An aerial view of Bluecliffs, perched next to the Waiau River and ocean. The small Southland township has been threatened by accelerated erosion this year. Photo: Emergency Management Southland/Supplied
Southland's mayor says the Bluecliffs community that is under threat from rapid erosion is facing hard decisions that do not have a cheap or quick fix.
Those in the small community have only been home about a week after evacuating so an old dump that potentially contained explosives could be cleared.
On Wednesday night, residents met with officials to discuss options for the future of their coastal community that lost three metres of land in a day.
The options included planned retreat, the use of mobile homes, physical protections and ongoing monitoring which ranged in cost from tens of thousands to hundreds of millions of dollars, as well as do nothing and monitor the erosion.
Southland District Mayor Rob Scott said any options needed to be explored with the community.
"We have to work this out together," he said.
"Whatever options are decided on have to be sustainable and affordable. At this stage no options are off the table."
Two reports were presented to the community, one by Tonkin + Taylor looked at the erosion damage.
It found the extent of the erosion in front of properties and west to Waimotu Creek ranged from five to 30 metres.
The planned retreat options discussed included moving homes towards the road to increase the erosion buffer to upwards of 50m.
The removal of an old dumpsite at Bluecliffs, Southland, has prompted the evacuation of residents for fear hazardous materials - including explosives - could be present. Photo: Emergency Management Southland/Supplied
The report said that might allow people to stay for several more decades, but it would cost between $20,000 to $100,000 per property.
Removing buildings so they did not collapse into the sea and spread debris along the coast would cost a similar amount per property.
It suggested ad-hoc protections commonly used by property owners could fail or provide limited protection when big storms or floods struck.
River training using groynes and an armoured channel would likely not be practicable and could cost between $20,000,000 to $100,000,000, the report found, but it was unlikely it would be consented.
Likewise, maintaining a river mouth by regularly clearing a channel with machinery would be difficult to unlikely to get a consent, cost between $500,000 to more than $1,000,000 per decade, and it was uncertain if it would do the job, the report said.
It found that erosion might threaten homes within the next one to three large floods or storms, and while it was unlikely this would happen within the next one to two decades, it could not be ruled out.
A report by Pattle Delamore Partners analysed the unsuccessful opening of the gravel spit to divert the Waiau River away from homes last month.
It found that the cut - which took roughly two weeks to make - would not survive more than a few hours due to the scale and complexity of the environment.
"It would be, in our view, impossible to maintain an open cut for any appreciable length of time unless very favourable conditions (high river flows and benign sea conditions) persisted," the report said.
It suggested a training line with a lot of rock would be needed to guarantee effectiveness, but that would cost at least $10 million.
The area is in a transition to recovery period after more than a month under a state of emergency.
On 8 March, residents were asked to evacuate so work to clear an old dump site that potentially contained explosives could start.
About 2000 tones of waste was removed including asbestos contaminated material before residents could move back home on 20 March.
A local recovery manager will take up the role after Easter with the next community meeting planned for April.