Resources - Construction

HORIZONTAL FLOW

Horizontal Sub-surface flow wetlands are shallow excavations with a synthetic or clay liner to prevent ingress or egress of water. They are filled with a media through which effluent must flow. This can be anything from soil to light expanded clay aggregate, but 10-14 mm gravel is the most common. An inlet zone of larger media ensures the influent liquid is distributed effectively into the media. A similar outlet zone collects the treated liquid in drainage pipes which pass through the liner into a level control chamber where a simple plastic tube or swivel pipe allows the liquid level in the wetland to be controlled.

Shallow excavation	Lined with clay or synthetic liner	Filled with gravel or soil media and planted with macrophytes

Horizontal Surface flow wetlands are amongst the most simple to construct. They are very shallow excavations or shallow earth banked lagoons enclosing an area of land. Soil, or some other media such as gravel provides the growing media for the plants. A liner may not be necessary. To avoid short-circuiting the surface should be virtually flat with a very gentle slope towards the outlet end. Multiple species of plant can be used, a particular benefit if biodiversity is important. A system of pipes or channels distributes the wastewater over the inlet end of the wetland, and a collection channel collects the treated liquid at the outlet end.

VERTICAL FLOW

Construction of a vertical flow system (ARM Ltd)

Vertical flow wetlands are shallow excavations or above ground constructions either built of impermeable materials or lined with synthetic or clay materials to prevent ingress or egress of water. At the base of the excavation are drainage pipes which are usually turned up so they reach the surface at their ends. This allows air to move in and out of the wetland. The pipes are overlain by media or a number of different layers of media. These range from soil to light expanded clay aggregate, but gravels and coarse sands are most widely used.