Scientist 'shocked' $300m irrigation scheme pushing ahead without studies

Scientist Christine Coughanowr says concerns raised in a 2002 study into the lower Derwent have not been disproved. (ABC News: Emily Smith) The $300 million Greater South East Irrigation Scheme will supply 37.2 gigalitres of water to farming areas near Hobart from 2030. A 2002 study recommended against extracting any more water from the lower Derwent over summer. A scientist says the 2002 study is yet to be disproved and should be reinvestigated ahead of the new scheme but stakeholders say environmental risks will be managed. Link copiedShareShare articleOne of Tasmania's leading water scientists fears the state government will plunge millions of taxpayer dollars into a new irrigation project without collecting crucial environmental data, potentially putting Hobart's major river at risk. The Greater South East Irrigation Scheme aims to supply 37.2 gigalitres (GL), or more than 14,000 Olympic swimming pools, of water per year from Lake Meadowbank, on the River Derwent, to one of the state's driest farming areas from 2030. It has been described as a key part of the state government's plan to increase the annual value of Tasmanian agriculture to $10 billion by 2050. But the idea has triggered alarm bells for Christine Coughanowr, the co-chair of the Tasmanian Independent Science Council, founder of the Derwent Estuary Program and author of Tasmania's State of the Environment Report rivers and wetlands section. She said the state government had not commissioned an independent study into the impacts of additional summer water extraction from the lower Derwent since a 2002 study strongly urged against the idea. "Given what I'd always been told, that the Derwent flows in summer were very low, that we were contemplating taking another 37,000 megalitres from the system. "And a lot of that would be taken in summer months." Greater South East Irrigation Scheme will supply farming areas north of Hobart. (Supplied: Tasmanian Irrigation) The 2002 study, commissioned by the state's environment department, recommended "no further abstraction take place in January-April, in order to avoid risks of further decline in riverine and estuarine environmental values". Ms Coughanowr said the study was taken seriously at the time, and in the years since, additional summer water allocations for irrigators in the area were only approved in 2004 and 2013. But asked whether it considered these concerns when planning the new irrigation scheme, Tasmania's Natural Resources and Environment Department said "using outdated data from more than two decades ago would be unreliable". Ms Coughanowr pointed out that it might be old, but it had yet to be disproved. "So you start with what you've got, which was very high quality at the time, and if you're not happy with that, redo that research and come up with a better plan. "We need the checks and balances, and we need a very precautionary approach to a river that's already under stress." Christine Coughanowr believes further studies are needed into the scheme's potential impacts on environmental flows. (ABC News: Emily Smith) But stakeholders — including NRE, Hydro Tasmania and Tasmanian Irrigation — said the scheme will source water upstream of the Lake Meadowbank dam wall, allowing water to be released into the River Derwent to maintain flow. An NRE spokesperson said a constant "flow regime" was intended to "protect freshwater quality and river health", and fulfil existing commercial water supply agreements. It also said some irrigation takes would be paused if flows drop below certain levels. Hydro Tasmania can release water from Lake Meadowbank, ensuring a flow regime at all times, which NRE says is intended to protect river health. (ABC News: Emily Smith) But Ms Coughanowr believed this flow regime was based on operational needs, not environmental ones. It is also understood that minimum flow is only one element in maintaining overall river health, with timing, frequency, duration and variability of flows also having impacts. Hydro Tasmania said the scheme represented only 1.6 per cent of the average water discharged from Meadowbank between October and March each year. "While this volume of water is certainly a factor to consider, it won't materially change how we operate the system," a spokesperson said. "And it won't affect our ability to maintain existing flow requirements and water supply commitments downstream of Lake Meadowbank". Ms Coughanowr said it would be more helpful to know what percentage of total discharge the scheme represented during the driest months between January and March. Scientists warn the River Derwent is already under significant pressure. (ABC News: Emily Smith) The scheme has secured $150 million in federal funding, $75 million from the state government and $75 million from irrigators. The Greater South East Irrigation Scheme is designed to support the production of cherries, apples, salad vegetables, wine grapes, stone fruit, lucer

Scientist 'shocked' $300m irrigation scheme pushing ahead without studies

Key takeaways

More in international