The most critical component of constructed wetlands is land. Because of the relatively
large surface area necessary for a given flow, use of constructed wetlands is generally limited
to smaller communities, usually down to single-family or single-building settings. The land is
shaped into basins, commonly (but not always) lined with impermeable membranes and
sloped to provide a gentle flow from the inlet to the outlet of the treatment system (Baker,
2008). A gravel lining is built above the liner and it can vary in thickness from a minimal root
zone to varying depths that might extend to above the water line. The flow diagram is shown
in Fig 1. In extremely hot and dry climates, a gravel or sand bed can help minimize
evaporative loss of water. A mix of aquatic plant materials (cattails, bulrushes, reeds, etc.)
growing either hydroponically or in a gravel substratum provide the media through which
polluted water is filtered and biologically treated