Flood Management and Drainage Strategy - Port Phillip and Westernport Region
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Port Phillip and
Westernport Region
Flood Management
and Drainage Strategy
i
“Ideally society would like to be free of the risk of flooding, but this is neither practically nor economically feasible. What constitutes an acceptable level of flood risk however is a vexed question. The immediate risk is borne by the community, which must have a significant input into defining the acceptable level. To this end, public consultation and risk communication is very important.” Floodplain Management In Australia Best Practice Principles and Guidelines, (SCARM 2000)
Development of this strategy has been guided by a steering committee headed
by an independent chair, Rob Joy, with representatives from the following
organisations:
• Department of Sustainability and Environment
• Office of the Emergency Services Commissioner
• Shire of Macedon Ranges
• Insurance industry
• Department of Human Services
• Municipal Association of Victoria
• Stormwater Industry Association of Victoria
• Institute of Public Works Engineers Victoria
• Port Phillip and Westernport Catchment Management Authority
• Melbourne Water.
The strategy has been prepared following extensive consultation with flood
management agencies and local government authorities in the Port Phillip and
Westernport region. Stakeholder workshops were undertaken to identify issues
of concern and submissions received in relation to a circulated discussion
paper assisted in the formulation of future strategic actions.
iii
Lollipop Creek, Werribee, February 2005 iv Flood Management and Drainage Strategy
Contents
2 Introduction
6 Background
6 What is flooding?
8 Types of flooding in the region
12 History of flooding
14 Flood damage
20 Managing floods
22 Responsibilities for flood management across the
region are shared
26 Flood management objectives
Objective 1: Completing the knowledge base
Objective 2: Potential long term future pressures on
existing drainage systems
Objective 3: An agreed approach to managing existing
regional flood problems
Objective 4: Enhanced community education, flood
awareness and preparation
Objective 5: Agreed responsibilities and improved
collaboration between flood management agencies
44 Glossary
Introduction
Floods are a natural and inevitable event. We cannot always
control them. Therefore, we must learn how we can live with
them while minimising risks to public health and safety, property
and infrastructure.
The Port Phillip and Westernport Region faces significant Aside from the likely multi-billion dollar cost and extreme
flood management and drainage challenges that require a disruption, the time frame to build such expensive
coordinated and collaborative approach by flood managers infrastructure would exceed the lifespan of the properties
and the community. they attempt to protect.
There are currently more than 100,000 properties in the This strategy recognises that although it is not possible
region that are known to be at risk from flooding of which to make the region completely free from flooding, there
82,000 properties are at risk of flooding from overland are some flooding risks that we may decide are intolerable
flows. More than 40,000 of these properties contain and almost regardless of the cost, the consequence of
buildings or dwellings that are at risk of flooding above flood should be reduced or eliminated. Consultation and
floor level. On average, the annual damage caused by research will be undertaken to reach agreement on what
flooding in the region has been estimated to be $245 constitutes intolerable flood risk.
million.
Our long term aim is to minimise all currently known
The Flood Management and Drainage Strategy has been intolerable flooding risks to public health and safety,
prepared following discussions between government property and infrastructure, and increase community
departments, councils, emergency service organisations, understanding and preparedness for floods.
and other agencies about how we can improve the
This strategy proposes the development and
management of flood risk in the Port Phillip and
implementation of an accelerated program, in consultation
Westernport Region. It complements other Melbourne
with stakeholders, to identify and deal with intolerable
Water programs that deal with river health, water
flood risk across the region as quickly as possible.
quality, floodplain environmental values, urban growth,
stakeholder communications and cultural heritage. As part of this strategy, Melbourne Water will continue to
map flood affected areas and will sponsor research into
Melbourne Water and councils have traditionally used
the intangible social and human health impacts of floods,
engineering solutions to improve flood protection in
to develop an improved flood risk assessment tool that
identified high risk areas.
takes these costs into account when determining flood risk
Millions of dollars, funded primarily by council and priorities and responses.
Melbourne Water drainage rates, are currently spent each
Throughout this strategy there is broad recognition that no
year on efforts to manage ongoing risks from overland
single organisation and no single approach can deliver an
flows and riverine flooding.
effective response to flood management issues.
While these efforts are effective at a local level they are
While Melbourne Water and councils will continue to
having little impact on the overall problem.
deploy engineering solutions to mitigate flood risks, it is
This is because it is not physically feasible to construct recognised that this approach must be accompanied by a
required works to protect all properties in the region from range of non-structural responses.
large events.
2
Flood Management and Drainage Strategy
Richmond, July 1891
There are other tools that are equally effective and Objective 1: Completing the
significantly less expensive, such as planning controls
and public awareness programs that can be deployed knowledge base
immediately to assist in treating the residual and future
flood risks. These tools will be developed in partnership Flood mapping
with other flood managers.
Actions
In particular, the strategy recognises the importance and
1.1 Melbourne Water will undertake and maintain ongoing
benefits of improved education in assisting the community
local flood extent, rural waterway and tidal mapping
to prepare, respond and recover from floods.
for the Port Phillip and Westernport region, taking
Part of this focus on existing flood risks will also involve into account the potential long term pressures of
working with councils to develop detailed local flood climate change and urban consolidation. This will
management plans, and working with the State Flood involve consultation with local government and the
Policy Committee, Office of the Emergency Services Department of Sustainability and Environment.
Commissioner and other stakeholders to develop an
1.2 Melbourne Water will update and maintain flood
integrated flood management planning framework.
information for municipal planning schemes to
These plans will outline roles and responsibilities, set
ensure appropriate standards of flood protection for
priorities, aims and goals, and establish work programs
new development in flood affected areas. This will
and targets to address flood management objectives
involve consultation with local government and the
identified in the strategy.
Department of Planning and Community Development.
The strategy defines five flood management objectives
and outlines actions that will be undertaken to achieve Understanding social impacts
each objective and guide priorities and expenditure by
Melbourne Water. Actions
1.3 Melbourne Water will support collaborative research
into the social and economic impacts of flooding on
the community.
3
We all have an important role to play – Melbourne Water,
emergency service organisations, local councils, government
departments, research organisations, developers and other
businesses, and the community.
Objective 2: Potential long-term future 2.2 Melbourne Water will develop flood risk management
measures in consultation with Department of Planning
pressures on existing drainage systems and Community Development, Department of
Sustainability and Environment and local government.
Development in established areas Solutions may include upgrading infrastructure,
planning and building controls to limit imperviousness,
Actions
and onsite measures such as water sensitive urban
2.1 Melbourne Water will work with Department of design and stormwater capture and reuse.
Planning and Community Development and local
government to understand the likely impact of urban
Climate change
consolidation on runoff volumes and flood risk in
existing urban areas. Actions
2.3 Melbourne Water will continue to support research
programs to better understand the impacts of climate
change on flood and drainage management.
2.4 Melbourne Water will develop adaptable flood
management programs to deal with changing rainfall
patterns, rising sea levels, and storm surge. These
programs will be developed in consultation with the
Commonwealth Scientific and Industrial Research
Organisation (CSIRO) and the Bureau of Meteorology.
4
Flood Management and Drainage Strategy
Objective 3: An agreed approach to Objective 4: Enhanced community
managing existing regional flooding education, flood awareness and
problems preparation
Actions Actions
3.1 Melbourne Water will sponsor research and consult 4.1 A community flood education, awareness and
with stakeholders to develop criteria to establish flood preparedness program, including flood warning, will
risk tolerability thresholds which take into account be developed and implemented for the Port Phillip and
relevant social or intangible flood impacts. Westernport region in partnership with Victoria State
Emergency Service, and other key stakeholders.
3.2 Melbourne Water will develop and implement a
program in consultation with stakeholders to eliminate
or reduce intolerable risks to an acceptable standard Objective 5: Agreed responsibilities
through the combination of engineering works and
non-structural measures. and improved collaboration between
flood management agencies
Actions
5.1 Melbourne Water will work with the State Flood
Policy Committee, Office of the Emergency Services
Commissioner and other stakeholders to develop and
implement an integrated flood management planning
framework for the region.
5.2 Melbourne Water will provide technical and financial
assistance to councils that have identified flood risk
for the preparation and review of flood management
plans.
Left: Aitken Creek, Craigieburn, February 2005
Below: Princes Freeway, Little River,
February 2005
5
Background
Melbourne Water The Port Phillip and Westernport
Melbourne Water is the waterway manager for the Port Region
Phillip and Westernport Region and as such is custodian The Port Phillip and Westernport Region covers an area
of the health of 8,000 kilometres of rivers and creeks that of approximately 13,000 square kilometres and includes
drain into Port Phillip Bay and Western Port. nearly all the land that drains to Port Phillip Bay and
Melbourne Water is also the regional drainage and Western Port. It extends from high up in the Yarra Ranges
floodplain management authority for the region and in the east, across to Ballan in the west, and from the
is responsible for the management and maintenance Mornington Peninsula and Phillip Island in the south,
of numerous retarding basins, water quality treatment to Lancefield and Kinglake in the north. It includes the
wetlands, levee banks, pump stations, flood gates and greater Melbourne metropolitan area and is home to 3.8
1,500 kilometres of underground drains. million people.
Melbourne Water’s area of responsibility matches the Prior to European settlement, the region’s rivers, creeks
Port Phillip and Westernport Catchment Management and their floodplains formed a vital part of the Aboriginal
Authority’s (CMA) operating area to ensure a whole of culture. They yielded many resources and were important
catchment approach to the management of flooding, places of spiritual and community activity, including
regional drainage and river health. birthplaces, burial sites, places of ceremony and transport
routes. A range of European and Aboriginal heritage values
The CMA plays an overarching strategic management role
exist in the regions waterways and floodplains.
in the development, co-ordination and delivery of the Port
Phillip and Western Port Regional Catchment Strategy Melbourne Water acknowledges the traditional owners
2004 – 2009. of the land, rivers and creeks we manage, and pay our
respects to their elders and ancestors. We recognise our
Melbourne Water’s responsibilities, overall goals and long
responsibilities to care for rivers and creeks in greater
term aims for the management of waterways, floodplains
Melbourne, mindful of the significance they represent for
and regional drainage in the Port Phillip and Westernport
our indigenous community.
Region are outlined in the Waterways Operating Charter.
Responsibilities for flood management across the region
The Operating Charter sets out how we will work with
are shared between all levels of government and the
government agencies, community, local councils, rural
community. There are 38 local government areas within
landowners, developers and other stakeholders to deliver
the region.
an integrated and holistic approach to the management
waterways, water quality and flooding. The region is made up of five primary drainage catchments
– Westernport, Dandenong, Yarra, Maribyrnong and
The Operating Charter outlines specific targets for a
Werribee. In addition there are a number of smaller
number of the initiatives contained in this strategy.
catchments such as Elster Creek and Kananook Creek that
The Operating Charter is required by government under drain directly to the bays. Each catchment has extensive
our Statement of Obligations and is independently audited areas of flood affected land.
and reported each year to ensure we meet our obligations
to our stakeholders and the community.
6
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7What is flooding?
Floods occur when flows generated by rainfall overtop the Floodplains dissipate the power of floodwater and reduce
banks of a river, creek or constructed channel, or when associated damage. Floodwaters retain and replenish
the amount of runoff exceeds the capacity of underground wetlands, and support the flora and fauna of floodplains
drainage systems. and river systems.
Floodplains have a fundamental role in managing the The majority of what is classed as problem flooding occurs
flow of water by providing natural storage areas where when urban development and infrastructure (such as
floodwaters can be retained and slowly released as stream roads) have constricted the floodplain or blocked natural
heights recede. drainage lines and flow paths.
Likelihood of flooding
Rainfall events and the floods that result from them are The 100 year ARI, or 1% AEP flood, is the generally
categorised by the frequency at which events of a given accepted event on which guidelines and standards are
size are likely to occur. based to protect new development. However flood
risk assessment and emergency response require
Annual Exceedance Probability (AEP) is the statistical
consideration of a range of lesser and greater events.
likelihood of occurrence of a flood of a given size or larger
in any one year, usually expressed as a percentage. Rainfall events vary in duration and intensity. A storm of
a certain duration and intensity will have different effects
Average Recurrence Interval (ARI) is a statistical
in different areas. As a result, there is no single 1% AEP
estimate of the average period in years between the
storm event for Melbourne, but rather a series of events
occurrences of a flood of a given size or larger. For
represented by the curve as shown in Figure 2.
example, floods with a discharge as large as the 100 year
ARI flood event will occur on average once every 100 This means that a 1% AEP event can occur in a small urban
years. The ARI of an event gives no indication of when a drain following a rain storm that lasts an hour or so but
flood of that size will occur next. has a very high intensity (48 mm of rain). Low intensity
rainfall (less than 5 mm per hour) that lasts for days can
Small events generally occur frequently (e.g. 50% AEP or
generate a 1% AEP event in a major waterway such as the
2 year ARI) and large events quite rarely (1% AEP or 100
Maribyrnong River.
year ARI).
However, as rainfall events are randomly generated, much
like the chances of a number coming up on a roulette
wheel, it is possible to experience several large events in
close succession.
8
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Lollipop Creek, Wyndham Vale and Greens Road,
February 2005
9Types of flooding
in the region
Most flooding in the region is caused by rainfall either in the form
of riverine flooding or overland flows. Other types of possible
flooding are coastal tidal flooding, storm surge and tsunamis.
Riverine flooding Overland flows
Riverine flooding is caused when the runoff from major Overland flows, or flash floods, occur when runoff from
storms exceeds the channel capacity of a river or creek and severe storms exceeds the capacity of the underground
overflows onto the surrounding floodplain. drainage system. When this happens, water begins to flow
downhill over the surface of the land along natural flow
Riverine flooding is relatively predictable in terms of
paths or valleys towards the nearest creek or river.
geography and timing. It can be known many hours or even
days in advance when and where a river or creek is likely to Overland flows usually occur with little or no warning
overflow its banks, so advance warnings and preparations following intense rainfall, often associated with short
can be made accordingly. duration thunderstorm activity. They can be localised
or widespread depending on the path or extent of
Around 20,000 properties across the region are known to
storm activity.
be at risk of being affected by riverine flooding in a 1% AEP
flood, and approximately 3,000 buildings could be flooded Flooding problems occur because the developers of many of
above floor level. Many of these properties are located Melbourne’s older suburbs were unaware of these risks and
within the Maribyrnong Township and the towns of the were not required to make provision for overland flow paths.
Koo Wee Rup Flood Mitigation District, such as Cora Lynn,
Flood mapping in catchments serviced by Melbourne Water
Tooradin and Koo Wee Rup.
drains has identified around 82,000 properties in the region
Flood mapping for all rural waterways, especially those that are at risk of flooding from overland flows in a 1% AEP
in the Werribee and Maribyrnong catchments is not yet flood with approximately 37,000 properties vulnerable to
complete and so the total number of properties at risk of flooding above floor level from overland flows.
flooding in these areas cannot be accurately determined.
However, the total number of properties and public
infrastructure at risk is likely to be greater, since this figure
does not include properties subject to inundation in smaller
local catchments serviced by council drains.
10
Flood Management and Drainage StrategyCoastal tidal flooding and storm surge
Ocean tides can affect normal sea levels and cause flooding
along the coastline and lower reaches of tidal rivers such
as the Maribyrnong and Yarra Rivers, especially when
combined with high rainfall.
However, the tidal effects along an estuary or river diminish
with distance inland.
Storm surge is another mechanism that can affect water
levels along coastal areas.
Storm surge occurs through a combination of low
barometric pressure, strong winds and large waves. It is
uncommon for extreme rainfall events and extreme storm
surges to occur simultaneously.
To date there has been little mapping undertaken to
indicate the extent of areas that would be subject to coastal
tidal flooding or storm surge should such an event occur.
Left to right:
Diamond Creek, Eltham North, February 2005
Corner of Normanby Avenue and Leinster Grove,
Thornbury, December 2003
Kororoit Creek, Altona, February 2005
11History of flooding
Riverine flooding
The original settlement of Melbourne was situated The 1974 flood was the second largest on the Maribyrnong
in a basin intersected by the paths of the Yarra and River, and occurred on 15 and 16 May when 110 mm of rain
Maribyrnong Rivers. Many of the early recorded floods fell on the catchment over a 48 hour period, with 70 mm
occurred when these rivers overflowed their banks and falling in 17 hours.
inundated the surrounding floodplains.
Approximately 385 hectares of land between the
In the Great Flood of 1891, newspapers reported that the Maribyrnong Township and Dynon Road Bridge were
Yarra River rose 14 metres above its normal level in some inundated by floodwaters up to one and a half metres
areas. It flooded the riverside suburbs of Collingwood, deep. About 120 houses and 50 commercial and industrial
Richmond and Prahran, and caused extensive damage. premises were flooded.
Approximately 3,000 people were left homeless.
Emergency services evacuated large numbers of people
In 1934, 350 mm of rain fell in 48 hours over the Yarra from the Maribyrnong Township.
catchment, with 140 mm falling over metropolitan areas.
Installed in July 1975, the Maribyrnong Flood Warning
Flooding was widespread across the region. Six thousand
System continuously monitors catchment conditions,
people were left homeless, and eighteen people died.
rainfall and flows. This system has been improved to
Since the 1891 flood, extensive remedial work has been provide automated telephone warnings to vulnerable
carried out on the lower Yarra River, including widening residents.
and redirecting its course to Port Phillip Bay. As a result,
Widespread riverine flooding that occurred across the Port
the impact of riverine flooding on the community has now
Phillip and Westernport Region in February 2005 caused
been substantially reduced.
little property damage but did cause localised disruption to
Major floods have also inundated the floodplains of transport infrastructure.
the lower Maribyrnong River on numerous occasions.
The Princes Highway was partially blocked at Werribee.
The three largest floods occurred in September 1906,
Traffic was also disrupted in Dandenong, Bulleen and
September 1916 and May 1974.
Diamond Creek.
12
Flood Management and Drainage StrategyOverland flows
Almost every year, even during periods of prolonged
drought, there is a thunderstorm somewhere across the
Port Phillip and Westernport Region that causes localised
flooding as a result of overland flows.
A well-known example of overland flows occurred in
Elizabeth Street on 17 February 1972, when 78.5 mm of
rain fell in one hour over the Central Business District.
This flooding caused significant disruption to the public
and damage to businesses.
In recent years a number of storms have occurred
causing significant damage to private property and public
infrastructure as well as significant disruption and stress to
the community.
On 3 December 2003, 106.5 mm of rain fell in 2.5 hours
over the cities of Darebin, Banyule, Whitehorse and
Manningham. The worst affected areas were Fairfield and
Thornbury.
On 29 January 2004, severe localised storms passed
across the eastern and north eastern suburbs of
Melbourne. In Kew, 66 mm of rain fell in 90 minutes,
Elsternwick recorded 73 mm, Deer Park, 71 mm and
Hawthorn, 70 mm. At Dunns Hill near Mount Dandenong,
31.6 mm fell in 30 minutes.
Localised flooding occurred again on 25 February 2006
when 75.2 mm fell in 30 minutes in Northcote and Coburg.
Punt Road, Yarra River floodplain 1891
13Flood damage
In December 2003 the City of Darebin was hit by
“the worst storm in 100 years”.
While the whole of metropolitan Melbourne was affected, The complex and long lasting effects of flooding on
areas within Darebin were hit hardest with homes, schools individuals, households and communities continue well
and businesses severely damaged by flooding. after the floodwaters have receded.
The following morning residents described the Fairfield Understanding the range of impacts of flooding is essential
shopping strip as a “war zone” – the street was strewn with to the development of effective flood management.
broken glass, debris and spoilt stock.
Flood damage can be broadly classified as tangible and
People were wandering around shocked and in a dazed intangible damage.
state. In the aftermath of the crisis people had to deal with
the stress of financial and emotional loss leading to the
experience of grief for many.
“I went down to Station Street at 8 o’clock in the morning and
many of the traders were just opening their doors in a shocked
state. There was an unreality about it all.”
After the Deluge, City of Darebin (2006)Tangible damage
Tangible damage from flooding can be measured in Examples of indirect damage include:
monetary or other quantifiable terms, i.e. dollar costs, • public clean-up costs
numbers of houses or businesses affected or destroyed.
• disruption to transport services (roads impassable
This includes both direct physical damage to properties obstructing movement and the ability to provide
and assets, and indirect damage arising from disruption of community services)
normal social and economic activities.
• disruption to utilities (water, sewerage,
Data on tangible damage is relatively easy to determine communication)
from insurance claims and replacement costs.
• disruption to public and emergency services
Examples of direct damage include:
• economic impacts of health issues (medical costs and
• damage to building and contents disruption to work activities)
• external damage (pools, gardens, fences, shed • loss of business or trade as people shop elsewhere.
contents)
Losses attributed to emergencies are generally described
• motor vehicles in monetary terms.
• infrastructure (roads, bridges and other services)
• clean-up costs for individual home owners
• loss of stock
• cost of re-instatement or rebuilding of houses and
buildings.
From left: Darebin Creek, Alphington, February 2005
Darebin Creek foot bridge, February 2005
15“I’ve never seen anything like it. Flash, flash, flash! When it rains
now I think, ‘How heavy is it? Will it flood?’ I always go out and
check the gutter.”
“After the floods there was a lot of anger. There was also an ugly
side to things like stories going around about people getting
flood relief money while others missed out who really needed
help. People are still hurting.”
After the Deluge, City of Darebin (2006)
Intangible damage
Much of the impact of flooding can be described as
‘intangible’ – effects which cannot be evaluated in
monetary terms.
Intangible impacts include loss of life, perceived loss of
security of the home, fear of continuing severe flood
events, loss of memorabilia, and physical and psychological
effects on human health and well being.
Psychological impacts resulting from the experience of
severe flooding are generally worse than the physical
health impacts, and can persist well after the event.
Intangible impacts are difficult to assess or quantify as a
number of factors can affect an individual’s vulnerability or
ability to cope and recover from a severe flood event.
Other factors that affect an individual’s experience of
flooding include current levels of health, networks of
support and degree of financial security.
An understanding and assessment of the full range and
variability of intangible or social impacts is important for
complete assessment of risks necessary to determine
priorities for future flood management.
Understanding intangible impacts is also important for
ongoing development of emergency management and
recovery programs, including education and awareness
programs.
16
Flood Management and Drainage StrategyFlood damage, Maintree Road,
Hawthorn, December 2003
17Estimating the damage
Large floods can cause damage that runs into the To understand the likely cost of flooding in any given year,
hundreds of millions of dollars. However, they occur rarely. the total damage caused by all floods over a period of time
Smaller floods that occur more frequently don’t cause as is divided by the number of years in that period.
much damage individually, but collectively the damage is
These likely losses are called Annual Average Damage
significant.
(AAD).
To better understand the risks of damage to areas
identified as subject to flooding, the likelihood and
consequences of flooding need to be considered.
By standardising or averaging damage, unit losses can be
assigned to enable an estimation of damage.
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8Economists use tools like the loss-probability curves shown By comparison, AAD associated with bushfires in the same
in Figure 3 to provide an estimation of the likely damage period was relatively smaller at $77.2 million. However,
in any given year. bushfires are the most hazardous type of disaster in terms
of deaths and injuries.1
Flood damage increases significantly once flooding occurs
above floor level, causing damage to household contents To understand the context of these figures, only the $30
such as floor coverings, curtains, furniture, plaster, million AAD figure for waterways flooding in the Port
particleboard and painted surfaces. Phillip and Westernport Region is comparable to the
national AAD for riverine flooding of $314 million.
Annual Average Damage (AAD) figures for the Port Phillip
and Westernport Region are shown in Figure 4. This is because in other major urban centres, or capital
cities little if any overland flow path mapping and analysis
This estimate takes into account all potential direct and
has been undertaken.
indirect tangible damage – that is, the level of damage
that would occur if no remedial action of any kind were In the Port Phillip and Westernport Region, the AAD
undertaken to reduce exposure to damage. It does not caused by overland flows identified by Melbourne Water
include the intangible impacts of flooding. is approximately three times greater than the riverine
flooding risk.
In Australia between 1967 and 1999, riverine flooding ($314
million AAD) and severe storms ($284.2 million AAD) were If the estimated local overland flow impacts are considered,
the most costly types of natural disaster. the impacts of these shorter duration events could be as
much as seven times greater than the annual damage
caused by riverine flooding.
1Report 103 Economic Costs of Natural Disasters in Australia,
Bureau of Transport and Regional Economics (2001)
D\cYflie\NXk\i
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NXk\inXpjManaging floods
Commonwealth, State, regional and local authorities, as Response: Activities undertaken to combat emergencies
well as local communities and individuals all have a vital and provide rescue and immediate relief services.
role to play in flood management.
Recovery: Activities aimed at providing assistance to
The scope of flood management is described within the people and communities affected by emergencies to
context of three overlapping activity clusters: prevention, enable them to achieve a proper and effective level of
response and recovery.2 functioning.
Prevention: Activities aimed at eliminating or reducing Activities required to manage a flood event, and the
the incidence or severity of emergencies and the relationships between them, are outlined in Figure 5 below.
mitigation of effects.
2 Victoria Flood Management Strategy, State Flood Policy Committee (1998)
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February 2005
21Shared responsibilities for
flood management
Australian Government Victorian State Government
The Australian Government has a supportive role in State governments are recognised as the key level
relation to flood management. of government responsible for natural resource and
emergency management.
Its primary role is in:
The main responsibilities of the Victorian Government in
• providing flood forecasting and warning
relation to flood management are to:
• supporting development of state emergency
• develop standards and strategic approaches for
management capabilities
floodplain management
• providing natural disaster financial support to state,
• apply standards and strategies in a co-ordinated and
local governments and agencies (e.g. Natural Disaster
integrated manner
Mitigation Program and Natural Disaster Relief and
Recovery Arrangements) • provide technical support, planning advice, impact
and needs assessments to aid emergency response
• providing policy and legislation in relation to the
and recovery planning and co-ordination of post
availability of insurance
emergency recovery support services
• supporting the development and implementation of
• develop the Victoria Planning Provisions
national strategies.
• develop the Victoria Building Regulations.
Agencies include the Bureau of Meteorology, the
Department of Transport and Regional Services, Groups include the Department of Sustainability and
Emergency Management Australia and Geoscience Environment, the Department of Human Services, Office
Australia. of the Emergency Services Commissioner, the Building
Control Commission, the Victoria Emergency Management
Council, the State Flood Policy Committee, and the
Victorian Flood Warning Consultative Committee.
22
Flood Management and Drainage StrategyEmergency Services Regional authorities
The State’s emergency services have a responsibility to Catchment Management Authorities and Melbourne
assist the community during natural disasters and to: Water are designated floodplain management authorities.
Primary flood management functions include:
• support local agencies in emergency planning
• undertaking flood studies and flood mapping
• participate in emergency response and recovery
planning, co-ordination and management • identifying flood affected land
• develop and maintain community preparedness • undertaking flood prevention works such as retarding
through awareness and education programs basins, levees and pipe augmentation
(household, industrial and commercial safety plans,
• assisting the Bureau of Meteorology with flood
council community awareness programs, signage,
forecasting and warning
building materials advice)
• advising planning authorities regarding appropriate
• develop and maintain total flood warning systems
land use and development of flood affected areas
• undertake impacts and needs assessments. through their role as planning permit referral
authorities
Agencies include the Victoria Police and the Victoria State
Emergency Service. • supporting community education and awareness
programs.
Throughout most of Victoria, Catchment Management
Authorities are responsible for the preparation of
catchment management strategies and floodplain
management plans.
Within this region, the Port Phillip and Westernport
Catchment Management Authority is responsible for the
development and monitoring of the Regional Catchment
Management Strategy but the Minister responsible for
the Water Act 1989 has delegated floodplain management
functions to Melbourne Water.
Melbourne Water is also responsible for:
• planning regional drainage systems to ensure new
urban development meets appropriate standards of
flood protection and environmental performance
• the ownership and maintenance of drainage assets
where the catchment area is greater than 60 hectares
• assessment of planning permit application referrals to
subdivide land or develop flood affected land.
23Local government
Local government is primarily responsible for the planning In relation to flood management, local councils are
and provision of services and facilities for the local expected to:
community, and for providing and maintaining community
• administer and enforce planning provisions and
infrastructure.
building regulations in relation to building and
Although local government is not a delegated floodplain development on flood affected land
management authority under the provisions of the Water
• provide for the conservation of natural resources and
Act 1989, it does have a critical role to play in flood
areas of environmental significance
management through its role as a planning authority and
emergency management agency. • develop flood sub-plans as part of their municipal
emergency management plans and participate in risk
There are 38 councils in the Port Phillip and Westernport
reduction activities
Region that manage an estimated 25,000 kilometres
of local underground drains and other drainage • provide the public with access to flood information
infrastructure. • implement and maintain local flood warning systems
• provide and manage local drainage infrastructure for
catchment areas less than 60 hectares
• support community education and awareness
• manage local level emergency recovery support,
clean-up and maintenance.
24
Flood Management and Drainage StrategyLocal communities and individuals
Managing flood risks is a shared responsibility between
individuals and communities, government and
non-government agencies, and the private sector.
An informed and prepared community that understands
the flood risk for its area and is familiar with local
emergency management programs is well placed to
protect itself from the impacts of emergencies.
Supported by agencies at all levels, the community is
responsible for:
• knowing the level and extent of flood risk for its area
• participating in risk assessment and risk reduction
prioritisation processes
• participating in reducing personal and community
vulnerability
Flood damage, Glenferrie Road, Hawthorn, December 2003
• managing its recovery from flood events
• preparing personal emergency flood plan.
25Flood management
objectives
Flood managers face a series of challenges. • Emergency Planning and Preparation. Mapping
identifies the areas at risk so that agencies can
They must:
implement flood warnings, plan flood evacuation,
• identify and understand current and future flood risks relief and recovery strategies, prioritise community
and the impacts they have on people and property information and awareness programs and develop
• develop criteria to agree what is intolerable flood risk warning arrangements.
• develop and implement a program to eliminate or • Mitigation priorities. Mapping identifies safety risks
reduce intolerable risks and damage potential, and assists in the development
of risk reduction targets, delivery programs and works
• manage residual risks through improved community priorities.
awareness, planning and preparedness.
In addition to knowing where floods may occur, an
understanding of flood depth, velocity, duration and rate
Objective 1: Completing the of rise is also required to fully understand flood risk.
knowledge base Such information is usually collated in the development of
flood studies that map flood extent.
Flood mapping to identify risks
Challenges
Melbourne Water’s floodplain management functions,
outlined in the Water Act 1989, include finding out how Flood modelling and mapping is an expensive and
far floodwaters are likely to extend and how high they are specialised activity. Additional flood mapping needs to
likely to rise. be in a format and to a standard that is consistent with
existing data held by Melbourne Water and suitable for
Mapping throughout the region is currently incomplete
the assessment of flood mitigation options and land use
and some information has not been included in planning
planning decisions.
schemes or made easily accessible to the public.
In addition, issues associated with the collection and
In particular, mapping is not complete for many rural
public release of such information, particularly through
waterways for flooding where the catchment area is less
the planning scheme amendment process, need to be
than 60 hectares, or for areas that may be subject to
carefully managed.
coastal or tidal inundation.
Not all agencies are appropriately resourced to
The identification and accurate mapping of flood risk
commission flood studies or to maintain and administer
areas is considered to be a critical foundation for the
flood information under current planning scheme
development of sound drainage and flood management
arrangements. Additional support and assistance to
activities.
complete these tasks may be required.
A detailed understanding of flood affected areas gained
Agencies have also expressed concerns regarding
through mapping is important to the development of the
potential liability issues and other obligations associated
following aspects of flood management planning and
with the collection of flooding information through
response:
mapping exercises.
• Land use Planning Policy and Controls. These
However, failing to identify these areas will not make the
controls protect the environmental values of
risk of flooding any less real, and can potentially increase
floodplains and prevent current flood risks increasing
the likely damage resulting from an event particularly if
through inappropriate development. They also ensure
further development is allowed to occur without taking
that proposals that may be affected by flooding or
flood risks into account.
have an adverse impact on existing flood regimes are
referred to floodplain management agencies. There are a variety of ways in which mapping studies and
planning scheme amendments could be undertaken.
26
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Figure 6. Mapping overland flows and urban systems
27Actions Challenges
1.1 Melbourne Water will undertake and maintain ongoing Floods affect people in different ways depending upon
local flood extent, rural waterway and tidal mapping their health, well being, economic status and other
for the Port Phillip and Westernport Region, taking personal circumstances i.e. their vulnerability or resilience
into account the potential long term pressures of to flooding.
climate change and urban consolidation. This will
Determining the impact of an emergency on a community
involve consultation with local government and the
is a complex task. There is currently no agreed process
Department of Sustainability and Environment.
or tool for assessing flood damage and intangible social
1.2 Melbourne Water will update and maintain flood impacts of flooding that can be used to determine risk
information for municipal planning schemes to ensure acceptability/tolerability thresholds.
appropriate standards of flood protection are achieved
Ongoing strategic research and further development of
for new development in flood affected areas. This will
our understanding of the social impacts of flooding is an
involve consultation with local government and the
issue that affects flood management agencies at all levels.
Department of Planning and Community Development.
There is currently no lead agency in Victoria with a clear
responsibility for the development and implementation of
Understanding social impacts
a research program into the social impacts of flooding.
Studies in emergency response and recovery management
Actions
have emphasised the importance of extending
investigations into the impact of natural disasters to 1.3 Melbourne Water will support collaborative, research
include psycho-social effects on individuals and the wider into the social and economic impacts of flooding on
community. the community and use this information to assess
flood management priorities.
Understanding the relative vulnerability of different
communities affected by flooding can also assist in the
benefit cost analysis of flood mitigation works. It can also
assist in the planning and development of education and
awareness, flood warning and response and recovery
programs.
There is currently little evidence-based information
available which captures the range of physical, mental
health and associated impacts of flooding on communities
in Victoria.
Flood management programs which do not seek and utilise
such knowledge could fail to meet community needs,
lead to inappropriate targeting of resources, and increase
community anxiety of an already traumatic event.
28
Flood Management and Drainage StrategyUrban consolidation, Parkville
29It is projected that between 2006 and 2031, the population of
Melbourne will increase by approximately 860,000 and adding
over 510,000 new households to the metropolitan area.
Objective 2: Potential long term Increased numbers of dwellings in an area may result in
increased hard surface coverage depending on the design
future pressures on existing drainage of the development and existing conditions.
systems If this occurs, an increase in runoff volumes and an
increase in peak flows can be expected. Unless managed,
Development in established areas
this increased runoff could result in a reduction in drainage
It is projected that between 2006 and 2031, the population infrastructure performance in some areas.
of Melbourne will increase by approximately 860,000 and
To a lesser degree, the replacement of older and smaller
adding over 510,000 new households to the metropolitan
structures by large new dwellings will also have an effect
area.
even when no increase in dwelling numbers occurs.
Even if the population did not increase, the reducing
Investigations into the impacts of development in
average size of households means that more dwellings will
established areas suggest that most of the metropolitan
be necessary in the future to house the same number of
area is able to cope with the forecast increase in dwellings
people.
and that any adverse impacts will be limited to a few
The government’s metropolitan strategy, Melbourne catchments.
2030 – Planning for sustainable growth (Department
In these catchments, there will be a range of outcomes that
of Infrastructure 2002), aims to make the city more
call for different forms of action. Increased runoff impacts
sustainable while managing the increase in population and
can be managed where new development is well planned
households.
for, such as in activity centres, major re-development sites
One important way to help achieve this is to make the and around transport nodes.
urban area more compact.
The government is currently working with local councils
Melbourne 2030 encourages a greater proportion of to develop strategy plans for principal and major activity
new development to be built in and around strategic centres that will address, amongst other matters,
redevelopment sites (such as principal and major activity drainage issues.
centres) that are supported by existing infrastructure,
Such planned growth enables authorities to better develop
particularly public transport, and are best able to cope with
strategies for infrastructure provision rather than ad hoc
change.
or uncoordinated redevelopment across the catchment.
The share of new dwellings in ‘greenfield’ and dispersed
The impacts of increased runoff resulting from such
development areas will be reduced accordingly.
dispersed infill developments are more difficult to manage
If the Melbourne 2030 housing distribution aspirations because it is not easy to quantify or plan for the extent,
are achieved, it would mean that 41% of new households timing and location of this form of development.
will be located in strategic redevelopment sites and 28%
The potential for infill development is influenced in some
in the remainder of the existing urban areas through infill
locations by factors such as heritage, neighbourhood
redevelopment.
character or environmental significance.
This will generally cause the overall density of dwellings
Similarly, such development in some catchments also
to increase although most existing residential areas will
needs to be sensitive to the capacity of the drainage
experience very little change.
system to accommodate additional runoff, or the ability of
drainage authorities to undertake augmentation works.
30
Flood Management and Drainage StrategyDandenong Creek, Dandenong North,
February 2005
In some catchments, it may be necessary to undertake Challenges
works to accommodate additional runoff to acceptable
It is difficult to plan and fund infrastructure to cater for the
levels.
impacts of dispersed infill development as the exact timing
In a very limited number of cases, there are parts of and location of such development is not always known.
catchments where works are not possible, practical or
There are some areas where it is not possible, practical or
affordable.
affordable to undertake works to accommodate additional
In these areas, where infrastructure cannot be upgraded, runoff and a variety of flood management measures will be
a more flexible range of activities may be appropriate, required to manage flood risk.
such as:
Action
• education and awareness programs
2.1 Melbourne Water will work with the Department of
• flood warning systems Planning and Community Development and local
government to understand the likely impact of urban
• revision of planning policies and controls (to limit
development on runoff volumes and flood risk in
the capacity for additional development or to control
existing urban areas.
impervious surface area)
2.2 Melbourne Water will develop flood risk management
• water sensitive urban design
measures in consultation with Department of Planning
• stormwater capture and reuse. and Community Development, Department of
Improved co-ordination between agencies responsible for Sustainability and Environment and local government.
statutory and strategic planning and policy development, Solutions may include upgrading infrastructure
and assessment of infrastructure capacity, will be required planning and building controls to limit imperviousness,
to ensure a closer match between land use intentions in and onsite measures such as water sensitive urban
the infill areas and infrastructure delivery. design and stormwater capture and reuse.
Melbourne Water is preparing strategies for individual
urban catchments where significant redevelopment is
occurring. These strategies identify the potential impact of
redevelopment on runoff levels.
Where levels of drainage service may be affected, the
strategy will identify the additional infrastructure, the costs
associated with these works, and appropriate charges to
be levied on developers to fund those works.
While this approach ensures developers fund works to
maintain existing levels of drainage service, it does not
seek to resolve existing problems.
However, the introduction of these strategies may provide
opportunities to undertake flood mitigation works at the
same time.
31Climate change In areas where side entry pits can cope with the volume of
water, the pipes fill quickly, again leading to overland flows.
The Intergovernmental Panel on Climate Change’s Fourth
Assessment Report 2007 concluded that warming of the CSIRO has suggested a preliminary estimate of a 5%
earth’s climate is unequivocal. increase in rainfall intensity per degree of climate
warming.
The management of the impacts of climate change
resulting from global warming is a worldwide challenge. A Melbourne Water sensitivity analysis of increasing
rainfall intensity by 5% per degree of temperature
However predicting the potential rate and extent of
increase, suggests a similar increase in runoff volumes of
climate change in Australia and the Port Phillip and
4% by 2020 to 25% by 2100.
Westernport Region in particular, is a challenge as our
climate is highly variable and there are limited historical Under these circumstances, what we currently consider
climatic records to compare with the present. to be a 1% AEP event will occur more frequently as shown
opposite in Figure 7.
Based on the available climate change predictions,
the interpreted trend for Melbourne is for increasing This could also mean more frequent flooding above existing
temperature, reduced annual rainfall and more extreme floor levels.
events.3
These more frequent events are also likely to stretch the
Melbourne Water funded the CSIRO to study the impacts tolerance of the affected community and affect in-stream
of climate change on water supply, sewerage and drainage values of urban waterways.
functions. The study showed that while the amount of
More frequent and larger flows have the potential to erode
overall rainfall received each year is predicted to decrease,
waterways and reduce the ability of flora and fauna living
the rainfall may occur in more intense storm events rather
within the waterways to endure the habitat disturbance
than our normal winter and spring rains.
associated with such floods.
This change in rainfall patterns is more likely to result in
Another predicted impact of global warming is a rise
an increase in overland flows rather than riverine flooding
in sea levels resulting from a number of factors such
because the short, sharp nature of these intense storms
as thermal expansion of the sea mass and melting ice
results in sudden large volumes of runoff water.
shelves.
Side entry pits struggle to cope with these volumes of water,
While the Port Phillip and Westernport region does not
and overland flows result.
experience significant coastal tidal flooding and storm
3Melbourne Water Climate Change Study Implications of Potential Climate surge, there is a possibility that a change in sea level may
Change for Melbourne’s Water Resources (2005), CSIRO increase these risks.
32
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Challenges We need to undertake sensitivity analysis of the impacts
of different rainfall intensities on various sized catchments
Knowledge regarding climate change is constantly
to determine which areas will be most sensitive to the
changing. Ongoing strategic research and understanding
possible impacts of climate change.
the impacts of climate change on drainage systems is a
State and national issue that affects flood management Understanding these effects will assist in the development
agencies at all levels. of appropriate adaptation strategies.
The implications of changed weather patterns on the Action
intensity and duration of storms in the region are not well
2.3 Melbourne Water will continue to support research
understood.
programs to better understand the impacts of climate
We need to continue working with other key stakeholders change on flood and drainage management.
such as the Bureau of Meteorology, CSIRO, Department
2.4 Melbourne Water will develop adaptable flood
of Sustainability and Environment, State Flood Policy
management programs to deal with changing rainfall
Committee, and the Westernport Greenhouse Alliance to
patterns, rising sea levels, and storm surge. These
develop greater understanding of the likely timing and
programs will be developed in consultation with the
impacts of climate change, and the areas that will be most
Commonwealth Scientific and Industrial Research
sensitive to the impacts of climate change.
Organisation, (CSIRO) and the Bureau of Meteorology.You can also read
