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A validation study of a rapid field-based rating system for discriminating among flow permanence classes of headwater streams in South Carolina
Citation:
Fritz, K., W. Wenerick, AND M. Kostich. A validation study of a rapid field-based rating system for discriminating among flow permanence classes of headwater streams in South Carolina. ENVIRONMENTAL MANAGEMENT. Springer-Verlag, New York, NY, 52(5):1286-1298, (2013).
Impact/Purpose:
Headwater streams represent most of the river miles in the United States and are often evaluated for Clean Water Act jurisdictional determinations, in part because they are prone to natural, periodic drying. There is a need by regulatory agenices to characterize flow permanence of headwater streams in a timely manner. This paper is the first to evaluate an existing rapid field-based method by directly comparing classification scores to continuous hydrologic data. Our findings will inform regulatory agencies about the strengths and weaknesses of using the rapid field-based method, and provide an approach for calibrating and fine-tuning the method for other regions.
Description:
Rapid field-based protocols for classifying flow permanence of headwater streams are needed to inform timely regulatory decisions. Such an existing method was developed for and has been used in North Carolina since 1997. The method uses ordinal scoring of 26 geomorphology, hydrology, and biology attributes of streams. The attribute scores are summed and compared to threshold scores to assign a flow permanence class. Our study objective was to evaluate the method’s ability to classify the flow permanence of forested stream reaches from Piedmont and Southeastern Plains ecoregions in South Carolina. Ephemeral reaches scored significantly lower than intermittent and perennial reaches, but scores from intermittent and perennial reaches did not differ across both ecoregions. Scores collected from reaches in the dry and wet seasons were strongly correlated, indicating that the method was seasonally stable. Scores had positive nonlinear relationships with the maximum recorded wet duration and the proportion of the record that reaches were wet, but were not related to drying frequency. Scores of the presence of baseflow in the dry season were more important in flow permanence classification than those from the wet season. Other important attributes and parameters in discriminating flow classes were macrobenthos, rooted upland plants, bankfull width, and ecoregion. Although North Carolina method did not consistently differentiate intermittent from perennial reaches, the indicator-based approach is a strong foundation from which to build a protocol for South Carolina. Adding measures like bankfull width, weighting by ecoregion, or shifting thresholds may be warranted modifications for South Carolina.
