By R Kadlec in the Bible of Treatment wetlands (2nd edition):
"The preliminary step in the design of a treatment wetland is to acquire a fundamental understanding of the site of the wetland. Site conditions dictate the physical, chemical, and biological environment of a wetland treatment system. Conditions that should be evaluated during planning of a wetland treatment system include climate, geography, groundwater and its chemistry, soils and geology, rainfall and runoff water chemistry, biology, and socioeconomic factors. The importance of each of these conditions may vary, but all should be investigated to some extent. Detailed studies may be needed to determine the importance of those site conditions that affect technical feasibility."
Well, stated this above how can we design and sizing a treatment wetlands?
It's true, we always need to know where we are! I've a friends in WWG that travel around the world from Africa to Asia, from cold to warm climate location and is really important knowing where we are before starting the wetlands sizing.
The design of subsurface flow wetlands may be roughly divided into two categories: sizing calculations and physical specifications. There are different sizing methodologies for sub surface wetlands. There are also physical considerations, including the number of cells, layout, liners, bed depth, media size, plants, and water level control. It is recognized that subsurface wetlands are not stand-alone treatment devices but rather form part of an overall treatment process (Kadlec 2nd edition, mod.).