The Conservation Department is reviewing the way it decides when to destroy nature to protect the public.
DOC came under fire from conservation groups in July after it blew up a sandstone overhang on the popular Truman Track in the Paparoa National Park, following a rockfall near a viewing platform.
flax-covered rock stack off beach at the end of Truman Track
near Punakaiki in 2013. Photo: Pseudopanax, via Wikimedia
It was accused of taking a 'blast now, think later' approach to a spectacular natural feature and registered archaeological site.
This month's West Coast Conservation Board meeting heard DOC had chosen to extend the track into a dangerous area without any expert assessment of the risk.
A report by board member and caving authority Neil Silverwood said DOC had recently invested in new stairs and a viewing platform, making the site more accessible to the 35,000 tourists who visited the Punakaiki track each year.
"This section passed beneath a sandstone cavern. Prior to building no geotechnical assessment of the cavern, or risk to new structures was undertaken."
In July, a four-tonne block fell off the cliff near the cave, and the track was closed for geotech assessment.
The findings showed that while there was no immediate danger, the sandstone cliff had natural weaknesses and might collapse over time, Mr Silverwood said.
The overhang was then brought down using explosives, releasing about 70 tonnes of rock.
"The cavern was a unique geological feature, containing a remnant blowhole and it was a registered geo-preservation site," Mr Silverwood said.
The blasting had been done largely to protect access, but tourism and recreation appeared inconsistent with the conservation of a landform that DOC was required by law to protect.
"The section of the track contains several other similar sandstone cliffs which are a large part of the attraction . . . all are vulnerable to collapse and there is a significant risk to visitors. That risk cannot be mitigated without removing the very thing visitors come to see," Mr Silverstone said.
The Opus consultants' report supplied to the Greymouth Star recommended the removal of the overhang.
However, it recommended against the use of explosives.
"We recommend engaging a contractor to scale back the overhang in small blocks ... the use of high explosives is discouraged to prevent blast damage to surrounding rock mass.
"Considering the natural beauty of the area it is important that any scaling back is done as sympathetically as possible," the report said.
A second Opus report, done after DOC blew up the overhang, found the blast had in fact caused further damage.
"Unfortunately the blasting has fractured the rock mass in the residual section of the overhang . . . this needs to be monitored . . . especially after heavy rain," the report said.
Robert Dickson, DOC's Buller district operations manager, said the department had taken further advice.
"We engaged an experienced geotechnical ground-engineering geologist independent of Opus to provide a more detailed site assessment of the overhang."
That had confirmed the necessity to remove the overhang as it posed a significant public safety risk, Mr Dickson said.
"The localised use of a shear explosive provided a quick, highly efficient and safe mechanism to manage the public risk at this site," Mr Dickson said.
DOC's Western South Island operations director Mark Davies said in such cases public safety was paramount.
"The department is carrying out an internal review into the removal of the rock overhang on the Truman Track. This will be looking at our systems and processes and how decisions about visitor hazard management are made."
However, Mr Silverwood said there had been no urgent danger of collapse; the track had been cordoned off and there were other ways of managing risk.
Conservation policy required DOC to manage natural hazards with minimal interference to natural processes and give people information to make their own decisions on risk, he said.
Conservation board member Coraleen White said DOC's hands were tied when it came to public safety, but there was concern over some actions it was taking to protect tourists.
"There was a big kahikatea tree cut down last month on the Old Ghost Road trail (in Buller) – they seem to have be a bit of a gung-ho attitude up there," she said.
The board's NZ Conservation Authority liaison officer, Gerry McSweeney said there had been trees cut down in Arthur's Pass National Park in case they fell on people.
"I think they just gave the boys the chainsaw. There was no discussion with the board," he said.
It was a question of where to draw the line, when so many old trees in West Coast forests, and other natural features could theoretically pose a safety risk, Dr McSweeney said.
"It's an important issue; if you look at the Oparara Arch (limestone arches in Kahurangi National Park) for instance, under this present model you'd blow it up. Maybe the track should not go under it."
DOC's West Coast statutory manager Joy Comrie said as a result of the Truman Track blasting, the department was reviewing its internal processes, and looking at the issue nationally.
thanked Mr Silverwood for his paper and voted unanimously to
tell DOC it regretted the destruction involved on the Truman
Track, and was awaiting the outcome of the