An area of loose fill material has been found below the railway line on an embankment. File photo. Photo: 123rf
Unstable land under the Wairarapa line could have "catastrophic" consequences for the tracks, according to documents released to RNZ under the Official Information Act
The modelling for the land under the line - 1.4 kilometres north of the Remutaka train tunnel - shows there is a medium to high risk of a slip occurring.
KiwiRail said there was an area of loose fill material, or localised instability, just below the railway line on an embankment.
If the slip did occur, KiwiRail rated the consequences as "critical / catastrophic".
"This means that if a slip were to occur, the track could be undermined and potentially closed for a number of weeks, preventing rail services from running."
KiwiRail has completed design work to install metal piles, designed to stabilise the land, but construction has not started.
KiwiRail said it was commercially sensitive to say how much the work could cost, and that no contract has been let at this stage.
Greater Wellington Regional Council Transport Committee chair Thomas Nash told RNZ that New Zealand's roading and rail network were vulnerable to slips and severe weather events.
"That's why the most important investment we can make in transport at the moment is to make sure our existing connections on rail and road are solid."
Nash said if specific transport links were knocked out, it had severe consequences on peoples' daily lives and the economy.
RNZ reported earlier this month that KiwiRail was investigating if new overhead lines in Wellington were badly installed, and whether they caused commuter trains to grind to a halt for hours in early January.
Greater Wellington Regional Council released a report in December that stated there was a $1 billion shortfall in funding for the capital's rail network.
The report also identified a significant backlog of maintenance renewal programmes that KiwiRail has to deliver in the region.
