Second Wave Barrier successfully installed

Date: 3 July 2017

Following on from the success of the first wave barrier that was established at Te Waihora/Lake Ellesmere last year, a second wave barrier has been established at the lake.

The wave barriers have been installed to enable submerged plants, known as macrophytes, to become established.

The first wave barrier was made of 59 New Zealand Oregon logs, each 10m long. While the second used European spruce which, like Oregon pine, has a low density and floats well. The logs were 10 m long and have a ‘short end diameter’ of c. 300 mm.

“Three parallel logs form the leading edge of the raft, with a saw-tooth arrangement behind to extend wave length interception and strengthen the structure. The raft is secured to the bed of the lake with screw anchors. Specialist mooring experts N-Viro were again bought it to install the anchoring system,” she says.

Second wave barrier established at Te Waihora

When discussing the need for the wave barrier Mary de Winton says “Strong winds quickly build waves on the lake and these waves can erode the lake bed and shoreline. So when considering habitat enhancements like in-lake or shoreline plantings, or even artificial structures to improve lake habitat, the first problem to solve is the destructive force of the wave environment. This needed a customised solution to the lake, a wave attenuation system that could work in shallow water and cope with sudden changes in depth when the lake is opened or rapidly fills after rain.”

“The Te Waihora wave barriers use some of the design features of commercially available wave attenuators available overseas but we have used logs as a robust and natural material instead of plastics-based components,” says Mary.

David Murphy, Programme Manager, Whakaora Te Waihora, says that the existing wave barrier has been installed for over a year and has stood up to a number of strong wind-wave events and has been found to reduce wave height by 20-40% on average.

Information on the first wave barrier established at Te Waihora can be found here.

Drone footage showing the first wave barrier can be found here.

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