Benmore Dam spilling

[vifferman]

The media said the latest spilling was to attempt to blow dydimo out of the river. Sounds like bollix to me - is it just someone trying to put positive spin on this, or is there some partial truth in that they made the discharge extra big in the hope it would help with the dydimo thing?

[Jantar]

Meridian's lakes are all over their maximum operating level, so spill is mandatory. As they have to spill anyway, it is obviously an ideal chance to see if flushing will reduce the amount of didymo.

Contact will possibly do something similar (but not as spectacular) in the Hawea river next month.

[Zippity]

The media said the latest spilling was to attempt to blow dydimo out of the river. Sounds like bollix to me

Must admit I laughed when I heard that "ill-informed" comment on TVOne news last night

Lake Aviemore is about 400 yards downstream of the spillway, then there is Lake Waitaki, before the river proper starts at its base - and that is just a couple of clicks upstream from Kurow

Once again another poor example of the "hand-out" journalism that is practised here in New Zealand. Maybe if the reporter got off his arse and went and saw for himself, we might have had a half decent story.

[Jantar]

Must admit I laughed when I heard that "ill-informed" comment on TVOne news last night

Lake Aviemore is about 400 yards downstream of the spillway, then there is Lake Waitaki, before the river proper starts at its base - and that is just a couple of clicks upstream from Kurow

Once again another poor example of the "hand-out" journalism that is practised here in New Zealand. Maybe if the reporter got off his arse and went and saw for himself, we might have had a half decent story.

It isn't possible to pass 960 cumecs through Benmore without it also going through Aviemore and Waitaki. With the tributaries coming in along the way its 1000 cumecs flowing down the river.

So where is that "ill-informed" comment"?

[Zippity]

To "flush out the river" as the reporter said, huge quantities of water must first be released into the river.

The Aviemore Dam (like Benmore) has a spillway also, Waitaki doesn't.

Waitaki relies on gravity to shed it's excess water - ie, once the lake is full, it flows over the top of the dam.

I'm not aware of this happening at this stage

[Jantar]

To "flush out the river" as the reporter said, huge quantities of water must first be released into the river.

The Aviemore Dam (like Benmore) has a spillway also, Waitaki doesn't.

Waitaki relies on gravity to shed it's excess water - ie, once the lake is full, it flows over the top of the dam.

I'm not aware of this happening at this stage

Waitaki is a weir type dam, so yes, water does flow over the top. It has been doing that for some weeks now.

If it wasn't happening then where is the water from Benmore going? As Lake Waitaki surface area is only around 5 km^2 then 1000 cumec inflow would cause the level to rise 1 mm every 5 seconds. That is 0.72 m per hour or 17 m per day. What is this new magic water storage system that Meridan have discovered that allows this amount of water to be stored in a small lake?

[Bass]

So where is that "ill-informed" comment"?

Well I'll admit to being ill informed, but doesn't he have a point?
I presume the hydro lakes will remain close to full during this process and therefore (I would guess) the current speed through the lakes is unlikely to be high enough to clear out didymo. On top of that, you mentioned Hawea as yet to happen.
If they were trying to flush didymo, would it not make sense to start as far upstream as possible and work downstream from there?
(Genuine questions BTW)

[Okey Dokey]

Great to see the new photos- they are impressive. The water flow in the Waitaki is phenomenal at the moment- also very impressive.

As well as possibly reducing the didymo levels, even temporarily, I heard that a nice clean river bed will be good for the salmon spawning later, too.

[k14]

Well I'll admit to being ill informed, but doesn't he have a point?
I presume the hydro lakes will remain close to full during this process and therefore (I would guess) the current speed through the lakes is unlikely to be high enough to clear out didymo. On top of that, you mentioned Hawea as yet to happen.
If they were trying to flush didymo, would it not make sense to start as far upstream as possible and work downstream from there?
(Genuine questions BTW)

Didymo doesn't grow in lakes, only in fast flowing rivers. The flush (using water originally from lake tekapo and pukaki) will flush all the way from benmore, through aviemore and waitaki and then down the waitaki river out to sea. I'd hazard a guess that most of the didymo is growing downstream of the waitaki dam and thus the 1000+ cumecs running down through there will do a good job at washing it away!

[Jantar]

.... On top of that, you mentioned Hawea as yet to happen.
If they were trying to flush didymo, would it not make sense to start as far upstream as possible and work downstream from there?
(Genuine questions BTW)

Hawea is on a totally different river system from the Waitaki. Meridian are starting as far upstream as possible by releasing water from Tekapo and Pukaki directly into Benmore, then down the river chain of Aviemore and Waitaki into the Waitaki river.

Hawea is currently releasing 30 cumecs, and that is likely to increase to 200 cumecs in late february.

[Bass]

Didymo doesn't grow in lakes, only in fast flowing rivers. The flush (using water originally from lake tekapo and pukaki) will flush all the way from benmore, through aviemore and waitaki and then down the waitaki river out to sea. I'd hazard a guess that most of the didymo is growing downstream of the waitaki dam and thus the 1000+ cumecs running down through there will do a good job at washing it away!

Downstream of the Waitaki I have some optimism about - 1000 cumecs is no small trickle - but the rest of it I'm not so sure about. I know we are only talking about a bit of a clean out here and that eradication is probably impossible. So perhaps you're right. I'll keep my fingures crossed

Hawea is on a totally different river system from the Waitaki.

Doh!! Marbles disappearing rapidly.

Meridian are starting as far upstream as possible by releasing water from Tekapo and Pukaki directly into Benmore, then down the river chain of Aviemore and Waitaki into the Waitaki river.

Hawea is currently releasing 30 cumecs, and that is likely to increase to 200 cumecs in late february.

Thanks for that. What's the extent of the didymo problem in the Clutha?

[Zippity]

Man I so much want to go back down to the Waitaki Hydro system for some fishing

There is nowhere like it on earth

[Jantar]

..... What's the extent of the didymo problem in the Clutha?

Its quite bad in the Hawea river, and getting worse in the upper Clutha. The lower Clutha is quite deep and slower moving so not too much of an issue there.

[Forest]

I still believe that NZ is too small to have competitive businesses producing electricity. Max Bradford was wrong. Central longterm planning by Government is best. But what is done is done.

Having said that, Meridian, Mighty River Power, and Genesis are all government owned. So is Transpower. So the government has the ability to direct these SOEs to do what it wants.

Unfortunately governments are gutless. Upgrading the transmission network requires money which means power price increases - and that's politically unacceptable. However government could commit taxation money to this work. Instead we've had 9 years of social engineering while basic infrastructure slowly crumbled.

It isn't quite that simple. Just look at the Waikato Transmission Line project.

The last government committed $500 million to run new transmission lines into Auckland, but the Waikato farming community has managed to hold the country to ransom by stalling the project.

[oldrider]

It isn't quite that simple. Just look at the Waikato Transmission Line project.

The last government committed $500 million to run new transmission lines into Auckland, but the Waikato farming community has managed to hold the country to ransom by stalling the project.

That's referred to as the NIMBY syndrome. IE: "Not In My Back Yard".

It's everywhere in New Zealand!

Give me the electricity but not the infrastructure! John.