Residents say that construction of a new roundabout at the intersection of Dairy Flat and Coatesville Riverhead Highways is having negative downstream effects on their neighbouring properties.
Auckland Transport (AT) began work on the roundabout a year ago.
Two residents, Peter Brydon and Jun Oh, have noticed a big increase in the amount of runoff into their bush-clad properties in the last six months. Both are conservationists, clearing invasive weeds, trapping pests and planting their sites.
Peter has lived on his 1.8ha block for more than 20 years and although runoff down the steep sides of Dairy Flat Highway onto his land is nothing new, he says what is happening this winter is way worse.
“Over the years we have had dry spells and wet ones, but this issue did not start until that project was underway,” Peter says.
He says the widening of the road and removal of bush on a steep bank on the opposite side has affected the water catchment, bringing torrents onto his land in heavy rain. This has led to slips that have brought down trees and gouged deep into the clay soil.
Two new stormwater drains on the road spill their contents directly down into the privately owned bush.
“If this was open pasture and you could see those scars on the land, I feel it would not be allowed to happen,” Peter says. “Because it is bush, ‘out of sight out of mind’ seems to be AT’s policy.”
The valley affected by this runoff is identified as a Significant Natural Area in Auckland Council’s Unitary Plan.
Jun Oh loves the bush on the 4ha block where he has lived since 2002. Recent runoff has caused subsidence and deepened gouges in the soil – some go more than 1m deep. In heavy rain, Jun says water overflows even these very deep ruts. After he spoke with AT’s contractors on the site, Dempsey Wood, Jun says a bund was put in place above his land to catch runoff, which he hopes will make a difference.
Jun says he clears the stormwater drains on the road himself as they often choke up with rubbish. “No one maintains them but me,” he says.
Peter says AT engineers and geologists need to come up with a proper plan.
“Their geologist told me it’s not their problem once it’s left their site, and the Council inspectors don’t look beyond the actual site either. But the runoff is not being contained – it’s being allowed to become our problem.”
He says the construction has altered the balance between the western and eastern side of the ridge, so now most of the run off comes east but says his complaints to AT and contractors, which included a meeting on site, have fallen on deaf ears.
AT spokesperson Mark Hannan says all of the required measures for stormwater control during construction have been implemented.
“Auckland Council monitors the site fortnightly with no cause for concern. There has been a high level of compliance with respect to environmental controls. The erosion is 250-300m away from where the work is being done and we do not believe the erosion is caused by the runoff from the site.”
He says AT has determined that the slump is a natural occurrence resulting from erosion over time due to the large stormwater catchment area that discharges through the location, undermining the area.
“It is possible this may have occurred very recently, perhaps as a result of the prolonged dry season then the recent heavy rains.”
The roundabout project was due to be completed around now but due to the lockdown, this has been revised to December at the earliest.