According to a council operations committee report dated April 20, reinstatement work on the pipeline was “largely like for like”.
In response to questions from Local Democracy Reporting, council director community lifelines Dave Wilson said damage to the pipeline had cost the council just over $2.8 million.
He would not say how long it would take to completely fortify the pipeline.
“Recovery is a period to consider and scope potential options toward risk mitigation, which will vary depending on the specific reach of (the) pipeline and potential risks from climatic and other natural events.
“Timing of new works has not been set yet.”
Mr Wilson said the next steps were to reinstate access tracks, scope solutions to better protect areas of pipeline near escarpments and slips and consider long-term solutions of getting more sections of the pipe underground.
Three pipe bridges on the treated water supply were damaged as a result of the cyclone, along with bridge access to the water treatment plant.
Five pipe bridges on the raw water supply were also damaged.
The council last week said it was well into the recovery of physical works, thanks to local contractors working at pace, but could be constrained by its ability to treat silt-laden water and provide a “base supply from Waingake that the city can rely on”.
“There will be an expectation from industrial, commercial and domestic users that future risks will be reduced (but) funding of such work and meeting those expectations will be a challenge, especially when they are event specific,” last week’s report said.
Gisborne city is supplied by two main water catchments — the Mangapoike dams and the Te Arai bush catchment.
Two of the three dams at Mangapoike are heavily affected by silt and present a major challenge to treat, the council says.
The council has plans to pump $1.5 million into a pre-filtration system at the Waingake plant to address the high silt content that has plagued its catchments following extreme weather.
The untreated water from the catchments is treated at the Waingake Water Treatment Plant before travelling through a 30-kilometre pipeline to the city’s reservoirs and reticulation network.
From there, it is delivered to the tap.
RNZ last week revealed Gisborne’s main water supply was identified as being at an unacceptable risk of catastrophic failures months before Cyclone Gabrielle hit.
The council completed its first government-ordered water safety plan three months before the cyclone hit but already knew the pipe was an issue before the report was undertaken.
Following the cyclone, council chief executive Nedine Thatcher Swann confirmed the mobilisation of pine — both whole trees and harvest waste logs — played a “critical factor” in damaging the pipeline.
The supply runs through the council’s joint-venture 1100-hectare commercial pine forest.
An assessment of woody debris impacting the pipeline is under way but the council will not say when it will be complete.
Steps are yet to be taken to mitigate future risk to Gisborne’s main water pipeline during the repair phase following Cyclone Gabrielle, the district council has revealed.