Why is Council identifying flood affected properties?

Flooding can cause significant damage to property and risk to life.  All Councils are required by the NSW State Government to undertake studies to determine what land has the potential to be affected by flooding. This is to ensure that new developments are adequately protected and do not make flooding worse.

How do I know if my property has been identified as flood affected?

Properties identified as flood affected are coloured in blue, red or both on the Flood Planning Area Map.

On this map, blue represents the Cooks River flood planning area and is defined by a line which shows the extent of flooding. Red indicates the overland flow flood planning area on a property-by-property basis.

What does being flood affected mean for my property?

Being flood affected will only impact the property if a development application is lodged.

All properties within the Flood Planning Area are subject to an assessment of flood impacts against the criteria in Section 2.22 of the Marrickville Development Control Plan whenever a development application is lodged. This may result in flood-related development controls being applied to the development consent, for example raising floor levels or using flood resistant materials.

Why has Council reopened community consultation on its flood mapping and the planning controls (Draft Marrickville Local Environmental Plan 2011 (MLEP) Amendment No.2 and Draft Marrickville Development Control Plan 2011 (MDCP) Amendment No.2?

At its 3 March meeting, Council resolved to defer consideration of updated flood planning controls to enable further consultation.

Do I need to re-lodge a submission I made about flood-related matters again?

No. All written submissions that have already been made will be considered in the final report to Council. There is no need to make a new submission unless there is additional information.

How did Council identify flood affected properties?

Council has adopted the following criteria for identifying properties in the Flood Planning Area (FPA):

  • FPA (Cooks River): Properties flooded by the Cooks River in a 1 in 100 year storm event including future climate change impacts, which require floors to be raised 0.5 metres above the flood level; and/or
  • FPA (local overland flooding): Properties flooded in a 1 in 100 year storm event by overland flow where more than 10% of the property area is inundated and depth is greater than 0.15 metres.

For properties identified as being in the FPA (local overland flooding), each property was then reviewed to ensure it was either:

  • Exposed to water depths generally in excess of 0.3 metres in or adjacent to the property, as this may be dangerous, cause property damage or both; and/or
  • Located in the floodplain of an original watercourse (which may now be piped, channelised or diverted), or sloping areas where overland flows develop along alternative paths once the capacity of the stormwater system is exceeded; and/or
  • Located in a major overland flow path through developed areas outside of defined drainage reserves.

The review involved:

  • Updating the flood modelling where a 1 in 100 year storm event was used, instead of the probable maximum flood model applied in the original assessment;
  • Assessing all flooding to ensure it was due to overland flow impacts; and
  • Doing site inspections to gain a detailed assessment of topography or built infrastructure in or around the property (including site inspections to all properties where a property owner specifically requested one).

What is a ‘100-year flood’?

A 100-year flood is the flood that will occur or be exceeded on average once every 100 years.  It has a probability of 1% of occurring in any given year.  Some parts of Australia have received a couple of 100-year floods in one decade.  On average, if you live for 70 years in the same area, you have a better than even chance of experiencing a 100-year flood.

My property has never been flooded - why is it considered flood affected?

Floods do not occur in a regular pattern.  There may be a period of no floods and a period of several floods.  For example, the last time the Brisbane River flooded before the 2011 disaster was in 1974. Residents who moved there in more recent times may never considered flooding an issue until the floods in January 2011. Following extensive rain every water course will flood.

What method did Council use to do the flood studies?

Council undertakes its flood studies and management plans in accordance with the NSW Floodplain Development Manual. NSW Floodplain Development Manual. 

Council originally undertook flood studies using a one-dimensional flood modelling program called DRAINS. This software uses design rainfall data generated from the Bureau of Meteorology data, and information on Council’s storm water system to model flood behaviour. Flood behaviour in critical locations is refined using localised survey data.

Two-dimensional flood modelling is becoming the industry standard and more accurately models overland flow paths and produces detailed maps of flood water depths.

Council has been applying this type of modelling since 2009 using a program called TUFLOW. This software uses aerial laser survey data of the entire study area, combined with design rainfall data generated from Bureau of Meteorology data, and information on Council’s stormwater system to model flood behaviour.

Two-dimensional modelling of the Marrickville local government area is a work progress and is expected to be completed by 2019.

Where can I look at flood mapping for my property?

A plan of Council’s area showing details of two-dimensional mapping for the 1 in 100 year storm event is available here. Please note that this map shows the depth of flooding from overland flow only and is limited to properties that have been part of the two-dimensional flood modelling.

As there are properties in the Flood Planning Area (FPA) that have been identified through one-dimensional modelling and/or are at risk of flooding from the Cooks River, please refer to this map for to identify if your property is in the FPA.

I still don’t think my property is flood affected? What can I do?

Members of the public can make a written submission to Council to raise flood related issues.  All written submissions will be considered by Council and this is expected to happen at the Infrastructure, Planning and Environmental Services Committee (IPESC) meeting on 7 July. Please check the Council's website closer to the time to confirm that the relevant business paper is on the agenda of the IPESC meeting.

Members of the public may speak on agenda items provided they give written notice to the General Manager before 12 noon on the day of the meeting. More information about this can be found here.

The floor levels in my property are above the flood level - why has it been identified as flood affected?

Properties can be identified as being flood affected, in accordance with the Council’s policy, regardless of the floor levels in the building. This is to ensure any future developments of the property are appropriate for the Flood Planning Area and not built below the flood level.

Property owners can seek flood level information about their property from Council. This information may be used with surveyed floor levels to confirm that properties floor levels are above the Flood Planning Level for insurance purposes.

How can I get a Section 149 Certificate for my property?

Section 149 Planning Certificates are issued in accordance with the Environmental Planning & Assessment Act 1979. They contain information on how a property may be used and the restrictions on development, including information whether a property is flood affected. For enquiries related to Section 149 certificates, please contact Kendall Banfield on, Team Leader, Planning Services on 9335 2179.

Will I have to undertake a flood study when I want to develop my land?

It depends on the scale of the development. This is not typically required for single residences.

Will being flood affected impact the value of my property?

There are many factors that can affect the value of any property including inflation, a change in interest rates, increased aircraft noise or construction of a new road or shopping centre nearby.  The extent to which a property’s value is affected once it has been identified as flood affected is impossible to determine.  While the notification may affect one potential buyer’s decision to purchase a property it may have no impact for another.  Ultimately, it is the market that determines the value. 

Will being flood affected increase my property insurance?

Council is not in a position to advise you on this matter. Your policy is a matter between you and your insurer so you will need to discuss this with them directly. 

Does Council have records of past flooding of my property?

Council does not retain specific flood records for individual properties, as it would be technically and financially impractical to collect this data. The flood modelling used to determine flood behaviour is based on the probability methods in the Floodplain Development Manual. Although a site may not have flooded in recent history, it may still be considered flood affected.

When was the last flood in the area?

The last large flood on the Cooks River was in November 1961 which was almost the size of a 100-year flood event. Small floods occur every few years including the events on the 8th March 2012 and the 14th October 2014 which were less than 1 in 5 year storm events.

What about flooding problems in my street that happen all the time?

Development over the past 100 years has left many areas with a legacy of undersized infrastructure which cannot adequately carry water from minor storms. This results in flooding of public and, in some cases private, property. Council undertakes upgrades of its piped stormwater system on a priority basis across the local government area as funding allows.

The current studies are the first stage of addressing the flood problem.  Management and mitigation measures will be considered in the next stage.

Why can’t council fix all flooding?

Council’s piped stormwater system is designed to convey minor storms with the aim of reducing day-to-day nuisance flooding, while major storms are conveyed via overland flow paths with the aim of protecting life and property in major events. This major/minor principle is standard industry practice, as it is impractical to provide piped drainage systems for major storm events.

What about climate change and sea level rise?

Council’s flood studies investigated the impact of potential sea level rise and rainfall increase on flood levels. It has adopted a climate change induced sea level rise of a 0.4 metre rise by the year 2050 for its flood modelling. This is aligned with the NSW Government's Sea Level Rise Policy Statement 2009 and the Coastal Planning Guidelines 2010.