Changes made to the river management plan for the Ashburton River have improved the river flow, according to a retired local hydrologist.

The minimum flow of six cubic metres per second (cumecs) aims to keep more water in the Ashburton/Hakatere River catchment. It came into effect at the beginning of July last year, after a consent review for the Ashburton River between 2018-2022.

Despite a dry summer, retired hydrologist John Waugh said the new minimum levels had improved water flow in the river.

"There's some quite good effects," John Waugh told local Forest and Bird members during a presentation on Tuesday evening.

The river flows this summer were above previous comparable drought years, based on data from Environment Canterbury's website - and double the flows in the 1980s.

Waugh said the amount of water taken from the Ashburton River in the past had been above the recommended levels.

"It's no wonder the river gets down to very low flows at times," he said.

Waugh said a level of six cumecs is believed to be enough to keep the Ashburton River mouth open.

Climate change would mean droughts would be more severe and last longer, while higher rainfall at other times would bring bigger floods.

"They'll happen more often. You just have to learn to live with it.

"Floods can happen literally any time. And sooner or later a big one will come. It's just a matter of when."

He said water storage for droughts and secondary stop banks for floods could provide some mitigation.

Waugh said the retreat of the Ashburton Glacier at the head of the South Ashburton River would reduce river flows by as much as15% over the next 25 to 30 years.

"It's at the top end of the South Ashburton. If the ice goes, it will affect flows by 10-15%."

The good news for Mid Canterbury is that the the upper catchment will continue to get spill over rain from the main divide, he said

In response to a question from the floor, Waugh said the Resource Management Act did a "pretty good job" for water management.

"Most catchments have a plan that sets out how water is to be managed and used. The problem lies with how acts are administered by councils."

Waugh said there could be some "bureaucratic nonsense" but it was much better than the alternative - which for Waugh was each for his own type of chaos.

The new rules have caused some disharmony for local farmers.

ECan has recently apologised for its handling of the Greenstreet Creek crisis where the new rules prevented farmers from diverting water to save the creek and its inhabitants.

A report into the impacts of the new minimum flows is expected in sometime this month.

By Sharon Davis