Hawkesbury-Nepean catchment, copyright NSW Office of Water

Located on the NSW Central Coast in Greater Sydney, the Hawkesbury-Nepean catchment is one of the largest coastal basins in NSW. With an area of 21,400 square kilometres, over 70 per cent of the catchment consists of mountainous terrain, with about 10 per cent of flat terrain. The south terrain, around 10 per cent of the total catchment, comprises undulating plateau type country. The maximum elevation is about 1,290 metres.

The catchment includes the coastal reaches from Turimetta Headland to Barrenjoey near its mouth, and catchments for Warragamba, the Upper Nepean and the Mangrove Creek dams, the main water supply reservoirs for the Sydney metropolitan area, including Gosford and Wyong.

Hawkesbury-Nepean Valley Flood Management Review

Stage One of the Review

The Hawkesbury-Nepean Valley Flood Management Review commenced in early 2013, in response to the Government's adoption of The State Infrastructure Strategy 2012-2032 and ongoing community concerns about flood risk. This Review concluded the first stage of the assessment of current flood mitigation arrangements.

In 2012, extensive flooding across south-eastern Australia, including the Hawkesbury-Nepean Valley, saw Warragamba Dam spill for the first time in 14 years. This raised awareness about the potential impacts of flooding.

In response, the NSW Government began the Hawkesbury-Nepean Valley Flood Management Review to consider flood planning, flood mitigation and flood response in the Hawkesbury-Nepean Valley.

The review was chaired by the NSW Office of Water and involved the Department of Premier and Cabinet, Sydney Catchment Authority, NSW State Emergency Service, NSW Treasury, Office of Environment and Heritage, Department of Planning and Infrastructure and Department of Finance and Services.

Read or download the Hawkesbury-Nepean Valley Flood Management Review – project overview (PDF 123 KB).

Stage One of the Review presented its findings to Government in late 2013.

Key findings of Stage One of the Review

The Review concluded that there is no simple solution or single infrastructure option that can address all of the flood risk in the Hawkesbury-Nepean Valley floodplain. The risk will continue to increase with population growth.

The review has identified that infrastructure options can reduce, but not eliminate the risk to life and property in the Valley.

Evacuation is the only mitigation measure that can guarantee to reduce risk to life, and that detailed investigation is required to support an integrated approach to reduce overall flood risk in the Valley.

The Review developed ten potential strategies for further consideration to improve flood risk management in the Hawkesbury-Nepean Valley - grouped under three major categories – infrastructure – governance – and non-infrastructure.

Management of the flood risk in the Hawkesbury-Nepean Valley includes mitigating the impact of flood, planning and preparedness for flooding, as well as response to and recovery from floods.

The potential infrastructure strategies include works that can be built to mitigate floods, as well as the enhancement of flood evacuation capacity through improved transport infrastructure.

The review identified several priority areas for action:

  • increasing flood awareness and preparedness in the community
  • the enhancement of emergency planning, response and recovery
  • better consideration of flood risk in land use planning
  • detailed cost benefit assessment of potential infrastructure options
  • reviewing effective flood management arrangements.

For more information on the review's findings, read or download:

Next Stage of the Review

The NSW Government has established a task force to lead Stage Two of the Review into flood management and preparedness in the Hawkesbury-Nepean Valley. Stage Two builds upon the preliminary investigations completed in Stage One which looked at the current flood management and planning in the valley to identify opportunities to improve the ways in which future floods are managed.

The task force will be working with key stakeholders as it undertakes its priority tasks, including local councils, the insurance industry, flood and water management and other government agencies.

The immediate priority of the task force is building the resilience and preparedness of the communities and businesses of the Hawkesbury-Nepean Valley to future flood.

Stage Two of the review will undertake a detailed cost benefit assessment of the most practical and cost effective flood mitigation options for the government to consider.

Additional information will be published here when it becomes available.

Major towns

Penrith, Gosford, Goulburn, Camden, Katoomba, Lithgow, Richmond, Windsor, Moss Vale, Mittagong and Bowral.

Rivers and tributaries

The main rivers and tributaries include the Hawkesbury-Nepean, Avon, Cataract, Colo, Cordeaux, Coxs, Grose, McDonald, Wollondilly, Warragamba and Wingecarribee rivers. There are also a significant number of creeks including Berowra, Bundanoon, Cascade, Cattai, Cowan, Mangrove, Sooley, South and Mooni Mooni creeks.

Real-time flow data

The Office of Water monitors the conditions of river systems in NSW and provides regular updates on water levels, rainfall, water temperature and electrical conductivity.

View real-time data from the Hawkesbury-Nepean catchment on this website.

Major water storages

While the basin is considered unregulated, river flows within much of the catchment are heavily controlled by five major dams, as well as various major weirs which retain river flows. These storages include Warragamba, Mangrove Creek, Nepean, Lyell, Avon, Cataract and Cordeaux.

Major water users

The Hawkesbury-Nepean River system supports a $259 million agriculture industry. Major water users in this catchment include Sydney Water Corporation, local councils, the irrigated agriculture, tourism, fishing and oyster industries, and various recreational users. Sydney Water supplies water to most homes and businesses within the greater metropolitan area.

Key water management issues

While the natural flow of many rivers and streams in the Hawkesbury-Nepean River Basin has been significantly altered by water storages such as dams and weirs, the basin is considered an unregulated system. This is because the water storages do not regulate flows downstream – they do not capture and then release water into the river downstream for extraction by users.

Most water storages in the basin are owned and operated by the Sydney Catchment Authority, so Sydney Water is able to supply homes and businesses in Greater Sydney with a reliable reticulated water supply.

Significant alteration of the natural river flow, intensive urban and industrial development as well as numerous, competing needs for water are key water management challenges.

Specific water management issues include:

  • water quality: pollution, algae and weed growth
  • river bank management: urban and agricultural development, construction of 'instream' development such as pontoons and wharves
  • environmental water: sufficient flows and freshes to maintain river health
  • increasing demand for water: urban population and industry growth
  • water accounting: the NSW Government is rolling out water meters to licence holders to account for water extraction.

Environmental values

The Hawkesbury-Nepean river is an important environmental asset. Dams and weirs in rivers affect the natural flow of water, water quality, fish migration and habitat. Environmental flows, or water released from a dam or weir, improve water quality, fish passage and habitat conditions.

To enable new environmental flows to be released to the river, a $39 million upgrade was carried out on dams and weirs across the river. Modifications included new environmental release outlets and fishways. A flow scheme which began in July 2010, mimics the natural flows of the river, allowing more water to be released when it rains, and less when it's dry. The improvements are part of the NSW Government's Metropolitan Water Plan.

Water sharing plans

To preserve water resources in river and groundwater systems for the long term, it is critical to balance the competing needs of the environment and water users. Water sharing plans establish rules for sharing water between the environmental needs of the river or aquifer, and water users, and also between different types of water use such as town supply, rural domestic supply, stock watering, industry and irrigation.

Water sharing plans in this catchment:

Under the Water Management Act 2000 all water sharing plans are required to have performance indicators to assess whether the plans have been effective in meeting their objectives. The Environmental flow response and socio-economic monitoring. Greater Metropolitan - progress report 2010 (PDF 2.3 MB) summarises activities undertaken in the previous water year and provides an interim assessment of outcomes from the investigations.