Building a Stream with a Spillway
Keep this in mind when creating a spillway: keep it in scale with the pond into which it empties. A small trickle will be lost emptying into a large pond and will contribute little in the way of oxygen and negative ionization. On the other hand, a torrent of water will produce a dynamic effect and a ton of oxygen.
Planning a Header Pool
A header pool is a 10-inch or deeper pool at the top of a spillway that creates a more natural look than water simply spilling out of an outlet pipe. Header pools emulate nature. One header pool, or catch basin, drops water over a spillway into the stream, which deposits the water into the next header pool, and so forth.
While you're still in the planning stage, think about what type of spillway you want to create: a smooth, broad, unbroken curtain of water that plummets into a header pool or a narrow, frothy cascade? The surface of the spill stone (the stone that forms the lip of the fall) determines the way the water will fall. For a curtain of water, use a smooth, flat stone. For a frothy cascade, find a spill stone with ridges and bumps, one that funnels water somewhat toward its center. For a trickling effect, use a series of rocks stacked up vertically that spread out gradually toward the stream below.
To mimic nature, make your stream bed meander lazily throughout your landscape while incorporating a variety of stones and plants scattered around in a seemingly random pattern. Remember: “random” means natural. Nothing in nature is ordered.
Excavating Your Stream Bed
Once you have a general idea of how you want your water feature to look, it’s time to start moving some dirt. If you’re fortunate enough to have an existing slope or hill, its fall line will largely determine the pitch of your stream. But if you're creating a watercourse on relatively flat land or if you want a greater pitch to your feature than naturally exists, you’ll need to build a berm, or high spot.
On either a natural incline or a constructed berm, start by defining the layout of the stream or waterfall on the ground. Use stakes and twine along the sides of the streambed as you define exactly where your stream will twist and turn.
Once you've finalized the course (or, at least, once you think you’ve finalized the course), use more stakes and twine to indicate the height of your finished project. In that way, you’ll know at a glance where you have to remove dirt and where you have to build up a berm. Use a level, if necessary, to make sure that both sides of the layout are at about the same elevation and that the stream bed moves steadily downhill. Otherwise, the water will want to spill over the sides of the stream.
Also, remember that water tends to travel in a straight line. If your stream bed features a sharp turn, make the outside bank at that point higher than the opposite bank. When the water hits that spot, it will tend to climb a little higher on the wall before bending around to follow the stream downhill. You don’t want to lose any water along the way. This is supposed to be a closed loop, after all.
While some people like to build a channel beneath their streams in order to run electrical conduit or water pipe from the pond to the stream head, I strongly advise against it. If anything ever goes wrong with your water-delivery system, you don’t want to have to tear out the entire stream to fix or replace it.
Instead, make provisions to run the pipe or hose alongside one bank of the stream or the other. You can disguise it with soil, rocks, and plants. In that way, if you need to get at it for any reason at all, it will be much simpler and less costly to do so.
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