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Managing floodplain watercourses

Located in northern New South Wales, the Clarence River is the largest coastal catchment in the State. It covers over 22,000 square kilometres. Its floodplain is characterised by low lying flat alluvial plains, intersected by a network of lagoons, channels and creeks. With an area of at least 800 square kilometres, the floodplain supports the largest commercial river fishery in the State, as well as significant sugar cane, timber and beef cattle industries.

The floodplain is transected by more than 700 kilometres of public and private drainage channels and is underlain with extensive deposits of high risk acid sulfate soils. Combined with acidic soils, the floods pose a substantial risk to the environmental, social, cultural and economic values of the Clarence Valley.

In 1997, as a result of industry and landholder concern about the affect of floodplain drainage on river health and water quality, the Clarence River County Council (now Clarence Valley Council Floodplain Services) began to coordinate the management of floodplain watercourses. It established the Clarence Floodplain Project.

At the time the concept was unique; a project based with the local council responsible for the management of public floodgates and drains, with a steering committee consisting of major stakeholders including industry and landholders.

The project funded a dedicated officer to work with landowners to develop on ground demonstration projects. This model has since been adopted in many other coastal catchments in New South Wales.

Important research and on ground works have been undertaken with funding from Clarence Valley Council Floodplain Services, the Australian Government’s $3 billion Natural Heritage Trust, the New South Wales Environmental Trust, Department of Land and Water, and fisheries research and development corporations. Forty-two creek and drain management plans have now been developed with more than 200 landholders now actively managing their waterways. Five former wetland areas have been re-inundated and restored, and the passage of fish has substantially increased. More than 20 kilometres of fish habitat has been opened, and results indicate a reduction in acid discharges, and fish kills.

The project has developed and tested new technologies including tidal floodgates. These provide flood protection, but allow regular controlled water exchange. They facilitate fish passage, increase oxygen levels in drain water and limit odours that occur in some drains from rotting vegetation.

The Universities of New England and Southern Cross are now undertaking research to examine pasture response to changed water regimes. They are also focusing on fish passage into wetlands via tidal floodgates and hydrological changes.

All sectors of the community have benefited from the project. An improved environment, better water quality, increased fish passage and improved relationships between various sectors of the community are just some project achievements. The project has also had a large positive impact on the local economy. Improvements in backswamp management have led to improved habitat.

New South Wales Fisheries has estimated the monetary value of restoring fish breeding areas to be in the order of $8,000 per hectare. Tourism and recreational fishing industries have also been enhanced.

The next priority is to consolidate completed works and develop management plans for other priority areas. These will then be extended to catchment based plans.

Backswamp management will also be improved and monitoring programs developed. Clarence Valley Council Floodplain Services also intends to investigate partnership opportunities with the local Catchment Management Authority.

The success of the Clarence Floodplain Project has been due largely to the support of landholders and their willingness to help develop and commit to management plans. Landholders are actively involved in planning the management of their waterways and the types of modifications undertaken to the flood mitigation structures. Essentially they own the land, do the work, monitor changes and have a vested interest in flood control and drainage management.

The Clarence Floodplain Project was commended in the 2004 National Awards for Local Government for opening more than 80 kilometres of waterways to tidal exchange. This has improved water quality in the floodplain creeks and Clarence estuary. It also allows for better management of acid discharges. Exchange with saline estuarine water, which has a higher buffering capacity, helps to neutralise sulfuric acid from acid soil runoff in drains.

By working together, government, the community and landholders will continue to demonstrate best practice floodplain management and flood control. Water quality and wildlife habitat areas will benefit, resulting in a more sustainable recreation industry for this area.

For further information, visit the Clarence Valley Council web site at www.clarence.nsw.gov.au or contact Cherie Smith on (02) 6642 3277.

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