A REPORT on an independent review of Department of Water and Environmental Regulation (DWER) "assumptions" in modelling for the $80 million Southern Forests Irrigation Scheme (SFIC) near Manjimup is expected in May.
The Department of Primary Industries and Regional Development (DPIRD) is negotiating with the CSIRO to have an independent senior hydrologist this month review water modelling scenarios into the future prepared by DWER for the Donnelly River and tributaries.
The Southern Forests Irrigation Co-operative (SFIC) is assessing expressions of interest for 1.7 gigalitres as yet unallocated under the SFIS and has based its project on DWER's "medium" climate change impact scenario.
That modelling, confirmed by DWER again in December 2018, showed up to 9.3gL a year above environmental flows will generally be available in the Donnelly River west of Manjimup from forest areas run off not currently available to agriculture.
But the accuracy of that choice of "medium" impact modelling and the modelling itself has long been questioned by Manjimup Water Security Group (MWSG), local farmers who have taken their own stream flow measurements in the forests for the past three years and more recently by hydrologist and former Department of Water director general Kim Taylor.
Rather than about a 95 per cent probability of 9.3gL of water being available annually in the Donnelly River out to 2030, as interpreted by the SFIC, Mr Taylor has previously claimed the probability by 2030 is likely to be down to about 20pc.
Mr Taylor's claim "simple" modelling techniques employed by DWER appeared not to take account of declining groundwater levels and subsequent reductions in run off in South West catchments, were reported in Farm Weekly last year.
Based on DWER's own stream monitoring data from the past 10 years, the SFIS would have only been able to extract its full quota of 9.3gL from the Donnelly River in about four of those 10 years, he has claimed.
In a joint letter to MWSG chairman John Kilrain early last month, Regional Development, Agriculture and Food Minister Alannah MacTiernan - who at the State election became a local MLC for Manjimup, as part of the South West Region - and Water Minister Dave Kelly acknowledged concerns over accuracy of water availability predictions.
While pointing out DWER's climate and catchment modelling was carried out to national guidelines and peer reviewed as "fit for purpose", Ms MacTiernan and Mr Kelly indicated they were not satisfied with the SFIC's adoption of the "medium 2030 scenario".
"We consider it prudent to plan for the worst-case scenario (dry 2050) which estimates the scheme would be able to supply the full 9.3gL about 30pc of the time," they wrote.
Under the dry 2050 scenario, the modelling predicted an average availability of about 6.5gL a year over the next 30 years and DPIRD had "revisited the economics of the scheme" using that scenario and advised "there would still be a positive benefit cost ratio", Ms MacTiernan and Mr Kelly said.
But they committed to undertaking a further independent review "of the modelling, its assumptions and conclusions", with DPIRD approaching the CSIRO to do the work.
Last week Ms MacTiernan said the review - expected to take four weeks - would likely start this month.
"DPIRD is working with CSIRO to establish a contract for an independent senior hydrologist to carry out a review of the water modelling in the scheme," Mr MacTiernan said.
"The terms of reference will include reviewing assumptions in existing water modelling, the impact of climate change and in particular the issue of run-off rates and ground water retention," she said.
"We expect the review will be undertaken in April and a report available in May.
"We know this is a contentious project in the Manjimup community.
"We all want to maximise our understanding of what the future is likely to hold."
Ms MacTiernan has said the independent review of the modelling will "run in parallel" with the environmental impact review of the SFIS by the Environmental Protection Authority (EPA).
The SFIS proposal is at stage two of the five-stage EPA approvals process, with a revised proposed timeline on the EPA website this week indicating the EPA last month should have approved an environmental review document for public release.
According to the timeline, this month the SFIC should release the environmental review document for a public review period of six weeks.
In June the EPA is proposed to provide a summary of public submissions and in July the SFIC is supposed to respond to submissions.
At this stage, the timeline proposes an assessment report to be published in November.
While welcoming the independent review of DWER modelling, Mr Kilrain has argued it would not be in the public interest to release the EPA-approved environmental review document until after the independent review is completed and the May report released.
"We believe it would be unnecessarily stressful to release the PER (Public Environmental Document) for public review simply to find that it may need to be withdrawn based on the review showing the modelling is flawed," Mr Kilrain has said.
"We have therefore respectfully requested the EPA to hold off releasing the PER until after the modelling review."
Comment was sought from the SFIC but was not received before Farm Weekly went to press.
- The SFIS proposes to pump up to 9.3gL a year from the Donnelly River during specified high-flow winter periods and to store that water in a 15gL dam proposed to be built across Record Brook, a tributary in the Donnelly State Forest west of Manjimup, with a previously logged area of forest to be cleared for the dam, access roads and car parks associated with public use water recreation.
From the storage dam, water purchased by SFIS subscribers would be pumped to two ridge-top header dams then gravity fed via underground pipelines to farms and horticulture properties up to 40 kilometres away.
In late 2017 and early 2018 about 70 local landowners signed 90 contracts with the SFIC for a total allocation of just under 7.8gL of scheme water - some subscribers own multiple properties and have contracts for each.
Based on winter and summer irrigation season one-off 'subscriptions' of $1000 and $1400 per megalitre, they paid more than $200,000 as a 2pc refundable deposit on the contracts.
They are due to pay a further 8pc when a formal decision is taken to proceed with the SFIS and the balance of the contracted amount when water is first delivered to their property.
Annual water charges under the scheme are $187/megalitre to $217/ML depending on delivery time of year requested.
When expressions of interest were called late last year for the remaining 1.7gL, the SFIC received applications totalling 3.885gL.
It has said it will work through the applications with DPIRD to try to accommodate as many as it can.
The previous Federal government promised $39m funding for the SFIS just before it went into caretaker mode for the last Federal election and the State government has promised to provide $18m.
Both promises are conditional on the business case for the SFIS continuing to stack up and that it receives EPA approval.
