Chapter 4.1.1 - North Carolina Division of Water Quality Methodology for Identification of Intermittent and Perennial Streams and Their Origins

Abstract

The Methodology for Identification of Intermittent and Perennial Streams and Their Origins and its associated numerical rating system were developed beginning in 1999 (the current version is Version 4.11, dated Sept. 1, 2010) in response to requests from the North Carolina regulated community for an objective, science-based method to distinguish among ephemeral, intermittent, and perennial streams. The need to distinguish these flow regimes arose from regulations that mandated buffers on all intermittent and perennial streams in the Neuse River Basin. The methodology has since been applied to other river basins in the state that have riparian buffer rules. It has also been used to identify streams as part of stream mitigation for the 404/401 Permit Program of the US Army Corps of Engineers and the NC Division of Water Resources. The narrative definitions of ephemeral, intermittent, and perennial streams are part of the North Carolina Administrative Code (NCAC) and the methods are tailored to these regulatory definitions. The methodology uses score thresholds to distinguish different flow regimes. In addition, a list of perennial indicators (designated aquatic macroinvertebrates) is used to determine which streams are perennial regardless of their score. The methodology was developed by a technical advisory team consisting of state and federal regulators, academic representatives, and private environmental consultants before formal adoption by the North Carolina Division of Water Quality. At least 300 field sites were evaluated during the initial development of the method.