Ōtaki pipeline costs well outside Council’s budget

The cost of supplementing the water supply for Paraparaumu, Raumati and Waikanae using water from the Ōtaki River has escalated to at least $33 million, according to information supplied to Council by its consultants.

The consultants have been working on a number of “in-catchment” options following a Council directive. However, to provide a “total picture” to Council, the consultants have also designed and provided costs for two Ōtaki options.

Their assessment was presented to councillors late last week and will be included in the full report to Council on August 19.

One option involves drilling shallow bores at the river’s edge and piping water 16.5 kilometres to the existing water treatment plant at Waikanae. This has a $37.8 million price tag.

The second option involves drilling shallow wells near the Ōtaki Gorge and a pipeline to transfer water to the top of the Waikanae River catchment. This has a $32.8 million price tag. The consultants say pumping and piping costs would be significant.

Mayor Jenny Rowan said the Ōtaki options had been costed on a like-for-like basis and were clearly outside the budget of $23 million set by Council. “It will be helpful to have these cost estimates, however, as we enter the final phase of the assessment of options for Waikanae, Paraparaumu and Raumati.”

Council initially looked at 41 options. They were reduced to six and then four. The four “live”options are:

River recharge with groundwater

This involves water from the bore field being pumped into the Waikanae River just below the current intake pipe during periods of low river flow. This means residents will be drinking river water. The project could be staged to match demand. The estimated cost is $20.7 million.

Lower Maungakotukutuku dam

This involves creating a reservoir in a natural amphitheatre on the Maungakotukutuku stream in the hills behind Nikau Valley. Water from the reservoir will be released into the Waikanae River to supplement the river’s natural flow as required. This option costs $27.3 million.

Aquifer storage and recovery

This involves using the aquifer below Waikanae area as a natural underground storage. During times of high river flow, water will be pumped into the aquifer for storage. During droughts, water will be pumped from the aquifer to supplement the river. This option costs $24.9 million.

Extended borefield

Under this option, bore water would supplement Waikanae River water during droughts. The bore water would be treated at a new filtration plant which would dramatically improve the quality of the water, including softening to reduce damage to household appliances. The cost estimate is $33.2 million.