We are in the process of reviewing and updating the Floodplain Risk Management Study and Plan for the Horsley Creek catchment. We know the catchment is subject to flood risk and inundation so we are committed to investigating solutions to reduce the impact of flooding.

The Horsley Creek catchment is located on the southern side of Lake Illawarra and mainly includes the suburb of Albion Park Rail and part of Oak Flats. The catchment has a combined area of 9.25km2, draining from the quarries in the south of the catchment into Koona Bay and Lake Illawarra at Horsley Inlet. The northern half of the catchment is largely covered by residential and light industrial development. The southern half of the catchment contains two large hard rock quarry operations. The buffer areas surrounding the quarries are currently used for cattle and horse grazing.

It is intended the updated Horsley Creek Floodplain Risk Management Study and Plan will include a program of flood management options and initiatives for Council and emergency services to implement in the study area.



Why this project is happening:

Council, with the assistance of NSW Department of Planning and Environment (DPE), adopted a flood risk management study and plan for this area in 2017. The previous study identified the behaviour of floodwaters within the catchment, gave Council detailed information on flood risk and identified actions that Council, SES and the community can take to reduce flood risk.

The March 2011 flood event was the most significant flood in living memory in the catchment and Council has collected a lot of data from this event. But your help is needed in collecting additional flood data.

What has happened to date:

Consideration and planning around putting in place some of the flood mitigation measures recommended in the 2017 study are ongoing as part of Council’s Floodplain Management Program. We have done a number of things from this plan already, this includes:

  • Flood-related development controls have been updated in Council’s Development Control Plan (DCP)
  • NSW State Emergency Services has been provided with updated emergency response plans.
  • Investigation and concept design of a proposed detention basin at Oak Flats interchange.
  • Flood information on Council’s website has been updated.
  • Development and implementation of a flood education and awareness program for the community.
  • Stormwater network upgrade works.

Since the completion of the previous study, a number of other significant developments have happened within the catchment. These include the construction of the Albion Park Rail Bypass which involved modification to the Green Meadows detention basin and creation of a basin at Croome Road.

Who is involved in this plan:

Council successfully applied for grant funding from the State Government to undertake this review of the Floodplain Risk Management Study and Plan. It will revisit the proposed flood risk management measures in light of the changes mentioned above and provide updated flood information for Council in accordance with current industry best practice.

The project is being managed by Council, with financial and technical assistance provided by DPE. The project is being steered by the Flood Risk Management Committee of Council.

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The PMF is the largest flood that could conceivably occur. It is typically estimated from probable maximum precipitation coupled with the worst flood producing catchment conditions. While it is a rare and improbable occurrence, every property potentially affected by a PMF is considered to be on a floodplain and has some element of flood risk. Under the State Government's Floodplain Development Manual (2005), councils must consider the full range of risk when managing floodplains.

A 1% AEP flood event (often referred to as the 100-year flood) is the flood that has a 1% probability of occurring in any given year. If you have experienced a 1% AEP flood event, it is still quite possible for you to experience another event of similar magnitude within your lifetime, as large flood events do occur randomly. Some parts of Australia have received two or three 1% AEP flood events within a few years of one another. On average, if you live to be 70 years old, you have a greater than 50% chance of experiencing a 1% AEP flood event.

Australian Height Datum is a reference of 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 meters AHD.

In 2005 the New South Wales Government put forward the updated Floodplain Development Manual which outlined the required method for councils to manage flood liable land. A key objective in this manual is to undertake flood studies for appropriate catchments to provide detailed information on flood behaviour.

Council has completed a number of Flood Studies and Flood Plain Risk Management Studies. The adopted studies are available on Council's website. If your property is flood affected and you require flood levels and velocities for your property, you can submit a request for flood level information to Council. Council will then provide you with property specific flood information letter that can be used to manage your risk and inform the design of your development proposal.

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.

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. Also, under changes to the NSW Government's Floodplain Development Manual in 2005, flood liable land became inclusive of land that is affected by the Probable Maximum Flood (PMF). Before this only land inundated by the 100-year flood level was considered.

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

No evidence has been presented to Council to suggest that there have been negative impacts on property values or development in study areas. Councils floodplain management program has been ongoing now for more than 15 years. Council first adopted a flood study for Lake Illawarra in 2001. A flood study was adopted for Elliot Lake Little Lake in 2006 and again for Horsley Creek in 2011. Concerns over effects on property values were raised from residents in these catchments prior to adoption by Council.

In 2012, a standard definition of flood was agreed upon by the Insurance industry. This is now known as:

The covering of normally dry land by water that has escaped or been released from

the normal confines of:

• any lake, or any river, creek or other natural watercourse, whether or not altered or

modified; or

• any reservoir, canal, or dam.

However, Insurance companies each have their own distinctive ways in which they calculate risk and determine insurance policy premiums. Many insurance companies will offer house and contents insurance, with each individual insurance company determining their own policy and conditions.

Flood insurance premiums generally reflect the level of flood risk at a property and the cost of repairing or rebuilding the property. In practice, this can be broken down to three factors which would be assessed by all insurers when setting a flood premium for a property:

  • Likelihood of flooding;
  • Expected depth of flooding relative to the insured building; and
  • Expected cost of recovery.

Likelihood and depth of flooding are assessed at an individual address level, using results from computer flood modelling which simulates how water flows through a catchment. Expected cost of recovery includes repair, rebuild and replacement costs, temporary accommodation, and other factors such as the potential shortage of materials and labour after a flood event. Some insurers may also consider property-specific information such as number of storeys, floor levels, building materials used and construction type.

Insurance policies and conditions may change over time or between insurance companies, and you should confirm the specific details of your situation with your insurer.

Floodplain Management Australia has developed flood insurance fact sheets to assist property owners in understanding the information surrounding this process.

Flood affected property may be developed if the proposed development meets the relevant standards and requirements. The applicable planning controls are largely determined by the proposed land use and the extent of flooding on your property.

A Local Environmental 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 provide criteria for assessing applications for properties potentially affected by flooding. The above documents are available on Council's website.

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.

Although the impact of vegetation on flood behaviour is very important, vegetation has an essential function in managing erosion and providing habitat to wildlife. 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 increase it in other areas. These issues are considered in the context of a Floodplain Risk Management Study.

Contact us:

Name Manager Floodplain and Transport
Phone 4221 6111
Email council@shellharbour.nsw.gov.au
Website www.shellharbour.nsw.gov.au/
In writing

Locked Bag 155

Shellharbour City NSW 2529