What are Floods?

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.

What is AEP? Explained

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 -

How to Prepare for a Flood

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:

• Know your flood risk: Find out if your property is located in a flood zone and understand the level of risk. This information can be found on your property's flood map, which can be accessed at on our website or through your local government or floodplain management agency.
• Create a flood emergency plan: This plan should include evacuation routes, emergency contact numbers, and a list of important items to take with you in case of evacuation. Make sure all family members and employees are familiar with the plan.
• Protect your property: If your property is in a high-risk flood zone, consider purchasing flood insurance. You can also make your home more flood-resistant by elevating the furnace, water heater, and electrical panel.
• Build or restock your emergency kit: This should include a flashlight, battery-powered radio, extra batteries, first aid kit, and a supply of drinking water and non-perishable food.
• Stay informed: Stay informed about weather conditions and flood warnings in your area. Listen to local radio or television stations or sign up for emergency alerts from your local government.
• Be ready to evacuate: If a flood is imminent, be prepared to evacuate your home or business. Follow the evacuation route and instructions provided by local authorities.

How Floods Damage your Home

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.

• Structural damage: This type of damage refers to damage to the actual structure of your home or building. Floodwaters can weaken or wash away foundations, damage walls and floors, and cause leaks and cracks in the structure. This type of damage can make a building unsafe to inhabit and can be costly to repair.
• Water damage: Floodwaters can cause water damage to walls, ceilings, floors, and personal belongings. Water damage can lead to mold and mildew growth, which can cause health problems and further damage to the structure.
• Electrical damage: Floodwaters can damage or destroy electrical systems, including wiring, outlets, and appliances. This can create fire hazards and make it difficult to restore power to a flooded home or building.
• Sewage damage: Floodwaters can overflow sewers and septic systems, leading to sewage contamination. This type of damage can be particularly dangerous as it can contain harmful bacteria and viruses.
• Landslide: Floods can cause landslides, which can damage or destroy buildings and infrastructure. Landslides can also create hazards for people and animals.

How to make your Home more resilient to Floods

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:

• Elevate your home: If your home is located in a flood-prone area, consider elevating it above the flood level. This can be done by building a raised foundation or by elevating the entire home on stilts.
• Install flood barriers: Flood barriers, such as flood gates, can be installed around windows and doors to prevent water from entering your home.
• Use water-resistant materials: When building or renovating your home, use water-resistant materials such as concrete, tile, or laminate flooring. These materials are less likely to be damaged by water and are easier to clean up after a flood.
• Seal your basement: Sealing your basement can help prevent water from entering your home.
• Install a sump pump: A sump pump is a device that pumps water out of your basement or crawlspace. This can help prevent water from entering your home during a flood.
• Create a flood plan: Make sure you have a plan in place for what to do in case of a flood. This should include evacuation routes, emergency contact information, and a list of important documents and items to take with you in case you need to evacuate.
• Be prepared: Keep sandbags, a portable generator, and other emergency supplies on hand in case of a flood.
• Keep insurance up to date: Flood insurance can help cover the cost of damage and repairs to your home and belongings. Make sure your insurance policy is up to date and that you understand what is covered.