Flood of interest in storage dam idea

The burgeoning Rangitata South Irrigation Scheme has led to a rush of applications for water storage dams.

Environment Canterbury's consents spokeswoman confirmed that none of the 21 applications within the Arundel-based scheme's 16,000 hectare "command area" were declined, because all of them fitted within its notified Land and Water Regional Plan.

"To clarify - these are off-channel storage dams (no waterways were dammed) and these include four certificates of compliance (where a dam met the permitted activity requirements and no consent was required)," she said.

The capacity of the storage dams ranged from 8000 to 210,000 cubic metres.

Work started on the scheme in 2011, and it will use a water harvesting and storage strategy to divert water from the Rangitata River when flows exceed 110 cubic metres per second.

The scheme is at the commissioning stage, with two of its seven ponds filled with water. Waimate businessman Gary Rooney has bankrolled the bulk of the $90 million scheme. Rangitata South Irrigation chairman Ian Morten said those involved in the scheme were required to build their own separate storage dams in addition to feeding off the main ponds.

"There is meant to be a good flushing flow (down the Rangitata) every 35 days or so, but this doesn't always happen. The storage ponds allow the land-holders to be masters of their own destiny," he said.

There were 41 registered shareholders in the scheme, but Mr Morten said some were property holders who "shared" their storage.

A recent ECan report to the Orari-Opihi-Pareora water management committee said the regional council would have to consider how floodwaters might be deflected on to surrounding properties and infrastructure.

"The cumulative effect of a large number of dams in the Rangitata plains is potentially difficult to deal with," the report said.

Lincoln University water scientist Dr Jenny Webster-Brown said if the land-holders took water from the river only during high flows, and then at less than 20 per cent of the flow, it would have minimal effects on the river environment.

"That would be a good use of water security," she said.

The Timaru Herald