Farmer unshaken by nearby dam
Masterton farmer James Perry is not too bothered by the prospect of living a few hundred metres downstream from a wall holding back millions of tonnes of water.
‘‘Nothing’s infallible, that’s just a fact of life. If it were to go, I think you’d have bigger problems during a magnitude 10 earthquake,’’ he said.
He broadly supported the Wakamoekau Community Water Storage in the foothills of the Tararua Range project and was confident the designs he had been shown were safe.
‘‘You could get all NIMBYish and say we don’t want it here, but at the end of the day, it’s a big picture thing. If it goes ahead it will benefit the whole of the Wairarapa.’’
Perry has a background in earthmoving and said the engineering of the project seemed to make sense as it was explained to him during an information evening for nearby residents in Masterton recently.
As part of the latest preparation work for the facility, the project’s planners released a seismic assessment of the proposal and what would happen in a 1-in-10,000-year earthquake.
They needed to draw up a hypothetical dam fail scenario which showed water from the dam would flood a path down through the centre of the Wairarapa valley.
The reservoir investigation work was being done by independent body Wairarapa Water, which commissioned the plans. The dams were designed by GHD Engineering Group and peer reviewed by Damwatch Engineering Ltd.
Graeme Boyd, of Damwatch, said the main dam’s design was such that even in a massive magnitude 9 earthquake, the like of which had never been recorded in New Zealand, the dam should continue to perform well.
Its wide base and its structure meant it could withstand a lot of ground movement and still retain its integrity, Boyd said.
‘‘What makes this type of dam so suitable is its trapezoidal shape with a wide base and shallow, low angled slopes and its ability to absorb earthquake shaking.’’
He said it was the best type of dam for this kind of territory.
Engineers concluded that in the hypothetical event of a dam failure it would create similar conditions in the Wairarapa valley to those experienced in a 1-in-100-year flood. That would put half of Masterton underwater.
Masterton Mayor Lyn Patterson said the benefit of having reliable access to water outweighed a risk of having a dam upstream. ‘‘The benefits that would come in the interim to our communities for security of water would outweigh that 1-in-10,000-year risk.’’