A stream or watercourse may be built by installing a number of pre-formed, interlocking modular units. This means that you can create a long-lasting and stable water feature of any height.

It is a good idea best to enlist the assistance of a helper when undertaking this type of project as you will find that you may need to adjust the levels of the unit; this is easier to do if one person lifts the unit whilst the other alters the soil level.

Method

1. Mark out the area where you want the watercourse to run using pegs and string.
2. Install the bottom pool using a flexible or rigid liner using the method described in our section on Ponds.
3. Working from the base pool upwards, dig out the watercourse area to the depth of each level, allowing for a 1 cm (1/2 in) layer of sand to cushion each unit.
4. Spread a 1 cm (1/2 in) layer of sharp sand along the base of each layer, and then put the first (bottom) unit into position so that it overlaps the main pool.
5. Check that the unit is level using a plank and spirit level - add or remove soil as necessary.
6. Remove this first unit and bolt it onto the vertical plate; this will determine the height of the fall. Use a silicon sealant around each bolt to ensure that it remains watertight.
7. Place the unit and vertical plate back into position, checking once again that it is level. Backfill behind the base of the plate. You may want to add some water to the first unit at this point to help keep it in position.
8. Install the rest of the units in the same way, checking each one is level before continuing with the next.
9. Dig a thin trench alongside the watercourse 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.
10. Fill the trench with soil and cover the edges of the units with stones and planting.
11. Fill the header pool with water, and then turn on the pump. You will probably need to adjust the flow to achieve the most pleasing effect.