The cost of managing an invasive "super weed", if it is not eradicated during construction of a billion-dollar Waikato development including 2500 new houses, will fall to ratepayers.
The presence of alligator weed at Te Awa Lakes is the largest upstream infestation on the Waikato River and if unmanaged has the potential to be a significant point source for it getting into the river. Photo: Supplied / Waikato Regional Council
And presence of the weed at the site north of Kirikiriroa means future residents might have to comply with and pay for stringent biosecurity restrictions on their properties.
Developer Perry Group believes it can rid the site of the highly invasive alligator weed by burying it under roads and buildings, but Waikato Regional Council (WRC) already has cost estimates in place should that plan fail.
Biosecurity and economic experts warned Perry Group in November 2019 that completely removing alligator weed from Te Awa Lakes was "extremely ambitious" due to the size and complexity of the site, and that if the residential, tourism and recreation development went ahead it could spread the destructive pest plant to other parts of Waikato.
Waikato Regional Council opposed Perry Group's application for a private plan change to rezone the 62 hectares of industrial land to residential over concerns there were no methods planned by the developer to manage the weed once construction was complete, if it was not eradicated.
The change to the Hamilton City Operative District Plan was subsequently approved by independent commissioners in March last year, paving the way for the project touted as the northern gateway to Hamilton including cafes, lakes, cycleways, a gym, medical centre, supermarket and a multi-million dollar adventure park.
The approval came with conditions that required Perry Group to undertake an Alligator Weed Management Plan.
The South American plant is considered one of the world's worst weeds - it can take over pasture, is toxic to stock and can cause cows to miscarry, clogs waterways and creates flood risk.
It can survive for up to 10 years underground and flourishes on both land and water, doubling in size in just two months.
A Restricted Place Notice has been applied to Te Awa Lakes under the Biosecurity Act 1993 meaning that under the Waikato Regional Pest Management Plan, future landowners could face up to five years' jail or a $200,000 fine for knowingly moving alligator weed.
For example, removing soil and green waste such as grass clippings off site, or digging a vegetable out of the garden and giving it to a friend, would be forbidden.
Alligator weed is well-established in Northland and northern Auckland and has been found at 140 sites in Waikato. It was discovered in Manawatū last year.
Waikato Regional Council biosecurity pest plants team leader Darion Embling said a plan to eradicate alligator weed from Te Awa Lakes was ambitious. Photo: Supplied / Waikato Regional Council
In a submission to the private plan change hearings in late 2019, Waikato Regional Council biosecurity pest plants team leader Darion Embling said the weed severely impacted crops, was difficult and costly to control, and eradicating it required herbicide spraying for many years.
The impact on agricultural land included reduced yields of 20 percent in vegetable crops and 45 percent in heavily infested kumara crops, some studies had shown.
In a worst case scenario, if the weed was not eradicated at Te Awa Lakes, council inspection costs to manage it were estimated at between $240 and $360 per year for each property; or between $4800 and $7200 each over 20 years, which over two decades could total as much as $18 million for 2500 houses.
Under the current rules, once construction is complete, Waikato Regional Council would be responsible for the ongoing management meaning those compliance costs would be borne by its 212,300 ratepayers.
"If their mitigation management plan doesn't work, and we're hoping it does, there'll be ongoing costs for ratepayers and landowners," Embling said.
"The cost will fall on ratepayers to fund control and surveillance, but there will be additional costs for landowners due to the stringent biosecurity measures, like disposing of any garden/soil waste, and hygiene requirements when a landowner undertakes an activity that moves soil or vegetation."
No money was set aside in Waikato Regional Council's 2021-2031 Long-Term Plan to pay for ongoing management of the weed at the former quarry site at Horotiu.
Alligator weed was first discovered at Te Awa Lakes in 2004.
"As a result of quarrying operations, it is anticipated alligator weed fragments have been dispersed throughout the soil profile to a depth of at least 9m across the Te Awa Lakes site," Embling said.
"If these fragments are brought to the surface, for example during earthworks, they will regrow."
Te Awa Lakes development, Hamilton Photo: Supplied
Te Awa Lakes chief executive Richard Coventry said the intention was to eradicate alligator weed through burying it on site and developing buildings and roading over the top.
"Our intention is not to burden homeowners with the cost of managing alligator weed."
Managing it was part of the project's earthworks costs, he said.
Resource consent for the first stage of the development was approved by Hamilton City Council in October.
That consent requires Te Awa Lakes to provide an Alligator Weed Implementation Plan which should include the location and management of wash down stations, identification of risk zones, movement routes and controls, and the movement of soil including the locations where high-risk soil is to be deep buried.
Hamilton mayor Paula Southgate said she was aware of concerns about alligator weed raised by the regional council.
"I've been assured all steps will be taken for it to be controlled appropriately. That's my expectation."
Coventry said the Te Awa Lakes management plan had been approved and would be monitored by WRC. Te Awa Lakes would fund all onsite works to manage alligator weed.
Stage one of the 10-15-year development was already underway and construction of 90 houses by GJ Gardner would begin late next year.
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