''It will lock us into failure - the design is wrong,'' executive director of the University of Adelaide's environment institute, Professor Mike Young, told a Senate rural affairs inquiry yesterday.

One of Australia's top hydrologists, former NSW chief scientist Professor John Williams, also told the inquiry the plan was ''misleading, simplistic and deceptive'' and should be withdrawn by the Gillard government.

Professor Williams, who recently retired as NSW Natural Resources Commissioner, told the Senate committee he was so alarmed by errors, omissions and ''poor science'' in the plan, he wrote directly to federal Environment Minister Tony Burke, calling for an urgent independent scientific review.

'' I think we're being sold a pup,'' Professor Williams said.

Speaking from London, where he is advising the British government on water management, Professor Young said administrative arrangements underpinning the proposed plan were far worse than current arrangements.

''It is a case of serious backsliding,'' he said. The draft plan should be ''thrown out'' and replaced by a system taking a ''region by region approach'' to water accounting, instead of using a single number to determine a proposed volume of water savings, he said.

Professor Williams said the plan showed a poor understanding of connections between surface and groundwater, and failed to factor in potential impacts of climate change on river systems, farms and regional towns. ''It does not have a scientifically rigorous basis,'' he said. Professor Williams wrote to Mr Burke last year, urging the minister to set up an urgent independent scientific review of the draft plan.

''He did listen and did ask CSIRO to look at the science, but I don't think that review went far enough. This is a seriously flawed plan, and I don't think the government, or the Australian taxpayer, can afford to trust it,'' he said.

The Senate rural affairs committee also heard evidence from the Murray-Darling Basin Authority - the federal agency set up to deliver a water management plan for the region that produces more than 43 per cent if Australia's food.

The agency's draft plan recommends returning 2750 gigalitres of water a year to the basin's river system, chiefly through a $9 billion federal investment in voluntary water buybacks and upgrades to infrastructure.

In response to questions from NSW Liberal senator Bill Heffernan and NSW Nationals senator Fiona Nash, the authority's chief executive, Rhondda Dickson, admitted there were ''large areas of uncertainty'' in the plan. These included impacts of climate change, data on the interception of water by forestry plantations and carbon farming, and projected groundwater use for coal seam gas mining,

Dr Dickson said modelling suggested 800 to 1600 jobs could be lost as a result of reforms outlined in the plan. But in response to further questions by Senator Nash, Dr Dickson acknowledged modelling of job losses had been ''limited''.