Flood Management and Drainage Strategy

Transcription

1 Port Phillip and Westernport Region Flood Management and Drainage Strategy i

2 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)

3 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

4 Lollipop Creek, Werribee, February 2005 iv Flood Management and Drainage Strategy

5 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

6 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 flood management and drainage challenges that require a coordinated and collaborative approach by flood managers and the community. There are currently more than 100,000 properties in the region that are known to be at risk from flooding of which 82,000 properties are at risk of flooding from overland flows. More than 40,000 of these properties contain buildings or dwellings that are at risk of flooding above floor level. On average, the annual damage caused by flooding in the region has been estimated to be $245 million. The Flood Management and Drainage Strategy has been prepared following discussions between government departments, councils, emergency service organisations, and other agencies about how we can improve the management of flood risk in the Port Phillip and Westernport Region. It complements other Melbourne Water programs that deal with river health, water quality, floodplain environmental values, urban growth, stakeholder communications and cultural heritage. Melbourne Water and councils have traditionally used engineering solutions to improve flood protection in identified high risk areas. Millions of dollars, funded primarily by council and Melbourne Water drainage rates, are currently spent each year on efforts to manage ongoing risks from overland flows and riverine flooding. While these efforts are effective at a local level they are having little impact on the overall problem. This is because it is not physically feasible to construct required works to protect all properties in the region from large events. Aside from the likely multi-billion dollar cost and extreme disruption, the time frame to build such expensive infrastructure would exceed the lifespan of the properties they attempt to protect. This strategy recognises that although it is not possible to make the region completely free from flooding, there are some flooding risks that we may decide are intolerable and almost regardless of the cost, the consequence of flood should be reduced or eliminated. Consultation and research will be undertaken to reach agreement on what constitutes intolerable flood risk. Our long term aim is to minimise all currently known intolerable flooding risks to public health and safety, property and infrastructure, and increase community understanding and preparedness for floods. This strategy proposes the development and implementation of an accelerated program, in consultation with stakeholders, to identify and deal with intolerable flood risk across the region as quickly as possible. As part of this strategy, Melbourne Water will continue to map flood affected areas and will sponsor research into the intangible social and human health impacts of floods, to develop an improved flood risk assessment tool that takes these costs into account when determining flood risk priorities and responses. Throughout this strategy there is broad recognition that no single organisation and no single approach can deliver an effective response to flood management issues. While Melbourne Water and councils will continue to deploy engineering solutions to mitigate flood risks, it is recognised that this approach must be accompanied by a range of non-structural responses. 2 Flood Management and Drainage Strategy

7 Richmond, July 1891 There are other tools that are equally effective and significantly less expensive, such as planning controls and public awareness programs that can be deployed immediately to assist in treating the residual and future flood risks. These tools will be developed in partnership with other flood managers. In particular, the strategy recognises the importance and benefits of improved education in assisting the community to prepare, respond and recover from floods. Part of this focus on existing flood risks will also involve working with councils to develop detailed local flood management plans, and working with the State Flood Policy Committee, Office of the Emergency Services Commissioner and other stakeholders to develop an integrated flood management planning framework. These plans will outline roles and responsibilities, set priorities, aims and goals, and establish work programs and targets to address flood management objectives identified in the strategy. The strategy defines five flood management objectives and outlines actions that will be undertaken to achieve each objective and guide priorities and expenditure by Melbourne Water. Objective 1: Completing the knowledge base Flood mapping Actions 1.1 Melbourne Water will undertake and maintain ongoing local flood extent, rural waterway and tidal mapping for the Port Phillip and Westernport region, taking into account the potential long term pressures of climate change and urban consolidation. This will involve consultation with local government and the Department of Sustainability and Environment. 1.2 Melbourne Water will update and maintain flood information for municipal planning schemes to ensure appropriate standards of flood protection for new development in flood affected areas. This will involve consultation with local government and the Department of Planning and Community Development. Understanding social impacts Actions 1.3 Melbourne Water will support collaborative research into the social and economic impacts of flooding on the community. 3

8 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 pressures on existing drainage systems Development in established areas Actions 2.1 Melbourne Water will work with Department of Planning and Community Development and local government to understand the likely impact of urban consolidation on runoff volumes and flood risk in existing urban areas. 2.2 Melbourne Water will develop flood risk management measures in consultation with Department of Planning and Community Development, Department of Sustainability and Environment and local government. Solutions may include upgrading infrastructure, planning and building controls to limit imperviousness, and onsite measures such as water sensitive urban design and stormwater capture and reuse. Climate change 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

9 Objective 3: An agreed approach to managing existing regional flooding problems Actions 3.1 Melbourne Water will sponsor research and consult with stakeholders to develop criteria to establish flood risk tolerability thresholds which take into account relevant social or intangible flood impacts. 3.2 Melbourne Water will develop and implement a program in consultation with stakeholders to eliminate or reduce intolerable risks to an acceptable standard through the combination of engineering works and non-structural measures. Objective 4: Enhanced community education, flood awareness and preparation Actions 4.1 A community flood education, awareness and preparedness program, including flood warning, will be developed and implemented for the Port Phillip and Westernport region in partnership with Victoria State Emergency Service, and other key stakeholders. Objective 5: Agreed responsibilities 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

10 Background Melbourne Water Melbourne Water is the waterway manager for the Port Phillip and Westernport Region and as such is custodian of the health of 8,000 kilometres of rivers and creeks that drain into Port Phillip Bay and Western Port. Melbourne Water is also the regional drainage and floodplain management authority for the region and is responsible for the management and maintenance of numerous retarding basins, water quality treatment wetlands, levee banks, pump stations, flood gates and 1,500 kilometres of underground drains. Melbourne Water s area of responsibility matches the Port Phillip and Westernport Catchment Management Authority s (CMA) operating area to ensure a whole of catchment approach to the management of flooding, regional drainage and river health. The CMA plays an overarching strategic management role in the development, co-ordination and delivery of the Port Phillip and Western Port Regional Catchment Strategy Melbourne Water s responsibilities, overall goals and long term aims for the management of waterways, floodplains and regional drainage in the Port Phillip and Westernport Region are outlined in the Waterways Operating Charter. The Operating Charter sets out how we will work with government agencies, community, local councils, rural landowners, developers and other stakeholders to deliver an integrated and holistic approach to the management waterways, water quality and flooding. The Operating Charter outlines specific targets for a number of the initiatives contained in this strategy. The Operating Charter is required by government under our Statement of Obligations and is independently audited and reported each year to ensure we meet our obligations to our stakeholders and the community. The Port Phillip and Westernport Region The Port Phillip and Westernport Region covers an area of approximately 13,000 square kilometres and includes nearly all the land that drains to Port Phillip Bay and Western Port. It extends from high up in the Yarra Ranges in the east, across to Ballan in the west, and from the Mornington Peninsula and Phillip Island in the south, to Lancefield and Kinglake in the north. It includes the greater Melbourne metropolitan area and is home to 3.8 million people. Prior to European settlement, the region s rivers, creeks and their floodplains formed a vital part of the Aboriginal culture. They yielded many resources and were important places of spiritual and community activity, including birthplaces, burial sites, places of ceremony and transport routes. A range of European and Aboriginal heritage values exist in the regions waterways and floodplains. Melbourne Water acknowledges the traditional owners of the land, rivers and creeks we manage, and pay our respects to their elders and ancestors. We recognise our responsibilities to care for rivers and creeks in greater Melbourne, mindful of the significance they represent for our indigenous community. Responsibilities for flood management across the region are shared between all levels of government and the community. There are 38 local government areas within the region. The region is made up of five primary drainage catchments Westernport, Dandenong, Yarra, Maribyrnong and Werribee. In addition there are a number of smaller catchments such as Elster Creek and Kananook Creek that drain directly to the bays. Each catchment has extensive areas of flood affected land. 6 Flood Management and Drainage Strategy

11 Port Phillip Bay Figure 1. Port Phillip Bay and Westernport region 7

12 What is flooding? Floods occur when flows generated by rainfall overtop the banks of a river, creek or constructed channel, or when the amount of runoff exceeds the capacity of underground drainage systems. Floodplains have a fundamental role in managing the flow of water by providing natural storage areas where floodwaters can be retained and slowly released as stream heights recede. Floodplains dissipate the power of floodwater and reduce associated damage. Floodwaters retain and replenish wetlands, and support the flora and fauna of floodplains and river systems. The majority of what is classed as problem flooding occurs when urban development and infrastructure (such as roads) have constricted the floodplain or blocked natural drainage lines and flow paths. Likelihood of flooding Rainfall events and the floods that result from them are categorised by the frequency at which events of a given size are likely to occur. Annual Exceedance Probability (AEP) is the statistical likelihood of occurrence of a flood of a given size or larger in any one year, usually expressed as a percentage. Average Recurrence Interval (ARI) is a statistical estimate of the average period in years between the occurrences of a flood of a given size or larger. For example, floods with a discharge as large as the 100 year ARI flood event will occur on average once every 100 years. The ARI of an event gives no indication of when a flood of that size will occur next. Small events generally occur frequently (e.g. 50% AEP or 2 year ARI) and large events quite rarely (1% AEP or 100 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. The 100 year ARI, or 1% AEP flood, is the generally accepted event on which guidelines and standards are based to protect new development. However flood risk assessment and emergency response require consideration of a range of lesser and greater events. Rainfall events vary in duration and intensity. A storm of a certain duration and intensity will have different effects in different areas. As a result, there is no single 1% AEP storm event for Melbourne, but rather a series of events represented by the curve as shown in Figure 2. This means that a 1% AEP event can occur in a small urban drain following a rain storm that lasts an hour or so but has a very high intensity (48 mm of rain). Low intensity rainfall (less than 5 mm per hour) that lasts for days can generate a 1% AEP event in a major waterway such as the Maribyrnong River. 8 Flood Management and Drainage Strategy

13 The yellow line represents a series of rainfall events (known as an Intensity Frequency Duration Curve) that are the hundred year storms for a range of catchment sizes Year Frequency Figure 2. Hundred year storms Lollipop Creek, Wyndham Vale and Greens Road, February

14 Types 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 Riverine flooding is caused when the runoff from major storms exceeds the channel capacity of a river or creek and overflows onto the surrounding floodplain. Riverine flooding is relatively predictable in terms of geography and timing. It can be known many hours or even days in advance when and where a river or creek is likely to overflow its banks, so advance warnings and preparations can be made accordingly. Around 20,000 properties across the region are known to be at risk of being affected by riverine flooding in a 1% AEP flood, and approximately 3,000 buildings could be flooded above floor level. Many of these properties are located within the Maribyrnong Township and the towns of the Koo Wee Rup Flood Mitigation District, such as Cora Lynn, Tooradin and Koo Wee Rup. Flood mapping for all rural waterways, especially those in the Werribee and Maribyrnong catchments is not yet complete and so the total number of properties at risk of flooding in these areas cannot be accurately determined. Overland flows Overland flows, or flash floods, occur when runoff from severe storms exceeds the capacity of the underground drainage system. When this happens, water begins to flow downhill over the surface of the land along natural flow paths or valleys towards the nearest creek or river. Overland flows usually occur with little or no warning following intense rainfall, often associated with short duration thunderstorm activity. They can be localised or widespread depending on the path or extent of storm activity. Flooding problems occur because the developers of many of Melbourne s older suburbs were unaware of these risks and were not required to make provision for overland flow paths. Flood mapping in catchments serviced by Melbourne Water drains has identified around 82,000 properties in the region that are at risk of flooding from overland flows in a 1% AEP flood with approximately 37,000 properties vulnerable to flooding above floor level from overland flows. 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 Strategy

15 Coastal 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

16 History of flooding Riverine flooding The original settlement of Melbourne was situated in a basin intersected by the paths of the Yarra and Maribyrnong Rivers. Many of the early recorded floods occurred when these rivers overflowed their banks and inundated the surrounding floodplains. In the Great Flood of 1891, newspapers reported that the Yarra River rose 14 metres above its normal level in some areas. It flooded the riverside suburbs of Collingwood, Richmond and Prahran, and caused extensive damage. Approximately 3,000 people were left homeless. In 1934, 350 mm of rain fell in 48 hours over the Yarra catchment, with 140 mm falling over metropolitan areas. Flooding was widespread across the region. Six thousand people were left homeless, and eighteen people died. Since the 1891 flood, extensive remedial work has been carried out on the lower Yarra River, including widening and redirecting its course to Port Phillip Bay. As a result, the impact of riverine flooding on the community has now been substantially reduced. Major floods have also inundated the floodplains of the lower Maribyrnong River on numerous occasions. The three largest floods occurred in September 1906, September 1916 and May The 1974 flood was the second largest on the Maribyrnong River, and occurred on 15 and 16 May when 110 mm of rain fell on the catchment over a 48 hour period, with 70 mm falling in 17 hours. Approximately 385 hectares of land between the Maribyrnong Township and Dynon Road Bridge were inundated by floodwaters up to one and a half metres deep. About 120 houses and 50 commercial and industrial premises were flooded. Emergency services evacuated large numbers of people from the Maribyrnong Township. Installed in July 1975, the Maribyrnong Flood Warning System continuously monitors catchment conditions, rainfall and flows. This system has been improved to provide automated telephone warnings to vulnerable residents. Widespread riverine flooding that occurred across the Port Phillip and Westernport Region in February 2005 caused little property damage but did cause localised disruption to transport infrastructure. The Princes Highway was partially blocked at Werribee. Traffic was also disrupted in Dandenong, Bulleen and Diamond Creek. 12 Flood Management and Drainage Strategy

17 Overland 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, 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

18 Flood 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, areas within Darebin were hit hardest with homes, schools and businesses severely damaged by flooding. The following morning residents described the Fairfield shopping strip as a war zone the street was strewn with broken glass, debris and spoilt stock. People were wandering around shocked and in a dazed 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. The complex and long lasting effects of flooding on individuals, households and communities continue well after the floodwaters have receded. Understanding the range of impacts of flooding is essential to the development of effective flood management. Flood damage can be broadly classified as tangible and intangible damage. 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)

19 Tangible damage Tangible damage from flooding can be measured in monetary or other quantifiable terms, i.e. dollar costs, numbers of houses or businesses affected or destroyed. This includes both direct physical damage to properties and assets, and indirect damage arising from disruption of normal social and economic activities. Data on tangible damage is relatively easy to determine from insurance claims and replacement costs. Examples of direct damage include: damage to building and contents external damage (pools, gardens, fences, shed contents) motor vehicles 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. Examples of indirect damage include: public clean-up costs disruption to transport services (roads impassable obstructing movement and the ability to provide community services) disruption to utilities (water, sewerage, communication) disruption to public and emergency services economic impacts of health issues (medical costs and disruption to work activities) loss of business or trade as people shop elsewhere. Losses attributed to emergencies are generally described in monetary terms. From left: Darebin Creek, Alphington, February 2005 Darebin Creek foot bridge, February

20 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. 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. After the Deluge, City of Darebin (2006) 16 Flood Management and Drainage Strategy

21 Flood damage, Maintree Road, Hawthorn, December

22 Estimating the damage Large floods can cause damage that runs into the hundreds of millions of dollars. However, they occur rarely. Smaller floods that occur more frequently don t cause as much damage individually, but collectively the damage is significant. To understand the likely cost of flooding in any given year, the total damage caused by all floods over a period of time is divided by the number of years in that period. These likely losses are called Annual Average Damage (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. Rare flood (200 year ARI) 100 year ARI 30 year ARI (1.0m overfloor) 20 year ARI (0.5m overfloor) AAD: Average Annual Damages ARI: Average Recurrence Interval AEP: Annual Exceedence Probability Area under curve represents AAD 10 year ARI (maximum underfloor damages) 5 year ARI (damages begin) Figure 3. Flood damage curve Floods are the most costly natural disaster in Australia 18 Flood Management and Drainage Strategy

23 Economists use tools like the loss-probability curves shown in Figure 3 to provide an estimation of the likely damage in any given year. Flood damage increases significantly once flooding occurs above floor level, causing damage to household contents such as floor coverings, curtains, furniture, plaster, particleboard and painted surfaces. Annual Average Damage (AAD) figures for the Port Phillip and Westernport Region are shown in Figure 4. This estimate takes into account all potential direct and indirect tangible damage that is, the level of damage that would occur if no remedial action of any kind were undertaken to reduce exposure to damage. It does not include the intangible impacts of flooding. In Australia between 1967 and 1999, riverine flooding ($314 million AAD) and severe storms ($284.2 million AAD) were the most costly types of natural disaster. By comparison, AAD associated with bushfires in the same period was relatively smaller at $77.2 million. However, bushfires are the most hazardous type of disaster in terms of deaths and injuries. 1 To understand the context of these figures, only the $30 million AAD figure for waterways flooding in the Port Phillip and Westernport Region is comparable to the national AAD for riverine flooding of $314 million. This is because in other major urban centres, or capital cities little if any overland flow path mapping and analysis has been undertaken. In the Port Phillip and Westernport Region, the AAD caused by overland flows identified by Melbourne Water is approximately three times greater than the riverine flooding risk. If the estimated local overland flow impacts are considered, the impacts of these shorter duration events could be as much as seven times greater than the annual damage caused by riverine flooding. 1 Report 103 Economic Costs of Natural Disasters in Australia, Bureau of Transport and Regional Economics (2001) Melbourne Water overland flow paths ased on detailed mapping million Waterways Extrapolated from available data 3 million Local overland flow paths Estimate from extrapolating limited council data 25 million otal 245 million Annual Average Damage for the region ($ millions) Figure 4. Annual Average Damage (AAD) 19

24 Managing floods Commonwealth, State, regional and local authorities, as well as local communities and individuals all have a vital role to play in flood management. The scope of flood management is described within the context of three overlapping activity clusters: prevention, response and recovery. 2 Prevention: Activities aimed at eliminating or reducing the incidence or severity of emergencies and the mitigation of effects. Response: Activities undertaken to combat emergencies and provide rescue and immediate relief services. Recovery: Activities aimed at providing assistance to people and communities affected by emergencies to enable them to achieve a proper and effective level of functioning. Activities required to manage a flood event, and the relationships between them, are outlined in Figure 5 below. 2 Victoria Flood Management Strategy, State Flood Policy Committee (1998) Flood Management Prevention Activities Planning Legislation Regulation Land Use Controls Enforcement Structural Works Prevention and Response Warnings Planning Preparedness Community Awareness Training Finance Response Activities Rescue Sandbagging Monitoring Rebuilding Restoration Community Action Advocacy Evacuation Relief Centres Temporary Accommodation Registration Recovery and Prevention Prevention Response and Recovery Recovery Activities Counselling Personal Support Material Aid Community Programs Financial Assistance Response and Recovery Figure 5. Flood management activities in Victoria 20 Flood Management and Drainage Strategy

25 Lollipop Creek, Wyndham Valle, February

26 Shared responsibilities for flood management Australian Government The Australian Government has a supportive role in relation to flood management. Its primary role is in: providing flood forecasting and warning supporting development of state emergency management capabilities providing natural disaster financial support to state, local governments and agencies (e.g. Natural Disaster Mitigation Program and Natural Disaster Relief and Recovery Arrangements) providing policy and legislation in relation to the availability of insurance supporting the development and implementation of national strategies. Agencies include the Bureau of Meteorology, the Department of Transport and Regional Services, Emergency Management Australia and Geoscience Australia. Victorian State Government State governments are recognised as the key level of government responsible for natural resource and emergency management. The main responsibilities of the Victorian Government in relation to flood management are to: develop standards and strategic approaches for floodplain management apply standards and strategies in a co-ordinated and integrated manner provide technical support, planning advice, impact and needs assessments to aid emergency response and recovery planning and co-ordination of post emergency recovery support services develop the Victoria Planning Provisions develop the Victoria Building Regulations. Groups include the Department of Sustainability and Environment, the Department of Human Services, Office 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 Strategy

27 Emergency Services The State s emergency services have a responsibility to assist the community during natural disasters and to: support local agencies in emergency planning participate in emergency response and recovery planning, co-ordination and management develop and maintain community preparedness through awareness and education programs (household, industrial and commercial safety plans, council community awareness programs, signage, building materials advice) develop and maintain total flood warning systems undertake impacts and needs assessments. Agencies include the Victoria Police and the Victoria State Emergency Service. Regional authorities Catchment Management Authorities and Melbourne Water are designated floodplain management authorities. Primary flood management functions include: undertaking flood studies and flood mapping identifying flood affected land undertaking flood prevention works such as retarding basins, levees and pipe augmentation assisting the Bureau of Meteorology with flood forecasting and warning advising planning authorities regarding appropriate land use and development of flood affected areas through their role as planning permit referral authorities 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. 23

28 Local government Local government is primarily responsible for the planning and provision of services and facilities for the local community, and for providing and maintaining community infrastructure. Although local government is not a delegated floodplain management authority under the provisions of the Water Act 1989, it does have a critical role to play in flood management through its role as a planning authority and emergency management agency. There are 38 councils in the Port Phillip and Westernport Region that manage an estimated 25,000 kilometres of local underground drains and other drainage infrastructure. In relation to flood management, local councils are expected to: administer and enforce planning provisions and building regulations in relation to building and development on flood affected land provide for the conservation of natural resources and areas of environmental significance develop flood sub-plans as part of their municipal emergency management plans and participate in risk reduction activities provide the public with access to flood information 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 Strategy

29 Local 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 managing its recovery from flood events preparing personal emergency flood plan. Flood damage, Glenferrie Road, Hawthorn, December

30 Flood management objectives Flood managers face a series of challenges. They must: identify and understand current and future flood risks and the impacts they have on people and property develop criteria to agree what is intolerable flood risk develop and implement a program to eliminate or reduce intolerable risks manage residual risks through improved community awareness, planning and preparedness. Objective 1: Completing the knowledge base Flood mapping to identify risks Melbourne Water s floodplain management functions, outlined in the Water Act 1989, include finding out how far floodwaters are likely to extend and how high they are likely to rise. Mapping throughout the region is currently incomplete and some information has not been included in planning schemes or made easily accessible to the public. In particular, mapping is not complete for many rural waterways for flooding where the catchment area is less than 60 hectares, or for areas that may be subject to coastal or tidal inundation. The identification and accurate mapping of flood risk areas is considered to be a critical foundation for the development of sound drainage and flood management activities. A detailed understanding of flood affected areas gained through mapping is important to the development of the following aspects of flood management planning and response: Land use Planning Policy and Controls. These controls protect the environmental values of floodplains and prevent current flood risks increasing through inappropriate development. They also ensure that proposals that may be affected by flooding or have an adverse impact on existing flood regimes are referred to floodplain management agencies. Emergency Planning and Preparation. Mapping identifies the areas at risk so that agencies can implement flood warnings, plan flood evacuation, relief and recovery strategies, prioritise community information and awareness programs and develop warning arrangements. Mitigation priorities. Mapping identifies safety risks and damage potential, and assists in the development of risk reduction targets, delivery programs and works priorities. In addition to knowing where floods may occur, an understanding of flood depth, velocity, duration and rate of rise is also required to fully understand flood risk. Such information is usually collated in the development of flood studies that map flood extent. Challenges Flood modelling and mapping is an expensive and specialised activity. Additional flood mapping needs to be in a format and to a standard that is consistent with existing data held by Melbourne Water and suitable for the assessment of flood mitigation options and land use planning decisions. In addition, issues associated with the collection and public release of such information, particularly through the planning scheme amendment process, need to be carefully managed. Not all agencies are appropriately resourced to commission flood studies or to maintain and administer flood information under current planning scheme arrangements. Additional support and assistance to complete these tasks may be required. Agencies have also expressed concerns regarding potential liability issues and other obligations associated with the collection of flooding information through mapping exercises. However, failing to identify these areas will not make the risk of flooding any less real, and can potentially increase the likely damage resulting from an event particularly if further development is allowed to occur without taking flood risks into account. There are a variety of ways in which mapping studies and planning scheme amendments could be undertaken. 26 Flood Management and Drainage Strategy

31 Determine area of interest to map the capacity of the drainage infrastructure Divide catchment into sub-areas and undertake hydrologic modelling to determine flows arising from different land use zones Obtain survey and construct digital elevation model and extract cross sections if valleys are defined Undertake hydraulic modelling to determine level and extent of overland flows Include extent of overland flows as special building overlay Figure 6. Mapping overland flows and urban systems 27

32 Actions 1.1 Melbourne Water will undertake and maintain ongoing local flood extent, rural waterway and tidal mapping for the Port Phillip and Westernport Region, taking into account the potential long term pressures of climate change and urban consolidation. This will involve consultation with local government and the Department of Sustainability and Environment. 1.2 Melbourne Water will update and maintain flood information for municipal planning schemes to ensure appropriate standards of flood protection are achieved for new development in flood affected areas. This will involve consultation with local government and the Department of Planning and Community Development. Understanding social impacts Studies in emergency response and recovery management have emphasised the importance of extending investigations into the impact of natural disasters to include psycho-social effects on individuals and the wider community. 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. Challenges Floods affect people in different ways depending upon their health, well being, economic status and other personal circumstances i.e. their vulnerability or resilience to flooding. Determining the impact of an emergency on a community is a complex task. There is currently no agreed process or tool for assessing flood damage and intangible social impacts of flooding that can be used to determine risk acceptability/tolerability thresholds. Ongoing strategic research and further development of our understanding of the social impacts of flooding is an issue that affects flood management agencies at all levels. There is currently no lead agency in Victoria with a clear responsibility for the development and implementation of a research program into the social impacts of flooding. Actions 1.3 Melbourne Water will support collaborative, research into the social and economic impacts of flooding on the community and use this information to assess flood management priorities. 28 Flood Management and Drainage Strategy

33 Urban consolidation, Parkville 29

34 It 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 future pressures on existing drainage systems Development in established areas It 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. Even if the population did not increase, the reducing average size of households means that more dwellings will be necessary in the future to house the same number of people. The government s metropolitan strategy, Melbourne 2030 Planning for sustainable growth (Department of Infrastructure 2002), aims to make the city more sustainable while managing the increase in population and households. One important way to help achieve this is to make the urban area more compact. Melbourne 2030 encourages a greater proportion of new development to be built in and around strategic redevelopment sites (such as principal and major activity centres) that are supported by existing infrastructure, particularly public transport, and are best able to cope with change. The share of new dwellings in greenfield and dispersed development areas will be reduced accordingly. If the Melbourne 2030 housing distribution aspirations are achieved, it would mean that 41% of new households will be located in strategic redevelopment sites and 28% in the remainder of the existing urban areas through infill redevelopment. This will generally cause the overall density of dwellings to increase although most existing residential areas will experience very little change. Increased numbers of dwellings in an area may result in increased hard surface coverage depending on the design of the development and existing conditions. If this occurs, an increase in runoff volumes and an increase in peak flows can be expected. Unless managed, this increased runoff could result in a reduction in drainage infrastructure performance in some areas. To a lesser degree, the replacement of older and smaller structures by large new dwellings will also have an effect even when no increase in dwelling numbers occurs. Investigations into the impacts of development in established areas suggest that most of the metropolitan area is able to cope with the forecast increase in dwellings and that any adverse impacts will be limited to a few catchments. In these catchments, there will be a range of outcomes that call for different forms of action. Increased runoff impacts can be managed where new development is well planned for, such as in activity centres, major re-development sites and around transport nodes. The government is currently working with local councils to develop strategy plans for principal and major activity centres that will address, amongst other matters, drainage issues. Such planned growth enables authorities to better develop strategies for infrastructure provision rather than ad hoc or uncoordinated redevelopment across the catchment. The impacts of increased runoff resulting from such dispersed infill developments are more difficult to manage because it is not easy to quantify or plan for the extent, timing and location of this form of development. The potential for infill development is influenced in some locations by factors such as heritage, neighbourhood character or environmental significance. Similarly, such development in some catchments also needs to be sensitive to the capacity of the drainage system to accommodate additional runoff, or the ability of drainage authorities to undertake augmentation works. 30 Flood Management and Drainage Strategy

35 Dandenong Creek, Dandenong North, February 2005 In some catchments, it may be necessary to undertake works to accommodate additional runoff to acceptable levels. In a very limited number of cases, there are parts of catchments where works are not possible, practical or affordable. In these areas, where infrastructure cannot be upgraded, a more flexible range of activities may be appropriate, such as: education and awareness programs flood warning systems revision of planning policies and controls (to limit the capacity for additional development or to control impervious surface area) water sensitive urban design stormwater capture and reuse. Improved co-ordination between agencies responsible for statutory and strategic planning and policy development, and assessment of infrastructure capacity, will be required to ensure a closer match between land use intentions in the infill areas and infrastructure delivery. 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. Challenges It is difficult to plan and fund infrastructure to cater for the impacts of dispersed infill development as the exact timing and location of such development is not always known. There are some areas where it is not possible, practical or affordable to undertake works to accommodate additional runoff and a variety of flood management measures will be required to manage flood risk. Action 2.1 Melbourne Water will work with the Department of Planning and Community Development and local government to understand the likely impact of urban development on runoff volumes and flood risk in existing urban areas. 2.2 Melbourne Water will develop flood risk management measures in consultation with Department of Planning and Community Development, Department of Sustainability and Environment and local government. Solutions may include upgrading infrastructure planning and building controls to limit imperviousness, and onsite measures such as water sensitive urban design and stormwater capture and reuse. 31

36 Climate change The Intergovernmental Panel on Climate Change s Fourth Assessment Report 2007 concluded that warming of the earth s climate is unequivocal. The management of the impacts of climate change resulting from global warming is a worldwide challenge. However predicting the potential rate and extent of climate change in Australia and the Port Phillip and Westernport Region in particular, is a challenge as our climate is highly variable and there are limited historical climatic records to compare with the present. Based on the available climate change predictions, the interpreted trend for Melbourne is for increasing temperature, reduced annual rainfall and more extreme events. 3 Melbourne Water funded the CSIRO to study the impacts of climate change on water supply, sewerage and drainage functions. The study showed that while the amount of overall rainfall received each year is predicted to decrease, the rainfall may occur in more intense storm events rather than our normal winter and spring rains. This change in rainfall patterns is more likely to result in an increase in overland flows rather than riverine flooding because the short, sharp nature of these intense storms results in sudden large volumes of runoff water. Side entry pits struggle to cope with these volumes of water, and overland flows result. 3 Melbourne Water Climate Change Study Implications of Potential Climate Change for Melbourne s Water Resources (2005), CSIRO In areas where side entry pits can cope with the volume of water, the pipes fill quickly, again leading to overland flows. CSIRO has suggested a preliminary estimate of a 5% increase in rainfall intensity per degree of climate warming. A Melbourne Water sensitivity analysis of increasing rainfall intensity by 5% per degree of temperature increase, suggests a similar increase in runoff volumes of 4% by 2020 to 25% by Under these circumstances, what we currently consider to be a 1% AEP event will occur more frequently as shown opposite in Figure 7. This could also mean more frequent flooding above existing floor levels. These more frequent events are also likely to stretch the tolerance of the affected community and affect in-stream values of urban waterways. More frequent and larger flows have the potential to erode waterways and reduce the ability of flora and fauna living within the waterways to endure the habitat disturbance associated with such floods. Another predicted impact of global warming is a rise in sea levels resulting from a number of factors such as thermal expansion of the sea mass and melting ice shelves. While the Port Phillip and Westernport region does not experience significant coastal tidal flooding and storm surge, there is a possibility that a change in sea level may increase these risks. 32 Flood Management and Drainage Strategy

37 120 Average Recurrence Interval ( ears) ear Figure 7. The storm that occurs on average once every 100 years in 2000 is likely to occur once every 50 years by 2100 Challenges Knowledge regarding climate change is constantly changing. Ongoing strategic research and understanding the impacts of climate change on drainage systems is a State and national issue that affects flood management agencies at all levels. The implications of changed weather patterns on the intensity and duration of storms in the region are not well understood. We need to continue working with other key stakeholders such as the Bureau of Meteorology, CSIRO, Department of Sustainability and Environment, State Flood Policy Committee, and the Westernport Greenhouse Alliance to develop greater understanding of the likely timing and impacts of climate change, and the areas that will be most sensitive to the impacts of climate change. We need to undertake sensitivity analysis of the impacts of different rainfall intensities on various sized catchments to determine which areas will be most sensitive to the possible impacts of climate change. Understanding these effects will assist in the development of appropriate adaptation strategies. Action 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.

38 There are currently more than 100,000 known properties in the region at risk of flooding in up to a one in one hundred year storm event. More than 40,000 of these contain buildings or dwellings at risk of flooding above floor level. Objective 3: An agreed approach to managing existing regional flood problems Overland flows, or flash flooding, are by far the most common cause of this type of flooding. Most people living in those areas are unaware of the flood risk. In most cases, flash flood events occur with little warning, last only an hour or less, are relatively shallow, slow moving and pose little risk of drowning. However, there are some areas where the combination of the water depth and velocity pose threats to human safety. A number of measures are used by agencies to manage existing flood risks in the region. However, it is clear that there is significant existing exposure to flood risks in the region and not all of these risks can be managed in the same way. In many cases, reducing risk using structural measures is too costly, not physically practicable or necessary. In other cases, risks may be still unacceptable even with actions to provide warnings, emergency response and recovery arrangements. Current efforts by Melbourne Water and councils to reduce the consequences of flooding in known flood affected areas are effective at the local level, but they are having little impact on the overall problem due to the large number of properties at risk of flooding. Even if it was physically feasible to construct all the required works, it would cost billions of dollars (based on the cost of current mitigation projects), to protect all properties in the region from a one in one hundred year flood. Mitigation works are currently funded through council or Melbourne Water drainage rates and the magnitude of works required may therefore exceed the capacity or willingness of the community to pay. In addition, at the current rate of construction, the timeframe needed to build such works would extend beyond the design life of the properties they are intended to protect. Climate change, urban consolidation Infrastructure improvements, design standards Planning building controls, on-site measures New floodplain development Planning controls, flood warnings, community education awareness, integrated flood management planning, flood management plans Figure 8. Intolerable flood risk 34 Flood Management and Drainage Strategy

39 Underground carpark, Hawthorn, December 2003 Intolerable risks Although we cannot remove all flood risk there are some flood risks that we may decide are intolerable. That is, a reasonable person would agree that almost regardless of cost, the consequence of the flood should be virtually eliminated or significantly reduced. If that cannot be achieved by engineering works then radical measures to reduce the consequences might be required such as acquiring properties. Factors which may make flood risks intolerable include: significant threat to life health or safety potential impacts to large numbers of people significant environmental impacts significant disruption to economic activity or public infrastructure. While many flood risks may not be regarded as intolerable, they may still be unacceptable to the community under certain circumstances. For example, the long-term computed probability of flooding in a certain area may not be high but floods may still occur several times over a short duration. Statistically the flood risk may not be intolerable, but the combined impacts of multiple floods within a short time frame may make this situation unacceptable. Another example of unacceptable flooding may be where even though the consequences of flooding are minor, a mitigation solution would be relatively inexpensive and easy to implement, such as regrading or the construction of a low levee. Other factors that can influence the acceptability of risk include. whether flooding is seen as natural (riverine) or human generated (development related) perception that risks are being managed through planning, preparedness, response (including warning) and recovery activities awareness of flood risks so that exposure to risks is partly based on conscious individual decisions cost of measures to reduce flooding relative to damage and impact on drainage rates. 35

40 Under current arrangements flood mitigation projects tend to be prioritised on the basis of the cost effectiveness of protection from above floor flooding. However, there is currently little formal understanding of what constitutes a socially acceptable level of risk or explicit use of this understanding in decision making particularly in relation to flood mitigation capital expenditure. Further work will be undertaken to identify and understand both flood extents and flood damage, both tangible (building and contents damage) and intangible (trauma, disruption, stress, anxiety). This work will improve assessment of flood risks required to undertake a benefit cost analysis of expenditure on flood mitigation projects. Action 3.1 Melbourne Water will sponsor research and consult with stakeholders to develop criteria to establish flood risk tolerability thresholds which take into account relevant social or intangible flood impacts. 3.2 Melbourne Water will develop and implement a program in consultation with stakeholders to eliminate or reduce intolerable risks to an acceptable standard through the combination of engineering works and non-structural measures. Challenges Determining an acceptable balance between structural works and non-structural measures, and levels of protection within an agreed risk management framework that maximises community wellbeing and sustainability is a key challenge for flood management agencies in the region. In order to develop this framework we need to undertake research, consult and agree with stakeholders around what is intolerable flood risk so that we can determine a safe and acceptable level of flood protection for both general and particular situations. We need to develop a consistent and transparent decisionmaking framework and a program to prioritise works to eliminate or reduce risks to an acceptable standard. Melbourne Water has engaged the Royal Melbourne Institute of Technology to conduct research, including focus groups, into what the community regards as intolerable flooding, and to develop tools for assessing intangible flood damage. Greater flexibility and reliance on non-structural solutions, such as community education programs and planning controls, will also be required to manage both intolerable risk in the interim and the remaining or residual risk, which would still have varying degrees of acceptability. 36 Flood Management and Drainage Strategy

41 Little River, Werribee, February 2005

42 Objective 4: Enhanced community education, flood awareness and preparedness Understanding the extent and full impacts of flooding is essential for planning for potential future pressures on the drainage system arising from climate change and infill urban development. Equally important is the capacity to share this information and engage with other stakeholders and the community. Melbourne Water and councils have made flood information available to property purchasers and developers by including information in municipal planning schemes and updating property information statements. Once flooding information is shown on planning scheme maps, it is also made available on planning certificates issued as part of any transfer of land documentation. Melbourne Water and councils have individually notified approximately 120,000 affected landowners and occupiers as part of the planning scheme amendment process. However, there is still a significant gap between community and agency flood awareness and knowledge. The risks associated with flooding, and urban flash flooding in particular, are poorly understood in the community. Apart from general flood awareness and preparation information available on a small number of local government and agency web sites, there is little specific information available on flash flooding from extreme weather events. In addition, there is little or no information on flash flooding relating to specific areas. Few community education flooding awareness and preparedness campaigns have been developed or implemented on a regional basis. This lack of understanding limits the effectiveness of flood warning systems and the community s ability to prepare and respond to emergencies. More community education and awareness programs would assist in raising levels of preparedness, aid response and recovery activities, and reduce the impacts and trauma associated with flooding. The community education strategies adopted by Victoria s fire response organisations (Country Fire Authority, Department of Sustainability and Environment, and the Metropolitan Fire Brigade) provide examples of the success of such awareness programs. These strategies reinforce the benefits of improved broad community awareness in enabling appropriate management actions to be undertaken by the community and individuals before, during and after an emergency situation.

43 Challenges Floods are a natural event and although we will develop a program to reduce intolerable flood risk over time, flooding will continue to occur across the region. There is a need to increase the degree of flood awareness and preparation across all levels of the community. Further effort is also required in the development of warning systems for urban catchments affected by overland flooding. Melbourne Water fact sheet Work to be undertaken to understand the relative vulnerability of communities will assist in the development of these programs. However, historically there has been no single Victorian agency with clear responsibility for the development and implementation of community awareness, engagement and education programs focused on urban flooding. The Victoria State Emergency Service is currently exploring options for the development of an enhanced total flood warning system including community education in flood risk for the State. Action 4.1 A community flood education, awareness and preparedness program, including flood warning, will be developed and implemented for the Port Phillip and Westernport region in partnership with Victoria State Emergency Service, and other key stakeholders. Detail of Greater Dangenong Planning Scheme Local Provision

44 Objective 5: Agreed responsibilities and improved collaboration between flood management agencies Historically, Melbourne Water has responded to flood events by undertaking engineering works to improve flood protection. However it is not practical to build infrastructure capable of alleviating all flooding. While intolerable risk areas will continue to be identified and addressed, there are many other flood management tools that can be used in combination to reduce and manage the overall risks posed by flooding. These tools include planning controls, flood warning systems, and programs of education, response and recovery. The broad parameters defining and governing drainage and flood management mean that no single agency can undertake all necessary activities on its own. Collaboration between flood management agencies is essential for developing co-ordinated and integrated flood management programs and activities. Such collaboration must recognise that key agencies involved in flood management may differ in mandate. Some agencies such as councils deliver a spectrum of community services. Other agencies such as the Victoria State Emergency Service and Department of Human Services have a more specialised focus and are uniquely positioned to provide specific skills and resources where needed. Melbourne Water, councils and flood management stakeholders have recognised the need for an integrated and sustainable approach where responsibility for activities is assigned on the capability of the agency to deliver. Examples of the key agencies providing specialised flood management skills and services include: The Department of Sustainability and Environment has the primary responsibility for the development of strategies and policy in relation to flood and stormwater management at a State-wide level. The Victoria State Emergency Service are responsible for flood response as well as assisting councils with their Municipal Emergency Management Planning, and can assist councils with education, awareness, warning systems and emergency management planning. The Department of Human Services impart expertise in emergency recovery management, and can assist with the development of Municipal Emergency Management Plans and public health sub plans. Councils undertake Municipal Emergency Management Planning, (Flood sub plans), provide community support, damage cleanup, and are responsible for administration of planning and building controls. Melbourne Water has primary responsibility for identification of flood extents, providing flood warning advice for major waterways, controlling development in floodplains, providing advice on flooding to local councils and the community, developing plans, and undertaking actions to minimise flooding and flood damage in the Port Phillip and Westernport region. 40 Flood Management and Drainage Strategy

45

46 Challenge Flood management agencies in the region are effective in dealing with immediate responsibilities, and much has been achieved in reducing flood risks. However recent reviews identify opportunities to strengthen regional flood management arrangements through greater collaboration and more efficient resource use. Reviews that support this view include the Flood Warning Service Development Plan for Victoria, Victorian Flood Warning Consultative Committee (2005), and Managing Stormwater Flooding Risks in Melbourne, Victorian Auditor-General s Office (2005). It is a challenge to co-ordinate the activities of the numerous flood management agencies that operate under different mandates and legislation, and have different priorities, resources and capabilities. There is currently no clear process or planning framework for flood management which brings together relevant agencies and groups and allows for community input to the development of integrated flood management activities at the State, regional, catchment or municipal level. It is anticipated that such a framework will coordinate and consolidate the various flood management initiatives identified by this strategy. Action 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. 42 Flood Management and Drainage Strategy

47 A storm approaches Goornong, north-east of Bendigo (picture by Clyve Herbert Australian Sky & Weather)

48 GLOSSARY Annual Exceedance Probability (AEP) The likelihood of occurrence of a flood of a given size or larger in any one year; usually expressed as a percentage. For example, if a peak flood discharge of 500m3/s has an AEP of 5%, it means that there is a 5% risk (i.e. probability of 0.05 or a likelihood of 1 in 20) of a peak flood discharge of 500m3/s or larger occurring in any one year. Average Annual Damage (AAD) The total damage caused by all floods over a period of time divided by the number of years in that period. If the damage associated with various annual events, (the consequences) is plotted against their probability of occurrence, the AAD is equal to the area under the consequence-probability curve. Average Recurrence Interval (ARI) A statistical estimate of the average period in years between the occurrence of a flood of a given size or larger (e.g. floods as big or larger than the 100 year ARI flood event will occur on average once every 100 years). The ARI of a flood event gives no indication of when a flood of that size will occur next. Catchment The area of land draining to a particular site. It always relates to a specific location and includes the catchments of tributary streams as well as the main stream. Development The erection of a building or the carrying out of work, including the placement of fill, the use of land or a building or work, or the subdivision of land. Infill development The development, within an existing subdivision, or vacant blocks of land that are generally surrounded by developed properties; conditions may be imposed on infill development (e.g. minimum floor levels). Redevelopment Rebuilding an area under the current or a similar land use zoning as urban areas age, it may become necessary to demolish and reconstruct buildings. Flash flooding Sudden and unexpected flooding caused by local heavy rainfall or rainfall in another area. Often defined as flooding which occurs within six hours of the rain which causes flooding. Flood awareness An appreciation of the likely effects of flooding and knowledge of the relevant flood warning, response and evacuation procedures. Flood awareness allows landholders to defend themselves, their property and their community from flood threats and to effectively evacuate themselves and their possessions when necessary. In communities with a high degree of flood awareness, the response to flood warnings is prompt and effective. In communities with a low degree of flood awareness, flood warnings are liable to be ignored or misunderstood, and residents are often confused about what they should do, when to evacuate, what to take with them and where it should be taken. The principal driver determining the degree of flood awareness of a community is usually the frequency of moderate to large floods in the recent history of the area. Flood damage The tangible (direct and indirect) and intangible costs (financial, opportunity costs, clean-up) of flooding. Tangible costs are quantified in monetary terms e.g. damage to goods and possessions, loss of income or services in the flood aftermath. Intangible damage is difficult to quantify in monetary terms and include the increased levels of physical, emotional and psychological health problems suffered by flood affected people and attributed to a flooding episode. Flood emergency plan An agreed set of roles, responsibilities, functions, actions and management arrangements to deal with flood events of all sizes. Such plans describe flood warning, defence, evacuation, clean-up and recovery arrangements. A local flood emergency plan forms an essential component of a floodplain management plan. Floodplain Area of land adjacent to a creek, river, estuary, lake, dam or artificial channel, which is subject to inundation by the probable maximum flood. 44 Flood Management and Drainage Strategy

49 Flood prone land Land subject to inundation by the probable maximum flood. Floodplain management plans should encompass all flood prone land, rather than being restricted to land subject to defined flood events. Flood storage areas Those parts of the floodplain that are important for the temporary storage of floodwaters during the passage of a flood. The extent and behaviour of flood storage areas may change with flood severity. Hydraulic analysis The study of the flow of water in waterways. In particular, the evaluation of flow parameters such as water level, extent and velocity. Hydrologic analysis The study of water and its constituents as they move through the natural processes that constitute the hydrological cycle i.e. rainfall, runoff, evaporation, and infiltration. Overland flooding Inundation by local runoff caused by heavier than usual rainfall. Overland flooding can be caused by local runoff exceeding the capacity of an urban stormwater drainage system or by the backwater effects of mainstream flooding causing urban stormwater drainage systems to overflow. Probable Maximum Flood (PMF) The largest flood that could conceivably occur at a particular location. The PMF defines the extent of flood prone land. It is difficult to define a meaningful annual exceedance probability for the PMF event. It is commonly assumed to be in the order of 1 in 10,000 to 1 in 1,000,000. Residual flood risk The remaining level of flood risk that a community is exposed to after floodplain management measures to reduce risk have been implemented i.e. untreated flood risk. Residual risk varies with flood severity and may be substantial for flood events that are larger than the defined flood event adopted for planning purposes or for the design of structural works. Risk Risk is defined (Standards Australia/Standards New Zealand, 2004) as the chance of something happening that will have an impact on objectives. It is derived from a combination of consequences and likelihood (or probability). Risk analysis A systematic use of available information to determine how often specified events may occur and the magnitude of their likely consequences, in order to establish the level of risk. This is normally undertaken as part of a flood study. Risk assessment The process used to determine risk management priorities by evaluating and comparing the level of risk against predetermined standards, target risk levels or other criteria. Risk identification The process of determining what can happen, why and how. Risk management The systematic application of management policies, procedures and practices to the tasks of identifying, analysing, assessing, treating and monitoring risk. Risk treatment Selection and implementation of appropriate options for dealing with risk. Runoff The amount of rainfall that enters the stormwater drainage system, (underground pipes, overland flow paths, floodway, and waterways) after losses such as infiltration have been taken into account. 45

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51 Copyright November 2007 Melbourne Water Corporation. All rights reserved. No part of this document may be reproduced, stored in a retrieval system, photocopied or otherwise dealt with without the prior written permission of Melbourne Water Corporation. Melbourne Water 100 Wellington Parade, East Melbourne PO Box 4342 Melbourne Victoria 3001 Telephone Facsimile melbournewater.com.au For information on Melbourne s water resources in languages other than English, call or visit melbournewater.com.au and click on the Community Languages link. ISBN Printed on paper manufactured at the Bernie mill in Tasmania, which has IS environmental system certification. Water at the mill is recycled and reused. The paper is acid free, has neutral ph and is made of pulp from plantation timbers and pre-consumer waste. Disclaimer: This publication may be of assistance to you but Melbourne Water and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Cover photo by Clyve Herbert.

52 48 Flood Management and Drainage Strategy