Building Waterfalls and Streams and Header Ponds
Question: I want to build a stream that is 5metres long ending in a waterfall into a water garden I have planned, but looking at what a friend of mine has built, the pool at the bottom loses about 15cm of water before the water starts coming in over the waterfall. Is the any way of avoiding this?
Answer: In order to limit the demand for water from the final pool, design any waterways, streams or waterfalls so that they are effectively a series of pools running from one into another. The most important is the pool immediately after the outlet from the pump at the top of the stream. This is the header pool and forms a reservoir for the rest of the water feature and evens out the forceful spray of the outlet from the pump in the bottom pool.
Having water retained in the waterfall feature means that any fresh water pumped into the waterfall does not immediately flow out into the next section or back into the pool thus minimising the draining of the bottom pool. Despite this though, the waterfall and a stream will take a certain volume of input for it to begin flowing throughout. This could mean the addition of 10 to 15mm over the surface of the stream and pools and much more than this if a powerful pump is delivering large quantities of water to a series of waterfall header pools with narrow outlets. Add on all the water moving within the pipe work and the hidden nooks and crannies the water finds as it rises, you find a considerable gallonage is taken from the surface of the bottom pond before you get back water into it from down the stream. A large series of waterfalls or a long stream can suck a small pool dry, and many water plants are particularly sensitive to radical water level changes that intermittent running would cause.
To minimise the effect of borrowed water by a stream, the idea of retaining static water is even more important than in water falls.
So in construction, as the ground rises in your excavation for the stream, lay a fillet of concrete or row of bricks that will be under the liner, at regular intervals. These intervals are governed by the fall of the ground, which should have an absolute minimum fall of 1 in 80. If the fall was 1 inch in 80 inches and we were using 4inch(10cm) bricks to create our humps, then we would need a hump within every 320ins(4 x 80ins) or 8mtres (10 x 80cm). The idea is to create a shallow pool that runs from the top of the obstacle back to the base of the next obstacle upstream. The stone, gravel and even a clay base can sit in this static water as visible surface water flows over it. Working up from the bottom, take a level from the top surface of the lower hump to the point that it is level with it up stream. The next hump must be laid before this point, but not too much before. In this way you are making static pools of water over which a visible moving sheet of water flows.
Construction details can be seen in my book The Perfect Pond Recipe Book