Disconnecting underground

Rainwater for the garden

Place a gravel box or infiltration crate

Underground drainage is ideal for paved gardens and driveways, but also for small gardens and front gardens. As with above-ground drainage, the downpipe is cut just above ground level. A pipe is used to channel the water to a specific spot in the garden. There, a hole is dug underground, into which the gravel box or infiltration crate is placed. This allows the rainwater to easily seep into the ground from the box or crate.

A gravel box consists of a large quantity of gravel, wrapped in a filter fabric (ground or root barrier fabric). This fabric ensures that the soil layer does not become clogged with sand. A fabric is also placed around an infiltration crate. To ensure that both the infiltration crate and the gravel box continue to function properly, it is also necessary to fit a sand and leaf trap at the end of the downpipe. This prevents the box or container from becoming blocked with sand or leaves from the gutter. An alternative is to install a rain barrel between the downpipe and the infiltration system. When the rain barrel is full, the water flows through a pipe towards the infiltration system and seeps directly into the ground.

The required capacity of a soaker box or infiltration box depends on the permeability of the soil. We recommend the following guidelines:

• For an infiltration crate, a storage capacity of 20 litres is required per square metre of unconnected roof area. Is the crate located beneath a terrace? If so, it must be buried to a depth of at least 30 cm.
• 50 litres of gravel are required for every square metre of unsealed roof surface.