A Guide to Ordinary High Water Mark (OHWM) Delineation for Non-Perennial Streams in the Western Mountains, Valleys, and Coast Region of the United States

Abstract

Abstract : This document provides technical guidance for delineating the ordinary high water mark (OHWM) in non-perennial streams in the Western Mountains, Valleys, and Coast (WMVC) Region of the United States. Under Section 404 of the Clean Water Act, the OHWM defines the lateral extent of federal jurisdiction in non-tidal waters of the U.S. in the absence of adjacent wetlands. The OHWM in the WMVC Region is consistent with the physical and biological signature established and maintained at the boundaries of the active channel. Delineation of the active channel signature, and thus the OHWM, is based largely on identification of three primary physical or biological indicators topographic break in slope, change in sediment characteristics, and change in vegetation characteristics. This guide addresses the underlying hydrologic and geo-morphic concepts pertaining to the OHWM and the field indicators, methods, and additional lines of evidence used to assess and delineate the OHWM in WMVC non-perennial streams. The technical guidance presented here increases the accuracy and consistency of OHWM delineation practices in the WMVC Region.