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Three excavators are rearranging the bed of the Hawea River, near Wanaka, to create what is expected to be the country's best purpose-built whitewater course for kayakers and rafters.
Two rock weirs have been cemented into the river just above the Camp Rd bridge to provide particular styles of rapids sought by kayaking competitors. They will be available for any river users.
The design is that of American Scott Shipley (41) who was responsible for the London Olympic kayaking course.
Mr Shipley is a three-time slalom canoe world champion and 10-time United States champion who "somehow managed" not to win a medal at the three Olympics he competed in.
He has designed more than 20 whitewater courses around the world - many of them artificial, with water recirculated from the bottom of the course to the top.
In contrast, the Hawea River course, when work is completed next month, will be returned to its relatively natural state except for the new rapids and landscaping that will provide a small amphitheatre for spectators.
The work is being paid for by Contact Energy which controls the level of the river with its structure at the outlet of Lake Hawea.
Contact agreed to build the course, requested by the Central Otago Whitewater Association, when it was renewing consents for its Clyde and Roxburgh dams.
The company would not reveal the cost of the course but Contact engineer Denis McEntyre said it was "not cheap".
During construction the flow of the river has been reduced to between 3cumecs and 5cumecs but once the course was finished "recreational flows" of up to 30cumecs would be released once a month from November to February each year.
During normal flows, of about 10cumecs, competition and recreational kayakers would still have rapids in the middle of the river to test themselves on.
Standing amid of a mess of excavated boulders, gravel and discoloured water this week, Mr Shipley explained to the Otago Daily Times a little of the pressure that goes with making a living designing whitewater courses.
In 2005-06 he designed the world's largest whitewater park, the $37 million United States National Whitewater Centre in Charlotte, North Carolina.
During construction, Mr Shipley said, there were "doubters everywhere".
But once the water began running, and the course was seen to be working as planned "everyone wanted to have a drink with you".
"It's like you are walking on water for a little while."
Mr Shipley said, once, whitewater course designs catered solely for canoe racing but now there was also demand for courses for family recreation.
However, all those who used the Hawea course would still need to wear life jackets, helmets and be comfortable in the water.
"What we didn't do was go out there and make big whitewater safe for the masses.
"So I would discourage someone coming out here with a floating duck ring and trying to go down it.
"But I would encourage people who are in a class or in a group, on low-water days, with a helmet and a life jacket to come out and enjoy it."
Mr McEntyre said Contact would provide notice of high recreational flows well in advance.
Mr Shipley's last task will be to tune the course.
"There are a bunch of tricks of the trade but it's simply looking at how to optimise it for certain levels."
Mr Shipley said whitewater courses in the United States had positive effects on local economies, attracting visiting paddlers who used restaurants and accommodation services.
The machinery will be out of the river by December 5.