Strategies

Content: Process | Measures | Flood risk management plan

Process
Local government councils have the prime responsibility for planning and managing flood prone lands in NSW. The NSW Government provides assistance on state wide policy issues and technical support. Funding is provided to councils to undertake flood and floodplain management studies and to implement the studies recommendations.

The NSW Government’s Flood Prone Land Policy and the Floodplain Development Manual form the basis of floodplain management in NSW. Councils must comply and abide by the principles set out in the policy and manual in all floodplain management works.

The floodplain management process diagram can be found on the right of this page.

The primary objective of the Flood Prone Land Policy is to:

• “Reduce the impacts of flooding and flood liability of individual owners and occupiers of flood-prone property, and to reduce private and public losses resulting from floods, utilising ecologically positive methods wherever possible.”

One of the primary aims of the Floodplain Management Manual is to foster the following floodplain risk management principles:

• to reduce the social and financial costs that result from the risks of occupying the floodplain;
• to increase the sustainable social, economic, and ecological benefits of using the floodplain;
• to improve or maintain the diversity and well-being of native riverine and floodplain ecosystems.

The management of floodplains is based upon a risk management approach. That is, it is best practice to avoid the flood risk, i.e. not building in a flood risk area. Whilst this may seem straightforward, development pressures means that it is not feasible to sterilise all the flood affected land.

It is important to understand that different levels of flood risk exist. Our Development Control Plan 54 (Managing Our Flood Risks) sets out these criteria, consistent with the NSW Government Flood Prone Land Policy. Council’s development controls make reference to the 100 year flood level and the flood risk precincts. You must therefore obtain and use this information when preparing a development application for your property.

Planning controls place restrictions on things like the minimum floor level, the types of building materials, appropriate development types, evacuation access etc. The use of planning controls does not mean the risk of flood has been eliminated, however, the risk has been minimised.

Measures
Measures available for the management of the flood risk are related to the way in which the risk is managed.

Risk can be defined as being existing, future or residual risk:

• existing flood risk - the existing problem refers to existing buildings and developments on flood prone land. Such buildings and development by virtue of their presence and location, are exposed to an 'existing' risk of flooding;
• future flood risk - the future problem refers to buildings and developments that may be built on flood prone land in the future. Such buildings and developments may be exposed to a 'future' flood risk, i.e. a risk would not materialise until the developments occur;
• continuing risk of flooding - the continuing problem refers to the 'residual' risk associated with floods that exceed management measures already in place, i.e. unless a floodplain management measure is designed to withstand the probable maximum flood, it will be exceeded by a sufficiently large flood at some time in the future. It is not a matter of if, but of when.

The least preferred floodplain management option is flood modification measures. Flood modification measures can be numerous but are typically engineering solutions such as building levees, modifying culverts, channel widening, etc. Generally speaking, mitigation measures are far more expensive than other options and are most likely to negatively impact on the natural environment.

The various risk management measures can be classified into three categories:

• flood modification (for the exisiting risk): 
  • purpose: to modify existing developments to limit flood losses by steering inappropriate development away from high risk areas and to encourage development that is compatible with the known flood risk; 
  • application: includes zoning and other development controls, voluntary purchase, house raising, flood proofing and access planning.
• property modification (for future risks): 
  • purpose: to modify the behavior of a flood by reducing flood levels or velocities, or by excluding floodwaters from areas under threat; 
  • application: options include migration dams, retaining basins, levees, floodways, channel modifications and floodgates.
• response modification (for the residual risk): 
  • purpose: to increase the ability of the population at risk by responding appropriately to the flood threat, or enhancing flood predictors/warnings and evacuation procedures; 
  • application: options include floodplains, flood education, community flood readiness and preparation, recovery planning and improved flood prediction/warning.

Key considerations common to all measures:

• intergrated and community involved framework; 
• environmental protection and enhancement; 
• asset management.

Methodology for identifying measures:

• catchment inspection;
• review of the flood study results;
• suggestions by the Floodplain Risk Management Committee;
• suggestions by residents via the questionnaire responses;
• suggestions by Council technical personnel and the Department of Natural Resources;
• review of appropriate approaches as listed in the Floodplain Development Manual(2005).

Flood risk management plan
We're responsible for preparing and implementing plans of management for the different catchments across the region. These plans are prepared on behalf of Council by consultants who specialise in flooding.  The steps involved in formulating a management plan can be viewed in the Floodplain Management Process diagram.

This process takes a significant amount of time and money to complete. On average, five years is required to reach the implementation plan phase of the process and may cost in the order of $500,000. The implementation phase of the process is by far the most expensive component with mitigation works for a catchment costing millions of dollars. Due to the enormous cost of implementing the works, implementation is phased accordingly. Furthermore, we must apply for funding from the Federal and State governments before work can be undertaken.

Due to the long process required, we have only achieved the following results:

• completed four catchments plans;
• commenced another three catchment studies;
• one catchment study still to commence.

The following list includes:

• the eight catchments in Wollongong;
• the surburbs included in each catchment;
• the consultants working on the flood studies;
• the status of the project.

 Allans Creek Catchment:
Surburbs: Mt Keira, Mt Kembla, Figtree, Cordeaux Heights, Farmborough Heights, Unanderra, West Wollongong, Mangerton.
Consultant: Cardno Lawson Treloar Pty Ltd.
Status: Completed and adopted by Council.

Collins Creek Catchment:
Surburbs: Woonona, Russell Vale, Bellambi, Bulli (parts of), Corrimal (parts of), East Corrimal (parts of).
Consultant: Lyall & Associates Consulting Water Engineers.
Status: Flood study commenced.

Hewitts Creek Catchment:
Surburbs: Bulli,  Thirroul.
Consultant: Forbes Rigby Pty Ltd.
Status: Completed and adopted by Council.

Fairy-Cabbage Tree Creek Catchment:
Surburbs:  West Wollongong (parts of),  Gwynneville,  Keiraville, Mount Ousley, Mount Pleasant, North Wollongong, Fairy Meadow, Balgownie, Fernhill (parts of), Towradgi (parts of).
Consultant: Bewsher Consulting Pty Ltd.
Status: Flood study commenced.

Minnegang Creek Catchment:
Surburbs: Warrawong (parts of).
Consultant: Kellogg Brown & Root Pty Ltd.
Status: Completed and adopted by Council.

Mullet Creek Catchment:
Surburbs: Dapto,  Koonawarra (parts of), Kanahooka, Horsley, Kembla Grange, Farmborough Heights (parts of), Wongawilli, Avondale, Penrose, Cleveland, Dombarton, Huntley.
Consultant: Bewsher Consulting Pty Ltd
Status: Flood study commenced.

Northern suburbs Catchment:
Surburbs: Austinmer, Coledale, Wombarra, Scarborough, Clifton.
Consultant: Not yet appointed.
Status: Still to be commenced.

Towradgi Creek Catchment:
Surburbs:  Tarrawanna, Corrimal, East Corrimal, Towradgi (parts of).
Consultant: Bewsher Consulting Pty Ltd.
Status: Completed and adopted by Council.