The District’s climate and natural landscape can create natural hazards such as heatwaves, bushfire, flooding and storms. Climate change will exacerbate these natural hazards. While planning for resilience has traditionally focused on responses to natural hazards and climate change, it is increasingly being used to consider a wider range of social and economic shocks and stresses.
Effective planning can reduce the exposure to natural and urban hazards and builds resilience to shocks and stresses. Planning for population growth and change needs to consider exposure at a local level as well as cumulative impacts at district and regional levels.
State agencies and councils use a range of policies and tools to reduce risks from natural and urban hazards. Centralised and coordinated collection of data on hazards, particularly on how infrastructure is exposed to hazards, will help embed resilience in land use planning and infrastructure planning.
Natural and urban hazards
The climate, vegetation, topography and pattern of development in the District mean that bushfire and flooding will continue to be a hazard. Placing developments in hazardous areas or increasing the density of development in areas with limited evacuation options increases risk to people and property.
Climate change is likely to result in a longer bushfire season with more bushfires and longer lasting heatwaves with more extremely hot days. Areas such as Blacktown experience on average 20 very hot days (above 35 degrees), with projections for an additional five to 10 very hot days per year in the near future. Heatwaves kill more people than bushfires, with disadvantaged and elderly people most affected.
Past and present urban development and activities can also create urban hazards such as noise and air pollution, and soil contamination. Compared to many cities around the world, Greater Sydney enjoys excellent air quality, which enhances its reputation as a sustainable and liveable city. However, the combined effect of air circulation patterns in the Sydney Basin, local topography, and proximity to different air pollution such as wood-fire smoke, can lead to localised air quality issues.
Transport movements along major roads and rail corridors generate noise and are a source of air pollution. The degree of noise or air pollution can be related to the volume of traffic and the level of truck and bus movements. The design of new buildings and public open space can help reduce exposure to noise and air pollution along busy road and rail corridors. Public transport, walking and cycling, as well as hybrid and electric cars provide opportunities to reduce air pollution. The NSW Government has recently strengthened regulation of ventilation outlets in motorway tunnels, which will also help reduce air pollution.
Soil and groundwater contamination is another urban hazard which will require careful management as the District grows and land uses change. This is particularly important when planning for more sensitive land uses such as schools, open space and low density residential neighbourhoods in areas with the potential for pre-existing contamination. State Environmental Planning Policy No. 55 – Remediation of Land and its associated guidelines manage the rezoning and development of contaminated land.
Greater Sydney, particularly its rural land, is at risk from biosecurity hazards such as pests and diseases that could threaten agriculture, the environment and community safety. Biodiversity hazards are managed by the NSW Government through the Greater Sydney Peri Urban Biosecurity Program.
Consideration of natural hazards and their cumulative impacts includes avoiding growth and development in areas exposed to natural hazards and limiting growth in existing communities that are exposed and vulnerable to natural hazards. In exceptional circumstances, there may be a need to reduce the number of people and amount of property vulnerable to natural hazards through managed retreat of development.
The impact of extreme heat on communities and infrastructure networks can also be significant. More highly developed parts of the District can be exposed to extreme heat as a result of the urban heat island effect. Increasing tree canopy cover is important to help reduce those impacts. The State Heatwave Sub Plan, which is within the NSW State Emergency Management Plan, details the control and coordination arrangements across State and local governments for the preparation for, response to, and immediate recovery from a heatwave.
Current guidelines and planning controls also focus on minimising hazards and pollution by:
- using buffers to limit exposure to hazardous and offensive industries, noise and odour
- designing neighbourhoods and buildings that minimise exposure to noise and air pollution in the vicinity of busy rail lines and roads, including freight networks
- cooling the landscape by retaining water and protecting, enhancing and extending the urban tree canopy to mitigate the urban heat island effect.
Minimising interfaces with hazardous areas can reduce risks. Clearing vegetation around developments on bushfire-prone land can help reduce risks from bushfire, but must be balanced with protecting bushland and its ecological processes and systems. Planning on bushfire-prone land should consider risks and include hazard protection measures within the developable area. The Rural Fire Service requires new developments to comply with the provisions of Planning for Bush Fire Protection 2006.
Traditionally, planning in NSW has considered the one in 100 chance per year flood event. Given the significant depths between the one in 100 chance per year flood and the probable maximum flood in the Hawkesbury-Nepean Valley, a risk-based approach that considers the full range of flood sizes is more appropriate.
Flooding constraints also exist in other areas of the District, many of which are undergoing significant growth and redevelopment. One notable example is that of the Parramatta CBD, which is the most flash-flood affected major CBD in Australia. A major flood in the CBD could cause very significant damage. Current flood management projects such as development of a flood warning system, combined with strategic planning for growth in flood-prone areas, must recognise the exceptional risk to public safety and consider appropriate design measures to strengthen the resilience of buildings and the public domain in a flood event.
The NSW Government has developed the Floodplain Development Manual 2005 to guide development on areas at risk of flooding. Councils are responsible for managing flood risk in their local government areas and typically impose floodrelated development controls in areas below the one in 100 chance per year flood level.
Flooding in the Hawkesbury-Nepean Valley
The size and topography of the Hawkesbury-Nepean Valley means it has the greatest flood exposure in NSW. Unlike most other river catchments in Australia, the Hawkesbury-Nepean Valley floodplain has significantly higher depths during flood events created by several narrow gorges in the Valley that constrict the flow of floodwater. There is a complex interaction between the main flow of the river and the multiple rivers and creeks that contribute to the catchment creating a ‘bathtub effect’.
Evacuation of people in extreme events is made complicated by the size of the area affected and the need to evacuate certain areas early, before they become isolated by rising flood waters.
Some communities are built on ‘flood islands’ that can also become isolated during floods, and key evacuation routes can face congestion or inundation during higher floods. This creates challenges for urban development and emergency management planning in the catchment.
Resilient Valley, Resilient Communities – Hawkesbury-Nepean Valley Flood Risk Management Strategy 2017 aims to reduce the potential risk to life, the economy and communities. This strategy highlights the importance of strategic and integrated land use and road planning and adequate local roads for evacuation.
Given the scale of the severity and regional-scale of the risk, more stringent consideration is warranted for areas affected by the probable maximum flood (PMF) as well as the one in 100 chance per year flood. The NSW Department of Planning and Environment is leading work to develop a planning framework to address flood risk in the Hawkesbury-Nepean Valley. This will include an examination of the cumulative impact of development within the Hawkesbury-Nepean Valley on flood risk. While this work is underway, the following planning principles will be applied to both local strategic planning and development decisions:
- avoiding intensification and new urban development on land below the current one in 100 chance per year flood event (one per cent annual exceedance probability flood event)
- applying flood related development controls on land between the one in 100 chance per year flood level and the PMF level
- providing for less intensive development or avoiding certain urban uses in areas of higher risk and allowing more intensive development in areas of lower flood risk, subject to an assessment of the cumulative impact of urban growth on regional evacuation road capacity and operational complexity of emergency management
- balancing desired development outcomes in strategic centres with appropriate flood risk management outcomes
- avoiding alterations to flood storage capacity of the floodplain and flood behaviour through filling and excavation (‘cut and fill’) or other earthworks
- applying more flood-compatible building techniques and subdivision design for greater resilience to flooding.