MP says anonymous brochure warning of 8m Waimea dam tidal wave 'scaremongering'

Nelson MP Nick Smith says an anonymous brochure warning Brightwater residents that a new dam may expose them to an 8m tidal wave is "irresponsible scaremongering". Photo / Supplied

An anonymous brochure warning that an 8m tidal wave could rampage through a small town if a proposed dam broke is being called misleading, dirty, and irresponsible scaremongering.

The brochure - titled "How the Waimea Dam could affect you, your family, your home and its value" - has been delivered to the people of Brightwater, which is 20km from Nelson and near the site of the proposed Waimea dam.

"If the dam failed, collapsed, or breached and released its 13 million cubic metres of water, it would hit the Brightwater township in a tidal wave up to 8m high," the brochure said.

"It would take all before it with catastrophic effect ... The school is in its direct path."

A note at the end says the brochure is from "concerned local residents/ratepayers".

But Nelson MP Nick Smith said the brochure was "garbage".

"It is dirty and sneaky for people to be scaring the bejesus out of people with claims of an 8m tidal wave for the town of Brightwater without any factual basis for it at all."

Smith said the brochure was "irresponsible scaremongering", and the dam was "a very safe dam and the right thing for the Nelson region".

"I've had older people scared witless by these claims of the township of Brightwater being exposed to potentially an 8m tidal wave, and even mothers in tears over these really extravagant and false claims."

He said the anonymous nature of the brochure was particularly concerning, as was the timing; his member's bill - which would transfer interests in Crown land to allow the dam to be built - is due for its second reading tomorrow, and local authorities are scheduled to make final decisions about the dam on Friday.

Dam designer Tonkin and Taylor said in a statement that the brochure was "very misleading", and the chances of the dam breaking were "extremely low".

It quoted its 2012 report that a rapid dam break would lead to peak flooding of half of Brightwater "inundated to depths ranging from 0.5m to 3m".

"Nowhere does our analysis say Brightwater would be hit by a 'tidal wave up to 8m high' ... The elapsed time for the peak water level to occur is 61 minutes, not 20 minutes as implied by the brochure."

The brochure quotes GNS geologist Mike Johnston on the "high probability of earthquake rupture on the Alpine Fault within the planned life of the Waimea Dam", and says that an 8.2-scale earthquake is due, according to GNS.

But Johnston, in a statement, said the dam is not on an active fault, and was some distance from the Alpine Fault and Waimea Flaxmore Fault.

"The GNS reference to the Alpine Fault is to the southern section and not to the northern section, sometimes referred to as the Wairau Fault, which has a much lower level of activity. Therefore what is quoted is, at best, mischievous."

Smith invited concerned residents to read the available reports to be better informed about the dam and associated risks.