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National Ordinary High Water Mark Field Delineation Manual for Rivers and Streams
Citation:
David, G., K. Fritz, Tracie-Lynn Nadeau, B. Topping, A. Allen, P. Trier, S. Kichefski, L. James, E. Wohl, AND D. Hamill. National Ordinary High Water Mark Field Delineation Manual for Rivers and Streams. US Army Corps of Engineers, Washington, DC, 2022.
Impact/Purpose:
The Ordinary High Water Mark (OHWM) defines the lateral extent of federal Clean Water Act jurisdiction for non-tidal aquatic features in the absence of adjacent wetlands in the United States. The OHWM defines the jurisdictional limits for both running and standing waterbodies, but this manual focuses solely on a methodology for identifying and delineating the OHWM in streams and rivers. The result of several years of effort by the standing National Technical Committee and extensive nationwide field work this is the first national manual describing a consistent approach for identifying these physical features (flora and geomorphic characteristics), in different climatic regions nationwide, to support OHWM delineation. This manual will improve consistency in OHWM identification within regions by 1) providing consistent definitions of OHWM indicators; 2) outlining a clear step-by-step process for identifying the OHWM using a Weight-of-Evidence approach; 3) providing a datasheet for recording OHWM evidence; 4) describing how to put streams and the observed physical features in a landscape context to better interpret observations; and 5) providing examples of how to include further support for difficult OHWM delineations.
Description:
The ordinary high water mark (OHWM) defines the lateral extent of nontidal aquatic features in the absence of adjacent wetlands in the United States. The federal regulatory definition of the OHWM, 33 CFR 328.3(c)(7), states the OHWM is “that line on the shore established by the fluctuations of water and indicated by physical characteristics such as [a] clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas.” This is the first manual to present a methodology for nationwide identification and delineation of the OHWM. A two-page data sheet and field procedure outline a weight-of-evidence (WoE) methodology to organize and evaluate observations at stream sites. This manual presents a consistent, science-based method for delineating the OHWM in streams. It also describes regional differences and challenges in identifying the OHWM at sites disturbed by human-induced or natural changes and illustrates how to use remote data to structure field inquiries and interpret field evidence using the principles of fluvial science. The manual demonstrates that, in many landscape settings, the OHWM may be located near the bankfull elevation.
