40478 Federal Register / Vol. 56, No. 157 / Wednesday, August 14, 1991 / Proposed Rules 



alteration? How much different and 

 why? 



(4) Characterize the hydrology that 

 previously existed at the area. Obtain 

 and record all possible evidence that 

 may be useful for characterizing the 

 previous hydrology. Consider the 

 following: 



(A) Stream or tidal gauge data — If a 

 stream or tidal gauging station is located 

 near the area, it may be possible to 

 calculate elevations representing the 

 upper limit of wetland hydrology based 

 on duration of inundation. Consult SCS 

 district offices, hydrologists from the 

 local CE district offices or other 

 agencies for assistance. If fill material 

 has not been placed on the area, survey 

 this elevation from the nearest USGS 

 benchmark. If fill material has been 

 placed on the area, compare the 

 calculated elevation with elevations 

 shown on a USGS topographic map or 

 any other survey map that predates site 

 alteration. 



(B) Field hydrologic indicators onsite 

 or in a neighboring reference area — 

 Certain field indicators of wetland 

 hydrology may still be present. Look for 

 water marks on trees or other structures, 

 drift lines, and debris deposits (for 

 additional hydrology indicators, see 

 other signs of wedand hydrology 

 section). If adjacent undisturbed areas 

 are in the same topographic position, 

 have the same soils (check soil survey 

 map), and are similarly influenced by 

 the same sources of inimdation, look for 

 wetland hydrology indicators in these 

 areas. 



(C) Aerial photographs — Examine 

 aerial photographs and determine 

 whether the area has been inundated or 

 saturated during the growing season. 

 Consider the time of the year that the 

 aerial photographs were taken and use 

 only photographs taken prior to site 

 alteration. 



(D) Historical records — Examine 

 historical records for evidence that the 

 area has been periodically inundated. 

 Obtain copies of any such information. 



(E) National Flood Insurance Agency 

 flood maps — Determine the previous 

 frequency of inundation of the area from 

 national floods maps (if available). 



(F) Local government officials or other 

 knowledgeable individuals — Contact 

 individuals who might have knowledge 

 that the area was periodically inundated 

 or saturated. 



(5) Determine whether weUand 

 hydrology previously occurred. Examine 

 available data. If hydrology was 

 significanUy altered recently (e.g., since 

 Clean Water Act), was wetiand 

 hydrology present prior to the 

 alteration? If the vegetation and soils 

 have not been disturbed, use site 



characteristics — vegetation, soils, and 

 field evidence of weUand hydrology — to 

 identify wetland. If vegetation and soil 

 are removed, then review existing 

 information (e.g., soil surveys, wetland 

 maps, and aerial photos), following 

 procedures in Step 6, substep 3. If no 

 evidence of weUand hydrology is found, 

 the original hydrology of the area is not 

 considered to meet the weUand 

 hydrology criterion. If evidence of 

 weUand hydrology is found, the area 

 used to meet the wetland hydrology 

 criterion. Record decision and return to 

 the applicable step of the onsite 

 determination method being used. 



Step 6. Determine whether weUand 

 hydrology still exists. Many wetlands 

 have a single ditch nmning through 

 them, while others may have an 

 extensive network of ditches. A single 

 ditch through a weUand may not be 

 sufficient to effectively drain it; in other 

 words, the wetland hydrology criterion 

 still may be met under these 

 circumstances. Undoubtedly, when 

 ditches or drain tiles are observed, 

 questions as to the extent of drainage 

 arise, especially if the ditches or drain 

 tiles are part of a more elaborate stream 

 channelization or other drainage project. 

 In these cases and other situations 

 where the hydrology of an area has been 

 significanUy altered (e.g., dams, levees, 

 groundwater withdrawals, and water 

 diversions), one must determine whether 

 weUand hydrology still exists. If it is 

 present, the area is not effectively 

 drained. If wetland hydrology is not 

 present, the area is still a weUand. To 

 determine whether weUand hydrology 

 still exists: 



(1) Describe the type or nature of the 

 alteration. Look for evidence of: 



(A) Dams; 



(B) Levees, dikes, and similar 

 structuures; 



(C) Ditches; 



(D) Channelization; 



(E) Filling of channels and/or 

 depressions; 



(F) Diversion of water; and 



(G) Groundwater withdrawal. 

 (See Step 5 above for discussion of 



these factors.) 



(2) Determine the approximate date 

 when the alteration occurred, if 

 necessary. Check aerial photographs, 

 consult with local officials, and review 

 other possible sources of information. 



(3) Characterize the hydrology that 

 presently exists at the area. When 

 evaluating agricultural land to determine 

 the presence or absence of weUand, it is 

 recognized that such lands are generally 

 disturbed and must be viewed in that 

 context. Wetland hydrology is often 

 altered on agricultural lands, so the 

 mere presence of soils meeting the 



hydric soil criterion is not sufficient to 

 determine that weUands are present. 

 Due to the common hydrologic and 

 vegetative modifications on agricultiu'al "* 

 lands, indicators of weUand hydrology, 

 together with soil-related properties, are 

 the most reliable means of weUand 

 identification. The following procedures 

 is designed to provide technical 

 guidance for determining whether an 

 area subject to some degree of 

 hydrologic modification stiU meets the 

 weUand hydrology criterion. In general, 

 the hydrology of most such areas can be 

 evaluated by revieviong existing site- 

 specific information, examining aerial 

 photographs, or conducting onsite 

 inspections to look for evidence of 

 weUand hydrology (substeps A-F). More 

 rigorous assessment (substep G) may be 

 done less commonly where despite the 

 lack of wetland hydrology evidence one 

 has a strong suspicion that weUand 

 hydrology still exists. The reason for 

 doing this more detailed assessment 

 should be documented. Caution: when 

 the hydrology of an area has been 

 significanUy altered, soil characteristics 

 resulting from weUand hydrology caimot 

 be used to verify weUand hydrology 

 since they persist after weUand 

 hydrology has been eliminated.) 



(A) Review existing site-specific 

 hydrologic information to see if data 

 support the weUand hydrology criterion. 

 If such data are unavailable or 

 inconclusive, proceed to Step 2. 



(B) Examine aerial photographs 

 (preferably early spring or wet growing 

 season) for several recent years (e.g.. a 

 minimum of 5 years is recommended), 

 look for signs of inundation or prolonged 

 soil saturation, and consider these 

 observations in the context of long-term 

 hydrology. (Note: Large-scale aerial 

 photographs. 1:24.000 and larger, are 

 preferred.) Be sure to know the ' 

 prevailing envirorunental conditions for 

 all dates of photography. Try to avoid 

 abnormally wet or dry dates for they 

 may lead to erroneous conclusions 

 about weUand hydrology. You are 

 attempting to assess conditions during 

 normal rainfall years. If the area is wet 

 more years than not during normal 

 rainfall years (e.g., 3 of 5 years or 6 of 10 

 years), then the weUand hydrology 

 criterion is presumed to be met. If the 

 area shows no indication of wetness 

 during normal rainfall years or shows 

 such signs in only a few years (e.g., 1 of 



5 years or 3 of 10 years), then the 

 wetland hydrology criterion is presumed ^ 

 not to be met. If conditions are between ^ 

 the two mentioned above (e.g., 2 of 5 

 years or 4-5 of 10 years), proceed to 

 substep C. 



