Flooding is a common natural disaster in Australia, with the risk of flooding being determined by a combination of factors including topography, rainfall in the catchment, and the location of the property. The areas at risk of flooding are not the same across a geographic region, with some areas being affected repeatedly over time while others are not. Floods can be deadly and can cause a number of fatalities, not to mention innumerable injuries and billions of dollars of property damage.
Flooding can occur in many forms, from river and creek floods to storm tide floods. Another type of flood that can occur is overland flow. This is run-off that travels over the land during heavy rainfall events and can be unpredictable due to its dependence on localised rainfall and urban features.
Flooding regularly occurs all across Australia and according to a fact sheet by the Waterfront Industry Council, over one million private properties, or about one in 10 homes, have some level of flood risk in Australia. The highest risk local government areas (LGAs) in each state are listed as Brisbane, QLD; Central Coast, NSW; Clarence Valley, NSW; Hawkesbury, NSW; Kempsey, NSW; Lismore, NSW; Shoalhaven, NSW; Townsville, QLD; Tweed, NSW; and Wollongong, NSW.
The location of a property is the main driver of flood risk. Properties located in low-lying areas or outside of flood plains are at the highest risk, while those that are raised or located on top of a hill or slope are at a lower risk. Additionally, properties with lower floor levels will be affected first as floodwaters rise, while properties elevated above the surrounding terrain may escape with little or no damage.
The measure used to describe the size and frequency of floods is the Annual Exceedance Probability (AEP). AEP describes how likely a given flood event is to occur each year, based on historical flood records and computer modelling of potential future floods. For example, a property may be described as being at risk of a 1-in-100-year flood, which means the property has a 1-in-100 or 1% chance of flooding in any given year. This does not necessarily mean it will only flood once every 100 years but is a measure of the chance of it flooding in any given year.
It is important for homeowners and prospective buyers to be aware of the flood risk in their area and take the necessary precautions to protect their property. This includes knowing the AEP for their property, elevating the structure, and purchasing flood insurance. It is also important to take action to prepare for and minimize the impact of a flood. This can include making your home or business more resilient to flooding, creating an emergency plan, and staying informed about the latest flood warnings and alerts.
By being proactive and prepared, homeowners can reduce the risk of flood damage and protect their property and their families.
Annual Exceedance Probability (AEP) is an analysis used to determine flood risk of a given location and is used by engineers and land planners to describe how likely a given flood event is to occur each year. The flood risk of a location is determined by a variety of factors, including topography, weather patterns, and land use and it describes the likelihood of a flood event occurring each year based on historical records and computer modelling.
Properties can be described as being at risk of a 1-in-100-year flood or a 1-in-20-year flood. This does not necessarily mean that the property floods once every 100 years or 20 years. Instead, it means that the property has a 1% chance (1-in-100) or 5% chance (1-in-20) of flooding in any given year. It is important to note that major floods can still occur in close succession over a few years, followed by long periods with no significant floods.
The AEP is also a measure of the likelihood of a flood of a certain size happening in any given year. For example, a flood with a 1 in 20 AEP (5% likelihood) is considered to have a high likelihood of occurring, while a flood with a 1 in 500 AEP (0.2% likelihood) is considered to have a low likelihood.
When it comes to river, creek and storm tide floods, areas with a high likelihood of flooding (1 in 20 AEP) are considered to be at Regular risk of flooding and residents and businesses are strongly advised to take action to prepare for and minimize the impact of a flood. Medium likelihood areas (1 in 100 AEP) are considered to be at Irregular risk, and residents and businesses should still take action to prepare. Low likelihood areas (1 in 500 AEP) and very low likelihood areas (1 in 2000 AEP) are considered to be at rare or extreme risk, and residents and businesses should still consider how flooding may affect their local area.
In the case of Overland Flows, High impact areas (1 in 20 AEP) are considered to be unsafe for people, vehicles and buildings, and residents and businesses are strongly advised to take action to prepare. Medium impact areas (1 in 50 AEP) and low impact areas (1 in 100 AEP) are considered to be less hazardous, but residents and businesses should still take action to prepare.
As an example, given below is a table describing how flood risk is categorised in Brisbane -
|River, Creek and Storm Tide||High likelihood (5% chance)||Regular||Prepare to minimize impact|
|Medium likelihood (1% chance)||Irregular||Prepare to minimize impact|
|Low likelihood (0.2% chance)||Rare||Consider how flooding may affect|
|Very low likelihood (0.05% chance)||Very Rare or Extreme Event||Consider how flooding may affect|
|Overland Flow||High Impact (5% chance)||Generally unsafe for people, vehicles and buildings||Prepare to minimize impact|
|Medium Impact (2% chance)||Generally unsafe for people, vehicles and buildings||Prepare to minimize impact|
Floods can be devastating, causing damage to homes, businesses, and infrastructure. The best way to protect yourself and your property from the effects of a flood is to be prepared. Here are some steps you can take to prepare for a flood:
Floods can cause a wide range of damage to homes and properties, both inside and outside. Understanding the different types of damage that can result from floods can help you better prepare for and protect against future flood events.
Floods can cause a significant amount of damage to homes and properties, and the best way to protect your home is to make it more resilient to floods. Here are some tips on how to do that: