The pipeline carries water from Deep Stream and the part that runs through the bed of the Silver Stream in North Taieri is considered to be at risk of damage from significant floods.
The risk is mentioned in council tender documents for assessment work required about the condition of Dunedin’s most critical pipelines.
Deep Stream and Deep Creek are the two main water sources for Dunedin.
Asked about the major risk to the Deep Stream pipe, a council spokesman said this was mitigated by regular visual inspections at the Silver Stream, including before and after significant wet weather.
Staff also placed additional rocks around the pipeline to protect it when that was required, he said.
The council has a list of the top 13 pipelines regarded as both critical and needing assessment of their condition.
Deep Stream is among them, but is considered to be priority 2, rather than priority 1.
Pipes are assigned priority scores, based on age-based condition grades and a multi-criteria assessment of how critical the assets are considered to be.
Deep Stream’s average priority score of 13.2 out of 25 is classed as high, but short of very high.
The Dunedin main interceptor sewer is one of the pipes on the "very high" list, registering an average priority score of 16.9 out of 25.
Council tender documents for the assessment work referred to fat build-up in the vicinity of the Mad Butcher site in South Dunedin.
The council clarified yesterday it was not suggesting the build-up was because of the Mad Butcher operation.
"Fat build-ups are a known challenge in many wastewater networks, but the reference to fat build-ups in our main interceptor sewer is not attributed to Mad Butcher," the council spokesman said.
"It’s indicating the location of the build-up is in an area from near Mad Butcher to further downstream."
A Mad Butcher spokesman said the shop had a grease trap, which was cleaned in line with council regulations.
The council spokesman said the location referred to was where the main interceptor sewer split into two smaller pipes to avoid other services, before re-converging, and fat could build up where the pipe was split.
"We utilise a range of methods to clear build-ups and manage discharges at source, as well as including details in our tender documents to ensure companies bidding for the work are aware of the challenge," he said.
Asked why there was a gap between a WSP report in 2022 and the council pushing forward to get a comprehensive condition-assessment programme going, the council spokesman said a wider integrated system planning programme was needed first.
This included "a number of studies of pipelines, other infrastructure and potential risks, to better understand the big picture before committing to further condition-assessment work".
The council intends to have a comprehensive and planned condition-assessment programme implemented by the end of June 2027.
The work would be aimed at determining when key pipes should be replaced and identifying high-level remedial action to be undertaken to prevent premature pipeline failures, the council said when it invited tenders.
