History of flooding. 12 Flood Management and Drainage Strategy. Riverine flooding

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1 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

2 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

3 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)

4 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

5 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

6 Flood damage, Maintree Road, Hawthorn, December

7 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

8 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

9 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

10 Lollipop Creek, Wyndham Valle, February

11 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

12 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

13 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

14 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