by Harriet Bond
(San Francisco, CA, USA)
You do not need heavy earth-moving machinery to dig a stream bed, but do allow plenty of time for the job, for the more carefully you shape the stream bed the better the stream will function and the greater will be your rewards.
The Gradient: In most gardens it will be necessary to provide the gradient by artificial means. However, no dramatic difference in elevation is required between the source and the end of the stream since you are building a stream, not a waterfall.
The numbers that follow can serve as a basic guideline: A gradient of 1 to 2 percent is sufficient; in other words, a difference in height of about a foot and a half (50 cm) between the top and the bottom of a stream about 20 feet (6 m) long is sufficient.
Supplying the Gradient: Simply piling up earth will not result in a solid base for a stream bed. Instead, the gradient should be supplied by building terrace-like steps into the stream bed. These steps, which may be quite wide and of different height have to be supported with laths, round or square logs, or rocks.
The gradient should not be the same throughout the stream’s course. A good pattern to follow is to have several drops at the beginning (a waterfall, an overflowing basin, a succession of small dams) and then to let the stream meander lazily along a shallow course as it approaches the inlet to the pool.
Materials to Hold the Water: Flexible pool liner, preformed shells, and so-called stream basins made either of fiberglass or of natural rock are used. You can also combine basins and pool liner.
If you have to glue several lengths of liner together, be sure to observe the directions that come with the adhesive (adhesive mate¬rials are available at aquarium supply stores and garden centers).
Fill: A stream bed with a liner should always be filled with gravel and larger stones, and some stones should also be added to the stream basins. You can use the various kinds of fill including fine gravel and quartz gravel (available at aquarium stores and building supply or garden centers). Do not use any limestone gravel because it may make the water too alkaline. You need about 50 pounds (25 kg) of fill per yard of stream bed.
Reinforcing the Banks: It is especially important to reinforce the places that are built up to provide gradient and the banks along bends because the current tends to wash away the soil there. Rocks, coarse river gravel, and round logs work well.
A Water Pump: Pumps with a capacity of 100 gallons (6 watt) to 500 gallons (19 watt) (250 and 1,000 L, respectively) are quite sufficient. Low-voltage pumps can also be used for propelling the water.
Pumps with a higher capacity (such as the ones used to run big water fountains) should not be used. They make the stream run too fast, since the speed of flow is determined not only by the gradient and shape of the stream bed but also by the volume of water.
A garden stream should flow slowly because a fast-flowing stream cannot develop the filtering action that is so beneficial for a garden pool. A fast-flowing stream is not desirable even if you have no pool, for most plants and animals do not like fast-moving water. A stream traversing a rock garden represents a special case; here more powerful pumps are needed.
The Source: The water for the stream comes either from the garden pool, or, if there is no pool, it can emerge from a bubbler stone or a water spout that is connected to the pump by a garden hose.
The End of the Stream: The stream can terminate by flowing into the garden pool, preferably by way of a small waterfall, which will supply an extra dose of oxygen for the pool. If there is no pool, the water can flow into a catch basin with a pump that will move the water back up to the source by way of an attached garden hose.
Instead of a simple water pump you may use a pool biofilter with a built-in pump (for pump capacity, see above). The fact is that because of the constant motion of the water, dust particles keep being carried along. Plain water pumps are equipped with a filter, but they tend to clog up quickly, and then the gallon capacity drops rapidly.
The result is that less and less water flows down the stream bed. That is why I recommend the use of a pool biofilter, which largely prevents buildup. A good filler material for such a filter is tiny ceramic tubes (available at aquarium stores).
Upkeep: During the summer, the stream should run continually day and night. No special maintenance is needed during that time. In the fall the stream is turned off, the pump taken out of the pool or the catch basin, the plants cut back or thinned, and the fish moved to an aquarium or pool where they are safe for the winter.
In the spring the fill has to be rinsed with a sharp spray of water. Then, when the pump is turned on again, the stream will resume its cheerful burbling for many months. If the stream is connected to a pool, a third of the pool water should be changed after spring cleaning to get rid of the dirty stream water.