Additional crossing of the Clarence River at Grafton: flood impact, levee upgrade, and structural considerations

Abstract

The Clarence River catchment, on the far north coast of New South Wales (NSW), is one of the largest catchments on the east coast of Australia, with an area of approximately 20,000km2. The lower Clarence River floodplain spans 500km2, within which lie the towns of Grafton and Maclean. These towns are home to over 20,000 residents collectively and serve as a rural centre for the surrounding agricultural lands. Both Grafton and Maclean are protected by levee systems which have been developed over time as a response to previous floods in the region. Roads and Maritime Services (RMS) is currently investigating options for an additional crossing of the Clarence River at Grafton to address short-term and long-term transport needs. All upgrade options for an additional crossing of the Clarence River will increase flood levels. RMS intends to maintain the current level of immunity and mitigate any adverse impact from piers and structures within the Clarence River by raising current levees. This paper draws upon and consolidates some of the findings from the options analysis to investigate considerations associated with spanning a 600m section of the Clarence River, mitigation of flood impacts, and modifications proposed to the existing levee systems.