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You would like to build something that looks like a natural waterfall, for which you would need natural rocks. They are not only heavy, but hard to handle as well. On top of this it’s really rather hard to get the water cascading from such a structure without water spilling somewhere.
You can go to How to build a complex water feature to see how I did that.
For the project under discussion I have used natural slate, which makes building the waterfall very easy.
The waterfall consists of 3 spillways (layers of slate). Every spillway is separated from the next one by means of 5.5 cm wide strips of slate (2 layers, 7 cm thick), as can clearly be seen in the picture.
These strips have been placed at the edges of each layer (except at the front where the water will be cascading to the next level) and fixed with cement used for tiling. The main reason for this is to make absolutely sure that not a drop of water can find its way over the edges and out of the pond. So, even if the water does gather on one of the layers while the water is cascading down, there will be no spilling. (In How to build a simple water feature I solved the problem in another way.)
Step 1: The bottom spillway of the waterfall
The bottom layer of the waterfall is the most important one. You have to get it right if you don’t want the rest to be a struggle. The first challenge is to have the bottom layer as far as possible protruding/hanging over the pond. You have to do this to prevent water from spilling. Water has a funny way of clinging to the bottom of a rock and finding a way over the side of the pond!
Slate is excellent for this, since they are all flat and you get real big ones. You get a big one and place it on the one corner as far as possible over the pond.
Remember that the water will cascade from the top layers onto this one from which it will fall into the pond. Using a level make sure that this piece of slate slants slightly towards the water.
Step 2: The second spillway
The second layer is slightly smaller than the bottom one, to ensure that the water cascades from this one onto the bottom one (and from there into the pond). If the level of the bottom layer is slightly slanting towards the pond, this one should do that as well (automatically), but just make sure that is indeed the case.
Step 3: The top spillway
For the top layer I had something special in mind. I wanted this layer to be a space for the birds to bathe, which means I had to make a weir, causing the water to “dam up” before spilling over and cascading down to the next level. I used the three layers of slate strips all around the edges of the top layer (10 cm thick in total), but only 1 layer at the front (3 cm thick) to create a weir where the water overflowed and cascaded down.
At first the birds bathed only after I switched off the pump (late afternoon) or early in the morning before I switched on the pump. I suppose the turbulence caused by the water being pumped into the top layer spooked them. Eventually they grew accustomed to that and now they’re taking baths throughout the day. Sometimes it gets quite crowded in there! What a sight to see!