Whether placing rocks up a steep slope, building a sheer wall, or creating a man-made wall to pour water over, there are a number of factors to consider in the building of a waterfall face - safety, waterproofing, if the wall is also serving as a retaining wall, and even possible construction codes. Of course, the water needs to be aesthetically pleasing, as well. There are many fine water treatments available on the market today to help with water clarity.
Placing Rocks: Placing rocks in a stream bed on a skewed or slight slope, tends to be easier than on a waterfall face; as gravity is working on your behalf. You can easily move rocks around as the water is flowing to get different effects and keep adding, moving and rearranging until you are happy with the outcome. However, on slanted or steep stream and waterfall slopes, you need to start at the bottom. I would use some sort of rigid, angular rocks rather than round rocks. If you want a river rock, use them in front of the more stackable stones because piling round stones is a house of cards. Place large, sturdy rocks at the base of the falls so that you can stack above it. Turn on the water and see if it meets your expectations. You will likely have to get back – go to your viewing area to take in the overall picture rather than up close. While testing the rocks with water, stuff rags temporarily in the cracks to get an idea of the flow over the rocks (rather than behind). Rotate rocks often while placing not only to find a stable, interlocking position, but see how the water behaves. Refer to photos in nature often. Sometimes, pick up random rocks and place them in a chaotic position. You may be surprised at the happy accidents! Once satisfied with a layer of rocks, turn the water off, remove any rags and continue to the next row above. Rinse / repeat…now you can see why this is a slow and tedious process!
Climbing the Face: This is where you will appreciate the terraces you placed beneath the liner every 18” to 24” up the face. Wet rocks are slippery. As they are not yet secured, they are also unstable. You will want to be wearing good gloves, shoes or boots since rocks can fall and roll down and smash a foot or hand. Since we have a flat area every 2’ or so, the rocks you are stacking are only resting upon one or two rows of rocks underneath. The next rock’s weight is really resting on the next terrace. It also gives you a stable place to stand, stage the next rock, set tools, etc. You may also find that you have a good rock, but some protrusion is in your way. Do have a hammer or chisel handing. Don’t do this over the liner. Always do this away from the liner as shards of rock when broken can be sharp. Ensure to knock off sharp pieces and use a smoothing stone, files, or the like to knock off sharp edges. Once you are to the top, turn off the water and let dry for a day. You may have to use a leaf blower to dry out the spaces in between rocks and cracks.
Securing the Stones: I use insulation closed-cell foam from a can for this (like black Handi-Foam or Great Stuff). Use a 5x expanding foam in the large spaces behind and in between stones but only fill up to near the top of the gaps and cracks – not all the way. Next, use black pond foam for smaller cracks of the surface of larger gaps. If you rocks are a light color, press a similar colored sand into the foam as soon as you spray it. Don’t worry, water flowing over rocks on a steep grade tends to be “white-water” so it doesn’t have be “perfectly” matched. The darker foam will just look like cracks and gaps in the rocks for the most part. Inevitably, some foam will expand beyond the rocks. Cut these off with a serrated knife flush. Wait a day for the foam to fully cure then test the water again. Why? Now that ALL water is flowing over the rocks, you may see that the flow has changed and water may be overtopping here or there, or splashing out, or not flowing over as it did during testing. This is when you find tune it. Take a video or pictures and mark what you see and turn off the water once again and dry it out. Now you might have to adjust the liner edges, add small rocks to alter flow (secure with liner sealant). This too will take a number of tries to get the water flowing just like you want.
Man-made Faces: Perhaps you have water emerging not from a natural waterfall, but rather down a brick or tile face, a wooden wall, etc. I have seen concrete walls that had ridges that were up-lit and cups that the water would fall into and down to the next and so-on. The possibilities are endless. No matter the look you are going for, a waterproof seal behind the façade is essential so that any stray water still finds its way back into the pond. If you are constructing a wall, use cinder blocks or tile backer board as a base (nothing that would rot). Before applying the surface tile, stone or brick surface to the wall, use a waterproof membrane. Follow the same process used in shower construction behind the finished materials to keep water out. If you are making a wooden wall – perhaps a rustic look, use the liner behind (do not attach or nail anything through the liner of course). The wall can extend past the liner and be attached there.
Sheer Walls and Overhangs: If you are constructing a weir overhang where the water will fall free leaving a space behind, depending on how far the overhang extends, consider a liner or waterproof material behind whatever façade you construct behind the waterfall. Why? Even splashing is a source of water loss. If water is soaking into a concrete façade that you sculpted to look like rocks, that water is “out of the pond”. It will soak into the hill side (perhaps even destabilizing it and the water is lost and will have to be replaced. Instead, place a liner that extends behind the falls down to the pond’s edge. If building a sheer wall, follow all proper structural codes especially anything over 3’ height.
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