| | Re: Brainstorming a multiple barrel patio "pond"
You can practice with just about any sort of container, no need to make the commitment to buy the special containers until you know you have the bugs worked out.
Simply stacking them is not enough. The water will sheet down the side and go wherever it wants. You need enough of a lip to direct it where you want. You can prove this to yourself in the kitchen. Try to pour water out of a coffee cup without it clinging to the side of the cup! Now try a measuring cup with a pinched area that directs the water, or a pitcher with a special lip. See how much easier it is to keep the water from seeping along the sides? When you pour too slow, however, even the containers that are designed to make pouring easier can allow water to seep along the side.
Now to design something like that for your stacked barrels that will work even if the water flow is slower than you thought. The ideas above, some sort of tubing that is large enough to carry some serious flow and aimed right so the water cannot flow anywhere else is the right idea.
Simpler, of course is the smaller container inside the larger. Like most tiered fountains it will work at any gallons per hour.
Optimum gph: If you were making a waterfall over the edge of a flat rock, then I would say a minimum of 1000 gph per foot width of the rock. That is, a waterfall a foot wide requires a minimum of 1000 gallons per hour to look and sound right. So, if you stack a small container, say 1' diameter above a larger, and you trim the rim of the upper container so all the water would flow out over about 1/3 of the circumference, so 1000 gph minimum. I am not sure how many gph you need when you are shooting it out through a pipe.
If you have several pumps, power heads or filters you can test the idea.
To find out how many gph you are really getting from any of these devices you can get a rough idea by setting them up to either empty or fill a 5 gallon bucket, and time it.
Then see it a certain design will work for you.