Backyard Aquaponics
A place to discuss aquaponics

Greatly appreciated Janet (and Les for the idea). My gates will be (slightly) bigger ie. 4.5M !! but anyway, what a great idea. My central pivot is square
I may have to design some round rings (maybe PVC) to attach the gates onto. Now I have to get into the dam and remove tons of mud. I'll be sure to post pics. I wonder if the mud will be good for my skin? Like mud from the dead sea. mmm, hopefully there's nothing dead down there !!

Ahhh
[font=Andalus]the Gates of Ell[/font]

that would be the way to go S'man, might look at utilising 100mm pvc to make rings/hinges to fit over my central post too

Might want to arrange to have the archaeologists there when you start digging.

I'm envisioning either a little round track around the square post so the gates could roll around the post -OR- hinges mounted on all 4 sides of the post with 4 gates. The only problem with hinges is that you wouldn't get a snug fit against the outer wall of the tank. Go with circular tracks.

How big is the column? and is it 4.5 meters from the center to the outside edge? At that kind of distance it may be better to use welded metal or to fill the pvc with expandable foam.

I would think placing some type of netting on the bottom of the pond before introducing the fry into it would work also. Just raise the netting when you need to harvest, eliminating most of the water column and making it easier to scoop fry.

Robert

I looked at the fish gates shown in the other post more closely. If you can find large pvc that will fit over the rectangular column it would just be a matter of finding t-fittings and sections of pipe to make it rotate properly. How many fittings you would use would depend on how many gates you needed. 4 t fittings for two gates, 6 for three etc.

Example: You need two gates 2.25 meters long to reach the outside wall. If the center post will accomodate a 100mm pvc pipe you would need 4 t fittings 100mm X 25mm or similar two would be used for each gate as a hinge, 25mm pipe would be used for the actual trapment gate and additional 25mmX25mm tees, ells and pipe would be used to make the gate structure.
Drop a short piece of 100mm pipe on the bottom, add 2-tees then another section of 100mm pipe, 2 more tees additional pipe and a cap could be placed on top(place a couple of set screws in it to keep it from riding up)
Attach gate 1 to the bottom tee and the third tee, attach gate 2 to the second tee and the top tee.
No gluing of the fittings on the central post would be needed, but the gate sections could be glued.

Hope this makes sense if not let me know and I will draw something up.
Robert

Robert, thanks for your help. I'll measure the column tomorrow, but I think it is WAY over 100mm. I'd say it's at least 500mm square. I could always just demolish the centre post if it really won't work and bolt a nice round (say 80mm) centre post and work from there. The net idea is a good one but I'd be capturing all of my brood fish up at the same time. Please keep the ideas coming. The placement of the two sets of grow beds and/or grow beds over the dam needs some thought.

We started the AP system on the farm today for my "landlord". Here is an image of the placement of the sump (in the centre) and the 4 x 3m diameter fish ponds. We are building a 9m x 9m concrete slab with all of the plumbing, drains and electric cabling cast in. We are then going to pop a 30m x 10m greenhouse over the top. The slab will be in the center with long 500mm wide grow beds 10m on either side. All in all about 100m of 500mm wide (250mm deep) grow beds with pathways in between.

Joel, got my CD, DVD, manual pack today. Now I'm REALLY fired up.

umm, what about putting 4 gates in the tank from the corners of the pillar, left semi-permanently in place and have four "tank" areas?

Jaymie, this is something I looked at yesterday, and it makes a lot of sense. When you close two of them you are left with an area 500mm x 4.5m (say 1.2m deep) Much easier to catch fish in this smaller area. The problem I think would be against the outside wall. Because with one end bolted to a square and the other to a round shape it would seal up to the perpendicular and then would gape. While it moves in the arc though it should seal against the wall pretty well. Of course the other problem is that this dam was built about 50 years ago by hand and is probably not perfectly round anyway. I think the "hinges" would be bolted on permanently and then I would just slip the gates over as I needed them. Also for them to be really effective I would definitely have to get all the mud off of the bottom.

What about very low-tech...
just a fish net that you can slide onto a fitting on the centre post, with the other end free. make the net long enough so that it has some slack when reached to the outer edge. Weight the bottom of the net so it drags along the ground, and put floats along the top.
You'll need at least one fixed Gate of Ell. The free net can be dragged around the perimeter. No fish will try to slip past you while you're holding the end of the net, and by the time you get back around to where you started, you'll have a nice loopy bit of net holding a squillion little fishies up against the gate of ell.

If you used nets with varying sizes of mesh you could remove different sizes of fry at different times also.

I have also seen where a hatchery near me uses fish traps with small mesh to collect fry out of the breeding area. They look like large minnow traps with a mesh cone on either end pointed inwards inside a larger mesh barrel type structure.

Robert

I can vouch for the fact that tilapia fingerlings are hard to catch with a hand net. Mine are hard to catch in a 20gal aquarium.

A couple of ideas for your consideration:
Solar might be good if you get good exposure to the sun. Would Baboons mess with your solar panels? Can they climb? (sorry about my ignorance -- my main threat to my plants are moose, black bears, wind, and cold weather) The advantage to solar panels is that they produce the most power when the heat is the most intense (and the plants are most likely to be transpiring -- and therefore at most risk of wilting.) the disadvantage is that they will not produce any power in the dark so you'd need some sort of battery bank.

Since you are on a hill, wind might be just the ticket. A while ago, there was an interesting discussion on barrelponics with a fellow named Paul who makes his own wind-powered water pumps. He uses low-tech sailwings for his windmill -- they have the advantage that they turn well in low wind tend to be somewhat self-regulating in a stiff breeze. If a gale comes up, the sails will (hopefully) be torn from the windmill before more damage is done.

If I remember correctly, he simply put a crank on the shaft of the windmill, and connected a drilled pipe to that crank. Then an assortment of marbles, washers, and other pipes made up the rest of the pump. Each revolution of the windmill makes the "sucker rod" move up and down -- causing water to rise in it. Once the water level reaches the top, it runs out of an opening in the "sucker rod" You can probably google the idea and get more info than I have. PM me if you want me to dig up the pictures I have on my home computer.

They wouldn't bother the solar panels. They're only really interested in edible things. And yes, they climb very well. They appear to have tried to get into the dam yesterday (probably attracted to the fish) and I found some branches broken in a tree that hangs over the water. Quite possibly he fell in and then climbed out using the branch. Also lots of baboon poop around. Also had a close encounter with a big snake today (about 90cm long, thick as mans arm), a Puffadder, deadly poisonous but pretty slow. I'll look up the windmill plan. I have been toying with a combination of solar and wind which should always give me some power. The secret is going to be low power pumps and making the most of gravity.

...wow and to think I get angry when rabbits/squirrels/deer screw around with my garden. I couldn't even imagine what you've got there syn.

We cleared some more bush yesterday on the two lower levels of the hatchery site. The big dam will overflow to a lower terrace of growbeds and then to a sump at the lowest part. The total head from bottom of sump to top of the four small tanks is about 4 meters. With the clearing, I now have a beautiful view of the valley below and a pine plantation in the distance. I'm sure the Tilapia will appreciate my efforts. No baboons today but I could hear a big troop barking from the other side of the valley. No snakes, but we were bothered by bees the whole day.