18 May 2016

Bay of Plenty Regional Council is trialling an innovative new solution to reducing mangrove spread in Tauranga Harbour this week. Auckland-based company Fieldmaster designed the solution which is a purpose-built hovercraft fitted with a mangrove seedling mowing unit. It’s the first of its kind in New Zealand.

“Regional Council tendered out the design and build of a mechanical mangrove seedling control option that won’t leave deep tracks or significantly disturb other wildlife in the harbour,” said Bay of Plenty Regional Councillor and Regional Direction and Delivery Committee Chair, Paula Thompson.

“We’re already doing a lot of work with landowners in the catchment to reduce the sediment run-off that promotes mangrove growth. In the meantime, mangrove seedlings continue to pop up in areas that the local community have told us they want maintained as open water. They want to be able to keep swimming, boating and collecting kaimoana (seafood) in those spots,” she said.

“Mowing efficacy has been refined following initial tests near Pahoia last year and a field trial in Athenree last month. Fieldmaster are now putting the hovercraft through its paces in Waikareao Estuary this week, to check that final refinements are working well before we take ownership of the machine. They’ll also be training some of our staff to operate it,” she said.

Councillor Thompson said that results from intensive environmental monitoring carried out during hovercraft testing to date have found that the seedling mower operation had no significant adverse impacts on wildlife (including birds, crabs and titiko or mud snails) and it could operate within resource consent conditions.   

“Tracking on the estuary bed was minimal; it left only light scuff marks that washed away soon after. Once the hovercraft is fully commissioned, there will be further environmental monitoring as it’s put into operation,” she said.

Councillor Thompson said that hovercraft was part of Regional Council’s commitment to helping Estuary Care Groups to hold the line on mangrove spread in consented areas.

“Volunteers have been using hoes to remove seedlings for the past ten years. It’s a back-breaking task so we agreed to explore mechanical options that will give them more time for restoration work like planting and pest control.

This is part of our work to keep Te Awanui Tauranga Harbour healthy and accessible. If this week’s trials are successful, we’ll continue to work with Fieldmaster and Maritime NZ to get the hovercraft through the necessary certification processes before it can be put into operational use,” she said.

Additional information:

  • A video of the hovercraft during trials at Athenree last month can be viewed at https://youtu.be/tOtZ6TkUERU.
  • Regional Council secured resource consent, subject to a successful trial, for mechanical mangrove seedling removal in October 2013. Consented areas total 600 hectares across eleven sites in the 21,800 hectare Tauranga Harbour.
  • The hovercraft mangrove seedling mower will not operate during bird breeding season (September to February inclusive each year) and it will not be used to remove mature mangrove plants.
  • Regional Council budgeted $361,000 for the hovercraft to be designed, built and tested.  It is expected to cost $180,000 per year for annual mowing of mangrove seedlings at consented sites.
  • Key hovercraft specifications:
       •    2190 kilograms unladen weight
       •    Six cutting blades
       •    0.17 psi surface pressure on estuary bed
       •    Maximum travel speed 30km/hour (16 knots)
       •    Maximum mowing speed 20km/hr (12 knots)
       •    Mowing height of approximately five centimetres
       •    Powered by Hyundai 2.4 litre common rail diesel engine

  • Further information about Bay of Plenty Regional Council’s work to care for the Tauranga Harbour and its catchment is available at www.boprc.govt.nz/taurangaharbour