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The NSW Government has prepared a new Regional Flood Study overview providing the most up-to-date information and maps on river flooding in the Hawkesbury-Nepean Valley.

Using new and more accurate data, and better modelling techniques, the three-volume study includes an atlas of maps that show flood extent, depth and likelihood to help people understand their flood risk. It identifies flood-affected areas in the valley and assesses the impact of climate change.

It was developed in conjunction with regional flood and geography experts to produce the best available information for planning and decision-making. It is also used for emergency management and evacuation planning; land use and road planning; to help infrastructure owners make decisions about flood risk mitigation measures; and to measure more accurately price insurance premiums in the insurance industry.


New data

The study makes use of more accurate, comprehensive data, derived from:

  • extensively tested rainfall probabilities released by the Bureau of Meteorology based on a wider range of information and longer rainfall records, and
  • new topography made available through ‘LiDAR’ surveys in 2011 and 2017, which used an aircraft to create high resolution mapping of the ground surface and show recent changes to the valley landscape.


New modelling

New modelling techniques using random combinations of the range of inputs that generate and influence flooding (a ‘Monte Carlo’ approach). Inputs including where and when rain falls, soil moisture levels, the storage level of Warragamba Dam at the start of an event, were applied to model close to 20,000 possible floods. This type of modelling better reflects the complexities of rainfall and flooding to capture the real variability of real floods.

The approach follows international best practice and the up-to-date flood guidelines of the Floodplain Development Manual and the 2017 Managing the Floodplain.

The complete Hawkesbury-Nepean Valley Regional Flood Study report (in 6 pdf volumes, including 382 maps) is publicly available on the SES Flood Data Portal.


My flood risk

  • The Flood Study data was used to develop new flood awareness resources on the NSW SES website, including an interactive mapping tool people can use to generate maps and information related to their suburb in the floodplain, as well as videos, fact sheets and Q&As.
  • The new information makes it easier for people living and working in the Valley to understand their risk and prepare for floods.