Actually, Loki, I feel your design still has a very good use in the Barge Farms.

Above, I talked about using the inflatable pools as a main water reservoir/pond. However, it wouldn't make much sense at all to simple leave them open and do nothing with the space. That's where your design comes in.

Basically, you would have the reservoir stocked with a few thousand fish. The pumps run up to a gutter system, which runs in whichever way uses space most efficiently. I would use a system that goes from above the pool out, and then back, 180 degrees, to the pool.

On the surface of the pool, you have several of these River Gardens, but each has no medium in it. The wire at the bottom keeps the fish from eating the duckweed you have growing there. The fish will still feed the duckweed, though. Whenever it's feeding time, just scoop from the Garden to the reservoir. Easy.

In addition, with the appropriate designs, you should be able to change back and forth, easily, between using each individual Garden for duckweed or for crops.

Only thing, though, is that in this situation, you would not be able to use the 55 Gallon HDPE barrels for each Garden's flotation. The barrels would take up too much space in the float area, as well as the fact they'd be better off used elsewhere. As such... I don't know as of yet.

Maby it would be best to use a PVC pipe frame? Or what? And stretch some fabric across? I would use, perhaps, something like the fabric that is laid down beneath home gardens, the stuff that is supposed to keep weeds from coming up. Then simply lay a few mid-sized rocks in the center to keep it down. The water should be able to flow through, the rocks will keep the fabric from floating and drying out the Duckweed, and the frame should be buoyant enough to float it all.
OH! I wonder if you could find a way to use old Pool Noodles as your flotation.... :)

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