Delineating Playas in the Arid Southwest: A Literature Review

Abstract : Playas of the arid Southwest can be unambiguously identified in a geologic context. However, identifying those portions of playas that are defined as Waters of the United States (WoUS) in the Clean Water Act (CWA) and thus under the jurisdiction of the Corps of Engineers (Corps) and other Federal agencies charged with enforcing the CWA is sometimes problematic. While the WoUS definition specifically includes playas, the guidance for playa delineation is not as highly developed as for wetlands. Delineating WoUS, as per-formed by the Corps or by others to comply with Corps regulations, involves determining Ordinary High Water (OHW). However, under certain circumstances, the indicators provided in Federal regulations and available technical information for determining OHW have been found to be insufficient when applied to playas. Consequently, some delineations performed to date have involved the development of local indicators by integrating observational data obtained during cyclical inundation, information available for delineating wetlands, and inference based on technical knowledge. Examples of local indicators include small-scale cracks in the soil surface, soil algal crusts, and phreatophyte mounds. This report summarizes the pertinent literature and provides examples of case studies in delineating playas.