Meridian Energy has launched a multi-year seismic upgrade programme at New Zealand’s Benmore Power Station, aimed at improving the earthquake resilience of the station’s penstock system and ensuring rapid recovery following a major seismic event.
At 552MW, Benmore is New Zealand’s second-largest hydroelectric power station and the largest facility within the Waitaki Hydro Scheme. Construction began in 1958, with the concrete penstocks installed in the early 1960s. The sloped sections of the penstocks are constructed from prestressed concrete segments, connected using reinforcing steel and mortar to maintain structural continuity and watertight performance.
The current project targets Benmore’s six concrete penstocks. Unlike most large hydropower facilities, which typically use steel penstocks, Benmore’s units were constructed from reinforced concrete. With increasing seismic risk associated with activity along the South Island’s Alpine Fault, Meridian is undertaking structural modifications to improve their performance under strong ground motion.
“Benmore will be critical to recovering from a large quake as it’s from here that the high voltage DC link runs between the South and North Islands. With Benmore generating enough power for around 300,000 Kiwi homes, the country can’t afford to have it out of action for long,” said Tania Palmer, Meridian GM Generation.
“There’s a 75% chance of a significant earthquake along the Alpine Fault in the next 50 years, so we’re investing now to make sure the penstocks have very little, if any, damage when it does inevitably happen. There’s no risk to the dam itself, but without this work it’s possible that one or more of the six penstocks would be unable to do their job for an extended period of time.”
Construction began in late 2025 and will continue through to early 2029. The strengthening programme includes modifying the upper joint of each penstock to allow controlled movement during seismic events, installing fluid viscous dampers to dissipate dynamic loads, and replacing existing rubber bearings with anti-seismic devices. Additional scope includes wrapping critical joints with fibreglass to increase structural capacity, as well as access route upgrades and enabling works to support construction activities.
Each penstock is installed on a 37-degree slope and measures approximately 130min length with an internal diameter of 5.3m. Under full operating conditions, individual penstocks carry loads approaching 3,000 tonnes. Engineering solutions have been designed to allow the work to be carried out while maintaining generation output and water conveyance.
Bearing replacement will be undertaken using a hydraulic jacking system that temporarily supports the penstocks while they remain in service. Installation of the fluid viscous dampers will require the use of a tower crane due to component size and placement constraints on the steep slope.
“While this work is not a high risk, we think it’s the first time a project like this has been undertaken anywhere in the world – we’re going to be reinforcing, stabilising and wrapping each penstock all while millions of litres of water are rushing through them,” Palmer said.
“The construction of Benmore was a brilliant piece of Kiwi innovation, so it’s only fitting that the work we’re doing now is equally innovative. Our hydro stations are incredible assets that have served the country well for a long time. We know we’re responsible for helping keep the lights on for Kiwi homes and businesses, and the work we’re doing at Benmore and other stations will help keep them generating clean energy for decades to come.”
