There is increasing flood risk in the highly populated and major growth region of the Hawkesbury-Nepean Valley. Over the long term, the annual average cost of flood damage in the Hawkesbury-Nepean Valley is expected to be in the order of $130 million (2018).
Hawkesbury-Nepean Valley flood management represents a long-term infrastructure resilience challenge. Increasingly frequent extreme weather events, combined with the impacts of population growth in new and more densely populated areas, will likely require an increase in the level of resilience of some infrastructure networks. Infrastructure should be able to continue operating through minor disruptions, and recover quickly from major disruptions.
The largest flood on record in the Hawkesbury-Nepean Valley occurred in 1867, when the river level at Windsor reached 19.2 m above mean sea level, compared to the normal river level, which is less than 0.5 m above mean sea level. If the 1867 flood levels were to occur today, it is estimated that the total tangible damages could exceed $8 billion. If a more extreme event were to occur, the total damages could approach $10 billion (for a 1 in 1,000 year event).