Lachlan Valley Water executive officer Mary Ewing has told the parliamentary inquiry into the rationale for, and impacts of, new dams and other water infrastructure in NSW that a majority of group's members support raising the wall at Wyangala Dam.
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The NSW Legislative Council is to report on the rationale for and impact of projects including the $650 million promised raising of the Wyangala Dam wall.
The first of the inquiry's hearings have been held at Parliament House, with two more to come.
Lachlan Valley Water, representing both groundwater and surface water users in the Belubula and Lachlan catchments, has made both a written submission and a presentation.
"We have recruited more than 500 water users in this catchment and what we have heard from our members is that the majority of them do support the project to raise the Wyangala Dam wall and increase security and reliability," Ms Ewing, who spoke at the inquiry on behalf of herself and Lachlan Valley Water chair Tom Green, said.
That is of course pending the release of the business case, addressing both the value of improved water reliability and the benefits from improved flood mitigation capability.
One of the issues of the Lachlan, Ms Ewing says, is a very high essential flow requirement.
"It takes 180,000 gigalitres a year to run the (Lachlan) river and meet basic needs and another 53,000 for high priority needs," Ms Ewing said.
"So under the highly variable conditions we have had in recent years, we could change very quickly from flood to drought and this makes it tough for everyone, particularly those who need constant supply, including the towns, stock, domestic intensive producers and industries.
"Yes, everyone wants to see the hydrological modelling to understand what the 21,000 megalitres a year average increase in reliability means.
"It might be nothing in 2017-18 but 60,000 megalitres in 2019-20, which would have made a huge difference to the region in that year given that droughts set in very quickly and very savagely.
"From our point of view, it is important that the Government continues not only with this work but with all of the necessary investigations to enable the project to progress," Ms Ewing told the inquiry.
The capacity of the dam to manage flood impacts was also highlighted: Lachlan Valley Water's understanding is that the main flood mitigation of raising the wall of Wyangala Dam will be in large flood events.
Lachlan Valley Water highlighted the widespread flooding of 2016/17, when the Newell Highway south of Forbes was closed for 42 days along with other district roads.
"In 2016/17 there were 1,495,000 ML inflows to Wyangala, the majority received between July and October 2016, and 900,000 ML of these inflows were released between August and November 2016," the submission says.
There were also large downstream tributary inflows.
"It is important that the detailed hydrological modelling is made available to stakeholders to allow better understanding of what the 21,050 ML/year average improved reliability translates to over different climate periods, and for stakeholders to have confidence in the information it is essential that full transparency of the models used is available," the Lachlan Valley Water submission said.
The inquiry has also heard from others questioning the project, particularly its fast-tracking.
Professor Jamie Pittock from the Fenner School of Environment & Society at Australian National University was the first witness to address the inquiry.
"What the dam raising might give in terms of irrigation water, it takes away in terms of disadvantaging the people downriver who rely on that river for the beneficial inundations for things like groundwater recharge, for pastoralism and, of course, the environment," Prof Pittock said.
He suggested investing in refurbishment of inefficient irrigation schemes would provide more water for different users for "one third of the price" and "have very little environmental impact, nor disadvantage communities further downstream".
The inquiry also heard that expanding Wyangala would completely undo the objectives of the (Murray Darling) Basin plan.
"Really, it is tearing up the basin plan," Maryanne Slattery, a director of Slattery & Johnson and legal representative for "a group of landholder and irrigators", told the inquiry.
