Flooding FAQs

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Flooding FAQs

Some large and rare floods have often not been experienced since European settlement commenced, computer models are used to simulate the depths and velocities of major floods. These computer models are normally established and operated by flooding experts employed by local and state government authorities.

Because of the critical importance of the flood level estimates produced by the models, such modelling is subjected to very close scrutiny before flood information is formally adopted by a council.

Maps of flood risks (e.g. 'low', 'medium' and 'high') are prepared after consideration of such issues as;

  • flood levels and velocities for a range of possible floods;
  • ground levels; flood warning time and duration of flooding;
  • suitability of evacuation and access routes; and
  • emergency management during major floods

Flood risk maps are currently not available on council’s online mapping tool, however flood risk information is presented in the flood certificate provided as part of a Flood Level Information Request.

​As part of the floodplain risk management process, flood studies and flood risk management plans are reviewed over time. As these reviews take place, computer models are revised and predicted flood levels and associated flood mapping can change. The resultant change in flood levels and flood mapping however is normally very small. These changes are not expected to occur very often and the intervals between revisions to the maps would normally be many years.

The reasons why the computer models are revised can include;

  • new rainfall or ground topography information becomes available;
  • new floods occur which provide additional data from which to fine-tune the models;
  • better computer models become available as the science of flood modelling improves and computer capabilities increase;
  • flood mitigation works may have been carried out,
  • development within the catchment may have occurred, that was not previously simulated in the models.

​Council has flood information for many areas across the LGA. This includes information about past and / or anticipated flood levels, and flood risk precincts.

There are two main ways you can get information from Council about how flooding affects your property;

  1. Apply for a Flood Certificate through the Flood Level Information request form
  2. Apply for a Planning Certificate. You'll need to request a combined 10.7(2) and 10.7(5) planning certificate to get information about whether the property is flood affected, the 1% AEP (100 year ARI) flood level and flood planning level.

Please note that Council does not have flood level information for all properties, so you should call us on 02 6648 4000 to check if information is available before you start an application. Alternatively, to check if your property is covered by the Flood Planning Level, please see Councils Online Mapping Tool.

For further general information about flooding and guides on how to stay safe and what to do in case of flooding, go to the NSW State Emergency Service website.

The Flood Certificate will provide the applicant with as much flood information as possible on the property in question. This form may be useful if you are looking to develop a property, or are considering purchasing within the floodplain. The form provides additional flooding information that otherwise would not be captured within a 10.7 (Parts 2 and 5) Planning Certificate.

If flood information is available for your property, Council aims to provide the following;

  • Flood Risk Precinct (if available)
  • Approximate ground level information
  • Floor Level data (if available)
  • Planning Levels (Design Flood Level, Flood Planning Level)
  • Estimated flood levels for a range of events (20% AEP, 1% AEP, PMF, etc)
  • Climate change flood levels (if available)
  • Historical flood levels in close proximity to the address (if applicable)
  • The associated Flood Hazard and Categorisation (if available)

The flood information we are able provide in this certificate will vary between catchments, and not all of the information may be available for all properties.

​Generally it means that your property would not be affected by a 100-year flood but still has a very slight chance of being affected from a larger (i.e. rarer) floods. (Also refer to sections on Probable Maximum Flood and Flood Prone Land).

If you are a residential property owner, there will be virtually no change to how you may develop your property. However, there will be controls on the location of essential services such as hospitals, evacuation centres, nursing homes and emergency services.

​Generally it means that your property may be affected by a 100-year flood, however conditions are not likely to be hazardous. If you are a residential property owner development controls will probably be similar to those that currently exist.

​Generally it means that your property will be affected by a 100-year flood and that hazardous conditions may occur. This could mean that there would be a possible danger to personal safety, able-bodied adults may have difficulty wading to safety, evacuation by vehicles may be difficult, or there may be a potential for significant structural damage to buildings. This is an area of higher hazard where stricter controls may be applied.

Any change in a council's classification of properties can have some impact on property values. Nevertheless, councils normally give due consideration to such impacts before introducing a system of flood risk classifications or any other classification system (e.g. bushfire risks, acid sulphate soil risk, etc).

If your property is suddenly classified as being in Flood Prone the real flood risks on your property have not changed, rather, present information regarding risk estimates has become more available for Council to inform decision making. A prospective purchaser of your property could have previously discovered this risk if they had made enquiries themselves.

Ultimately, the market determines the value of any residential property. Individual owners should seek their own valuation advice if they are concerned that the flood risk estimation may influence their property value.

Yes, more than 93% of home building and contents insurance policies contain flood cover as a standard inclusion. However, it is important to read your Product Disclosure Statement (PDS) to know exactly what you are covered for.

Further information on flood insurance.

A 100-year flood is the flood that will occur or be exceeded on average once every 100 years. It has a probability of 1% of occurring in any given year and is sometimes referred to as the 1% AEP Flood.

If your area has had a 100-year flood, it is a fallacy to think you will need to wait another 99 years before the next flood arrives. Floods do not happen like that. Some parts of Australia have received a couple of 100-year floods in one decade. On average, if you live to be 70 years old, you have a better than even chance of experiencing a 100-year flood.

The probable maximum flood (PMF) is the largest flood that could possibly occur. It is a very rare and improbable flood. Despite this, a number of historical floods in Australia have approached the magnitude of a PMF.

Every property potentially inundated by a PMF will have some flood risk, even if it is very small. Under the State Government changes implemented during 2001, councils must now consider all flood risks, even these potentially small ones, when managing floodplains. As part of the State Government changes, the definitions of the terms 'flood liable', flood prone' and 'floodplain' have been changed to refer to land inundated by the PMF.

The Flood Planning Level is a height used to set floor levels for property development in flood prone areas. For the majority of development it is defined as the level of a 100-year flood (1% Annual Exceedance Probability) plus 0.5 metres freeboard. This level may be higher for vulnerable land uses (e.g. hospitals or schools).

​​The flood planning level area is the area below the Flood Planning Level and as such subject to flood related development controls.

Areas affected by indicative flooding have been determined through '1st pass' flood modelling. The '1st pass' flood modelling is a preliminary assessment of flooding, it is not a detailed flood study and does not truly represent the 1% AEP (100 year ARI) flood level; however, Council is confident that this area is flood affected. The Indicative flooding extent is primarily designed to identity flood prone land in areas that do not have detailed flood studies.

Some of the indicative flood areas may also come from flood modelling submitted to council that has not been thoroughly quality controlled as yet. These areas may in the future become part of the 100 year flood extent layer once council is satisfied with quality of the data.

Areas affected by indicative flooding are subject to flood related development controls. However if development or rezoning is proposed, then further detailed flood assessment may be required.

​Freeboard is a factor of safety expressed as the height above the design flood level to compensate for uncertainties in the estimation of flood levels across the floodplain, such as wave action, localised hydraulic behaviour, unforeseen blockages and impacts that are specific event related, including levee and embankment settlement, and other effects such as climate change. Freeboard is usually 0.5m above the design flood level.

​​AHD refers to Australian Height Datum, a common national plane of level approximately equivalent to the height above sea level. All flood levels, floor levels and ground levels in Council studies have been provided in metres AHD.

​​The chance of a flood of a given or larger size occurring in any one year, usually expressed as a percentage. E.g. if a peak flood discharge of 800 m3/s has an Annual Exceedance Probability of 1% it means that there is a 1% chance (that is a one-in-100 chance) of a 800m3/s or larger events occurring in any one year.

​It is the property owner's responsibility to ensure stormwater overflow from development works, buildings and paved areas is collected, mitigated and/or directed to the street.

If you have concerns about stormwater issues please contact council on 02 6648 4000.

Generally if it is a recent subdivision, councils Subdivision Engineer will investigate. If it is coming off defective guttering or being directed by pipes or similar (for example a concrete path) onto your property our Building Compliance Team will investigate.

​If you have concerns about a natural waterway or stormwater drain please contact our Council on 02 6648 4000.

​If your question about flooding/flood risks in the Coffs Harbour LGA isn't answered on our flooding webpage or by our online mapping, you can obtain more detailed information such as flood levels for a specific property by submitting a Flood Level Request Form with the appropriate fees.

For further general information about flooding and guides on how to stay safe and what to do in case of flooding, go to the NSW State Emergency Service website.