Drought conditions have developed over the past three years in many parts of the U.S. Army Corps of Engineers’ South Pacific Division. Regulatory project managers, permit applicants, wetland consultants and others have inquired as to what expectations, guidance, or direction is available for wetland delineations under these conditions.
Both currently applicable Regional Supplements to the Corps of Engineers Wetland Delineation Manual for the Arid West and Western Mountains, Valleys, and Coast include sections titled, Difficult Wetland Situations which describe tools used to evaluate temporal shifts in vegetation and periodic lack of hydrology indicators during periods of below-normal rainfall, drought conditions and unusually low winter snowpack. These documents identify specific sampling and analytical approaches for evaluating both vegetation under extended drought conditions and hydrology in drought years, and are found at the following links:
http://www.spk.usace.army.mil/Portals/12/documents/regulatory/pdf/trel08-28.pdf
http://www.spk.usace.army.mil/Portals/12/documents/regulatory/pdf/west_mt_finalsupp.pdf
To the extent possible, the hydrophytic vegetation decision should be based on the plant community that is normally present during the wet portion of the growing season in a normal rainfall year. The evaluation of hydrology should consider the timing of the site visit in relation to normal seasonal and annual hydrologic variability, and whether the amount of rainfall prior to the site visit has been normal. In drought conditions, direct observation of plants and hydrology indicators may be misleading or problematic, so other methods of making wetland decisions may be appropriate.
For example, if the vegetation on the drought-affected site is substantially the same as that on a wetland reference site in the same general area having similar soils and known wetland hydrology, then the vegetation may be considered hydrophytic.
Application of the procedures in these sections of the supplements should facilitate better decisions about vegetation and hydrology. In some cases there may be a need to defer field work and/or a wetland determination, but there is no guarantee conditions will be closer to normal the next wet season. In general, wetland determinations on difficult or problematic sites must be based on the best information available to the field inspector, interpreted in light of his or her professional experience and knowledge of the ecology of wetlands in the region. Corps wetland determinations are based on a preponderance of all available information, including in many cases remote sensing and longer term data, not just the field data collected under drought conditions.
Questions or comments may be addressed to:
Michael Finan, Wetland Specialist, U.S. Army Corps of Engineers, Sacramento District, Regulatory Division, 1325 J Street, Room 1350, Sacramento, CA 95814-2922, PH: 916-557-5324 (9am-3pm); FAX: 916-557-7803, michael.c.finan@usace.army.mil