Let’s press pause on water scheme

The most recent national State of the Environment report in 2016 – another was due in 2021 but has yet to appear – drew attention to a lack of information about the state of Australia’s freshwater resources.

It said that in the period since the first SOE report, in 2011, “efforts to analyse, integrate, assess and report holistically on the state of inland waters have generally decreased”.

The report does not explain why this was so, but assuming it wasn’t because scientists and other field workers simply gave up, it could only be because research institutions – and ultimately government – withdrew support for their work. 

Is there any task more necessary than keeping tabs on the flow of water down our rivers? If we want to live in cities and towns, and to grow food while also conserving natural ecosystems, we need a steady supply of water. It’s that fundamental. Any government that reduces support for this work is failing its citizens.

Most of Hobart’s drinking water comes from the Derwent river system. At the end of a warm dry spring in 2019, city users were suddenly faced with the prospect of restrictions, learning in the process that they shared their water supply with irrigators in the Coal River valley. 

While the cause of the shortage wasn’t clear at the time it was speculated that irrigation for high-value water-intensive crops – mainly fruit, nuts and green-leaf vegetables – had a lot to do with it. For their part, the irrigators were told to cut their water use in half. Faced with the loss of expensive crops they were very unhappy.

With summer still ahead, this wasn’t a good look either for the state’s town water administrator, TasWater, or for Tasmanian Irrigation, which manages farm supply. Questions came thick and fast. Why did this happen without warning? And why were irrigators using water that had been treated at ratepayers’ expense for human consumption?

Tasmanian Irrigation set about finding other ways to deliver water to thirsty farms, and ten days ago announced its solution, to combine three existing schemes into a single “Greater South East” scheme. It will take water from the Derwent’s Meadowbank Dam – above the water treatment plant at Bryn Estyn– for irrigators in the Derwent and Coal valleys.

Water minister Jo Palmer delivered the news. The $408 million scheme, to be Tasmania’s largest, would help future-proof against climate change, she said, while removing the risk to farmers from investing in irrigation.

That’s a brave call. Sure, town users won’t have to share their treated water with irrigators, but there remains the question that no-one in government seems to want to talk about. How can you guarantee a greater water supply to more irrigators from the same river system that caused such grief in 2019? It’s still the same river.

This has a long back-story. In 2002, an intensive government-funded study to determine environmental flows for the lower Derwent found that no additional water should be taken from the river in summer, while specifying minimum daily flows in other months and regular five-day “flushing” events. No such measures have been put in place.  

Since that study, a number of low-flow periods in the Derwent between Meadowbank and the river’s tidal limit at New Norfolk have increased the risk of degraded water quality, algal blooms, contaminated seafood and damaged seagrass beds and wetlands, with consequential impacts on wildlife and humans. 

We don’t know how far this damage has already progressed, nor the impact of taking even more water out of the river system, because there has been no comprehensive follow-up study of lower Derwent water chemistry and flow over the 20 years since 2002. 

Yet Tasmanian Irrigation is putting out for public comment a “preferred option” to build new pump stations pushing water to new and existing irrigators in the districts of Gretna, Jordan River Valley, Brighton, Cambridge, Richmond, Tea Tree, Colebrook, Campania, Sorell, Forcett and Pawleena. It expects to put water entitlements up for sale early next month.

Engineers and farmers can do wonderful things with water, but they’re not miracle-workers. They can move water from one river system to another but they can’t create it from nothing, and they can give no guarantees against bad consequences arising from a radical change in water supply, like degraded water at one end or rising surface salinity at the other.

In the face of past near-misses, and lacking detailed, long-term flow studies or any current, comprehensive investigation of the state of the Derwent catchment to guide them, it is foolhardy in the extreme for the Rockliff government to push ahead with this scheme.

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