A Review of Land and Stream Classifications in Support of Developing a National Ordinary High Water Mark (OHWM) Classification

Abstract : Under Section 404 of the Clean Water Act, the ordinary high water mark (OHWM) defines the lateral extent of federal jurisdiction in non-tidal waters of the United States in the absence of adjacent wetlands. Extensive research pertaining to identification and delineation of the OHWM in rivers and streams of the Arid West and Western Mountains, Valleys, and Coast regions has been conducted to better understand the occurrence and distribution of OHWM field indicators and to develop reliable methods for delineating the OHWM in these regions. Ongoing expansion of OHWM investigations into other regions of the U.S. stems from a need for nationally consistent and defensible OHWM delineation practices. A comprehensive framework is needed to foster the expansion of OHWM research and the development of delineation methods and indicators. A key element of this framework is the implementation of a classification system that allows for systematic sampling of the range of stream types and regions that exist throughout the U.S. This report reviews existing land and stream classifications and assesses the benefits and limitations of each approach for the purpose of developing a national OHWM classification. Additionally, it presents a preliminary version of a national OHWM classification.