What happens when a dam rises? (Fitzy)

[Mak579]

What happens when a dam rises?

The deluge currently being experienced in the North sees alot of the barra impoundments double in size. What immediate impact does this have on water quality and fishability?

Does the sudden submersion of green vegetation and the following decay deplete oxygen levels?

Would the dam turn or flip?

How would the fish react?

How long until things get back to normal?


Any thoughts appreciated,

Matt C

PS Here's hoping the rain spreads further south!

[Fish Guts]

will be interested to see the info this thread brings. great topic mate. always wondered aswell

[warrior]

i have seen a couple of the dams in the NT rise very quickly ,the water clarity is pretty bad at first but the fish dont seem to mind they still hunt very aggresively,the first few weeks are exsplosive while the vegitation is fresh,all the bugs and other crawlies get flushed out bringing in the small bait fish which lures the big ones in.after those good weeks i have also seen the dam turn bad as the vegitation rots and causes i think high oxegen levels which can kill a lot of the water life and result in these fish kills you see,but i look at it as a way of life and its been happening for a long time and doesnt seem to have a great impact on the fishery itsself,they take a while to recover but they do.cheers AL

[McCod]

Gday Matt! Great to see some rain up there, just checked out some dam levels on the net…. Some huge level increases up your way….. Faust , Eungella, Teemburra haven’t seen levels like that in years! The fish will be going off big time while there filling but may only last a while… depending on PH changes from run off etc? Then once the veg starts to decay the fishing could be hard for weeks or even months depending on how much grass, weeds, weed beds etc are left to rot? With huge water increases the dam usually de-stratifies at lest for a while anyway! While the edges decompose the fish tend to hang in the deeper part of an impoundment but will not necessarily always be down deep as sometimes they will be in the top few feet depending an O2 levels etc. While the edges decompose all this can have an effect on the PH of the water as well which can effect the fish also! Once the oxygen & PH etc comes good a dam will usually fish excellent if you can find the fish as there is a lot less larger food source per area of water and the top of the food chain will have to be more aggressive to get there fill. Places like Faust & Awoonga may loose there weed beds for a few years which will change things big time… Not hard to guess where most of the fun will be had then;) In the long term things will look up as the baitfish breed up big time and that means bigger fatter Barra ;D

Cheers Les

[robyoung2]

I don't fish those places, so I'm just speculating of course, but iIS it possible a big fishkill could result from all the decaying organics; reducing the oxygen?

rob

[McCod]

I don't fish those places, so I'm just speculating of course, but iIS it possible a big fishkill could result from all the decaying organics; reducing the oxygen?

rob

Yep! It's not common but possible given the right conditions and it’s the big fish that go first! Many fish can not survive once the dissolved O2 gets down around 2.5 parts per million .

Cheers Les

[devocean]

Ill let you guys know heading to Faust as soon as the road clears of water

[nuggstar]

keen to find out what happens

[Mak579]

Hey Les,

Thanks for taking the time to reply and shed some light on what will happen over the next couple of months. It's going to be quite interesting to say the least with the majority of impoundments up here tripling in capacity!!

I guess keeping an eye on the sounder would be the best way to diagnose any de-stratification (if there is such a word) and the weed beds will well and truly be sunk by now. Might be time to tighten up the drag and hit the timber!

Hopefully I'll be heading down there early march to see what's happened.

If anyone else has any input feel free to post


Cheers
Matt C

[shayned]

Seven or eight years ago Nth Pine filled to spill over. The result was some great fishing from the bank. also some good fishing below the dam wall on escaped fish. A year or two later an explosion of redclaw, after presumably feeding on rotting vegetation.

[the_matrix]

G'Day Matt.
Although you directed your question to Fitzy, and Im sure he will answer in time, I thought I might add some food for thought.

When dams rise due to rainfall, the first thing that happens is a decrease in water temp. We know Barra are not fond of that. You will possibly see a brief flurry of activity, but then the weather will drive the next scenario.

After that, the dam mixes, which effectively spreads the fish population throughout the medium.
Once the dam de-stratisfies, the fish become "entrapped" in the oxygen rich water, effictively halving the fish holding area's. They will not be able to hold in low O2 area's, so will compress in the oxygen rich environment. Its possible to see a big oxygen dump with the influx as well, making the fish sluggish and very un-interested.

It does depend a lot on what the dam was doing prior to the increase in water level, but I'd expect a period of tough fishing until the weather comes good.
The weather may need to be at least a week or so of good, stable weather (depending on its makeup before it rose) before the fishing will see a marked improvement. This is purely in the hands of the wind and weather gods.

The dam will turn over quickly if you see a constant windstream, which we all know means tough fishing. The strength/length of the blow will dictate how quickly it turns over, and its during this period that we see very tough conditions for fisherman.
Oxygen levels will drop in turn, but nutrient rich water will lay below, awaiting its turn to become the target for smart anglers. And part of the impoundment cycle.
What I mean by this is, find an upwelling in a downwind scenario,(historically very close to a deep drop-off or sunken river bed, at least in my experience), and you will find what you are looking for, which is willing, feeding fish. They will be there because of the nutrient rich upwelling.
In this will be the remnants of the thermocline, a tonne of nutrients, blooming algae, bony bream, catfish..............and the mighty barramundi. All there for the same reasons.

You have to remember that this doesnt happen overnight, planktom blooms will take time to kick start, as will their discovery by apex preditors. But the cycle WILL kick in. Its incredibly important what weather patterns follow a dams increase, its the driving force.
Rotten vegetation etc plays a VERY small role in the scheme of things, there a more important factors at play than the weedbeds. As stated, the wind is the key. It may determine where Barra fisherman fish, but not where Barramundi are. They will have moved from the weedbeds because of unfavourable conditions.
The littoral zones within a dam are ever changing. Yes this is important, but further down the track of the cycle.

What we also have to understand is that impoundment Barra have a high fat content, and can ride out the tough times. They may not feed during this period, knowing full well that this cylcle will have its advantages.
Barra will expose this when the variables line up, but these important factors may not be glaringly evident to the impoundment angler.
Dont expect sounders to give you the info you require. It may also decieve you by saying you have a surface temp of 28 degree's, but in reality, its only the top foot or two that is that temp, under that...........cold, under that maybe warmer that the surface temp. This is where a Temp probe earns its keep.

You may have to use your nouse to identify these locations, although Awoonga usually has certain keys that tip off the zones I have mentioned. If you can distinguish, what is a Cattie, and what is a Barra, you will be half way there. I find Catties lead me to these sweet spots. (they will be there in bloody huge numbers!!!) The Barra will not be far away either.

The fishing may seem "as tough as it gets", but really, somewhere, some depth, the fish are actively feeding.
So, as you can see........the weather rules the impoundment Barra, and what happens to these man made lakes.

Hope this hasnt confused you, it really is impossible to predict where and when the fishing will become good again, just like it is to predict the weather.
But with some info and an open set of eyes, you will get on with your discovery.
Good luck with it.
Jas W

PS. Got your pics mate, great stuff. Keep 'em coming!

[lorby]

Lake Awoonga dam turned over a few months back, weed surfaced the lake for a few days which made it hard to lure, few campers packed up and left the same day. sure barra were caught around the same time or within a few days

Lorby

[Mak579]

Hey Jas,

Thanks for the info mate, not confusing at all, I'm actually looking forward to getting down there and seeing what the conditions are like. I crave information, the more info, ideas, theories the better!

I haven't really fished conditions to these extremes before, generally when there's a little rain I've found fish head up the rivers creeks etc but ..... dams tripling size in a week??? I'd imagine it's a whole new ball game - I'm looking forward to the challenge!

Great info, thanks again, I'll chat to you in the near future as I'm heading down that way soon.

Cheers
Matt C

[the_matrix]

Matt,
Another factor to ponder, particuarily at dams like Faust and Tinaroo, Barra may very well stack up in big numbers within close proximity of the dam wall after a big influx.
Even though dam barra evolve to impoundment conditions, they will still have an overwhelming desire to find the salt so as to reproduce.
I have seen this at Awoonga, during the build up to the wet. They know whats going on in my opinion.

I wouldnt mind betting there would be some big numbers of fish near the wall, and Faust, unlike many other dams, lets you get pretty close to it.
Worth checking out.
Cheers
Jas

[smee]

Jas does this mean that barra use the flow into the dam to know which way to the sea . what makes them school up if there has been no rain and no flow . I know certain animals assimilate direction as to the sun pigeons aprime example.
very interesting.

regards smee

[the_matrix]

Paul,
Yep, your on the right track.
With the build up to the wet, the most noticable change is water temp, so that would certainly be a trigger.
The physics of the moon would be another. Firstly, Barra can see the full moon, and secondly, the influence it has over water movement.
You may find it hard to believe but there would be SOME tidal influence in dams like Prossy and Awoonga. It may only be a few centimeters..........but its there.

September through to November would see the fish build up condition for the hard task ahead. (temp rise would trigger)
Then as the fish roe up, combining those other factors would lead fish to the dam wall.

In Prossys case at present, obviously the big influx would have them searching for the way out. The tidal influence would direct them.
Because there is so little data on impoundment Barra, I cant explain why the bigger fish dont all do it. Maybe they dont all roe up?
Maybe they have tried unsuccesffully too many times?
But, when a dam breach's, there is evidence supporting that big numbers of fish go over the wall. (Tinaroo is an example)

Going off the Fitzroy river tagging data, there may only be ONE singular flood event a year where the Barra can breach the causeway.
You probably guessed it, they dont miss out.
Even though they are saltwater fish, the same rules apply to an extent to hatchery fish. They are still Barra.

Also a particular waterway/causeway in Gladstone that has been stocked has proven (to me at least) the last two summers in a row that the Barra are right up against the wall waiting for their chance. Those fish are no different to Awoonga's.

Its what Barra do.................. inherant genetically.
Pretty amazing really, when you think about it.
Cheers
Jas

[Dicko]

Some good info in that lot, thanks boys.

Looking forward to heading down to Faust this year seeing the tide has come in a bit, hopefully it'll rekindle the fishing up in the timber 8-)

Just checked sunwater & it's at 34%, that 'd be about the highest it's been for the last 4 or 5 years I think.

[Stumpthumpa]

I agree, very interesting stuff, thank for all the information.

[the_matrix]

Just to add to the above string. talking to a couple of mates yesterday who fish Faust regularly, two locals fished Faust when the water was rising and in one big session landed 46 Barra, 16 over a metre!
I'll give you one guess where they were fishing.

Yep..........near the dam wall.
Jas

[Mak579]

Apologies to the regulars for bringing up an old post but heres what I experienced after visiting faust a couple or so weeks ago.

The first thing I noticed was the temperature, the water was quite cool, the fish were in the shallows. Secondly the water was dirty and I failed to find any dirty/clear interface.

Fishingwise, the fish were found around the dam wall, as well as up the creeks and tributries where water was still incoming.

The fish I found weren't overly aggresive, but fought quite hard once hooked and were very healthy.

The dam still appeared unsettled and I'm sure will continue to change until things normalise, can't wait to get back.

Once again, thanks to those who contributed, you guys were spot on.

Cheers
Matt C