We identified approximately 5,800 properties at risk of flash flooding during rare rainfall events. We have notified all properties that have been identified as at risk.
If your property was identified in the study, you need to submit your plans for flood level approval for all building, renovation and addition works.
We will assess your plans and tell you about any changes you need to make to reduce your flood risk. If you are unsure if your property was identified in the study, contact us on 9278 4444, or email [email protected]
Melbourne Water overlays
The type of flooding the study looked at is known as overland stormwater flow. This type of flooding is usually as a result of high intensity bursts of rainfall. They may happen with very little warning. In these events, the drainage network becomes overwhelmed and stormwater moves overland and onto streets and properties.
Depending on the location of the property, this type of flooding may be our responsibility, or the responsibility of Melbourne Water. The areas under the authority of Melbourne Water are included in the Boroondara Planning Scheme as a Special Building Overlay (SBO). They are included as a result of flood modelling completed by Melbourne Water.
Overland stormwater flow is different to floodplain flooding that rises up from rivers and creeks. Areas that are at risk from rivers, creeks and open channels have been identified by Melbourne Water. They are included in the Boroondara Planning Scheme as a Land Subject to Inundation Overlay (LSIO).
If your property is in any of these overlays, you need to get flood advice from Melbourne Water instead.
To find out if your property is in a Melbourne Water overlay, visit VicPlan and search for your property address.
Step 1: before you plan works
If you are thinking of building or renovating on flood prone land, you should request free flood advice before you draw up your plans.
We will tell you general information about the flood risk to your property. We will also tell you the requirements your designs need to meet, which will help you make an informed decision about your plans.
General flood advice includes:
- a map showing the extent of the expected flooding
- a description of the expected flooding
- comments on potential impacts on existing buildings and works on the property
- comments on potential impacts on future development of the property.
To request flood advice, you can:
- call us on 9278 4444, or
- email us at [email protected]
Step 2: submit plans for flood level approval
After your plans are drawn up, you need to submit them to us for flood level approval.
You may be told to request flood level approval in any of the following situations:
- You have submitted a planning or building enquiry, and we have told you that the property is likely to be affected by flooding.
- We advised you that the property is likely to be affected by flooding via the building or planning process.
- You have requested a Property Information Statement, or property plans and reports for a property that is likely to be affected by flooding.
- A professional consultant, such as an architect, builder, or building surveyor, has advised you to submit the request.
- It is a condition in your Planning Permit.
- We advised you in your legal point of discharge certificate to submit the request.
- A Report and Consent matter affects your proposal.
Documents required for submission
To request flood level approval, include the following documents in your submission:
- Survey plan showing levels for the footpath, naturestrip, kerb and channel and drainage pits
- Floor plans of the proposed development showing ground and basement levels, vehicle and pedestrian entries, as well as any other possible entry of flood water into the building.
The assessment fee is $250.00. The fee does not incur GST.
Request approval online
Step 3: we assess the plans
We will assess your plans and tell you about any changes you need to make to reduce the risk of flooding.
We may request more information, including evidence that the proposed works do not negatively affect the flood behaviour outside the property boundaries.
Our assessment will make sure that the property is:
- built with a finished floor level above the relevant flood level (the approximate height of the floodwater), plus 300 mm additional height (freeboard)
- appropriately set back from overland flow paths (the paths that take the main flow of floodwater).
Step 4: flood levels are approved
We will send you a confirmation letter within 20 business days. We will tell you which version of the plans have been approved for addressing the flood risk.
If a Report and Consent matter affects your proposal, you still need to apply for Report and Consent to build in a flood-prone area.
If you make any further changes to the finished floor levels, you need to resubmit your plans for reassessment.
Send the revised plans via email to [email protected].
About the Flood Mapping Study
It is typical industry standard practice to design buildings and infrastructure for an extreme rainfall event. This extreme event is normally the 1% Annual exceedance probability (AEP) flood event. It refers to an infrequent, high-intensity storm that has a 1% statistical probability of being exceeded in any one year. It was previously referred to as a 1 in 100 year Average Recurrence Interval (ARI) event.
The major design flood for the majority of works within the City of Boroondara is the 1% AEP event. This is the design event that private developments need to build to, so as to meet Victorian Building Regulations. Therefore, the flood mapping and advice we give is for the 1% AEP event. If your project needs a different design event (as a specific project requirement), please contact us to discuss what information we can provide to assist you.
Purpose of the Flood Mapping Study
As is typical practice throughout Australia, the drainage system in Boroondara is designed to handle minor storm events. This is normally the 20% or 10% AEP storm, depending on the location and age of the infrastructure. This is because it is not practical or cost effective to build infrastructure that can only handle less frequent events.
The Flood Mapping Study helps us understand the behaviour of stormwater flow along overland flow paths when the drainage system is over capacity.
As a result of the study, we can advise property owners on how to reduce their flood risk, and the flood risk to surrounding properties.