Council focuses on cross harbour pipeline

Greater Wellington Regional Council today approved the progression of the Cross Harbour Pipeline as the preferred project for an alternative water supply to Wellington City, a major project aimed at improving water supply resilience for the metropolitan region.

Wellington City's water is piped from the Hutt Valley along State Highways 1 and 2, and crosses known earthquake fault-lines multiple times. If damaged in a large earthquake, the pipes could take months to repair. That could leave parts of the city, particularly the eastern and southern suburbs, without water for up to 100 days.

"Getting the water back on as soon as possible after a major earthquake will be critical to the region's recovery and is a major focus for us as water suppliers," said Chris Laidlaw, Greater Wellington Regional Council's chair. "The regional council and the four cities have worked together to develop an emergency water supply system for the days after a major quake. This project to improve bulk water supply is vital to making sure there's enough water to keep Wellington going in the months following that."

The pipeline will carry water from the Waiwhetu Aquifer, in Lower Hutt, through a high density polyethylene pipe nestled into the harbour floor, coming ashore in Evans Bay. Currently funded for $116 million in the regional council's 10-year plan, the next stage of the project is to determine the best locations for the supporting infrastructure and pipeline itself, and then finalise designs and costings.

The pipeline will also provide much needed resilience for day-to-day water operations, said Wellington Water's general manager of design and delivery, Tonia Haskell. "We are limited with our bulk water supply options into Wellington at the moment. This pipeline will give us an alternative supply line to Wellington, in the event we need to carry out some major repairs or maintenance work on our existing pipes and reservoirs."

The confirmation of the pipeline comes after two exploratory bores were drilled into the harbour floor showed that water quality and quantity from the aquifer closer to Wellington was not suitable for the resilience goals the councils were seeking.

"We needed the water to be available in sufficient volume to meet our expected needs," Ms Haskell said. "Unfortunately, both bores came up a bit short in that respect. In addition, there were quality issues that meant we would have had to invest more money in treating the water from the bores. So unfortunately that option didn't stack up."

"If we had found a sufficient flow of water of acceptable quality, extracting water from beneath the harbour could have made significant cost savings," Mr Laidlaw said.

"What we now have however is the confidence to get on with planning the cross-harbour pipeline, in the knowledge that all alternative options have been adequately explored and considered."