Wave barrier at Te Waihora a first of its kind

A 100m long wave barrier on the south western side of Te Waihora/Lake Ellesmere has been placed to enable submerged plants, known as macrophytes, to become established.

NIWA freshwater ecologist Mary de Winton believed the barrier to be the first of its kind in the world for this purpose.

“This barrier idea was conceived by NIWA and was installed in late May,” says Mary.

The barrier will enable young, transplanted macrophytes to become established so they can help prevent erosion and improve water quality at the Lake.

The transplanted macrophytes will come from a culture nursery that has been established at Taumutu on land leased from the owner.

“Whānau from Taumutu Marae have offered extensive local knowledge on the lake and its history and shown researchers the best places to source seeds and plants, including from the neighbouring Halswell River,” says Mary.

“We’ve chosen the sites we think will give them the best chance of survival. If we can get them to re-establish long term, we are confident they will have significant benefits for the future of the lake,” she says.

“I’m not aware of anyone working internationally to restore submerged macrophyte beds on this scale either,” she says.

“That”, she says, “is both daunting and exciting.”

Macrophytes are multi-tasking plants that buffer waves, improve water quality and provide diverse habitats for fish.

The floating wave barrier comprises 59 New Zealand Oregon logs, each 10m long. The logs are arranged three deep side-by-side, with the remainder placed in a triangular pattern to brace the structure which will be anchored to the lake bed in several places. A cable will run the length of the barrier to hold it in place.

Programme Implementation Manager David Murphy said he was very pleased to see the macrophyte project reach this important milestone.

”This project has an important place in the Whakaora Te Waihora programme as a whole and the science programme in particular,” says David.

“It is very pleasing to see the progress that has been made to get us to this point,” he says.

Mary says ‘‘even if the beds fail to re-establish long term, we hope we may better understand why they never recovered naturally and why they struggle to survive in current conditions.’’

Whakaora Te Waihora is an extensive cultural and ecological restoration programme led by Ngāi Tahu and Environment Canterbury. The programme has been running since 2011.