Scientific approach to forest flooding

ENVIRONMENTAL water has now been flowing into Gunbower Forest through the newly constructed Hipwell Road Channel for over 80 days, flooding and replenishing over 3800 hectares of forest. 

Water from the $13.5 million channel project, funded through The Living Murray program and delivered by the North Central Catchment Management Authority, has now filled the majority of the flood runners, creeks and wetlands of the forest. 

Ensuring the watering achieves optimal outcomes has meant bringing to bear the latest science and research into the life and history of the river and its floodplains. 

Dr Darren Baldwin, a biogeochemist with the Murray-Darling Freshwater Research Centre in Wodonga, is just one member of the team advising the catchment management authority on planning, operation and now delivery of the water into a thirsty forest. 

A graduate of James Cook University, his career has also seen him serve in roles at the University of Southern California in Los Angeles and at the Research School of Chemistry, Australian National University, Canberra. 

"The watering underway here is a tremendous example of a project balancing the needs of producers, the community and the environment," Dr Baldwin said. 

"The challenge we face as a community, and in fact the challenge the forest faces, is just how much change there has been in the way the river is managed, over many generations now. 

"There are very few people alive now who would have a clear memory of the Murray before it was altered." 

Dr Baldwin cites the example of the Hume Dam, construction on which began in 1919 and finished in 1936. 

"So much of the Murray River's water comes through the Hume Dam, it was specifically designed to capture all the run-off from the mountains to the north east, so without the dam that water would be making its way here right now, through August. 

Dr Baldwin said even in drought years, the plains were flooded for extended periods, with research showing the water would be held on the floodplains for up to four months. 

"Another case in point where our knowledge has developed greatly is in the area of blackwater, many people are still surprised to hear that blackwater is an essential building block of river eco-systems like this one. 

"As organic matter breaks down it releases carbon, nutrients and tannins into the water which turn the water a dark colour, an event known as blackwater. Bacteria in the water consume that carbon and as they do they also use dissolved oxygen in the water. 

"We keep an eye on this through a monitoring program and recognise the concerns people have about this, but, we also need to be clear that blackwater is a normal and in fact essential part of a river in flood; blackwater is an important part of the Murray River's health. 

"To be clear here, I'm not talking about what is known as hypoxic blackwater, the most obvious recent example occurred during the floods in 2011, after the Millennium drought - that event occurred late in the year, there was warm water and high levels of organic matter creating a tremendous demand on dissolved oxygen in the water. 

"This is different, the water here is being delivered in winter, it's cold, there is less organic matter on the forest floor and we have a through-flow system, with water continually moving out of the forest and back into the Murray. 

"In fact, 70 per cent of the water you see flowing through here heads back out and is available for use downstream by farmers and other users; this greatly reduces ponding on the forest floor. 

Freshwater fish scientist, Dr Martin Mallen-Cooper is an expert on the Murray Darling Basin's native fish life and, like Dr Baldwin, was also brought in by the NCCMA team. 

"We know through radio tracking that large-bodied species, Murray Cod and Golden Perch, just love to get out onto these floodplains to feed, they can 'smell' the tannins in the water and know that food is there to be had before moving back to the river," he said. 

"The changes we've seen in management of the river have meant this network of floodplains has been greatly reduced, that's where the Hipwell Road project is so amazing and will mean that both those larger fish and the small-bodied native fish floodplain specialists like the Southern purple-spotted gudgeon and Southern pygmy perch, fish that have evolved in these places, will now have a restored habitat for their feeding and breeding," Dr Mallen-Cooper explained. 

Dr Baldwin says that while we'll never see a return to the way things were before the changes in river management "natural conditions saw some flooding occur out to 50 kilometres either side of the river", projects such as the Hipwell Road Channel were a positive sign for the future of the mighty Murray. 

"The watering of Gunbower Forest through the Hipwell Road Channel is an example of the sensible use of environmental infrastructure to optimise and balance the many needs we have for water," Dr Baldwin said. 

Inflows will continue into the forest until the end of October. As irrigation season begins, flows will reduce as the environment shares the capacity of Gunbower Creek with irrigators.

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