floodplain management

Clarence Valley Council is responsible for floodplain management and flood mitigation infrastructure on the Clarence floodplain, the largest coastal catchment in NSW.

Historically, major and moderate flooding of the Clarence Valley has occurred 71 times in the past 166 years (that is greater than 3.6 m at the Prince Street Grafton gauge). Prior to 1959, floods had devastating impacts on both agriculture and urban areas in the Clarence Valley. Major flood mitigation works were carried out in the valley during the 1960s and 1970s; with the majority of flood mitigation works being constructed during this period.

The major urban centres of Grafton and Maclean have been protected against floods since completion of their levees in the 1970s. South Grafton now enjoys that same level of protection. Urban levees have also been constructed at Ulmarra and Iluka.

In more recent years, Council's research has identified innovative management practices for flood mitigation drains to minimise the effects of potential acid runoff, poor water quality and restricted fish passage.

Through the 'Clarence Floodplain Project', Council has embarked upon a new and successful program of active floodgate management to better manage flood mitigation drains. The process involves opening of floodgates to allow improved tidal exchange which leads to better water quality, improved fish passage and significantly reduced acid runoff.