similar, (i.e., has the same dominants or the sub- 

 ject area has different dominants with the same 

 indicator status as the reference site) then the area is 

 considered to be wetland -- the wetland hydrology 

 criterion is presumed to be satisfied. If the vegeta- 

 tion has changed to where FACU and UPL species 

 or UPL species alone predominate and OBL spe- 

 cies are absent, then the area is considered effec- 

 tively drained and is nonwetland. If the vegetation 

 is different than indicated above, additional work is 

 required - go to substep 3E if the area is ditched, 

 channelized, or tile-drained, or to substep 3F if the 

 hydrology is modified in other ways. 



E) Determine the "zone of influence" of 

 the ditch (or drainage structure) and the effect on 

 the water table by using existing SCS soil drainage 

 guides. Obtain the appropriate guide for the project 

 area's soil(s) and collect necessary field measure- 

 ments (e.g., ditch or other drainage structure 

 dimensions) to use the guide. The zone of 

 influence is the area affected by the ditch. The size 

 of this zone depends on many factors including 

 ditch dimensions, water budget, and soil type. The 

 guide should help identify the extent of the zone as 

 well as the water table within the zone. If the zone 

 of influence has a water table that fails to meet the 

 wedand hydrology criterion, then the zone is effec- 

 tively drained and is nonwedand, while hydric soil 

 areas outside of the zone remain wetland. If the 

 wedand hydrology criterion is met within the zone, 

 the entire area remains wetland. 



F) Conduct detailed groundwater stud- 

 ies. Make direct observations of inundation and 

 soil saturation by establishing groundwater wells 

 throughout the site, being sure to place them in a 

 range of elevations so that the data obtained will be 

 representative of the site as a whole. To maximize 

 field effort, it may be best to collect data during the 

 wetter part of the growing season (e.g., early 

 spring in temperate regions). These direct observa- 

 tions, when made during a normal rainfall year, 

 should show whether the wedand hydrology criter- 

 ion is met. It is advisable, however, to take meas- 

 urements over a multi-year period. {Note: One 

 must be aware of regional weather patterns. For 

 example, observations made during a number of 

 consecutive dry years may lead to erroneous con- 

 clusions about wedand hydrology.) 



If wetland hydrology still exists, return to the 

 applicable step in the onsite determination method 

 being used and continue delineating the wetland 



Problem Area Wetlands 



4.24. There are certain types of wedands and/or 

 conditions that may make wetland identification 

 difficult because field indicators of the three wet- 

 land identification criteria may be absent, at least at 

 certain times of the year. These wedands are con- 

 sidered problem area wedands and not disturbed 

 wedands, because die difficulty in identification i» 

 generally due to normal environmental conditions 

 and not the result of human activities or catastroph- 

 ic natural events, widi die exception of newly creat- 

 ed wedands. Artificial wedands are also included in 

 this section because their identification presents 

 problems similar to some of the natural problem 

 area wedands. — 



4.25. Examples of these problem area wedands 

 are discussed below. Be sure to learn how to rec- 

 ognize these wedands. 



1) Wetlands dominated by FACU plant species 

 (or communities with a prevalence index greater 

 than 3 J). Since wedands often exist along a natu- 

 ral wetness gradient between permanendy flooded 

 substrates and better drained soils, the wedand 

 plant communities sometimes may be dominated by 

 FACU species. Although FACU-dominated plant 

 communities are usually uplands, they sometimes 

 become established in wetlands. In order to deter- 

 mine whedier a FACU-dominated plant community 

 constitutes hydrophytic vegetation, the soil and 

 hydrology must be examined. If the area meets the 

 hydric soil and wedand hydrology criteria (see pp. 

 6-7), dien die vegetation is hydrophytic. 



In diese plant communities, take die following 

 steps to make a wedand determination: 



Step 1 . Are 25 percent or more and 50 per- 

 cent or less of the dominant plants in the plant com- 

 munity OBL, FACW, and/or FAC species, or does 

 the community have a prevalence index greater than 

 35 and less than or equal to 4.0 ? If the answer is 

 YES, then proceed to Step 3. If NO, proceed to 

 Step 2. 



Step 2. Is the community located: (1) in a 

 depressional or flat area, (2) along a river, stream 

 or drainageway, or (3) adjacent to a more typical 

 wetland plant community (i.e., where greater than 

 50 percent of the dominants are OBL, FACW, and/ 

 or FAC, or where the prevalence index is less than 

 or equal to 35)? If YES, proceed to Step 3. UNO, 



55 



