It rated such a loss of supply as “possible” with “catastrophic” consequences.
The end result was an “unacceptable” risk rating.
RNZ asked if the council did enough quickly enough to address the risk its own experts had identified.
“The risk . . . cannot be eliminated and can only be partially controlled, with the nature of such extreme events as a direct hit of a cyclone and flooding or a major earthquake,” the council told RNZ.
After it got the report, it took two immediate steps, it said.
It did a stocktake of critical spares and assessed the pipe for cathodic protection from corrosion.
But it did not address the threat of forestry slash and the safety plan does not specifically mention slash or what to do about it.
Slash debris smashed into bridges carrying the pipe which zigzags across the Waingake River.
“Nine were damaged or destroyed, with sections of the pipe severely damaged,” the council said on its website.
A related Source Hazard report said large areas of the Pamoa forest in the catchment had recently been harvested.
“Slash left from harvesting activity is both a fire risk and poses hazards to the supply pipeline during flooding events.
“Areas of exotic plantation in proximity of the supply pipeline remain that present very high risk during future harvest activity and post-harvest due to steep topography and erosion of clear-felled land.”
It would take years working with iwi to revert the land to native bush, it said.
“The years between without substantive vegetation cover, soil erosion and landslides are hazards to pipeline and pipe-bridge structures. Risk to infrastructure will remain high for years until plantings are established and land is stabilised.”
The water safety plan, for its part, said the long-term goal was to refurbish the pipe and bridges and turn the surrounding area back into mostly native bush, instead of slip-prone, council-owned pine forest.
About 100km of the 285km of water pipe network was damaged.
Shortly after the cyclone, the population was warned to drastically cut water use.
Industries suffered and people organised crews to do others’ laundry, using tank water where they could.
It took 45 days to fix the pipes.
The city still only has one-and-a-half day’s storage in the city’s reservoirs if something else goes wrong.
The new water safety plan in November also rated 13 other risks to the water supply as “unacceptable”, among the 117 hazards it assessed — many of them around contamination, such as from animals, not physical damage.
It shows that work to address the threat of damage taking out mains piped supply entirely, as happened with Gabrielle, is just one out of 24 “high priority” areas for improvement.
It is not clear how the council was deciding what to do first, among this long list of high priorities.
It was considering getting its water from somewhere else or shifting the pipe, it told RNZ.
“Longer term, we are considering the potential for other supply location options and bulk main realignment options,” it said.
The pipe was snapped by a landslide in 2014, taking out water supply for a week.
Last year Gisborne’s spending on roads and paths was six times greater than the $7m it spent on water supply.
Its annual report said: “Customers continue to be very satisfied with the water supply system . . . highlighting council’s successful approach to providing high quality water to our community.”
The water safety plan shows a recurring problem in combating the risks was high turnover of water staff at its contractor, Fulton Hogan.
The council has acknowledged slash played a big role in wrecking the pipe during Gabrielle, though it is still investigating just how much.
Its annual report last year said climate change was the most significant long-term issue facing Tairāwhiti and it was expecting “damage to infrastructure such as roads and pipes because of erosion”.
Despite this recognition, some of its key plans do not appear to have been updated.
Its water main emergency response plan dates from 2011, and its quality management plan from 2012 — well before the 2014 water-pipe break and the triple storms around 2017.
The water safety plans are a new requirement imposed on councils and other major water suppliers by Crown water watchdog Taumata Arowai.
Gisborne District Council alone has three main reports that run to 150 pages. There are now thousands of such plans nationwide.
The annual report shows the council had more than $2m generated from forestry harvesting last year to push that on.
Its private forestry partner, Juken New Zealand, has denied that any current harvesting contributed to wrecking the water pipe.
Juken has been harvesting the forest in stages since 2018 — prior to which it has admitted to doing little monitoring of slash — with the aim of turning 1200 hectares back to native forest to secure the pipeline.
Deputy Mayor Josh Wharehinga has previously called for more protection of the water pipe in the council-owned Pamoa forestry block.
