The purpose of doing a wetland delineation is to establish the wetland boundary. This can be done either using the soil or the vegetation in that area. The US Army Corps of Engineers manual on Wetlands Delineation is considered the standard although there are different supplemental manuals depending the region that you are in. It is mandatory to use the manual to identify and delineate wetlands that could be subject to regulation under Section 404 of the Clean water act. While mudflats are protected under section 404, the manual only deals with vegetated sites, aka wetlands. Both the list of plants and soils listed in the manual are considered obsolete. A newer list of plants is available here and a newer list of soils is available here.
In order to defer something as a wetland it has to meet three key criteria; saturated soils from a permanent or periodic inundation of groundwater, vegetation adapted for life in saturated soils, and the presence of “normal circumstances”. More specifically soil must be classified as hydric and the mean water depth is less than 6.6 feet deep. Wetlands may be surrounded by either deepwater aquatic habitats or nonwetlands. See the Army Corp manual on pages 10 and 11 for more specific definitions of these habitat types.
It is important to note where looking at the plant community that a wetland community may have upland species in it and vice versus. You shouldn’t use this data to conclude that a community is a wetland or an upland but rather you should rely on the percent composition of the whole community. For example, a community with 99 percent wetland species is considered to have obligate wetland plants. A community with 67 to 99 percent wetland species is considered to have facultative wetland plants. And so on an so forth. A table of this information is available on page 14 of the manual. Wetland plant guides are typically based on the region you are in as the plants vary from region to region. Soils also vary from region to region. More on soil classification can be read here and on pages 22-28 of the manual.
Hydrology is one of the hardest factors to define when doing a wetland delineation. Scientist look at drainage patterns, drift lines, sediment deposition, watermarks, stream gauge data, and historical records to gain an understanding of the hydrology. The manual outlines detailed descriptions of primary inductors of wetland hydrology, anyone, one of these factors is present then the area is said to have wetland hydrology.