Engineer slams dam as ‘high risk’
Water resource engineer Dr Mike Harvey says the proposed Waimea dam is a high-risk project.
‘‘My biggest concern with the Waimea dam project: I don’t believe that the costs have been really worked out for this dam,’’ he said. ‘‘As a ratepayer, I’m concerned about that ... because it’s under designed, it’s under costed.’’
Harvey has a home at Mariri, near Motueka, but a lot of his work has been carried out in the United States – much of it in connection with dam projects.
From his Mariri property, Harvey said he had just been working on two US dam projects: A proposed hydroelectric dam in Alaska and a planned dam to provide urban water for the expanding Dallas metropolitan area of Texas.
Harvey said his speciality was rivers and his role for the US projects had focused on sedimentation including the likely effects of the absence of sedimentation on the rivers below the proposed dams.
He also had experience with tailings dams for mine operations and in every project he had worked on, the final cost ‘‘way exceeded’’ the initial estimate, he said.
That unknown final cost was his biggest concern with the Waimea dam project, along with a suggested funding model, that has ratepayers responsible for a 50 per cent share of the first $3 million of any cost overruns before picking up the tab alone for any budget overshoots above that.
Tasman District Council and Waimea Irrigators Ltd are proposed joint-venture partners in the $82.5m project, which is tipped to be funded by a mix of ratepayer, irrigator and Crown funding.
The council in October called for submissions on ownership and funding options for the scheme, receiving more than 1500. It held a hearing over four days at different locations including one at Motueka on December 15 where Harvey spoke. He expanded on his submission after the hearing.
‘‘Everything I read about the geology and seismology says to me it’s very complicated.
‘‘I see numbers in there that don’t reflect the seismic reality. I would be very loath to build a dam in that location.’’
The construction estimate for the dam is $50m.
However, a final likely cost is not expected before March or April. It will incorporate a finalised design that will take into account the findings from the Canterbury and Kaiko¯ura earthquakes along with updated guidelines from the New Zealand Society on Large Dams.
Harvey said concerns about seismic risk including potential vertical motions were ‘‘eminently addressable’’.
‘‘I don’t believe anyone wouldn’t take these factors into consideration but what’s the cost,’’ he said. ‘‘The irrigators’ costs have been capped; everything else is for the ratepayers.’’
If an earthquake did affect the Waimea dam, it might not fail catastrophically ‘‘but you’ve got a broken dam and a broken dam is not any good to anyone’’.
Harvey said the available design information he’d seen indicated the dam would have limited outlet capacity and he estimated it could take a week or 10 days to drain the water if it was damaged.
He doubted a ruptured dam would be repaired and wondered if the likely cost of decommissioning the structure had been considered.
Harvey said the proposal ‘‘confounds me in many ways’’ because there was no constant need for the water.
‘‘The goofiness about the project is it’s not designed to be used all the time; it’s sort of an insurance policy, a top-up.’’
Harvey said he got all of the water for his property from his roof.
‘‘How much of the urban demand could be satisfied by a joint roof-top [collection] and council top-up supply?’’
Harvey said he grew up in Christchurch. He had bachelor and masters degrees in agricultural science from Lincoln and a PhD in water resources form Colorado State University.