Using Flexible Liners to Create a Stream
Flexible liners cans be used to produce a naturalistic looking stream or watercourse, either to run gently over a shallow gradient or to cascade dramatically over several levels and falls.
In most cases, you will need to provide the feature with a header pool, large enough not to show any variation in water level when the pump is switched on or off. A hidden header pool may be created by lining a hole with a flexible liner and then covering it with a sturdy mesh. This may then be hidden by a layer of cobbles or other rocks and the water allowed to flow out between the stones and down the stream.
Measuring the Lining
Before starting work on this project, you will need to calculate the amount of liner needed to cover the length of the route. If the stream is fairly straight, you may be able to use one piece of liner. Use the calculation:
Liner width = Max width of stream + (2 x depth) + 60 cm (24 in)
Liner length = Max length + difference in height from the top of the stream to the bottom + 30 cm (12 in)
The additional 30-60 cm (12-24 in) of liner is to allow for an overlap at the sides and into the header and base pools.
If you are building a meandering stream, you may need to join a number of pieces of liner together. These should overlap by at least 15 cm (6 in). When joining two pieces of liner together, make sure that you arrange the overlap so that water flows away from the join, not into it.
Read on for more information on flexible liners ...
Forming the Stream
Mark out the shape of the watercourse using string and pegs, adding or removing soil to create a slope of the right gradient. Working from the bottom, cut out steps into the slopes to form the falls and cascades. The tread of each step should be angled slightly towards the back so that water will remain in each section if the water is turned off. When you reach the top of the watercourse, dig a header pool; this should be at least 40 cm (16 in) deep and 60 cm (24 in) along each side.
Adding the Lining
Lightly rake the base of the stream and pools and remove any stones. Tamp the area down firmly and then line the course with a layer of polyester matting, cutting it to fit. Spread the flexible liner on top of this cushioning layer so that the bottom edge overlaps into the base pool. Smooth the liner into the contours of the stream, making sure that it is wide enough to overlap the sides by about 30 cm (12 in).
Before spreading a liner in a pond, stream or rill, lay it out on the ground for 20-30 minutes to let it soften in the sun.
Installing the Pump
Dig a thin trench alongside the stream from the base pool to the header pool. Lay a flexible pipe along this trench; attach one end to a submersible pump in the main pool and place the other end deep down into the header pool. Refill this channel with soil.
Positioning the Rocks
Starting at the base, position a number of rocks at the back of each 'tread' to form the risers of the steps of the stream. You will also need to place rocks on top of the liner along the sides of the watercourse. Lift the remaining liner up behind these stones and hold it in place there by backfilling with soil. This will prevent the stream from flooding. Fill this area with plants to soften the edges.
Carry on working your way upwards arranging rocks and pebbles to form the falls and sides of the watercourse. Make sure that the sides are sufficiently steep to prevent water from flooding over. You may decide to mortar the rocks into position to keep them in place.
Fill the header and the base pool with water, and then turn on the pump. You will probably need to adjust the flow to make sure that the water runs at the right rate and with the desired effect.