FAQs - Please note the FAQs may be amended to provide further information or clarity as required.

Integrated Water Management (IWM) is a collaborative approach to the way we plan for and manage all elements of the water cycle. This includes: 

• managing and protecting the health of our waterways and bays
• wastewater management 
• Alternatives to potable water supplies 
• stormwater management and
• water treatment. 

This collaborative process allows us to identify and deliver greater value water cycle initiatives to improve the resilience and liveability of our city. 

A strategy is needed to review our management of water for the future and to respond to emerging challenges, including:

• population growth
• climate change and variability 
• increasing flood and drought risk.

The strategy will need to address a range of constraints and influencing factors, such as:

• legal obligations including Council's duty of care in respect of Section 9.2 of the Local Government Act 2020
• State Government Policy and coordination with other agencies and tiers of government with responsibilities as part of the water cycle
• financial constraints
• community expectations that include amenity and environmental protection.

A suite of actions is necessary to best manage increasing flood and drought risk for our community and address the above challenges. 

The strategy will guide consideration and prioritisation of opportunities to reduce reliance on potable water, consider alternative water sources and contribute to the achievement of a resilient and liveable city. 

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) Impacts, Adaptation and Vulnerability 2022 provides the following insights for Victoria:

• Multi-day heatwave events have increased in frequency and duration across many regions since 1950;
• April to October rainfall has decreased 12% between 2000-2019 in south-eastern Australia since the 1970s. Hourly extreme rainfall intensities increased by 10–20% in many locations between 1966 and 2013;
• More frequent and intense extreme precipitation will increase the number of people, area of urban land, and damages impacted by floods;
• The main driver for increased heat exposure and stress is the combination of global warming and population growth, particularly in urban centres.

The strategy will:

• focus on solutions for the future
• identify actions to contribute to planning for the achievement of sustainable and liveable communities
• identify opportunities to maintain green open spaces in a more water constrained environment
• improve ability to withstand future droughts and floods 
• compliment the development of other Council climate related strategies, including the proposed Urban Forest Strategy.

Integrated water management initiatives consider opportunities to treat stormwater as a resource, rather than a waste for disposal. The strategy will consider actions to reduce the demand on potable water supplies through the appropriate use of alternative water sources.

The development of the Integrated Water Management Strategy, based on a sound understanding of risk and of the challenges facing our community will facilitate timely and proactive planning for a sustainable future for our community.

Potable water is intended as drinking water and should materially meet the Australian Drinking Water Guidelines 2004, or equivalent.

Melbourne Water is the Regional Drainage and Floodplain Management authority for Port Philip and Westernport region. Melbourne Water is responsible for:

• regional drainage (large drains, creeks, the Yarra River and stormwater infrastructure) 
• floodplain and waterway management, and; 
• contributing to the protection and improvement of waterway health across greater Melbourne. 

Manningham Council is the statutory planning authority, responsible for the economic, social and environmental sustainability of the municipal district. This includes mitigation and planning for climate change risks and safeguarding our community assets. Council is also responsible for the provision and maintenance of the local drainage network and management of stormwater overflows from its drainage system.

Large cities like Melbourne will always experience some type of flooding – it’s an inevitable part of our weather cycle. Flooding can involve riverine or flash flooding.  

Riverine flooding is typically associated with larger catchments where watercourse flow levels can rise over periods of days before the peak level is reached. There is generally a greater period of advance warning of flooding. Rivers and creeks often have flows of water at most times of the year.

Flash flooding is typically associated with smaller catchments where the peak flow depth can be reached in less than an hour from the start of the storm. Overland flow paths associated with flash flooding events are typically dry when there is no rain.   

Standards for land development changed in the 1980’s, when the concept of providing opportunity for overland flows to run along natural valleys, roads and through open space was introduced. Most of Manningham was developed prior to this time and as a consequence, there are many instances where overland flow paths run through private properties.

Although Council is incrementally upgrading older drainage infrastructure, it is not possible to build a drainage system that can cope with all floods. An opportunity exists to ensure that new buildings and works are constructed to reduce flooding in areas with the greatest flood risk. We can also make sure new developments are better planned, and work to minimise flood risks and impacts.

Overlays are ordinances (mapped) in the planning scheme that apply special controls over land. The overlay triggers the need for a planning permit for buildings and works. Various types of overlays may respectively be applied to a given property (e.g. a Land Subject to Inundation Overlay or a Special Building Overlay). 

They require a developer to seek a planning permit for buildings and works. Flood overlays are planning scheme controls that identify areas prone to flooding. Flood overlays ensure that new development is designed to minimise potential flood damage to the property and will not increase flooding of surrounding areas.

A Special Building Overlay (SBO) specifically identifies areas prone to overland flooding. The term ‘overland flooding’ refers to floods that result from severe storms that generate more water than the drainage system can carry.

The SBO applies to properties identified as being at risk of overland flooding where the drainage system capacity is exceeded. The SBO shows the location and extent of land affected by overland flooding that would result from a storm with a 1% chance of occurrence in any given year. This terminology has replaced previous references to a 1 in 100 year storm event.

The purpose of these overlays is to set appropriate planning permit conditions and floor levels for development. They aim to minimise any flood risk to developments and ensure that the development proposal does not increase flood risk for abutting lands.

If your property has a flood overlay (e.g. Special Building Overlay) applied, the risk of flooding will need to be considered as part of any planning permit application required in order to undertake certain building works to your property.

The permit process will ensure that building works consider the potential impact of overland flooding to the property and the surrounding area. This will ensure that drainage issues are considered at the planning permit stage when building works are proposed at any affected property, based on the best available flood modelling.

It cannot be assumed that flooding has not previously or will not occur at any given property simply because there are no recollections of flooding at that property. The property may simply not have been subjected to a major storm event based on the experience of the current occupier.   

The Special Building Overlay is based upon the extent of flooding that would result from a storm event with a 1% chance of occurrence in any given year.

The 1% Annual Exceedance Probability (AEP) flood event is the probability that a flood of a given magnitude will occur within any given year. 

It was previously known as the 100-year Average Recurrence Interval flood. 

However, a flood of this size or greater may occur more frequently than this and can happen more than once in any year. 

The 1% AEP flood is the current standard to regulate and protect new developments through the planning and building process in Victoria. 

The impacts of floods rarer than the 1% AEP flood are not regulated through the planning and building processes but can occur.

Well-designed, contemporary flood studies can be used to predict the likelihood and impact of floods with sufficient accuracy for planning purposes. Flood mapping involves computer modelling of complex natural systems, which simulates how stormwater runoff travels through catchments. 

The modelling takes account of data including:

• the terrain 
• the existing drainage network (including the pits and pipes)
• the perviousness of the catchment
• rainfall data. 

The software model calculates overland flow widths, depths and velocities throughout the catchment, resulting from rainfall events of various probabilities. 

Flood mapping cannot cause flooding or increase flood risk.

A catchment in the context of flooding is an area of land which falls to an outlet point.

Under Regulation 148 of the Building Regulations 2018, Council is required to prepare mapping for areas under its control that are liable to flooding.

There is a need for current and reliable flood mapping information to forecast the likelihood and impact of floods and understand flood risk. Outputs of flood modelling include the extent, depth and the velocity of overland flows, which are key factors in assessing flood risk.

Flood modelling is used to:

• assess the frequency, severity and location of flood risks within catchments
• better plan and prioritise mitigation activities 
• plan for future development 
• target investment. 

Flood mapping information can also be used to inform planning for flood emergencies, as well as developments, to protect neighbouring properties from increased flood risk. 

Communication of flood risk information to affected property owners helps to build a more resilient community and allows property owners to take action to address flood risk on a property scale.

Flood models are not perfect and these methods involve some data and model uncertainties. 

Limitations of the information underpinning flood modelling can be managed through the use of industry standard methods, community consultation, sound engineering knowledge and judgement in reviewing the maps and industry peer review. The verification process will involve: 

• checking of the outputs against known flood behaviour
• site inspections 
• consultation with the community to test the model outputs. 

The modelled flood extents will be placed on public exhibition to assist in identifying any discrepancies between observed flood behaviour and the mapped flood extents. 

Any identified issues will be reviewed as part of the final preparation of the modelled flood extents.  

This flood mapping process will be informed by the latest available data and guidance recommended under the 2019 version of Australian Rainfall and Runoff. 

Planned for completion in June 2025, the Manningham Flood Mapping Project involves flood mapping in respect of local catchments under Council control and Melbourne Water assets. The project is being delivered jointly by Melbourne Water and Council. 

Expert consultants will be engaged to prepare and run the models and filter the outputs based on: 

• the latest available data
• specifications based on Melbourne Water documents, and; 
• in accordance with the requirements of Australian Rainfall and Runoff 2019. 

The Manningham Flood Mapping Project will also include the modelling of the climate change scenario to better inform understanding of the likely impacts of climate change on local flood behaviour.

The drainage system comprises:

• waterways 
• underground drains and pits within road reserves, parks and easements within private property 
• culverts
• open drains and channels
• retarding basins, and 
• other infrastructure.  

In major storm events, excess stormwater runoff exceeding the capacity of the underground drainage network travels along overland flow paths, along roads and through reserves and private property.  

Responsibilities for drainage infrastructure rests between Melbourne Water, Council and private property owners.

Melbourne Water (MW) is the regional catchment manager and is generally responsible for trunk or main underground drains and waterways. Typically, MW is responsible for drainage assets from the point where the upstream catchment is greater than an area of approximately 60 hectares. These responsibilities include:

• asset planning 
• maintenance and refurbishment
• flood risk identification and mitigation
• prioritising new works
• flood emergency management, and
• other functions.

Council is responsible for the vast majority of the public drainage infrastructure within the City of Manningham. Generally, this infrastructure relates to local catchments, which are typically under 60 hectares in area. Council is responsible for its assets in local catchments as the asset manager and for flood risk management for local catchments. Council also has flood emergency management responsibilities. 

Owners of private property are responsible for private drainage systems internal to their properties, aside from Council and Melbourne Water drains located in easements.  Property owners are also responsible for house drain connections to Council drainage systems, as well as vehicle crossing culverts.

Floods are unavoidable natural occurrences and result when the capacity of the drainage system is exceeded, resulting in uncontrolled overland stormwater flows.

Rainfall is the most important factor in creating a flood, but there are many other contributing factors. When rain falls on a catchment, the amount of rainwater that reaches the waterways depends on the characteristics of the catchment, particularly its size, shape and land use. Some rainfall is 'captured' by soil and vegetation, and the remainder enters drainage pipes, overland flowpaths and waterways as flow.

Riverine flooding is associated with larger catchments with substantial flows. Larger watercourses often convey flows of varying magnitude at most times of the year. Slower and more predictable development of the flood peak is expected. Larger scale and more sustained flood extents are expected. 

By contrast, flash flooding is usually associated with overland flow paths and smaller catchments and short flood event durations. Flash flooding is characterised by rapid onset of the flood peak. Outside of rainfall events, overland flow paths are often dry and do not convey flows at most times of the year. The impacts of local catchment storage and ground surface depressions on flood extents is significant for flash flooding.

Council and Melbourne Water will arrange their own flood mapping for areas under their respective jurisdictions. 

They will use separate flood mapping methodologies based on suitability and location.

These will take account of the difference in flood characteristics between regional scale and local scale catchments. 

Overland storm water flows in urban catchments involve a different flood process compared with increasing flood depths in waterways at the bottom of larger, regional scale catchments.  

The flood mapping process, for both Melbourne Water and Council, will be informed by the latest available data and guidance recommended under the 2019 version of Australian Rainfall and Runoff.

All flood mapping will also be subject to verification, including an independent peer review.

With the introduction of Australian Rainfall and Runoff 2019, there has been significant advances in the guidance and data available to underpin flood mapping.  

LiDAR data describing the topography in Manningham has also been updated since the previous flood mapping project was undertaken. 

The current Manningham Flood Mapping project will involve the exhibition of the mapped flood extents prior to the finalisation of the Flood Mapping Project. 

Council will not be considering any planning scheme amendment option until the flood mapping has been finalised. 

LiDAR or Light Detection and Ranging is a remote sensing method used to examine the surface of the Earth, typically involving data collection from survey aircraft. LiDAR data can be used to generate land contours to inform modelling work.

LiDAR data has an accuracy of ±0.1 m, as compared with field surveys which have an accuracy of ±0.01 m. 

Whilst points in field surveys are more precise, overland flows derived from flood models are more dependent on the land profile (relative heights in the digital topography) and key features and not absolute values of elevations. The flood mapping information indicates the depth and path of water flowing over the land in a storm event of a given duration and probability. 

It is not possible, affordable or necessary to field survey all properties in a Council area to inform flood modelling or mapping. High resolution digital topography derived from LiDAR is more than adequate for the assessment of flood risks.

The community will be invited to comment on the draft flood extents when the results are provided for public exhibition. This information will be used to test the modelled flood extents and where there is justification, the flood extents will be reviewed as part of the final preparation of the modelled flood extents. 

In addition, a Community Reference Panel has been formed to work with Council officers throughout the flood mapping and development of the Integrated Water Management Strategy.

Council’s investment in drainage improvements since 2017 is set to exceed the $10.8 million target at the end of June 2022.

The Manningham Planning Scheme controls how affected land can be used and / or developed. Planning zones and overlays define controls applicable to specific properties. From time to time, changes to the Planning Scheme are proposed to reflect new circumstances or to improve the scheme. 

Planning scheme amendments often change the way land can be used or developed through changes to existing controls or the introduction of a new planning control. This is a formal process, initially requiring a Council resolution, prior to submission to the Victorian Minister for Planning for consideration and approval.

The Manningham Flood Mapping project will result in: 

• updates to the Melbourne Water flood extents, which have informed existing Special Building Overlay 1 and the Land Subject to Inundation Overlay. 
• The development of flood extents associated with local catchments under Council control across Manningham.  

The new flood mapping may inform the extent of new Special Building Overlays (or other relevant flood-management overlays) for incorporation into the Manningham Planning Scheme. 

If Council intends at any time to introduce new planning overlay controls or amend existing controls, it would need to commence an entirely new planning scheme amendment process. Any planning scheme amendment would need to be based on strategic justification and would involve consultation with the affected property owners.

Any future planning scheme amendment process could potentially include properties impacted by Planning Scheme Amendment C137mann, which is a corrective amendment affecting properties in and around Hillcroft Drive Templestowe.

The CRP partners with Council to better understand the stormwater management and flooding challenges facing our community, arising from climate change and population growth. 

The impacts of these challenges are forecast to include:

• the extremes of increased risk of flood and drought; and 
• pressures on potable water (drinking water) supplies. 

We need to consider how alternative water supplies, such as stormwater, can be mobilised to ensure a sustainable water future and to ensure appropriate water management moving forward for our community.  

Based on this shared understanding, the CRP provides a diverse community voice to guide the development of the Integrated Water Management Strategy and the Flood Mapping Project, and shape project related communications. 

In informing Council’s deliberations, the CRP supports quality decision making to best place the Manningham community to proactively and sustainably meet the challenges ahead.

The role of the CRP is to provide a direct link between Council and representatives of the Manningham community. Community Reference Panel members will:

• become informed of the project context, including challenges faced by our community and the environment in relation to stormwater management, flood risk and climate change
• provide feedback on issues pertaining to the:
  • integrated water management opportunities
  • flood mapping process
  • draft flood extents 
  • water and flood risk management 
• partner with Council to develop and assess options to address the associated challenges
• provide advice relating to themes associated with: 
  • the development of the draft Integrated Water Management Strategy
  • submissions received following public exhibition of the Integrated Water Management Strategy and the draft flood mapping results
  • other matters referred to the CRP.
• review and provide feedback on communications approaches and materials, including public exhibition and the process for addressing submissions
• bring relevant community concerns to the attention of the CRP

The CRP acts in an advisory capacity. Participation is voluntary. 

All Manningham residents and property owners are welcome to apply.  

Applicants with direct community links, and who are actively participating in the Manningham community, or work or study in Manningham are preferred.

The CRP will be comprised of community members from a range of areas across Manningham and be generally representative of the diversity of our community.

Applicants with relevant experience, background knowledge or interest or skills in the following areas are preferred:

• water management and understanding of the water cycle
• stormwater management including storage and treatment options,
• water and the natural environment including watercourses in Manningham 
• climate change impacts, adaptation and resilience 
• water or environmental engineering 
• biodiversity and the natural environment  
• flooding in localised areas of Manningham  
• risk management 
• city planning 
• public communications and engagement   
• other relevant experience, background knowledge or interest or skills to be specified by the applicant. 

Submissions for Expressions of Interest close at midnight on Friday 29 November 2024.  

All applicants will be notified of the outcome of the Expression of Interest process by mid-January 2025. 

Expressions of Interest for the Community Reference Panel can be submitted electronically via the Your Say Manningham Flooding and Stormwater Management page, by completing the online form.

This is the second two-year term of the CRP. New panel members will be appointed for a two (2) year term commencing early in 2025. 

The CRP typically meets quarterly on Wednesday or Thursday evenings, generally for a period of two hours. Meeting dates are agreed with the CRP members in advance of each calendar year to best suit the project program and members.

The option of video conferencing will be offered to CRP members who are unable to physically attend occasional meetings, but face to face attendance at meetings is preferred. Members are expected to have access to their own IT devices to facilitate access to conferencing where necessary. 

Reasonable costs to facilitate panel member involvement are to be met by Council, where agreed up front.  

The need for Council support to meet specific panel member needs will be assessed on a case-by-case basis. 

When expressing interest in participating in the CRP, applicants are to advise of any specific requirements, to assist Council in meeting your needs.