headwater or backwater flooding, tidal influence, ground water, or some com- 

 bination of these sources. The frequency and duration of inundation or soil 

 saturation varies from nearly permanently inundated or saturated to irregu- 

 larly inundated or saturated. Topographic position, stratigraphy, and soil 

 permeability influence both the frequency and duration of inundation and soil 

 saturation. Areas of lower elevation in a floodplain or marsh have more fre- 

 quent periods of inundation and/or greater duration than most areas at higher 

 elevations. Floodplain configuration may significantly affect duration of 

 inundation. When the floodplain configuration is conducive to rapid runoff, 

 the influence of frequent periods of inundation on vegetation and soils may be 

 reduced. Soil permeability also influences duration of inundation and soil 

 saturation. For example, clayey soils absorb water more slowly than sandy or 

 loamy soils, and therefore have slower permeability and remain saturated much 

 longer. Type and amount of plant cover affect both degree of inundation and 

 duration of saturated soil conditions. Excess water drains more slowly in 

 areas of abundant plant cover, thereby increasing frequency and duration of 

 inundation and/or soil saturation. On the other hand, transpiration rates are 

 higher in areas of abundant plant cover, which may reduce the duration of soil 

 saturation. 

 Classification 



48. Although the interactive effects of all hydrologic factors produce 

 a continuum of wetland hydrologic regimes, efforts have been made to classify 

 wetland hydrologic regimes into functional categories. These efforts have 

 focused on the use of frequency, timing, and duration of inundation or soil 

 saturation as a basis for classification. A classification system developed 

 for nontidal areas is presented in Table 5. This classification system was 

 slightly modified from the system developed by the Workshop on Bottomland 

 Hardwood Forest Wetlands of the Southeastern United States (Clark and 

 Benforado 1981). Recent research indicates that duration of inundation and/or 

 soil saturation during the growing season is more influential on the plant 

 community than frequency of inundation/saturation during the growing season 

 (Theriot, in press). Thus, frequency of inundation and soil saturation are 

 not included in Table 5. The WES has developed a computer program that can be 

 used to transform stream gage data to mean sea level elevations representing 



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