Science adviser and report author Andrew Tait said a predicted rise in sea levels of between 0.5 to 1 metre by 2100 would see waves overcome both natural and built defences, flooding land and waterways with seawater and silt for extended periods.

 

Department of Conservation operations manager Mark Townsend said the national park  experienced significant inundation in low lying areas during the tropical storms of February 2018. 

 

The storm surge created by ex-tropical cyclone Fehi culminated with a perigean-spring tide, or king tide, which meant low lying areas of the park experienced severe flooding, with several campsites completely inundated by the sea.

It was the first time Townsend could recall such intense flooding along the coast, with the repair bill costing more than $1m.

He said sea level rise was "definitely on the radar". Tait's report showed a conservative estimate of a 0.5m sea level rise by 2100 and called for more detailed work to be done at a regional level to pinpoint the vulnerability of specific assets, which Townsend said was well under way.

The ability to camp on sandspits within the Abel Tasman was one of the attractions of the popular national park, but over time some of them would need to be moved to higher ground. 

During Fehi, three-metre waves crashed onto the Bark Bay sandspit and half a metre of sand was deposited on the campsite at Onetahuti. At the time, the campsites had to be evacuated. 

The decision was made to permanently close the Tonga Quarry campsite on the sandspit as it was too exposed to allow for safe camping. While the campsite at Bark Bay would be retained for now, the plan was to move it to an elevated site near the Bark Bay Hut within three years.

"Knowing that the sea level is going to rise at least half a metre in the next 80 years, we've got to make sure our investment is future-proofed."

Further south, the campsite at Appletree Bay was also located on a sandspit and Townsend said there was potential to relocate it to higher ground.

Townsend said a storm surge response plan had also been created, detailing when to relocate visitors from campsites.

It used Metservice data and NIWA's red-alert calendar, which forecasted the days when the tide and the mean sea level was unusually high. 

"When we know we have a king tide coming up we are extra cautious on forecasting and we can alert people, close camps and relocate people.

"We are tuned into it, we have a plan and we are actively managing the safety of our visitors when one of these events happens again."

He said most of the track was protected from sea level rise and didn't need realignment, but there were sections along the beach, like at Onetahuti, where it was vulnerable.

"I think long term we will adapt, there will always be that wonderful experience in the Abel Tasman but things may just look slightly different."