Backyard Aquaponics
A place to discuss aquaponics

Did a search and didn't get anywhere. Been thinking (yes my brain hurts!) but is anyone using a large body of water like a dam for a recirculating AP system? Can't see any reason it wouldn't work but I don't want to reinvent the wheel.

The dam nearest the house is biggish at approx. 13 mega litres (+/-5 olympic pools) and there is no way I could cycle all that water through grow beds once an hour!! But the nutrients are already there (via silvers, ducks, yabbies, turtles, children, etcetra) and the water level is reasonably constant due to being spring fed (varies approx. .5metre in level over the seasons). Power is at the dam wall, so pumping to grow beds that then drain back into the dam is simple. Any aeration and filtering of the dam water can only help the fish.

Problems?
Surface water temps are max 30C in summer and min 5C in winter, a thermocline at approx .7m down where the water feels like ice but should be approx 16C but will measure it (the year round earth temps are 16C 1m below the surface in this neck of the woods).
No idea of the pH, ammonia, nitrate/nitrite levels etcetera, but will measure. Obviously OK for Silver Perch, they went in as fingerlings 18 months ago and are now 300mm, so can't be too bad? Don't fancy trying to pH buffer 6 meg of water when the our soils are predominantly acidic (around 6.2).
Occassional flushing of system when it rains hard for more than a few hours - used to happen 6 times a year but the drought/climate change now means it happens once or twice a year. The spillway does not release fish as it has a baffle, but animal manures get washed in during heavy rains and would cause a nutrient spike. Fish have survived so far and the plants should like it?
The dam was origibnally very silty due to the yabbies (zero vis), but I suspect the Silvers have culled a lot of them as the vis/clarity has improved to approx 1.5m (got rid of the aquatic leeches too ). Silt could clog up the grow beds quickly?

Anyway all thoughts appreciated, or pointing me to a thread that discusses same.
Cheers, MC

Bit of a hard call McFarm...

Traditional purpose built aquaculture ponds usually go to great lengths to filter their source water to screen out competing aquatic organisms....

Partly so as to allow good natural feed for the fish... and partly to screen for contaminants and disease carrying organisms..

Dams on the other hand are usually just low intensity, natural feed water bodies... stocked lightly and left to their own devices...

Water from either is often drained to settling ponds... particularly after a drain harvest.... or pumped to field crops... or wetlands/reed beds....

As you say... setting up a growbed style aquaponics operation would be both costly, time consuming and probably IMO ineffective....

Ammonia levels in a dam situation... with low stocking rates are likely to be low... and dealt with by natural algael bloom processes....

RAS operations generally... (other than deliberate green water culture)... avoid bloom creation and management... go to great lengths to remove solids and fine dissolved solids and particulate matter...

Both for stocking density reasons, feed management and fish health....

You could try running an NFT style operation where you pump some water to a holding tank...filter the water and either use it straight in the NFT... or as a base for hydro nutrients

IMO... the dam would be stocked so lightly, that nutrient levels wouldn't be sufficient to promote viable, sustained growth....

And as the water is constantly refreshed by the "spring" and other periodic inflows... trying to maintain a nutrient level... without generating an algael bloom and managing it...

Would IMO just not make it worth while... other than as a field crop irrigation...

Pond/dam based aquaculture.... RAS... and AP all have required differences in managment of feed and water quality...

And you need to decide where you focus lies IMO... and manage accordingly...

Using the water from the dam as a source for a RAS tank... carries with it the need to extensively filter it, possible and difficult to manage contaminant issues... both water and airbourne.... and disease issues...

And nutrient enrichment/ algael control and DO management issues

Particularly if you were attempting to recirculate back through the dam...

Used as a source water, appropriately filtered.. for a seperate RAS or AP system... very possible...

If used in a RAS system... then ultimately you'll need to deal with solids filtering management... and nutrient water disposal...

The examples of Barramundi Blue and Taylor Made shows how these issues can be effectively addressed...

And you could always setup a UVI style floating raft system using the source water....

Thanks Rupert, was only thinking of growing some vegies and it hadn't occurred to me that there may not be enough nutrients in the system. There are only a couple of hundred silvers in the dam, plus the other biota, so not a lot of excess nutrients based on the volume of water. In fact the existing dam system is probably in balance as you say.

Hadn't thought about uvi style rafts, but a continuous flow system with some sort of aeration at the inlet might work for the less nutrient demanding leafy greens. There are all sorts of aquatic insects in the dam, they would end up in the uvi raft channels too - probably not a problem and solvable if it is. I could use a header tank to filter and aerate the dam water before it went to the channels. Could be as simple as a largish trickle filter.

Yep, think I'll play with the UVI system fed from the dam, cause it'll be cheap/easy to set up. One sump pump in dam feeding an IBC media based trickle filter, which gravity feeds to some raft channels, which drain back to the dam - I guestimate total cost <$500 for 26m2 of raft system (plus running costs). I'll allow space for a fish tank and fish if there isn't enough nutrient to drive plant growth, then I'll cut the dam from the loop. Worst case I'll end up with more fish But the thinking is that by oxygenating the dam water a little by the return splashing, and some mixing of the otherwise still water, it should stir the system up a little anyway and the addition plants will become part of the additional activity.

If it works, I should be able to house the lot in a polytunnel. A polytunnel housing the bio/trickle filter and rafts should give reasonable growth year round if I draw from below the thermocline which should be at 16 degrees C - might be onto something here?? If the water in the system is somewhat stable at 16 degrees C it might be good for plant growth year round - day length and light not being limited.

End of thoughts for the time being - off to measure the area, levels and so on.

Cheers, MC

Mcfarm,
I know its not AP but have you thought of building a hot house up hill of the dam. By having the HH you could be recycling the water that comes out of the dam and over time that water will go back to the dam with its natural flow under the earth.
It's just a thought, considering you have your fish and would like to grow vegies.

The UVI model is basically an intensive RAS aquaculture system that generates the required nutrients McFarm...

The dam probably wont supply enough nutrients on its own to support much vegetable growth...

But could be of benefit in a hothouse/polytunnel feeding plants grown in raceways filled with media.... and being drained back to the dam...

Maybe like the original "bengal" hydro systems.... It's all there anyway... may as well experiment...

Maybe you'd want the muck at the bottom of the pond rather than just the water? Maybe stir it up (with a jet of water) and pump it on top of some gravel, analogous to digging the bottom mud out and putting it on top of a dirt garden?

At any rate the dam water should be a good source to get your system going quicker should you choose to have it separate.