Submission by
City of Port Phillip
as Planning Authority
Part B
18 August 2015
Contents
PART B ................................................................................................................................................1
1.
INTRODUCTION TO PART B .................................................................................................2
1.1
Structure of Council’s submission................................................................................................................ 2
2.
ISSUES RAISED IN SUBMISSIONS .........................................................................................3
3.
COUNCIL’S RESPONSE TO SUBMISSIONS .........................................................................5
4.
5.
6.
7.
3.1
Consideration of submissions by Council .................................................................................................. 5
3.2
Previous Planning Panel Commentary ......................................................................................................... 5
3.3
Response to issues raised in submissions ................................................................................................... 6
FLOOD MODELLING ..............................................................................................................27
4.1
Introduction ..................................................................................................................................................... 27
4.2
Modelling Methodology – Overview ......................................................................................................... 29
4.3
Assumptions behind the modelling ............................................................................................................ 29
4.4
Drainage Inputs ............................................................................................................................................... 31
4.5
Translation to SBO Mapping ....................................................................................................................... 31
4.6
Calibration by ‘Ground-truthing’ against past storm events ............................................................... 32
4.7
Preparation for Amendment C111 ............................................................................................................ 32
4.8
Climate Change .............................................................................................................................................. 32
FURTHER TECHNICAL REVIEW ..........................................................................................34
5.1
Overview .......................................................................................................................................................... 34
5.2
Considerations ................................................................................................................................................ 34
5.3
Outcome / proposed changes to Amendment C111 ............................................................................ 35
FLOODING MAINTENANCE AND CAPITAL EXPENDITURE ........................................36
6.1
Drainage Maintenance Program .................................................................................................................. 36
6.2
Identification of Areas for Possible Pipe Upgrade Works .................................................................... 36
CONCLUSION..........................................................................................................................38
7.1
Amendment C111 .......................................................................................................................................... 38
7.2
Council’s final position on the Amendment ............................................................................................ 38
APPENDICES ...................................................................................................................................39
Figures
Figure 1 – Diagram showing the flood modelling process .................................................................................... 28
PART B
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
PAGE 1
1.
INTRODUCTION TO PART B
1.1 Structure of Council’s submission
This submission has been prepared having regard to Practice Note 46 – Strategic Assessment Guidelines for
Preparing and Evaluating Planning Scheme Amendments (DTPLI, July 2014).
The submission is structured as follows:
Part A
The Part A Submission was provided prior to the commencement of the hearing on 18 August 2015
and contained the following information, as set out in Panel Directions dated 31 July 2015:





Background to the Amendment
Chronology of events
Strategic Assessment
Identification of the issues raised in submissions and its response
Changes to the Amendment documentation proposed as a result of the issues raised in
submissions
At the hearing, Part A will be taken as read by all parties.
Part B
This part, to be presented at the Panel Hearing, contains the following:
1.
2.
3.
4.
5.
6.
7.
Introduction to Part B
Issues raised in submissions
Council’s response to submissions
Flood modelling information (including methodology)
Further technical review
Flooding maintenance and capital expenditure
Conclusion (including final position on the amendment)
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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2.
ISSUES RAISED IN SUBMISSIONS
The following issues were raised in the submissions received (including late submissions received):
Issue
1. Individual properties have
not flooded in the past and
should not be subject to the
Special Building Overlay
2. Questioned the accuracy of
the modelling or modelling
that doesn’t account for real
life flood events (only
computer modelling)
Discussion

Twenty (20) of the submissions objecting to the
Amendment referred to previous flood events (or the
lack thereof) in their local area that did not affect their
property to explain their position that the modelling
must be incorrect.

Fourteen (14) submissions stated that the modelling
should be based on real life flood events, rather than
computer modelling, which may not account for
structures that may impede the flowpath.

Fourteen (14) submissions stated that the inclusion of
their property in the SBO would negatively impact on the
value of their property.

Where a property is only marginally affected by the
proposed SBO, ten (10) objecting submissions pointed to
existing walls, buildings, garages or other structures (on
the site or adjoining sites) that has blocked the flowpath
for previous floods or would potentially block the
flowpath of flood water from entering their property in
the future.

Eleven (11) submissions stated that the inclusion of their
property in the SBO would be an administrative burden
that could result in increased costs associated with future
redevelopment or extensions to existing buildings.

Nine (9) submissions stated that the inclusion of their
property in the SBO would result in higher insurance
premiums.

Five (5) submissions used the opportunity afforded by the
Amendment to provide feedback to Council about:
particular drains that they observed were blocked by leaves
and other material causing problems for the runoff of water
(during light and heavy rainfall events), the design of
particular storm drains or the inadequacy of the existing
drainage to cope with normal runoff. Note: where specific
drains were referred to in the submission, then customer
requests were logged so that they could be investigated).
3. Impact on property values
4. Buildings or structures on a
property are unaffected
5. Financial or administrative
burden for future
development or
redevelopment of the site –
including additional costs
associated with raising floor
levels
6. Impact on insurance
premiums
7. Problems with specific
blocked or poorly designed
drains near their property
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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Issue
8. Council and Melbourne
Water should maintain
and/or upgrade the drainage
system to cope with overland
flow from the 1 in 100 year
flood event
9. Climate change impacts
10. Further design requirements
are needed
Discussion

Three (3) submissions stated that the entirety of the
drainage system should be upgraded to accommodate
overland flows from the 1 in 100 year flood events, again in
lieu of pursuing expanding the SBO to cover more
properties.

A further three (3) submissions stated that lack of
maintenance of the drainage network by Council and/or
Melbourne Water was causing the flooding issues and that
these issues should be investigated, in lieu of pursing an
expansion of the SBO to cover more properties.

Two (2) submissions were received that discussed the lack
of consideration of the impacts of climate change in the
revised modelling of the Special Building Overlay.

One of these submissions raised the issue of increased
rainfall intensity associated with climate change as
justification to retain their property completely within the
SBO.

The second submission was critical of the approach taken
with the Amendment to not include consideration of the
impacts of climate change. Specifically, this submission stated
that there is no justification for not incorporating the
impacts of climate change because climate change increases
rainfall intensity, higher sea levels reduces the capacity of the
drainage system and future impacts of coastal climate change
have already informed planning decisions. Furthermore, the
submission stated that the SBO should be based on flood
levels derived from modelling for the assumed impacts of
climate change because the design life of these buildings will
be 50-100 years.

One (1) submission recommended that design standards be
changed to require buildings to be constructed on more
permeable foundations (e.g. stilts or other openings) to
allow flood water to pass underneath and reduce the flood
risk compared to constructing more solid foundations.
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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3.
COUNCIL’S RESPONSE TO SUBMISSIONS
3.1 Consideration of submissions by Council
At its meeting on 14 July 2015, Council endorsed responses to the issues raised in submissions outlined
in the Consultation Report (Attachment 3 to the Council Report – provided in Appendix 5 in the Part A
Submission).
3.2 Previous Planning Panel Commentary
Planning Panels Victoria (PPV) have considered and reported on a significant number of planning scheme
amendments relating to flood overlays or zones (including the SBO), since the introduction of these
provisions into the Victoria Planning Provisions more than 17 years ago.
Most of the issues raised by submitters to Amendment C111 have been raised in previous Planning
Panel hearings considering the introduction (or change to) the SBO or Land Subject to Inundation
Overlay (LSIO).
Previous Planning Panels have consistently made the following points with respect to the application of
the SBO:
The drainage system

The application of the Special Building Overlay complements other flood
mitigation, drainage maintenance and upgrade works undertaken by
floodplain management authorities or local councils. 1

Upgrading the entire drainage system to present day standards in order
to accommodate for 1 in 100 year flood events would cost billions of
dollars, and is not practical for floodplain management authorities (e.g.
Melbourne Water) or for local councils to deliver. 2

The flood prone nature of some land ‘represents an existing fact’. 3

The SBO is a tool to advise landowners and potential purchasers of the
potential for the land to flood in a 1 in 100 year flood event, and allows
authorities to consider any development proposals to reduce
detrimental impacts. 4

The SBO does not prohibit development 5 and the requirements in the
SBO only apply to development and works proposed within the area
covered by the overlay. 6
Purpose of the SBO
1
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p8 & p31
Ibid, p31
3
Moreland Planning Scheme Amendment C50 Panel Report (March 2008), p17
4
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p20
5
Ibid, p28
6
Ibid, p37
2
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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
The shape of the overlay is based on the overland flow paths identified
through best practice computer modelling and is the most reliable
estimate that can be made from existing information and techniques. 7

It is unlikely that a single storm event will cause the extent of inundation
shown on the SBO. Flooding tends to be localised, because a single
storm event is unlikely to cover the whole of the SBO area at one time.
Flood modelling
8

The cost of gaining more intensive terrain information (via land surveys
of individual properties) would be prohibitive 9,10 and the most
appropriate time to assess the flooding risk to a particular property is at
the planning permit stage, where accurately surveyed levels area
provided. 11

The full disclosure of property information is appropriate and beneficial.
12

Development costs,
property values &
insurance
The prospect of improved planning for the community is more
important than the possibility of decreased property values or the
increased costs associated with raising the floor level of a new building.
13,14

There has generally been no correlation found between the application
of the SBO and property values. 15

A potential increase in insurance premiums is not a relevant
consideration as to whether the SBO should be applied. 16
3.3 Response to issues raised in submissions
The following section provides the following in relation to each of these 10 issues:



A short outline of the issue;
A Council response to the issue; and
Relevant commentary from previous Planning Panel reports where the issue has been previously
considered.
7
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), p45
Bayside C1, op cit, p10
9
Ibid, p37
10
Stonnington C18, op cit, p45
11
Final Report on the New Format Planning Scheme (April 1999), p64
12
Moreland C50, op cit, p17
13
Glen Eira Planning Scheme Amendment C16 (November 2001), p7
14
Bayside C1, op cit, p28
15
Stonnington C18, op cit, pp57-58
16
Bayside C1, op cit, p30
8
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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Issue 1
Property has never flooded: Individual properties have not flooded in the past and
therefore should not be subject to the Special Building Overlay.
Outline of Issue
Submissions objecting to the Amendment referred to previous flood events (or the lack
thereof) in a local area. In this context, advice that their property had not experienced
flooding was used to substantiate their position that the modelling must be incorrect.
Council response

The shape of the overlay is based on the overland flow paths identified through best
practice computer modelling. It is the most reliable, cost-effective estimate that can
be made from existing information and techniques.

The lack of historical evidence about flooding on a particular site does not mean the
property may not be inundated by overland flooding in the future.

Storm events vary considerably and the factors that contributed to flooding in one
storm event may not be repeated for the next. The relevant consideration is;
where the water is likely to flow in during a 1 in 100 year storm event when the
local and main drainage systems are unable to cope with the volume of water.

Buildings and structures within the flowpath may currently divert or otherwise
hinder flood waters. If these structures were removed, then the flowpath would
change and a property further down the flowpath may be impacted.

A number of submitters’ properties are only marginally impacted by the proposed
SBO. The removal of these properties from the proposed SBO because there is no
anecdotal evidence of past flooding would be inconsistent with good planning and
risk assessment.

A further technical review (refer to Section 5) has been undertaken to investigate
whether there are any anomalies with the floodshape on affected properties with a
minor coverage of the proposed SBO2.

Other than to correct any anomalies based on a more detailed technical and on-site
assessment, there is no justification to remove properties from the model simply
because a submission has been made requesting this on the basis of an absence of
recent / past flooding.
Previous Panel findings
The Planning Panel in relation to Amendment C1 to the Bayside Planning Scheme considered
the view of the Planning Authority that:


“The technical basis for the derivation of the SBO is appropriate an accords with industry
practice.
It is unlikely that a single storm event will cause the extent of inundation shown on the
SBO. Flooding tends to be localised because a single storm event is unlikely to cover the
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
PAGE 7



whole of the SBO area at one time.
Varying the input parameters of the models would result in relatively minor variations to the
flood levels on which the SBO is based.
The general absence of severe flooding in the past 80 years does not undermine the validity
of the SBO.
Application of more rigorous prediction methods is unlikely to result in a significantly
different outcome.” 17
These points were also submitted to the Planning Panel in Amendment C18 to the
Stonnington Planning Scheme:
“Melbourne Water stressed to the Panel that the SBO was not based upon a known or
historical flood event. It was based upon the overland flows that would result from a storm
event that occurs, on average, once every one hundred years. These overland flow paths
were identified through computer modelling techniques.” 18
In both cases, the Panel accepted these arguments and, in relation to the latter case, the
Panel noted:
“Whilst there may be no record of flooding on a property, however this did not mean that
overland flows had not or would not occur at the site. Although flooding may not have
previously been witnessed at the site, each storm event occurs independently of previous
ones and it cannot be assumed that flooding has not previously or will not occur, on the
basis that there are no records of such an event.” 19
In Amendment C36 to the Boroondara Planning Scheme, the Panel made the following
further points in relation to properties only marginally affected by the SBO and the need to
maintain the integrity of the approach to flood mapping and controls:
“A number of the submitters sought the removal of these fringe elements of the SBO from
their properties on the basis that no local knowledge existed to indicate that their land had
been subject to flooding, even in recent heavy downpours. Others drew attention to
constraining elements on their properties or adjoining properties that would serve to divert
or withhold floodwaters from the natural flooding boundaries if the SBO flood levels were
experienced. It was contended that common sense consideration of these aspects should
result in a decision to remove their property from the SBO…
The Panel can appreciate where a property is partially impacted by what some may view as
a relatively small encroachment that these owners could experience a sense of frustration
and view any variance that would relieve their property from the SBO as being an
extremely minor variation, when viewed in context against the broad picture of the overall
area impacted by any projected 1:100 flood.
However if such variations were granted in a piecemeal approach then the whole integrity
of the SBO would be challenged. It is important to appreciate that the SBO boundaries
have been based upon rigorous application of both flood modelling and terrain modelling
principles and each section of the SBO has been ultimately plotted and presented using
prescribed and best practice of cartographic principles. To randomly vary boundaries
without any substantial justification is inappropriate.” 20
17
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p10
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), p23
19
Ibid, p45
20
Boroondara Planning Scheme Amendment C36 Panel Report (February 2005), pp30-31
18
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Issue 2
Accuracy of the modelling: Questioned the accuracy of the modelling or stated that
modelling doesn’t account for real life flood events (is only computer modelling).
Outline of Issue
Submissions question the fundamentals of the modelling and (similar to Issue 1) why a
property that is only marginally affected should be included in the SBO. This includes
questioning the data that was used as a basis for the modelling.
Council response

The use of computer based flood modelling has been consistently accepted by
Planning Panels as an appropriate basis for application of the SBO.

The use of computer modelling is the only practical method to reliably map the
extent of changes to the floodshape across the Port Phillip municipality, recognising
that it:
Is the most densely populated municipality in the state;
Was largely settled in the late 19th century and early 20th century – well before
design standards were developed to consider overland flows from 1 in 100 year
flood events;
Is 20.6km² in size; and
Has a significant diversity of built form and surface treatments.

The terrain map used as the basis for the model is based on aerial photography and
LIDAR point data provided by Melbourne Water. The 2m grid size of the terrain
map is within the appropriate scale range (as specified in Melbourne Water
guidelines) for flood mapping in urban catchments.
The boundaries of the revised SBO show the maximum extent of flooding during a 1
in 100 year flood event. This is conservative and it is appropriate to include
properties that may only be marginally affected – as development within even these
parts of the floodshape may impede the flowpath or exacerbate flooding risk.
Local stormwater drains that are principally designed for 1 in 5 year storm events
(with some drains able to cope with up to 1 in 10 year storm events) have an
insignificant effect on the 1 in 100 year storm event flooding and modelling.
Melbourne Water do not take into account local stormwater drains in the flood
modelling and mapping of their own drainage network because of their low impact
on the results.
It is also important to ensure that new development near a boundary (such as a
fence) does not impede the flowpath, or that new works do not redirect the
flowpath and pose a significant flood risk to an adjoining property. This is based on
an assessment at the planning stage of the process that would look closely at the
direction and velocity of the flowpath in the TUFLOW model and the surveyed
levels provided with the planning application.





Council and Melbourne Water have gone to lengths to ensure that the boundaries
of the SBO are mapped as accurately as possible (including undertaking further
analysis following exhibition). It has never been paramount (to the architects of the
SBO and similar tools in the planning scheme and to Planning Panels) that these
boundaries be absolutely accurate.
A further technical review has been undertaken to investigate whether there are any
anomalies with the floodshape on affected properties with a minor coverage of the
proposed SBO2. Refer to Section 5 and APPENDIX 1.
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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

Fully assessing the flooding impact to an individual property will rightly occur at the
planning application stage – when more detailed, site-specific information can be
assessed. At this stage any specific conditions for development can be most
appropriately determined. Council officers have undertaken a very limited further
technical review in response to submissions for properties with marginal coverage
of the proposed SBO2.
The model is based on assumptions and has an inbuilt margin of error from the
input data. It is a tool only to determine a certain level of flood risk. It would be
prohibitively time and resource intensive to undertake a further technical review for
all minimally impacted sites across the municipality, and even then the result would
not be precise.
Previous Panel findings
The use of computer based flood modelling has been consistently supported by Planning
Panels in the past.
This position is clearly outlined in the Panel Report on Amendment C18 to the Stonnington
Planning Scheme:
“It is important to appreciate that the SBO boundaries have been based upon rigorous
application of both flood modelling and terrain modelling principles and each section of the
SBO has been ultimately plotted and presented using prescribed and best practice of
cartographic principles. To randomly vary boundaries without any substantial justification is
inappropriate.
This aspect is best appreciated by taking an instance where a development on a property
may incorporate a proposed underground car park and it is intended to grade the driveway
from the street alignment down to the car park. The presence of a sliver of SBO across the
property frontage would bring under scrutiny the levels of the driveway and if it was
revealed that the proposed grade change was to introduce a significant change in levels
that could result in a dramatic extension of the SBO not only over the property under
development but also an adjoining property, then the presence of the SBO has fulfilled
valuable role.” 21
It has been accepted by all Planning Panels that a full assessment of the flooding risk to a
particular property is most appropriately undertaken at the planning permit stage, where
accurately surveyed levels are provided by the permit applicant.
In the Final Report on the New Format Planning Schemes, Chief Panel Member, Helen Gibson
raised the following points in relation to the Land Subject to Inundation Overlay (and which
are equally applicable to the SBO):
“In the Panel's view, if accurate flood mapping is not being completed by DNRE
[Department of Natural Resources and Environment], the relevant flood plain management
authority should determine what land is potentially or likely to be affected by flooding and
that land should be included in a Land Subject to Inundation Overlay. It does not matter
that the boundaries may not be accurate at the time the overlay is applied. The Land
Subject to Inundation Overlay only requires that a permit be obtained for buildings and
works. It does not prohibit either use or development. The time to examine the evidence in
detail about where flood levels lie in fact is at the time a permit application is made.
21
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), pp51-52
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
PAGE 10
The same approach needs to be adopted even when flood levels have been verified by
DNRE but individual landowners dispute their accuracy. Panels do not have the resources to
examine in detail competing arguments about where the flood levels lie on an individual
property when there is a lack of agreement about this. At the amendment stage it is usually
irrelevant. It is a matter more appropriately sorted out at the time any permit may be
applied for.” 22
22
Final Report on the New Format Planning Scheme (April 1999), p64
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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Issue 3
Property values: Negative impact on property values.
Outline of Issue
Submissions stated that the inclusion of their property in the SBO would negatively impact
on the value of their property.
Council response





The flood prone nature of some land is an existing fact. Excess floodwater may still
follow natural valleys and drainage paths that existed prior to the subdivision and
development of the area.
The SBO has an important function to reflect this underlying condition of the land
transparently to current owners and future purchasers of affected properties – so
that they can make informed decisions about the property and about planning for
their own safety during flooding events.
Property values are determined by many different factors, including location,
streetscape and amenity, the current economic conditions, as well as planning
controls. It is therefore difficult to assign what effect, if any, the identification of land
as liable to overland flows by the SBO may have on the value of a property.
Even if it was found that the SBO had a significant impact on property values, it
should not have any bearing on the application of the SBO.
A previous study23 undertaken by the City of Stonnington (at the time the SBO was
proposed to be applied to that municipality) looked at the values of comparable
properties in Port Phillip that were inside and outside of the SBO respectively. This
study concluded that there was no correlation between the application of the SBO
and property values.
Previous Panel Findings
The Planning Panel, in relation to Amendment C18 to the Stonnington Planning Scheme
concluded that:
“Panels have consistently found that there is no justification for setting aside of any SBO
amendment on the basis of requests for compensation, loss of property value and possible
increase in insurance premiums.” 24
The Planning Panel, in relation to Amendment C50 to the Moreland Planning Scheme stated
that:
“The value of any property is determined by the complex interplay of many different factors
such as overall economic conditions, public economic policies, location, streetscape and
amenity, and it is difficult to assign what effect, if any, the identification of land as liable to
overland flows may have on the value of a property.
This view consistent with the conclusions of the Planning Panels for Amendment C3 to the
Yarra Planning Scheme and Amendment C18 to the Stonnington Planning Scheme. These
Panels generally found no correlation between the application of the SBO and property
values.
23
24
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), pp57-58
Ibid, p59
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
PAGE 12
Melbourne Water also reported that the Stonnington Council commissioned Charter Keck
Kramer (CKC) to review the effects on property prices of the application of the SBO. CKC
examined property prices in the City of Port Phillip and found no correlation.
The Panel was not provided with any contrary evidence and concludes that the SBO or the
LSIO are highly unlikely to affect property prices, and that it is appropriate that the
condition of the land be recorded and available to interested people.” 25
Specifically, the Charter Keck Kramer study concluded (as reported in the Panel Report to
Amendment C18 to the Stonnington Planning Scheme):
“[T]here is a general purchaser awareness of the SBO within the City of Port Phillip, and
that purchasers understand the consequences that some properties affected by the Overlay
may, in the course of renovation and extension, have to meet special planning and building
requirements that would otherwise not apply. Notwithstanding, the pattern of sales and
analysis, gives no evidence or cause to believe that the application of the SBO to any of the
properties has had a measurable effect on the value of those properties when offered to
the market on normal reasonable terms and conditions. Simply stated, the application of
the Overlay within the City of Port Phillip appears to have had no adverse impact on the
property values.
For the reason that there is a strong socio-economic and demographic similarity between
the City of Port Phillip and the City of Stonnington, and as many of the properties affected
in the City of Port Phillip are of a similar style, construction mode and market value range
as many of those likely to be affected within the City of Stonnington by the proposed
introduction of the SBO, we consider it reasonable to anticipate that the introduction of the
SBO in Stonnington will, similarly, have no measurable impact on the value of properties to
which it will apply.” 26
25
26
Moreland Planning Scheme Amendment C50 Panel Report (March 2008), pp17-18
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), pp57-58
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
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Issue 4
Financial or administrative burden: There would be a financial or administrative burden
for future development or redevelopment of a site (including additional costs associated
with raising floor levels).
Outline of Issue
Submissions stated that the inclusion of their property in the SBO would be an
administrative burden and could result in increased costs associated with future
redevelopment or extensions to existing buildings.
Council response

The SBO provides important and relevant information for property owners, and is
an appropriate planning mechanism to maintain the free passage of floodwaters,
minimise flood damage, and allow a range of government and non-government
agencies to plan for these events and ensure public safety.
Burden on development

A planning permit is only triggered if the buildings and/or works proposed on a site
are fall within the area of the land covered by the SBO. This would include any
requirement to refer the application to Melbourne Water under Section 55 of the
Planning & Environment Act 1987.

There are very few properties in Port Phillip that are unencumbered by an existing
overlay (e.g. a Heritage Overlay) or where a planning permit would not already be
required under the zone to construct a building or extension.

Only 887 properties across Port Phillip currently containing single dwellings in a
residential zone that are on lots of 500m² or more and not encumbered by an
existing overlay (and therefore would not trigger a planning approval for new
development). The proposed SBO would affect 320 of these sites (which equates to
only 1.5% of the total properties proposed to be included in the SBO by
Amendment C111).
Development costs

The SBO does not prohibit development.

Costs associated with redevelopment in SBO areas will vary depending on the site
context, how the SBO covers the site and the proposed design of the development.

The additional costs of increasing floor levels should be considered as safeguard
against and the consequential reduction in costs to the property owner and to the
community as a whole in relation to flood damage to new buildings.
Previous Panel findings
In relation to the issues associated with redevelopment, the Planning Panel for Amendment
C50 to the Moreland Planning Scheme has highlighted that the SBO is a necessary planning
mechanism to ensure that development responds to flood risk at the permit stage. It stated:
“The Panel notes that under the Overlays, a planning permit is required for buildings and
works, and applications are referred to Melbourne Water. Upon application for a permit,
PANEL SUBMISSION – AMENDMENT C111 – REVIEW OF THE SPECIAL BUILDING OVERLAY
PAGE 14
each site can be investigated further, and a detailed assessment be made. Melbourne
Waterʹs requirements generally relate to the raising of floor levels or changes to site layout.
The Overlays ensure that development proposals are tested prior to being implemented.
This process ensures the proposed development is safe and minimises the risk of personal
injury or property damage that may arise from periodic inundation. Often the referrals
process is likely to improve the design of the development. The Panel also notes that
applicants have the right to seek a Review by VCAT if they consider that the Responsible
Authority or referral authority are being unreasonable.” 27
Furthermore, the Planning Panel for Amendment C1 to the Bayside Planning Scheme has
stated:
“The overlay provides important and relevant information for any landowner and
prospective developer. It does not prohibit development but allows drainage matters to be
considered in detail at the appropriate time, namely, when a development application is
submitted to the responsible authority.” 28
27
28
Moreland Planning Scheme Amendment C50 Panel Report (March 2008), p21
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p28
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Issue 5
Unaffected buildings: Buildings or structures on a property will be unaffected by flooding
/ will protect the property.
Outline of Issue
Submissions have stated that existing walls, buildings or fences (on their property or
adjoining properties) currently protect their property from flood damage.
Council response







There is no certainty that development on a site or on adjoining sites will remain
and continue to block the flowpath of water. If these structures are removed, then
properties on the site or further down the flowpath may be affected by overland
flows.
In relation to existing buildings, once the flood water reaches floor level, the building
is inundated and becomes part of the flow path.
It is important to assess the impact of future development within the SBO,
particularly development that may impact on the flowpath.
Adding further information to the terrain map in relation to the building locations,
walls and fences and other structures and their impact on flows would be extremely
complex and resource demanding.
Therefore, a general depiction of the likely flooding impact is the most effective
approach in deriving the SBO boundaries (and this is reflected in the terrain map
used as the basis for the model – refer to Section 4).
As discussed under Issue 2, it is also important to retain the SBO on part of a
property to ensure that proposed developments (including those with basements)
are appropriately designed so that the development is not detrimentally impacted by
flooding (including the potential for flooding to a basement).
For all of these reasons, the presence of built form on an adjoining or nearby site, or
on the site itself does not warrant removal of the property from the SBO.
Previous Panel findings
In relation to Amendment C18 to the Stonnington Planning Scheme, the Panel provided a
response to this particular issue:
“Whilst the model does embody some elements that deal with the recognition of flows in
urban areas, the overland flow path projected by the model is based on the ground levels
and assumes that no blockage of drainage infrastructure exists at the time of flooding and
that structural barriers such as fences, houses and brick walls are less permanent…
[It is has been] consistently stressed in previous Panel hearings… that the SBO should be
viewed as a planning tool that aims to identify areas subject to the 100 ARI event… and it
must be recognised that hydrological analysis was based on statistical concepts that were
susceptible to change as more data became available. Consequently, hydraulic and
hydrological analysis can be continuously refined.” 29
29
Stonnington Planning Scheme Amendment C18 Panel Report (September 2004), p46
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The Panel in relation to Amendment C2 to the Moreland Planning Scheme also stated:
“The purpose of the Overlay is to identify land affected by flooding or overland flows as a
result of a 1 in 100 year rainfall event. The Panel accepts that a prime function of the
overlay is to ensure that any future development within the affected portion of the site is
appropriate in terms of the identified flood potential. The removal of the overlay could
result in a development application that may seek to introduce a floor level that has an
inappropriate relationship with the flood level.” 30
30
Moreland Planning Scheme Amendment C2 Panel Report (March 2001), p11
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Issue 6
Insurance: Negative impact on insurance premiums
Outline of Issue
Submissions stated that the inclusion of their property in the SBO would result in higher
insurance premiums.
Office response





The potential impact on insurance premiums is not a matter that should have any
bearing on the application of the SBO.
The application of an SBO does not cause or change the likelihood of flooding, but
recognises the existing condition of land.
Melbourne Water and Council can provide, upon request, maps showing the extent
of the land that is floodprone (where the land is partially affected) and the specific
flood level. This information can be provided to insurance companies to accurately
inform the level of risk.
Insurance companies should adjust premiums based on the potential flooding impact
to the land and to any buildings based on the best available information provided to
them.
The Insurance Council of Australia has advised Melbourne Water that most
insurance policies provide coverage for storm damage, include cover for damages
resulting from overland flows. However, this needs to be confirmed by the property
owner’s individual insurer.
Previous Panel findings
The impact on insurance premiums has been consistently dismissed as a relevant issue by
previous Panels.
Whilst other panel reports generalised and combined these issues, in Amendment C1 to the
Bayside Planning Scheme there was a significant discussion on this topic. Both the Council
and Melbourne Water put the following to this Panel:




31
“This is not a relevant consideration in the determination of whether a development overlay
should apply.
Insurance contracts have always imposed an obligation of disclosure on policy holders. The
application of an SBO does not cause or change the likelihood of flooding, but recognises
the existing condition of land.
Insurance companies would continue to calculate their premiums on the basis of what is
known, and the properties identified in the overlay would still be subject to flooding in a 1 in
100 year rain event.
The Insurance Council of Australia has advised Melbourne Water that most insurance
policies that provide coverage for storm damage, include cover for damages resulting from
overland flows. However this would need to be confirmed by the household's individual
insurer.” 31
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p29
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The Panel agreed with these points and added:
“The Panel agrees that [the impact on insurance] is not a matter which should affect the
imposition of the overlay. Such a position, if accepted, may also affect the imposition of
other overlays such as the Wildfire Management Overlay. The inclusion of the overlay in the
scheme represents an important piece of information for property owners and potential
purchasers and developers.” 32
32
Ibid, p30
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Issue 7
Blocked or poorly designed drains: Problems with specific blocked or poorly designed
drains near their property
Outline of Issue
Submissions and enquiries that have raised specific issues about drains blocked with leaves
and other litter, or specific problems with the design of the local drainage network, were
logged in Council’s customer requests system. Actions taken included cleaning out the
relevant drain, marking it up for future or special attention, taking on board any comments
in relation to drainage design, and contacting the submitter / customer about the action
taken.
Office response

Council and Melbourne Water continue to maintain and upgrade their respective
drainage systems to ensure drains continue to cater for the 1 in 5 year standard
(design standard applied to the system). More information on what Council’s capital
improvement program is in Section 6.

Council also provides regular street sweeping services to reduce the amount of leaf
(and other) litter that could collect in the drainage system, and does respond to
specific complaints or issues raised by customers about specific drains.
Maintenance issues do not have any direct bearing on proposed Amendment C111 –
noting however, the organisation’s broader obligation to respond to these issues.

Previous Panel findings
The Planning Panel in relation to Amendment C2 to the Moreland Planning Scheme provided
the following points in relation to this topic:
“It is to be expected that the introduction of overlays will tend to draw from the community
responses to perceived inadequacies in the existing drainage systems and submitters will
endeavour to utilize the process as a forum for focusing on such matters. However the
Panel has no power to deal with such concerns and it can do little but to draw such
concerns to the attention of the Council administering the Planning Scheme.
The occurrence of overland flows is due primarily to the limited capacity of the drainage
infrastructure, which, in accordance with design standards of the time, was generally only
required to be designed and constructed to the 1 in 5 year standard.
Although incremental developments throughout the catchment may contribute to increases
in runoff, this would only impact marginally upon what is an existing risk of inundation from
the large storm events.” 33
33
Moreland Planning Scheme Amendment C2 Panel Report (March 2001), p12
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Issue 8
Maintain and upgrade the drainage system: Council and Melbourne Water should
maintain and upgrade the drainage system to cope with overland flow from the 1 in 100 year
flood event
Outline of Issue
Submissions stated that the entirety of the drainage system should be upgraded to
accommodate overland flows from the 1 in 100 year flood events and / or commented that
the lack of maintenance of the existing system was causing the flooding events. Submissions
stated that these measures should be undertaken in lieu of expanding the SBO to cover
more properties.
Council response






The drainage system in Port Phillip was entirely constructed prior to 1975, and was
constructed to accommodate 1 in 5 year flood events which was the standard at the
time.
Overland flooding associated with 1 in 100 year flood events in new residential areas
on the urban fringe is considered at the subdivision stage; together with the design
of streets, layout of the allotments and the filled ground level for each property.
Upgrading the entirety of the drainage system in Port Phillip to a 1 in 100 year
standard would not simply necessitate the use of drainage pipes with larger
diameters, but in some areas it would also necessitate realignment and widening of
existing roads, demolishing existing buildings and increasing the natural ground level
of all properties that are affected. This would result in significant disruption and
displacement for many residents – and a considerable financial cost to property
owners and Council / Melbourne Water.
The imposition of the SBO, requiring new buildings to be protected from flooding
and for an assessment to be made about the impact of development on flowpaths, is
comparatively less costly than dealing with the damage caused by flooding events.
Upgrades of the local drainage network are aimed at achieving the 1 in 5 or 1 in 10
year storm capacity. In the 1 in 100 year storm modelling, the local drainage
network may be entirely disregarded because of its low impact on the larger storm
event.
Refer to Section 6 for more information on local drainage maintenance and drainage
system upgrades.
Previous Panel findings and background information
In Victoria, the use of the 1 in 100 flood level has been in effect since 1975 following the
introduction of the Drainage of Land Act 1974. This provides the basis for declaring flood
levels and flood areas, and has since been incorporated into the Water Act 1989 and the
Building Act 1993. 34 The standard and best practice prior to 1975 was for the drainage
system to cope with 1 in 5 year flood events. 35
This measure is also in the planning system, including the Special Building Overlay, which has
as its stated purpose to:
“identify land in urban areas liable to inundation by overland flows from the urban drainage
system as determined by, or in consultation with, the floodplain management authority”.36
34
Bayside Planning Scheme Amendment C1 Panel Report (May 2001), p15
Ibid, p31
36
Clause 44.05 to the Port Phillip Planning Scheme.
35
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Planning Panels have regularly considered this issue and have consistently agreed with
Melbourne Water’s comments about the true cost of addressing this legacy issue:
“To upgrade the whole Metropolitan system to accommodate a 1% flood standard would
cost billions of dollars. [Melbourne Water’s] current budget provides for a capital
expenditure of approximately $6-8,000,000 per annum on the main drainage system and
therefore it is necessary to adopt other complementary approaches to deal with the issue.”
37
“A massive injection of funds into improving stormwater drainage in settled suburbs would
be at the expense of other community aspirations… it would not be reasonable to inhibit
the normal expectations of owners to develop their properties, awaiting some future time
when community priorities favour a massive injection of funds towards drainage
improvements.” 38
37
38
Bayside C1, op cit, p31
Glen Eira Planning Scheme Amendment C16 (November 2001), p11
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Issue 9
Climate change: Amendment does not address the impacts associated with climate
change, including sea level rise and an increase in storm events
Outline of Issue
Two submissions were critical of the approach taken with Amendment C111 not to include
consideration of the impacts of climate change – specifically the associated increase rainfall
intensity, and higher sea levels reducing the capacity of the drainage system.
Office response
Sea Level Rise



The flood modelling was completed approximately 6 months prior to the approval
and gazettal of Amendment VC94, which revised Clause 13.01 to provide differential
rates for sea level rise 0.2m by 2040 for urban infill areas and 0.8m (by 2100) for
greenfield development. This Amendment also removed the ‘precautionary
principle’. Please refer to APPENDIX 6 for the previous wording contained in
Clause 13.
The flood modelling did not include modelling of 0.2m sea level rise as this was not a
factor at the time, and modelling for 0.8m SLR no longer had any basis in State
Planning Policy – so it would be difficult to use this as the basis for the amendment,
particularly with the removal of the ‘precautionary principle’.
The updates to the SBO proposed by Amendment C111 do not reflect changes to
flood potential arising from coastal climate change. Council is undertaking a number
of studies in conjunction with the Association of Bayside Municipalities (ABM) to
gather information about coastal processes to assist our understanding of future
coastal flooding, how this will combine with catchment flooding and what impacts
this will have over time. These include a review of current and historic sea level and
wave climate. Additional information about storm bite is yet to be gathered. A full
suite of data will not be available for some years, however, in the interim it is
Council practice to advertise major developments (including any development
proposing a basement) on a low-lying property proximate to the coast and not
covered by an SBO to Melbourne Water (pursuant to Section 52(1)(d) of the Act)
for comment.
Increased Rainfall


As discussed in Section 4.8, Melbourne Water’s practice is not to include any
predicted increases in rainfall as a result of climate change for catchments, and this
will continue for any new planning scheme updates in the immediate future because
the ARR is currently under review.
Furthermore, whilst climate change may impact the frequency of the storm events,
this may not equate to changes to 1 in 100 year flood levels or extents as
represented in planning scheme overlays.
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Council’s Commitment to Planning for Coastal Climate Change








Council is committed to responding to climate change and this is demonstrated
through education, advocacy and action.
Council, in its submission to the Coastal Climate Change Advisory Committee,
stated that one of the key principles for responding to climate change in coastal
areas is for the introduction of an overlay to manage future development to
“delineate vulnerable ‘at risk’ areas; and to define development requirements which will
mitigate the effects of flooding and inundation in urban areas”39. A new planning tool can
respond to a specific, transparent and integrated manner to the effects of coastal
climate change – in addition to updating the existing flooding overlays (e.g. SBO,
LSIO) to manage climate change impacts on inland areas.40
An integrated, regional response is required for the Port Phillip Bay area and cannot
rely on individual Local Councils to prepare varying responses and to progressively
update planning schemes and to use ‘best fit’ planning tools that are not specifically
designed to address the impacts of climate change (e.g. the LSIO).
The Draft Central Regional Coastal Plan (2015-2020)41 has stated that there is a need
to develop a Coastal Hazard Vulnerability Assessment for the central region
(encompassing Port Phillip Bay), which would be a necessary precursor to the
development of a planning tool to deal with coastal hazards and inundation
associated with sea level rise, and would inform the science underpinning the tool.
Council, in its submission to Plan Melbourne, highlighted that this plan had not
detailed how the government will respond to the impacts of climate change,
including flooding and sea level rise, and was a major gap in a long term strategy for
the development of Melbourne.42 Furthermore, Council identified that a priority
initiative should include the commitment to planning for climate change and sea level
rise – including delivery of drainage and coastal management infrastructure. 43
It is Council’s position that a bay-wide Coastal Hazard Vulnerability Assessment
(CHVA) needs to be undertaken for Port Phillip Bay and a specific tool in the
Victoria Planning Provisions (VPPs) needs to be developed by the State government
to implement this CHVA in an integrated way for all bayside municipalities.
The ABM, of which Council is an active member, is collecting data and this will
inform the CHVA (which would need to be undertaken by the State government)
and a future tool (again, developed by the State government) and the decision
guidelines that would be made for individual planning applications.
In the meantime, Council is committed to responding to the challenges of climate
change, and will continue to undertake advocacy through all possible channels to
ensure that:
o Climate change is properly addressed at state and regional level;
o Our planning for climate change is based on a bay-wide assessment and
robust data; and
o We have the appropriate tools to specifically and transparently consider the
impacts of climate change.
39
Submission to Coastal Climate Change Advisory Committee – Issues and Options Paper (City of Port Phillip,
February, 2010), p1
40
Ibid
41
Finalised version of this plan is currently being considered by the Victorian Government.
42
Plan Melbourne – Final Submission by the City of Port Phillip (10/12/2013), p4
43
Ibid, p6
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
The SBO addresses a particular type of flooding and is not the ‘best fit’ to deal with
climate change impacts (including sea level rise). Amendment C111 simply updates
the SBO based on new modelling and it is premature for us at this stage to make
changes to the amendment to factor in sea level rise without a bay wide CHVA, and
without support in the State Planning Policy Framework.
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Issue 10
Design requirements: Further design requirements are required in policy to encourage
built form that would allow flood waters to flow under buildings
Outline of Issue
A submission recommended that design standards be changed to require buildings to be
constructed on more permeable foundations (e.g. stilts or other openings) to allow flood
water to pass underneath and reduce the flood risk compared to constructing more solid
foundations.
Council response

The requirement to construct new buildings on stumps allowing water to flow
underneath can be appropriate in some areas, particularly when the main flow path
runs across a property or collection of properties. However, it is not suitable
everywhere and could be problematic for some sites. It is important that
assessments are made on a site by site basis by Melbourne Water (for SBO1 and
SBO3 areas) and Council’s Development & Drainage Engineer (for SBO2 areas),
taking into account the location of the main flow path and the depth and velocity of
flooding.

Council and Melbourne Water continue to use the Guidelines for Development in
Floodprone Areas (Melbourne Water, 2007), along with best practice principles,
policies and guidelines developed by State and Federal governments – which provide
a technical basis to assess the flooding risks associated with proposed developments.
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4.
FLOOD MODELLING
4.1 Introduction
The flood modelling undertaken by Council is considered to be industry best practice. The techniques
to construct the model and to undertake simulations have vastly improved since Council initially went
through this exercise, leading to the introduction of the SBO into the Port Phillip Planning Scheme in
1998.
The modelling tool used ‘TUFLOW modelling software’ is well established and internationally
recognised as the world’s most powerful 2D/1D hydrodynamic computational engine.
There is complete confidence by Melbourne Water and Council engineers in the model and the
floodshapes ultimately generated to inform the boundaries of the SBO. The floodshapes were
determined using the best available data and techniques at the time. The floodshapes and flood levels
will be used within the planning application referral system that then considers the subject property on
an individual and more detailed basis.
The key stages involved in the modelling process are:
1.
2.
3.
Constructing the model
Undertaking model simulations
Reviewing and filtering the model outputs
Figure 1 on Page 28 provides an illustrative summary of this process.
Melbourne Water Flood Modelling
Melbourne Water will provide a separate submission that will include an outline of the flood modelling
that they have undertaken.
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Figure 1 – Diagram showing the flood modelling process
4.2 Modelling Methodology – Overview
The Flood Modelling Report produced by URS for the City of Port Phillip in December 2011 (available
in APPENDIX 5 encompassed the following scope of works:





Data Collation and Review
Preliminary Flood Modelling
Detailed 1D/2D Flood Modelling
Climate Change Impacts
Flood Maps and Report
The computer modelling program TUFLOW was used. TUFLOW is a 1D/2D hydrodynamic model
developed to simulate flooding situations where flow patterns are poorly defined and/or unsteady and to
effectively model the one dimensional network of pipes and pits.
Using a GIS based approach, model inputs can be produced in layers which has major benefits:


It enables the model components to be developed and overlayed on maps containing
information such as contours and aerial photographs where catchment features can be easily
understood.
It allows for the interpretation, analysis and comparison of the model results such as multiple
modelling scenario and/or modelling of several ARI events.
Melbourne Water’s Guidelines and Technical Specifications for Flood Mapping Projects (2010) (the
‘Melbourne Water Guidelines’) was adopted for the study.
The municipality was divided into seven (7) sub-catchments, each of which were analysed in isolation to
the others.
The following four (4) scenario runs were modelled for each of the seven (7) sub-catchments based on
Melbourne Water Guidelines and climate predictions for 2100 (0.8m sea level rise and 32% rainfall
intensity):




5 year base case (1.22m Sea level)
5 year climate change (2.02m Sea Level and 32% increased rainfall intensity
100 year base case (1.22m Sea Level)
100 year climate change (2.02 m Sea Level and 32% increased rainfall intensity)
Note: as discussed in Section 3.3 (under Issue 9), the modelling was in response to State Planning Policy
at the time that referred to sea level rise of 0.8m by 2100.
4.3 Assumptions behind the modelling
Catchment Features
In order to simulate water movement through an urban catchment during flood events, it is important
that features which may impede the flow, such as roads, buildings, walls, fences, vegetation, etc. are
represented in the flood model. Individual representation of all these features is difficult and deemed
unnecessary in this instance. Instead, as is often the case in flood mapping, the catchment impedance to
overland flow was modelled by assigning six (6) roughness coefficients (Manning’s n value) to the 2D
domain/catchment surface areas delineated by similar land-use or surface type from aerial photographs.
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





Waterways (n=0.022)
Paved areas such as roads, laneways and car parks (n=0.02)
Open space such as parks and gardens (n=0.035)
Medium density residential properties (n=0.25)
Higher density residential properties (n=0.30)
Large buildings and other impermeable obstructions (n=3)
The initial loss for the entire area (except for waterways with 0mm initial loss) was assumed to be
10mm as stipulated by Melbourne Water for a typical urban catchment. The entire area was also
assigned a value of zero continuous loss for the same reason.
All piers and beaches, as well as the island in Albert Park Lake were not included in the model because
any rainfall in these areas would drain directly into the surrounding water and cause negligible flooding
and instabilities in the model.
1D Network Development
The 1D pipe network in the TUFLOW model comprises Melbourne Water Drains and drains adjacent
to these drains with a diameter of 300 mm or larger. The inclusion of every pipe would produce
instability in the model and increase processing times. Smaller diameter drains were included in areas
were local pondage could be expected. Pits were included in the model based on the defined pipe
network, modelled with an unrestricted inlet capacity and assigned a level which was known or in some
cases estimated using engineering judgment based on surrounding topography and a minimum cover
level of 600 mm. All pipes were assigned a Manning’s n roughness of 0.015 and open channels 0.04 as
stipulated in the Melbourne Water Guidelines.
1D and 2D Boundary Conditions
Port Phillip Bay – Sea Level
For all catchments adjacent to Port Phillip Bay – 1.22m AHD for base case, 2.02m AHD for climate
change scenarios as per Melbourne Water Guidelines at the time.
Pipe Outlet Boundaries
The following tail water levels on the pipe outlets were adopted:




0m AHD to Port Phillip Bay
3m AHD to Albert Park Lake
1.22m AHD to Yarra River
Elwood Canal – as per sea level for particular model run
These levels were selected to ensure a conservative ‘worst case scenario’ for the flood mapping as they
would essentially assume that the water body is full throughout the simulation period.
Model Runs
Determination of Critical Storm Durations
Intensity-Frequency-Duration (IFD) curves supplied by the Bureau of Meteorology were used to give
rainfall intensities for each storm duration and ARI (average recurrence interval) for the region.
Australian Rainfall and Runoff (ARR) Vol 2 was used to determine a temporal pattern of the storm. A
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PAGE 30
number of storm durations were tested and two durations were run for each of the sub-catchments and
the results were spliced together to ensure that the maximum modelling flooding levels were
determined:


45 minute and 1.5 hour storm durations for catchments 1, 2, 3, 4, 6 and 7; and
30 minute and 45 minute storm durations for catchments 5.
Model Checks
An extensive quality checking process of the hydraulic modelling results was undertaken by URS.
4.4 Drainage Inputs
Before the TUFLOW model was developed, several data sets needed to be gathered and pre-processed:







GIS data provided by Council and Melbourne Water of the drainage network (pits and pits)
Existing RORB and TUFLOW models provided by Melbourne Water of the behaviour of the
network outside the Council area
Aerial photography of the area provided by Council .
LIDAR data of the area provided by Melbourne Water – accurate to within ± 100mm vertical
and ± 350mm horizontal.
Flooding “hot spots” provided from the Stormwater Action Plan (URS 2009) which represent
areas that have historically known to flood (community complaints and Council staff
knowledge).
Melbourne Water 100 year ARI flood extents developed using RORB in 1998.
Special Building Overlays developed in 1998 by Council.
4.5 Translation to SBO Mapping
Flood Mapping
Flood extent maps were generated for each of the four (4) scenarios for all seven (70 sub-catchments
taking the maximum depths of the results of the two storm durations.
Filters were applied according to Melbourne Water Guidelines as follows:




All areas with above 50mm depth of flooding and a velocity of above 0.008m/m/s
All areas above 100 mm depth of flooding
All island within the flood shape smaller than 100 m² were removed
All inundation of less than 100 m² in area were removed
Flood maps were constructed with the base case superimposed on top of the climate change scenarios
to give an understanding of the increase in flood extents that can be expected in the future.
The flood extents generated in this study were then combined with current Melbourne Water flood
shapes and to produce the updated proposed SBO mapping.
Identification of Pipes Running Full
The TUFLOW output files were used to map which pipes ran full during the simulation as well as how
long these pipes were running at capacity for the 5 year base case and 5 year climate change scenarios.
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This was done in order to easily identify which pipes were under –capacity and which pipes were
running full for the majority of the simulation period (>75% of the time).
Property Flood Depths and Levels
The flood depths and flood levels for all four storm event scenarios were determined for all properties
within the filtered flood shapes.
No attempt was made to further define properties affected by flooding and/or define the flood shape
after consultation with Melbourne Water. The flood shape should be used within a referral system that
considers each property individually. Further filtering of the flood shape may threaten the integrity of
such a referral system.
4.6 Calibration by ‘Ground-truthing’ against past storm events
The modelled sub-catchments are ungauged and therefore it is not possible to calibrate the model
against known flood events. However, Council’s Stormwater Action Plan (URS 2009) identified a number
of known flooding “hot spots” which represent locations that have historically been known to flood
from local knowledge and reports. Overall, there was a good level of agreement between the modelled
data and historical “hot spots” observation across the seven sub-catchments.
4.7 Preparation for Amendment C111
Melbourne Water underwent a similar modelling process for Catchment 7 only (an area incorporating
the Elwood Canal, Shakespeare Grove and Byron Street main drains).
Following the finalisation of the changes to the floodshapes for SBO2 by Council and SBO1 by
Melbourne Water, there was a period of review undertaken to ensure that no single property was
covered by more than one of the proposed schedules (i.e. SBO1 or SBO2).
SBO3 was later developed to divide areas of the SBO affected by Melbourne Water’s drains, to define
and apply additional planning permit exemptions to areas where the flood levels are relatively stable.
This reduces the need for planning permits, and referrals to Melbourne Water. Further analysis was
undertaken to ensure no single property was covered by more than one SBO schedule.
4.8 Climate Change
Using Melbourne Water Guidelines and climate predictions for 2100 (0.8m sea level rise and 32% rainfall
intensity, the effects of climate change was analysed with the use of maps for the 5 year and 100 year
climate change scenarios and comparing them to the base case scenarios. The flood extent comparison
maps show as expected, that there is a larger flooded area with the climate change scenarios although
this did vary with each sub-catchment. For the coastal catchments (catchments 1,3,5,6 and 7) certain
areas of increased flood close to the shoreline can be almost solely attributed to sea level rise. For the
100 year storm event, the increase in flooded areas ranged from 1% (catchment 4), 4% (catchment 6),
6% (catchment 2), 9% (catchment 1 and 7), 11% (catchment 3 and 5).
Melbourne Water is not including any predicted increases in rainfall as a result of climate change for
catchments. Whilst Melbourne Water may have informally completed some initial analysis, this has not
been included. Therefore any new planning scheme updates in the immediate future will not include
predicated increase.
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Furthermore, Australian Rainfall and Runoff (Engineers Australia, 1987) is currently under review, with
projects underway which include revisions to rainfall estimations increases as a result of climate change.
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5.
FURTHER TECHNICAL REVIEW
5.1 Overview


As resolved by Council in response to individual submitters (and to further inform the Planning
Panel), Council officers undertook a further individual technical assessment of properties in
SBO2 where the proposed coverage of the property by the SBO is minor, and where a
submitter has expressed a view that the property should be removed from the proposed
overlay (16 properties in total).
A property is considered to have minor coverage if the proposed SBO covers less than 15m²
and less than 6% of the total area of the site.
5.2 Considerations
The final flood mapping used to produce the proposed SBO included a set of filters in accordance with
Melbourne Water Guidelines (refer to Section 4.5). The fact that there may be only a small percentage
or width of a property covered by the SBO flood shape is no justification for the removal of the
property from the SBO.
For reasons given earlier, it is not desirable to further filter the flood shape and undertake a more
detailed assessment of each property without detailed development proposals.
However, a methodology has been developed to provide a consistent assessment of each property
which has been referred for a further technical review. This same methodology is already and will
continue to be applied at the planning application stage. The five criteria and weightings have been
chosen by Council’s Drainage and Development Engineer based on his experience and technical
expertise in the understanding of the modelling data and outputs. His recommendation to retain or
remove the property from the SBO is his assessment endorsed by his Co-ordinator, and the full
assessments are contained in APPENDIX 1 to this submission.
The five criteria and weightings to assess the flood risk are as follows:
Criteria
Assessment
Weighting
Overland flow path relative to property
How much of the water flows onto the property from
the main flow path?
50%
Surface flow characteristic
What is the direction and velocity of the flow onto the
property?
15%
Ground LIDAR level in property
Are the LIDAR points on the property higher or
lower than the main flow path?
15%
Flood Shape in property
How much of the property is covered by the flood
shape?
10%
Max Flood Depth in property
What is the maximum flood depth on the property?
10%
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5.3 Outcome / proposed changes to Amendment C111
This technical review has been undertaken and very minor refinements to the SBO2 floodshape are
recommended. All affected submitters have been advised in writing of the recommendations and the
following is a summary:
Submission No.
Location
Proposed Outcome
111-SUB021
Station Street, Port Melbourne
Remove from SBO
111-SUB026
Dow Street, Port Melbourne (2 properties)
Remove from SBO
111-SUBL060
Richardson Street, Middle Park
Remove from SBO
111-SUB018
Raglan Street, Port Melbourne
Remove from SBO
111-SUB019
Lambeth Place, St Kilda
Remove from SBO
111-SUB031
Richardson Street, Middle Park
Must be retained
111-SUB045
Docker Street, Elwood
Remove from SBO
111-SUB022
Phyllis Street, Elwood
Must be retained
111-SUB043
Dundas Place, Albert Park
Remove from SBO
111-SUBL058
West Beach Road, St Kilda West
Must be retained
111-SUB050
Spray Street, Elwood
Remove from SBO
111-SUB033
Little O’Grady Street, Albert Park
Must be retained
111-SUB017
Milton Street, Elwood
Remove from SBO
111-SUB057
Barrett Street, Albert Park
Must be retained
111-SUB035
Cruikshank Street, Port Melbourne
Remove from SBO
In summary, of the 16 properties subject of the technical review, the proposed SBO2 could be removed
from the following 11 properties:











141 Station Street, Port Melbourne
233 Dow Street, Port Melbourne
235 Dow Street, Port Melbourne
279 Richardson Street, Middle Park
147 Raglan Street, Port Melbourne
11 Lambeth Place, St Kilda
14 Docker Street, Elwood
40 Dundas Place, Albert Park
69 Spray Street, Elwood
50B Milton Street, Elwood
97-101 Cruikshank Street, Port Melbourne
Full details of the technical review are available in APPENDIX 1.
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6.
FLOODING MAINTENANCE AND CAPITAL EXPENDITURE
6.1 Drainage Maintenance Program
On average, Council spends around $900,000 per annum on drainage maintenance services. On 26 May
2015, Council awarded Contract 1912-Drainage Maintenance Services to Veolia Water Network
Services commencing on 1 July 2015 for a period of three years (with an option for a further term of
two years). The contract service specification includes:









Side Entry Pit (SEP) and Grated Pit (GP) inspection and cleaning
Increased maintenance in known flooding areas (pit inspection and cleaning monthly in High
Maintenance Zone includes Frequent Flooding Areas at 56 locations. Refer to APPENDIX 2
for more information.
Gross Pollutant Trap (GPT) inspection and cleaning
Litter basket inspection and cleaning
Junction pit, pipe and culvert cleaning
CCTV inspections
Depot wash bay & Transfer Station sump pit cleaning
Reporting, inspections and asset management
Standardised asset grading according to the industry standard Water Services Association of
Australia (WSAA) 05 “Conduit Inspection Reporting Code of Australia”.
The new contract also contains improved data collection and reporting to:






Ensure we report on asset condition to industry standards
Allow recording of servicing details in the asset management database
Improve access to information to ensure that drains which require more frequent maintenance
is appropriately scheduled.
Update spatial data in our Geographic Information System (GIS)
Provide information to prioritise locations for civil upgrades or renewal
Provide accurate drainage and flooding information.
6.2 Identification of Areas for Possible Pipe Upgrade Works
On average, Council spends around $1 million per annum on drainage capital works. Using the flood
inundation maps and the maps showing the pipes running full from the 2011 URS study, it has been
possible to identify areas that may be in need of pipe upgrade works to achieve the 1 in 5 year service
level (refer to APPENDIX 3 for more information). In a number of cases, increasing pipe sizes will not
reduce flooding and alternative measures will be required.
A number of drains discharge to the Bay or to the Yarra River and the outlets are submerged at high
tide or under peak flows. This prevents the free flow of stormwater and will result in flooding in the
network. To overcome this, a number of mitigation measures are possible, including retarding basins or
underground storage (to store and hold back stormwater until the water level drops) and tide gates on
the outlets (to prevent sea/river water filling the stormwater drain).
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The Citywide Drainage Upgrade Program (URS, 2014) was commissioned to undertake an analysis of the
Council drainage network in order to improve hydraulic performance and identify practical flood
mitigation solutions for the 5 year Average Recurrence Interval (ARI) storm combined with climate
change scenario (0.8 m sea level rise and 32% increase in rainfall intensity by 2100).
The study focussed on ten (10) sub-catchments which contained only Council drainage assets.
Catchments containing Melbourne Water assets, which drain catchment greater then 60ha (including
catchments external to the City of Port Phillip) require regional scale flood mitigation assessments were
beyond the scope of this study.
The study identified potential options for each sub-catchment; modelled the preferred option’s to
determine their effectiveness in mitigating localised flooding; and undertook a benefit cost analysis of the
preferred option/s.
A total of nineteen (19) location were identified for investigation of which six (6) were eliminated
because of limited benefits and thirteen (13) found to have potential. Costs estimates for each solution
ranged from $97,000 to $7.7 million (total estimated cost for all solutions was $28.5 million.
A value assessment on the relative costs and benefits for each option was developed with the benefit
based on the number of properties and building no longer subject to flooding as a result of the flood
mitigation measure. The mitigation measures were then ranked in terms of value for money (cost per
building saved from inundation) to provide twelve (12) options ranging from a cost per building saved of
$15,900 up to $415,250.
These options include:





Tide gates (3)
Retarding basin (1)
Underground storage (4)
Pipe upgrade (3)
Raised pedestrian crossing (1)
Further detailed investigation of these options has commenced and a Business Case will be developed
for capital works funding in future years.
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7.
CONCLUSION
7.1 Amendment C111
Council as the Planning Authority for Amendment C111 respectfully requests that the Panel support
adoption of the proposed amendment to update the SBO in the Port Phillip Planning Scheme.
This amendment proposes to amend the Special Building Overlay to reflect the revised flood extent, by
amending maps and replacing the existing schedule to Clause 44.05 with three new schedules to reflect
the relevant authority responsible for the drainage network and to introduce additional planning permit
exemptions in certain areas.
The amendment is consistent with the State and local planning policy frameworks, and the mapping
undertaken by both Council and Melbourne Water is in accordance with industry best practice and is
accurate for the purpose of the broad application of an overlay.
Council considers it important to fulfil its duty as Planning Authority to keep the planning scheme up to
date. This includes ensuring the SBO reflects the most current assessment of properties subject to
flooding, thereby reducing risk, increasing awareness and ensuring that flooding impacts do not worsen.
7.2 Council’s final position on the Amendment
In considering all written submissions at its meeting on 14 July 2015, no specific changes to the exhibited
amendment were proposed by Council. Council did, however, determine to do undertake the further
technical review of 16 properties subject of submissions. The outcomes of this review have been
detailed in Section 5 and APPENDIX 1, and propose that 11 properties be removed from the SBO as
exhibited. Subject to the advice of this Panel, these changes to Amendment C111 will be recommended
to Council at the adoption stage.
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APPENDICES
Appendix 1
Further Technical Review
Appendix 2
Drainage Maintenance Program
Appendix 3
Pipe Upgrade under Capital Works Program
Relevant Panel Reports
Appendix 4*
A.
B.
C.
D.
E.
F.
Bayside Amendment C1
Final Report NFPS Panel Report
Glen Eira Amendment C16
Moreland Amendment C2
Moreland Amendment C50
Stonnington Amendment C18
Appendix 5*
Flood Modelling – Updating Port Phillip Council Flood Modelling and Assessing the
Impact of Climate Change (URS Aust. Pty Ltd, 2011) (main content only)
Appendix 6
Clause 13 of the State Planning Policy Framework (prior to gazettal of Amendment
VC94)
*All appendices, except for 4 and 5 are included with the copies of the submission circulated at the
hearing. Appendices 4 and 5 can be made available on request.
All appendices to this report (including 4 and 5) will be made available online at after the Panel
Hearing: http://www.portphillip.vic.gov.au/amendment-c111.htm
Advice for Panel Members (only): A complete copy of the URS Report (Appendix 5) has been
provided to the Panel and is in Tab 6 in Folder 2.
APPENDIX 1
Further Technical Review
APPENDIX 2
Drainage Maintenance Program
APPENDIX 3
Pipe Upgrades under Capital Works Program
APPENDIX 4
Relevant Planning Panel Reports
A.
B.
C.
D.
E.
F.
Bayside Amendment C1
Final Report NFPS Panel Report
Glen Eira Amendment C16
Moreland Amendment C2
Moreland Amendment C50
Stonnington Amendment C18
APPENDIX 5
Flood Modelling – Updating Port Phillip Council Flood Modelling and
Assessing the Impact of Climate Change (URS Aust. Pty Ltd, 2011)
(Referred to as “URS Report” in this submission)
APPENDIX 6
Clause 13 of the State Planning Policy Framework
(Previous version – prior to gazettal of Amendment VC94)