KEY POINTS:
An earthquake could send tidal waves over the top of a proposed dam on the West Coast's Mokihinui River, says Forest and Bird.
Meridian Energy wants to erect the dam as part of a hydro-scheme on the Mokihinui, 40km north of Westport and 3km upstream from Seddonville.
"I don't live underneath it, but I think if I did I'd be very concerned," said Forest and Bird's South Island field co-ordinator, Chris Todd.
The area was prone to earthquakes and the back country there was already filled with slips, he said.
"We think that by undermining that slope with a lake there will be an awful lot more slips. Particularly if there's an earthquake, they'll just slide into the lake."
That could cause tidal waves which overtopped the dam, Mr Todd said.
Meridian says the scheme would supply enough power for up to 45,000 homes.
It hopes to start building in 2010 and begin operating the scheme three years later.
Mr Todd said a dam would also prevent gravel going downstream to build up the eroding coastline. Coastal erosion could increase from 0.5m to 1.5m a year as a result.
The Mokihinui was a pristine river above the proposed dam, he said.
"Everything that would be drowned is indigenous forest, basically and a beautiful gorge."
The dam would ruin the habitat of endangered blue duck and native fish and eels.
Meridian's proposed "trap and transfer" programme to help migrating fish upstream meant fish would go into a lake rather than a river, he said.
"You're going to have a lot of attrition of those fish."
Forest and Bird realised the West Coast needed more secure, cheaper power.
However, the society preferred out-of-river hydro schemes, where a small amount of water was taken from a river, then returned.
That would be much less destructive than the planned 85m-high dam across the whole river, he said.
"There's a lot of pressure for renewable power at the moment. But I think if there's ever an example of a dam that shouldn't be built it's this one, because of the unmodified nature and the conservation values of the area to be drowned."
Forest and Bird would be making submissions against the proposed scheme.
Meridian spokespeople were unavailable to comment.
- NZPA
