Project Details

Clients: Roads and Traffic Authority, Kempsey Bypass Alliance, Abigroup

Location: Kempsey / Frederickton, Macleay River, NSW

Project Involvement: Route Selection, Feasibility, Environmental Impact Assessment, Concept Design, Construction


The Kempsey Bypass is the initial stage of the Kempsey to Eungai Upgrade project, involving a 14.5km four-lane divided highway which crosses the Macleay River floodplain to the east of Kempsey. The 3.2km bridge across the Macleay River and floodplain is the longest in Australia. WMAwater were heavily involved in all phases of the project.

The project involved extensive mitigation works to compensate landholders for impacts on flood behaviour resulting from the bridge, including:

  • A new levee at Frederickton increasing flood protection for existing properties from the 10 year ARI to 100 year ARI level;
  • House raising and structural reinforcement to improve the level flood immunity for individual homesteads; and
  • Earthen mounds to provide temporary refuge for stock during floods.

Image copyright Roads and Maritime Services 2012. Reproduced with permission.

Scope of Work

In all, WMAwater undertook over 20 detailed hydraulic modelling assessments for various aspects of the project. Major assessments included:

  • Hydrologic and hydraulic modelling for route assessment;
  • Impact assessment of various bridge configuration options and mitigation workst;
  • Community liaison to negotiate flood mitigation works;
  • Assessment and advice to construction team relating to flood impacts of the construction platform in the Macleay River and other temporary works; and
  • Detailed modelling of specific areas to identify impacts of mitigation and localised construction works on individual properties.
  • Consultation with a wide variety of stakeholders including Council, SES, and local community regardign the impact of the bypass.