Scientist Fears Tasmania's Irrigation Scheme Risks River Health Without Data

One 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."

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concerns when planning the new irrigation scheme, Tasmania's Natural Resources and Environment Department said "using outdated data from more than two decades ago would be unreliable".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."

'Flow regime' maintained

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.

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.

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.

Significant taxpayer funding

The scheme has secured $150 million in federal funding, $75 million from the state government and $75 million from irrigators.

Premier Jeremy Rockliff said he had "every confidence" the state would get the natural resource management of the scheme right.

"We've got it right to date, and I'm sure we're going to get it right into the future," he said.

But Ms Coughanowr said taxpayers needed more assurances, given the River Derwent was already under stress.

"For example, poor water quality or toxic algal blooms could prevent swimming, fishing, water skiing, all kinds of activities that people really enjoy," she said.

Environment Tasmania's Lucy Tremain warned many of the state's rivers were already at risk, due to climate change, increasing water demand and mismanagement, and urged the state government to improve its approach.

"This is another clear example of the government's failure to support evidence-based management of water," she said.

Scientific studies will be done at later point, irrigators say

Tasmanian Irrigation's general manager of major projects Jacob Gerke said it would make commitments around tracking environmental data as the project moved forward, and expected monitoring water quality would be among them.

"We'll be doing a range of environmental studies for this project in consultation with the state and federal regulators to determine the impacts of the project," he said.

Tasmanian Irrigation CEO Mike Sylvester was asked who would be doing studies to ensure the environment "won't be adversely impacted" by the scheme, and when they would be completed and released, during a parliamentary committee hearing last year.

"Collaboratively, Tas Irrigation and Hydro Tasmania will continue to work together as the project progresses to refine Hydro Tasmania's initial view that there's no impact," he said at the time.

"Tas Irrigation will take the lead on that with Hydro Tasmania. That study will be materially important to our EPBC submission for the project."

But with water from the scheme already sold, as is standard practice to prove demand ahead of a new irrigation project, Ms Coughanowr questioned when they would occur.

"I was campaigning well before the water was sold that these studies should be done,"