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A minimum flow for the Waitaki River does not need to be changed, according to the Central South Island Fish and Game Council's calculations of the amount of water available in the river.
Hydrologist Frank Scarf yesterday presented the council's case for no change to an Environment Canterbury (ECan) panel considering a plan change to the Waitaki catchment water allocation regional plan prepared in 2005, which became operative the following year.
The aim of the proposed change is to ensure irrigators, including those in major schemes such as Lower Waitaki and Morven-Glenavy-Ikawai, do not lose the reliability of the water supply they had before the plan was prepared.
The fear is those irrigators will be subject to the original plan's minimum flow of 150cumecs, instead of the zero to 130cumecs they enjoyed before water is cut off which will affect their investment in their schemes and which the infrastructure is designed for.
The plan change proposes lowering the minimum flow to between 102cumecs and 144cumecs, depending on the month, for those who had water consents before the plan was implemented in 2006.
It also proposes allocating 11cumecs to Ngai Tahu for mahinga kai enhancement, among other changes.
However, while there has been agreement among some parties on the plan change, the Fish and Game council believes the proposed minimum flows are not needed to protect those early consent holders or, if some change needs to be made, not as drastic.
If the panel was considering changes, the council's proposal was for minimum flows of 125cumecs from October to March (the main irrigation season), 140 in April and September and 150 (the present minimum flow) from May to August.
''We do not believe there is a need to change the minimum flow [from 150cumecs], but if you think there is a need then we are asking you to consider this middle-of-the-road proposal,'' he said.
Mr Scarf outlined figures which supported his contention those irrigators' reliability would not suffer as much as was projected in figures supporting the plan change.
In fact, he said that his calculations indicated water in consents to irrigate 67,000ha in the lower Waitaki Valley was being used inefficiently, and exceeded the volume allocated in the plan.
Mr Scarf said 2.2 times more water was being used.
If more efficient use was made of the water, then that would free up extra to help cover any loss of reliability for early consent holders.
However, after a question from the panel, Mr Scarf did acknowledge his figures included water that was taken for irrigation but diverted back to the river because it was not needed. Those diversions were not monitored so no measurements were available.
Moeraki resident Wilson MacTavish said the 2005 plan gave certainty to everyone and expected every sector to live within its allocation.
''A tension will always exist between the stakeholders' access to water and the needs of the river, and keeping that balance is the point of the plan.
''What was the point of the whole  process if the regulatory function of the plan can be put to one side and all sectors can have another go at increasing their allocations?''
Mrs MacTavish requested the panel to ask, before it even looked at the proposed changes, whether the plan actually needed to change.