted only where they are the
best practicable option for the future.The abandonment or relocation of existing
structures should be considered among the options.Where coastal protection
works are the best practicable option, they should be located and designed so as
to avoid adverse environmental effects to the extent practicable.
3.6.4 Policy critique
A number of shortcomings have been identified in recent reviews of existing coastal
hazard provisions.There are particular problems with the implementation of policies.
In addition, some of the NZCPS policies have been found to lack direction, and are
neither effective nor specific enough;many have not been given full effect in existing
planning documents, such as district plans.There is also concern about the lack of
integration between regions and districts.
Risk reduction is a key message of the new Civil Defence Emergency Management Act
2002. This message is strongly linked to planning provisions that avoid developments
being located in high risk areas.
The long-term effects of sea level rise combined with climate change mean that
a national framework for managing hazard risk from these is needed.
There is a general lack of understanding of how coastal processes work. Beaches
have long-term and short-term trends in the movement of shorelines and sand supplies.
There is an expectation that structures will be placed to protect property,but there is
not a good understanding of the impact such structures have on the beach.
Protection works can cause loss of public access and cause beach degradation;
they also threaten coastal habitats and ecosystems. While the existing NZCPS policy
on hazard protection works is useful, it needs to be strengthened to ensure structures
are the best solution and that public access and amenity values are maintained.
There is no one solution that suits all sites where coastal erosion is occurring.
As coastal erosion is a natural process, there will be differences in how it affects property
in different areas. A combination of approaches such as avoiding the risk, living with
the risk and protecting property from the hazard may all need to be used.

3.5 Maintenance and Enhancement of Public Access To and Along
the Coastal Marine Area
Policy 3.5.1
In order to recognise the national importance of maintaining public access to and
along the coastal marine area, a restriction depriving the public of such access
should only be imposed where such a restriction is necessary :
(a) to protect areas of significant indigenous vegetation and/or significant
habitats of indigenous fauna;
(b) to protect Maori cultural values;
(c) to protect public health or safety;
(d) to ensure a level of security consistent with the purpose of a resource consent;
or
(e) in other exceptional circumstances sufficient to justify the restriction
notwithstanding the national importance of maintaining that access
Policy 3.5.2
In order to recognise the national importance of enhancing public access to and
along the coastal marine area, provision should be made to identify, as far as
practicable:
(i) the location and extent of places where the public have the right of access
to and along the coastal marine area;
(ii) those places where it is desirable that physical access to and along the coastal
marine area by the public should be enhanced;and
(iii) those places where it is desirable that access to the coastal marine area
useable by people with disabilities be provided.
Policy 3.5.3
In order to recognise and provide for the enhancement of public access to and
along the coastal marine areas as a matter of national importance, policy
statements and plans should make provision for the creation of esplanade reserves,
esplanade strips or access strips where they do not already exist, except where
there is a specific reason making public access undesirable.

NZ Impacts: Coasts

Sea-level rise is virtually certain to cause greater coastal inundation, erosion, loss of wetlands, and salt-water intrusion into freshwater sources, with impacts on infrastructure, coastal resources and existing coastal management programs.

The likely rise in sea-level, together with changes to weather patterns, ocean currents, ocean temperature and storm surges are very likely to create differences in regional exposure. In New Zealand, there is likely to be more vigorous and regular swells on the west coast.

Future effects on coastal erosion include climate-induced changes in coastal sediment supply and storminess. In Pegasus Bay, for example, shoreline erosion of up to 50 m is likely between 1980 and 2030 near the Waipara River if southerly waves are reduced by 50%, and up to 80 m near the Waimakariri River if river sand is reduced by 50%.

Coasts are also likely to be affected by changes in pollution and sediment loads from changes in the intensity and seasonality of river flows, and future impacts of river regulation.

this post yet to be filled with information about the history of Ocean beach and its current status re: shoreline protection options and Dunedin City council process

this post yet to be filled with information about the use of Sand Replenishment for shoreline protection and their effects on the environment.

this post yet to be filled with information about the use of Groynes for shoreline protection and their effects on the environment.

Above the Plymouth Breakwaters.

Sea walls and groynes
source
A common response to erosion has been to construct sea walls and groynes (low barriers built out into the sea). Sea walls are common around the Waitematā Harbour in Auckland and the Wellington waterfront. Although these structures stabilise the coast, they cause more erosion at adjacent coasts, merely shifting the problem or creating a new one. They also cause the loss of any beach in front of the structure at high tide (this occurred at Wellington’s Oriental Bay).
In recent years it has been argued that constructing sea walls and groynes is inconsistent with the principles of the Resource Management Act.


We can learn from Auckland's experience. source
Auckland City are spending millions of dollars on fixing up the beach erosion caused by seawalls and stormwater drains. They wish they could get them back to a natural state like we still have at Tahunanui.


Coastal Hazards FAQs
Source
Planning for Coastal Hazards is a statutory requirement for the Whakatane District Council under the Resource Management Act 1991 (RMA). The requirements include:

Illegal seawalls being constructed at Mokau
source
source

"The use of patented "Undercurrent Stabilizer" systems is being employed to work with nature by utilizing her wave, current and tidal energy carrying sand to the beach area from offshore deposits. This natural process actually accomplished the same result as artificial beach nourishment but without disturbing the natural ecology of the ocean bottom. An additional benefit is that it does not require continual replenishment, cause an increase in the erosion rate or the harmful effects that offshore dredging and strip mining does to maintain the beach (U.S. Corps of Engineers, 1989)"

MINUTES OF A MEETING OF THE
COMMITTEE OF THE WHOLE HELD IN
THE EDINBURGH ROOM, MUNICIPAL
CHAMBERS, ON MONDAY 30 AUGUST 1999,

(abridged)
3
Lyndon Weggery
Mr Weggery expressed concern that access to Middle Beach at St Clair was being
eroded away, thus preventing access, and he requested Council to take a proactive
approach to resolving this and the Esplanade Sea Wall problem. He recognised
that Council had no surplus funds to allocate to the Esplanade Sea Wall
investigations, but he believed that Otago Regional Council consent would not be
obtained until fundamental hydrological investigations had been undertaken. He
asked Council to consider allocating some funds to the project so that such a study
could be undertaken in the near future.
4
Tony Ryder
Mr Ryder noted with concern the ongoing effects of the sea on the St Clair
Esplanade Sea Wall, and suggested a potential solution to the present problems.
He believed that the situation could be alleviated by the placement of a sandbag
reef out to sea, which would create a type of breakwater. This would have the
effect of dissipating the energy of the waves. He noted that new technology was
available to construct large sandbags of this type, and the strategy would have the
effect of producing good surfing waves and sheltered in-shore areas
Mr Ryder noted that the University of Otago Marine Science Department would
be able to undertake the necessary studies on the beach profile and current.
Although he was unsure of the exact costs involved, he was aware of similar
systems which had been successfully installed at overseas sites.

It was moved (Benson-Pope/Bezett):
“That $60,000, being the first of two allocations for a hydrological
study, be committed to the Esplanade Wall report as an authorised
over-expenditure.”
It was commented that there were many theories and proposals with respect to the
Esplanade Wall, and that further information was necessary before an informed
decision on the best way of addressing the problem could be made.
Cr Benson-Pope noted that a Working Party had been formed for this purpose, and
could report on these matters at the next meeting of the Planning and Environment
Committee.
With the agreement of the seconder, the motion was withdrawn.
It was moved (Hanan/The Mayor):
“That the Working Party examine the issue of the Esplanade Wall,
and report on this matter at the next meeting of the Planning and
Environment Committee.”
Motion carried.
Cr Benson-Pope requested staff to include for consideration the costs of the design
and incremental replacement of the Esplanade Wall as an item in the 2000/2001
draft Annual Plan.