Identifies the natural drainage conditions of the soil and refers to the frequency and duration of wet periods. The soil drainage classes are defined in terms of (1) actual moisture content (in excess of field moisture capacity) and (2) the extent of the period during which excess water is present in the plant-root zone. Soil drainage class categories conform to the FGDC Soil Geographic Data Standards, September 1997. (http://www.fgdc.gov/standards/documents/standards/soils/soil997.PDF.) Definitions are derived from Grossman et al. (1998) and Sims et al. (1997).