EXCLUSIVE: The NT Government’s recently announced water allocation figures have been called into question by scientists after it inexplicably doubled the estimated annual re-filling rate provided by a hydrologist for one aquifer, then created its own figure for another aquifer which it attributed to his model despite the consultant not providing an estimate for the recharge.

Both Chief Minister Natasha Fyles and Environment Minister Lauren Moss have refused to answer questions and to explain the science behind both the the massive increase for the Georgina basin and the creation of a figure for the Wiso basin – numbers which they attributed to have been arrived at by consultant Anthony Knapton in his 2020 DR2 modelling report.

The allocation plan has been widely criticised by water experts from Australian universities who accused the government of lacking a proper methodology for determining water allocation and failing to meet national standards.

A 2020 consultancy was struck to model the recharge figure for the Georgina, Wiso and Daly basins, which are all interconnected parts of the greater Cambrian limestone aquifer, which importantly, sits in part above the Beetaloo basin, and to calculate how much water could be distributed for intensive agriculture, mining, and fracking.

In his 2020 report for the government, Mr Knapton came up with an annual recharge figure of 315 gigalitres (GL) for Georgina basin based on a three-dimensional surface water and groundwater modelling system called DR2.

Professor Matthew Currell, from the RMIT engineering department, said Mr Knapton did not produce a recharge estimate for the Wiso basin in his report, possibly he said, because there was insufficient reporting data to get a reasonable estimate.

However when the government released its Georgina and Wiso allocation plan on November 18, it said the annual recharge for the Georgina was 607GL and 45GL for the Wiso, which it directly attributed to Mr Knapton’s DR2 modelling.

Mr Knapton, who worked for more than 14 years as a hydrologist or water modelling manager for the NT Government up until 2013, did not return a phone call to answer how he felt about his modelling figure being doubled, and if he could explain why and how it was done.

In a recently released report on the hydrology of the Cambrian aquifer, Prof Currell was engaged to produce for the NT Environment Centre, he cites seven studies, including his own, that give recharge estimates for various basins in the Cambrian aquifer. The government’s background paper is the only one that provides an estimate for the Wiso.

In Mr Knapton’s earlier report, he states that while the work was an update to the 2009 coupled modelling system encompassing the entire Cambrian aquifer, he said the focus was on the area surrounding Mataranka, the head waters of the Roper River and the groundwater system hosted by the Georgina Basin to the south and did not mention the Wiso.

The report also addresses the reliability of recharge figures for the basins: “There is some uncertainty regarding the estimated distribution of recharge, particularly in the semi-arid zone of the Wiso Basin,” he wrote.

“The recent CSIRO led Gas Industry Social and Environmental Research Alliance studies examining recharge and groundwater dating will provide valuable constraints to the current model inputs and additional work to incorporate this work is highly recommended.”

When the government’s allocation plan report was released, the government stated it had been created with reference to scientific studies, and recent water monitoring undertaken as part of a Strategic Regional and Environmental Baseline Assessment (SREBA). However the SREBA, which was recommended by 2018’s Scientific Inquiry into Hydraulic Fracturing in the Northern Territory, is not due to be finished until next year.

In a separate 2021 NT Government report under the title of “knowledge gaps”, it puts the understanding of recharge process for one part of the Georgina basin at “poor” and another part at “good”. It lists it as “information essential to establish pre-development baseline assessment for the aquifer”.

Complicating matters is that the estimates on recharge from the basins varies wildly.

The NT Government’s own Environment and Natural Resources Department 2019 Georgina Basin Groundwater Assessment: Daly Waters to Tennant Creek report stated the recharged figures for the entire Georgina basin to be only between 71GL and 230GL per year. This was using a chloride mass balance method.

That report also stated a recharge figure for the Wiso of 192GL to 576GL, which was massively reduced under the government’s own presentation of Mr Knapton’s model, for reasons that have not been explained.

Chloride mass balance is considered an important tool for estimating recharge, but it generally only reflects the average seepage to the water table from rainfall over large areas and long time periods. It isn’t very good for estimating recharge from large events or specific landscape features like sinkholes and lakes, experts say.

And other figures using different methods included in a recharge table in the background paper have the Georgina annual recharge at either 1000GL, 2700GL, or 4900GL, and corresponding figures for the Wiso at 2800Gl, 1700Gl, and 1300Gl.

Prof Currell was one of 18 water experts from Australian universities who wrote to Ms Fyles soon after the government released its allocation plan, calling for a halt to new extraction licences and labelling the Territory’s water regulations as poor.

“You do not have the detailed methodology and science behind the figures in the table, so you don’t know if they are robust or not,” he said.

In the letter to Ms Fyles, the experts said the Northern Territory’s record of water planning did not meet national standards, with departures from the principles of national water policy.

“The recently released Georgina Wiso Water Allocation Plan(2022-2030) is particularly poor and regressive,” they wrote.

“It breaches water planning guidelines of the National Water Initiative, committed by all jurisdictions and the Australian Government.

“It risks many significant environmental and Indigenous values. No water advisory committee was put in place, compounding the problem of absent environmental or cultural requirements for water or trigger rules for assessing unacceptable impacts.

They said the government needed to “dedicate resources to developing extensive baseline science for large, data-poor regions, such as the Cambrian Limestone aquifer, and more robust monitoring programs for all water allocation plans”.

One explanation for the higher Georgina basin figure

One explanation for the doubling of the recharge figure, which Prof Currell and the NT Environment Centre executive director director Kirsty Howey believes is likely, is that the government, for an unexplained reason, cut the number of year’s worth of data used by more than half.

Mr Knapton’s report states he used data from 1900 to 2018 while the government’s background paper to the allocation plan states they used data from 1970 to 2020.

Prof Currell said this point was particularly important in that the wettest year on record was 1974, which is by some estimated to have added 21,280GL to the groundwater of the Georgina basin, whereas the current data indicates recharge in most years may be “negligible”.

That figure accounts for about two thirds of the water calculated to have recharged the Georgina between 1970 and 2020.

“One thing I and a couple of colleagues have noticed, is that almost all of the recharge that has taken place in the modelling took place in one very large event in 1974,” he said.

“So the modelling figure, and the estimated sustainable extraction rate, is dependent on a large and poorly understood recharge event that took place nearly 50 years ago.

“At that time the groundwater wasn’t being monitored very effectively.

“Using this approach to determine average recharge and then set a yearly extraction rate based on this average, is very risky.

“If most recharge occurs during unusually wet climatic events, there could be many years in a row where groundwater extraction at the rate proposed in the plan far exceeds recharge to the aquifer.

“We still have some fairly big uncertainty around how much rainfall actually replenishes that aquifer each year. We don’t know how resilient the aquifer and the ecosystems it supports are to this kind of extraction.”

When releasing the allocation plan, the NT Government’s executive director of water resources Amy Dysart told the ABC the water allocation was sustainable.

“We’ve identified this level of sustainable extraction as the right balance between those competing uses,” she told the ABC’s Country Hour.

“[It ensures] the majority of the water is primarily retained in the resource for ecological [uses] and supporting cultural uses, and some of the water is also available for supporting development in that region.”

Another of the 18 scientists is Monash University’s Emeritus Professor Barry Hart, who was also a panellist on the NT’s Scientific Inquiry into Hydraulic Fracturing.

“We are urging … the Northern Territory Government … to really upgrade their current water planning and regulation processes — they are way out of kilter,” Professor Hart said.

A un-named spokeswoman for Ms Fyles was quoted by the ABC justifying the science and the allocations by saying there were “significant reforms” made by the government to water use in the Territory.

“We are also developing a comprehensive, long-term strategic water plan which will look at sustainable water for all our regions,” she said.

The allocation of water of agriculture, mining and fracking

The allocation plan states about 243GL of water can be taken from the Georgina Basin, and 19GL can be taken from the Wiso Basin “sustainably” every year.

The Georgina figure is below Knapton’s total annual recharge figure but above the chloride mass balance figure.

This allocation includes 10GL annually for “petroleum activities”, which includes Beetaloo basin fracking. There is also a push for the expansion of the cotton industry in the Northern Territory but according to the Industry Tourism and Trade Department website, other broadacre crops are grown such as rice, sorghum and hemp.

The plan also allocates 24GL annually for “Indigenous economic benefit” with an Aboriginal reference group to be established with advice from traditional owners.

The Top End has long had an 80:20 rule, which means 80 per cent of water flow is allocated for the environment, essentially saved, and 20 per cent can be used by industry.

The government said the current allocation equals about 40 per cent of the basin’s annual recharge. Ms Howey said it was double the contingent allocation for the Top End in the NT water allocation planning framework, and there was nothing in the allocation plan or the background document to explain how taking 40 per cent of recharge was sustainable.

“And why is it being engineered to development needs, with absolutely no regard and no mention of environmental and cultural objectives, and no consultation with key stakeholders?

The allocation plan covers an area about 155,000 sq km in total, which is more than twice the size of Tasmania. The area is 600km north to south and 500km east to west, and includes Daly Waters and Elliott.

Prof Currell said the government needed to use a panel of scientists to determine the allocations based on an assessment of the available data.

“I and some of my colleagues think it is very concerning that the NT Government did not assemble an expert scientific panel to look through the relevant data and modelling carefully and come up with scientifically robust mechanisms to allocate groundwater in the Georgina-Wiso) plan,” he said.

However NT Farmers Association chief executive officer Paul Burke told the ABC Country Hour it was a “significant amount” but “seemed to be set sustainably”.

“I know that there’ll be a lot of interest from some of the larger players in that area, who have aspirations for significant cropping operations,” he said.