Hawkesbury-Nepean Development Dilemma

Calculations have shown that the adoption of a 100 year ARI flood as the designated flood in the Hawkesbury-Nepean valley would cause the average annual flood damage bill to increase by 2½ times within 50 years to $100 million each year. If a PMF is adopted as the designated flood, there would be a minimal increase in future flood risk, but large areas of land would be affected by planning and development controls. However, a flood damage assessment and adoption of a particular designated flood, makes up only one component of a much larger equation of 'non-flooding' issues.

Therefore, the issue of flood risk in the Hawkesbury-Nepean Valley should ideally be tackled with a total catchment management approach, with cooperation among all councils and the community. It is not unreasonable to expect compliance with the Hawkesbury-Nepean Floodplain Management Strategy (1997) prepared by the Hawkesbury-Nepean Floodplain Management Committee and as a minimum similar emergency response outcomes required in the above documentation should be required to be undertaken before occupation of new growth centre release areas.

The recent opening up of the North West and South West sectors of Sydney to greatly increased development will potentially expose possibly thousands of homes and businesses to one of the most devastating floodplains in Australia, the Hawkesbury-Nepean River and its tributaries.

If the NSW State Government and strategic land use planners are to learn a lesson from the horrors, distress and cost of the floods of Brisbane and its surrounding areas, it is that flood risk is related not just to the chance of a severe flood occurring but also to the consequences thereof. The 2011 Brisbane flood was not a “flood of record”, that flood was some 2m higher than the 1974 flood; nor was the 2011 flood as high as the 1974 flood. Indeed, the 2011 flood event at Brisbane is considered to be less than a 50 yr ARI flood event, yet major damage has occurred. The financial and social impacts of a flood disaster must be fully considered and appropriate planning undertaken.

If today’s politicians and planners do not wish to be condemned by tomorrow’s victims of destructive floods, they must learn that floodplains deserve respect and appropriate planning. At the very least, when building in the floodplain, resilience measures should be mandatory; where developments are allowed which require evacuation in flood events then appropriate notation on all planning certificates and individual property floodsafe plans must be compulsory. Resilience measures are well known and documented. Planners need to be decidedly flood aware when zoning land, approving sub-division design and in requiring flood-compatible designs for dwellings and buildings even well above the current planning levels. A set of three guidelines covering these aspects should be available at most council libraries within the Hawkesbury area and can be found on the internet at:

Reducing Vulnerability of Buildings to Flood Damage: Guidance on Building in Flood Prone Areas

Designing Safer Subdivisions: Guidance on Subdivision Design in Flood Prone Areas

Managing FLood Risk through Planning Opportunities: Guidance on Land Use Planning in Flood Prone Areas

These are simple measures which if adopted will add a small cost to development but provide significant reductions in the costs of recovery from flooding and could save lives. Proper consideration of floods can greatly reduce the risk to life, damage and inconvenience to individual owners and occupiers and reduce the large scale liability to governments, insurers, commerce and charities.