"Waters of the United States" (WoUS) are regulated by the U.S. Army Corps of Engineers under Section 404 of the Clean Water Act (33 U.S.C. 1344). The Corps lateral jurisdictional extent in Arid West stream channels is the upper level of the ordinary high water (OHW). The channel shape, fluvial textures, and vegetation patterns of these arid stream channels are heavily influenced by short-term, high-intensity or "flashy" events, which create distinctive physical features and vegetation responses. To determine vegetation and channel morphology responses, sequential aerial photos and stream gauge data for eight ephemeral and intermittent stream channels in the Arid West were analyzed. The observed patterns associated with various discharge event levels are consistent with the Corps OHW delineation manual. The use of remote sensing resources provides another critical component for aiding in the delineation of the extent of the OHW in Arid West stream channels.

The U.S. Army Corps of Engineers is currently regionalizing and updating the national wetland delineation manual. This manual will use new ecosystem boundaries for the nation. A separate effort by the Corps will update the National Wetland Plant List within these same new ecosystem boundaries. The Arid West is an area of particular interest in the revision of the plant list because of the problematic indicator statuses for certain groups of plants. Many species in the Arid West have morphological and physiological adaptations that allow them to occur in specialized habitats, ranging from wetlands to uplands. In delineations, the indicator status of these species is not always accurate for the specific location. A combination of literature reviews and recorded species data from previous studies for six specialty habitats are presented and discussed; the species groups are playa edge species, dry wash species, dry wash phreatophytes, hygro-halophytes, xero-halophytes, and phreatophytes with salt tolerance. A total of 421 species, with 93 of those species shared in more than one habitat type, are reported, including 48 playa species, 346 dry wash species, 62 dry wash phreatophytes, 32 hygrohalophytes, 47 xero-halophytes, and 17 phreatophytes with salt tolerance. The list for each specialized habitat will be used to better understand species ecology and occurrences across the region and will ultimately help in assigning and increasing the reliability of wetland plant indicator statuses.

Over the past few years, a series of Regional Supplements to the 1987 U.S. Army Corp of Engineers (USACE) Wetland Delineation Manual have been published, and currently the National Wetland Plant List is being updated. To support these efforts, we generated a list of floras and field guides for each USACE region-Alaska, Arid West, Atlantic and Gulf Coastal Plain, Caribbean, Eastern Mountains and Piedmont, Great Plains, Midwest, Northcentral and Northeast, Pacific Islands, and Western Mountains, Valleys and Coast. Each list includes regional floras, state floras, local floras, regional field guides, state field guides, and local field guides. We also prepared a list of floras and field guides that cover the entire U.S. This list is divided into the following categories: forbs, shrubs, trees, grasses and sedges, ferns, orchids, cacti and agave, and references and help guides. The flora and field guide lists can serve as tools for wetland delineation and restoration, assigning of wetland indicator statuses to vegetation species, and other vegetation activities.

We evaluated the potential for regulating wet boulder fields as wetlands or other "Waters of the US" under Section 404 of the Clean Water Act. We monitored hydrology in two boulder fields in Maine during the 2011 growing season and documented the presence/absence of hydric soil, wetland hydrology, hydrophytic vegetation, and Ordinary High Water Mark (OHWM) indicators. The wetland hydrology criterion was statistically associated with the presence of primary hydrology indicator C4, hydric soils, FACU-dominated wetland, and a separation between the folist layer and the soil surface. The occurrence of hydrophytic vegetation and the combined use of primary and secondary hydrology indicators were not associated with the wetland hydrology criterion. Wet boulder fields should be delineated as wetland/nonwetland mosaics that contain problematic wetland types. We strongly suggest discontinuing the use of secondary hydrology indicators and primary indicator B8 (sparsely vegetated concave surface) in wet boulder fields. Alpha,alpha-dipyridyl paper strips are the most accurate method for determining if a primary hydrology indicator is present. We recommend applying this test several times over 14 days. IRIS tubes and hydric soil indicators are reliable, but we suggest that alpha, alpha-dipyridyl paper strips be used to confirm a determination of nonhydric soil when a soil lacks a hydric soil indicator. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.