‘Rethink library site’

Rising seas a challenge for $44.4 million riverside project, says councillor

Plans to build a new Nelson library on a riverside site near the coast should be halted as new data shows the sea is rising twice as fast as previously thought in the region, a councillor says.

The Nelson City Council plans to build the library – at an estimated cost of $44.4 million – along the Maitai River, at the edge of the CBD, near the river mouth.

City councillor Rachel Sanson said the council should pause the project and reconsider its location, following findings from the NZ SeaRise programme that Nelson and Tasman district was experiencing on average double the global rate of sea level rise.

Sanson said the council needed independent expert advice on indications the flood risk at the library site had

significantly increased, presenting a growing risk of insurance and finance retreat.

‘‘[The planned library] is debt funded, so that means we’re essentially taking out a mortgage to build this asset.

‘‘What happens for the community if in 20 years, it’s no longer insurable, and the ... debt gets recalled?’’

The mapping showed Nelson and Tasman district’s coastline was sinking by 3mm a year on average.

Tasman district’s largest town, Richmond was subsiding at almost the highest rate – 4.28mm a year. Victoria University of Wellington Professor and SeaRise

programme co-leader Tim Naish said the port area of Nelson, near the planned site of the library, was sinking at around 2mm a year.

‘‘Given also the river is going to back up, I would think the whole Trafalgar Park area is in trouble.’’

The area would have 40cm of sea level rise by mid century, with ‘‘the hundred year coastal flood’’ happening every year by around 2050/2060, Naish said.

A one-in-20 year event could happen there ‘‘within years, to a decade’’, he estimated.

A one-in-20 year event was a point at which insurers had been to shown to withhold insurance.

Sanson didn’t think building the library in an area known to be vulnerable would be a ‘‘defensible decision’’.

The costs could balloon out to more than $100m, she said.

‘‘The expected financial life of the asset is 65 years, so if we are paying interest on this debt over 65 years, and then potentially repaying that debt in 65 years, the true cost of that is in the proximity of $140m.’’

‘‘I would feel that if I was to make a decision to support this investment in a location where there is known hazards ... that it would be bordering on negligent on my part.’’

While a new library there could be used for 65 years, accommodating ‘‘some inundation and flooding impacts from time to time’’ with a raised ground level and potential for raising the floor level, that was still a short-term view, she said.

‘‘Given also the river is going to back up, I would think the whole Trafalgar Park area is in trouble.’’

Tim Naish

SeaRise programme co-leader

‘‘Our community might not be in a position to make this kind of investment in another 65 years, and we will have completely lost the opportunity and really cost future generations the benefit of something that could have been built elsewhere, and could be of benefit for future generations for hundreds of years.’’

Nelson City Council chief executive Pat Dougherty said staff were now taking stock of the SeaRise data, and would be able to respond to it in more detail later this week.

‘‘Council has been clear that when new data comes to light we take it into account in our decision-making process. We therefore welcome the information provided by the SeaRise project and intend to take account of these changes in further flood mitigation work in our CBD and other impacted areas of Nelson.’’

Dougherty said the data was particularly well-timed as the council would be talking to the community in June about how sea-level rise would affect the coast, and the consequences it would have. ‘‘Council will then develop detailed options and assess the associated costs before holding further conversations with the community to decide on our adaptation plan.’’

Tasman District Council said a report it commissioned in 2019 differed considerably from the SeaRise projections.

Environmental policy manager Barry Johnson said the report found most of the district’s coastline was subject to slow long-term uplift, with slow subsidence in the Nelson/Richmond coastline.

‘‘It is hoped that as further detail of the NZSeaRise predictions and the data that it is based on becomes available, a better understanding of the relative sea level rise rates across Tasman’s coastline can be achieved.’’

An estimated 8400 people in the district lived in areas vulnerable to storm inundation and sea level rise, according to the council’s coastal hazard mapping.

MARTIN DE RUYTER/STUFF Nelson city councillor Rachel Sanson pictured at the Maitai River at a 3.9 metre high tide. She says pushing ahead with plans to build a library on the opposite side of the river, in the right of the photograph, is unwise, given findings that the sea level is rising faster than previously thought.

An artist’s impression of the proposed new Nelson library on its riverside site.