frequency and duration of inundation or soil satura- 

 tion are important in separating wetlands from non- 

 wedands. Duration usually is the more important 

 factor. Areas of lower elevation in a floodplain or 

 marsh have longer duration of inundation and satu- 

 ration and often more frequent periods of these 

 conditions than most areas at higher levels. Flood- 

 plain configuration may significantiy affect the du- 

 ration of inundation by facilitating rapid runoff or 

 by causing poor drainage. Soil permeability related 

 to the texture of the soil also influences the duration 

 of inundation or soil saturation. For example, clay- 

 ey soils absorb water more slowly than sandy or 

 loamy soils, and therefore have slower permeabili- 

 ty and remain saturated much longer. Type and 

 amount of plant cover affect both degree of inunda- 

 tion and duration of saturated soil conditions. Ex- 

 cess water drains more slowly in areas of abundant 

 plant cover, thereby increasing duration of inunda- 

 tion or soil saturation. On the other hand, transpira- 

 tion rates are higher in areas of abundant plant cov- 

 er, which may reduce the duration of soil 

 saturation. 



3.31. To determine whether the wetland hydrolo- 

 gy criterion is met, one should consider recorded 

 data, aerial photographs, and field indicators that 

 provide direct or indirect evidence of inundation or 

 soil saturation. 



Recorded Data 



3.32. Recorded hydrologic data usually provides 

 both short- and long-term information on the fre- 

 quency and duration of flooding, but little or no in- 

 formation on soil saturation periods. Recorded data 

 include stream gauge data, lake gauge data, tidal 

 gauge data, flood predictions, and historical flood 

 records. Use of these data is commonly limited to 

 areas adjacent to streams and other similar areas. 

 Recorded data may be available from the following 

 sources: 



1) CE district offices (data for major waterbod- 

 ies and for site-specific areas from planning and 

 design documents) 



2) U.S. Geological Survey (stream and tidal 

 gauge data) 



3) National Oceanic and Atmospheric Adminis- 

 tration (tidal gauge data) 



4) State, county and local agencies (flood data) 



5) SCS state offices (small watershed projects C 

 data) 



6) private developers or landowners (site- 

 specific hydrologic data, which may include water 

 table or groundwater well data). 



Aerial Photographs 



3.33. Aerial photographs may provide direct evi- 

 dence of inundation or soil saturation in an area. In- 

 undation (flooding or ponding) is best observed 

 during the early spring in temperate and boreal re- 

 gions when snow and ice are gone and leaves of 

 deciduous trees and shrubs are not yet present. 

 This allows detection of wet soil conditions that 

 would be obscured by the tree or shrub canopy at 

 full leaf -out. For marshes, this season of photogra- 

 phy is also desirable, except in regions character- 

 ized by distinct dry and rainy seasons, such as 

 southern Florida and California. Wedand hydrolo- 

 gy would be best observed during the wet season 

 in these latter areas. 



3.34. It is most desirable to examine several con- 

 secutive years of early spring or wet season aerial 4- 

 photographs to document evidence of wetiand in- 

 undation or soil saturation. In this way, the effects 



of abnormally dry springs, for example, may be 

 minimized. In interpreting aerial photographs, it is 

 imponant to know the antecedent weather condi- 

 tions. This will help eUminate potential misinterpre- 

 tations caused by abnormally wet or dry periods. 

 Contact the U.S. Weather Service for historical 

 weather records. Aerial photographs for agricultu- 

 ral regions of the country are often available at 

 county offices of the Agricultural Stabilization and 

 Conservation Service. 



Field Indicators 



3.35. At certain times of the year in most wet- 

 lands, and in certain types of wedands at most 

 times, wetland hydrology is quite evident, since 

 surface water or saturated soils (e.g., soggy or 

 wetter underfoot) may be observed. Yet in many 

 instances, especially along the uppermost boundary 

 of wetlands, hydrology is not readily apparent. 

 Consequently, the wetiand hydrology criterion is 



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