Professor Pittock has also stated raising the wall at Wyangala Dam is "the wrong way to manage flood risk along the Lachlan".

"This flood is not particularly unusual or high, rather the flood risk has been poorly managed by the NSW Government," he said.

Prof Pittock said raising the dam wall isn't the answer to flood management.

"This flooding is awful news for the people whose homes, farms and other businesses will be badly impacted. However, raising the dam is the wrong way to manage flood risk along the Lachlan River." he said.

Flood 'control' infrastructure usually makes flood damage worse, not better, he said.

"There are cheaper, more effective flood management alternatives; and the high water levels generate a lot of socio-economic and environmental benefits that would be lost if medium sized floods are captured by a higher dam.

"Raising the dam will inevitably make flooding impacts worse.

"Globally this phenomenon is known as the 'levee paradox'.

"This is where flood control infrastructure results in development on the floodplain that makes damage worse when inevitably there is a big flood that is not contained by infrastructure.

"An egregious Australian example is that the flood control capacity built into the Wivenhoe Dam in Queensland after the 1974 floods was insufficient to prevent extensive damage in the 2011 Brisbane floods because too much development was permitted in the floodplain.

"In general, learning to live with floods is safer than fighting floods and failing," he said.

In contrast Member for Riverina Michael McCormack, after visiting the flood-affected areas in Forbes this week, called for the wall raising to go ahead.

"We need to raise that dam wall ... to put water behind the wall for agriculture, and to protect people in Forbes, Condobolin, West Wyalong and the Newell Highway," Mr McCormack said.

"The (Newell) highway was shut for six and a half weeks in 2016 ... that's one of the busiest freight corridors in Australia closed for business for six weeks.

"We can't have that again," he said.

Mr McCormack said he and (Deputy NSW Premier) Paul Toole are working very hard to ensure investment in Wyangala.

"If it requires more money - well the Federal Government is up for the challenge," he said.

Prof Pittock blames neglect from the NSW State Government for flood impacts.

"Any flood impacts are due to years of NSW Government neglect in not implementing their own three Floodplain Management Plans along the Lachlan, which have particularly recommended actions to enable low level flood waters to pass safely by and not build up behind floodplain infrastructure (like road, railway and irrigation canal embankments).

"Despite anecdotal claims of flooding in the valley being a major problem, the few recent publicly available assessments of flooding in the valley demonstrate only modest impacts that could be significantly reduced at little cost if the NSW and local governments thoroughly implemented their findings."

He says flood risk reduction interventions examples like raising the Newell Highway carriageway which was cut for months by flooding in 2016 and rebuilding the Forbes to Stockinbingal rail line would be much cheaper and faster than raising the dam.

Professor Pittock also says there are benefits to be gained from floods which need to be maintained.

"High water levels in the Lachlan River, which have some negative impacts, are also a boon to the region's environment, communities and industries," he said.

"The Lachlan Valley has 470,000 hectares of nationally significant wetlands that depend on beneficial flooding to remain healthy, such as the Great Cumbung swamp.

"These wetlands ecosystems are vital for supporting fish and waterbird populations.

"The inundation of the floodplain is especially beneficial for pastoralists along the river, and can significantly enhance livestock turnoff.

"Crucially in a dry region, the inundation of the floodplain is vital for recharging aquifers that supply farms and towns with high quality water. Indigenous nation's cultural and economic values depend in large part on the environmental benefits of wetland inundation.

"Raising Wyangala Dam would jeopardise these benefits for people and the environment.

"The proposal to raise Wyangala Dam is a knee-jerk, pork barrelling proposal that will fail any independent cost-benefit analysis.

"Ecosystem based climate change adaptations, such as giving rivers room to flood safely, will provide more benefits to society," he said.

Mr McCormack said he isn't going to listen to a Legislative Council Greens-led movement saying that they can't build Wyangala Dam.

"I'm not going to cop the Greens telling the people of Forbes that their houses need to be flooded," he said.

"I'm not going to cop the Greens saying that our farmers don't need that productive water to grow agriculture.

"We are all in this together to grow agriculture to a $100 million enterprise by 2030, but we aren't going to do it if we don't invest in water.

"Paul Toole and I are investing...that's what the Nationals do in government.

"We need to make sure that dam wall gets raised and damn the Greens," he said.

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