Dams that Turn Over

[ttone]

Hi Fisho's,
Many years ago I had an experience that was one to behold. It was through the winter when the Cania Dam turned, killing may thousands of fish in its wake. I dont really understand "How" or "Why" it happened, but I'm told that it happens regularly. Have any of you seen such a thing, and why it happens.
I was on the water early that morning, with a very low fog, and gee it was an errie feeling. Apart from being SO COLD! I've never seen that again.
Cheers ttone

[last_cast]

ttone,

The turning of a lake or dam requires two things. The fist is that the lake is stratified (ie layer of cold water at the bottom and warmer water on top). The second is an unusual cold snap. This cools the warm water on top very quickly causing it to become more dense than the water underneath. This causes the water on top to sink and push the water at the bottom of the lake to the surface. Thus the term turning over. That is why it happens, but I am not sure what aspect of this kills the fish. I guess it is either the sudden change in tempertaure, dissolved oxygen levels or even silt stirred up which would normally be very undisturbed. A large fish kill sound bad, but this sort of thing killed 2000 people in Camerooon in 1986 when a lake overturned near a village. The problem was that the lake depths had been dissolving CO2 from its bottom for many thousands of years. When the lake overturned, this CO2 was released in massive amounts and caused death by asphyxiation for anyone (and aything) unfortunate enough to be close by. Now that is some bad luck. Interesting to hear that it happens regulalry at Cania. May be due to the influence of the warm water from the power station (there is a power staion there right?), meaning that the surface does not have to get as cold to overturn as it otherwise would.

Cheers

[Feral]

Happens most dams as winter comes on, the top cools, the bottom is warmer, the warmer water rises. Unless the temp differences are drastic, its rarely moticeable except for a bit of murkiness.

Does not usually end in fish deaths though.

[ibbo]

Agree with feral have known about it my whole fishing life, havent heard of fish deaths tho.

Just found that the water which sinks has good oxygen so fish can go deeper when this happens which spreads fish out making them even more harder to catch in winter.

Have caught yellowbelly in 60ft water when dam rolls over. :)

[A_DIFF_PERSPECTIVE]

Last_cast,
Cania does not have the power station, that belongs to Lake Callide. Both in the same paddock almost, and both begin with 'C'.
Roll overs are often responsible for fish kills. We see it many times, the smaller the body of water, the worse it seems to be.
Just a quick note.
Regards,
Johnny M

[TinarooTriumph]

G'day fella's.

This happens an awful lot where i live. Some of the larger dams arnt too bad, e.g. Tinaroo, Koombooloomba, Copperlode, Quade, mainly beacuse of the sheer size and habitats of those dams. It sure does get cold at those dams, but during the day the sun heats up and alot of the fish move to the flattier teritory to gather heat. At night when you get those freezing nights the fish move around like crazy to find warmish water. But overall its not too bad up here when it comes to turns.

Theres alot of smaller impoundments around my region that have very very bad turns. Last year we went out for the weekend camping in winter, and on the saturday night we had -8', it was freeeeeezing. Woke up next morning to find dead bream and cod all over the place at our location. It was really really bad. We spent the next two days buzzing around in afew tinnes collecting dead fish.

I bet you guys wont beleive this, i also have my doubts, but i do beleive it after some of the photo's ive seen from my father. In 1988 they had a -16 night up here in Herberton, i kid you not. They had what they call a 'king black' frost. Everything was dead, everything.

Cheers.

TinarooTriumph 8-)