by Chris Tobin
Hedging and fencing next to the eroding Patiti Point cliff edge was removed earlier this week, before it could be claimed by the sea.
Timaru District Council spokesman Stephen Doran told The Courier on Monday that the council was cutting down the macrocarpa hedge which surrounds the Deerstalkers Club land at the Point, so it could remove the fencing on the seaward side.
This was to prevent the fencing from falling into the sea, due to the rate of erosion, he said.
“[It is] for safety and environmental reasons.”
However, the stumps and roots of the hedge would remain to help stabilise the land.
KiwiRail monitoring line
Big storms have cut into the coastline near Saltwater Creek and waves have reached the main trunk rail line but KiwiRail says there is no immediate risk, although active monitoring is being undertaken.
“It is an area that is being actively monitored with extra inspections during king tides,” South Island general manager operations Jeanine Benson said.
There were no immediate plans to re-align the track, she said.
“We have had discussions with the Timaru District Council about the area.
“KiwiRail keeps a close eye on th coastal areas alongside the Main South line between Christchurch and Dunedin and carries out extra track inspections after high seas and heavy storms.
“We carry out remedial work as and when required to ensure the continued safe and efficient operation of our rail services.”
Environment Canterbury made an aerial photographic analysis comparing historic shorelines between 1938 and 2013.
This showed the coast is retreating at about 40cm a year, 30cm more than it had been at Patiti Point between 1990 and 2016.
“There have been several large storm events that have impacted the Saltwater Creek shoreline since this analysis, which have caused a noticeable amount of erosion,” Justin Cope, ECan’s principal science adviser natural hazards, said.
The reintroduction of a passenger service between Christchurch and Invercargill was still being considered.
“KiwiRail is awaiting the findings of a feasibility report before considering whether to undertake further investigation into the viability of the proposed service,” Alan Piper, executive general manager sales and commercial for KiwiRail, said.
Mr Doran said since February 2018 there had been about 10m of erosion in some areas.
“We’re working with the Deerstalkers Club on relocation of the building to a site 500m away.”
This “retreat” from the area follows rapid erosion of the cliff face over the past two years, as documented by Environment Canterbury (ECan) records.
ECan’s principal natural hazards science adviser Justin Cope said the council had monitored the rate of erosion at a Patiti Point site every six months since 1990.
Its data showed the massive rate of erosion at the point could be traced to a succession of big storms which battered the coastline two years ago, he said.
ECan’s records showed erosion had been occurring at a modest rate of about 10cm between 1990 and 2016, which was as expected since the headland was exposed to the ocean.
“However, at our monitoring site, between 2017 and March 2019 the cliff has eroded about 4m and the level of the beach has dropped by about 3m, making it the lowest it has been since we began surveying it,” Mr Cope said.
A series of large coastal storms had depleted the volume of gravel in front of the Patiti cliffs during the first half of 2017, and Mr Cope said this had made the area vulnerable to the full blast of the ocean.
“The height and amount of gravel in the beach in front of the cliff is an important factor in protecting the cliff from wave action during storms.
“If there is a depleted buffer of beach sediments in front of the cliff, then it becomes vulnerable to a wave attack.
“Because the storms happened in quick succession, there was no time for the beach to replenish its sediment supply and the cliffs bore the brunt of the waves in subsequent storm events.
“Regular storms have further prevented a recovery of the protective layer of beach gravels and cliff erosion has continued.”
Mr Cope said the erosion was worse at other sections of Patiti Point along from ECan’s monitoring site.