Posted on August 27, 2015
The problem: Improving the skiing experience
At Lake Tikitapu, or the ‘Blue Lake’, the Rotorua Water Ski Club wanted to replace some old blue drums to help keep the water flat on a popular water skiing course. During the last 10 years, club members and other skiers have debated how to make the water on the slalom course consistent and smooth.
“It was a daunting prospect for a small club looking to improve the quality of our slalom course and the water quality of the lake at the same time,” said club president Ian Barker.
The design concept: Floating wetlands
The Rotorua Water Ski Club approached WaterClean (a business division of Kauri Park Nurseries) over three years ago and expressed their interest in our floating wetland concept as a barrier between the recreational area and the ski zone on Lake Tikitapu. The Floating Island needed to be 500m long and sit 10m west of the slalom course.
We worked with Golder Associates, Bay Underwater Services and Hampidjan New Zealand to design an extremely robust floating wetland. We settled on a design that consisted of 20 floating islands, each 24m long x 2.3m wide. These would be wrapped in heavy duty fishing net and then anchored individually on the lake, one metre apart.
The challenges: Island construction
Constructing the floating islands presented many challenges, particularly the length of the islands, which made them difficult to handle. Construction took place over four steps: roll out, foaming, finishing touches, then stacking them. Once all 20 floating islands were manufactured and stacked, they then had to be wrapped in the heavy duty fishing net. This was done by laying out the net on the factory floor, placing a floating island into the net, folding the net over the floating island, stitching the net together and then restacking on the opposite side of the factory ready for despatch.
Delivery of the islands was also a challenge. The plan was to deliver the floating islands in two loads, 10 islands per load. Finding a trucking company with a long enough trailer was the first step. Auckland Cranes was the trucking company we chose for the delivery as they had a flat trailer that extended to 23m long and also years of experience with over dimensional loads. We loaded the floating islands by manoeuvring them out of the factory, five at a time on 14 drum dollies. This made them very easy to move. Once they were outside the factory, we rolled them into position alongside the 23m long trailer. They were then picked up with four forklifts and placed on the trailer. This was then done for the remaining five. The load was then strapped down and trucked to site. Permits and two pilot vehicles were required – one at the front and one behind. Once onsite, the truck reversed down as close to the lake as possible and a crane parked in beside. A 16m spreader bar was rigged up which had eight lifting straps. These straps were d-shckled to the heavy duty fishing net that wraps around the floating islands. The crane then lifted the floating islands, one at a time and placed them directly onto the lake where they were then floated out of the way and tied up on the beach.
The divers went through ahead of us and installed 42 GPS-plotted anchors into the base of the lake. Their conditions were depths ranging from 10m through to 25m, with a water temperature of 7˚C and poor visibility. Once they had installed an anchor, they then attached the correct length of rope with a float attached. We planted all floating wetlands with Carex secta while they were tied up on the shore. We then towed them out via boat, two at a time. This took quite some time, given that the ski course was located around 1km across the lake. Once we were out there, we floated the islands into position and connected them to their anchor ropes and tied them off. Once all 20 floating islands were connected to their anchors, we went through checking all connections and adjusting them where needed to ensure the wetland was sitting in a straight line.
A end result is a 500m long floating wetland which acts as a barrier and wave mitigation to the slalom course.