Hawkesbury-Nepean Valley

What causes significant floods

Most significant floods in the Hawkesbury-Nepean Valley are caused by intense low-pressure systems called East Coast Lows.

These weather systems can happen at any time and can occur several times a year. They often intensify rapidly overnight, making them one of the most dangerous weather systems to affect the region.

Official warnings and advice

Official warnings and flood advice are provided by The Bureau of Meteorology (the Bureau) and the NSW State Emergency Services (NSW SES) on radio stations and social media.

The Bureau uses rainfall and flood gauges to predict the arrival time and depth of floodwater.

Working in cooperation with NSW SES, the Bureau issues three types of related forecasts and warnings:

• A Flood Watch provides early advice that flood-producing rain is expected to happen in the near future. Note: a flood watch is updated daily but it is not a warning of imminent flooding.
• A Flood Warning is issued when the Bureau is more certain that flooding is expected in a specific area and is typically issued when rainfall has started to fall.
• A Severe Weather Warning is issued for very heavy rain that may cause flash flooding or abnormally high tides that can affect flooding. Localised flash flooding occurs after intense rainfall and is also referred to as overland flooding.

Leading up to and during a flood, NSW SES issues the following warnings:

• Stay Informed - Advice warns a community that flooding has started and provides information on likely flood consequences and what actions people should take to protect themselves and their property.

• Do Not Enter Floodwater - Watch and Act warns that a flood situation is becoming more serious and instructs people not to drive, walk, ride, play or swim in floodwater - it is dangerous, toxic, and may void car insurance.
• Prepare to Isolate - Watch and Act warns people that they are likely to become isolated by rising floodwater and that they should stock up on essential items before roads and evacuation routes close.
• Prepare to Evacuate - Watch and Act warns people that they need to prepare to evacuate so they can act quickly if evacuation is necessary. Flooding is likely to cut evacuation routes and potentially inundate property. This warning advises the safest actions for the community to take in a flood emergency.

• Evacuate Now/Before - Emergency Warning warns that lives and properties are at-risk due to dangerous flooding, and that people need to evacuate an area immediately or when instructed by emergency services. Flooding is likely to cut evacuation routes and inundate property. This warning advises people what to do if instructed to evacuate and where to go.
• Shelter Now - Emergency Warning warns people that it is too late to leave a flooded area safely as evacuation routes are likely to be cut off. People should instead seek shelter inside a sturdy raised structure or building that can be safely accessed and call for help if needed.
• Move to Higher Ground - Emergency Warning warns people that rising floodwater is making it unsafe to evacuate an area. People in the impacted area should move away from floodwater, as high above ground as possible and call for help if needed.

• Avoid the Area - Watch and Act warns people that a specific area is unsafe due to dangerous flooding and should be avoided until further notice.
• Reduced Threat: Return with Caution - Advice advises evacuated communities that they should take care when returning to flood impacted areas as damage can be widespread and dangerous. People must be cautious, ensuring their property is safe before re-entering.
• Monitor Conditions - Advice advises people that the flood threat has eased but they must remain vigilant and consider potential hazards like damage to roads, bridges and infrastructure.

It is vital that you leave if you receive an Evacuate Now - Emergency Warning.

Learn more about evacuations and what to do under During a flood.

View All Current Warnings

Are you prepared for a Future Flood?

Research shows that during major floods in 2021-2022, 70%* of people in the Hawkesbury-Nepean Valley who saw or heard evacuation warnings did not leave.

In the above video you’ll hear the stories of four residents who stayed home during recent floods and see what makes them rethink how they will act next time.

Their stories reflect research showing that people rely on advice from family and friends or look to validate SES alerts through other sources before acting, despite them being the single most important source of information. The SES always has the most up to date information and predictions and if they ask you to leave it’s because it’s not safe to stay where you are.

The 2022 floods were a 1 in 20 chance per year floods – which means there is a 5 per cent chance of a flood of that size happening in that or any other year. A 1 in 100 chance per year flood would reach the height of a second story balcony, while a 1 in 500 chance per year flood (like one recorded in 1867) would see the second story submerged.

Every flood is different. It doesn’t take much rain to cause a flood that puts homes completely underwater.

The best way to protect yourself, your family and your pets is to make a flood plan and follow the advice given by the SES.

*Source: SEC Newgate Research, November 2022

Please note: This information has the potential to evoke feelings of anxiety, stress, or bring up unpleasant memories.

If you’re struggling, you might benefit from some support. Reach out to a mental health professional by contacting Head to Health at 1800 595 212, or visit their website at https://www.headtohealth.gov.au

Call 1800 595 212 to connect with Head to Health (Mon-Fri, 8.30am-5:00pm) to speak to a trained mental health professional from our region, who will take the time to listen and understand your needs.

Know when and how to leave

The Hawkesbury-Nepean Valley has a long history of damaging and dangerous floods. Floods can happen with little warning. You may only have a few hours to get out following an Evacuate Now - Emergency Warning. You will typically be asked to leave well before you see any sign of floodwater in your neighbourhood. It is not safe to stay and shelter in your home once you have been ordered to evacuate.

To find out about evacuations and which routes are open listen to your local and ABC radio, or follow NSW SES Facebook, or NSW Police Facebook and Twitter.

Get familiar with the local routes

You need to be prepared and get to know your evacuation routes, to keep you, your family and pets safe.

There are 12 designated evacuation routes that provide the quickest and safest way to exit the Wallacia, Penrith-Emu Plains, Richmond-Windsor, South and Eastern Creek floodplains.

You need to be aware of more than one route because each flood behaves differently and evacuation routes will get cut by floodwater at different points. Some routes can get cut quite early in relatively small floods. For example, Windsor Road is cut by a flood that has a 98% chance of happening in an 80-year lifetime (also known as a 1 in 20 chance per year flood).

Even relatively new infrastructure can be affected by large floods. The Jim Anderson bridge at Windsor would be cut in a flood with a 55% chance of occurring in an 80-year lifetime (1 in 100 chance per year flood).

Once you know your best routes, have a conversation with friends or relatives to organise a place to go to. Remember, as each flood can be different, it’s important to follow an Evacuate Now - Emergency Warning when it is given.

Follow the signs

More than 150 new flood evacuation signs have been installed across the Hawkesbury-Nepean Valley to guide drivers. There are several different types of signs, including a number of folded signs designed to be opened during a flood emergency to provide extra direction for drivers.

Why you need a kit

A significant flood in the Hawkesbury-Nepean Valley will cause damage to people’s homes. It will also cause major disruptions to essential services such as water, electricity, gas, roads and rail lines.

By the time you know a flood might impact your property, there may be very little time before you have to leave. A key step to getting ready for floods (or for any other natural hazard) is to prepare a Get Ready to Go kit.

• The kit should contain what you will need during and immediately after evacuation, whether you are going to family and friends, or to an evacuation centre.
• Some key items to include in your kit are a battery-powered radio which will be handy if the power and internet goes out, a torch and batteries, waterproof bag and some personal hygiene items.

For more information and examples of what items to include in your kit, download the Get Ready to Go Kit Factsheet in the resources section above.

Maintaining and storing your kit

• Your kit should be kept in a waterproof storage container and stored in a safe place that is easy to access.
• On a regular basis, check your Get Ready to Go kit (remember to check use-by dates on batteries and medications) and restock items if you need to.
• Also, keep a list of emergency numbers near your phone or on your fridge.

Introduction

The Hawkesbury-Nepean Valley floodplain is divided into 5 key areas. You can find handy information about your local area in the resources section.

To understand your flood risk you can use our flood risk tool in the useful links.

Richmond and Windsor

Watch the video to see how flooding can impact bridges and roads in the Hawkesbury as well as turning some suburbs into flood islands.

Penrith and Emu Plains

Watch the video to see how flooding can impact local icons such as the Bridge to Bridge walking track, the Joan Sutherland Centre, and Victoria Bridge.

South and Eastern Creeks

Watch the video to see how flooding can impact suburbs such as Riverstone, Schofields, Shanes Park and Llandilo many kilometres away from the main Hawkesbury River.

Why floods are so dangerous in the Hawkesbury-Nepean Valley

The Hawkesbury-Nepean Valley covers a wide area in Western Sydney from Bents Basin near Wallacia to the Brooklyn Bridge. The area has a long history of dangerous and deep flooding.

The unique geography in the valley affects the extent and depth of flooding in the region. Most river valleys tend to widen as they approach the sea. The opposite is the case in the Hawkesbury-Nepean Valley, which means floodwaters flow into the valley more quickly than they can flow out, causing them to back up and rise rapidly.

Much like a bathtub with five taps (the major tributaries) turned on, but only one plug hole to let the water out. Watch this video to learn how the ‘bathtub effect’ makes this valley have one of the greatest flood risks in Australia.

The recent March 2021 flood was only the 15th largest recorded flood in the region – though the impacts were felt far and wide. Floodwater severely impacted over 600 homes, over 30 caravan parks, hundreds of farms, and transport routes and essential services such as electricity and water were cut. The estimated damage bill was several hundred million dollars.

However, there have been much larger floods in the valley including the worst flood on record. In 1867, river levels reached 19.1 metres above normal river height at Windsor and the region was decimated. If a similar flood happened now the consequences would be catastrophic – many lives would be at risk and almost 90,000 people would have to evacuate.

Flood are random, naturally occurring events. It’s impossible to predict when the next major flood will happen. History has shown that serious floods can happen many times in a single decade, and not again for many years.

What are the natural warning signs?

Every flood is different, so you can’t rely on what you might have experienced or heard about in the past.

It’s important to pay attention to weather reports and be aware of some of the early warning signs
such as:

• predictions of heavy and/or prolonged rainfall
• East Coast Lows affecting the region
• heavy, sustained rainfall is occurring in upstream catchments such as the Blue Mountains, the Southern Highlands, Goulburn and Wollondilly regions.

In the Hawkesbury-Nepean Valley, there may be only a few hours warning between heavy rainfall and being told to evacuate.

In most cases you won’t see flooding in your neighbourhood before being told to evacuate. This means your best source of information is the official warnings.

What to do during floods

If your area is at risk, go to high ground away from flooded areas. 

Never enter floodwater. If it’s flooded, forget it. 

The major cause of death during floods is from people entering or travelling through floodwater. This includes driving, riding and walking through floodwater and children playing in floodwater. 

• Floodwater may be deeper or faster flowing than it appears and contain hidden snags or debris. 
• Floodwater may contain chemicals, raw sewage, snakes, spiders and much more that could cause illness and even death. 
• Roads and surfaces underneath floodwater often wash away and may not be visible from the surface. 

Never drive, ride or walk through floodwater.

When a Flood Warning is issued

• Stack possessions, records, stock or equipment on benches and tables, placing electrical items on top. 
• Secure objects that are likely to float and cause damage. 
• Relocate waste containers, chemicals and poisons well above floor level. 
• Activate your home or business emergency plan. 
• Keep listening to your local radio station for information, updates and advice. 
• Keep in contact with your neighbours. 
• Be prepared to evacuate if advised by Emergency Services. 
• Act early as roads may become congested or close. 
• Never drive, ride or walk through floodwater. 

For more information on what to do during a flood, download the During a Flood Factsheet  in the resources section.

When a Prepare to Evacuate - Watch and Act is issued

When a Prepare to Evacuate - Watch and Act is issued, you should prepare to evacuate. Staying inside a house, even one which you think is high enough, may be very dangerous. If you are warned to evacuate it is always safest to move to a location away from the flood affected area before floodwater arrives. 

• Locate important papers, valuables and mementos. Put them in your emergency kit.
• Keep listening to your local radio station for information, updates and advice. 
• Follow instructions given to you by Emergency Services. 

When an Evacuate Now - Emergency Warning is issued

When an Evacuate Now - Emergency Warning is issued and you leave your house: 

• Turn off the electricity and gas at the mains before you leave and turn off and secure any gas bottles. 
• Take your pets with you. 
• Never enter or travel through floodwater. 
• Keep listening to your local radio station for information, updates and advice. 
• Follow your home or business emergency plan. 
• Follow all instructions given to you by Emergency Services. 
• Stay with family or friends, if possible. 
• Evacuation Centres may be set up if an Evacuate Now - Emergency Warning is issued.  
• Choose the safest route to travel where roads along the route are open. 
• Roads may become congested or close, ensure you leave enough time to travel safely. 

For information on roads, contact your local council for local road closures.