Vegetation and Channel Morphology Responses to Ordinary High Water Discharge Events in Arid West Stream Channels

Abstract

Abstract : 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 support tool for delineating the extent of the OHW in Arid West stream channels. The results of this study consistently show that the majority of work, whether it affects vegetation or channel morphology, occurs within the bankfull channel and active floodplain. This study also showed that the terrace floodplain maintained its vegetative and morphology composition with discharges as large as an 18.7-year flood event, the largest we studied. Data analyzed by flood events support the theory that the bankfull and active channels of intermittent and ephemeral streams in the Arid West function as one channel and that the outer boundary of this single channel represents the extent of the OHW.