River eco queried

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Manapouri Power Station

A GROUP formed to care for the water quality of the lower Waiau River has taken Environment Southland (ES) to task about the negative effects of the Manapouri hydro scheme on the environment.

Lower Waiau Rivercare Group co-chairman Paul Marshall said his group explained to the council, at its meeting last week, how Meridian Energy’s Manapouri lake control structure, part of the Manapouri hydro scheme, was responsible for negatively altering the lower Waiau River’s ecosystems.

The lower Waiau flows south of Lake Manapouri, through Tuatapere and out into Te Waewae Bay.

Mr Marshall said since the Manapouri hydro power station diverted 97 percent of the river’s flow in 1971, he believed the essential character of the lower Waiau River had changed dramatically.

The river once had an average flow rate of about 450 cubic metres of water a second, but this was now reduced to about 16, he said.

The rest of the water normally feeding the Waiau now diverted through the power station on the western arm of Lake Manapouri, with discharge into Doubtful Sound.

During a flood, the power station would fully open gates feeding the lower Waiau, releasing a torrent of sediment and gravel-filled water into the river, Mr Marshall said.

When the full flow into the Waiau was cut off again, the river no longer had the ability to move gravel and sediment along, he said.

“If you stand on Tuatapere bridge now and look south you’ll see an island of gravel in the middle of the river. The riverbed is higher now and the river is becoming more flood prone.”

The community also believed the power station had caused “catastrophic damage” to Blue Cliffs Beach, he said.

The beach was once sandy with dunes.

“With the power station’s operation, the beach is now a rocky wasteland.”

Beds of edible shellfish along the beach had also disappeared, he said.

“We are not scientists, but we are passionate observers of the river over time. Our oldest member is 89 years old, she’s been part of this community her entire life and has witnessed these changes. When I see the changes to the river, I have a sense of profound sadness.”

Meridian Energy statutory and compliance strategy manager Andrew Feierabend said Meridian Energy operated the Manapouri hydro scheme in accordance with consents set and overseen by ES.

Erosion and flooding in the lower Waiau River were part of natural river processes, he said.

Mr Marshall said: “We agree, but it’s the result of an unnatural flow regime. If I were to take your cellphone and hold it above my head and drop it on the concrete pavement, that’s a natural process called gravity – but I would be culpable. By the same line of logic, Meridian Energy is responsible for how that river flows.”

Mr Marshall said he was confident ES would take the group’s concerns seriously, but the group had so far received no assurances from the council.

“What we have said to ES is we expect the resource consent manager to direct Meridian to take precautionary measures, and also to deal with the flooding and erosion downstream.”

ES chief executive Rob Phillips said he realised how important the concerns raised by the group were to its members, but the situation was complex.

“The council will be working with the various parties involved in this, including the rivercare group, to find a way forward,” he said.

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