Dam a positive impact on community

Looking back now, Tom Henderson says the timing of the Opuha Dam scheme was superb.

12-03-2007 | Sandra Taylor

The Opuha Dam has been a very positive exercise for the community, the environment and indeed for the nation.

These enthusiastic remarks were made by Timaru-based Canterbury Regional councillor Mark Oldfield, who has seen first hand the improvement the dam has made on both the health of the local economy and the river environment.

Like generations before him, Oldfield lives alongside the Opihi River, a river now fed by the Ophua dam.

Over the years he has seen the river ebb and flow as hot dry summers have reduced the river to a trickle or indeed dried it up all together, and he remembers hearing tales of Model T Fords being driven up parts of the dried up riverbed. This of course happened long before the advent of large scale irrigation.

Since the building of the Opuha dam, operators have maintained minimum flows in the Opihi river and this has been to the benefit of the river environment.

According to Oldfield, fishermen on the river are claiming the Opihi is now one of the best fishing rivers in the region, and these fishermen all have a positive impact on the local economy.

They stay in camping grounds and spend money in local shops, all of which adds to the huge $124 million impact the dam has had on the South Canterbury economy.

As far as water quality is concerned, Oldfield believes the Opihi is no better or worse than any other river in the region.

Initially there were problems with water in the lower part of Lake Opuha becoming anaerobic due to the static nature of the lake. This resulted in poor quality water being released into the Opihi river as water is drawn from the lower part of the lake.

However this problem has been overcome with the installation of an aerator to keep all the water oxygenated.

The other problem has been with the river weed Phormidium which has thrived in patches along the river due to seasonal issues and the constant flow of water.

Naturally, flushing flows and dry periods would help control the weed and the dam’s operators along with NIWA are now looking at trials to flush the river periodically to help manage the problem.

Oldfield, who set up the South Canterbury Water Enhancement Group, a group of interested parties concerned with the environmental health of the district’s water bodies, was congratulatory of the way the dam operators address problems such as Phormidium.

He says they go above and beyond what would be typical of most operators of irrigation schemes in an effort to enhance the environment and maintain water quality in the Opihi river.

Timaru-based Peter Shutt is a keen angler, was a Fish and Game councillor for 25 years and was on the committee of the original Opihi Augmentation Society back in the 1980s.

He says many years ago the Opihi River was once considered the third best river in the country as far as fisheries were concerned, but the river died away in the 1970s as a result of drought and abstraction.

However the environmental flows afforded by the Opuha dam has since rejuvenated the river back towards what it once was.

“It is now a living river, previously it was a dead river.”

Shutt says salmon have returned, most likely as a result of Fish and Game implanting salmon eggs, and trout fisheries have recovered to the point that visiting anglers remark that the Opihi is one of this country’s “best kept secrets”.

The river now has an environmental flow aimed at keeping the river mouth open as well as satisfying the requirements of fisheries.

To this end, flows are varied to suit the seasonal needs of fish stock. For example flows were increased on March 1 to allow the passage of spawning fish.

Shutt described the Opihi as no longer being just a river, but a managed environmental flow for the maintenance of fisheries, and this job it does very, very well.

A report into the impacts of the dam released last year states that while the intensification of land use and application of phosphate (P) and nitrogen (N) has the potential to be associated with water quality issues, there has been no evidence of this occurring, although it suggests results of monitoring may have been too early in the uptake of the scheme to show a solid trend information.

Like Tom Henderson and Tom Lambie, Oldfield attributes the success of the dam to having the whole community involved in the whole process.

“They are now reaping the benefits of having an environmental flow in the river as well as water for irrigation.”

Irrigation, he says, has assured quality of production for the regions’ farmers, rather than simply increasing production.

The Opuha dam is in Oldfield’s eyes, the perfect ideal model for the benefits of storage.

He says in Canterbury, only around 10% of the water that falls in the catchment is used, indicating that while there is plenty of water available for all users, pressure comes on this resource at critical times of the year.

Like many in Canterbury he believes the key to the future of Canterbury is storage.

South Canterbury farmer and chairman of the Levels Plain Irrigation Scheme, Peter Scott, says the water from the Ophua Dam gives farmers on the scheme the reliability of water required to grow high value crops.

While the Levels Plain Irrigation scheme was built during the depression, until 1998 the scheme was at the mercy of the restrictions placed on the Opihi river from which the scheme drew water.

To secure a reliable water supply, the Levels Plain irrigators collectively bought shares in the Opuha Dam and have been reaping the rewards ever since.

Scott says since linking to the Ophua Dam, land use on the Levels Plain has and continues to change as farmers are growing more intensive, higher value crops such as potatoes and onions. All of these require more water than the more traditional cereal crops.

This intensification has lead to greater employment opportunities within the district.

As well as greater reliability, Scott points out the Ophua dam has ensured there is always water in the river for amenity uses such as swimming and fishing.

“So it is of benefit to the whole community.”

James and Fiona Fraser are livestock farmers on “Sterndale” in the Totara Valley.

They took up shares in the Opuha Dam seven years ago and have used it to irrigate 140ha of their farm through a centre pivot.

Initially they used the water to grow potatoes and barley as part of their development process, but then set up a Technosystem on free-draining ground that had previously produced little in the way of dry matter.

This Technosystem is used to finish Angus steers and Friesian bulls.

Another 40ha of irrigated land is used to grow feed for their Angus stud cattle.

James says the irrigation has made a big difference in their operation in terms of drymatter production and there is more development to come.

He says they have shares for half as much water again and while this water will be used to grow more grass, they are still considering what the best options are in terms of means of application.

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