SECRET documents reveal the NSW Water Minister has ignored the warnings of department staff about proposed changes to the state's floodplain harvesting rules, which may not be compliant with the state government's own Water Management Act.

In an email, a senior official said a legal challenge was "considered likely" if suggested changes were not made to the proposed flows targets, which would only restrict floodplain harvesting during the "first flush" after a dry period.

Department staff point out the flow targets were so low, they were unlikely to make a noticeable difference to the overall floodplain harvesting take and were in conflict with a key tenet of the Water Management Act.

The flow targets were also found inadequate in a study by the Wentworth Group of Concerned Scientists.

Group member and ANU Professor Jamie Pittock said the flow targets only stopped floodplain harvesting when there was the "barest of trickles" down the Darling River.

"Our concern is these targets don't actually help the government meet its own targets around protecting domestic water and conserving environmental assets," Prof Pittock said.

"What floodplain harvesting does is kill those small pulses that come down the river after rain. We lose those variable flows that sustain environments like wetlands and red gum forests that rely on them."

Read the full article at The Land website (subscriber article).