FAQs about floodplain management

• What's changed since the last FRMS&P?

• Our most recent FRMS&P for this catchment area was completed in 2016. While this is still relatively recent, significant changes have been made to the Australian standards for flood estimation. Additionally, new developments and changes in land use across the catchment area are likely to have affected local flooding patterns.

  Therefore, a new hydraulic model has been created for this study. The main changes in the new model are:

  • Incorporation of the ARR2019 methodology;
  • Extension of the model boundary to include more of the catchment area;
  • Updates with recent terrain and bathymetric survey; and,
  • Conversion of the model from SOBEK to TUFLOW.

  Further details of the model updates and revisions are provided in Appendix B of the FRMS&P.

• Why did Council develop this FRMS&P?

• We know the catchment area is subject to flooding, which has negative effects on both the community and infrastructure.

  This study & plan identifies actions that Council, SES and the community can take to reduce flood risk.

• What's in the FRMS&P?

• The Floodplain Risk Management Study carefully looks at the risk of flooding in the Elliott Lake - Little Lake catchment area. We checked how floods might affect homes, businesses and public infrastructure like parks and roads, and we also studied what to do in case of a flood.

  We considered different ways to reduce this flood risk and ranked them based on various factors. The best options, considering things like cost or how well they work, are presented in the Floodplain Risk Management Plan. We've sorted them by how easy they are to do, how much they cost, any limitations, and how well they work.

  Options that are cost-effective, easy to deliver and effective in preventing damage or danger are our top priorities.

• What mitigation measures are in the plan?

• There are three broad categories of flood risk mitigation:

  1. Flood modification measures - options which aim to modify the movement of flood water
  2. Property modification measures - options focused on protecting existing properties and putting planning controls in place for future development
  3. Emergency response modification measures - options focused on how to respond to a flood event when it does happen

  Further details on our recommended mitigation measures are provided in Section 3 of the Plan (page 153).

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

• Flood behaviour, including flood levels, velocities and hazard is calculated using detailed computer models to simulate floods of varying magnitudes. These models may be reviewed periodically when:

  • new data becomes available from new flood events
  • flood mitigation works are undertaken
  • developments occur, and
  • more advanced computer models become available.

FAQs for those who live and work within the catchment area

• How can I get detailed flood information for my property?

• If your property is flood affected and your require flood levels and velocities for your property, this can be provided upon request to help manage your property risk and inform the design of your development proposal.

  You can lodge a Flooding Requirement Certificate request via our website.

• My property was never classified as 'flood prone' or 'flood liable' before. Why is it now classified as flood affected?

• Many parts of Shellharbour City have little or no flood data or records available at Council. Over time as new data is received and new flood studies are adopted by Council, more flood liable land will be identified and mapped accordingly.

  If your property is now classified as flood affected, the real world flood risks to your property are not likely to have changed; only that new information has been made available.

• Will my property value be altered if my house is flood affected?

• Council's floodplain management program has been active for more than 20 years. A flood study for the Elliott Lake - Little Lake catchment area was first adopted in 2006, and residents expressed concerns at this time about possible impacts on property values. However, no evidence has been presented to Council indicating any negative effects on property values or development in these areas.

• Will I be able to get house and contents insurance if my property is flood affected?

• Many insurance companies will offer house and contents insurance, with each individual insurance company determining their own policy and conditions. Insurance companies each have their own distinctive ways in which they calculate risk and determine insurance policy premiums. You can check your policy wording and talk to your insurer to clarify what you're covered for.

  Learn a little more about flood insurance here or check out Floodplain Management Australia's flood insurance fact sheets to assist in understanding this process.

• If my property is identified as flood prone what development controls are likely to apply?

• A Local Environment Plan (LEP) is a legal document which allows Council to regulate land use and development. They are prepared by Council and approved by the State Government.

  A Development Control Plan (DCP) provides detailed planning and design guidelines to support the planning controls in the LEP. Sections of Council's DCP provides criteria for assessing applications for properties potentially affected by flooding. The above documents can be viewed on Council's website.

• How does Council maintain its stormwater drainage network?

• Council owns and manages a significant number of stormwater pits, pipes, channels, culverts, basins and Gross Pollutant traps throughout the city and we are committed to maintaining this infrastructure within the limits that current funding and resources permit.

  Council has an annual budget for cleaning and maintaining this infrastructure, as well as a budget for Capital Works (upgrading and building new infrastructure). All works are scheduled on a priority basis, where those works that are most critical become highest priority.

• Why doesn't Council remove the vegetation that clogs up creeks and waterways?

• Unless identified within an adopted Floodplain Risk Management Study & Plan, the flood impacts associated with the removal of vegetation from creeks and waterways is relatively unknown. For example, carrying out such works may have little to no benefit in reducing flood risks. Alternatively, such works could reduce the flood risks in one area, whilst increasing it in other areas. These issues are considered in the context of a Floodplain Risk Management Study.

  Removing vegetation in creeks and waterways is often raised by the community as a solution to flooding. However, it has an important role to play and can often help mitigate potential damage during floods. It does this by:

  • Stabilising the banks of creeks and waterways, reducing erosion during high flows
  • Slowing down the flow of water, making it less dangerous
  • Healthy vegetation helps absorb water and reduces surface runoff
  • Trapping sediment, debris and pollution, stopping it from entering our Ocean or causing further issues downstream
  • Creating an overall healthier ecosystem which can bounce back faster after a flood event

  The removal of vegetation won’t stop flooding, it will just move the water somewhere else. What might look like a solution to you can end up having worse consequences for your neighbour.
  

  It should be noted that maintenance of watercourses on private property are the responsibility of the landowner, not Council.

Glossary of Terms

• What is the Defined Flood Event (DFE)?

• The Defined Flood Event (DFE) is the flood event selected as the general standard for managing flood risk to development. Selecting a DFE aims to reduce the frequency of flooding but does not remove all flood risk.

  Council uses the 1% AEP flood level and the projected impacts of climate change to determine the DFE.

• What is the 1% AEP flood event (100-year-flood)?

• A 1% AEP (Annual Exceedance Probability) flood event, also known as a 100-year flood, refers to a flood that has a 1% chance of occurring in any given year. This doesn't mean it happens once every 100 years; rather, it means there's a 1 in 100 chance of it happening in any year. It's a way to express the likelihood of a significant flood occurring and is used for planning and managing flood risks.

  On average, if you live to be 70 years old, you have a better than even chance of experiencing a 1% AEP flood event.

• What is the Probable Maximum Flood (PMF)?

• The Probable Maximum Flood (PMF) is the biggest possible flood that could conceivably happen. It's estimated by looking at the heaviest possible rainfall and the worst conditions within the catchment that could cause a flood. Although this kind of flood is very rare, any property that could be affected by it is considered to be on a floodplain and has some risk of flooding.

  According to the State Government's Flood Risk Management Manual (2023), all land which falls below the PMF level is technically classified as ‘flood prone’.

• What is the Flood Planning Level (FPL)?

• The Flood Planning Level (FPL) is a specific height above which new buildings and other infrastructure must be constructed to reduce the risk of flood damage.

  It is calculated by using the DFE plus an additional freeboard for extra safety. Freeboard is added to account for uncertainties like wave action, debris and other factors that affect flood levels.

  The Flood Planning Level (FPL) is used to determine the Flood Planning Area (FPA).

• What is the Flood Planning Area (FPA)?

• The FPA is the area within which developments may be subject to flood related controls.

  The FPA is calculated as the areas which fall below the Flood Planning Level (FPL).

• What does Australian Height Datum (AHD) mean?

• Australian Height Datum (AHD) is a reference to the elevation of any object or point above mean sea level, which is taken as 0m AHD. All flood levels, floor levels and ground levels are given in metres AHD.