UNSW research has revealed that earthworks are having a devastating impact upon the lower Macquarie River and its floodplain.
The mapping and satellite-based study identified 338 km of levees, 1,648 km of channels, 54 off-river storages and 664 farm dams on the floodplain of about 4,300 square kilometres.
UNSW's Professor Richard Kingsford, an author of the new research report, says: "This is the first time such an extensive study has been done for any river in the Murray-Darling Basin and the extent of development is surprising as it is making a significant impact on the river and its ecology."
The study identified that earthwork structures, such as levees, channels, storage reservoirs and farm dams, were spread throughout the floodplain of the Macquarie River between Warren and Carinda on the lower Macquarie River.
The study also identified that most of the earthwork development occurred between the 1980s and 1990s, with ongoing development after governments of the Murray-Darling Basin agreed to a cap of diversions from the rivers of the Murray-Darling Basin.
This floodplain contains flood-dependent vegetation, including river red gums and reed beds. Most of the development has occurred in the southern region (72 percent), and small areas of the central and northern parts of the Macquarie Marshes.
The combination of reduced flows resulting from river regulation, and the cutting off of flows by channels and levees, has had considerable impact on floodplain trees, killing many hectares, according to UNSW Science Honours student, Celine Steinfeld, the report's co-author. At one point, levee banks and channels have constricted the floodplain from about 14km in width to about 2.5km.
The study also analysed how government policies and guidelines for floodplain works had been implemented. In the early 1980s, the NSW Government identified floodways designed to remain unimpeded so that flows could pass downstream. The study found that these guidelines had been breached.
There were 101 km of levees, 368 km of channels and 16 off river storages within the floodways. Revised guidelines in 2006 shifted the guideline boundaries so that 88km of levees, 338 km of channel and 8 off-river storages were within the revised floodways.
Professor Kingsford claims while this is a difficult area for policy and regulation, there has been no assessment by government on whether the structures are legal or may be diverting water from environmental flows despite almost a decade of discussion.
Media contact: Dan Gaffney, 0411 156 015