The Hawksbury-Nepean Valley area includes Penrith, Richmond and Windsor population centres and covers 425 square kilometres of floodplain associated with the Hawkesbury and Nepean Rivers. Currently, up to 134,000 people live and work on the floodplain and could require evacuation in a flooding event. As one of the fastest-growing areas of Western Sydney, this number is expected to double over the next 30 years[1].

The Hawkesbury-Nepean Valley Flood Evacuation Road Resilience Program (the program) established by Transport for NSW (Transport) aims to improve the resilience of flood evacuation routes to better withstand local flash flooding and increase the number of cars that can evacuate during major flooding events. The program proposes over 100 improvements across the Penrith, Hawkesbury, The Hills and Blacktown local government areas. The improvements are based on extensive flood modelling and consultation with the NSW State Emergency Services (SES) and NSW Reconstruction Authority (NSWRA). The program will progress alongside NSW Reconstruction Authority’s Disaster Adaptation Plan that will include a suite of integrated measures to reduce risk where possible and adapt where the risk cannot be adequately reduced.

AECOM has been engaged to undertake the Concept Design and Review of Environmental Factors for some of the proposed improvements along flood evacuation routes.

Designing safer flood evacuation routes
In 1867, the Hawkesbury-Nepean Valley recorded the largest flood on record. Today, if such a flood were to occur again, up to 90,000 people would require evacuation. Evacuation constraints and complexities in the Valley mean that during major flooding events it’s not possible to safely evacuate the whole population on time. Across the Valley, communities rely on common roads to evacuate, resulting in constrained and congested flood evacuation roads during flood events. Many roads across the area have low points and are cut off before the higher inhabited areas are inundated, creating flood islands. This isolates population centres, potentially placing people at risk.

This program focuses on improving the flood immunity and efficiency of key flood evacuation routes and roads that connect to evacuation routes. This will provide residents with a safe, reliable road network during large flood events – rather than general road network performance.

AECOM’s team aims to improve the road network by:

  • Increasing the road evacuation capacity during major flood evacuation events by widening the road shoulder to provide a second evacuation lane.
  • Making the evacuation routes work better by upgrading pinch points such as intersections and roundabouts.
  • Raising sections of road and improving drainage at key low points to make the road network more resilient to flash flooding and able to stay open for longer.
  • Proposing a new bridge to keep an evacuation route open for longer, in the event of localised flash flooding

Through a collaborative design process with Transport for NSW, AECOM will also investigate the opportunities, innovations and challenges associated with working across four local government areas and interfacing with separate workstreams.

[1] https://www.infrastructure.nsw.gov.au/media/2855/infrastructure-nsw-resilient-valley-resilient-communities-2017-jan.pdf