The cost of Auckland's Quay St streetscape enhancement has blown out by $13 million in the past year because of an unbudgeted rain-garden stormwater system.
The Quay St construction began in December 2018 with a budget of $59.2m and has reduced the four-lane arterial CBD route running parallel to the harbour to a single lane each way.
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In August, Auckland Transport (AT) announced 19 rain-garden systems containing 200 native trees would be installed along Quay St.
The pōhutukawa and other natives filter stormwater run-off flows before they reach the sea.
However, the increased cost to $72.15 million was not mentioned at the time.
"Due to a request from Auckland Council Stormwater and iwi to provide enhanced levels of stormwater treatment via a series of rain gardens, extra funding was required to deliver improved stormwater and pollution control outcomes," AT's downtown programme director Eric Van Essen said this week.
Another contributor to the $13m increase was some components of the planned Britomart East Bus Interchange having to be built by the Quay St project, to the west of the intersection with Commerce St intersection, Van Essen said.
Auckland Council's chair of the finance committee Desley Simpson said organisations like AT had to remember they were spending ratepayer money and their decision-making needed "a lot more transparency".
"Some people are going to say a garden that costs $13 million is exorbitant and that's understandable. It's a huge amount," Simpson said.
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"[However] that figure isn't all garden. It's a natural stormwater filter that will improve water quality aiming to allow people to swim in the Viaduct Basin, costing about the same as an engineered system, which would just have pushed the contaminated overflows into the harbour."
Auckland Council's general manager of healthy waters, Craig Mcilroy, said the existing stormwater system had been "reaching the end of its useful life" but there had been little room on Quay St before the enhancement project to construct additional stormwater infrastructure.
Mcilroy indicated consultation with mana whenua was the catalyst to add the rain-garden system.
"The [original] 2018 drainage design and costs considered a number of stormwater improvements and aligned with the Downtown infrastructure improvement programme, including stormwater treatment for the new areas of the project," Mcilroy said.
"However, through consultation with mana whenua, we saw the clear benefits of providing additional treatment in an area where public transport orientated much of the street."
Mcilroy said council's healthy waters department contributed $6m to the total $13m rain gardens cost.
AT also confirmed that the Quay St cycleway, which was opened in July 2016 at a cost of $2.85 million, was being ripped up for the project.
Despite then-Prime Minister John Key and Transport Minister Simon Bridges riding the cycleway for its official opening, AT this week said it was always "an interim facility".
"The Quay St enhancement project makes the cycleway permanent and integrates the section between Lower Hobson St and Commerce St. The current on-road separated cycleway will remain in place between Commerce St and Plumer St," Van Essen said.
About 300,000 Aucklanders used the Quay St cycleway this year.
Auckland Ratepayers' Alliance spokesperson Jo Holmes said AT should be "hauled over the coals" for a $13m blowout "equivalent to the annual rates bill for almost 4000 Auckland homes".
"Auckland Council loves wasting our money on cycleways so much it's built the same cycleway twice," Holmes said.
"We were told it would last five to 10 years, but it's been torn up after three. It's madness."
Van Essen confirmed the Quay St enhancement work was on schedule to be completed by December next year, in time for the beginning of the 2021 America's Cup.