Occurrence and distribution of Ordinary High Water Mark (OHWM) indicators in non-perennial streams in the Western Mountains, Valleys, and Coast Region of the United States

Abstract : This study explored the occurrence and distribution of ordinary high water mark (OHWM) indicators in non-perennial streams in the Western Mountains, Valleys, and Coast (WMVC) Region of the United States. Physical and biological indicators of the OHWM were recorded and ranked (weak, moderate, or strong) at 150 ephemeral or intermittent stream sites sampled across the region. Three primary OHWM indicators topographic break in slope, change in sediment characteristics, and change in vegetation characteristics were found to be ubiquitous throughout the WMVC Region. At each stream sampled, a combination of at least two of these primary indicators was found to express a signature on the landscape, generally consistent with the lateral boundaries of the active channel. The distribution of the primary indicators and their rankings within the region showed no relationships to various climate, watershed, or channel characteristics ex-amined using multivariate statistical analysis. This suggests the robust nature of these primary indicators and the active channel signature for delineating the OHWM in non-perennial streams throughout the WMVC Region. These findings support a more informed and consistent approach to OHWM delineation in the WMVC Region.