The pond question I get asked most frequently is, "How do you build a waterfall?" And it is a hard question to answer. The easy answer is that I stack the rocks up until I like they way they look. Wouldn't it be nice if that is all there was to it?
Waterfalls are a mix of art and engineering, a strong back and willingness to get wet. You must be in the pond with the pump turned on to properly build a waterfall.
Building a waterfall is either simple or difficult, depending on the point of view of the builder. We want them to look natural, like they just started happening in the rocks of our gardens. Never mind that we had to buy the rocks because we live where no rock has ever been found. New Orleans, where I live, has never grown a rock in its existence, so we have to buy them and make them look as if they, indeed, did grow here and so did the waterfall.
Keep it in scale
Most people want a huge waterfall that is completely out of scale for their pond and would look better in front of a casino in Las Vegas. Others want a tiny waterfall that just trickles. My job is to know what they really want, build it and know ahead of time that they will love it.
Using a weir
The easiest way to build a waterfall is to use a weir. A pond weir is a plastic box. It collects water that the pump has pumped into it. One side of the box is lower than the rest and has a lip on it so water will go over it and back into the pond.
These can be effective when building a waterfall. Simply elevate them above your pond, usually positioning them level in the dirt you have dug out to make your pond. Put tubing from your pump into the weir. When the weir fills up, a sheet of water will fall over the weir and into your pond. You can hide the weir with rocks so no one can see the plastic box. Also, if you have a biofilter, you can put it in the weir. As an aside, if you do have a biofilter and use lava rocks in it, put them in several mesh bags, not just one. It takes several strong men to lift just one bag out, so use at least three. I usually float some hyacinths or other floating plants in the weir to further camouflage the plastic box.
Building a natural waterfall
My favorite way to build a waterfall is to start with a semi-level surface, slightly raised in the back, at the same level as your pond in front. From there, standing in the pond, build the waterfall using the same kind of rocks you used in your pond construction. Start with large, flat and thin rocks. You can't build a waterfall with either round rocks or little ones. Always put your rocks on top of your liner. After you put the first large rock down, run water from the pump over it to make sure the water flows into the pond. If it does not, shim up the rock in the back. If you don't start on a slight angle, water will fall off the back and drain your pond dry in a few hours. Next, stack two or three thick and chunky rocks on each end of the bottom rock. Those rocks can be as much as 5 or 6" thick. Make sure they are flat on two sides, because you are going to build the rest of your waterfall on top of them. If you have two large flat rocks on the ground level, you need more chunky rocks to rest the second level on.
Use two large, thin rocks side by side on the bottom to make a wider waterfall. Wide is better than high.
Next, place the second level of flat, thin and large rocks on the chunks. Run water over them again to make sure the flow is going in the pond and not over the edge. Continue making levels, shimming as needed, until you like your waterfall or you run out of rocks.
I have found that the easiest way for me to build the falls is for me to be in the water and have a couple of strong helpers placing rocks for me. I can then move them around until they are where I want them.
The engineering part of waterfall building
The back of the waterfall is equally important. Shimming must be done to keep the angle toward the pond, and proper placement of rocks is most important to ensure stability of the falls. You don't want the entire structure falling in the water during the first wind, nor on someone's foot when they walk close by.
The art part of waterfall building
To finish your waterfall, place your hose or hoses where you like them and put a rock on top to hold them in place. Now put a tiny rock in front of the hose to spread the water out. Put some plants in the back to hide your hoses and soften the rocks.
You will be amazed at your talent and so will your friends.
Jan Goldfield, the pondlady, owned the first pond design/build company in the Southern US. She has written extensively about ponds and water gardens for 20 years.
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