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In April, Melbourne Water released new flood modelling for the Maribyrnong River to help the community and agencies better understand flood risk across the catchment.

The modelling takes into account the impacts of climate change and other changes in the catchment, including further urban development. It uses sophisticated technology to get the most accurate picture of potential risk for certain flood events.

It’s important we have this information so we can be prepared. This preparation includes informing the community about their flood risk and actions they can take to be flood ready, supporting future planning decisions, and investigating potential flood mitigations such as levees, drainage and retarding basins.

The modelling was released with mapping showing the extent of floodwaters. We have now developed additional mapping to help illustrate flood depth information. You can find the flood mapping here.

If you would like to find out the specific flood information for your property you can call us on 131 722 or email [email protected].

Further assessment of the Flemington Racecourse flood wall

The Independent Panel looked at the impact of the racecourse flood wall during the 2022 flood event.

Now that the new flood modelling for the Maribyrnong River has been completed, Melbourne Water has undertaken further assessment of the impact of the Flemington Flood Wall.

This analysis of the floodwall impact against the new 2024 and 2100 flood scenarios shows no impact from the flood wall at Kensington Banks, but a slightly bigger impact in the Maribyrnong township.

The report finds that under the projected 2024 scenario – which maps a flood event with a one per cent chance of occurring in any given year – the average impact in the Maribyrnong township is 3.8cms of extra depth in a flood that is 130 centimetres deep.

The analysis finds that in Kensington Banks there is no added depth caused by the Wall – and in fact, the wall has the effect of reducing the estimated flood depth by 5.1cms.

Note the projected 2024 flood event with a one per cent chance of occurring is more serious than the Maribyrnong River flood of 2022.

The report finds in the 2100 scenario there is little or no impact from the flood wall on Maribyrnong township or Kensington Banks as water overtops the flood wall.

The impacts of climate change and an evolving urban landscape can change the flood risk to people, places and communities.

To address this, and factor in new flood modelling standards, we’re updating all flood models across the Port Phillip and Westernport region to include climate change projections to the year 2100, by 2026.

Now we have the new Maribyrnong River flood modelling, we will work together with our partners and community to incorporate the new model into emergency planning, land use planning, decisions on flood mitigation, and other measures to address flood risk.

We understand new flood risk information can be concerning. That’s why we’re actively working with communities (together with VICSES and councils) to raise awareness about people’s flood risk, and to provide guidance on how to prepare for a flood.


What’s the new Maribyrnong flood model?

The new Maribyrnong River Flood Model is a riverine flood model and provides the latest flood information for the Maribyrnong River. It uses the most up to date data about rainfall and run-off, the physical features of the floodplain and nearby urban areas, and the most recent flood in October 2022 for accurate results.

As a more advanced 2D model than the previous model, it can simulate water flow across an entire area and in multiple directions. With this improved capability, the model gives a more accurate picture of how water flows, which helps predict flood patterns and their effects.

Current climate change guidelines have been used, including recommended values for rainfall intensity increases and sea level rise. The new modelling has been prepared according to the latest standards and industry best practice set out in the Australian Rainfall and Runoff Guidelines 2019 (ARR 2019).

View maps of the flood model and a summary report on how the model was developed.

What different flooding scenarios have been mapped?

Two different flooding scenarios of the new Maribyrnong River Flood Model are mapped. A current day 2024 flood scenario - and a forecasted 2100 flood scenario.

Both of these scenarios are based on a flood event that has a one percent chance of occurring in any given year. This is known as a 1% Annual Exceedance Probability (1% AEP).

Where the new 1% AEP flood maps indicate an area that is subject to flooding - this doesn’t necessarily mean that each building in this area will experience over floor flooding during such a flood event. The extent to which buildings are impacted depends on the way they are built. For instance, the level of clearance between the ground and the floor of the building.

What’s next?

We’ll be initiating work with VICSES and Councils to translate the 2024 flood scenario information into municipal Flood Emergency Management Plans and community Local Flood Guides. This is the information to use to develop your own individual flood emergency plan. This will also be used to assist flood awareness and preparedness information and activities for households, communities and businesses so we can be ready for any future flood event.

The forecasted 2100 flood scenario information will be used for land use planning decisions once it is translated into planning scheme controls. If you are intending to renovate or redevelop your home or make changes to your property, this will be the flood information to use. The Planning Scheme Amendment process provides an opportunity for the community and stakeholders to review proposed new controls and make a submission – impacted community will be advised when this public exhibition stage commences.

Flood mitigation study

Now the new Maribyrnong River flood modelling has been completed, detailed assessment of long-term sustainable flood mitigation options is being progressed.

This work began last year with a preliminary desk top review of past flood mitigation studies for the Maribyrnong River (Maribyrnong Flood Mitigation Options, Evaluation of past options, 22 June 2023).

The new modelling will be used to support comprehensive identification and assessment of previously identified traditional solutions, as well as any new innovative solutions for the riverine flood hazards. We will also use the new modelling to understand the impact of each option. In addition, comprehensive economic, environmental, social and cultural impact assessment will be undertaken.

The study will consider feasible flood mitigation solutions for the riverine flood hazards, that prioritise the safety and resilience of the communities within the catchment and have the greatest impact on reducing the flood risk, both now and anticipated by the year 2100 and beyond.

The community and stakeholders will be invited to participate in the development and assessment of options later this year.

In the meantime, you can register your interest in the mitigation study and provide your preliminary input by completing our short survey below.


How can I get involved?

  • Click FOLLOW at the top of this page to be kept up to date with progress, and opportunities to contribute
  • Come along to an awareness and preparedness event
  • Ask our team a question by filling out the form at the bottom of the page or calling our call centre on 131 722
  • Register your interest in participating in the flood mitigation study above.

Frequently asked questions

Flood depths

Flood level refers to the height of flood water measured in metres to Australian Height Datum (AHD).

Flood extent refers to how far flood water will reach.

Flood depth across a property is measured from the ground levels of the property and can vary considerably, depending on the landform of the property – for this reason, when providing individual property information, we provide property owners with the estimated minimum and maximum depth on their property.

The impact of a flood at your property depends on the flood depth but also the clearance between the ground and the floor of your house or other buildings.

If you would like to find out the specific flood information for your property you can call us on 131 722 or email [email protected]

Melbourne Water can provide local residents with information on flood level and flood depths for their property by calling 131 722 or emailing [email protected].

Please provide your full name, property address and email address. A flood information letter with this information will be sent out to you. Please note, this can take up to 14 days. 

Melbourne Water will provide the flood level and depth for a flood event that has a one percent chance of occurring in any given year. This is known as a 1% Annual Exceedance Probability (1% AEP). We will provide this information for the new 2024 and 2100 scenarios. The depth of flooding across a property can vary considerably, depending on the landform of the property – we therefore provide the minimum and maximum depth for your property.

The extent to which buildings are impacted by a flood event depends on the flood level and also the clearance between the ground and the floor of the building.

Individual property owners may wish to engage a licensed surveyor to determine their floor level and whether any of the structures on their property are below the flood levels advised by Melbourne Water.

Please note, the flood information letter is not a formal Flood Certificate for planning and development purposes or for a ‘section 32’ property statement prepared to support the sale of land. 

Individual property owners could engage a licensed surveyor to determine their floor level and whether any of the structures on their property are below the flood levels advised by Melbourne Water.

Melbourne Water can provide local residents with information on flood level and flood depths for their property by calling 131 722 or emailing [email protected].

The extent to which buildings are impacted by a flood event depends on the flood depth and also the clearance between the ground and the floor of the building.

FLEMINGTON FLOOD WALL

The modelling by Jacobs finds the flood wall resulted in an average increase of flood extent across the catchment of 1 per cent in the October 2022 flood event. This includes an increased depth ranging from 0.8 to 3 cm (an average of 1.7 cms) for approximately 240 properties in the Maribyrnong township area - in an area where the overall flood depth was 80 cm. 

The racecourse flood wall did not lead to flooding of the Kensington Banks community in the October 2022 flood event. 

You can find more information on the assessment of the racecourse wall impact in the October 2022 event undertaken by the Independent Review Panel here.

Modelling by Jacobs finds that under the projected 2024 scenario – which maps a flood event with a one per cent chance of occurring in any given year – the average impact in the Maribyrnong township is 3.8cms of extra depth in a flood that is an average of 130 centimetres deep.

The analysis finds that in Kensington Banks there is no added depth because of the wall – and in fact the wall has the effect of reducing the estimated flood depth by 5.1cms in this location.

Note the projected 2024 flood event with a one per cent chance of occurring is more significant than the Maribyrnong River flood of 2022.

The Jacobs modelling finds in the 2100 scenario there is little or no impact from the flood Wall on Maribyrnong township or Kensington Banks as water overtops the flood wall.

You can find the report here.

The evidence we have, including the findings of the Independent Review of the 2022 flood, does not justify removal of the Flemington flood wall. 

However, we will now incorporate an examination of the mitigations associated with the flood wall into our broader investigation of potential mitigation measures across the catchment.   

You can find more information about the mitigation study above.

PROPERTY VALUES AND INSURANCE

Melbourne Water's responsibility is to provide advice on flood risk to support flood awareness and preparation, to inform planning decisions and consider potential mitigations such as retarding basins, drainage or levees.

This new modelling represents the flood risk that exists – and is used to help mitigate that risk.

These climate change impacts are global issues that the insurance industry has been dealing with and taking into account in setting their premiums. 

We would advise householders to engage with their insurance companies to understand their own circumstances.

It is Melbourne Water’s responsibility to ensure that planning and emergency agencies, communities and individual landholders are able to understand their flood risk so that as a community we can best prepare before any flood and in the event of any flood.

Melbourne Water is not best placed to speculate or comment on property values.  

We are releasing modelling information so that we can prepare for the impacts of climate change and plan for the future. 

This new modelling represents the flood risk that exists and is used to help mitigate that risk.  

It is Melbourne Water’s responsibility to ensure that planning and emergency agencies, communities and individual landholders can understand their flood risk so that as a community we can best prepare before any flood event. The models and detailed maps will help inform decisions about flood mitigation infrastructure such as drainage, levees and retarding basins, and other options to manage flood risk. 

RENOVATIONS AND REDEVELOPMENTS

In regard to renovations and redevelopment - once the new flood data is incorporated into planning schemes, any modifications to a property or new builds which would trigger the need for a planning permit, would need to be considered in light of the new flood information. Assessment would include what appropriate design measures and floor levels might be needed to appropriately manage risk in a flood event.

For flood modelling to be used in land use planning and development decisions, it needs to be translated in appropriate zones and overlays in planning schemes. This is done by a Planning Scheme Amendment (PSA) process. In line with Victorian Planning Policy directions for climate change, the new 2100 flood information is used to underpin planning scheme controls.

We’ll be working with Local and State Government to use the new model to update municipal planning schemes. The planning scheme amendment process ensures there is an opportunity for community feedback via a public exhibition process. We’re anticipating the amendment process will commence in the second half of this year.

You can find out how to retrofit your home with flood resilient design approaches and materials that reduce the impact of flooding by downloading our Flood Resilient Guide to Retrofitting Your Home on our website here. The guide has been developed for homeowners who have experienced flooding and want to reduce the impacts of future flood events. It is for information purposes only.

For resources and community education sessions on how to be prepared for a flood, including how to sign up to flood alerts and create your own flood emergency plan, visit our website here. 

Flood models

The function of a flood model is to simulate the behaviour of stormwater and flood flows within drainage and waterway networks and determine urban and floodplain inundation.  

A flood model is a suite of hydrologic and hydraulic computations that have been programmed into a computer model.  Typically, the hydrologic model determines how much water is delivered into the drainage network or riverine system.  The drainage network is represented in the hydraulic model.   

The flood model takes as input:  

  • a representation of the terrain and landform features, land use types, waterways and drainage network, flood control infrastructure and boundary conditions (e.g. starting water levels), and   
  • a suite of “design” rainfall events that are based on historic rainfall and climate conditions for the location.  

A flood model provides (as output) flood extent (the areas impacted), depth (how high flooding might occur) and velocity (how quickly an area might flood) across the range of rainfall events that are modelled.    

Updating flood models ensures up to date flood information is available to inform flood risk and build community resilience across the region. The information from flood modelling helps the state government, local councils, developers, businesses and the community understand how best to minimise the impact of flooding.     

An important part of minimising flood risk is to ensure new development takes account of the flood risk in the area.  Melbourne Water uses flood information to comment on development and subdivision applications and, if necessary, place conditions on planning permits. This ensures that all new developments are designed to protect occupants from flooding and that Melbourne’s drainage system functions like it should.

Melbourne Water has committed to a significant uplift in its mapping and modelling program delivery.    

We know with climate change there will be more frequent and severe events, there will also be impacts from rising sea levels in some coastal areas. This is why we are using the best available information to update flood modelling.     

Melbourne Water is updating modelling to take account of the impacts of climate change, in line with the Australian Rainfall and Runoff Guidelines 2019, and this will be used to update land use planning controls in Planning Schemes and subsequently to inform planning and development decisions.  The new information will also be used to update municipal Flood Emergency Management Plans and community Local Flood Guides. 

Melbourne Water has committed to updating all flood models for every catchment in Melbourne by 2026 (both riverine and overland flow model). These updates will include climate change assumptions projected to the year 2100.    

The Australian Rainfall and Runoff Guidelines (ARR) 2019 sets out best practice for flood modelling in Australia, including climate change assumptions.

ARR 2019 notes that a number of factors considered in flood model development will be impacted by climate change, including rainfall intensity, duration, the conditions of the catchment the rain falls onto, and downstream conditions affected by sea level rise.

Current guidance focuses on changes to rainfall intensity and Melbourne Water is consistent with national guidelines.

A planning horizon to 2100 has been selected by Melbourne Water for consistency with Victorian State Planning Policy.

OUR ROLE

Melbourne Water as the ‘flood plain manager’ is responsible for: 

  • Catchment level and coastal flood modelling of 1% AEP flood risk (note, DEECA with CSIRO have undertaken the most recent coastal hazard mapping). 
  • Melbourne Water is responsible for modelling for riverine floods. 
  • Melbourne Water is responsible for modelling stormwater flooding/overland flow above 60 ha and local councils are responsible for less than 60ha, reflecting ownership of these drainage assets.  
  • Together this modelling is used as inputs into land use planning controls, Councils’ Municipal Flood Emergency Plans, VICSES local flood guides, and in assessing feasible mitigation solutions.  
  • A referral authority for planning and building permits in relation to flood risk (see below for further info on our role in land use planning).  
  • Running flood prediction models in real time before and during an event and providing that information to other agencies to inform flood warnings and emergency response actions.  

Melbourne Water does not: 

  • Issue warnings to the community - this is done by Bureau of Meteorology and VICSES, using Melbourne Water flood predictions.
  • Issue planning or building permits - these decisions are made by local councils or the Minister for Planning
  • Lead recovery from flood events, except where we own or are responsible for the assets. 

Melbourne Water has key roles in land use planning for flood resilience in the context of climate change:

  • Undertake flood modelling and determine development controls in partnership with Councils
  • As Floodplain management authority under the Water Act 1989 and related functions under the Planning and Environment Act 1987 (PE Act) and the Building Regulations 2018
  • Assesses permit proposals and requires conditions of permit to ensure developments are compatible with any flood risk. If the flood risk is determined too high, Melbourne Water can recommend refusal of a permit.
  • Provide advice to other government agencies and authorities where development and infrastructure is proposed in flood affected areas.

In terms of Melbourne Water’s role as a referral authority, there are two types of referral authorities:

  • A determining referral authority
  • A recommending referral authority

Melbourne Water is usually a determining referral authority which means if we object, the responsible authority e.g. Council) must refuse to grant a permit, and if a determining referral authority specifies conditions, those conditions must be included in any permit granted.

TYPES OF FLOODING

The Maribyrnong River flood model is a riverine model, it does not include flooding associated with the stormwater drainage system (overland flow flooding). Where possible, flood modelling to predict stormwater flooding is undertaken jointly with local Councils who own much of the related drainage infrastructure. 

At Melbourne Water, we manage various types of flooding including that of our river systems (riverine flooding), our drainage infrastructure (overland and flash flooding) and along our coastlines (coastal flooding or tidal inundation and sea level rise). 

Melbourne Water prepares flood models for different types of flooding (outlined below). 

  • Riverine floodinghappens when widespread, prolonged rain falls over the catchment of a river. Inundation of normally dry land occurs when water overflows the natural or artificial banks of a stream, river, estuary, lake or dam. Riverine flooding generally excludes watercourses constructed with pipes or artificial channels considered as stormwater channels. Riverine flooding can be a slower process, occurring at a rate that allows advance warning. Flood waters may last for days. 
  • Creek flooding – happens when intense ran falls over a creek catchment. Run-off from houses and streets also contributes to creek flooding. The combination of heavy rainfall, run-off and the existing water in the creek causes creek levels to rise. Flood water from creek flooding can rise quickly and be very fast moving, and then recede quickly. 
  • Flash (stormwater) flooding – Inundation by local runoff caused by heavier than usual rainfall. Inundation can be caused by local runoff that exceeds the capacity of urban stormwater drainage systems; overland flows that are on the way to waterways; or riverine flooding causing urban stormwater drainage systems to back up and overflow. Flash flooding from the stormwater system tends to be rapid and dangerous due to the speed and depth of flows and difficulty in providing a timely warning to people. 
  • Coastal flooding – Increases in coastal water levels above the predicted tide level resulting from a range of storm-related factors such as wind and waves. Coastal flooding in a storm surge gives some advance notice but sea level rise will mean some areas are permanently underwater.