Why is the Flood Study being updated and what’s changed?

We use computer flood models to estimate where it might flood, and by how much. From time to time, the models are updated and predicted flood levels may change. For the Allans Creek Flood Study, we’ve considered Council's revised Blockage Policy, which helps us work out how blocked stormwater structures might affect flooding. We have improved information, such as recent data from land and waterway surveying. We've included an extended network of drainage pits and pipes and used more improved and detailed modelling techniques. We’ve also extended the mapping to capture additional flood-prone areas and waterways that were not previously mapped.

In many areas, the updated flood levels are lower than or comparable to the 2008 flood levels, however there are some areas where the levels have increased. The updated Blockage Policy generally gives us lower flood levels upstream of main culverts. A culvert is a tunnel or drain structure built under a road or railway to allow water to flow underneath. The maps in the report show what the flood levels are in different areas in the catchment. You can view the report on our website, at the drop-in information sessions, or at Unanderra or Wollongong Libraries.

What about historical floods?

The Allans Creek catchment has experienced several significant floods over the past decades. The1998 and 1999 events in particular caused significant disruption and damage to public and private property. The 1998 flood in this area was not as big as a 1% Annual Exceedance Probability (AEP) flood, which explains why residents in some areas mapped as flood affected may not have experienced flooding. A 1% AEP flood is extreme. There is a 1% chance of a flood of this size or larger occurring at a particular location in any given year.

What happens next?

After we’ve completed the flood study, we’ll review the Floodplain Risk Management Study to look at what the risks/damages from floods might be and what we could do to mitigate (reduce) those risks. Next, we’ll review the Floodplain Risk Management Plan, to give us a prioritised plan of flood mitigation measures proposed for the catchment. Then we’ll roll out the Plan! Every 5-10 years, we go back to the beginning of this process and start with a review of the flood study to consider new survey data, policy changes, recent major flood events and changes in the catchment such as flood mitigation works or new development.

What flood mitigation work is Council doing in this catchment?

We’ve purchased nine houses that were identified in the Allans Creek Floodplain Risk Management Study and Plan for Voluntary Purchase, as they were at high risk of serious flooding and not safe to live in. Houses we buy as part of the Voluntary Purchase Scheme are knocked down and the land is turned into parks and open space.

We’re progressing the detailed design of structures that will help stop debris from blocking a drain at The Avenue, Figtree (next to Figtree RSL Bowling Club), with construction expected in the next 2 years.

We’ve done weed control, work to maintain creek banks and planting at various locations along Council-owned portions of creeks throughout the catchment. We’ve also done some work to protect the creek bed and bank at Charcoal Creek, downstream of Blackman Parade, Unanderra.

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 Customer Service team on (02) 4227 7111 or email council@wollongong.nsw.gov.au to find out what’s available for your property.

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 doesn’t Council clear out creeks?

Council is responsible for maintaining watercourses (e.g. creeks, overflow paths or drainpipes) on Council-owned land and has a maintenance program for this. Most watercourses in our city are on private property and their maintenance is the responsibility of the land owner. In these cases, Council is unable to perform any work on the watercourse. If you need advice on maintaining watercourses, please contact our Customer Service team on (02) 4227 7111 or email council@wollongong.nsw.gov.au.

Why aren’t you using Australian Rainfall and Runoff 2016 guidelines for this Flood Study?

For the last 30 years, councils have used the national guideline Australian Rainfall and Runoff (ARR) 1987 for flood estimation. A new version was released in 2016, but it uses data that isn't relevant to our region, so we get modelling results that don’t match flood events that have already happened. With our region’s history of floods, we have a responsibility to make sure the data we use is relevant to our area, so that we get reasonable results. We're working to resolve the issues, but until then, we'll continue to use ARR1987, which has been improved and fined-tuned to our area over the last 30 years.

How will my feedback be used?

At the conclusion of the engagement period, all feedback is read and considered. A report will be produced and provided to Councillors, and they will consider whether to adopt the Flood Study.

How can I join the conversation?

Write: Locked Bag 8821, Wollongong DC 2500 

Phone: (02) 4227 7111

Drop-in Information Sessions:
  • Figtree Community Hall, 11 Princes Highway, Figtree
    Wednesday 7 August 4pm - 5:30pm
  • Berkeley Community Centre, Winnima Way, Berkeley 
    Saturday 10 August 10:30am - noon
You can also submit feedback via the online form.