Flooding is a natural phenomenon that occurs when water covers land that is usually dry. Floods can have a major impact upon communities. Learn what to do in a flood, and how to find
Flooding comes in different types, sizes and durations:
- Catchment flooding occurs from prolonged or intense rainfall (e.g. severe thunderstorms and East Coast Lows). Examples include water running off catchments leading to:
- Breaking the banks of creeks and rivers: Hawkesbury River, Erina Creek, Narara Creek, Ourimbah Creek, Wyong River, and many others.
- Filling coastal lakes and lagoons: Tuggerah Lakes, Wamberal lagoon, Terrigal Lagoon, Avoca Lake, Cochrone Lagoon, Pearl Beach Lagoon.
- Flowing overland across normally dry land in both urban and rural areas on its way to waterways.
- Coastal flooding due to tidal- or storm-driven coastal events, including storm surge and wind-induced waves in coastal waterways. Examples include:
- Brisbane Water and the lower reaches of Narara Creek and Erina Creek,
- Hawkesbury River
- Coastal beach fronts.
- Combinations of both catchment and coastal flooding in the lower portions of coastal waterways where both can be produced by the same storm or a series of storms. How these sources of flooding interact and which is dominant will vary with the location and configuration of the catchment, floodplain and waterway, and the specifics of the storm cells.
Duration of flooding: The most frequent flooding in the Central Coast region is flash flooding. It is caused by sudden local or nearby heavy rainfall which generally peaks within six hours of the onset of rain. Areas that are affected by Coastal Flooding, such as foreshore communities in Brisbane Water, may experience flooding, which can typically last only 2 hours associated with a high tide. Land adjacent to creeks and rivers can be flooded for a day or more; foreshore land around Tuggerah Lakes can be flooded for up to four days.
The interactive flood mapping tool currently shows flooding in areas up to the 1% AEP or 1 in 100 year flood event. This represents a very large flood event however the largest flood that can occur is the Probable Maximum Flood event. Council is progressively undertaking additional flood studies for all areas of the Central Coast.
What to do in a flood
- Listen to local radio. Check Bureau of Meteorology updates.
- Be prepared to evacuate.
- Act early before roads are closed by floodwater.
- Never drive or walk through floodwaters.
Who can help in a flood?
The State Emergency Service (SES) is responsible for responding to floods in NSW.
The local SES personnel will provide flood information, safety advice and arrange for the delivery of essential supplies to people isolated by floodwater. Where appropriate, the SES will conduct evacuations and undertake flood rescue.
As many homes, farms and businesses across NSW are susceptible to flooding, the SES has developed Flood Safe guides. These explain how to prepare for flooding and what to do when waters rise.
For help during a flood or storm, call the NSW State Emergency Service on 132 500, or for life threatening emergencies, call 000.
Living with floods
Flooding is generally a rare event and it is not always possible to predict when, where, or how big the next flood will be. However, the likelihood of different sizes of floods and their consequences can be estimated by computer flood modelling. This information is essential for council to plan appropriately for development.
Floods can bring considerable environmental and human benefit. Groundwater is replenished, wetlands recharged, alluvial soils renewed and flood debris provides habitat and food for many species. For the floodplains to be both healthy and productive, periodic flooding is essential.
However, there are also negative consequences as a result of flooding. This includes potential risk to life and financial losses through damage to buildings and/or the building contents, public infrastructure, utility services and the environment.
Flooding also has the potential to disrupt essential services and cause human trauma. This can be especially true in Central Coast urban areas and small tributaries where flooding can occur very quickly and with little or no warning due to the steep nature of the surrounding topography.
There are no quick fix solutions to the flooding issues in the Central Coast region.
It is therefore necessary to find cost effective solutions to manage and live with the flood risks throughout the Central Coast. Council in consultation with the community develop floodplain risk management plans that identify measures to address existing and future flood risks.
Flood planning and management responsibilities
Council has a duty of care to manage lands subject to flooding within its Local Government Area. Under the NSW Government’s Flood Prone Land Policy, the local government has responsibility for managing flood liable land.
Council is responsible for formulating and implementing Floodplain Risk Management Plans in accordance with the policy.
See our Strategies and plans page for all Floodplain Risk Management Plans.
The policy aims to reduce private and public losses resulting from flooding and encourages the development of:
- solutions to existing flood problems in developed areas; and
- strategies for ensuring that new development is compatible with any identified flood hazards and does not create additional problems in existing developed areas.
Central Coast Council, with the assistance of an Advisory Committee, is responsible for this task in each drainage catchment. Council seeks assistance from State and Federal Government in the form of technical advice and grant funding for studies and works.
Flooding on Private Property
Council relies on information from the general public to monitor flood issues on the Central Coast.
If you have experienced consistent minor flooding on or near your property which has originated from a local stormwater drain, natural stream or estuary please reported it to council.
This information is important to help identify new or repeated areas of flooding, assist with determining flood heights for future flood events, and identifying areas for priority investigation and potential works to alleviate the problems.
Flooding issues can be reported by contacting Central Coast Council.
How do I obtain flood information for my property?
Council has flood maps available for its main waterways which give an indication of areas that will most likely be affected by various flood events. However, these maps are not detailed enough to provide flood levels for individual properties.
If you require more detailed information from that supplied on the maps and in relation to a Development Application, you can complete a Flood information application.
Note: It is not Council's general practice to provide flood information about a property over the phone.
Is my house protected by flood mitigation measures?
Many areas on the Central Coast have flood mitigation measures in place. These measures may include a levee bank, channel that has been widened, a floodgate, a detention basin or larger drains which aim to reduce the frequency of flooding and the length of time the stormwater remains on flood liable properties.
However these measures can fail in severe and prolonged storm events, therefore it is important to be prepared for a major flood if your house is located on identified flood liable land or within close proximity to a creek, water course, water body, depression, etc.
To find out whether your property is within an area identified as being affected by flooding up to a 1% AEP flood event, please refer to the flood mapping section.
Am I liable for any work I do in a drainage easement, flood area or watercourse?
In short, yes. A solution to solving your problem may adversely affect your neighbour. You should not construct any works that divert stormwater flows onto your neighbour’s property as you could be held liable by your neighbour for any damage as a result of such action.
A common problem in built up residential areas is the construction of boundary fences and gates which impede natural overland flow paths.
You should be careful, when making these types of improvements to your property, that you choose construction materials which will not dam or divert overland flood waters. These types of improvement works may require development approval if located within a floodplain or overland flow path.
Likewise, placing fill on flood liable land may cause an increase in floodwaters upstream and downstream. Placing fill around your house and blocking or diverting pipes may also lead to serious flooding problems either to yourself or your neighbours. Many properties which were once flood free can be made flood liable because of these types of works.
You should always check with council before placing any fill material on or near an existing pipeline, overland flow path or watercourse.
Similarly, do not attempt to change the location of a natural watercourse. There is a good reason why nature has placed the watercourse in that location and by relocating it you could cause damage to both your own and other people’s properties and cause detrimental impacts on local flora and fauna.
Before undertaking any type of work near or within a drainage easement, on flood prone land or within a watercourse, please check with council to seek advice on whether the work is permissible and whether a development application will be required.
Flood insurance issues
Any property which is identified as being flood prone and that attracts development controls will have a message placed on the property’s planning certificate.
Council is aware that some insurance companies are also identifying flood prone land as a result of undertaking their own flood studies, analysis and flood mapping exercises, or using data from studies conducted by NSW Councils.
This information is being used by individual insurance companies to assess the hazard and risk and to then set premiums for flood insurance.
The insurance industry also uses its own estimates for flood risk assessment and its own definitions for flooding. These may differ when compared with Council’s information. To assist the insurance industry in using the best flood information to determine flood premiums, Council has shared its flood information with the insurance industry.
From enquiries made of a number of insurance companies by Council, it would appear that the method of setting policies and premiums is done on an individual company basis. This leads to some difference with premiums and flood liability across many properties under different insurance companies.
You should therefore make your own enquiries about how your insurance company classifies flooding (and stormwater), and how this relates to your insurance provisions and premiums.
More detailed information can be found on Council’s interactive mapping pages.
Common flooding terminology
1% AEP or 1 in 100 year flood
A 1:100 year Average Recurrence Interval is the result of statistical data which estimates the probability that a particular rainfall event (or intensity) will be equalled or exceeded at a particular place within a certain period of time, i.e., 100 years.
This is also referred to as the 1% Annual Exceedance Probability flood, which is a flood that has a 1% chance of reaching or exceeding a particular magnitude in any one year.
It should be noted that if a 1% or 1 in 100 year flood is experienced in a certain year, that does not mean that there will not be another 1 in 100 year flood occurring in the same year or during the next 99 years.
The probable maximum flood (PMF) is the largest flood that could possibly occur. It is a very rare flood (much rarer than the 1% AEP 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. Councils are required to consider all flood risks, even these potentially small ones, when managing floodplains.