The Hawkesbury-Nepean River is one of the major river systems of NSW, draining a catchment area of 22,000 square kilometres. Exceptionally heavy rainfall in this area can lead to severe flooding.
This is worsened below Richmond by the fact that water flows into the valley much faster than it can flow out.
In the largest flood of record, which occurred in June 1867 flood waters reached approximately 12 metres higher than the deck of the present-day Windsor Bridge. Even larger floods than the 1867 are possible. Maps of the areas inundated in the 1867 flood are available for download.
Flood Risk Management Planning Guides
One of the key findings of the Hawkesbury-Nepean Flood Management Strategy (1998) was that the planning and construction of urban development on the floodplain must be improved to reduce the impact of flooding on people and property. To this end, the Hawkesbury-Nepean Flood Management Advisory Committee commissioned the production of flood-specific planning guidelines. The three guidelines published here are the result of a collaboration between state and local government and also involved research and testing by independent research organisations including several NSW universities (Sydney, Macquarie, Newcastle) and the CSIRO. Flood emergency management is focussed on protecting people first and then their property. The capability to evacuate people off the floodplain is the key flood emergency management strategy.
The guidelines recognise that all new development should be designed and built to ensure that emergency management action can be safely and efficiently implemented when a flood threatens. The guidelines will also assist individuals and businesses to minimise the damage that would otherwise be done to their property when it is flooded. Houses and buildings cannot be moved as a flood approaches but basic modifications, some required at the time of construction, can make the difference between a total flood loss and a recoverable asset.
These guidelines are voluntary and are not part of any mandatory State planning code or regulations in NSW. The guidelines are provided for the advice of individuals and organisations that are genuinely interested in producing better flood emergency risk management outcomes.