22/06/2012 12:00:00 a.m.
Work on assembling and planting what is believed will be the world’s largest man-made floating wetland is underway in Rotorua.
Twenty thousand native plants on the Rotorua District Council-coordinated environmental enhancement initiative will help improve Lake Rotorua water quality while promoting the district with the word ‘Rotorua’ spelled out in giant letters floating on the lake.
After several months of constructing the floating wetland framework contractors commenced assembly of the structure at Sulphur Point alongside Lake Rotorua last week.
When completed the 4,000 square metre floating wetland will be anchored in Lake Rotorua off-shore from Rotorua International Airport. At 160 metres in length by 40 metres wide the wetland will be similar in size to a full rugby field.
Rotorua District Council Infrastructure Services group manager Nico Claassen said assembly involved modules being progressively bolted together at the water’s edge, “like knitting a scarf row by row.”
“As each new row is attached the wetland is pushed further out onto the water, growing in size each time.”
A total of 76 modules have been assembled to complete the first section which forms the letter 'A', with another six sections yet to be built. The seven sections will then be fastened together in their final form shaping the word 'Rotorua'. Planting is being carried out as each section is completed with assembly and planting expected to be finished by the end of July.
Mr Claassen said the vegetation layer will involve more than 20,000 native plants being hand-sewn, all of which have been grown from Rotorua sourced seeds.
“The wetland structure will be moored temporarily in the sheltered bay to the west side of the Sulphur Point boat ramp to allow the plants to fully establish their root systems. It will then be towed five kilometres across the lake and anchored at its final mooring 200 metres offshore from the airport.
"The $900,000 environmental initiative is a partnership of Rotorua District Council, Bay of Plenty Regional Council and Te Arawa Lakes Trust. The Bay of Plenty Regional Council is putting in $225,000 with an additional $225,000 funding from the Crown via the Rotorua Lakes Funding Deed. Rotorua District Council's investment in the project is $450,000."
Rotorua mayor Kevin Winters said the building of a large-scale wetland was an environmental consent requirement to compensate in part for reducing an area of land-based wetlands when the city’s airport runway was extended.
“Because floating wetlands have proved substantially more effective as environmental remediation tools, this project’s key focus is on a lake-based wetland device rather than land-based wetlands,” said Mr Winters.
“We expect it to capture attention worldwide as an innovative environmental improvement measure and we anticipate it will also become an intriguing addition to our region’s diverse tourism product.”
Bay of Plenty Regional Council chairman John Cronin said wetlands played an important role in filtering out water-based nutrients that otherwise impact on water quality and lead to intermittent outbreaks of algal bloom. He said science showed that strategically located floating wetlands were at least four times more effective at stripping nutrients from water, like Nitrogen and Phosphorus, than conventional terrestrial wetlands.
Te Arawa Lakes Trust chairman Toby Curtis said the trust was also right behind the initiative as it will be a significant contributor to the future sustainability of the district’s largest lake.
Mr Claassen said a temporary security fence had been installed for public safety while construction is underway at Sulphur Point.
“We’re asking members of the public to stay clear of the assembly area as it contains hazards, such as cables being tensioned. The floating wetland surface isn't stable and isn't designed for walking on. Therefore access has to be restricted to trained staff wearing appropriate safety gear.”
Mr Winters said a ceremony to mark construction of the wetland and to bless the structure will take place on its completion in approximately six weeks time.
“A further ceremony is planned for when the wetland makes its five kilometre journey across the lake from the rohe of Ngati Whakaue to its final anchorage near the airport in the rohe of Ngati Uenukukopako in about six months time.