Frequently Asked Questions About Planning Schemes
- What is Melbourne Water’s role in planning schemes?
- What is an overlay?
- What is an overland flow path?
- What is the 1 in 100 year flood event?
- Why has a 1 in 100 year drainage standard been adopted?
- How can a property be considered subject to flooding when it has never flooded?
- Can you still build if your property floods?
- If your property is only partially affected, would you need a permit for buildings or works outside the area covered by the overlay?
- If the proposed amendment affects your property, can you comment?
- Has placing this information in the planning scheme affected property values?
- Will this information stop redevelopment of your property?
- Why is this information being provided? What are the benefits?
- Why does this information have to be included in the planning scheme?
- Why do we need information on the drainage system?
- Is Melbourne's drainage system adequate?
- Why don't the drainage authorities upgrade the drainage system to meet the needs of new developments?
1. What is Melbourne Water’s role in planning schemes?
Melbourne Water is a referral authority in the planning system under Section 55 of the Planning and Environment Act 1989. We receive applications for subdivisions and other developments from councils. This allows us to comment on applications and if necessary, place conditions on town planning permits. These ensure that the drainage system and the new developments are adequately designed to protect occupants and to ensure that the drainage system functions appropriately.
2. What is an overlay?
3. What is an overland flow path?
An overland flow path is an above-ground component of the drainage system. Overland flows occur when underground drainage pipes reach their capacity and cannot cope with more run-off from heavy rainfall. The excess run-off then travels overland, following low-lying, natural drainage paths.
4. What is the 1 in 100 year flood event?
The 1 in 100 year flood event is the storm that happens on average once every one hundred years (or a 1% chance of occurring in any given year). Melbourne Water requires that any new development is protected in the 1 in 100 year flood event.
5. Why has a 1 in 100 year drainage standard been adopted?
This standard has been adopted as it is considered an appropriate balance between the likelihood of occurrence and the consequences of flooding for most developments. In some special cases higher standards may be applied. For example proposed essential services like hospitals, which need to function continuously during emergencies, may need to be protected from 500 year events.
It is a commonly used international drainage standard, and has been applied in Melbourne since the late 1970s. The standard, correctly referred to as the 100-year Average Recurrence Interval (ARI) is a statistical estimate of the average period (in years) between the occurrence of floods of this magnitude or larger. It is also sometimes expressed as a probability, such as "there is a 1% chance in any one year of such an event occurring".
Melbourne Water uses the 100-year ARI standard to define the extent of the overland flow along the drainage system or along rivers or watercourses, to quote flood levels for example in flood warnings and to assess development application.
6. How can a property be considered subject to flooding when it has never flooded?
It cannot be assumed that flooding has not previously or will not occur at a property simply because there are no recollections of flooding at that property. The overlays are based upon the extent of flooding that would result from a 1 in 100 year storm.
7. Can you still build if your property floods?
If your property is in an area subject to flooding, your development must be designed to ensure that buildings are protected and any impact on neighbouring properties is minimised.
8. If your property is only partially affected, would you need a permit for buildings or works outside the area covered by the overlay?
The requirements of the overlay only apply to buildings and works proposed within the area covered by the overlay and where it is necessary for the relevant council and Melbourne Water to manage development to minimise the effects of overland flows and flooding on new buildings and ensure new development does not adversely affect other existing properties.
9. If the proposed amendment affects your property, can you comment?
Yes, you will be able to comment while the amendment is on exhibition. The amendment documentation and associated maps can be viewed at the relevant council office and on their website. Comments on the amendment must be lodged in writing.
For further information on the planning scheme amendment process, please contact your local council.
10. Has placing this information in the planning scheme affected property values?
Property values are determined by the market, taking into account a whole range of factors. The information obtained by Melbourne Water through its investigations is used to identify whether there may be special building requirements to be addressed in relation to any development proposed for that property. The information enables informed and responsible development to occur.
It is important to note that identifying the drainage information has not changed the likelihood of a severe storm occurring or the potential of the drainage system to cope with a severe storm.
11. Will this information stop redevelopment of your property?
Generally not. It will only be used to ensure than any redevelopment is planned in a way that recognises the location of the overland flow path and any public health and safety risks.
12. Why is this information being provided? What are the benefits?
The drainage information identified by Melbourne Water is used to provide a better planning framework. This will lead to greater awareness of the impact of severe storms upon people and property and, therefore, to better planning and development decisions to minimise these impacts.
13. Why does this information have to be included in the planning scheme?
By including the information in the planning scheme, owners considering development have immediate access to necessary information about the drainage of a property very early in the development process. Information will also appear on planning certificates.
14. Why do we need information on the drainage system?
Information on the drainage system is required to enable Melbourne Water to provide local councils with technical advice to ensure responsible decisions are made regarding urban development. This information is increasingly required as redevelopment in existing areas increases to accommodate population growth through dual occupancy and unit/town house development in the suburbs.
15. Is Melbourne's drainage system adequate?
Melbourne Water has a program in place to regularly monitor the condition of the drainage system to ensure it remains in good condition. We invest $16 million a year on inspections, maintenance and drainage upgrade projects, which are prioritised following surveys and inspections.
However, from time to time, storms occur of such intensity or duration that the stormwater run-off exceeds the capacity of the drainage system, causing overland flows. It would cost the community billions of dollars to upgrade the existing drainage system to cater for these very large but infrequent storms, as well as causing significant disruption and inconvenience. The most practical and equitable solution is to ensure redevelopment in existing areas addresses the overland flow issues. Today, new developments and redevelopments incorporate stormwater management measures that provide greater flood protection. However, when there are recurring local problems with the drainage system, Melbourne Water has a capital works program in place to address these local issues.
16. Why don't the drainage authorities upgrade the drainage system to meet the needs of new developments?
For established urban areas, it would cost the community billions of dollars to mitigate the effects of overland flows, and this could only be undertaken incrementally over a period of many years. As part of its capital works program, Melbourne Water allocates funds to drainage improvement works. These works are identified through the drainage survey program and prioritised according to frequency and severity of flooding and maximum community benefit.