How does 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 need to be reviewed over time?

There’s a chance that floods of any size will occur in future. As the size of a flood increases, the chances of it occurring becomes smaller. Some rare types of floods may not have occurred for over 100 years, so we have to predict the height of future floods using computer models. These models produce different flood levels and velocities (speeds) for a variety of different-sized floods. To predict flood levels, Council works with experts to establish and operate the computer models. Council also gets valuable community input on historical floods so we can adjust the model and make sure it copies what’s happened in the past.

From time to time, these models are reviewed and predicted levels may change. The reasons why can include:
  • New floods occur, providing additional data to fine-tune the model
  • More advanced computer models or methods for estimating flood levels become available
  • Changes in the catchment, such as flood mitigation works or new developments
  • Changes in policy (such as Council's culvert Blockage Policy)

How are flood affected properties identified?

Council’s flood modelling shows 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 has changed in the updated Wollongong City Flood Study?

  • We’ve considered Council's revised Blockage Policy 
  • We have improved information, such as recent data from land and waterway surveying
  • The new flood model was checked against the June 2016 and March 2017 events and was able to produce the same flood levels recorded by the community
  • The pedestrian bridge across the waterway is modelled as being partly blocked, in line with the updated Blockage Policy 
  • We’ve considered the upcoming lowering of the Gurungaty causeway
  • The increase in mangrove growth over the last 10 years has been included 
The combination of all these changes generally resulted in similar flood levels in some areas, decrease of flood levels in the upper part of the catchment and increase in flood levels mainly in South Wollongong (up to 0.2m).

What does the Study say about flooding in South Wollongong?

We’ve aimed to respond to residents’ concerns about the floods experienced over the last 5 years in South Wollongong. We’ve found that: 
  • There has been an increase in intense rainfalls that are causing the floods
  • The changes in Gurungaty waterway have only minor impacts
  • The volume of wet weather sewer overflows is relatively small and results from stormwater flows from within the catchment. Wet weather sewer overflows are not considered to be a contributing factor to the flooding issues at Swan Street and adjoining streets. 
  • Sea levels can impact on flooding in the area, as stormwater takes longer to drain out to sea from low-lying coastal areas in high tides
  • New developments do not increase flows to this area
The study recommends investigating in more detail the potential impacts of wet-weather sewer overflows and changes in the Gurungaty waterway as part of the floodplain risk management study, which is the next step in our floodplain risk management process.

What other flood mitigation work is Council doing in this catchment?

The detailed design to lower the Gurungaty Causeway is finished and work will start shortly. This will help reduce flood impacts in Swan St for smaller flood events.

We’ve finished constructing a floodway through JJ Kelly Park that stores additional run-off in mid-sized storms and helps floodwaters drain away faster in larger storm events. We’re also working on a study to see if it’s possible to lower the ground at JJ Kelly Park so it temporarily stores run-off. We’ve completed soil sampling, lab testing and initial designs. We’re now working on a Cost Benefit Analysis to compare the costs of the project with its benefits. If achievable, it could help reduce flood impacts in Swan St for smaller flood events. 

We’ve completed detailed design on maintenance access for the culvert in Swan St opposite Church St. A culvert is a tunnel or drain structure built under roads, bridges and railways, to allow water to flow underneath. We’re also working on a proposal to improve maintenance access to the culvert in Swan St, opposite Kembla St, which is currently limited due to a high pressure pipeline. These improvements will help the culverts work more efficiently in small floods. Works on the culvert access opposite Church St will start later this year.