How does Wollongong City Council manage flood risk?

Each year, Council spends millions of dollars on stormwater and floodplain management. Our team of flood experts prepare flood studies and floodplain risk management studies that help us understand the flood behaviour for a particular catchment and see if there are any ways of reducing flooding risk in an area. 

Floodplain risk management studies  include a plan of potential solutions aimed at reducing the existing and future flood risk. Examples of these solutions include: 
  • emergency response plans based on detailed understanding of flood behaviour
  • building new structures that collect and carry stormwater into drains or creeks, such as detention basins and swales, or improving existing ones to better manage stormwater and floods 
  • land zoning that says what can and can’t be built on flood-prone land
  • voluntary purchase of houses built in high flood risk areas

Why do flood levels and information need to be reviewed over time?

There is a chance that floods of any size will occur in the future. As the size of a flood increases, the chances of it occurring becomes smaller. Because some rare types of floods have not occurred for over a century, the height of future floods is predicted using computer models. These models simulate different flood levels and velocities for a variety of different sized floods.

Given the importance of accurately predicting flood levels and information, Council engages experts to establish and operate these computer models. From time to time, computer models are reviewed, and predicted flood levels may change slightly. The reason why the models are revised can include:
  • New floods occur, providing additional data to fine-tune the model 
  • Flood mitigation works undertaken may change flood levels
  • More advanced computer models become available
  • Development within the floodplain (which may be outside Council’s control)

How are flood affected properties identified?

Council’s flood modelling figures out the size of flooding throughout the catchment and which properties are partially or fully impacted by flooding. 

Where can I get information about flood levels on my property?

Council has historical flood level records and/or our completed flood studies for some properties, but not all. Please contact our Drainage Duty Officer on (02) 4227 7111 to find out what’s available for your property.

What is a “1 in 100 year” flood?

A flood event that has the probability of occurring on average once every 100 years, i.e. there is a 1% chance of a flood of this size occurring at a particular location in any given year. This doesn’t mean that if a location floods one year, that it won’t flood again for the next 99 years. Nor, if it hasn’t flooded for 99 years, that it will necessarily flood the next year. Some parts of Australia have experienced more than one “1 in 100 year” floods within a decade of each other. Within the Floodplain Risk Management Study and Plan, the “1 in 100 year” flood is called the 1% AEP flood event.

What is the Flood Planning Area?

The area within which developments may be conditioned with flood-related development controls. The flood planning area is calculated as the area below the Flood Planning Level.

What is the Flood Planning Level?

The height used to set floor levels for property development in flood prone areas. It is generally the 1% AEP flood level plus an appropriate freeboard. This level may be higher for vulnerable land uses. Vulnerable land uses are those that are occupied by people that have less capacity to respond to flooding, which may pose evacuation challenges, e.g. hospitals or schools.

What is a Freeboard?

A height above the 1% AEP flood level that is included in the Flood Planning Level to account for factors such as wind, waves, unforeseen blockages, other localised hydraulic effects. Freeboard is usually 0.5m above a flood level.

What should I do in the event of a flood?

If the situation is life threatening, you should call 000. For other assistance during an emergency such as flood, storm or tsunami, please contact the NSW State Emergency Service (SES) on 132 500 or visit www.ses.nsw.gov.au It’s best to be prepared for any flood. The SES provides advice on how to prepare at www.floodsafe.com.au

Be safe around floodwater. It’s dangerous and full of nasty stuff like chemicals and sewerage, so don’t play in or try to drive through it. 

Why does Council study flooding?

Councils in NSW are responsible for managing flood risk and keeping the community informed. Councils follow the NSW Flood Prone Land Policy, which outlines how Councils should manage flooding to reduce the risk to people and properties.

What is the difference between a Flood Study and a Flood Risk Management Study and Plan?

A Flood Study looks at the flood behaviour for a particular catchment (which might be a river or creek). Council’s flood studies help to understand existing flooding behaviour and see if there are any ways of minimising or reducing flooding risk in an area. 

A floodplain risk management study and plan analyses flood behaviour, then details options that can help protect people and property through better planning, emergency management and infrastructure works. 

What can I do around my yard to help keep watercourses clean?

  • Be careful not to dispose of grass clippings and other garden cuttings in or near watercourses and remove any obstructions that may cause blockages or divert flood waters. 
  • Be aware of any drainage easements or overflow paths that affect your property. Seek Council approval before altering your driveway or footpath levels, as this may cause water to flow off the road and down your driveway.
  • Take care when planting trees near drainage pipes. Certain species with aggressive root systems e.g. Jacaranda, Poplar, Willow, Fig, Camphor Laurel and Rubber Trees can cause pipes to become blocked or cracked. 
  • Don’t lay any pipes, construct a bridge or divert a watercourse without first consulting Council. Unapproved work can increase flooding for both you and your neighbours. 
  • Don’t fill low-lying areas of your yard without seeking Council approval, as this may cause water to pond and increase flooding potential on your and your neighbours’ properties. 
  • Keep drainage inlets on your property clear of any rubbish or blockages. Remember, large paved areas will increase runoff, so you may need extra drainage. 

How can I join the conversation?

There are a number of ways to ask questions or share your 
feedback with us: