Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
You are thinking about what would be called a "Vanishing edge" in swimming pool terminology.
The main pond might be say... 2' above the patio, and 3/4 or more of the rim is indeed at 24" above the patio. 1/4 of the rim (maybe 3-4' long) (the part nearest the house) is at 23" high. Just that 1" of difference.
Here is why:
If you turn off the pump, the water in the pond that is 24" high will continue to drain over the vanishing edge until all the water in the pond is at 23". That 1" of water draining down must fit into the catch basin nearest the house, so make sure it is large enough.
Example: if the whole pond is 120 square feet, then 1" deep is 10 cubic feet, so the catch basin must hold at least 10 cubic feet more than when it is running. Maybe 20 cubic feet.
For a pond that is more than a couple of hundred gallons I would go with a remote pump and filter system if that is at all possible. The intake would be in the overflow part nearest the house.
Size your pump by measuring the length of the waterfall (the vanishing edge). To make a nice looking waterfall you want 1000 gallons per hour for every foot of length. So, if your vanishing edge is 4' long, the pump ought to be at least 4000 gph. I say at least, because there is also flow loss from the size and length of the pipe, and the filter.
Return to the pond via a wide waterfall that pours over boulders above the pond. Not high, but wide. This area will be built with pond liner under it, and expanding foam between the boulders to force the water over to make it look like a rippling stream. Yes, the higher you go the more like white water rapids it will get, but the higher you go the more of a view you are blocking off. If the maximum height you are looking for is 4', and the main pond is at 2', then this rippling stream effect would be 2' above the pond. If you can stretch it out (probably back into the garden) it is more stream-like. If it is closer to the pond then it is more like a 2' drop, a waterfall with just a few boulders.
Look into gravity block wall material.
Versa-Lok, Keystone, Allen Block and others.
These are concrete blocks, but they are...
a) Intended to be installed without adding concrete fill.
b) Nicer looking on the outside, available in several colors that look more natural than CMU blocks.
c) Movable (in case you are renting and may need to take it down and not leave a mess)
d) Make better curves and irregular outlines
e) Are available in 'pocket' designs so you can plant the outside of the wall
f) Can be stacked up at different levels so you can build a higher area at the back, mid-height areas around most of the pond, and lowered area near the vanishing edge. You can build a wall 3' high without engineering using most of these products. (Read the literature from each manufacturer, they do vary)
g) Incredibly easy to install. No rebar, no concrete, no custom tools.
I do landscape design for a living, and I know materials pretty well. These blocks are about twice or more times the cost of CMU blocks, but all the advantages make them very much worth looking into.