The Hawkesbury-Nepean Valley (the HNV) is one of the highest-risk floodplains in Australia, flooding 8 times since 2020. Floods in the Valley can be more frequent and get much worse than the recent floods. In the largest possible flood, 234,000 people who live and work in the HNV would need to evacuate.
This DAP builds on many years of work to understand the impact of floods and how to reduce risk to life and property. The 2017 Resilient Valley, Resilient Communities Flood Risk Management Strategy for the Valley was highly regarded by the Independent Flood Inquiry (2022) and considered a blueprint for DAP development.
The DAP is being developed with community, councils, government agencies, emergency services and technical specialists. Building on the SDMP tools to reduce exposure and vulnerability, options being investigated for the HNV DAP include mitigation infrastructure, such as levees, improvements to evacuation roads, different ways to manage Warragamba Dam and better prepare the community.
Download the Hawkesbury-Nepean Valley DAP fact sheet (PDF 324.17KB)
Visit the DAP information hub to learn more about disaster adaptation planning in NSW and access key DAP resources
Learn about previous work undertaken in the Hawkesbury-Nepean Valley to reduce flood risk.
Get involved in disaster adaptation planning for your community
Community input is vital to the success of the DAP. If you live or work in the Hawkesbury-Nepean Valley, visit our Have Your Say page to complete a short survey and share your thoughts, ideas and experience with floods to help shape the DAP.
For more information email us at hnv_dap@reconstruction.nsw.gov.au
Flood risk in the Hawkesbury-Nepean Valley
The Hawkesbury-Nepean Valley (HNV) is a complex catchment. The floodplain spans a 670km2 area on the outskirts of metropolitan Sydney, from Wallacia in the south to Brooklyn in the north and touches on 8 local government areas (LGAs), Hawkesbury, Penrith, Blacktown, The Hills, Hornsby, Liverpool, Wollondilly and the Central Coast.
It is often described as a bathtub, with 5 taps, or tributaries, flowing in, and only 1 drain, constricted by steep sandstone gorges and river bends to let the water out. This leads to deep and fast-rising floods that spill out over the floodplain, isolating communities and creating large flood ‘islands’. This video explains the bathtub effect and why it leads to dangerous floods.
European records show that the HNV experiences drought dominated and flood dominated periods – often lasting for decades. This cyclic pattern is also suggested by Aboriginal Dreaming stories. The impacts of climate change are expected to increase both the intensity of droughts and rainfall events. The latter is likely to increase frequency and size of floods in the large HNV catchment. The scale and topography of the HNV means that the impacts of climate change are expected to be more severe than in other catchments in NSW.
Supporting resources
Find out your flood risk with this SES mapping tool
Use this interactive map to see how your suburb can be affected by floods of different sizes from the Hawkesbury-Nepean River.
SES resources for Hawkesbury-Nepean Valley
If you live and work in the Hawkesbury Nepean Valley you are at risk of flood. The SES has prepared a suite of resources to help plan and prepare.
Hawkesbury Nepean Valley Residents Future Flood
Why floods are so dangerous in the Hawkesbury Nepean Valley
Hawkesbury-Nepean Valley DAP updates
Living with the River photo competition
The RA held a photo competition called Living with the River to celebrate the community’s connection to the Hawkesbury-Nepean, or Dyarubbin as it is also known, and raise awareness of flood risk. More than 600 entries were received, and a selection will be shared in exhibitions at Penrith Regional Gallery and Hawkesbury Central Library. The exhibitions showcase the beauty of the river, its cultural significance and the sheer power of the waterway. They also expose the risk to communities who live on a floodplain and recognise the resilience of people and places in the Valley. Winners have been announced across 6 categories.
Hawkesbury-Nepean Valley DAP - Frequently asked questions
The Hawkesbury-Nepean Valley (HNV) floodplain stretches from Wallacia in the south to Brooklyn in the north and includes parts of 8 local government areas: Hawkesbury, Central Coast, Blacktown, Hornsby, The Hills, Liverpool, Penrith, and Wollondilly. The HNV floodplain describes the area that may be flooded in the rarest, largest flood. If you live, work, or visit these areas, you should be aware of the flood risk. More details are available via the NSW State Emergency Service interactive mapping tool.
Were recent floods 1 in 100 events?
No. In Penrith, the largest recent event was a 1 in 20 chance per year flood in March 2021. In the Hawkesbury, the largest of these events, in March and July 2022, were both 1 in 20 chance per year floods. Every flood is different, and floods can be much larger in the Hawkesbury-Nepean Valley. This video explains flood chance.
The NSW Reconstruction Authority (RA) is developing a high-priority regional Disaster Adaptation Plan (DAP) to address flood risk in the HNV, the first in the State. The RA was established in 2022 to proactively reduce the impact of future disasters across NSW and to support communities to recover faster.
A DAP is a staged and collaborative process that aims to reduce the impact of disasters on community. DAPs bring together natural hazard data and information to understand the risk now and, in the future, and to identify options to reduce risk.
The RA is developing the HNV DAP in partnership with community, local councils, government agencies, emergency services, and technical specialists to focus on mitigating and adapting to flood risk in the Valley. It will be delivered by the RA to the NSW Government mid-2025.
The HNV DAP is the first in the State and builds on many years of work to understand the impact of floods and how to reduce risk to life and property in the Valley. Every flood is different and population growth, development, and climate change can increase risk for places and communities. We know floods will be more frequent in the future, so the DAP needs to reduce risk, better prepare communities, and support faster recovery.
The HNV DAP is the first single hazard (flood) plan in the State, prioritised due to high risk. With its unique landscape and large population, the Valley is considered the highest-risk floodplain in Australia. Since 2020 there have been 8 flood events. The Valley is often described geographically as a bathtub, with 5 ‘taps’ flowing into 1 drain. This means floodwaters can be extensive, deeper, and rise more quickly than other areas. RA is leading a multi-hazard DAP in the Northern Rivers and has commenced early planning for more DAPs across the state.
There is no single solution to reduce all flood risk in the Valley. The HNV DAP will include a range of measures to reduce risk where we can and adapt where we can’t. Options being investigated include mitigation infrastructure such as levees, improvements to evacuation routes, and ways to help the community be better prepared.
To better understand the issues and what can be done to make insurance more affordable and equitable, the RA is currently investigating home and contents insurance.
This includes research in the HNV, Northern Rivers, and across the State, and we are working with other NSW Government agencies, the insurance industry, and National Emergency Management Authority (NEMA) to better understand and reflect insurance affordability in disaster adaptation planning and considerations of tolerable risk.
Major dredging of the Hawkesbury-Nepean River for flood mitigation has been modelled and found to only provide moderate flood mitigation benefits. An independently reviewed report by the Department of Public Works found the cost of dredging far exceeds the sale price of the recovered sand (by 80%). Any dredging would need to be maintained to have even a moderate effect.
As well as the huge cost, widespread and ongoing dredging would have considerable environmental impact including accelerating bank erosion, disruption to river ecosystems, and cause saline water intrusion to migrate upstream. Mining the riverbanks and riparian corridors for sandstone would cause environmental devastation.
Warragamba Dam was built to supply water for Greater Sydney and supplies around 80% of Sydney’s drinking water. In line with regulatory framework, the dam cannot be, and has never been, used for flood mitigation. Options being considered through the DAP include different ways to manage Warragamba Dam to mitigate flood risk, but this would rely on alternate sources of drinking water being secured. As the population of Greater Sydney continues to grow, water security is increasingly vital. In addition, climate change is expected to increase the severity and length of droughts.
We want to hear from people who live or work in the Valley. Visit our dedicated Have Your Say Page to share your thoughts and experiences. You can also email the HNV DAP team at hnv_dap@reconstruction.nsw.gov.au