often impracticable for delineating precise wetland 

 boundaries. Despite this limitation, hydrologic in- 

 dicators can be useful for confirming that a site 

 with hydrophytic vegetation and hydric soils still 

 exhibits wetland hydrology and that the hydrology 

 has not been significantly modified to the extent 

 that the area is now effectively drained. In other 

 words, while hydrologic indicators are somedmes 

 diagnostic of the presence of wetlands, they are 

 generally either operationally impracticable (e.g., in 

 the case of recorded data) or technically inaccurate 

 (e.g., in the case of some field indicators) for de- 

 lineating wetiand boundaries. In the former case, 

 surveying the wedand boundary according to ele- 

 vation data related to recorded flood data, for ex- 

 ample, is generally too time-consuming and may 

 not actually be a true correlation. In the latter case, 

 it should be quite obvious that indicators of flood- 

 ing often extend well beyond the wedand boundary 

 into low-lying upland areas that were flooded by an 

 infrequent flood. Consequently the emphasis on 

 delineating wetland boundaries should be placed on 

 hydrophytic vegetation and hydric soils in the ab- 

 sence of significant hydrologic modification, al- 

 though wetland hydrology should always be con- 

 sidered. 



3.36. If significant drainage or groundwater alter- 

 ation has taken place, then it is necessary to deter- 

 mine whether the area in question is effectively 

 drained and is now nonwetland or is only pardy 

 drained and remains wedand despite some hydro- 

 logic modification. Guidance for determining 

 whether an area is effectively drained is presented 

 in die section on disturbed areas (p. 50). In the ab- 

 sence of visible evidence of significant hydrologic 

 modification, wedand hydrology is presumed to 

 occur in an area having hydrophytic vegetation and 

 hydric soils. 



3.37. The following hydrologic indicators can be 

 assessed quickly in the field. Although some are 

 not necessarily indicative of hydrologic events dur- 

 ing the growing season or in wedands alone, they 

 do provide evidence that inundation or soil satura- 

 tion have occurred at some time. One should use 

 good professional judgement in deciding whether 

 the hydrologic indicators demonstrate that the wet- 

 land hydrology criterion has been satisfied. When 

 considering these indicators, it is important to be 

 aware of recent extreme flooding events and heavy 

 rainfall periods that could cause low-lying nonwet- 

 lands to exhibit some of these signs. It is, diere- 

 fore, best to avoid, if possible, field inspections 



during and immediately after these events. If not 

 possible, then these events must be considered in 

 making a wedand determination. Also, remember 

 that hydrology varies seasonally and annually as 

 well as daily, and that at significant times of the 

 year (e.g., late summer for most of the country) the 

 water tables are at their lowest points. At these low 

 water periods, signs of soil saturation and flooding 

 may be difficult to find in many wedands. 



1) Visual observation of inundation - The most 

 obvious and revealing hydrologic indicator may be 

 simply observing the areal extent of inundation. 

 However, both seasonal conditions and recent 

 weather conditions should be considered when ob- 

 serving an area because they can affect whether 

 surface water is present on a nonwetland site. 



2) Visual observation of soil saturation - In 

 some cases, saturated soils are obvious, since the 

 ground surface is soggy or mucky under foot. In 

 many cases, however, examination of this indicator 

 requires digging a hole to a depth of 18 inches and 

 observing the level at which water stands in the 

 hole after sufficient time has been allowed for wa- 

 ter to drain into the hole. The required time will 

 vary depending on soil texture. In some cases, the 

 upper level at which water is flowing into the hole 

 can be observed by examining the wall of the hole. 

 This level represents die depth to the water table. 

 The depth to saturated soils will always be nearer 

 the surface due to a capillary fringe. In some heavy 

 clay soils, water may not rapidly accumulate in the 

 hole even when the soil is saturated. If water is ob- 

 served at the bottom of the hole but has not filled to 

 the 12- inch depth, examine the sides of the hole 

 and determine the shallowest depdi at which water 

 is entering die hole. Saturated soils may also be de- 

 tected by a "squeeze test," which involves taking a 

 soil sample within 18 inches (actual depth depends 

 on soil permeability) and squeezing the sample. If 

 free water can be extracted, the sod is saturated at 

 the depth of the sample at this point in time. When 

 applying the soil saturation indicator, both the sea- 

 son of the year and die preceding weather condi- 

 tions must be considered. (Note: It is not necessary 

 to direcdy demonstrate soil saturation at the time of 

 inspection. If the NTCHS criteria for hydric sod 

 are met, it can be assumed that an area is saturated 

 to the surface or inundated at some point in time 

 during an average rainfall year.) 



3) Oxidized channels (rhizospheres) associated 

 with living roots and rhizomes - Some plants are 



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