The treated wastewater is collected in a drain pipe at the bottom of the constructed wetland.   The drain pipe is equipped with aeration pipes.
The water level in the system is controlled with an adjustable upright pipe. This level control determines the hydraulic gradient and prevents overland flow (Darcy formula).
The drain pipe is covered with coarse gravel or rock.
Horizontal Subsurface Flow CW's: Outlet structures
Constructed Wetlands