BARK being buried by the truckload in land next to Gisborne Airport is blocking the flow of water around natural wetlands in the area, says a long-term resident.
The area is known as the Makaraka wetlands and is classified as a flood zone.
Eastland Group Ltd has had resource consent to infill the land with bark, soil and gravel from its log yard at the port since September 2006.
Eastland Port project development manager Martin Bayley said the bark was reducing the threat of bird strike to aircraft by filling up an area at the end of Runway 21, which periodically accumulated water.
The removal of the wetland meant ponded areas no longer attracted bird life.
But it is the effect on flood plains not airplanes that is concerning a long-term Makaraka resident and some conservationists — with one saying that bark is known for its “suppressant” qualities.
Pat Collins, a Makaraka resident for 20 years, said the bark was hindering the free flow of water.
Flooding this year was the worst he had experienced and it had been getting steadily worse over the last five years.
He was aware up to five truckloads of bark a day were being taken to land behind the airport, which also borders the showgrounds, race course and golf course.
“We’re having problems at Makaraka with water getting away,” said Mr Collins “It’s just not going anywhere, it’s stagnant.”
About three acres of the wetland had been reclaimed by the buried bark and had raised the land by more than a metre, he said.
“It is so built up that it is stopping the water from draining properly,” said Mr Collins. “It’s got to have a bearing on the Makaraka flooding. The area is no longer doing its natural job of helping the water drain away.”
Eastland Group Limited also has consent to discharge ponded water at the site on Aerodrome Road to Waikanae Creek, which weaves through the area.
The consent for the activity expires at the end of 2013, by which time Mr Bayley said the port was planning to have exited the site.
Over the seven-year consent period, two areas of pasture that had some depressions and tended to hold water and drain poorly, would have been filled in through depositing bark on a 2.5-hectare site adjacent to, but still within, Gisborne Airport boundaries, he said.
“The consented site is more than 90 metres from the concerned subsidiary stream that drains the Makaraka area via Hansen’s drain then joins the Waikanae Creek.
The cleanfill operation had not impeded and never would impede the flow of this water course draining properly, he said.
Conservationist Murray Palmer did a survey a couple of years ago to look at the biological condition of Waikanae Stream.
“It was almost abiotic. That means there is not much living in there and in this setting that is a sign of some sort of contamination. When you’re changing the flood plains, that’s pretty significant in terms of both hydrology and ecology.”
Gordon Jackman is in charge of the chemical strand of investigation in the technical working group looking at wastewater consent in Gisborne. Bark was an interesting substance because it gave off tannins that made everything brown, he said. Tannins were not very toxic but it was the resin acids in bark that worried him.
“Pine trees survive well because they have a dab hand at chemical warfare to keep pests away.”
These substances, when they leak into waterways, can be very toxic to marine life, even in very small quantities like parts of a billion, he said.
“Low concentrations will have significant effects on larvae, and sea water makes it even more toxic.
“So if you are dumping them in the wetland there is a risk you are having a negative effect on the eco-system.”
Bark was a suppressant, he said.
“You see bark gardens all over the place and that’s because they supress competition.”
Gisborne District Council team leader water conservation Dennis Crone said the activity was inspected regularly and there had been need for only one corrective action after it was found drainage from the pile of bark was going into Waikanae Creek.
But he said a 10m buffer zone between the creek and the area of buried bark, as required by a consent condition, meant he would be surprised if there were any further negative impacts from it.
“No site inspections have revealed any encroachment within the ten-metre buffer.”
Bark was a good soil conditioner and could assist with drainage, he said. The airport also benefited from reducing ponding areas that attracted birds close to the runway.
“That needs to be balanced with any negative aspects, which might be run-off of tannins from the bark and pine resin from woody material.”
Council engineering and works manager Peter Higgs said Hansen’s drain by the racecourse in Makaraka was due to be cleaned out in October or November this year and was surveyed last summer. This maintenance would help stagnant drain and flow issues.
One of the principal issues when the council granted resource consent for the land use consent for land disturbance and/or vegetation clearance and a discharge to water, was the potential contamination of the Waikanae Stream from discharge.
The resource consent also said the area was not identified as a significant wetland area and all bare surfaces created from burying the bark were to be sown with grass seed every autumn throughout the duration of the consent.
Rongowhakaata spokesman Stan Pardoe said it was important to get answers on the medium-to-long-term impact the bark would have on the aquatic life environmentally and ecologically around the creek.
“We should proceed with caution. It is a practice that will continue to grow with the wall of wood still coming in and all that bark is going to have to go somewhere.”