Surveying: As discussed in earlier articles, you need to keep in mind all of the tools and safety measures for excavating trenches, troughs or pools. Fountain, spitter or bypass returns are basically plumbing (also discussed in length, this section will concentrate specifically on streambeds and waterfall beds. Just like pools, you are manually digging a trough (but of course shallower and typically longer). The important part of this is the slope. Starting at the end of the return where the water meets a pond, cistern, skimmer intake, etc., mark the level of the predicted surface. Now measure the stream trough back in feet from this point. The slope MUST be at a minimum ¼” per foot rise. Using a 4’ level with the far end touching the stream bed, holding the level flat, the near end should be at least 1” above the surface at the mouth. If you are making it steeper, then you have no issues (using a 2’ level, the other end should be ½” above the mouth). Next, the width is very important as the wider you make it, the more the water will spread out. Keep this in mind on what you are trying to achieve. You can vary the width, slope and depth throughout the bed or falls. Just be conscience that you don’t create choke points that will cause water to flow out of the bed area.
Bed Foundation: Just like ponds, you want to use an underlayment – especially if the ground has lots of rocks. I always pull out rocks and sift the dirt back in so that I am starting with a good surface. Tamp if necessary. Remember, streambeds will draw dogs, children or wildlife that may run through your stream. You want to ensure that the foundation is solid and the underlayment and liner are against this with no gaps or spaces. This does not mean you can’t have bumps and rises in the bottom of the bed (which will cause riffles in the water!). If you are on a rather steep slope and you will be supporting heavy rocks or small boulders, use flagstones, pavers or the like in a terraced step fashion every 18” to 24” beneath your underlayment to give your rocks a good foundation to rest upon (each terrace supporting 2-3 stacks of rocks before the next terrace). That way, there is weight relief at these points rather than everything resting on the bottom. If you plan to have crossings, be it stepping stones, a bridge or such, get the foundations on either side set as you build the stream (do not wait until afterwards as the weight of the water may deform the bank if you are digging down). Stepping stones should have a solid base. Stack 1’x1’ pavers then a cap stone above if it is deep using construction adhesive made for wet or submerged locations. Pay attention to the banks. The liner will go up and over about a foot to 18” beyond the stream. Hump the bank a bit and slope down so that the liner can go up and over and down. This will later get filled up to grade so that the liner is secured. If you have movement, extend the liner 2’ beyond the bank, dig a bit deeper trench and use bricks or pavers to weigh the liner down; then bury to grade.
Placing the Liner: Also discussed earlier in previous articles are the use and types of liners. For this discussion, I am assuming EDPM liner material. This comes in black, gray and sometimes brown. If making a seam, overlap in the downstream direction (like roofing). This will be extras insurance that water will break through a seam over time. The first step will be to seam the liner and get it securely placed, and then run water through it to ensure everything is waterproof. It is at this point you may want to put a hump, divot, narrow or widen the channel or change the slope here and there. Carefully raise or move the liner and/or underlayment out of the way to make the adjustments. Carefully place it back and turn on the water again. If you have a splitting of pathways, be careful to seam the openings and pay attention to how much flow you want diverted to each and if the flows are sufficient for you needs. If you plan to have a waterfall or stream falling down a slanted or steep slope (not falling free) and there will be considerable splashing, seam on a triangular apron so the water still reaches the pond rather than soak into the surrounding banks.
Camouflage: Many streams are wide and shallow and the water is not always “white water” meaning you can see through. In this case, you have a number of options. You can buy PVC liners that come in myriad of natural colors, and a few even are printed with a multicolored pebbled surface. For a contemporary or modern look, they have mosaic tile patterns as well. However, I would not use PVC as your primary liner, but rather as camouflage over the plumbing line if you want some sort of streambed-look. You can always make a realistic stream bed using gravel and small rocks (but not sand or dirt). Ensure the rocks are big enough so that the water cannot move them. Just like gravel filters, this is harder to clean, but gives more surface area for bacteria and algae. Banks can be lined with larger rocks that blend into the grade beyond, pavers or something decorative like lashed bamboo canes (however, these will rot in time). Remember though, the liner is behind these sides. And of course, you can have large rocks placed in the bed for water to flow over and around, through and such.
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