What is the minimum thickness for topsoil in a filter bed?

What is the minimum thickness for topsoil in a filter bed?

• A. 5 cm
• B. 10 cm
• C. 15 cm
• D. 20 cm

Answer: (C)

The depth of topsoil over a filter bed must be thick enough to support healthy plant growth and contribute to treatment through filtration and root activity. A minimum of 15 cm (about 6 inches) provides a sufficient root zone for grasses or other vegetation, helps with evapotranspiration, and protects the underlying gravel and pipes from erosion and surface disturbance. Too little topsoil, like 5 cm or 10 cm, would hinder plant establishment and increase the risk of erosion and clogging of the bed. A depth of 20 cm meets the requirement but isn’t the minimum.

The depth of topsoil over a filter bed must be thick enough to support healthy plant growth and contribute to treatment through filtration and root activity. A minimum of 15 cm (about 6 inches) provides a sufficient root zone for grasses or other vegetation, helps with evapotranspiration, and protects the underlying gravel and pipes from erosion and surface disturbance. Too little topsoil, like 5 cm or 10 cm, would hinder plant establishment and increase the risk of erosion and clogging of the bed. A depth of 20 cm meets the requirement but isn’t the minimum.